DrD

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DrD last won the day on January 17

DrD had the most liked content!

About DrD

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    Member
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Profile Information

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

More Information

  • 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. Industrial safety does not have a whole lot to do with the mass moment of inertia. Industrial safety is largely common sense. If you don't understand what is going on in an area, stay out of it. If there is the possibility that there may be something moving so fast you cannot see it, stay away. If there is the possibility of something falling on you, don't go under it. If there is the possibility of you falling, use a safety belt, a safety line, or stay out. Always wear your hard hat and watch for overhead obstructions (like pipes, machine parts, etc) and holes in the floor. (My hard hat from my steel mill days if covered in black marks where I ran into things while I was looking at the floor to avoid pitfalls.) Stay out of high noise areas. If you must, wear hearing protection and limit your exposure time. (I'm deaf because I worked too long one high powered sonar transducers.) Wear safety glasses wherever indicated. They are a pain in the neck, but they sure beat being blind! Wear gloves, aprons, steel toed shoes, etc as indicated for the situation you are going into. That's about it. DrD
  2. Just what does M.S. pipes refer to? I read this as "Main Steam pipes," but perhaps you had something else in mind. It would be really nice if that actual question had a direct relation to headline. DrD Just what does M.S. pipes refer to? I read this as "Main Steam pipes," but perhaps you had something else in mind. It would be really nice if that actual question had a direct relation to headline. DrD
  3. Off hand, I cannot see any reason why this would not be possible, provided you had sufficient power available. More to the point, why would you want to do this? What is the point? In what circumstance can you see this being useful? DrD
  4. And the design of a gantry crane has what to do with bolts in bending? It would be a real benefit to other readers for the title and the question to have some obvious connection!! DrD
  5. Have any of you ever worked on an actual IC engine? This is absurd!! Such an engine would produce power only once in 3 crank revolutions. It would require a huge flywheel simply to keep it moving during the remainder of the time. If this was a viable idea, why do you think it is not already in production? Someone would have already done it, except that it does not work well at all. DrD
  6. Much of the answer depends on whether your system is static or dynamic. If it is static, alpha is zero, so that I*alpha is also zero. For a static system, you usually do not need to know I. If your system is dynamic, then you will need a value for I in many situations. DrD
  7. I think you are asking what is the use for the mass moment of inertia (MMOI) in mechanical design. Any time you want to apply the rotational form of Newton's Second Law, T = I * alpha, you will need the MMOI calculation to provide the value for I. If you are asking specifically about the expression for a solid, homogeneous sphere, the I might suggest that you consider writing the T = I * alpha relation for a ball, such as a single ball in a ball bearing. DrD
  8. Yes, JAG, I too see dimensions. I also see an incorrect FBD, despite the label. This is a matter of economy in a textbook, where every additional figure means more space and more effort. That does not make it correct, but rather only expedient. Expediency is rarely correct. DrD
  9. I would like to thank all those who have written comments above. I may yet be around in some form, yet to be determined, but that is all undefined at this point. DrD
  10. Mechanics Corner A Journal of Applied Mechanics and Mathematics by DrD © Machinery Dynamics Research, 2017 Last Post Time to Hang It Up This will be the final post of Mechanics Corner here on Mechanical Engineering Forums. It has run almost exactly two years, and there have been ups and downs along the way. In this final post, I want to reflect a bit on my original goals for the blog, and also on what has actually happened. When our host first proposed to me that I might write a blog for ME Forums, I was excited about it. About half of my career had been spent in engineering education, and I always loved working with students. It seemed like a way to get back to something that I had long enjoyed, and so I accepted his suggestion. A long time ago, back when I was about 14 or 15 years old, in Junior High School, my shop teacher mentioned, in an off-hand way in class, that various curves could be described mathematically. I’d never heard that before, but I thought immediately, “This has interesting possibilities.” Moving ahead a few years, I discovered that I wanted to study and build my career around was the area known as Applied Mechanics, although it was a time before I first heard that term. In my freshman physics class, I discovered the laws of motion, and thought to myself, “This is great stuff! I can use math to describe how things move!” All of that happened back in the 1950s, and I’m still doing the same thing today (some might say I am in a rut!). As a teacher, I taught mostly undergraduate engineering courses, although I taught my share of graduate courses as well. It was the undergraduate courses that I liked most, because I firmly believe that the economy of a nation is strongly dependent on the quality of the baccalaureate level engineers produced in that nation. Engineers with graduate degrees are valuable as well, but the vast majority of the national engineering workload falls to BS level engineers. Thus, I envisioned Mechanics Corner as a sort of continuation of the several undergraduate courses I most enjoyed