DrD

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Everything posted by DrD

  1. Dear Bob, What you have drawn is simply a form of a slider-crank mechanism, and well known mechanism described in countless sources. Do a Google on that name and you will find more information than you ever imagined. DrD
  2. Is this club going anywhere? Where is out leader, the club owner? What does he do if not provide leadership and direction? I ask again, is this club going anywhere? DrD
  3. Mechanics Corner A Journal of Applied Mechanics and Mathematics by DrD, #39 (c) Machinery Dynamics Research, 2017 Comments on a Textbook Theory of Machines by R.S. Khurmi & J.K. Gupta 1 Introduction Recently, through the wonders of the Internet, I have come across a copy of the textbook Theory of Machines by R.S. Khurmi and J.K. Gupta (S.Chand & Co., Ltd., 2005). Since theory of machines has been my primary technical interest since the early 1980s, I was interested to see what would be in this book, particularly in view of the many favorable comments posted in regard to it. Many people seem to think that this is a most excellent book, and I’m always interested to see what brings forth comments of that sort. As I looked through the Table of Contents, I saw that one of the last chapters was given to the topic of Torsional Vibrations (Ch. 24). Since the area of torsional vibrations has been a topic of intense personal interest for 40+ years, I was naturally drawn to this chapter. The comments that follow are based on what I found in that chapter; I have not reviewed the remainder of the book at all. In my comments below, I will refer to the authors, Khurmi and Gupta, simply as K&G to avoid writing their names out repeatedly. One of the things I think is necessary in a textbook is that it should be directed toward teaching students to solve real problems, not simply textbook examples. Certainly, textbook examples should be simple so that they can be easily understood, but they should also be as general as possible. Where they involve special, limiting assumptions that may likely not be true in actual practice, this should be made clear. Failure to do that marks an author as one who has never actually done engineering in the real world. If the assumptions are not made clear, there is a tendency for students to later want to simply apply directly the results from the textbook problem, not realizing that they may not apply at all. So, what did I find? Comments on Textbook - Khurmi.pdf
  4. New Blog Post

    When you ask about IT, I presume that is the same IT I spoke about when I wrote "Where would you publish IT"? Is that what you had in mind? For the blog post, I had not particular thing in mind, but most probably a technical paper presenting some sort of engineering solution. It could also be a book, but for that, it is a bit easier to locate a publisher. DrD
  5. I would like to encourage all members to read my latest blog post over at Mechanics Corner. The title is Where Would You Publish It? Check it out!! DrD
  6. You are asking for a huge amount of help. The design of such a device is a very large project, one that will take many hours. I strongly suggest that you start your design, do the preliminaries, and then ask questions about specific details. DrD
  7. Not my area either. I really do not want to lead you astray, so I better stay out of this. DrD
  8. ODE Solution --- Fail!!

