Learning Center
Plans & pricing Sign in
Sign Out

Marine life interaction with tidal turbines interim report front page


									“Marine life interaction with tidal turbines”

Interim report

5th Year M-Eng Group Project

Supervisor: Dr A. Grant

Group C

Bruce Henry
Neil Koronka
Ross Turbet
Jonathan Meason

Executive Summary
Tidal stream currents have the potential to provide a significant proportion of
the UK’s energy needs. The harnessing of this clean and reliable resource
has recently been made possible through the development of marine current
turbine technology. This technology is as yet relatively untested in a wild
marine environment, however, and the impact upon marine wildlife is not fully
understood. This document summarises the initial period of work carried out
by a group of undergraduate mechanical engineers in the context of the
Masters project. This work aims to investigate the interaction between marine
turbines and wildlife through a combination of theoretical analysis and
practical experimentation in order to gauge the level of danger presented to
various marine mammals and fish.

The document initially defines the group roles and discusses issues relating to
the teams dynamic and project management style. A summary of the literature
review findings is presented and a case study is introduced which relates to
fish deterrence at a coal-fired power station cooling water inlet. A simple
mathematical model is described which uses statistical methods to estimate
strike probabilities and will allow the importance of several parameters such
as animal size, flow speed and turbine design to be gauged. An overview is
also given of some of the computational fluid dynamic work being carried out
in order to characterize the flow around the turbines. Finally a small scale-
testing model is described and the testing procedures discussed. It is hoped
to carry testing of a 1/42 scale model before the end of November.

Throughout the document progress is reviewed against originally stated goals
and deadlines. Overall progress is perceived to be good with the group
functioning efficiently and all tasks being on schedule for completion within the
project timescale.


Executive Summary .........................................................................................2
1.0       Introduction ...........................................................................................5
   1.1       Background .......................................................................................5
Section A: Team, project and research............................................................6
2.0       Definitions .............................................................................................6
   2.1       Measure of success of project ...........................................................6
   2.2       Interim report .....................................................................................6
   2.3       Project Objectives..............................................................................6
   2.4       Team Roles .......................................................................................6
   3.1       Team Dynamic ..................................................................................8
      3.1.1         The Merits of Team working .......................................................8
      3.1.2         Forming an effective team ..........................................................9
      3.1.3         Team dynamics and structure ..................................................10
   1.3       Gantt Chart ......................................................................................13
   3.3 Critical Path Analysis............................................................................14
   3.4        SWOT Analysis ..............................................................................15
   3.5       Budget .............................................................................................18
4.0       Research Summary ............................................................................20
   4.1       Original goals as set out in project scope ........................................21
   4.2       Revised aims, objectives and strategy.............................................21
   4.3       Tidal Power Background..................................................................21
   4.4       Marine Current Turbines Ltd............................................................25
   4.5       Environmental Impact Assessments................................................26
   4.6       Fish Strike Models ...........................................................................28
   4.7       Bird Strike Models ...........................................................................30
   4.8       Fish Friendly Turbines .....................................................................32
   4.9       Effects of Turbulence and Shear .....................................................33
   4.10      EMEC Tidal Stream Test Site..........................................................35
   4.11      Seals................................................................................................37
   4.12      Case Study: Longannet Power Station ............................................39
      4.12.1        Time line for activity surrounding Longannet power station......40
      4.12.2        Fish Screening Summary .........................................................43

Section B: Assessing the risk of turbine on fish and mammals.....................45
5.0      Mathematical Collision Risk Model......................................................46
   5.1      Objective from original scope ..........................................................46
   5.2      Revised objectives of statistical analysis work.................................46
   5.3      The Statistical Model .......................................................................46
   5.4      Results.............................................................................................51
   5.5      Blade Contours................................................................................54
   5.6      Timescale ........................................................................................55
   5.7      Future Work.....................................................................................55
6.0      Computational Fluid Dynamics............................................................56
   6.1      Objective from original scope ..........................................................56
   6.2      Revised objectives of CFD work......................................................56
   6.3      Modelling Specification ....................................................................56
   6.4      Design constraints ...........................................................................56
   6.5      Initial designs...................................................................................57
   6.6      Results and discussions ..................................................................59
   6.7      Timescale ........................................................................................61
   6.8      Future work......................................................................................61
7.0      Scale Model Experimentation..............................................................62
   7.1      Original goal as set out in Project Scope .........................................62
   7.2      Revised objectives of scale model testing .......................................62
   7.3      Design specifications .......................................................................62
   7.4      Design Constraints ..........................................................................63
   7.5      Model Scaling ..................................................................................63
   7.6      Conceptual design ...........................................................................65
   7.7      Testing procedure............................................................................68
   7.8      Timescale ........................................................................................68
   7.9      Larger scale testing .........................................................................68
8.0 Conclusions and final words ....................................................................70
   8.1      Project Status ..................................................................................70
   8.2      Future Activities ...............................................................................70
APPENDIX A .................................................................................................73
APPENDIX B .................................................................................................76

1.0 Introduction

1.1    Background

With the search for new renewable energy resources to meet government
targets, tidal power is now becoming a prominent area of development.
Unfortunately due to the infancy of this technology the adverse effects on the
local marine wildlife have not yet been investigated in any great depth.
Environmentalists have raised concerns about the possibility of fish, mammals
and some birds striking the turbine blades, which at present would seem to be
the significant obstacle in the widespread development of this technology. The
technology has the ability to play a large role in the future of the UK’s, if not
the world’s renewable energy due to its reduced visual interference with the
landscape and much greater power density compared to other renewable
energy resources on the market.

The project idea was born from a need to carry out comprehensive
environmental impact assessments during tidal power development, an area
that Dr. Grant of the ESRU department is heavily involved in. By approaching
the department with the desire to complete a self-generated project in the
area of renewable technology, the subject of tidal strike research created an
opportunity to undertake work that could assist the industry and the
department. As there has been little investigation into the subject of tidal
turbine interaction with marine wildlife, conclusions could either be
constructive or deconstructive to the technology’s progression. With this in
mind, it seemed sensible to prepare for the possibility of requiring utilisation of
fish deterrent technologies. With one of the group completing work experience
with ScottishPower and encountering this same requirement at coal power
station cooling water intakes, a practical case study was found to assist the
project. Any conclusions drawn from the research could now be applicable
across the energy production industry.

Section A: Team, project and research
2.0 Definitions

2.1    Measure of success of project
The measure of success as set out in our statement of purpose has remained
unchanged and sets out the primary goal for the project.

“To research and understand the effects of tidal turbines on the surrounding
wildlife with a view to producing information and statistics which will be
beneficial to the progress and development of this emerging technology”.

2.2    Interim report
The interim report was one of the deliverables in our initial statement of
purpose and sets out to summarise the progress made by group over the first
5 weeks of the project. It will detail the findings thus far, the methods that have
been employed by the group and the future work that will be necessary to
ensure the satisfactory achievement of our goals.

2.3    Project objectives
The various objectives as originally set out in the group’s statement of
purpose will be referred to throughout the document and revised as

2.4    Team roles
The following roles were chosen at the outset by the team in order to best
exploit each group member’s strengths and experience.

Bruce Henry                                 Ross Turbet
Environmental and Ethics Manager            Supervisor
Lead Simulation Engineer                    Website Development Manager

Jonathan Meason                             Neil Koronka
Technical Manager                           Design Team Leader
Test Team Leader                            Research Coordinator

The responsibilities that are relevant to each role are outlined below.

Lead Simulation Engineer – To oversee computational simulation activities
and be the group’s technical authority in this domain.

Environmental and Ethics Manager – To evaluate the environmental and/or
ethical impact of any significant decisions that are made by the team.

Supervisor – To coordinate and manage the group activities while
maintaining group focus on key goals.

Website Development Manager - To take charge of the construction of the

Technical Manager – To be the group’s technical authority, particularly
relating to any turbine issues.

Test Team Leader – To coordinate activities during testing and to ensure
fabrication of parts proceeds smoothly.

Design Team Leader – To ensure that a structured design process is
followed and encourage creativity amongst group members.

Research Coordinator – To oversee the group research activities and
document all findings in a suitable manner.

3.0 Project Management Strategy
3.1    Team Dynamic

3.1.1 The merits of team working
A team is defined as a small number of people with complimentary skills who
are committed to a common purpose, performance goals and approach for
which they find themselves mutually accountable (Katzenbach & Smith,
1993). This statement describes the difference between an effective project
team and an assembled group of individuals mistakenly branded as a ‘team’.
This common misconception often leads to problems within organisations,
with little or no thought applied to the fluency of the group and each
individual’s ability to work with others, causing tension, disagreement and a
lowered productivity. The structure of the 5th Year mechanical engineering
project allows the undergraduate engineer to understand the importance of
team dynamics, helping them develop to the skills and qualities needed to
solve problems effectively, creating an environment that is widely practiced in

Teams are brought together in engineering to solve problems or to generate
innovative ideas. Bringing individuals together allows organisations to pool
their collective resources to arrive at improved decisions, assuming that
members are willing to effectively apply abilities and experiences to progress
the group. Until recently engineers throughout industry were viewed as
commodities and they would have to rely on individual talent to achieve the
best solution possible. The move towards teamwork in modern times has
created a setting where engineers are viewed as intellectual resources, whose
skills can be utilised and stimulated by like-minded individuals. ‘Brainstorming’
is common practice, which if executed properly, can create solutions that
would have been previously missed by the individual. By utilising the right
combination of skills from a carefully selected group, barriers to progress can
be overcome quickly and with improved result.

Establishing a democratic group structure also protects the organisation from
any careless actions that may have previously been followed through. The
critical scrutiny of colleague’s ideas and plans eventually should eventually
uncover any potential problems, creating reliability and security in all
deliverables.   This is an area of teamwork that will be essential to the
successful completion of the project, as it will maintain the teams focus on
objectives that will be regularly assessed by each individual. This screening
process therefore adds further benefit to the implementation of a team

3.1.2 Forming an effective team
Assessing team dynamics and understanding project management idealisms
would only be beneficial to the project if lessons could be learnt and suitable
roles undertaken by each member. Before any structuring of the group could
commence, it was essential to research the fundamentals of team
management, highlighting the ways in which maximum productivity could be
achieved. The project group was brought together and placed in a problem-
solving situation in order to fully test the team dynamics, discovering whether
motivation, work rate and effectiveness could be improved in comparison to
individual work. With research into basic principals, it was found that the
characteristics that make an effective team are:

•   Common agreement on high expectations for the team
•   A commitment to common goals
•   Assumed responsibility for work that must be done
•   Honest and open communication
•   Common access to information
•   A climate for trust
•   Support for decisions that are made
•   A focus on process as well as results

If working well as a team, it is these characteristics that should be visible
throughout the duration of the undergraduate project.

3.1.3 Team dynamics and structure
During the initial stages of the project, it was felt that the group dynamics
could be further explored by undertaking personality tests and profiling. This
would provide the group with evidence on how each individual can work with
others, where their strengths and interests lie and what they can bring to the
team dynamics. The personality profiles would also allow the team to create a
structure that would most effectively cater for each member. This would
eventually increase effectiveness as a team and overall productivity.