teaching — kinematics, dynamics of machines, vibrations, and mechanics of materials. For the most part, I have stuck to the plan, so that most of the technical posts I have made have dealt with problems that I considered suitable for undergraduate engineering students, say perhaps, junior level. I have posted a few topics from my industrial experience, but those have been situations that baccalaureate level engineers would be expected to handle. Now I knew it would not be exactly like continuing to teach my classes. In particular, you would not have any homework or tests, and I would not have any grading to do – a win-win, or so I thought. I did hope, that even with no assigned homework, readers would take an interest in the problems discussed, even to the point of working through the details for themselves (I was terribly naive, apparently!). I knew from my own experience that the only way I ever really learned a new idea was to get in and work with it, work some problems, make some numbers, plot some curves, until I really understood what it was all about. I’ll venture to say that nobody ever learned any technical material simply by reading only. In actual fact, in the early days, I had one or two folks say that they would in fact work through the problems, so I was encouraged. What I was not prepared for, however, was the fact that the vast majority never seemed to even read very carefully, much less work through the problems! The questions that have come, and there have been a few, have largely been about matters totally unrelated to the posts. The most common question has been, “Suggest a topic for my final project,” which relates to not a single post. Needless to say, that aspect of my vision was totally unfulfilled. But there is another side. I ventured to write a few “philosophical” articles, items dealing with academic integrity and cheating, with how to ask for help, with how to write a report or a paper, and various other matters. I really thought all of this would be considered obvious and trivial, so I was completely unprepared for the excitement that some of these articles generated. There were, in some cases, many, many comments, and people seemed to really be interested. I’m left to wonder: why? Are these ideas foreign to the culture of India and SE Asia? Are these things not all taught at home and in the public schools? I don’t know, but there was a lot of interest in these matters. But Mechanics Corner was intended to be primarily a technical blog, and there, it just did not excite the interest of the readership. As time passed, there was less and less interest. First, the comments dropped off to just about zero, and later, there were fewer and fewer who even bothered to “like” the articles. Finally, the number of reads has dropped to almost nothing (there may be no one left to read this final note). Well, there could hardly be any more clear indication that it is time to stop. I asked for opinions about this from some of the administrators, and was told that the blog was just over the heads of the readership. That makes me sad; that was never the intent. If it is true, I do not see how engineering has a very bright future among this readership. Even so, I wish all of you the best for your careers. I hope that you are able to find rewarding and beneficial work in which you will be happy and make a real contribution to your societies. To use an old cowboy metaphor perhaps familiar to many of you from Bollywood, “It is time to hang up the bridle and saddle, and say, ‘Adios’ (Adios is literally, “to God”).
  11. In practice, a FBD is a tool, and you can use the tool anyway you like. You can draw the precise shape of the body, or you can simply draw a blob. You can draw it in black lines, or you can draw it in red lines. You can put no dimensions on it, or you can put a few dimensions on it, or you can put a whole lot of dimensions on it. You can use the FBD anyway that suits you. On the other hand, in the classroom, if the teacher asks for a FBD, the fastest way to loose 5 points is to put a few dimensions on it. I will stand by my statement that you quoted. DrD
  12. I never intended to indicate that the force locations are unknown, only the dimensions do not belong on the FBD. The reason for this is to focus attention in the FBD on the forces. Dimensions have arrow heads also, and there are often many of them, to the point that the forces can easily be lost. The FBD is usually a very quick sketch, frequently just a blob, intended to list all the forces in their proper relative locations. All dimensions needed are always assumed to be available on another drawing, but not on the FBD. I'm pretty sure you knew that, JAG! DrD
  13. The term is almost self explanatory if you examine its parts. A FBD is a diagram (a picture) showing a body cut free from all attachments, and and showing ALL of the forces acting on the body. In the usual case, forces act at points of attachment. In addition, for many problems, it is necessary to show the force of gravity (the body weight) acting at the CM. A FBD does not include dimensions, or other data, but forces only. And I should emphasize that this means actual forces only, not "inertial forces" (mass * acceleration terms). The FBD usually does not show much geometric detail, but only the minimum required to make it evident where various forces act. Get a good understanding of this matter. It is absolutely essential to countless engineering problems. DrD
  14. I think you are going to have to describe what a "telescopic conveyor" is before anyone can help you with a drive mechanism. DrD
  15. Michael, you absolutely astound me! It is evident that you need to have a long talk with your girl friend, your wife, your mother, or perhaps your dad, about the way babies are brought into the world. This board is probably not the best place to get into the details of human anatomy/reproductive biology, but there are details you seem to have clearly missed!! DrD