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DrD last won the day on March 5

DrD had the most liked content!

About DrD

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  • Gender
  • Location
    Iowa, USA
  • Interests
    Kinematics, dynamics, mechanics of materials, Theory of Machines, machine design, vibrations
  • Present Company
    Machinery Dynamics Research
  • Highest Qualification
  • Engineering Qualification
    Registered Professional Engineer, TX, WI (Ret'd)

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  • Achievement /recognition/ Certifications
    Consulting work for a variety of industries, particularly in the IC engine related area (Torsional vibration analysis, shaking force analysis, engine cam design, system simulation).

    Author of several books, including one widely used textbook for Theory of Machines.

    Life Member ASME
    Member SAE
    Member SNAME
  1. The sad part, Rick, is that today (2017), critical thinking is essentially prohibited at most schools; they have become simply indoctrination institutions. That said, however, there is more to the Doonesbury strip. The point, as I see it, is the complete lack of student participation in the learning process. Students then, and students today, want the faculty to simply open their skulls, pour in a spoonful of knowledge, and close the lid tightly lest any leak out and be visible. They are unwilling to do even so much as to ask a question. My reason for posting this on ME Forum is to point to the same problem. Most readers on ME Forums are unwilling to participate. They are usually unwilling to ask any questions. They are unwilling to think through a problem presentation. They seem to simply want to have the knowledge wash over them, in the hope that they will absorb enough by osmosis. No one ever really learned anything that way. DrD
  2. Recently I was looking at the well known textbook, Mechanical Vibrations by S.S. Rao. I found an interesting problem there that seemed to be worth investigating further. The attached note is the result of that investigation. I challenge all of you to work through the details! DrD TwoSprings.pdf
  3. To design something implies an objective, a goal to be accomplished. We design a machine, a system, to accomplish that goal. What does this accomplish? That was the thrust of my previous comment. DrD
  4. Hey, JAG ... You're telling me that you think you have a book older than I am? Why, when I was learning to write, it was still done with a stylus pressed into damp clay (later to be fired); papyrus and ink had not yet been invented! DrD
  5. And the point is ......? DrD
  6. Questions like this make me crazy!! The difference is that they are made differently, rather like the difference between a pig and a bird. DrD
  7. Ah, once again, we have a communication gap!! When I look at the quadrant labels in the original question, I see that the labelling convention at at least some of you are familiar with is not the one I know. The labelling sequence shown in the question moves clockwise from the first quadrant; the convention that I (and I suspect others in the USA at least) am familiar with is the opposite. Thus, I would exchange the labels for the 2nd and 4th quadrant. Neither is more right or wrong than the other, but it points to the need to communicate carefully. If you say "Second quadrant" to me, I have to ask, "just what do you mean?" As to why one system is used and not the other, I think it is purely a matter of convention and long accepted practice. We can use any view that is useful to show the necessary information about a part. DrD
  8. You will get more useful feedback if you do a couple of things different: 1. Put more information in your question title. To simply say, "Engineering" does not tell the reader anything at all about what you are interested in learning. Most will simply ignore your questions. 2. Elaborate your question more completely. I do not know exactly what you mean when you say "iron grades." What kind of iron are you talking about? Cast iron? Wrought iron? Pig iron? Or something else? Tell us more abut what you mean and why you want to know. In many cases, as in this example, the terminology is not completely universal, so some of us will not know what you mean by a particular term. DrD
  9. That question has no general answer. The contact ratio for a gear pair depends upon the particular gears and the way they are mounted (it cannot be determined for an unmounted pair). Tell your "question paper" that it is nuts, that the question is ill posed, and shame on it! DrD
  10. The contact ratio is the average number of teeth engaged in a gear mesh over a full mesh cycle. Higher contact ratios generally mean more evenly spread loading and quieter operation. DrD
  11. The fundamental law of gearing states that for a constant velocity ratio, the pitch point must be stationary. DrD
  12. I regret to point out that ianbates1 has led us on a wild goose chase with his mathematical presentation. 1. The universal gravitational law, describing the force of attraction between two masses, is not relevant to a discussion of the bending of an I-section. 2. The resulting expression for a, the acceleration, is irrelevant as the beam bending problem is usually applied to static structures. 3. The bending deflection expression, FL^3/(3EI) is relevant for a uniform cantilever tip deflection only, but has no general applicability. 4. The expression for the area MOI, bh^3/12, is for a rectangular section as shown, which has no significance for the I-sect ion. 5. The stress-strain relation through Young's modulus explains nothing about the I-section. Other than that, yeah, sure .... why not? DrD
  13. Several of the previous comments speak of "stress concentration" avoidance as the reason for the use of the cylindrical form. This is a misunderstanding of the term "stress concentration." A stress concentration occurs when there is a sharp change in section area such as a hole, a notch, or a reenternant corner. This would not be the case with a pressure vessel with flat sides such as a rectangular box. If a flat sided vessel is used, the problem that dominates is the bending stresses at the edges of the flat plate. These are required to sustain the required angle at the corner, and they can often be severe. DrD
  14. There is a problem with the original question. The term "superior material" is undefined. What is a "superior material"? Is it superior with respect to strength? With respect to wear? With respect to heat conduction? With respect to workability? With respect to ductility? With respect to toughness? Etc, etc. Until this is defined, the question is not very meaningful. DrD
  15. And the point of this is ......????? Does this have something to do with Mechanical Engineering? If so, what???????? DrD