Before the team began work on the project, each member completed a Belbin
personality test. This is a process practiced commonly in industry, becoming
an integral part of ‘Six Sigma’ project management. Dr Meredith Belbin, UK
academic and consultant developed the Belbin roles model in the late 1970’s,
demonstrating that balanced teams compromising people with different
capabilities performed better than teams that are less well balanced. The tests
pigeonhole team members into one of nine personality types, which describe
how they can operate within a team, the strengths and weaknesses of the
individual and ways to improve and develop. The results of the profiling
showed each member carried a different personality style:

•   Bruce Henry (completer finisher)
•   Neil Koronka (team worker)
•   Jonathan Meason (specialist)
•   Ross Turbet (plant)

It was then essential to understand what each role involved and what this
meant in terms of the actual team dynamic. These descriptions are used to
assist team working and encourage the individual to increase effectiveness
within a group.

Plant (Ross)
The Plant is the ideas person and can take a team out of a condition of dull
mediocrity into new realms of performance, but only if the team members are
prepared to listen and respond to him. The Plant is the teammate who comes
up with strange and innovative solutions to problems. They will often retire to
a private corner to work while the rest of the team deliberates and return once
they have had a "Eureka moment”. This person usually serves as a
springboard toward innovative thinking and fresh solutions.

To improve and develop, the Plant should learn to focus on relevant issues
instead of drifting into new innovations, listen to the other member’s views
during meetings and contribute their time carefully between ideas. With these
taken into mind the plant can improve input to the group dynamics.

Teamworker (Neil)
A Teamworker makes sure that everyone in a working group is getting along.
They are good listeners and diplomats, talented at smoothing over conflicts
and helping parties understand each other without becoming confrontative.
Because of an unwillingness to take sides, a Teamworker may not be able to
take decisive action when one is needed. The team worker has effective
interpersonal skills and is adept at developing team cohesion and is good at
reading moods and feelings within the group.

In order to improve individual effectiveness the teamworker should learn to
take constructive criticism, heal relationship breakdowns within the group and
consider their own development needs.

Completer Finisher (Bruce)
The Completer Finisher is a perfectionist. They often go the extra mile to
make sure everything is "just right," and the things they deliver can be trusted
to be double-checked and then checked again. The Completer Finisher has a
strong sense of duty and will complete painstaking and unpleasant tasks if
they believe they will improve quality. They may frustrate their teammates by
worrying excessively about minor details and refusing to delegate tasks that
they do not trust anyone else to perform. With a completer in the team, it is

more than likely that the output will be accurate and on schedule, and that
nothing important will be omitted. However, it does not mean that the work is
necessarily creative or that it incorporates stunning ideas; that is not his role.

To further the group dynamics throughout the project duration, the completer
should give encouragement to colleagues, avoid being submerged in trivial
ideas and communicate all expectations effectively.

Specialist (Jonathan)
The specialist is exactly what their name implies; a person with an extremely
high level of skill in one given discipline. They may bring a high level of
concentration, ability, and skill in that given discipline, but can only contribute
on that narrow front and is often lost or isolated in the details of their work.
The specialist is the team member who proivides the expertise and knowledge
which is often vital for effectively completing tasks. They are self-motivated,
somewhat opinionated and dedicated to their own particular area of expertise.
This role is essential when specialised and technical decisions need to be
made and is useful for providing technical information to the team and helping
the team to remain objective.

In order to improve, the specialist should learn to simplify complex concepts,
communicate effectively and be patient with other members.

The results from the Belbin personality profiling is used to create a structure
catrering for all members’ strengths and weaknesses, bringing out all the
benefits to improve the team and project progress. The team is working well
together and is constantly improving due to the recommendations provided by
the personality profiling. During the duration of the project, personality types
can change as improvements are made. The final report will highlight any
team development and will outline the importance of interacting with other
personality types.

1.3   Gantt chart

                                                  Figure 3.1- Project Gantt Chart (Revised)

Figure 3.1 shows the team’s Gantt chart, which is a collation of all tasks that we aim to complete along with the allowable timescale
for each item. The chart has been revised since the initial statement of purpose to incorporate project management understanding
and statistical modelling. The Gantt chart provides a reference for all project work and the team’s progress can be marked against
the timeline set during the initial stages. It also maintains the team’s focus and make sure they are working to the set deadlines.

3.3 Critical path analysis

                                                                Ascertain what (if anything)
                                  Develop CFD skills            we can achieved with this                CFD modelling

                                                                                                     Investigate key
                                      Key research (marine                Develop analytical         parameters
                                      profiles/strike models)             model                      analytically

                                                                                                                                                  Compare      Decide potential
          Concretise            Determine                                                                                                         analytical   for fish deterrence
          project                                                         Detail                                        Is rig /test
                                specification        Brainstorm                           Rig                                                     & scale      being required for
          goals and                                                       design                                       performing                                                    END
 START                          and goals for        & concept                            fabrica        Test                               YES   model        marine turbine
          set team                                                        (CAD                                               as
                                practical            design                               tion                                                    results -    applications and
          roles                                                           drawing)                                     anticipated?
                                work                                                                                                              draw         apply lessons
                                                                                                                                                  conclusion   learned
                                                                                 Identify problem and attempt
                                                                                 to design out the issue                 NO

               Visit Scottish                   Detailed fish deterrent                 Site-specific                         Deliver
               Power                            research                                evaluation (possibly                  feedback to
                                                                                        some CFD)                             company

                                        Web design familiarisation                        Website

                                                                                Figure 3.2 - Critical Path Analysis

The critical analysis path analysis defines the routes that will be taken by the
team throughout the project and helps to identify key tasks and paths. From
the start of the project in week three, it was essential that the team plan the
next steps and the areas intrinsic to the successful delivery of the research.
Figure 3.2 shows the critical path analysis for the project. Each white box
contains a task set out in the planning stage and its position on the chart
reflects its importance to the team’s success. When the project enters the
area highlighted in purple, particular caution should be taken, as this is where
problems can often occur. If problems are encountered during this phase then
the team can resort to a contingency plan that had been prepared to cover
any eventuality. This includes the construction and implementation of a 1m
diameter turbine rig, similar to the design of standard Marine Current Turbine
(MCT) blades. The final report will highlight how the critical path analysis was
negotiated and how any problems were overcome.

3.4     SWOT analysis

The group decided to carry out a SWOT analysis to assess the strengths,
weaknesses, opportunities and threats relevant to the project. The results of
this analysis are detailed below.

•  The group has four members, which is ideally suitable to the project brief
    due to its size and scope. Any more members and tasks would become
    difficult to delegate and could overlap.
•   All members of the group have a keen interest in renewables and energy
    production    in   Scotland,    with   CV’s   showing    experience    with
    ScotRenewables (leading name in tidal power), Renewable Energy
    Systems Ltd, ExxonMobil and ScottishPower. This experience will ensure
    that the team are motivated to meet the project objectives.
•   The team members have all worked together before on previous projects,
    lived together and played sport for the university together. From the
    beginning of the project there was mutual feeling that the team would work
    well together as a unit.
•   The group all have the same timetable and are well organised, arranging
    meetings every week at the sixth floor common room of the James Weir
    building. During these meetings minutes are recorded, progress reports
    are updated and ideas are brainstormed. It is also at these meetings that
    tasks are delegated and goals are set for the week.
•   The team members have all demonstrated initiative in completing tasks
    without prompt and going the extra distance to help the group.
•   The group have created an online file sharing facility and contact network
    to maintain good communication links and access to public files. With the
    members living a distance apart it allows the sharing of knowledge and
    research findings to be accessed immediately.
•   In Dr Grant the team have a supervisor who is passionate about the
    subject and very willing to assist in the progress of the project. The
    findings of the team’s research will eventually go towards Dr Grant’s own
    research interests.
•   The team has vast computer simulation software experience including
    ANSYS, ProEngineer, MathCad, Excel, Fluent and Microsoft FrontPage.

• The project is limited by the timescale set in the statement of purpose.
•   The project is constrained by the budget of £400.
•   Tidal research and development is based mainly around sites with high
    tidal resource and is therefore almost impossible to visit or gain access to
    facilities due to distance. The greatest tidal resources in the UK are around
    the Orkney Islands and Islay, meaning logistics are a major barrier to

•   Research in this area (fish strike modelling) has never been properly
    undertaken and so there is limited resources and material to back up any
    findings found from project research.
•   Large portions of the development are purely hypothetical as there are
    very few examples of tidal turbines being utilised in open water channels. If
    there were operational sites then data could be generated and the issue
    could be understood in greater depth.
•   Testing facilities for tidal research are sparse around the UK and are
    therefore very expensive to hire. With the limited budget of the project,
    using theses facilities would not be possible.

• Through previous experience in industry, the group was able to establish a
    network of contacts in the tidal power and renewables sector.
•   The group was undertaking research that had never properly been
    explored previously, making the research very significant to the
    progression of tidal power as a viable solution to global energy problems.
    Project findings could form an integral part of any environmental impact
    assessments presented by tidal turbine suppliers.
•   Research    findings   would    reduce   the     potential   for   conflict   with
    environmental legislative bodies that may request impact assessment data
    on the utilisation of marine current farms.
•   The group have to the opportunity to uncover the issues related to tidal
    turbine interaction with marine wildlife in areas of high resource.
•   Testing has been made possible by the discovery of a flowing water
    channel in the Civil Engineering Department of Strathclyde University. The
    group will have access rights to the facilities and can create environmental
    conditions similar to that experience in tidal power applications.

•  The testing facilities only allow for a small scale test, and this may be such
    a reduction that similarities become less distinct. The model will eventually

    be a 1/42 scale and will have all the characteristics of a tidal turbine,
    however flow characterics may be comprimised by the significant scale
•   The conclusions of the research may be undesirable to turbine
    manufacturers and installers, forcing them to reconsider the technology
    due to it’s large environmental impact. Very little resource is allocated to
    this area and so if findings are negative towards tidal power, then results
    may not be welcomed across the industry.
•   Research may be ignored or missed by those involved in tidal power
    development due to the status of a university group. Industry may question
    the reliability of results generated by the group’s research and testing, due
    to the lack of experience in the area. This would deem the project pointless
    as no impact has been made, positive or negative.
•   Results may be inconclusive as they cannot be verified by real-life
•   Testing results may compromise statistical analysis.
•   Other university commitment may hinder progress of the project.
The group found the SWOT analysis useful as it outlined the benefits created
by working as a team and it highlighted the areas that required close attention.
The group hope to progress smoothly by utilising our many strengths to
overcome the issues brought up in the weaknesses and threats sections.

3.5    Budget

The budget was set by the university at £400 and is the same for all project
groups. Throughout the year, if funds are required for any purpose then they
must be applied for and then verified and signed for by the studies advisor.

In the initial stage of the project funds were allocated to:
•   Rig design and build. This included buying all the materials in order to
    house the turbines in the flowing water test tank. The design will be

        described in greater detail later in the report. The table below shows the
        price of design and how it affects our overall budget.
•       Propeller blades for the small scale testing. In order to simulate the tidal
        turbines in open water we felt it was suitable to buy smaller blades, already
        constructed rather than build our own. The solution to this was to buy
        propeller blades from model planes and attach them to the completed rig.
        The shape is very similar to that of tidal turbines and provides an accurate
        scaled version of the project application.

The only expenditure by the group so far has therefore been the purchase of
equipment and materials for the scale model test. Details of the orders are
shown below. The running total is £67.88 however we do not anticipate any
further purchases.

