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Lecture 6An Exercise on Writing

MathLuis San Andres

Mast-Childs Tribology ProfessorTexas A&M University

http://rotorlab.tamu.edu/me489

February 8, 2011

ME 489 Practices of Modern Engineering

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Lecture 6Date: February 8, 2011

Today: Writing MathSolve a technical problem and write it

Classic Style

presents:Assignments & reading: A2 due today

Other: complete ONE MINUTE PAPER

? A surprise ?

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Schedule group presentations

• Select ONE EW, listen and discuss as a group• Group prepares presentation (15 slides max) for (max 15 min) +discussion in class• Play EW and lead discussion in class

Note: MUST reference all material copied from URLs, journals,

textbooks, etc

Group Name

The Wrecking Crew

A&M Team

Classic Style

The Better Team

Team Alpha

Last Pick

Gilligan's Blade

LeftOvers

Feb 15 TuesdayUnder the Alps

Feb 10 Thursday The Reactor Down The Street

PLEASE E-mail me a pdf file of presentation for

posting on class URL site

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Comments on last lecture and group presentation

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China New Year

In China they no longer light fireworks to celebrate due to environmental issues & safety. In America, we obviously don’t follow this.

Practices of Modern Engineering – Spring 2011

Every city in the US has the strictest rules on fireworks handling and lighting. One can only do it outside the city limits or under strict safety guidelines.

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About Virtual Rehabilitation

How are other countries using technology to help their veterans?

I’d like to know more about the technical design of the CAREN system

Practices of Modern Engineering – Spring 2011

How much research is being done linking neurology to prosthetics?

I also thought of innocent victims of war (land mines) in poor countries. To manufacture inexpensive prosthesis is a worthy pursuit

PLEASE SEND PDF for posting

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Questions on communication

The article sent(*) listed oral communication as more important than written communication. How can we be better oral communicators?

Practices of Modern Engineering – Spring 2011

Oral communication is paramount in the workplace (daily activities). To become a better oral communicator, begin to ask questions

(*) Nixing Engineerese

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Questions on communication

Need good resources/examples of how to write technical memos/reports and/or lab reports

Practices of Modern Engineering – Spring 2011

Please visit TAMU Writing Center: Business & Professional Writing

http://writingcenter.tamu.edu/c/how-to/business/

Includes CVs, Memos, Executive Summaries, Lab reports, etc

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Questions on writing

When writing a tech report for an experiment you performed, how can you avoid both 1st person and passive voices? Examples:

Practices of Modern Engineering – Spring 2011

“We measured…” Active but 1st person

“…. was measured” Third person but passive

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Avoiding passive voice

Practices of Modern Engineering – Spring 2011

AWFUL

We measured the temperatures at the inlet and exhaust of the engine ..

Inlet and exhaust engine temperatures were measured….

BETTER

During the experiments, thermocouples recorded temperatures at the inlet and exhaust of the engine….

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From technical memo examples

Practices of Modern Engineering – Spring 2011

AWFUL

Seal loads were reported by Authors () …….

The loads were shown to decrease with increasing rotor speeds…..

The results are shown in Figure X

To improve the accuracy, Authors () introduced a 3 control volume method to calculate seal forces

BETTER

Authors () report(ed) loads for seals

The experimental results show the load to decrease as the rotor speed increases

Figure X depicts the results

Authors ( ) introduced a three control volume method to predict more accurately seal forces

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Questions on oil prices

Practices of Modern Engineering – Spring 2011

Why do oil prices have such an effect on jobs lost? Does the $ rise in cost means an increase in # jobs for engineers?

Gas prices influence directly the cost of transportation (goods and people). Companies struggle to keep costs down (ask an airline company). The $ increase reflects the uncertainty in the supply market. It will not create new jobs.

A $10 increase in a barrel of oil (causes in the US) 25 cent increase in gallon of gasoline drop of ¼% in economic growth a reduction of 200,000 jobs!

NPR 02/03/117:30 am

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More about the world

I’d like to learn more about other economies. I feel like some of the comments brought up about GDP and other countries’ economies are valid points that should be explored further

Practices of Modern Engineering – Spring 2011

Soon, I hope. Topic is too broad. Give me a few pointers, pleeeeaaasssssssssse!

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Exercise Writing mathematics

Zero gravity(?) flight

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A weightless flight (zero-g) ??

http://gozerog.com (weightless flight experience)

The experience starts at 7,700 m while the AIRBUS A300 cruises at 500 miles/hour. Engines are shut off! An instant later, the world inside the plane becomes chaos: people screaming as they are lifted, as if they are weightless. 20 seconds later, the engines roar back to life. The people inside, some pinned to the cabin roof, slam back against the floor.