    Mechanics Corner A Journal of Applied Mechanics and Mathematics by DrD, # 31 Machinery Dynamics Research, 2016 ODE Solution --- Fail!! Introduction Digital computation has become a major tool for engineers, and it is a great benefit. It can also lead to many pitfalls for the unwary. This note is about the latter, a potential pitfall that many engineers risk on a daily basis, most of them with little awareness of the danger. Early in the development of digital computation, every problem required that the user write a program specific to the problem at hand. If speed was a very important issue, the programs were written in machine language, so that they would execute as fast as possible. If speed was a little less critical, programs were written in so-called "high level languages." This included FORTRAN, BASIC, ALGOL, C, C++, and a host of other such names. But even with a high level language, there was the problem of generating a program for the solution of the specific problem at hand. As things have continued to evolve, it was soon evident that a lot of the work in writing each program was the same from one problem to the next. The major mathematical operations, such things as numerical integration, matrix operations and the solution of systems of linear equations, plotting, and many other steps were re-usable from one problem to the next. It was natural that this would eventually lead to the development of general purpose programs, able to solve broad classes of problems. This group includes programs like Mathematica, Maple, MatLab, SciLab, Maxima, TKSolver, and numerous others. Most of those just mentioned have built-in capability to solve ordinary differential equations, in some cases by analytical means, and in practically all cases, by numerical means. This has taken the sting out of working with differential equations from many engineering problems, and we must all be grateful for that. At the same time, we must also be somewhat skeptical about any general purpose solver when applied to a particular problem. How do we know that the solution generated is correct? How do we even know if it is reasonable? Most of the time, when engineers resort to numerical solutions, it is because there is no readily available analytical solution. Thus, when faced with a problem that cannot be solved in closed form, how can we know when to trust the numerical solution? This is a very serious question, one that all must consider. It you blindly trust a numerical solution, the old excuse, "The computer said it was OK" will not get you very far. The computer cannot be fined, fired, or (in extreme cases) possibly sent to prison, but all of these things can happen to an engineer! So, what can the engineer do when the differential equation has no known solution? Well, there are several options. (1) He can resort to any physical principles that apply to the situation. For example, if the system is such that energy should be conserved, then he can add code to calculate the total system energy at every instant. Just verifying that energy is conserved does not "prove" that the solution is correct, but if energy is not conserved when it should be, you can be sure there is an error in the solution. (2) He can try various approximations that may apply to see if they are in reasonable agreement with the computed solution. (3) He can verify the solution code by applying it to a similar problem for which there is a known solution. It is this last approach that I want to talk about in this post. ODE_Soln_Fail.pdf
  9. Rocket Homework Problem

    Mechanics Corner A Journal of Applied Mechanics and Mathematics by DrD, #38 Machinery Dynamics Research, 2017 Rocket Homework Problem Introduction Most engineers find problems involving rockets to be exciting. There is something about a rocket that fires our imagination, whether we think of going to the moon or one of the planets, or simply of shooting down an incoming missile. The subject of this post involves a rocket on a mobile launcher. The rocket is intended to be transported in a horizontal position, but it must be elevated in order to be fired. Both positions are shown in the accompanying figure. Read the attached PDF for more on this problem. RocketHWProblem.pdf Addendum: One reader has posted a proposed solution for this problem as a comment. It was not my intent that solutions be posted in the comments at all. I only want solutions sent to me by the personal message system. DO NOT POST YOUR SOLUTION IN THE COMMENTS!! Regarding the solution that has been posted, let me say the following: 1. Some of the answers are correct, while others are not. Do not be misled into following this solution because there are errors therein. 2. Even where the results are correct, there are a number of methods that I would not recommend using. Thus again, I say to all other readers, do not follow this solution, but work it out for yourself. 3. Be sure to document your solution, so that if someone else were to ask how you obtained a particular result, you would be able to explain it in a clear and reasonable manner.
  10. Rocket Homework Problem