    Order Form                                                      Date         27/10/2006

    Quantity   Description                            Part          Supplier     Value        Total
    2          15x8 Master Airscrew 2 Bladed Prop     103208        Mart         £7.25        £14.50
    2          15x8 Graupner 3 Bladed Prop            ES538/20      Mart         £12.50       £25.00
    2          2" 3 Blade Spinner                     JP7352        Mart         £0.79        £1.58
    2          2" 2 Blade Spinner                     5507320       Mart         £0.90        £1.80

    Test Rig Frame                                                               09/11/2006

    5m         25mm Al 6063 Box Section 2mm Wall                    University   £25.00       £25.00

                                    Table 3.1 – Expenditure chart

Due to the limited budget, some transactions could not be completed due to
their significant cost:
•       All offsite testing is carried out in test tanks throughout the UK, each
        capable of holding much larger rig designs. In order to hire one of these
        tanks for a day it would have cost the group around £1500, meaning we
        would need to raise significant funds. It would be more desirable to create
        a larger test, but unfortunately the budget constraints did not allow for this

•   During the initial stages, the group were made aware of a conference that
    might aid the research being carried out for the project. With key speakers
    from the tidal industry present, information could be gained from engineers
    with first-hand experience. Unfortunately, high attendance prices again
    made this unfeasible.

4.0 Research Summary

4.1      Original goals as set out in project scope
“Research of the marine profile for a specific test site in Orkney, identifying
influencing factors for tidal turbines and any work previously carried out in this

“Review of available measures to deter marine wildlife and then investigate
their possible implementation for tidal turbines”

4.2      Revised aims, objectives and strategy.

The nature of the studies demanded a diverse range of research topics. To
facilitate efficient completion of the research activities and to ensure that no
work was duplicated, the research co-ordinator divided the research work into
distinct areas as described below. These were then divided between the
members of the group as interest/speciality permitted.

•   Tidal power background
•   Fish strike models for hydro turbines (analytical and physical models)
•   Effects of turbulence and shear on marine life
•   Bird strike models for wind turbines (analytical and physical models)
•   Computational methods for modelling flows for intakes and turbines
•   Fish friendly turbines
•   Fish deterrent methods currently under development
•   Commercially available fish deterrents
•   History and background of Longannet site

4.3      Tidal power background
Tidal energy exploits the natural ebb and flow of coastal tidal waters, caused
principally by the interaction of the gravitational fields of the earth, the moon

and the sun. This energy source has long been recognised as a resource with
enormous potential for the sustainable generation of electrical power, however
technical challenges have until recently slowed progress. The high load
factors resulting from the fluid properties of water gives a very high energy
density compared with wind power, while the predictable nature of the
resource make marine currents particularly attractive for power generation.
Tidal currents also offer very small and manageable extremes in condition.
These factors together make electricity generation from marine currents
particularly appealing when compared to other renewables such as solar and
wind energy.

Tidal head or barrage schemes are one way of capturing tidal energy and are
effectively hydro schemes that explot sea water that has been impounded
whilst the tide falls outside the scheme. When released, the impounded water
flows back to the sea. There are two mechanisms for extracting the energy:
one using conventional horizontal axis turbines, the other using the venturi
effect and generating suction. This form of tidal power extraction has however
come under fire from environmentalists, as the generation is energy intensive
with the construction of a dam and associated facilities.

The energy from the tide is often further magnified by topographical features,
such as headlands, inlets and straits, or simply the shape of the seabed
causing water to be forced through narrow channels. Tidal stream devices,
which are similar to submerged wind turbines, are used to exploit the
increased kinetic energy in these tidal currents. These devices tend to take
one of four forms:

A) Horizontal axis, bottom mounted. These turbines sit upon the seabed on
either a plied or a gravity foundation, as shown in figure 4.1

               Figure 4.1 - Horizontal axis, bottom mounted turbines

B) Horizontal axis, surface piercing. These turbines are pile mounted to
allow the turbine to be raised above the water level for maintenance.

C) Horizontal axis, floating. The turbine is mounted under a floating
structure, which is moored in the tidal stream.

D) Vertical axis, floating. Similar to horizontal axis, floating, but the turbine
axis allows the generation equipment to be sited above the water level.

There is much to be learned about these devices from technology transfer
with wind turbines and ship propellers, however there have been relatively few
large scale tests set up to investigate marine current turbines performance in
depth. This is surprising since, based on the UK electrical consumption of
401TWh/year for 2003 (Digest of UK Energy Statistics, 2004), marine current
turbines could supply 2.5 to 7.5% of the current UK energy demand. The
University of Southampton are heavily involved with
marine current turbine research and commissioned
a recent study to look at the power, thrust and
cavitation characteristics of a 1/20th scale model of
a 16-metre diameter horizontal axis tidal turbine [2].
An experimental procedure was set up to test
turbines with an 80cm rotor in a cavitation tunnel
with a working section of 2.4x1.2m and a maximum
flow speed of 8m/s. Power coefficient, thrust tidal
and speed histograms were all built up over a month
                                                              Figure 4.2 The Darrieus

For installations employing the vertical axis turbines such as the Darrieus
turbine, shown in figure 4.2, it has been found that tidal power is only effective
for generation where there is a tidal range of 5 metres [3]. In areas where the
tidal range is lower than 5 metres, power from the tidal current is not feasible.
These turbines are able to extract power from the tidal current regardless of
the direction of flow.

Commonly quoted barriers to development of marine current turbine
technologies include high operation and maintenance costs and potential
hazards for maritime routes. Technological barriers are also only now
beginning to be overcome: high working stresses are inevitable (the site is
chosen for its strong tide and therefore severe environment) and cavitation at
blade tips has been an issue. The other main issue raised by
environmentalists concerns potential effects upon marine life and habitats.
Although there exists little concrete evidence of effects due to the limited
testing carried out to date, it is clear that the issue of migratory fish passage
across tidal power barrages was one of the major barriers to tidal power
development in the 1980’s. These early developments are centred around the
‘tidal barrage’ concept which give passing fish no option but to pass through
the device. Some evidence has been produced by Dr Andrew Turnpenny in
his capacity as head of the Aquatic Technology section of the Central
Electricity Research Laboratories in the UK Tidal Programme of the 1980’s
[4]. This evidence relates to strike probabilities for fish passing through tidal
barrage devices and not marine current turbines.

For a nine-metre diameter turbine design for the Severn the probability of
collision is quoted as follows:
•   Adult salmon (100cm)           40%
•   Adult Eel (70cm)               28%
•   Juvenile Shad (7cm)            53%

With reference to the figures above it would appear that the early concerns
over the potentially serious impacts on migratory fish are justified. Physical
screens would not be practicable to implement diversion in this case, but the
development of acoustic fish guidance, originally investigated for tidal power
applications, has advanced from a concept to reality. It is now regarded as the
‘best available technology’ for fish screening. The Fisheries Committees want
to consider small-scale schemes before passing large tidal schemes and a
study was set up at Fawley to evaluate the effectiveness of underwater sound
against the UK species in question. The field study was carried out at Hindley
Point Nuclear power station in Somerset, with some systems demonstrating
an 80% diversion efficiency.

4.4    Marine Current Turbines Ltd.
One of the technical authorities in the tidal turbine domain is Marine Current
Turbines Ltd. (MCT). MCT is backed by the UK government and is developing
tidal stream technology with a view to exploitation for large-scale power
generation. Exploitation of this technology would require currents of 2-3m/s at
sites of maximum 40m depth at low tide, to allow existing drilling vessels to be
used. Several potential sites have been identified including the current site of
the world’s first 300kW turbine off the Devon coast.

The technology under development by MCT consists of twin axial flow rotors
of 15-20m in diameter, which drive a generator via a gearbox. The power units
are mounted on wing like extensions to the tubular steel monopile set in the
seabed and sit just below the surface of the water. The units can be raised to
allow maintenance to be carried out easily during calm periods without the
need for divers or ROV’s. The steel pile has cathodic protection while the
blades can be made from glass or carbon reinforced composites. Designers
first considered producing the required stiff, unyielding marine rotors in steel.
However, achieving the necessary compound-curved profile in steel proved to
be expensive. Moreover, steel is heavy, prone to fatigue and susceptible to
corrosion induced by salt water. These disadvantages prompted a decision to
instead adopt composites [6]. Plastic-based materials ease the fatigue

problem, both through their inherent fatigue tolerance and by reduced blade

             Figure 4.3 - Impression of a marine turbine farm development

The full size turbines will be rated at 750-1500kW and will be grouped in
arrays. The units will be much smaller than wind turbines for the equivalent
power rating since approximately 800 times more power can be extracted
from water as compared to an equivalent flow of air. They will also rotate
roughly ten times slower than a ship propeller, which suggests intuitively that
most animals would stand a good chance of avoidance. From an economic
perspective, the technology is modular and so small investments can initially
be made with subsequent units being easily integrated at a later stage. As the
site grows, the marginal cost of installing and maintaining new units will

4.5   Environmental impact assessments
In accordance with the Food and Environmental Protection Act of 1985 all
companies involved in operating and developing marine current turbines who
wish to apply for permission to construct on a site are required to submit an
environmental statement to support the application. This statement must
follow recognised environmental impact assessment procedure. The task is

normally allocated to a specialist contractor who will apply a standardised
procedure designed to raise and discuss all pertinent environmental concerns
[8]. The process therefore involves consultation with numerous third parties
and information collected is used to aid the Environment and Heritage Service
(the competent authority in this case) in determining the likelihood of any
protected features of the flora and fauna being detrimentally affected.

Broadly speaking the purpose of the assessment is to inform, to obtain
information and to voice any concerns.

Some steps which are typically undertaken as part of the assessment are
listed below:

•   A description of the scope of the project, motivations and intended
•   Procedures to be used for installation of the devices e.g. consider if access
    to the site will be a problem, what drilling needs to be done and if grid
    connection will require the installation of significant underwater cabling.
•   Modelling of the water movement at the site (before and after turbine
    installation) to assess the potential impacts upon water speed; distribution
    of fine particles and the removal of energy from the tidal stream.
•   Detailed analysis of the plants and creatures that are found in the area to
    identify in particular any species of special scientific interest or that are
    protected. Analysis of creature behaviour in the area such as seals,
    basking sharks and harbour porpoise. Historic movement and population
    observations along with discussions with experts are vital.
•   Monitoring and projection of underwater noise levels and the possible
    effect upon marine life.
•   The effect of the project on navigation is analysed, for example the
    frequency of use of the area for other purposes and requirement for
    consultation with other sea users. Appropriate warning methods and
    information sources need to be identified and recommended.

•   Visual pollution – how visible will the development be from various
    surrounding areas. Do local residents have any concerns?
•   Probable effect for local businesses (e.g. fishing) and tourism in the area.
    Invitation for written views by all interested parties (council, crown estate,
    coastguard, fisheries committee, environment agencies).
•   Decommissioning and the long-term effect (if any) upon the surrounding
•   General impact summary in tabular form that summarises the scale,
    duration, residuals and significance of each concern.

In most instances it is recognised that the likely impact upon seals, basking
sharks and other such creatures cannot at present be estimated with great
confidence. Behavioural uncertainty makes it almost impossible to predict how
these creatures will react to the new installations therefore comprehensive
monitoring programmes are being implemented along with the first wave of
developments to ensure that the risk to these and other creatures (e.g. birds)
is acceptably low. If these programmes highlight any problems then
operations will be modified or ceased. This essentially remains the only major
‘grey area’ for developers, as they have up to now been unable to
categorically state what the potential impact on such creatures will be. The
work being carried out by the group could therefore be extremely valuable in
terms of providing developers with an initial idea of the potential
strike/mortality rates for these creatures, assuming no abnormal behaviour
(particular species being attracted toward the blades) is noted during the initial
monitoring programmes.