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Weightless (?) flight experience

jotting formulas w/o explanatory sentences counts very little

Tasks At the end of the weightless experience, at t=20 sec, (a) What is the aircraft speed (km/hour) and its acceleration (g‘s)?

How many meter does the aircraft fall? How many km does the aircraft travel along the horizontal direction?

(b) Demonstrate that the relationship between Y and X is indeed a parabola, i.e. Y~ X2

(c) At a price tag of $ 4,950 USD, would you pay for the weightless experience?

(d) Tell about other examples where you already feel the weightless experience?

Objective: Develop mathematical analysis, based on physical principles and assumptions, towards prediction of the plane motion

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The fundaments in words

Airplanes fly by forcing air over their wings so there is an

excess of the upwards force, lift. While in the air, the plane stays up thanks to lift and the engines thrust that makes the plane move forward. The aircraft works against two forces trying to slow it down and pull it out of the sky; air drag and gravity. On a normal flight, the amount of thrust is equal or greater than air drag and the lift equals the weight so that the plane stays up.

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The fundaments in physics

ThrustDrag

Weight

Lift

speed

M

Abstraction: the concept of forces

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The fundaments in mathematics (I)

Free body diagram

T: Thrust

D=Drag

W=Weight

L= Lift

VX: velocityM

D T

L

W

g

g=gravity

M: mass

a =dV/dt: accel.

V: velocity

Define Symbols:

Forces

Constant

Parameter

Variables

VY: velocity

Tell the tale: count assumptions

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The fundaments in mathematics (II)

Newton’s Law of motion

VX: speedM

D T

L

W g M aX = T - D

M aY = L - W

X

Y

Define INERTIAL coordinate system

(1)

(2)

Note beauty and simplicity

(in description of natural phenomena

& economy of words)

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The fundaments in mathematics (II)

Newton’s Law of motion (equilibrium)

VX: speedM

D T

L

W g

T = D

L = WX

Y(1’)

(2’)

For flight at constant speed and height:

aX = dVX/dt=0

aY = dVY/dt=0

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Parabolic flight

During a parabolic flight, thrust is set to equal drag while lift is removed (L=0)Hence, weight is the only force

acting on the plane and, like any unpowered object fired into the air, the plane will move along a parabolic path as it free falls.

0 = T - D

M aY = - WEOMS simplify to

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Weightless flight experience

jotting formulas w/o explanatory sentences counts very little

Tasks At the end of the weightless experience, at t=20 sec, (a) What is the aircraft speed (km/hour) and its acceleration (g‘s)?

How many meter does the aircraft fall? How many km does the aircraft travel along the horizontal direction?

(b) Demonstrate that the relationship between Y and X is indeed a parabola, i.e. Y~ X2

(c) At a price tag of $ 4,950 USD, would you pay for the weightless experience?

(d) Tell about other examples where you already feel the weightless experience?

Objective: Develop mathematical analysis, based on physical principles and assumptions, towards prediction of the plane motion

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Weightless flight experience

Objective: To develop mathematical analysis to predict the plane motion

In short:(a) Where is airplane after 20 s?(b) Demonstrate flight path is

parabolic(c) Is the zero-g claim true? (d) Would you pay for it?

Known: At t=0 s, when plane is at 7,700 m and flying with speed of 500 miles/hour; engines are shut off (?). Time elapsed for zero-g experience is 20 s

0 5000 1 104

1.5 104

1 104

1.5 104

2 104

2.5 104

3 104

parabolic gravity fall

X [ft]

Y [

ft]

*

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Weightless flight experience

Work problem individually & as a group – tell me how you solve it (during class)

Ask questions – I am a part of your group (team)

No need to turn in anything but work problem (writing math and words)

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Summary

(a) Engineers work with different physical units. Conversion of units is a must knowledge.

(b) Formulation of problem statement (need) is crucial. It must convey all information (knowledge and assumptions). WORDING is IMPORTANT.

(c) Combining mathematical statements (equations) with prose sentences must be learned and practiced.

(d) Do not leave out anything. Do not assume the reader knows as much as you do or is familiar with your way of doing things.

Knowledge acquired today

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See “solution” posted on classURL site

Practices of Modern Engineering

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Questions?

Next lectureAbout plagiarism in academia and engineering practice

Ethics in the Workplace

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Practices of Modern

Engineering© Luis San AndresTexas A&M University2011

http://rotorlab.tamu.edu/me489