ME 120 Experimental Methods Laboratory

1. ME 120 Experimental Methods Laboratory Ananda Mysore Ananda Mysore

2. 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 Ananda Mysore

3. 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 Ananda Mysore

4. 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 Ananda Mysore

5. 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 Ananda Mysore

6. Basics Every physical body has infinite number of natural frequencies ωn1< ωn2< ωn3 ME 120 Experimental Methods Laboratory Ananda Mysore

7. 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 Ananda Mysore

8. 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 Ananda Mysore

9. 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 Ananda Mysore

10. 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 Ananda Mysore

11. 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 Ananda Mysore