4.6    Fish strike models
Although very limited study has gone into strike modelling for marine turbines,
studies into fish interaction with complex hydraulic environments have been of
great use to those concerned with hydroelectric power, leading to a significant
body of research. Great effort is being invested in an attempt to better
understand the path of fish through complex hydraulic environments, such as
turbines intakes for dams. Indeed the relationships between fish orientation,

fluid velocities, pressure conditions, and fish injury mechanisms are being
explored using both experimental and computational tools. The US
department of energy have commissioned several studies, which attempt to
come up with strike probability models and evaluate their efficiency. Blade
strike is seen as an example of a “Bio-indexing” variable, which could be used
to compare performance of hydro turbines and ultimately to optimise passage
conditions for fish by identifying operations for new and existing turbine
designs that minimize the probability of injury. This is being done using both
numerical and physical turbine models to generate hypotheses that can then
be tested at prototype scale using live fish.

Two numerical models were in fact developed by the authors of these studies
[9, 10]. Through comparison of numerical blade strike models with physical
turbine models, using beads as well as prototype scale live fish tests, the
stochastic blade-strike model was found to be more accurate than the
deterministic model. Stochastic elements included were for example the
probability of fish having a certain orientation relative to runner blade edges as
they enter a turbine runner. The stochastic model assumed uniform
distribution and random passage radius and aspect.

Blade-strike models such as the one examined provide a good overview of the
general blade-strike probabilities for prototype hydro turbines, however it is
acknowledged that numerical modelling will therefore likely need to move
towards Computational Fluid Dynamic methods to better quantify and capture
the differences critical to improved biological performance of operating hydro
turbines. The most widely used blade strike model is a series of equations that
calculates the probability of blade-strike. These equations take into account
the turbine axial velocity; angle between axial velocity and water velocity;
number of blades; runner speed (RPM); fish length and critical passage time
(time between sweeps of two successive blades). This model leads to a
worst-case scenario, assuming fish to be rigid bodies orientated perpendicular
to the leading edge of the blade. All estimates of blade strike probability
therefore tend to exceed observed injury and mortality rates. Of course not all

strikes lead to injury/mortality. To take this into account, the concept of a
“mutilation ratio” has been introduced (this is the ratio between proportion of
fish struck and proportion actually injured). This ration has been calculated as
an empirical regression equation principally dependent upon fish length.

For the scale model high-speed cameras were used to track the beads/fish
travelling through the turbine model and a grading system was used to
classify the number and type of collision in each case. Beads were released
from different locations and results compared. A relationship between the
distribution of fish at the turbines wicket gate and the location of entry into the
turbine runner was obtained using CFD. For the stochastic model software
was used to identify the input distributions that are most critical to simulation
results. Mean length was found to be the most important factor followed by
bead passage radius and discharge.

4.7    Bird strike models
Wind turbines are clearly at a far more commercially advanced stage than
marine turbines, yet these devices have and continue to provoke significant
unrest amongst bird conservationists. Bird strikes are deemed the largest
environmental problem with wind turbines, and many wind developments have
been heavily opposed for ornithological reasons. The RSPB, which is an
institution set up specifically for the protection of birds, views climate change
as the largest threat to wildlife and therefore support a broad mix of
renewables to meet the future energy needs of the nation. The RSPB state
that evidence points towards correctly positioned wind farms having no
adverse affect on the bird population, however badly position wind farms can
have major impacts and as such the RSPB have objected to 76 UK wind
farms applications between 2000 and 2004. In order to ensure the sensible
location of wind farms, the sites have rigorous environmental assessments
implemented, with applications being rejected if any threat is presented to
sensitive bird populations or their habitat.

It is understood however that the installation of wind farms can affect birds in
manners other than simply collision potential [12]. The wind turbine farms can
act as barriers, which the birds try to avoid during natural migrations or flight
paths leading to birds not being able to find feeding or roosting grounds,
which causes negative affects on the bird populations. The actual construction
of the wind farms can also destroy the habitat in which certain species of bird
thrive and also, due to the noise and frequency of visitors, drive the birds
away from these areas. It is therefore important to be able to understand the
bird activity in an area before a wind farm is constructed. Various methods
can be employed to study this [13]. Some of the more popular methods
involve acoustic monitoring to pick up different species and radar and thermal
monitoring of the area to execute bird counts. The most popular method by far
is to have a person on site recording number, altitude and species of bird

In an effort to further understand the phenomenon of bird collisions, several
mathematical models have been developed, such as the one developed by
Tucker [15] in 1996. This was the first complete theoretical analysis of bird-
rotor collision, with the following paper [16] determining how the results could
influence the design of new ‘bird friendly’ rotors. The bird is essentially
modelled as a two dimensional rectangle entering the swept area of the rotors
turbine blades. The blades are three dimensional with length, cord and angle
of twist. The model incorporates a variable to account for the reduction in wind
speed as the wind passes through the turbines. A collision is said to occur
when any part of the bird and a blade occupy the same space for the same
instant in time, leading to an overall probability figure. The model takes into
account bird behaviour (passively passing through or attempting to avoid the
blades), rotor geometry, size of bird and speed of turbine rotation. All wind
speed calculations are averaged since the wind speed can change from
second to second. A Weibull distribution is used to represent the wind speed.
As the probability of a strike differs at different parts of the blade, a probability
map can be drawn and an overall probability gained through integrating the

probabilities. Near to the rotor hub, due to the low velocity it is assumed that
birds can avoid the moving obstacle and so this section is neglected.

The latter part of the paper looks at three specific cases:
•   One-dimensional blade and flight parallel to the wind direction
•   One dimensional blade and flight oblique to the wind direction
•   Three dimensional blades and flight parallel to the wind direction

It is concluded that it is indeed possible to predict the probability of bird strike
using a mathematical model. The strike probability is found to increase nearer
to the hub than at the peripherals and the probability of impact is lowest for
downwind flight. The paper finally describes a means of reducing the safety
index for different characteristics of the turbine in order to produce a ‘bird
friendly turbine’. It is expected that by redesigning turbines with bird strikes in
mind the probability of bird strikes could be reduced by 90% without any
significant reduction in energy. Clearly both considerations of bird strikes and
loss of electricity would have to be made to ensure that the project is still
economically feasible

It should be possible to replicate some of these calculations and then adapt
the model for tidal turbines such that collision probabilities could be
investigated for varied species of fish/mammal, various tidal patterns and
various turbine designs. The behavioural aspect will be the most difficult to
capture within these calculations. Similarly to birds, perhaps animals such as
seals may be less aware of turbines blades if they are tying to catch prey.

4.8    Fish friendly turbines
Great efforts have been made in pursuit of a so-called ‘fish friendly turbine’.
The Advanced Hydropower Turbine System Program (AHTS) aims to design
an environmentally friendly hydropower turbine. To assist in the design
studies into fish mortality, causation of injuries to fish and available biological
design criteria have been undertaken. The various fish injury mechanisms
noted include: increasing pressure, rapidly decreasing pressure, cavitation,

direct strike, grinding, shear and turbulence [17]. Several new designs are
based around screw shaped concept to allow the safe passage of fish through
the system. It has been found that injury and mortality mechanisms are
dependent on the zone which the fish takes to pass through the turbine
system. Presumably the same will be true for tidal turbines. At Wanapum Dam
in Washington, fish that passed through a zone near the turbine hub
experienced 5% higher mortality than fish that passed through the zone in the
middle of the runner [18]. Fish encountering the zone surrounding the blade
tended to sustain injury due to blade strike, blade end gaps, and local fluid
flow effects. However, quantifying exact sources of turbine passed fish injury
and mortality is difficult due to the lack of controlled experiments. Injuries
caused by pressure appear to be related to the difference between the
acclimation pressure upstream of the turbine and the exit pressure within the
draft tube zone. The turbine operating point has a significant effect on fish
survival. Tests at Wanapum Dam showed that peak fish survival did not
coincide with peak efficiency, but occurred at a discharge where the predicted
blade strike probabilities were low and before cavitation became significant.

4.9    Effects of turbulence and shear
Fish injury or mortality, as mentioned earlier, is not limited to situations
whereby the blade strikes the fish themselves. Fish can be exposed to
damaging levels of fluid shear stress and turbulence while passing through
installations such as hydroelectric power plants, particularly during passage
through the turbine. The effects upon fish of rapid and extreme pressure
changes, shear stress, and turbulence are poorly understood. Understanding
the physical stresses that fish experience as they pass through is a challenge
that is now beginning to be taken up.

When water velocities change on scales comparable to the size of the fish
then shear becomes a damaging effect. When two water masses of different
velocities intersect, the shear is defined as the change in velocity over a given
distance. Estimates of shear must be combined with estimates of viscosity to
obtain shear stresses and resultant forces on the fish. Turbulence intensity is

a measure of the magnitude of the turbulent fluctuations about the mean. If a
series of instantaneous velocity measurements are taken at a point then the
turbulence intensity can be expressed as the root mean square of these
measured values

The largest values of shear in a turbine would occur near the blade tips and
near the hub. Estimates for typical shear stresses in such regions are
available [19] and are in fact comparable with shear stresses that occur in
natural environment (rivers, flash floods). The advanced hydropower turbine
system programme of the US Department of Energy has begun experiments
using live fish and advanced tracking techniques that are aimed at
determining whether the shear stress and turbulence that occur within
hydroelectric turbines are actually injurious to fish.

The Pacific Northwest National Laboratory (PNNL) in Richland, Washington
have also investigated the effects of shear on
several species of andromous fish, the objective
being to identify threshold shear strain values
that result in fish injury [20]. Juvenile salmon
were introduced into a shear stress test facility.
Water velocities in the shear zone were
measured at a fine scale and were used to                   Figure 4.4 - Juvenile salmon being
                                                            introduced to the test facility [17]
estimate the strain rate to which the fish were
                                           exposed. A full-scale test facility was
                                           constructed to estimate injurious shear
                                           stress values upon which to develop turbine
                                           design criteria. The jet introduced high
                                           velocity water into the tank - creating a zone
Figure 4.5 - Juvenile salmon injuries
resulting from passage through the shear   of high shear in the boundary layer between
zone [17]
                                           the fast and slow water. Test groups of
fishes were introduced into this shear zone, both head-first and tail-first. The
paths of fish in the shear zone were videotaped and fish were collected and
visually examined for evidence of injuries. Sensitivity to the strain rate was

found to vary among the species tested. American shad were the most
susceptible to shear strain-caused injury, salmonids were generally
intermediate, and juvenile Pacific lamprey were relatively unaffected by shear
strain. It was found that localized fish injuries due to the forces associated with
small-scale turbulent eddies may cause mortality, even though shear stresses
appear to be small.

In another study [21] juvenile rainbow trout, spring Chinook salmon and
American shad were exposed to shear environments in the laboratory to
establish injury-mortality thresholds based on estimates of strain rate. Fish
were exposed to a submerged jet having exit velocities of 0 to 21.3 m/s,
providing estimated exposure strain rates up to 1,185/s. Turbulence intensity
in the area of the jet where fish were subjected to shear was minimal, varying
from 3% to 6% of the estimated exposure strain rate. Injuries and mortalities
increased for all species of fish at strain rates greater than 495/s. Resistance
to injury was found to depend upon both fish species and orientation.

