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“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 1 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. 2 Contents 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 3 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 4 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. 5 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 appropriate. 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 6 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 website. 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. 7 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 industry. 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. 8 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 structure. 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. 9 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. 10 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 11 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. 12 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. 13 3.3 Critical path analysis Ascertain what (if anything) Develop CFD skills we can achieved with this CFD modelling technology 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 construction Figure 3.2 - Critical Path Analysis 14 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. Strengths • 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. Weaknesses • 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 development. 16 • 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. Opportunities • 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. Threats • 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 17 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 reduction. • 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 applications. • 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 18 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 Balsa 2 15x8 Master Airscrew 2 Bladed Prop 103208 Mart £7.25 £14.50 Balsa 2 15x8 Graupner 3 Bladed Prop ES538/20 Mart £12.50 £25.00 Balsa 2 2" 3 Blade Spinner JP7352 Mart £0.79 £1.58 Balsa 2 2" 2 Blade Spinner 5507320 Mart £0.90 £1.80 £42.88 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 19 • 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. 20 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 field” “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 21 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 22 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 . 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 Turbine 23 cycle. 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 . 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 . 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% 24 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 . Plastic-based materials ease the fatigue 25 problem, both through their inherent fatigue tolerance and by reduced blade weight. 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 decrease. 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 26 normally allocated to a specialist contractor who will apply a standardised procedure designed to raise and discuss all pertinent environmental concerns . 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 duration. • 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. 27 • 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 environment. • 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, 28 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 29 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. 30 It is understood however that the installation of wind farms can affect birds in manners other than simply collision potential . 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 . 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 observed. In an effort to further understand the phenomenon of bird collisions, several mathematical models have been developed, such as the one developed by Tucker  in 1996. This was the first complete theoretical analysis of bird- rotor collision, with the following paper  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 31 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, 32 direct strike, grinding, shear and turbulence . 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 . 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 33 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  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 . 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  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  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 34 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  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 35 Figure 4.6 – Promotional material for the EMEC test site  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, 36 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 . 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 37 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. 38 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. 39 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 40 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. 41 • 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. 42 4.12.2 Fish screening summary There are several key drivers for broadening the requirement for fish screening: • 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 43 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  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 44 commercially available technologies has been carried out and can be found in Appendix B. Section B: Assessing the risk of turbine on fish and mammals. 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) 45 • 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 fish/mammals. 5.3 The statistical model The model developed here uses the same principals as the bird strike model developed by Turner 1996 . There are three modes of collision described 46 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  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. 47 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 48 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 2 p= ( π R − r02 2 ) ∫ ∫ p ⋅ r ⋅ dr ⋅ dψ 0 r0 (5.2) 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 follows. Change in azimuth angle: Δψ = (Δψ )x + (Δψ )s (5.2) Ω ⋅ Δx (Δψ )x = (5.4) Vx b Δx = (5.5) A V x = Vbx + (1 − a ) ⋅ U (5.6) Δs (Δψ )s = (5.7) r 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. 49 p = p1D + p c (5.10) From  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 ⎟ (5.11) 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 Warness. ⎡ ⎛ 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. 50 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. 51 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 . 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 . It is estimated 52 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 2 1.8 1.6 1.4 1.2 Mean 1 Max 0.8 0.6 0.4 0.2 0 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. 53 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. 54 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. 55 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. 56 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 formation. 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 . 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. 57 Figure 6.1 - Mesh used in initial CFD simulations Turbines attached to same base 80m Turbines attached to same base 10m 15m 40m Figure 6.2 – Tidal farm layout 58 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. 59 Figure 6.3 - Velocity flow around tidal turbines Figure 6.4 - Pressure contours created around Turbines 60 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. 61 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 interaction. 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 . An artist’s impression of the full size Seagen turbine is shown in figure 7.1. 62 Figure 7.1 – Seagen turbine artist’s impression  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 conditions. 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 1.8cm. To maintain dimensional consistency with the actual Seagen in operation a dimensional analysis was undertake. The most significant dimensionless 63 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. . ω⋅R XT = = 4.2 (7.1) U 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) h 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. 64 Model Test Speed Setting 90 80 70 60 Turbine RPM 50 Dimensionless Scaling Free Driven 40 30 20 10 0 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. 65 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 considered. 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 66 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 Projectiles 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. 67 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 impact. 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 68 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. 69 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. 70 Bibliography  http://www.emec.org.uk/index.asp, November 2006.  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.  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, Tokyo.  Memorandum Submitted by Dr Andrew Turnpenny, Fawley Aquatic Research Laboratories. Appendices to minutes of evidence: www.parliament.uk  www.marineenergy.soton.ac.uk, November 2006.  Tidal turbines harness the power of the sea. Peter Fraenkel, Marine Current Turbines.  www.marineturbines.com, November 2006.  Marine Current Turbines Ltd., The Seaflow Project, Environmental Statement, Non-technical Summary. S. Lowther, Casella Stanger, November 2001.  Comparison of blade strike modelling results with empirical data. G. Ploskey, T. Carlson, US dept of Energy Efficiency and Renewable Energy, March 2004.  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.  http://www.rspb.org.uk/policy/windfarms/index.asp, November 2006.  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  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 71  The most frequently asked questions about wind energy, AWEA, http://www.awea.org, November 2006  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.  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.  A Summary of Environmentally Friendly Turbine Design Concepts. M. Odeh, U.S. Department of Energy Idaho Operations Office, July 199).  Shaken not Stirred: The recipe for a fish friendly turbine. G. F. Cada  Exploring the role of sheer stress and severe turbulence in downstream fish passage. G. Cada, T. Carlson, J. Ferguson, M. Richmond, M. Sale, March 1999.  http://hydropower.inel.gov/turbines/direct_strain.shtml, November 2006.  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.  http://seamap.env.duke.edu/, November 2006.  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.  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 Southampton.  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.  Marine Current Turbines, Environmental Impact Assessment, Seaflow Project, 2001.  http://www.esru.strath.ac.uk/EandE/Web_sites/03-04/marine.htm, November 2006. 72 APPENDIX A 73 74 75 APPENDIX B • 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 76 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 fish. 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 77 • 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” Devices: SOUND PROJECTOR ARRAY (SPA) 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. BIO ACOUSTIC FISH FENCE (BAFF) 78 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 sweeps. 79 Figure 3 – BAFF Schematic GRADUATED ELECTRIC BARRIER 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. 80 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 81 82
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