    This comment removed by DrD.
  11. Over at Mechanics Corner, there is a new problem posted involving a rocket on a launcher. This is made to order for folks interested in Kinematics of Machines, so be sure to go read the post and solve the problem. DrD
  12. @ HydraBob: How do you see a bell crank meeting this need? Can you explain, please? @ JAG: Its worth a shot. But I think it has risks as well. The confused questioner may simply accept whatever is proposed as an easy way out of having to think more carefully and express the problem better. Who knows?? DrD
  13. Sounds like JAG is proposing a face cam. Perhaps JAG understand what AAFAA wish to accomplish. I wish I could say that I understand as much! If the face cam that JAG proposes is indeed an acceptable answer, the motion analysis (determining position, speed, and acceleration) is just a simple kinematics problem. The big question, as I see it, is this: "Is this what AAFAA wanted to accomplish?" DrD
  14. Wow!! I'm totally confused. What is this, and what are you trying to accomplish with it? Does this thing exist, or is this simply some device you have imagined? DrD
  15. Hard automation tends to be heavy on mechanical engineering. I am thinking, for example, of cam controlled automated systems. I have seen a number of examples of this sort of automation, including (1) a pick-and-place robot that puts finished CDs in plastic cases, (2) a yogurt cup filling machine, where cams control the lowering of the dispenser nozzle, starting and stopping the material flow, and retraction of the nozzle, and (3) a paper cup making machine where all operations were cam driven to cut out blanks for a paper cup, roll the blank into the form of a cup, seal the edge, place a bottom in the cup and crimp the edge, and finally roll the top edge. In each of these cases, there were vast quantities of product to be produced in identical form. Soft automation, with electronic controls that enable different forms for the basic product lend themselves to things like automobile production where there are many variations on the basic car. Some cars will have one feature while the next on the order lacks that feature. Automated assembly must be able to adjust and compensate on the fly for these variations. While the assembly operation itself may remain largely a mechanical problem, the control tends to be more electronic using computer logic to adjust to each order. The word MECHATRONICS is a relatively new term, one that usually denotes systems that involve a high degree of electronic logic with a few mechanical components. This brings to mind things like tape recorders, CD players/recorders, cameras, phones, and similar products. I'd be interested to hear from other readers just what word do you use for electromechanical devices such as electric motors, generators, electric brakes, solenoid actuators, gear motors, etc? Does this fall under mechatronics in your thinking, or is there another term you think is more descriptive? DrD
  16. who can help me that? ( solid mechanical)

    I cannot help if it is not in English. DrD
  17. who can help me with that? ( solid mechanical)

    It is already solved for T. What did you want to solve for? I don't think you have given enough information to determine X, Y, and Z. DrD
  18. What do you know about FEA ?

    FEA is a technique that began in the 1960s (or perhaps even slightly before that) in the aerospace industry. As DaveHoward said, it involves modeling the actual physical body as an assembly of much smaller pieces, and then writing and solving the equations that apply for each element, where it be for stress/strain, for temperature, or whatever. On the one hand, it is an extremely powerful technique that is applicable to many, many complex engineering problems. The results are often in the form of impressive colored plots that show graphically whatever the computed result is. The negative side is that it is easily misapplied by those who do not really understand either the subject matter or the method (or both). This often results in equally impressive colored plots that man absolutely nothing at all, but since the computer said this is the answer, .... who dares to argue with the computer? The use of FEA has led to a decline in actual understanding on the part of engineers who are using it. They never worked similar problems the long way, so they often have no conception of what should happen. But again, the computer represents authority, and who dares to argue with the computer? On another site, a student was seeking to model a bus seat supported by two very stiff beams. He thought he should make the beams rigid members, and was having some difficulty doing that. I suggest instead that he simply model the beams as beams with large, but finite, stiffness. This is what the system is in reality; there is nothing that is infinitely stiff. He was amazed at the simple concept of modeling the system as it actually is, rather than modeling something that can never actually exist! DrD
  19. Hey, alpha1729 --- This design question has exactly what to do with why the casing is called a volute? DrD
  20. Where Would You Publish It?

    JAG, thanks for the comment. I did not intend to imply that every job will demand publications, but I can think of few that will not be helped by it. Back in the early 1980's, I was a part of an industrial consulting group associated with Southwest Research Institute (San Antonio, TX). Those guys published a lot. I used to marvel at how they could write so many papers but give away so little. Before I joined that group, I used to read their work and I never could quite follow it all the way through. They would always omit some critical detail, such that the results were useless to every reader, but they were getting the message out, "We know how to solve this (or that) class of machinery vibration problem." It was evidently pretty effective. I did not stay there long enough to write any papers there, although I did do some work that could have made a very good paper or two. I think the idea of posting case studies is very good, and the only concern is whether they can be found or not. If not, I'd look for a better venue. Case studies attract a lot off attention, because people are always looking for help. I did not talk about it in the post, but there are essentially two types of publications. There are publications in trade journals and on web sites, both of which have no serious review. Then there is peer-reviewed publication, where 2 or 3 qualified folks are expected to review every paper. This last is the academic's sine qua non. Non-reviewed publications do not count for much in the academic world, although they can be very helpful in the real world. DrD
  21. Mechanics Corner Where Would You Publish It? Since long before my time, there has been a desire to have important results published where they become accessible to many others. Some of the great names, such as Newton, Euler, Bernoulli, and others, we know primarily because of what they published. Their work formed the fundamentals upon which modern engineering and science is built. Publication of research results has long been particularly important to faculty members; it is often taken as a measure of just how intelligent and useful they are (there is a lot of doubt about the validity of this measurement, but that has not prevented it use). When I was a young faculty member (many, many years ago), there was the mantra "Publish or Perish." This referred to the idea that those faculty members that did not publish research work would not receive tenure, and would be out of employment after several years. Agencies that funded research were eager to see publication of results that they had funded; it was considered evidence of the importance of the work supported by the agency. This was particularly true of the National Science Foundation (NSF) and other governmental funding sources in the USA. It was not too long before publication was replaced as the measure of academic value, to be replaced by funding. A faculty member was expected to write research grant proposals, and the Dean's Office expected a significant cut of the proceeds, ostensibly for their role in "supervision." In practical terms, Dean's Offices almost never contributed anything of value to research efforts, but this was a form of graft to assure their cooperation. But publication remained essential as well. Any research that could not be published in a reputable journal was considered to be unworthy, a waste of time. So the criteria for success became, get money and publish, a tougher goal that simply publishing. More recently, the goal posts have been moved again. Today the big cry is for "undergraduate research." To my mind, this is the height of absurdity. For folks who are just beginning to learn a profession, how can anyone think that they are capable of fundamental new discoveries? For undergraduates that are still struggling with Mechanics of Materials, do we really expect them to discover new understanding of fatigue or fracture mechanics? For a student laboring to understand dynamics, do we really expect them to come up with breakthroughs in orbital mechanics, seismic shock resistance, or multidegree of freedom models for gear box noise? But, rest assure, there is no place more insane than a university!! The utterly absurd is treated as absolutely essential!! Thus far, I've talked a lot about academia, but we must not neglect industry. Publication is important to industrial firms as well, although for different reasons. Published research, done by your firm, is a way of establishing the technical excellence of your company. If you want to be known as an industry leader in your area, you want your employees to publish work that makes the company look like it is on the cutting edge of new technology. Often industry imposes constraints on what can be published; they do not want proprietary information to be put into the public domain. But they really like to have results published that make them look sophisticated, ahead of the pack, so to speak. For consulting engineers, publication can be important as a means to establish your expertise in an area. If you publish a lot in a particular subject area, people begin to think you kow something about the area and come to you when they have problems. New work is the life blood of consulting engineers, so this can be very important. You will also be asked to review the work of others and to sit on panel discussions and other public appearances that can upgrade your image and bring in more work. I hope that it is evident that most engineers will need to publish some work at some point in their career. It may be a central matter of those in more research oriented areas, or it may be only occasional for those in less cutting edge business sectors, but everyone will eventually need to publish something. So, back to the original question: Where Would You Publish It? Most professional societies publish research work, and there are also a vast number of trade magazines. Fifty years ago, when the volume of "research" was much less, it was not too difficult to publish through any number of venues. I have published articles through the various Transactions of the American Society of Mechanical Engineers (ASME), through the Transactions of the Society of Automotive Engineers (SAE), and the Journal of Mechanism and Machine Theory. I have also published through some much less well known venues such as Machine Design magazine, and most recently through IPTEK Journal, a small journal headquartered in Indonesia (that was an experience!) and other places. But the game is ever changing! When I first began to publish papers back in the 1960s, it was a fairly simple process. You wrote up your text, with figures and equations, and mailed it to the editor in type written form (this before the days of word processing). After a few months, you would get something back from the editor. It might be an outright acceptance (rare), a conditional acceptance which meant that the paper would be accepted with certain modifications/corrections that were described in the letter (fairly common), or it might be a flat rejection (not extremely uncommon). If you got a conditional acceptance, you made the revisions, and about 6 months later, it would be published in whatever journal you were dealing with. The classier the journal, the higher the standards were, but all worked about the same. Many of these organizations that publish papers also hold meetings, and they want people to come to the meetings. I have presented papers at the ASME Winter Annual Meeting (always in New York), at various SAE meetings, etc. But, there is a problem. It is expensive to go to these meetings. There is the travel expense (transportation, hotel, food, etc), and there is usually an admission fee (you have to pay money to present your own paper, an absurdity, but very real). Often the papers is only accepted for publication if you agree to come to the meeting to present it and pay the admission fee. Now if your paper is the result of funded research, or if your employer will pay the expenses, this is usually not a personal burden. If neither of these apply, the burden of the costs fall of the individual, and it is often prohibitive, often approaching $1000. The publisher then sell your work for a subscription fee, usually several hundred dollars per year. Libraries are the principal subscribers (university, municipal, and industrial libraries), along with a few individual. In recent years, there has been a glut of material offered for publication, and everybody thinks that their paper is extremely important for the world to see. The volume of publications have increased drastically, but so has the cost. Who will pay for all the paper, printing, etc.? For years, it has been common to impose what are called "page charges," typically around $100 per page, to publish in most journals. Funded research usually included a line item for page charges, so that paid those bill. In the past, any unfunded research, if it was accepted, would usually be published with the page charges waived. Today, that is not longer true, and page charges are usually mandatory. But it gets worse. We all know the Internet is a wonderful thing, but it does have some downsides as well. One of those downsides is in the area of publication. There is a relatively recent trend in publication called "Open Access," and it is particularly popular with a number of on-line journals. These journals are free to all on the internet, but the journals charge the authors a very steep price to publish their work. Thus you, as an author, must prepare the article according some very demanding rules about formatting, style, etc, then you must pay several thousand dollars, just so the world can see your work. It means that your work becomes available to all for free (which is a good thing), but it means that you the author must bear the full cost of supporting the publishing operation. I know that I, as an individual, cannot afford this, and thus it is almost impossible for me to publish anything now. It means that those with money will get their work published, and those without money will not. The quality of the published work is virtually certain to decline, but that is modern life. What can you do? As a closing note, I'm currently writing another technical paper that I would like to publish, preferably where folks who work with IC engines will read it. I think I have something of real value to present, but I have no idea where I will publish it, or if I will be able to find a publisher at all. If any readers have a suggestion for an appropriate journal, I would certainly appreciate a suggestion in the comments. DrD
  22. How do you see shipping tools as something unique to automated systems? Can't tools be shipped in non-automated systems as well? I seem to be missing something here. DrD
  23. Simple Machines

    Does design failure grade on a curve? DrD
  24. One of the most interesting examples of automation that I have worked on is a paper cup making machine. Everyone has seen paper cups. They come in many different forms, from simply conical forms to more complex truncated cones with a flat bottom. The come in small, medium, and very large sizes. How do you make such things cheaply, cleanly, and fast? Starting with a long coiled sheet of paper, the pattern must be cut out, rolled up, a bottom added, and the whole thing sealed. This is quite a sequence of operations, and the machines that do this consist of a number of stations, each station performing one operation and then passing the work piece on to the next station. The machines that I worked on were all cam controlled, which is to say they were a form of hard automation. Cam driven systems are extremely repeatable, but they are fairly difficult modify for a different product. They are also capable of operating at incredible speeds. I saw machines making 1200 paper cups per minute. The literally come flying out the end to be caught and packaged for distribution. The machines are quite expensive, but the number of paper cups they can make is absolutely huge! DrD