4.10 EMEC tidal stream test site
Following initial investigation into suitable tidal sites, it was decided that the
EMEC tidal test site would be an appropriate choice since the group was able
to use some contacts to attain information relating to the site. This information
could then be used as a basis for our analytical model, CFD model and to
gain insight into typical marine profiles. The test facility for tidal stream energy
converters is situated in one of the strongest current paths in Orkney waters.
Spring tide peak flows can reach 4 m/s (7.7 knots) and sea conditions can be
very challenging. The tidal test berths will be located off the southwestern tip
of the island of Eday, in an area known as the Fall of Warness. The facility
offers five tidal test berths at depths ranging from 25 to 50 metres in an area 2
kilometres wide and approximately 3.5 kilometres in length

          Figure 4.6 – Promotional material for the EMEC test site [1]

Each of the test berths has an 11kV 5MW underwater cable, which is fed back
to a sub station on the island of Eday. The substation contains all of the
necessary switchgear for the control of devices on test and a link to the
national grid. The site is in the final stages of completion and the first
developer, Open Hydro is in the process of installing their device. From the
shoreline of Eday the depth of water decreases steadily from one metre to 34
– 51 metres in the main deployment channel. The seabed contains sand
banks to the east, with smooth bedrock ridges and platforms towards the
centre. Any loose sand and gravel in the area is swept away by the current.

The marine life know to frequent the area is wide ranging. Common and grey
seals have colonies on uninhabited islands nearby. The grey seal population
in Orkney is estimated at 14,000, representing around 20% of the UK
population. Other mammals recorded in the area are White beaked dolphins,

Harbour porpoise, and Minke whales. Otters and basking sharks are also
known to have passed through the test site very rarely. Pods of Killer whales
have also passes though Orkney waters in summer months.

Fish common to Orkney waters are wide ranging. Those likely to be found
near to the site include: mackerel, which will be most numerous in summer
months, pollock, cole fish and cod. Other known species are herring, haddock,
ling, and saithe.

4.11 Seals
For the investigation into collisions in Orkney, it is thought that seals will be of
principal concern since they are a sizable mammal that is relatively common
at the site, yet not of enormous population worldwide. It is considered that
smaller fish would be swept along by the blades and that shear/pressure
changes would be of greater concern than physical collision. The two species
found at the EMEC site are the Atlantic grey seal and the harbour (common)
seal. Seals can become entangled and drown in fishing nets, while in the UK,
Canada and Norway, it is legal to shoot any seals that come near fisheries. It
is illegal to commercially hunt common seals, but some hunting for
subsistence still occurs.

The grey seal population is at present healthy and growing, with the worldwide
population estimated at 220 000 [22]. Half of the world’s population live in
and around British coastal waters. At sea they are usually solitary, or found in
small dispersed groups. They will rest at the surface in a vertical "bottle"
position, treading water with only the head and upper neck exposed. The
maximum depth of dives is approximately 300 meters and up to 30 minutes.
Most dives are from one to ten minutes, and to 60 metres or less. A common
cause of natural premature mortality within seals has been attributed to
distemper virus outbreaks among colonies.

Harbour seals are mainly found in the coastal waters of the continental shelf
and slope, and can be found commonly in bays, rivers, estuaries, and

intertidal areas. While in the water, these essentially non-migratory seals can
be curious, often craning their necks to peer at people on shore or in boats.
Most harbour seal haul-out sites are used daily, based on tidal cycles,
although foraging trips can last for several days. They are most often seen
alone when at sea, but occasionally occur in small groups.           Localized
aggregations can form in response to feeding opportunities and concentration
of prey. Harbour seals live in coastal areas in the middle of some of the most
heavily fished waters on earth, and as a result there are entanglement issues
as well as effects on the food chains they depend on for their prey. Combining
recent estimates yields a worldwide population in the region of 300,000 to
500,000 animals.

4.12 Case Study: Longannet Power Station
Longannet Power Station at Kincardine-on-Forth is the second largest coal-
fired power station in the UK and one of the largest in Europe. It has an
installed capacity of four 600MW units and can produce enough electricity to
meet the needs of two million people. The plant has played an important role
in meeting Scotland's energy needs since 1972. Electricity from Longannet is
also sold in England, Wales and Northern Ireland. The site was chosen by the
group as a case study to examine fish deterrence issues. The plant is situated
on the banks of a narrow stretch of estuary (see figure 8) and has a
requirement for 72 million gallons of cooling water every hour. This is an
enormous quantity of water that needs to be drawn in from a very narrow
stretch of water and this has raised concerns as to the number of fish that
could potentially be getting drawn through the intakes. No estimates of the
numbers of fish involved are available, but the issue has been recognised as
a problem and a team have for the past few years been actively seeking to
find a workable solution.

We hope that in examining this case study we can summarise the work that
has been done thus far before examining all possible solutions for fish
deterrence currently available on the market and drawing conclusions. We
then hope to evaluate the potential for transfer of any of this technology to
marine turbines, if required.

    Figure 4.7 - Arial view of he Longannet coal-fired power station and the cooling
                              water intake from the forth

4.12.1           Time line for activity surrounding Longannet power station

It was important to summarise the significant events that have occurred at
Longannet previous to our investigations commencement. Longannet power
station has been operating successfully for almost 40 years, however recently
concern has been voiced by several outside parties looking to protect Forth
estuary fish populations and conserve the rivers surrounding environment.

•     September 1998. The first communication regarding the issue is received
      and recorded. The Fisheries Committee (FC) requests data from
      Longannet Power Station on fish populations in the Forth and counts at
      the fish screens.

•     September 1998. Postgraduate undertakes studentship at Stirling
      University to measure the impact of Longannet on fish population in the

    Forth. The project aims to evaluate fish populations in terms of species
    composition, abundance, seasonal and special distribution.

•   May 2000. Concerns expressed by FC regarding the size of the screen
    used and whether it may affect salmon and smolt populations

•   April 2001. FC express serious concern at the number of fish being killed
    at the drum screens at Longannet.

•   Dec 2001. Interim report from studentship shows that main factors to
    entrainment are the seasonal (spring) and tidal state (high tide).

•   July 2002. Scottish Power register first interest in possible fish deterrent in
    form of an acoustic device.

•   September 2002. Scottish Power approach The Carnie Consultancy
    regarding fish screening technology. The consultancy then outline screen
    types (physical, behavioural) and make proposals for a plan of action:
    o Investigate site characteristics
    o Assess screening options (meshes, louvers, acoustic and bubble
       screens) and suitability
    o Identify proven manufactures of such systems
    o Prepare technical specification
    o Enter into discussions around specifications
    o Scottish Power put contract out to tender

•   December 2002. Colin Carnie of The Carnie Consultancy specifies
    acoustic screens for Longannet. This system is manufactured by Fish
    Guidance Systems Limited and the specification includes survey,
    modelling, costing, objectives and plant specification.

•   February 2003. Acoustic screen system advised to be in the 2003/04
    Scottish Power budget.

•   May 2004. Proposal of a fish deflection system at Longannet Power
    Station is submitted by Fish Guidance Systems Limited. The document
    covers all areas of the proposed system outlining specifications,
    installation, assumptions and costs. Quotations range from £46k to £750k
    depending on the number of transducers fitted.

•   October 2004. Acoustic barrier deflection system deemed non-viable
    solution by Scottish Power due to very small guaranteed deflections rates
    and high capital and installation costs. A £600k investment would only
    provide, at best, a 40% deflection rate.

•   January 2005. FC address the seriousness of the issue and feel that no
    action at the by the utilities provider is unacceptable. They urge Scottish
    Power not to discard the acoustic system without further investigation. FC
    proposes that Longannet stops generating during the spring, which is
    clearly not an option as it provides a large percentage of Scotland’s energy
    needs. ScottishPower respond to concerns by outlining the problems
    associated with acoustic barrier system and demonstrate it is not an
    economically viable or sufficient solution.

•   February 2006. FC involve Scottish Power Chief Executive Phillip Bowman

•   December 2006 (pending). New fish return system incorporated into
    existing fish drum screens.

4.12.2         Fish screening summary
There are several key drivers for broadening the requirement for fish
•   The developing legislative framework
•   Broadening scope of species to be protected
•   Changing water resources perspectives
•   Establishing ‘green’ credentials

Fish screening techniques have long been employed for cooling water intakes
and hydropower applications; however the unavoidable problem is the trade-
off that must be made in terms of the screen size. Too coarse and young fish
will almost certainly be able to pass through, but too fine and there will be
greater frequency of screen blockage causing often-impossible maintenance
workloads and reduced plant performance. Guidance technology has more
recently come onto the market and is still perceived as something of a ‘black
art’. Different species react in different manners to different stimulants and it is
very difficult to prove a performance standard for a given technology.

Positive exclusion screening methods for larger fish
•   Traditional Passive Mesh Screens
•   Vertical or Inclined Bar Racks
•   Rotary Disc Screens
•   Spillway Screens
•   Band or Drum Screens Modified for Fish Return
•   Econoscreen

Physical screening for juveniles and small fish
•   Passive Wedge-Wire Cylinder Screens
•   Wedge-Wire Panel Screens
•   Sub-Gravel Intakes and Wells
•   Micro-filtration Barriers

Other positive exclusion fish screens
•   Barrier Nets

Behavioural barrier and guidance methods
•   Behavioural Deterrents Background
•   Louvre Screens
•   Bubble Curtains
•   Electric Barriers
•   Acoustic Guidance
•   Light-based Systems
•   Velocity Caps and Other Flow Control Measures for Offshore Intakes

Other behavioural guidance techniques
•   Turbulent Attraction Flow
•   Surface Collectors
•   Eel Bypasses

Performance Criteria are essential in order to evaluate and compare new
emerging technologies. Timing of fish movement when exposed to certain
stimuli are gathered as well as data on intake velocities and fish swimming
performance for various species such as salmonid smolts, salmonid kelt and
other freshwater fish species. For screens, fish behaviour in front of screens
can be examined in detail as can the effect of screen angle to flow and the
effect of mesh aperture as discussed previously.

Studies have been carried out to look at the effectiveness of systems such as
sound barriers. For example an acoustic deterrent system producing 20–
600Hz sound was used in one such study [25] to repel estuarine fishes away
from a power station cooling water inlet. During sound emission, total fish
impingement decreased by 60%. The avoidance response varied among
species from no effect to highly efficient deflection. A more detailed review of

commercially available technologies has been carried out and can be found in
Appendix B.

Section B: Assessing the risk of turbine on fish and
The following section makes steps towards quantifying and evaluating the
impact of tidal turbines on marine wildlife through statistical, computational
and experimental methods. To appraise the likelihood that adverse effects
may occur to individual fish or mammals or to populations of fish or mammals
it is necessary to consider several questions.
•   What is the probability of avoidance of the turbines?
•   What is the probability of any marine wildlife passing through the turbine
    colliding with the blade?
•   What is the probability of marine wildlife that passes through the turbine
    being affected by turbulence and shear effects?
•   What is the expected number of fatalities per species / group?
•   What is the amount of potential habitat lost due to avoidance behaviour?
•   What is the relationship between marine life activity, the height of the
    turbine in the water and the potential for blade strikes?
•   What methods can be used to quantify actual mortality and injury?

