Mechanical Engineering

# DrD

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2. ## A Calculus Challenge

Dear Amin, There are a few problems with your answer. 1) If you are going to cite Roark, you should surely say which edition. There are many, and they are not all the same. I have two of them myself, but quite likely not the one you use. 2) You don't give your final result for the area. You simply cite Roark, but there is nothing here that I can check. Roark has been known to be wrong. 3) You give an answer for something you call "static moment," but you do not locate the centroid. 4) You say, "The same for moment of inertia." The same what? You have given any answer before (unless you meant your area result), so this is no answer at all. 5) You seem to think actually answering the question is beneath you because you know how to look in a book. What do you do if the book is not at hand? 6) You said, "When I had to deal with these kind of problems, I used to go to handbooks." Do you think handbooks have all the answers? Do you no longer do engineering? Overall, I'd say this is a fairly poor effort by someone who really is not very interested. DrD
3. ## A Calculus Challenge

Well, as of now (4 Jan 2019), over 1000 people have looked at this problem, one person has worked one part of the problem statement, and another says he know how to do this without integration (and thus far, without results). You folks are real balls of fire!! DrD
4. ## A Calculus Challenge

Dear Jarek, Your figures help a lot to explain your logic. Thank you. I'd say you definitely have the answer for the first part. Now, can you extend this to obtain the other answers ? DrD
5. ## A Calculus Challenge

Dear Jarek, Your final result for the enclosed area is correct (if we ignore some notational inconsistency, r in place of R). Congratulations!! That said, I cannot follow your development. Would you explain your reasoning with some words, perhaps? In particular, you show the sum of two integrals equal to a third integral. How is that equality established? I cannot follow it. Also, you write in the integrand in one place xtgalpha; what is this? Is "tg" the tangent function? If so, it would help if you would enclose the argument in parentheses. Now, to all others, I hope you see that the problem is not impossible. Why are you so unwilling to try it yourself? DrD
6. ## A Calculus Challenge

My word! An answer ... I'm simply stunned! If you are sure it can be solved without integration, go ahead. This will serve as a check on the results obtained by integration. If you use formulas from a book, please be sure to give their derivation as well. DrD
7. ## A Calculus Challenge

Today, 29 December, there have been over 300 people look at this problem, and yet not a single comment! What is it with all of you? What are you thinking? Is the problem unrealistic, so that it would not be useful to know how to do it? I can cite cases where this geometry really appears. Is the problem too hard? You are supposed to be engineers, able to confront new situations and find ways to deal with them. Why is this any different? Is the problem too easy, and therefore beneath your dignity? If so, please humor an old man, and indulge him by answering the questions. Whatever the situation, somebody please say something!! DrD
8. ## 10 lý do khiến chiếc xe của bạn bị rung lắc

Sorry, JAG. It does not happen on my Win7 machine. I'm just old and past my "use by" date! DrD
9. ## 10 lý do khiến chiếc xe của bạn bị rung lắc

Wow!! Great article!! Just what language was that in, anyway?
10. ## A Calculus Challenge

As I check this on 26 December, there have been over 200 people look at this problem. Thus far, not a single one has ventured even the first bit of an attempt. What do you folks do when confronted by a problem that is not in the textbook? DrD
11. ## A Calculus Challenge

Mechanics Corner A Journal of Applied Mechanics and Mathematics by DrD, #45 (c) DrD, 2018 It has been quite a while since I last posted anything here, but an interesting problem has come to mind that I wanted to share with you. If you really know calculus, this should be straight forward; if you don't know calculus, don't even try! MEForumChallenge.pdf *********************************************************************************************************** THE CHALLENGE IS NOW ENDED. I WILL NOT RESPOND TO FURTHER ANSWERS. i EXPECT TO POST A SOLUTION AND A FEW COMMENTS IN THE NEXT FEW DAYS. ***********************************************************************************************************
12. ## mechanical design tutor needed, any help?

It is possible that I may be able to help you, but again, I may not. Please answer a few questions for me. 1) What college level math courses have you taken? 2) What college level mechanics courses have you taken (statics, dynamics, vibrations, theory of machines, etc)? 3) Where are you located? 4) Are you able to pay for tutoring? DrD
13. ## Can you use a car Caliper Brake to slow/stop stop a winch?

A brake is a brake is a brake. Any brake has the potential to stop any rotating object. Whether it is a good idea or not is another matter, but certainly an automotive caliper brake has the potential to stop a winch drum. You really need to learn the difference between "brake" and "break." They are entirely different words, even though they sound alike in English.
14. ## How did they manage to make the gear rotate?

Wow! That was one boring video! I could not stay interested enough to watch it to the bitter end. The whole idea seems ludicrous. If you want to generate energy by human effort, why not apply it directly? Perhaps simply ride a bicycle, rather than try to generate electric power by pushing things. Talk about grasping at straws ...
15. ## Dissertation Project Starting From Scratch

I rather doubt that you will ever get to the point where you fully understand the problem. Most of us find that there is always something more we can learn. At the same time, it seems foolhardy to commit to designing something about which you know so little. There is nothing about which I know everything, yet I would undertake to design some things but not others. I would design those things about which I already know enough to make a good start. I would avoid attempting to design something about which I now know nothing. Do you see the difference? DrD
16. ## Defense products

What a fabulous post! Not a complete sentence in it, just a string of terms describing destruction and destructive devices. This makes no sense at all, so it is posted in exactly the proper place. DrD
17. ## Dissertation Project Starting From Scratch

What a great idea to commit yourself to a project you know nothing about! This is utter foolishness!! Engineers do not do such things. DrD
18. ## Kinematics of Machines

What are Z-Kinematics U-Kinematics? I've never heard these terms before, so I'd be interested to know what you are talking about.

20. ## Flywheel and DC motor

Why in the world do you want to put a flywheel on a DC motor? The purposes of a flywheel are (1) to smooth out irregularities in the rotational motion of the shaft (torsional vibration), and (2) to store energy in order to continue operation though a power interruption. You did not mention either of these, so I ask again, "why do you want to put a flywheel on a DC motor?"
21. ## In  a multi-cylinder engine,why  the firing is done at different time ? what are the firing order for a four cylinder petrol engine?

"It gives balance to engine and load is uniformly distributed in crankshaft." This statement is totally incorrect. Torque is delivered to the crankshaft as a series of pulses, in no way uniform. In a multicylinder engine, torque will be positive at one location while it may be negative at another. What is a "four stage engine"? Do you mean four cylinder, or perhaps four stroke, or something else? All the pretty animations in the world are not worth much if the accompanying statements are nonsense. DrD
22. ## Can anyone help me solve this problem related to gear trains

The PDF file below will show you how to solve this problem. DrDPlanetaryProb.pdf
23. ## Mass Inertia calculation of planetary gearbox

As a starting point, you must know the MMOI for each individual component; without that, you cannot begin. Assuming that the individual component MMOI values are known, do a kinematic analysis of the planetary train to determine the velocity of the CM of each component. The use that information to formulate the kinetic energy of the entire system, all moving according to the kinematic relations. You will have to choose some rotation as a reference value, usually either the input or output rotation. The kinetic energy will have the form T = (1/2) theta-dot^2 (term1+term2+...+termlast) where theta is the reference rotation. The sum of terms indicated is the effective MMOI for the gear train. DrD
24. ## Two stroke &four stroke

So, what else is new? DrD
25. ## LATHE CHUCK MECHANISM

Wow!! That was super exciting!! DrD
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