# ME 120 Experimental Methods Laboratory

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```							       ME 120 Experimental Methods
Laboratory

Ananda Mysore

Spring 2008             Ananda Mysore
Sound Pressure Measurements

    Objectives
   Become familiar with hardware and techniques to
measure sound pressure
   Measure Sound level of various size fan modules
   Calculate S/N of acoustic measurements
   Fan Noise = f(size & operating speed)

ME 120 Experimental Methods Laboratory
Spring 2008                           Ananda Mysore
Basics

    @ 20deg C Vel of sound = 344m/sec
    Audible frequencies - 20 to 20000Hz
    Bruel &Kjaer 2236 Precision Integrating sound level
meter
   Condenser Microphone
  Thin metal foil stretched like drumhead over a frame. Pressure
changes > diaphragm movement > changes in capacitance>
milli-volt signal > pre amplifier > other amplifier stages > A/D
converter
   Free-field response Microphone > one direction only
   Random-incidence Microphone > Equally from all directions

ME 120 Experimental Methods Laboratory
Spring 2008                                Ananda Mysore
Basics

    SPL is a measurement of sound strength on a logarithmic
scale
    L = SPL = 10 log(Signal Power/Ref Power)
    L = 10 log (Prms/Pref)^2
    L = 20 log(Prms/Pref)
    Pref = Ref value for sound pressure in air = 20 micro pascals
    Sound level meter computes Prms in db based on sound
pressure over a period of time

ME 120 Experimental Methods Laboratory
Spring 2008                        Ananda Mysore
Vibration Measurements

    Objectives
   Find first natural frequency of a cantilever beam using both
theoretical and experimental techniques and to estimate
first mode’s damping
   Find the second natural frequency of a cantilever beam by
locating 180deg phase shift

ME 120 Experimental Methods Laboratory
Spring 2008                              Ananda Mysore
Basics
Every physical body has infinite
number of natural frequencies

ωn1< ωn2< ωn3

ME 120 Experimental Methods Laboratory
Spring 2008              Ananda Mysore
Measurement

    Frequency measurement using:
    Electromechanical shake table
    Accelerometers
    Oscilloscope
    Goals
   Ratio of the amplitude of the end of the beam
   Phase relationship between Input and output signals
   Plot Phase angle and amplitude ratio vs frequency
   Estimate first mode’s damping ratio
   Use phase change to locate the second modal frequency
   At constant frequency measure phase at different amplitude ratios
   Repeat the experiment with plastic beam

ME 120 Experimental Methods Laboratory
Spring 2008                              Ananda Mysore
Static Deflection Measurement

    Objective
   Compare the results from static beam deflection
measurement with the result computed from the analytical
prediction

ME 120 Experimental Methods Laboratory
Spring 2008                              Ananda Mysore
Basics

    Area moment of inertia > resistance to bending
    For a rectangular cross section area moment of inertia:
   I = bh^3/12 b= width and h = height
    LVDT: Linear Variable Differential Transformer

Source: http://www.macrosensors.com/

ME 120 Experimental Methods Laboratory
Spring 2008                                       Ananda Mysore
Viscosity Measurement

    Objectives
   Learn to operate and take data with a rotating spindle
type viscometer
   Investigate 10W-30 oil is a Newtonian or non-Newtonian
fluid
   Determine the viscosity of 10W-30 motor oil as a
function of temperature

ME 120 Experimental Methods Laboratory
Spring 2008                           Ananda Mysore
Basics

    A Newtonian fluid :
    is a fluid that flows like water—its shear stress versus rate of strain curve is
linear and passes through the origin.
    Viscosity depends on temperature and pressure and not on the forces acting
on it
Application of non-Newtonian fluids:
Body armor development(bullet proof
vest) - shear resistant vs paint -
shear thinning

Source:http://en.wikipedia.org/wiki/Image:Non-Newtonian_fluid.PNG

ME 120 Experimental Methods Laboratory
Spring 2008                                             Ananda Mysore

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