Evidently the scope of this project means that we can only consider a certain
number of these points. Some initial thoughts as to important issues we might
consider are listed below:
•   Number of animals passing through the site (radar / count survey)
•   Probability of swimming at or above minimum tip height for each species
    (Species behavioural information / survey information)
•   Probability of turbine operating during critical migration period
•   Probability of encountering swept area if swimming at swept height (area
    calculation / simulation / computational fluid dynamics)
•   Probability of collision if encountering swept area (collision model)
•   Probability of injury upon collision (mutilation ratio)

•   Probability of injury due to adverse shear / turbulence effects (CFD and
    information from other studies)
•   Avoidance probability (behavioural aspects / physical testing)
•   Overall probability of collision / injury – multiply all these factors

5.0 Mathematical collision risk model
The development of tidal stream turbines is now underway in earnest, with the
first few devices in the UK having being installed. Many of the devices being
developed are similar in design to wind turbines, with two or three bladed
rotors. As was noted in section 4 much work has been carried out to
investigate the collision risk for birds flying in the path of wind turbines, but as
yet there has been very little work to investigate the risk of a collision between
a tidal stream turbine and marine life. With our study being based on the
EMEC tidal stream test site in Orkney, marine life studies have shown the
most abundant marine life in the area is to be harbour and grey seals. A
typical grey seal has a length of around 2 metres and an approximate width of
0.5 metres.

5.1    Objective from original scope
“Evaluation of the impact of a tidal turbine on the local marine wildlife through
computational simulation and statistical analysis”

5.2    Revised objectives of statistical analysis work
•   To develop a model which will be able to determine the probability of a
    fish/mammal being struck by a rotor as it passes through a turbine.
•   To produce a collision probability map of the turbine showing biggest
    danger areas for passage by fish/mammals.
•   To produce an informative table of data about tidal turbine strikes on

5.3    The statistical model
The model developed here uses the same principals as the bird strike model
developed by Turner 1996 [15]. There are three modes of collision described

by the bird model; downwind flight, upwind flight, and cross wind flight. Only
downstream and upstream swimming have been considered for the tidal
model thus far.

After performing a basic 1D analysis it became apparent that the risks from
upstream swimming were unreasonable due to the very small relative velocity
of the creature approaching the turbine. This meant that the creature would be
stuck by multiple blades in the time passing through the rotor. It is considered
however that creatures that regularly spend time in regions of rapid currents
are agile and very perceptive, therefore if approaching a turbine upstream at
such a slow relative velocity they could quite easily take evasive action.

The basic bird model from [15] is shown in figure 5.1. The model assumes a
bird to be a flat plate with wingspan, b, and aspect ratio, A. A collision occurs
when the bird flying through a random point of the turbine occupies the same
volume in time as a blade. This model does not determine the severity of a
collision, as it may be a slight clip of a wing, or a blow to the head. Figure 5.2
shows the coordinate system as a collision occurs.

                     Figure 5.1 - 3D View of Collision Model

                     Figure 5.2 - Collision Coordinate System

The probability of a collision is proportional to the ratio of the time for a bird to
fly though the blade and for the period of rotation. This is defined by equation

5.1 with the mean probability over the whole rotor given as the double integral
of the probability over the radius and angle given by equation 5.2.
                                    B ⋅ Δψ
                               p=                                       (5.1)
                                     2 ⋅π
                                          π R
                          π R − r02
                                        ) ∫ ∫ p ⋅ r ⋅ dr ⋅ dψ
                                          0 r0

For the simplest case of the blades being 1D represented by single lines and
the creature swimming parallel to the stream, the probability can be found as

Change in azimuth angle:
                               Δψ = (Δψ )x + (Δψ )s                     (5.2)

                                            Ω ⋅ Δx
                               (Δψ )x   =                               (5.4)
                               Δx =                                     (5.5)
                               V x = Vbx + (1 − a ) ⋅ U                 (5.6)

                               (Δψ )s   =                               (5.7)
                               Δs = b ⋅ sin (ψ )                        (5.8)

Combining equations 5.3 – 5.8 with equation 5.1 yields the probability of a
collision at any point of a blade, equation 5.9. To obtain the mean probability
equation 5.2 is used with p coming from equation 5.9.

                          B ⋅b ⎛⎜          Ω               sin (ψ ) ⎞
                     p=                                  +              (5.9)
                          2 ⋅ π ⎜ A ⋅ Vbx + (1 − a ) ⋅ U
                                ⎝                             r ⎟   ⎠

For the more complex case of three-dimensional blades with chord, c, and
twist, β, the probability of a collision can be found by a similar method to that
for one-dimensional blades. Pc accounts for the chord and twist.

                                          p = p1D + p c                          (5.10)

From [12] pc can be found by equation 5.11. To calculate the mean probability
of a collision, equations 5.9, 5.10, and 5.11 are combined in equation 5.12 to
find p for equation 5.2.

                               B ⋅ c ⎛ cos(β )      Ω ⋅ sin (β ) ⎞
                        pc =         ⎜         −                    ⎟
                                                 Vbx + (1 − a ) ⋅ U ⎟
                               2 ⋅π ⎜ r
                                     ⎝                              ⎠

     B ⋅b ⎛
          ⎜         Ω              sin (ψ ) ⎞ B ⋅ c ⎛ cos(β )
                                            ⎟+                  Ω ⋅ sin (β )   ⎞
                                 +                  ⎜                          ⎟ (5.12)
p=        ⎜ A ⋅ V + (1 − a ) ⋅ U
     2 ⋅π ⎝                                 ⎟ 2 ⋅ π ⎜ r − V + (1 − a ) ⋅ U     ⎟
                 bx                   r ⎠           ⎝         bx               ⎠

In order to evaluate the mean probability of a collision over a full tidal cycle the
value of U was given a sinusoidal function to fit the flows found at the Fall of

                           ⎡ ⎛ 2 ⋅π        ⎞ ⎤ ⎛ 2 ⋅π         ⎞
                       U = ⎢sin ⎜
                                ⎜        t ⎟ + 3⎥ sin ⎜
                                           ⎟          ⎜      t⎟
                                                              ⎟                  (5.13)
                           ⎣ ⎝ TL          ⎠ ⎦ ⎝ TP           ⎠
Here TL is the period of the spring and neap cycle, 14 days, and TP is the
period of the tidal cycle, 12 hours 25 minutes. Figure 5.3 shows the variation
of the tidal velocity over the full cycle.

                              Figure 5.3- Tidal Stream Velocity
To further refine the model “if” functions were used to take account of times
when the rotors do not turn at the change of current. If the rotors are not
turning then there is no collision risk. Most tidal stream devices have a cut in
velocity of around 1.0 m/s.

5.4    Results
For a device from Marine Current Turbines with a rotor diameter of 16 metres
turning at 15 rpm the collision risk for a seal 2 metres long with an aspect ratio
of 0.25 was calculated. A summary of the results is shown in table 5.1.

                                                  Collision Risk (Probability)
     Seal Velocity (m/s)   Tidal Velocity (m/s)   1D       3D        3D Averaged
     0                     1.5                    0.858    0.866
                           2.5                    0.525    0.554     0.812
                           3.5                    0.382    0.420
     1                     1.5                    0.479    0.511
                           2.5                    0.358    0.298     0.569
                           3.5                    0.288    0.332
     2                     1.5                    0.337    0.378
                           2.5                    0.275    0.319     0.455
                           3.5                    0.233    0.280
     3                     1.5                    0.263    0.308
                           2.5                    0.225    0.273     0.388
                           3.5                    0.197    0.247
     4                     1.5                    0.217    0.265
                           2.5                    0.191    0.241     0.344
                           3.5                    0.172    0.223
     5                     1.5                    0.186    0.236
                           2.5                    0.167    0.219     0.313
                           3.5                    0.153    0.205
     0.42                  1.5                    0.642    0.664
                           2.5                    0.438    0.472     0.682
                           3.5                    0.335    0.376

                           Table 5.1 – Collision Risk Results

It can be seen from table 5.1 that as the tidal velocity increases the probability
of a collision decreases. Also as the velocity of the seal increases the risk
decreases, both as expected. The risks for the three dimensional blades are
slightly higher than for the one-dimensional blades. This is as expected and is
similar to the results for wind turbine collisions found in [15].

Plotting the averaged values over the full tidal cycle shows that the probability
of a collision decreases exponentially as the velocity of the seal increases
(figure 5.5). The maximum speed of a grey seal is not known, however the
average speed over 3000 dives was found to be 0.42 m/s [26]. It is estimated

that the maximum speed of a seal will be around 5 m/s as similar creatures
such as a bottle nosed dolphins have a maximum speed of 7-8 m/s. At the
average speed the probability is 68%, however at 5 m/s this drops to 31%.

                                MCT Collision Probability











           0     1          2                   3                  4   5   6

                                  S e a l Ve l oc i t y ( m / s)

                            Figure 5.4 - Collision Probability

For the scale model test we will attempt to verify these collision probabilities,
however as the blades used are not exact scale models, a separate risk
assessment was carried out for these blades.

Figure 5.4 shows the results plotted with the probability of a collision over a
range of projectile speeds and blade revolution speeds.

                            Figure 5.5 - Test Blade Collision Probability

5.4    Blade contours
To give an indication of the parts of the blade which carry the most risk of a
collision for a creature, contour plots showing lines of equal probability across
a rotor can be found using equation 12. A contour plot for the MCT device is
shown in figure 5.6 with a tidal velocity of 3.5 m/s and a seal velocity of 3.0
m/s. It can be seen that the greatest risk occurs near the centre of the rotor,
however at this point the velocity of the blade is very small, and therefore the
creature may be more likely to avoid a collision compared to at the tip where
the blade is moving much faster.

              Figure 5.6 - MCT Collision Contours

For the same conditions it can be seen from table 5.1 that mean probability
over the whole rotor is 0.25, which fits to the contour pattern. The probability
of a collision is only high towards the centre, where as discussed previously
the rotation speed of the rotor is low, therefore the seal may be able to avoid a
collision or have a greater chance of survival if a collision does occur.

5.6    Timescale
The initial model has been completed within the timescale set, and small
developments to the model are on going.

5.7    Future work
The results of the small scale testing will give an indication of the accuracy of
the model. Combining the test results, initial model and CFD results will give a
complete collision model.

6.0 Computational Fluid Dynamics

6.1    Objective from original scope
“Evaluation of the impact of a tidal turbine on the local marine wildlife through
computational simulation and statistical analysis”

6.2    Revised objectives of CFD work
•   To look at the effect of the tidal turbine on the local flow characteristic and
    to evaluate changes in velocities and pressure levels.
•   To evaluate whether the flow patterns around the turbines (notably shear
    forces and pressure gradients) will cause mortality/injury to any fish or
    mammals in close proximity.
•   To gain an increased knowledge of how turbines interact with each other in
    terms of the flow surrounding them.

6.3    Modelling specification
In order to compare the CFD model to a ‘real’ situation it was decided to
model the initial CFD simulations on an actual set of turbines in operation. The
turbines chosen were the Seagen turbines produced by MCT. We have
created a typical turbine layout and supposed the site of the farm to be the
EMEC test site at the falls of Warness, near Orkney. In this case the diameter
of the turbines was 15m, a 10m clearance between turbines on the same
base and a spacing of 120m between bases.

6.4    Design constraints
All the team members have had little experience with this software, and are
hence unsure of its limitations therefore lack of experience may be a
constricting factor.

6.5    Initial designs
The first simulation exercise using the computational software was to model
the flow past a 2D representation of the Seagen turbines laid out in farm

The mesh created for the simulation was a simple triangular mesh, which was
refined around the area of the turbines and larger where the velocity gradient
was not thought to be too severe; this aided in the reduction of computation
time. The mesh is shown in figure 6.1 and the farm layout in figure 6.2.

