Engineers are tinkerers and problem solvers NASA has more engineers than scientistsMechanical Engineering is one of the importantEngineering Discipline

Mechanical Engineering encompasses many aspects:• Aerospace• Automotive • Manufacturing • Utility Industries• Biotech

  Impossible to name an industry that does not employ mechanical engineers

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

Steps in Engineering Design

1. Identify the need2. Define the problem

3. Search for information4. Set Design Criteria and Constraints

5. Consider a number of solutions6. Analyze the design

7. Make a decision 8. Develop specifications

9. Communicate the design solution

However sometimes it helps to first reverse engineer and then design

what is reverse engineering?

• Dissecting a product• Understanding how it functions• Learn basic principles• Designing/building a new product with the knowledge from dissection

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,And structural vibration

It may be added that when something vibrates at a natural frequency, it is called resonance (and usually should be avoided)

Human Vibration

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

Machines and Vibration

Machine condition monitored by vibration

Structural Applications

Now let us look as some structural vibration applications

1) vibration of an windmill2) Tacoma Narrows bridge failure3) Vibration of a car

Windmill Vibration

Tacoma Narrows Bridge Failure

Automobile Vibration

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

How about Shock absorberWe know what a typical shock absorber does

Saves us from unpleasant vibration (recall that 5 Hz abdominal mode)by dissipating energyBut why not try to recover the energy?

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

Let us look at a quarter bus/truck/car model

u = road profile inputkt = tire spring constantmu = unsprung massxu = displacement of unsprung mass

ks = suspension spring constantcs = suspension damping constantms = sprung massxs = displacement of sprung mass

Lab Testing of EM Shock 1

Lab Testing of EM Shock 2

Mark2 EM shock test across 1 ohm

0.00

0.20

0.40

0.60

0.80

0.00 5.00 10.00 15.00

Velocity in in/s

Volta

ge a

cros

s 1

ohm

in V

Series1

Vehicle Testing(ATV and close up view)

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

Sound and Human Being(some are music, some are noise,

and some in between)

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.

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 reverse engineer a quiet hand held vacuum cleaner

Acknowledgement

• CEET Associate Dean’s office• Bruel & Kjaer• Argonne National Laboratory• NASA