• Content count

  • Joined

  • Last visited

  • Days Won


Everything posted by DrD

  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
  16. Just to muddy the waters a bit, consider this: Most of the comments above relate the word "engine" to a heat driven machine, such as a diesel engine. But have you heard of a "dividing engine"? Yes, the word was common when I was young (back before the last Ice Age). It refers to any mechanism for marking graduations on an instrument. Thus, to make a glass thermometer, you would use a dividing engine to place the degree marks on the tube that will contain the mercury, alcohol, or other fluid. To make a slide rule (do you know what that is?), a dividing engine was used to place the marks on the several parts. And so on .... I bring this up to reinforce my contention above. Questions like this depend entirely on the definition of words, and that in turn depends entirely on social convention. Social convention varies from place to place, so we can argue/discuss these questions at length without gaining any real knowledge. Such discussions are a royal waste of time!!! Please, let it stop!!! DrD
  17. Really, Eng. Michael Vegard Berg! You say "... and almost the same body structure." Perhaps you have not thought through the implications of that "slight difference" in body structure. Please take a good look at a girl! It is a universal fact that men simply do not get pregnant. Check this out, and by all means, tell us of any exceptions you find. Bringing children into the world brings new responsibilities that fall on the woman in ways different from the ways they affect men. Yes, both are affected, but not in the same way. Men do not require maternity leave, they do not suckle babies, and they do not develop the same sort of emotional ties to children (I'm not saying that they have no emotional ties, only that they are different.) Anyone who thinks men and women are biologically equivalent is simply blind! I stand by my earlier comments in this thread. The cost to society at large is, in most cases, too large when women are educated as engineers. DrD
  18. I'll second the motion -- Happy New Year to everyone! DrD
  19. How To Become An Expert

    Mechanics Corner A Journal of Applied Mechanics and Mathematics by DrD © Machinery Dynamics Research, 2016 How To Become An Expert Introduction This is going to be another of those personal experience/opinion pieces, so if these bore you, be warned! This may be the time to click on something else. A reader recently wrote to me asking how to become an expert. I have to tell you, I don't spend much time thinking about being an expert, but I suppose on some reflection, the shoe probably fits. (Most of the time, I see myself as simply a tired old man, still enjoying the things I have done almost all my working life.) In the discussion below, I will describe a few events and observations that seem to relate to the question at hand. Find Your Place Nobody can hope to be an expert on everything, there is simply too much to know. You have to find the area that excites you, the area that really makes you want to dig in more. If you do not really enjoy it, you will never be an expert! I was very fortunate in this regard. When I was in High School, I was rather good in Mathematics, and my school advisers all told me, "You should become an engineer." Sadly, I really had no idea what that meant, and neither did they. The town where I grew up had rather little industry, and no one in my family knew an engineer of any sort. I did a little bit of research on engineering (this was thousands of years before the Internet), and it sounded interesting in a very vague way; there seemed to be little specific information available to me. But I went off to college, intending to study mechanical engineering, whatever that was. In my first semester of college, I took a Physics course in classical mechanics, and I really enjoyed it. This was exactly what I wanted to do, I just did not know the right name for it. I thought Newton's Second Law was the greatest thing ever discovered, and when implemented with Calculus, it was really fun. I was astounded at the power of it all, the questions that could be answered. If I could just get a job doing mechanics problems, I was sure I would be happy. HowToBecomeAnExpert.pdf
  20. Actually, Manjunatha k has it exactly backward. The gear form comes from the geometric curve called an involute, not the other way around! Saurabh U evidently did not read what I wrote earlier. The pump casing is a VOLUTE, not an INVOLUTE. Please people, read what has already been said!! DrD
  21. Questions like this depend entirely on the definition of words, and that in turn depends entirely on social convention. Social convention varies from place to place, so we can argue/discuss these questions at length without gaining any real knowledge. I simply despair of questions like this. They do not lead to greater knowledge and understanding. DrD
  22. Mechanics Corner A Journal of Applied Mechanics and Mathematics by DrD, # 34 © Machinery Dynamics Research, 2015 A Problem in Statics & Dynamics Introduction A problem was recently posted on this Forum, requesting help, that has led me to consider a somewhat more general problem for this post. The scope of this post will include the original problem, although not by the method required there, but will also go beyond to a more general geometry. We begin here by stating the present problem; interested readers are invited to search back for the original problem posted 19 December, 2016, by iivii. Assembly Drawing, with Dimensions StatDynProb.pdf
  23. Mechanics Corner A Journal of Applied Mechanics and Mathematics by DrD, # 7 © Machinery Dynamics Research, LLC, 2015 Degrees of Freedom & Constraints Introduction The term "Degrees of Freedom" (often abbreviated as DOF) has been carefully avoided for the most part in these presentations up to this point, although it has crept in unavoidably a time or two. In this article, we attempted to face the matter squarely and deal with it fully. It is an important concept, one that is very widely confused, and is critical to correct understanding of countless mechanics problems. There are several other concepts that must be discussed along with degrees of freedom including the idea of a particle or point mass and the idea of various types of constraints. This article is different from those that went before in that there is (almost) no calculation involved. It is almost entirely focused on matters of philosophy, a perspective or point of view, that has proven useful for countless generations of workers in the field of mechanics. DOF-Constraints.pdf
  24. Here is a product ad made specifically for Mechanical Engineers! Enjoy!! https://www.youtube.com/watch?v=Dxy4n0UT82o DrD
  25. Mechanics Corner A Journal of Applied Mechanics & Mathematics by DrD, #6 © Machinery Dynamics Research, LLC, 2015 AC Power in Real Variables Only Most mechanical engineers get a pretty good understanding of DC circuits, and this carries over fairly well into single phase AC circuits. The difficulties come when we get into industry and discover that almost everything is powered by three phase AC circuits. This is where it starts getting sticky! In the discussion of three phase AC electrical power, it is almost universal to use complex notation, otherwise known as phasor notation. For most purposes, the results might just as well be simply pulled out of the blue for all the understanding that complex mathematics gives, because everyone knows that the quantities involved -- voltage and current -- are fundamentally real, physical variables. These real quantities are not described by complex numbers, but rather by real numbers. The customary mantra says, "... we are considering the real part ...," but that really does not explain things very well because all of the mathematics being done is using complex algebra which considerably obscures the picture. Complex variables are, to use a colloquial term, "unreal." What is needed is a simple, straight--forward presentation of the problem in terms of real variables. We will give that a shot here. ACPowerInRealVariables.pdf