The left hand wall of the model was set at a velocity inlet of 4m/s, which is the
maximum speed, which would be available to the tidal turbine farm in location
at the Falls of Warness. The top and bottom walls were set as symmetry to
replicate the remainder of the tidal turbine farm and the right wall was set as a
pressure outlet. To represent the turbines a porous-jump was used as the
boundary condition. The porous jump allows a permeability to be set, in this
case 1e10m2. The depth of the porous face was set at 1 metre and the
pressure drop coefficient set to 25(1/m). These values were taken from a
similar CFD model of tidal turbines [27]. The model was then exported from
Gambit where the model was constructed and solved using Fluent Version
5.5. The solution was solved to a 2D segregated, implicit, steady state
solution with 3000 iterations.

Figure 6.1 - Mesh used in initial CFD simulations

                    Turbines attached to same base

                    Turbines attached to same base



         Figure 6.2 – Tidal farm layout

6.6    Results and discussions
The post processor was used to produce detailed information of the flow
characteristics around the turbines in various different charts. The most
relevant chart for this investigation is the velocity vector chart; this can be
seen in figure 6.3. This chart showed that as expected the turbines greatly
affect the flow within which they are situated, the main anomalies created with
relevance to the fish and mammals being:

•   The velocity of the water between the turbines is accelerated from the
    4m/s inlet velocity up to 6.4m/s.
•   The velocity of the water is reduced to approximately 3m/s at the entrance
    to the turbine when the tidal stream is 4m/s. This reduction in velocity
    relates to the reduction factor of the turbine and quantification of this value
    is very important for any statistical analysis.
•   There is a significant shear stress created in the wake of the turbines
    where the water velocity changes from 6.4m/s to less than 1m/s over the
    distance of approximately 1 metre. As was stated in section 4 large shear
    stresses can prove harmful, if not fatal to fish.

Fish are also very susceptible to rapidly increasing or decreasing pressure
gradients; these are clearly noted in the pressure contours output from the
post processor (figure 6.4). It can be seen that any fish passing through the
turbine and managing to avoid collision, or passing closely around the outside
of the turbine will experience a pressure change in the region of several
thousand Pascal.

    Figure 6.3 - Velocity flow around tidal turbines

Figure 6.4 - Pressure contours created around Turbines

6.7    Timescale
The initial period of the project has involved becoming proficient with the
software packages - GAMBIT for modelling and FLUENT for the actual
computational simulation. This was achieved by looking through examples
and online tutorials. The timescale with respect to the original Gantt chart is
still on target as the basic familiarisation work has been completed. Modelling
of actual turbine related work commenced on the 6th of November.

6.8    Future work
The simulation shown here is a very simplified two-dimensional representation
of MCT’s tidal turbine, but it has highlighted areas which may be of interest to
us and which should be investigated further.

The logical follow-on work would be to attempt to:
•   Improve the quality of the mesh and although at present a porous-jump
    boundary condition proves to be the best method for modelling the actual
    turbines, investigate more accurate alternatives.
•   The model, once refined will require to be validated so that values can be
    confidently taken from the post processor outputs.
•   The velocity and pressure gradients around each blade will then be
    evaluated in 2 dimensions.
•   The feasibility of creating a 3 dimensional model of the turbines in-situ will
    be evaluated then constructed in order to gain velocity and pressure
    distributions in three dimensions.

7.0 Scale Model Experimentation

7.1    Original goal as set out in project scope
“Development of a scale model test which will enable a greater understanding
of the interaction between tidal turbines and the local marine wildlife within
close proximity”

7.2    Revised objectives of scale model testing
•   To observe projectiles passing through a tidal turbine in a simulated
    environment that represents reality as closely as is practicable.
•   To observe the paths which the projectiles take through the turbine.
•   To provide some initial statistics in terms of strike probabilities on
    fish/mammals passing through the blades of the turbine which can later be
    compared to mathematical based models.
•   To highlight any anomalies in projectile trajectory as it passes through the
    turbine which might affect the statistical model, for example fluid/structure

7.3    Design specifications
The scale model will be loosely based upon the ‘Seagen’ tidal turbine design,
which is currently under development, by Marine Current Turbines Ltd. The
design consists of twin axial rotors of 16-meter diameter, which are mounted
on wings either side of a 3-meter diameter steel monopole. The whole
structure is held in place through its base which is pile driven into a pre-drilled
hole in the seabed. The speed of the rotors will be 15RPM in normal
operation. The basic requirement for cost effective power generation for these
devices is a mean spring peak velocity exceeding 2.25 to 2.5 m/s and a water
depth of 20 to 30 metres [7]. An artist’s impression of the full size Seagen
turbine is shown in figure 7.1.

               Figure 7.1 – Seagen turbine artist’s impression [1]

7.4    Design constraints
In order to undertake the experiment in a safe and controllable environment it
was decided to use Strathclyde Universities Civil Engineering Department’s
flowing water test tank. This tank can provide controllable depth and velocity
of water whilst having a raised platform for ease of access and glass walls to
enable an unobstructed view of the experiment. The constraints of this tank
are its dimensions: 1 metre wide by a maximum water depth of 50
centimetres; and the maximum flow rate of approximately 1 m/s. The scale
model will therefore have to be sufficiently small as to work within these

7.5    Model scaling
Due to the constraints placed on the scale model test the scaling will be such
that the dimensions of the rotors will be to a 1/42nd scale of the original model.
Hence, the scale model blades will have a diameter of approximately 38cm
and by looking at the maximum cord of the real turbine blades of 1.5m and
taking the average pitch of 30° the width of the blades was calculated as

To maintain dimensional consistency with the actual Seagen in operation a
dimensional analysis was undertake. The most significant dimensionless

parameter to be kept the same in the scale model testing is the tip speed
ratio, which relates the velocity of the current ( U ) to the angular velocity ( ω ),
and radius of the rotor ( R ). For the case of Seagen; in a tidal velocity of
3.0m/s, operating at a rotor speed of 15rpm and with rotor radius of 8m, the tip
speed ratio can be calculated as per equation 7.1. [27].

                              XT =         = 4.2                         (7.1)

If the turbine rotational speed is kept constant at 15rpm, with the radius of the
scale model already set at 0.19m then to keep dimensional accuracy the flow
velocity must be reduced to 0.07m/s. Under actual test conditions the speed
of rotation and the stream velocity can be altered until an adequate
relationship is found, as long as the tip speed ratio constant.

The rotors that were chosen for this experiment were model aircraft propellers
of a known pitch ( h ), which meant that the rotational speed with relation to the
fluids velocity could be calculated as follows:

                                  2 ⋅π
                             ω=        U                                 (7.2)

The actual rotational speed of the scale model rotor within the fluid could then
be plotted, and compared with the plot of the rotational speed and fluid
velocity from the dimensional analysis for a speed tip ratio of 4.2 (as was the
case for the full size turbine). The results can be seen in chart 7.1.

                                          Model Test Speed Setting




   Turbine RPM

                                                                           Dimensionless Scaling
                                                                           Free Driven




                      0   0.05   0.1       0.15         0.2   0.25   0.3
                                  Stream Velocity (m /s)

   Chart 7.1 – RPM vs. Velocity profiles for dimensionless scaling and the free
                                        driven scale model

The pink line is the rotational speed at which the rotor will turn in the stream
due to its pitch and the blue line is the speed it is required to turn at to
represent the full-scale model accurately. It seems that for a given RPM the
rotational velocity of the model will need to be reduced to bring it in line with
the dimensionless scaling. A variable level of friction will therefore be imparted
on the shaft of the rotor.

7.6               Conceptual design

A number of key issues were highlighted for the design of the scale model
test. A period of brainstorming yielded suitable solutions and alternative ideas
were suggested in case of experimental difficulties.

Turbine rotors
The department has a set of scaled down rotors, which were planned to be
used for this test but proved too large for the test tank. Therefore 38cm
diameter model aeroplane rotors were purchased, as these were cheaply and
easily available, whilst still resembling the real turbine blades fairly accurately.

Rig Construction
There were many options available for the construction of the rig to hold the
rotors. The key concern was to ensure that it would be structurally sound
enough to resist the force of the flow, the impact of the projectiles and would
not be adversely affected by water. There is a great choice of materials
available through the department, which could be used for such a rig,
including plastic or metal tubing and box sections. Various fixing methods
such as welding, gluing or purpose built connecting pieces were also

It was decided to use aluminium box section for the frame, as this is
lightweight, strong and easily constructed.

Rig Design
The rig design is shown in figures 7.2a and 7.2b below.

        Figure 7.2a / 7.2 b – Detail for rotor connection and rig assembly

Figure 7.2a shows the rotor attachment to the box section frame. It was
realised that a bearing would be necessary to allow the rotor to run freely,
however to implement bearings within this design would be costly as bearing
seals and thrust races would also be required. It was therefore decided to use
a PTFE bush as this would allow the rotor to turn more freely than if the shaft
were in contact with bare metal, but also will cause more friction than with
bearings which may help in the reduction of the rotor speed as was outlined in
section 6.5. A grub screw will provide extra friction if necessary.

The manufacturing drawings are contained in the APPENDIX A

It is important to be able to replicate the fish/mammals that will be projected
through the turbine as accurately as possible. Various different types of
projectiles and release methods have been considered and will be tested
once the scale model has been manufactured to find the most effective.
•   The projectile, which will be used to replicate larger mammals, will consist
    of a fishing bubble float coated in plasticine, this is thought to be the most
    effective option available. By changing the amount of water within the float,
    the buoyancy will be easily changed and hence it can be tuned to float at
    specific depths, whilst the plasticine will show where the turbine blade has
    struck and give an indication of force. To represent smaller fish/mammals
    beads will be used; by projecting a large number of beads it would be
    possible to replicate a shoal of fish approaching the turbine.
•   The release of the projectile will initially be done by hand, which will be the
    most straightforward method. This means that the projectile will only travel
    at the speed of the flow. Alternatively the projectiles might be projected by
    air from launch traps that will be placed into the water.

Due to the unknown effects of the turbine on the projectiles it is expected that
the design of the release mechanism and design of the actual projectiles will
change once testing commences.

Data Collection
It is necessary to collect the data about the passage of the projectile through
the turbine in order to analyse. The most important data being: whether a
strike on the projectile has taken place, the severity and location of the strike
and finally the path the projectile has taken through the turbine rotor. To
accurately record data we will use video cameras, both in the water and
looking through the glass walls of the test tank, this will allow detailed analysis
of the passage through the turbine to take place. It will also allow details of the
strike to be gained such as if it were a full strike or a glancing blow. Visual
inspection of the projectile itself will also give evidence of location and force of

7.7    Testing procedure
The projectile will be released upstream of the turbine and its motion tracked
by video camera as it passes through the turbine. In order to view all
eventualities the projectile will be released so as to pass through the turbine at
different radii. Each position will be repeated several times (as time in
laboratory will allow) in order to gain a good statistical impression of the strike
rate and projectile path over the whole turbine. The projectile will then be
passed through the turbine with increased velocity to note any changes in
strike rate.

7.8    Timescale

The scale model testing is currently on target with its intended time scale,
currently the end of the detailed design block is approaching and construction
will commence on the 20th of November with testing to follow shortly after.

