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  • saurabhjain

    Calling Mechanical Engineers to collaborate on Twitter

    By saurabhjain

    If you are a mechanical engineering professional and have a twitter account .. we invite you in our mechanical engineering  campaign to collaborate on twitter.. Retweet the following status on https://twitter.com/mechportal/status/646544243649961985 Look forward for your presence. Regards Mechanical Engineeirng forum
    • 5 comments
    • 1,561 views
  • DrD

    #20 -- A Question of Stability (Revised)

    By DrD

    Mechanics Corner
        A Journal of Applied Mechanics and Mathematics by DrD, #20
        © Machinery Dynamics Research, 2015
    A Question of Stability Introduction     The word stability in its several forms is widely used in nontechnical communication. A person whose life it highly consistent from day to day is said to have a stable life. When the political situation in a particular area appears to be unlikely to change, it is said to be stable. A person who is well balanced and unlikely to be easily provoked to anger is said to be a stable person. When the medical condition of a sick or injured person ceases to get worse, the person is said to be stabilized. A company on the verge of bankruptcy is said to be an unstable company. But what does the word stability mean in a technical context? Each of the foregoing examples hints at the technical meaning without really being explicit about it.   A factor g = accel of gravity was missing in the potential energy expression. That is now corrected.
        
     
        Stability.pdf
    • 16 comments
    • 5,736 views
  • DrD

    A Question for Readers

    By DrD

    Many of you have asked me various questions, so now it is my turn. Let me lay a bit of background first, and then the questions.   I have had some conversations recently with JAG (one of the other writers here at ME Forums) regarding the choice of software for 3D modeling and analysis. JAG has made some excellent suggestions, specifically a cloud based program called Onshape. Unfortunately, for reasons that are unclear, my computer cannot run Onshape; I have worked with their help people for several hours, all to no avail. JAG recommends this in part because there is a "free version for the hobbyist" and a relatively inexpensive "full version for the professional." That is pretty attractive, but since I can't run it, I'm stuck.   I gather that virtually all engineering colleges these days are teaching some sort of 3D modeling and analysis software, but that raises a few questions in my mind. 1. If your college teaches brandX 3D software, what will you do when you go to work for a small company that cannot afford anything more than 2D drafting (simple CAD), with no analysis capability at all? How will you do your job then? You probably have your own pocket calculator, but will you have your own copy of ANSYS or Pro-E? 2. What software does your school teach (every students should have an answer to this question, so I expect lots of replies on this one!)? 3. If you have used software extensively for analysis of engineering problems (beam deflections, stress analysis, fluid flow, heat transfer, etc), are you confident  that you will be able to work all of those problems if there is no such software available to you on the job?   I might add, as sort of a postscript, most of you know that I am older than dirt (I just had another birthday, so the situation is even worse!), so I tend to look at things from an elderly perspective. One of my great fears as a working engineer was "What will happen when I'm ask to do something that I don't know how to do?" It happened more than once, and it usually resulted in a flurry of intense research to come up to speed on whatever topic was involved. I could usually do that because I have a pretty good library, and I knew how to use a university library as well. But in terms of software, I was always concerned that I had no FEA program, so how could I do problems that others were doing by FEA? I have come up with some interesting work-arounds, including writing my own FEA for some problems, but I never wanted to be dependent on software that I could not afford to own. So, back to my questions about: How are you going to buy your own copy of ANSYS? DrD
    • 28 comments
    • 2,919 views
 

