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Mechanical Engineering


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Everything posted by DrD

  1. That's pretty fuzzy. I doubt you will get a lot of takers. Maybe you could at least identify what sort of help you expect to need? DrD
  2. My own experience left me permanently traumatized by the law. I see justice as accidental at best. When they told me to destroy work I had done that was the truth, in so far as I was able to approach the truth, I discovered that winning was all that mattered to the lawyers. Truth and justice are the lowest concern of an attorney, while winning and greed are upper most. DrD
  3. Where did you get this force expression? Did you check the derivation? DrD
  4. You have a rather difficult problem. The span of 278 m is quite long if you don't accept intermediate supports. Your bridge will be rather expensive to build because it will have to be very strong to support this length. DrD
  5. Do you have a specific purpose in mind for this brush? That will guide many of your choices, and it is essential to giving you much help. Tell us more. DrD
  6. DrD


    In saying that you are a student, I presume this means that you are enrolled in a college. Your school will guide your program of studies. In general, you need a lot of math and physics. Good luck. DrD
  7. I agree with most of what GB Reid has said. Brittleness is certainly the tendency to fracture rather than deform under load. I would disagree with the example of glass, however. It is my understanding that glass is actually a supercooled fluid ( although materials is not really my area). DrD
  8. Sure looks like school work. I think I'll pass. DrD
  9. Much depends upon what loads act to prevent this motion and also on the positional accuracy required. Have you considered something like a hydraulic or pneumatic cylinder? What about a screw drive? DrD
  10. DrD


    The simple answer is "yes, there is evidently something wrong with your calculations." Now you will probably ask what is wrong. That is harder. Where did you get the data for your calculations? What do you think you are calculating? To just through out a bunch of numbers with no statement of your approach to the problem is pretty meaningless. DrD
  11. Have you downloaded a copy of my Theory of Machines text available at this web site? If not, I suggest you might want to do so. While this problem is not given there, a lot of similar things are discussed. Take a look. DrD
  12. Well, I got one good comment from JAG. I presume that means that he and I are the only folks left who don't know everything. I suppose that stands to reason; we are both old men! I had no idea the rest of you were so brilliant and over-informed! To answer JAG's question, "What drives the design?" let me respond by saying "many factors." We might consider -- * cost and availability of materials (steel, concrete, stone, etc); * cost and availability of a work force familiar with construction in various materials; * cost and availability of machines to fabricate and erect the various bridge types; * local and national laws and ordinances regarding height of structures, visibility blockage ("must not interfere with airport approach," "don't block the view of the mountain or the lake"); * past experience of each designer/erector (some have never worked in steel but have lots of experience in concrete and vice versa); * opinions on aesthetics of various bridge types (suspension bridges look graceful, etc), There are probably some more factors, but this is a start. DrD
  13. What Would You Like to Know? If you could ask me any question you want, what would you like to know that you think I might know? I certainly do not know everything, but through the years I have accumulated a certan amount of knowledge that I'd like to pass on to you. Therefore, I ask, what would you like to know? Many readers are still in college, and no doubt they would like to know what is going to be on the next exam. I'm sorry, but I have no way to know that. What I might be able to tell you is some examples of where your present studies might be useful in the future. I recall my own student days, and I often wondered, "Where am I going to need to know xxxx?" I simply could not imagine where xxxx might arise in the future. Other readers are out of college and in the industrial workplace. Some are doing fine with the knowledge they acquired in school, but others are discovering that they need knowledge and skills that were not taught in college. I know that this certainly happened to me. When I went out into industry, there were all sorts of problems that had never been mentioned in my college days and presented me with new learning challenges. That is a part of being an engineer; your whole career is a learning experience. At the same time, there are many situations where you might like to ask someone with more experience about a particular topic. So, I repeat, "What would you like to know?" Please comment on this blog post and give me your thoughts. DrD
  14. Look up the definitions, and you will have your answer. DrD
  15. If you are looking for steady operating power, the SumTorq = I * alpha does not help. In steady operation, all of the power input must be converted to heat. Where is it going? What are the torques that act on the system in steady state? Perhaps some viscous drag? Is there a brake? Is there a friction rub? Find these and figure out how much power they consume at operating speed. That is the required input power.
  16. In what context? For what purpose are there benefits? DrD
  17. The notches at the ends of the slot look like stress concentration factor relief. The small rib on the side wall can't be that at all. They may all be artifacts of the extrusion process that forms the section. DrD
  18. Well, are you trying to accelerate this rotor, or are you concerned only with steady running? You have to define the problem before it can be answered. As for the mass moment of inertia, you can't calculate such until you have a proposed design. After you define a design, you can calculate the MMOI and see if the system performance is satisfactory or not. On the first try, it often is not, so you propose a better design and try again. This is why design is described as an iterative process. DrD
  19. I don't know what you mean by Wt. Is this a weight, or something else? Further, does the belt run continuously, or is this a start-stop type operation? How do the boxes get onto the belt? Are they places on a stationary belt, or are they dropped on a moving belt? You need all of this to get a handle on the system forces before you can really get into the gear design. DrD
  20. What does having a spare do for getting an exact replacement? I do not see this. DrD
  21. This is a really tough question because plastic deformation is involved. In forming a ring this way, the material must be permanently deformed (partially moved into the plastic state) so that it does not spring back. I suspect you might make some FEA calculations, but the ultimate proof is in the testing. I think I would opt to go straight to testing. DrD
  22. Look at the accidents that have already happened. What sort of failures led to those accidents? What sort of inspection would be required to identify the potential for those accidents before they happened? I suspect you may find a host of causes, such as 1) Metal fatigue 2) Manufacturing defects (bad welds, loose nuts, missing pins, etc) 3) Motion control problems, leading to sudden violent motions and resulting overloads Again, look at what has happened, the history, to guide your inspection procedure. DrD
  23. Automotive engineering involves both the mechanical design side and the thermal power side. Even if we narrow it just to engines, the statement above is still true. The truth is simply that you have to know both sides to some degree, even if your interest is primarily on one or the other side. DrD
  24. The term "hands-on" seems to fit, but I don't think I've ever seen the phrase "manual side." What is this last phrase intended to convey? DrD
  25. The term "steam power plant" usually refers today to an electric generating plant driven by a steam turbine supplied by a boiler. DrD
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