7.9    Larger scale testing

Due to the department having a larger scale model of a turbine, if a suitable
location can be found it may be possible to replicate this experiment on a

larger scale and gain a better idea of how the scale of the model may affect
the results and hence extrapolate the data gained to the real turbine. It was
intended for this experiment to originally take place in the cooling water outlet
of Longannet Power Station, but has since been deemed a health and safety
hazard. Dependant upon the results of the small-scale test a decision will be
mode on whether to further pursue this option.

8.0 Conclusions and final words
8.1    Project status
As the project has progressed the group has become more aware of the work
that has previously been carried out and the work that now requires to be
done in this field, allowing the group to therefore draw up more specific goals.
By researching the marine profile an understanding has now been gained of
exactly what information will be of most use to MCT developers and
environmental groups and how the group will be able to produce this
information within the available timescale. Significant achievements to date
include the creation of a simple numerical model to predict strike rates, design
of a small-scale test rig and securing of suitable testing facilities, completion of
a significant body of research work and the development of the team
member’s skills in terms of both CFD and Dreamweaver.

With reference to the Gantt chart (figure 3.1) it is clear that the group has
been performing satisfactorily. In terms of the scale model testing, the detailed
design phase has been completed, putting the team at least one week ahead
of schedule on this front. Research has progressed well and is yielding some
fruitful information; work on this is ongoing. The CFD work is on schedule with
the direction now moving towards a more realistic tidal farm model and some
two-dimensional blade models.

8.2    Future activities
The group intend to press on and take advantage of the strong base that has
been set down. Testing should be underway before the end of the month,
which will put the group in a good position to collect a large data set. It is then
hoped to compare the results of the testing with the numerical model in order
to validate the model, once it has been fully developed. The CFD work should
provide results that will aid in drawing the final conclusions as to the severity
of the impact of marine turbines on marine ecosystems.


[1], November 2006.

[2]   The Experimentally validated numerical method for the hydrodynamic
design of horizontal axis tidal turbines. W.M.J. Batten, A.S. Bahaj et al. Ocean
Engineering, April 2006.

[3]    The Power Generation from Tidal Currents by Darrieus Turbine. S
Kiho, M. Shiono, K. Suzuki. Department of Electrical Engineering, College of
Science & Technology, Nihon University, l-8 Surugadai Kanda Chiyoda-lot,

[4]  Memorandum Submitted by Dr Andrew Turnpenny, Fawley Aquatic
Research   Laboratories. Appendices to  minutes   of   evidence:

[5], November 2006.

[6]   Tidal turbines harness the power of the sea. Peter Fraenkel, Marine
Current Turbines.

[7], November 2006.

[8]   Marine Current Turbines Ltd., The Seaflow Project, Environmental
Statement, Non-technical Summary. S. Lowther, Casella Stanger, November

[9]   Comparison of blade strike modelling results with empirical data. G.
Ploskey, T. Carlson, US dept of Energy Efficiency and Renewable Energy,
March 2004.

[10] Evaluation of blade strike models for estimating the biological
performance of large Kaplan hydro turbines. Z. Deng, T. Carlson, G. Ploskey,
M. Richmond.
US dept of Energy Efficiency and Renewable Energy, November 2005.

[11], November 2006.

[12] Potential Impacts of Wind Turbines on Birds at North Cape, Prince
Edward Island. A. Kingsley & B. Whittam, A report for the Prince Edward
Island Energy Corporation, December 2001

[13] Remote techniques for counting and estimating the number of bird–
wind turbine collisions at sea: a review. M. Desholm, A. D. Fox, P. D. L.
Beasley & J. Kahert. Ibis (2006), 148, 76–89

 [14]    The most frequently asked questions about wind energy, AWEA,, November 2006
[15] A mathematical model of bird collisions with wind turbine rotors. V.
Tucker, Journal of solar energy engineering, Vol. 118-No 4, p253-262,
November 1996.

[16] Using a collision model to design safer wind turbine rotors for birds. V.
Tucker, Journal of solar energy engineering, Vol. 118-No 4, p263-269,
November 1996.

[17] A Summary of Environmentally Friendly Turbine Design Concepts. M.
Odeh, U.S. Department of Energy Idaho Operations Office, July 199).

[18]   Shaken not Stirred: The recipe for a fish friendly turbine. G. F. Cada

[19] Exploring the role of sheer stress and severe turbulence in downstream
fish passage. G. Cada, T. Carlson, J. Ferguson, M. Richmond, M. Sale, March

[20], November 2006.

[21] Survival estimates for juvenile fish subjected to a laboratory-generated
shear environment. D. Neitzel, D. Dauble, G. Cada, M. Richmond, G.
Guensch, R. Mueller, C. Abernethy, B. Amidan. Transactions of the American
Fisheries Society 133 (2): 447-454, March 2004.

[22], November 2006.

[23] Sea Energy Conversion: Problems and Possibilities. G. Buigues, I.
Zamora, A. J. Mazón, V. Valverde and F.J. Pérez. Electrical Engineering
Department E.T.S.I.I., University of Basque Country.

[24] Fundamentals applicable to the utilisation of marine current turbines for
energy production. A.S. Bahaj, L.E. Myers, Sustainable Energy Research
Group, Department of Civil and Environmental Engineering, University of

[25] Field evaluation of a sound system to reduce estuarine fish intake rates
at a power plant cooling water inlet. J. Maes, A. W. H. Turnpenny, Journal of
Fish Biology (2004) 64, 938–946.

[26] Marine Current Turbines, Environmental Impact Assessment, Seaflow
Project, 2001.

November 2006.


•   Fish Deterrents
•   Types of Fish deterrents developed
•   Types being developed
•   Commercially Available

Main Types

• Acoustic
Acoustic systems use a high level of sound barrier, which are repellent to fish.
The ideal sound field should form a steep acoustic gradient approaching the
entrance, free from acoustic nulls caused by destructive interference within
the sound field. The presence of such nulls could cause fish to be guided into,
rather than away from the intake.

Currents have to be slower than the swim speed of the fish to allow the fish to
escape when repelled, rather than swept through the barrier. Currents also
have to flow in appropriate relative directions to the sound field so as fish are
directed to safety and not directed into danger.

There are three classifications of fish species, which react with different
efficiencies to acoustic repellents.

These groups can be drawn up from the way with hearing. Fish mainly hear
through vibrations, making use of the good propagation of low frequency

sounds through water. The main sensory organs involved are the lateral-line
system, which detects low-frequency (<100 Hz) particle motion in the water
contacting the flanks of the fish, and the inner ear, located within the head of
the fish, sensitive to frequencies of up to 1-3 kHz. The inner ear, which lies
within the skull of the fish, is sensitive to vibration rather than sound pressure.
In teleost species (bony fish) possessing a gas-filled swimbladder, this organ
acts as transducer that converts sound pressure waves to vibrations, allowing
the fish detect sound as well as vibration.

Sensitivity to noise and vibration differs among fish species, especially
according to the anatomy of the swimbladder and its proximity to the inner
ear. Species with no swimbladder (e.g. elasmobranchs) or a much reduced
one (many benthic species including flatfish) tend to be of relatively low
auditory sensitivity and may be only weakly repelled by acoustic deterrent
systems other than those designed specifically for that purpose. Fish having a
fully functional swimbladder tend to be much more sensitive.

Best results are obtained with those species in which there is some form of
close coupling between the swimbladder and the inner ear. In the clupeids
(herring family), this takes the form of a gas duct connecting the swimbladder
to the hearing system, whereas e.g. in cyprinid fish, a bony coupling is formed
by the Weberian ossicles. This creates a super-league of hearing-sensitive

Deflection is usually the best course of action, as the fish are moved swiftly
from the source of danger (e.g. water intake) into a safe flow. Blocking can be
more difficult if the fish are not moved away from the area, as the risk of
habituation to the sound signals becomes increased. This can be overcome to
some extent by changing the signal pattern at intervals but acoustic deterrents
are essentially a mild form of stimulus less effective e.g. than electric barriers
purely for blocking.

•   Light

•   Electric

•   Bubble

Commercial Deterrents

Company:       Fish Guidance Systems (FGS)

Overview:      FGS was formed in 1994 to produce underwater acoustic
systems to guide fish away from water intakes. Since then the company has
developed a complete range of cost-effective behavioural fish guidance and
protection systems

Quote:         “A number of behavioural systems have been tested and
acoustic systems have been found to be the most effective systems”


SPA systems are used to block/deflect fish movements at the entrance to
water intakes and are harmless to fish. The SPA system uses underwater
sound projectors powered by audio amplifiers and electronic signal
generators, to create a repellent acoustic field ahead of a water intake. FGS
supply different models of SPA system to suit different site conditions.

The SPA system is analogous to a public address or domestic hi-fi system.
The signal is recorded onto an EPROM-chip and the signal generator may
contain a number of these that can be manually selected or played at random
or in rotation. One or more high-powered audio amplifiers that are matched
and filtered to suit the sound projectors amplify the signal.


The BAFF is used to divert fish from a major flow, e.g. entering a turbine, into
the minor flow of a fish pass channel. It may be regarded as analogous to a
conventional angled fish screen.

It uses an air bubble curtain to contain a sound signal, which is generated
pneumatically. Effectively, this creates a "wall of sound" (an evanescent
sound field) field that can be used to guide fish around river structures by
deflection into fish passes.

Physically, the BAFF comprises a pneumatic sound transducer coupled to a
bubble-sheet generator, causing sound wave to propagate within the rising
curtain of bubbles. The sound is contained within the bubble curtain as a
result of refraction, since the velocity of sound in a bubble-water mixture
differs from that in either water or air alone. The sound level inside the bubble
curtain may be as high as 170 dB re 1mPa, typically decaying to 5% of this
value within 0.5-1 m from the bubble sheet. It can be deployed in much the
same way as a standard bubble curtain, but its effectiveness as a fish barrier
is greatly enhanced by the addition of a repellent sound signal. The
characteristics of the sound signals are similar to those used in SPA systems,
i.e. within the 20-500 Hz frequency range and using frequency or amplitude

                             Figure 3 – BAFF Schematic


One of the most important features of this fish barrier design is the graduated
electric field. As fish advance into a graduated field, they feel an increasingly
unpleasant sensation. When the sensation is too intense, fish are unable to
advance further and cannot keep their body orientated with the water flow.
They turn perpendicular to the field, and are either swept clear by water flow
or swim in the opposite direction from the increasing electric field.

The Graduated Field barrier uses from two to six pulse generators to provide
ascending levels of field intensity. The pulsators (pulse generators) have their
outputs connected to an array of evenly spaced electrodes placed across a
stream bottom. Each pulsator can be adjusted to provide an increasing
voltage between successive electrode pairs. This creates a gradually
increasing electric field along the array. The pulsators are simultaneously
triggered to cause the electric field lines to become additive and oriented with
stream flow. Longer fish receive more head-to-tail voltage and are affected at
an earlier stage, while smaller fish can penetrate the barrier further before
being overcome or repelled.

Typical Installation:

Company:      Pisces Engineering

Device:       Ringolite is a patented device using a combination of low
voltage, high intensity LEDs mounted in a tube filled with a light dissipating gel
to give an intense but localised area of bright light within a pipe, which acts as
a deterrent to fish and other aquatic creatures.

•   Ideal for outlet shrouds, degassers and other dark areas that fish find
    attractive but are not desirable
•   Safe, 24vdc operation
•   Option of basic power supply or time switch operation
•   Manufactured from shock resistant plastic tubing with no corrodible parts -
    suitable for warm seawater
•   Available for any size of pipe or channel


To top