A Question for Readers

Many of you have asked me various questions, so now it is my turn. Let me lay a bit of background first, and then the questions.   I have had some conversations recently with JAG (one of the other writers here at ME Forums) regarding the choice of software for 3D modeling and analysis. JAG has made some excellent suggestions, specifically a cloud based program called Onshape. Unfortunately, for reasons that are unclear, my computer cannot run Onshape; I have worked with their help people for several hours, all to no avail. JAG recommends this in part because there is a "free version for the hobbyist" and a relatively inexpensive "full version for the professional." That is pretty attractive, but since I can't run it, I'm stuck.   I gather that virtually all engineering colleges these days are teaching some sort of 3D modeling and analysis software, but that raises a few questions in my mind. 1. If your college teaches brandX 3D software, what will you do when you go to work for a small company that cannot afford anything more than 2D drafting (simple CAD), with no analysis capability at all? How will you do your job then? You probably have your own pocket calculator, but will you have your own copy of ANSYS or Pro-E? 2. What software does your school teach (every students should have an answer to this question, so I expect lots of replies on this one!)? 3. If you have used software extensively for analysis of engineering problems (beam deflections, stress analysis, fluid flow, heat transfer, etc), are you confident  that you will be able to work all of those problems if there is no such software available to you on the job?   I might add, as sort of a postscript, most of you know that I am older than dirt (I just had another birthday, so the situation is even worse!), so I tend to look at things from an elderly perspective. One of my great fears as a working engineer was "What will happen when I'm ask to do something that I don't know how to do?" It happened more than once, and it usually resulted in a flurry of intense research to come up to speed on whatever topic was involved. I could usually do that because I have a pretty good library, and I knew how to use a university library as well. But in terms of software, I was always concerned that I had no FEA program, so how could I do problems that others were doing by FEA? I have come up with some interesting work-arounds, including writing my own FEA for some problems, but I never wanted to be dependent on software that I could not afford to own. So, back to my questions about: How are you going to buy your own copy of ANSYS? DrD

DrD

DrD

 

Rule and equation

Hi guys, can someone here help me to understand this better, explain in a teoretical way to understand Chvorinov's Rule and Bernoulli`s equation? Not just in a simple way, but deeper, can someone here do that, or knows how?   Thanks in advance!!!!

Ajarn Basin

Ajarn Basin

 

Nobody Told Me This Was a Math Class

Since a lot of young people visit this forum I thought it could be of value repeat what I learned 40 years ago. I did learn the following from one of my professors not in the classroom but during a meeting with her as my adviser. I did not fully appreciate what she suggested though I did follow her advice and it was the correct thing for me. I was in a city community college (CC). The four year city colleges were somewhat prestigious. The CC prepared students to transfer within the city university system and planned the curriculum to match the methods at the four year city colleges. I had the option to take mechanics (statics and dynamics) at the CC or wait until I went to a 4 year college. At that time I thought a class was class was a class. My advisor suggested that I take statics and dynamics at the CC if I were to go to the 4 year city college. That would better prepare me for the more theoretical approach I will find at the city college. If I planned to attend a particular private college, which the adviser had attended and taught, that I was better to take statics and dynamics at the private school. Here the subject matter was taught on a more applied and practical bases. I now appreciate how subject matter can be presented in different ways. This is important because not all people can absorb material the same way. If you are still in the planning mode for college or an advanced degree do some research about how the material is presented. A coworker several years ago commented about his master’s degree from a famous college in the San Francisco Bay Area. He said "regardless of the tile of the class, the professors turned it into a math class. Only one class was of any practical value to me."
 

Economical Robotic Vacuum cleaner

Robotics brings together several very different engineering areas and skills. There are various types of robot such as humanoid robot, mobile robots, remotely operated vehicles, modern autonomous robots etc. This survey paper advocates the operation of a robotic car (remotely operated vehicle) that is controlled by a mobile phone (communicate on a large scale over a large distance even from different cities). The person makes a call to the mobile phone placed in the car. In the case of a call, if any one of the button is pressed, a tone equivalent to the button pressed is heard at the other end of the call. This tone is known as DTMF (Dual Tone Multiple Frequency). The car recognizes this DTMF tone with the help of the phone stacked in the car. The received tone is processed by the Arduino microcontroller. The microcontroller is programmed to acquire a decision for any given input and outputs its decision to motor drivers in order to drive the motors in the forward direction or backward direction or left or right direction. The mobile phone that makes a call to cell phone stacked in the car act as a remote. 27_Shahul Gasnikhal__Economical Robotic Vacuum cleaner.pdf  

Shahul Sgk

Shahul Sgk

 

The Dumbest Guy in the Room.

Over the years I have witnessed a particular mistake repeated. It is usually with an old product that has a problem, or the old product requiring a change or a feature added. The mistake manifests itself with everyone believing they carry the true operation and understanding in their heads. Aside from Scotty aboard the USS Enterprise, most should assume there is something they may not know. When a new product is being developed the team usually follows some development process with defined tools. Oversight is likely in place with design reviews and gatekeepers of some kind. But humans grow complacent and subconsciously assume these systems must be as they believe it to be. After all we have been making it or using it for years. If you get involved with Value Stream Mapping you will come to realize everyone has their own reality of how things work. This could almost be a money making parlor tick. Do a demonstration of some process with 15-20 steps to an audience of 20 people. If two in the audience come up with the same detailed step by step process after watching the demonstration, I would be surprised. Usually 2 or 3 people are asked and I have never witnessed two agreeing or any of them being correct on the first pass. The tasking of writing it down will indentify to others what was missed. With repeated passes a complete process can be documented. Having been a manager of experts in a variety of specialties I have often been the dumbest guy in the room. I know what I don’t know and I am less likely to develop a mental understanding good enough to convince myself I understand. One example in particular comes to mind. I sat in a meeting to develop a system consisting of electronic devices. This was an add-on or a fix – not new product development where checks and balances are in place. I can’t recall the specifics but the experts were discussing this with great confidence. I was lost and asked that the oral conversation to be turned into a block diagram on the white board. Just as with Value Stream Mapping the first attempt at the block diagram received corrections from people who a few minutes ago were in oral agreement. I believe it took seven iterations of the block diagram before all the experts agreed. This is not an attempt to discredit experts. Without them the job would not get done. This illustrates that experts, except Scotty of course, can easily get over confident. When a team is involved it is seldom the case that everyone knows everything. Add the element of time for aged products/systems and it is almost a certainty. If you are part of a meeting where everyone is in oral agreement it would be prudent to ask for a flow chart or block diagram. The dumbest guy in the room may save the day.
 

DIY 3D Printer Kits From StuffMaker

3D printing technology is attracting every science and technology enthusiast whether it is a mechanical, civil, architecture, electrical, manufacturing or medical application. Everybody is interested in creating models, prototype using 3D printing technology. It’s not a technology but a 3D printing evolution. The pace at which this industry is growing and the novelty that 3D printing has introduced, it is predicted that additive manufacturing will affect almost all the fields of daily life including trade and commerce in near future.     Checkout these Affordable & High Performance 3d Kits From Stuffmaker

Arpit.v

Arpit.v

 

INTERVIEW QUESTIONS AND ANSWERS – MECHANICAL ENGINEERING DESIGN, SAFETY AND MAINTENANCE

Mechanical Engineering Interview Questions and answers for freshers on design, safety and maintenance. 1) What is an accident ?
An accident is a unexpected and unforeseen event which may or may not injury to a person or a machine tool. 2) What are the standard sizes of drawing board as per Indian Standards? As per Indian Standards :1250×900,900×650,650×500,500×350,350×250 sizes are available. 3) What are the functions of a scale ? (a) To measure distance accurately.
(b) For making drawing to scale either in full size, reduced size or enlarged size. 4) What is a sketching ? This is freehand expression of the graphic language. 5) What do you mean by First Aid ? First Aid is immediate and temporary care given to a person who affected accidental injury or a sudden illness before the arrival of doctor. 6) What is a Drawing ? It is a graphical representation of a real thing to define and specify the shape and size of a particular object by means of lines. 7) What is Engineering Drawing ? A drawing which is worked out an engineer for the engineering purpose is known as Engineering Drawing. 8)  What are the methods of extinguishing fire ? 1) Starvation. Separating or removing the burning material from the neighbour hood of the fire.
2) Blanketing. Preventing the air flow to the fire.
3) Cooling. Lowering the heat created by burning materials. 9)  What are the precautions to be taken to avoid fire ? 1) The buckets along with sand should be placed inside the workshop.
2) Switches and other electrical parts must be made of fireproof material.
3) Carbon dioxide gas should be place at required points in special containers.
4) Fire extinguishers of suitable type should be placed at accessible places.\ 10) What safety precautions should be observed while working in the workshop ? 1) Keep shop floor clean, free from oil and other slippery materials.
2) Wear proper dress and avoid loose clothing and loose hair.
3) Wear shoes and avoid chapels.
4) Avoid playing, loose talk and funning inside the shop floor.
5) Keep good housekeeping and put all unnecessary items and rejected items in scrap box.
6) Learn everything about the machine before starting and clear all the doubts.
7) Keep a safe distance from rotating and sliding parts.
8) Never store inflammable materials inside or around the shop.
9) Never play with electricity, fire, parts with sharp edge etc.
10) Keep fire buckets and extinguishers ready for use.

saurabhjain

saurabhjain

 

Becoming An Expert -- Part 3

Mechanics Corner
    A Journal of Applied Mechanics and Mathematics by DrD
    © Machinery Dynamics Research, 2016
Becoming An Expert -- Part 3      Introduction     In the previous article on Becoming An Expert--Part 2, I mentioned that there were two big issues for the engineering analysis section at my Houston position, the first being the matter of seismic survivability and the second being torsional vibration. The first item was dealt with in Part 2, and in this article we will take up the second item of concern.
    When I joined the engine distributor in Houston in the mid-1970s, the company was about 65 years old, and the torsional vibration problem was not new. This was a problem that they had been dealing with, in one way or another, for many years. There were lots of old torsional vibration analysis reports available to study. I was not at all familiar with torsional vibration of machine trains; I had not studied anything quite like that in school and it had not come up in my previous industrial experience. So I eagerly began reading the old reports, and that is when the problem became acute for me: They did not seem to make any sense. I could not, with any integrity, continue to write reports like that when I thought they were complete nonsense, but I did not know how to analyze the problem correctly. I was in a jam!
    There were three major difficulties:
    1. The entire crank assembly rotates endlessly, so the stiffness matrix for the system is singular. This results in a zero eigenvalue, something that did not take too long to figure out.
    2. It is obvious that the system does more than just go round-and-around; it goes up and down as well. I was baffled for a long time about how to deal with the kinematics and their impact on the dynamics.
    3. It is apparent that there is a torque acting on the crank, but it is not directly applied to the crank by the combustion process. There is the slider-crank mechanism between the two, and I was at a loss as to how to transfer the cylinder pressure into a crank torque. This is again directly related to the kinematic problem mentioned just above. BecomingAnExpert--Part3.pdf

DrD

DrD

 

A Comment Remembered

Mechanics Corner
    A Journal of Applied Mechanics and Mathematics by DrD
    © Machinery Dynamics Research, 2016
A Comment Remembered     
    Recently, in connection with one of the posts on Becoming An Expert, one of the ME Forum readers made a comment to me, something about seeing everything in terms of differential equations. That comment brought to mind a comment made to me many years ago that I want to pass along to you today.
    Most of my college education was at the University of Texas at Austin. It was there that I received BS, MS, and PhD degrees in engineering, and I was there studying for most of a decade. After I finished my PhD, I was asked to stay on the faculty for a year as an Assistant Professor, so that was my first post-graduate teaching position as well.
    One of the well known faculty members at UT-Austin was Dr. E.A. Ripperger, a man with a national and international reputation for his work in plastic stress wave propagation. In addition to his teaching responsibilities, Dr. Ripperger directed a laboratory at the Balcones Research Center, a research arm of the University. He had many graduate students working under his direction, and he was riding high in terms of his reputation. He was a rather august figure, somewhat austere and above everyone else.
    While I was still a struggling and confused undergraduate, one of Ripperger's graduate students had taught my Mechanics of Materials course, and I had done well in that class. This fellow liked me, and when a job opening came up out at the lab, he let me know about it and helped me to land it. Thus I was working a few hours a week as a lab assistant for this particular graduate student who was himself working under Dr. Ripperger. Before long, I signed up to take a class in Intermediate Dynamics, and Dr. Ripperger was the assigned teacher. Truth to tell, he was only mediocre teacher, nothing to get excited about.
    The class was fairly difficult, and I was having trouble keeping up with it all. In particular, the solution of the many differential equations just overwhelmed me. Since I was working out at the lab, and Dr. Ripperger was out there from time to time, I thought it might be a good idea to go in to to see him at the lab to discuss the class. I found him at his desk one afternoon, and screwed up my courage to go into talk with him.
    I told him that I was finding the class difficult, even though I thought I had a good understanding of dynamics. I told him that my difficulty was particularly with the differential equations, not with dynamics. He listened quietly while I spoke, and then he fixed me with a withering gaze when he spoke, calling me first by name and then saying, "Did you think there was anything else besides the differential equations?"
    He said no more, and I slunk away to lick my wounds! I don't think I ever spoke to him again.
    
    DrD is a retired Professor of Mechanical Engineering in the USA. He can be reached for comments, questions, or requests via the ME Forum message system. Be sure to check back soon at www.http://mechanical-engineering.in/forum/blog/206-mechanics-corner/ for more articles.

DrD

DrD

 

Becoming An Expert -- Part 2

Mechanics Corner
    A Journal of Applied Mechanics and Mathematics by DrD
    © Machinery Dynamics Research, 2016
Becoming An Expert -- Part 2      Introduction     In the previous article on How To Become An Expert, I covered a lot of points in generalities with some short anecdotes from my own experience. In this article and the next, I will describe in considerably more detail a critical period in my own formation, an time of considerable professional embarrassment which was a real spur to learning.
    In the summer of 1974, I took a position as the head of the engineering analysis section with a large diesel engine distributor in Houston, TX. This company purchased diesel engines, mostly from General Motors (GM) and packaged them on a skid with some driven machine such as a generator, a pump, air compressor, or other driven machine, along with the required controls. For me, it was a fascinating place to be as I had always been intrigued by diesel engines. I soon found out how little I actually knew about the whole matter.
    The analysis section consisted of three other engineers (two men from India and a lady from Turkey) and myself. The men were there before I came, and I hired the lady. They were all good workers, but they were best at following directions. They did not ask "Why?" very often. If this is the way it had been done previously and nobody objected, they would repeat that same pattern over and over without wondering why we do it that way. More about that aspect later.
    This was a time of great activity in terms of nuclear power plant construction in the USA, and the company was building a lot of very large engine-generator sets to serve as standby power in nuclear power plants. In a nuke plant, pumps continuously supply cooling water to the core to take away the heat and as a means to move heat to the steam generators. If those pumps fail for any reason, the core can over heat and meltdown, a major catastrophe. The great fear was that the pumps would lose power from their regular supply, in which case the standby generators would need to start up and provide power to the pumps. The proposed cause of loss of power was an earthquake, and that meant that the standby generator set must survive the earthquake and be able to start and run. BecomingAnExpert--Part2.pdf

DrD

DrD

 

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

DrD

DrD

 

Dump Trucks Vs Donkeys.

Nearly Forty years ago, a fellow engineer told me a story that must now be 70 years old. This engineer was born and educated in Egypt. His first job was a large civil engineering project with massive amounts of earth moving. Having a formal education but no local real world experience, he started to estimate how many steam shovels and trucks were required for the job. A Sr. engineer asked, what he planned do with all the equipment once the project was done, and what about the 99 local laborers left idle for each machine that does the work of 100 men and requiring only one operator? The Sr. engineer told the young engineer to base his calculations on the required number of donkeys, basket weavers, strong men, little boys, and laborers that would be required. I was puzzled as was my colleague that many years ago. The Sr. engineer explained that picks and shovels would be the main tools and the local laborers the muscle. The laborers loosen the soil and then fill the woven baskets with the soil. The strong men would lift the baskets onto the donkeys. The young boys would ride the animal off site and dump the soil. This kept the local population employed and able to feed their families. Manual labor as it was may not have been a great way to make a living but it was far better than starvation. The situation in ancient Rome was similar. The Romans build magnificent structures but the preferred method was brute force. There was no push for efficiency as we think of it today. Even then, there were labor issues. Better to keep everyone working and fed, if only at subsistence levels, than to have massive unemployment and the making of a revolt. If the laborers were in a position to demand higher and higher wages mechanization may have advanced faster. It will be interesting to see how many jobs robots and computers will replace as the minimum wage increases to $15/hour regardless of the local economies.

JAG Engineering LLC

JAG Engineering LLC

 

#28 -- Analytical Design -- Part III

Mechanics Corner
    A Journal of Applied Mechanics and Mathematics by DrD, # 28
    © Machinery Dynamics Research, 2016
Analytical Design -- Part III      Introduction     In Parts I and II of this series, we began looking into the design analysis for an emergency steam cut-off valve for a nuclear power plant. Part I simply posed the problem, and Part II got into the detailed kinematic analysis of the four bar linkage that is to control the motion of the plug as it shuts off the steam flow. We would like to move on to the dynamic simulation of the motion to get an idea about the time required to close and ultimately to a force analysis so that the links can be appropriately sized. Before that can be done, it is necessary to spend some effort on the design of the plug itself so that the dynamic properties of the plug (mass, mass moment of inertia) can be estimated.
    In the stress analysis of the plug, I am at somewhat of a disadvantage with respect to most of you. I know that many of you have access to Finite Element programs which enable you to do a fairly complete and correct stress analysis. Because I am no longer connected with a university or an industry that would give me that access, I have do not have access to FEA. Thus the analysis that I will present here is somewhat crude, rather approximate, and not recommended where better methods are available. You may choose to look at this as somewhat of a "historical approach" to the stress analysis, the way it would have been done before the arrival of FEA. The model that I will present is overly simplified, but it is the best that I can provide for this series.
    The maximum temperature and pressure for the steam system are given as P = 1000 psi, T = 1000 deg F or equivalently, P = 68.95 bar, T = 538 deg C. These are the targets specified for the plug design. AnalyticalDesign-Pt3.pdf

DrD

DrD

 

John Deere & Culture Shock

More than once, I have remarked in this blog about the lack of participation. I have been mystified by the lack of questions and comments on my articles. Even those that get several thousand views, often have no comments at all. I just don't understand it! Yesterday, I had a visit. My visitor is a former student of mine, a fellow that I taught back in the early 1980s. His name is Bob, and Bob was an Ag Engineering student, if I recall correctly. He took my theory of machines class as an elective (something not many people would do), and he really got into it. One of my earliest recollections of Bob in class was having him yell out, all of a sudden while I was lecturing on some mechanism, "That's just like on the combine." Bob was from a farming background, and had grown up with ag machinery. A combine (for those who are not familiar with the term) is a very large, very expensive, harvesting machine. With different attachments, they can harvest a variety of crops; in my area, we see them primarily in the fall, harvesting corn about 12 rows at a time as they lumber along at a fast walk. Bob had made a connection between what we were studying in class and what he was familiar with on the farm. After finishing that class, he graded that class for me for a couple of semesters until he graduated and left. Even while he was an undergraduate student, Bob knew what he wanted to do. He wanted to work for John Deere & Co (JD). John Deere is the premier ag machinery manufacturer in the USA. They have a number of competitors, but JD is always ranked right at the top. When Bob graduated, JD was not hiring, and he was crushed. He went for a Masters degree, and when that was finished, he got on with JD. I live in the US state called Iowa (after an American Indian tribe), a very agrarian state in the upper midwest, pretty much in the middle of the USA. JD has several really large manufacturing plants in Iowa, and a few test facilities, etc scattered across the country. The JD plant in my city builds construction machinery and forestry products. Another of my former students runs the plant where I live. They also have plants around the world. I am aware of them having one or more plants in Russia, in India, and no doubt elsewhere. Their machines are characteristically painted a light green with bright yellow details. Bob now works at the JD Research Center in Waterloo, IA, about 100 miles west from where I live. They are very secretive about what they do there; JD is very sensitive about their company secrets! He has finished a PhD about 10 years ago, and is now one of their senior people in the area of gearing. He tells me that he is now being asked to teach some of the younger engineers, so the wheel continues to turn! As we were visiting yesterday, I mentioned writing this blog and the lack of participation from readers. That prompted Bob to tell a story. He said that an engineer from one of their plants in India has been assigned to come over here for a 6 month period, a short while back. When the man first came, he hung back, reluctant to speak up, to get his hands dirty, to get involved with the equipment. