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My research interests

Engineering Design (Perspective of a Mechanical Engineer working in Vibration related problems) Abhijit Gupta, Ph.D, P.E. Associate Professor of Mechanical Engineering Northern Illinois University, Dekalb, IL 60115. My research interests .

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My research interests

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  1. Engineering Design(Perspective of a Mechanical Engineer working in Vibration related problems) Abhijit Gupta, Ph.D, P.E.Associate Professor of Mechanical EngineeringNorthern Illinois University, Dekalb, IL 60115

  2. My research interests • Measurement of Dynamic Modulus (Including Damping) of Viscoelastic Materials (related to make cars and trucks quieter) • Accelerated Life Testing (how can you give warranty for 7year/100000 miles while testing for few hours) • Damage Detection (How do we know it is damaged and how much) • Passive and Active Vibration and Noise Control (Minimize vibration and Sound) • Electromagnetic Shock Absorber (makes more sense with high gasoline prices)

  3. First some thoughts on engineering in general • Engineers are tinkerers and problem solvers • NASA has more engineers than scientists • Mechanical Engineering is one of the important • Engineering Discipline • Mechanical Engineering encompasses many aspects: • Aerospace • Automotive • Manufacturing • Utility Industries • Biotech Impossible to name an industry that does not employ mechanical engineers

  4. Mechanical Engineers are involved with • Conversion of energy (engine, turbine, motor, fuel cell, etc.) • Conversion of motion (gears, piston-cylinder, etc.)  • Design and Analysis   • Choosing the correct material • Manufacturing the product

  5. Steps in Engineering Design 1. Identify the need 2. Define the problem 3. Search for information 4. Set Design Criteria and Constraints 5. Consider a number of solutions 6. Analyze the design 7. Make a decision 8. Develop specifications 9. Communicate the design solution

  6. However sometimes it helps to first reverse engineer and then design

  7. what is reverse engineering? • Dissecting a product • Understanding how it functions • Learn basic principles • Designing/building a new product with the knowledge from dissection

  8. Examples Before we get serious let us see some examples of Mechanical Engineering in the field of Vibration and Acoustics and have some fun We will look at human body vibration, machinery vibration, structural vibration, and vibration issues in sports It may be added that when excitation frequency equals to natural frequency, it is called resonance (and usually should be avoided)

  9. Natural frequency of a simple single degree of freedom system is given by the equation ωN = square root of (stiffness / mass) Usually we do not want structures to vibrate in resonance (though there are some special cases where resonance is desirable)

  10. Human Vibration

  11. Resonance Frequency Ranges of Human body sections • Eyeball, Intraocular Structure (20-90 Hz) • Head (axial mode) (20-30 Hz) • Shoulder Girdle (4-5 Hz) • Chest wall (50-100 Hz) • Arm (5-10 Hz) • Hand (30-50 Hz) • Abdominal Mass (4-8 Hz) • Spinal column (axial mode) (10-12 Hz) It may be noted that the abdominal mass mode (around 5 Hz) makes us nauseating and is avoided in automotive design. Top gun pilots had problem with a particular maneuver when the eyeball socket went into resonance.

  12. Machines and Vibration

  13. Machine condition monitored by vibration

  14. Structural Applications Now let us look as some structural vibration applications 1) vibration of an windmill 2) Tacoma Narrows bridge failure 3) Vibration of a car

  15. Windmill Vibration

  16. Rotating Wind Turbine 8

  17. 35

  18. Testing of a small object 9

  19. Testing of a large object (bridge) 38

  20. Tacoma Narrows Bridge Failure

  21. Causes of the Tacoma Narrows Bridge Failure The bridge survived only 4 months (July 1 – Nov 7, 1940) Possible causes of Failure mentioned: Resonance (it was not a case of steady-state excitation, so resonance was not the cause) Vortex Shedding (Again not a cause because the frequency observed (0.2 Hz) and frequency calculated (1 Hz) were not same Aerodynamic Flutter (due to restricted wind flow when the architect changed the design suggested by the engineer). New design addressed that issue.

  22. Automobile Vibration

  23. 20

  24. Points where the car is excited

  25. Components of a car For comfortable ride in a car requires analysis of car frame and many other components, e.g. exhaust systems (bellows), shock absorber, tire etc. We will look into a shock absorber in more detail

  26. How about Shock absorber We know what a typical shock absorber does Saves us from unpleasant vibration (recall that 5 Hz abdominal mode) by dissipating energy But why not try to recover the energy?

  27. Electromagnetic Shock Absorber • Need for Improved Vehicle Fuel Efficiency • In traditional Shock Absorber Energy is wasted as heat (In a semi-tractor trailer shocks are hot within fifteen minutes of driving) • Information about car/truck available. Also information about road profiles are available • Design criteria is that it should behave similar to a conventional shock. There may be space and weight constraints

  28. Let us look at a quarter bus/truck/car model u = road profile input kt = tire spring constant mu = unsprung mass xu = displacement of unsprung mass ks = suspension spring constant cs = suspension damping constant ms = sprung mass xs = displacement of sprung mass

  29. Lab Testing of EM Shock 1

  30. Lab Testing of EM Shock 2

  31. Vehicle Testing(ATV and close up view)

  32. Aerospace Applications 18

  33. 61

  34. 63

  35. Vibration in sports Golf Clubs, Tennis Racquets, Spring Board diving, Baseball - all has vibration applications. Even a traditional sport like Baseball has been studied for vibration related issues. Solid bats have only bending modes whereas aluminum bats or composite bats also have hoop modes with desirable trampoline effect.

  36. Acoustics Sound is caused by vibration, so the science of studying sound (acoustics) and vibration are related If you are into music (and especially so called audiophile), you may already have looked at vibration response of speakers and decided what kind of speakers you want Quite often it is the low frequency response that drives up the price. Last year two Mechanical Engineering students made a pair of concrete enclosure speakers in their final design project and the speakers were almost as good as thousand dollar worth speakers

  37. Sound and Human Being(some are music, some are noise, and some in between)

  38. Designing a product Sometimes products are designed so that vibration is minimum and sometimes products are designed so that sound is minimum ( or maximum). Eventual goal is to either make human being more comfortable or make a machine or building last longer Now may be the time to take apart a product and think all engineering aspects of it. Vibration and acoustics may be one concern, material and manufacturing issues are also of concern and sometime there may be interdisciplinary i.e. electrical or industrial engineering issues need to be addressed.

  39. The Future Of course there are more challenging problems which are beyond the scope of this class but later in your career someday you may want to be involved with those. For the time being you may start with a small project like designing a flashlight which would not depend on battery.

  40. Acknowledgement • CEET Associate Dean’s office • Bruel & Kjaer • Argonne National Laboratory • NASA • Sandia National Laboratory

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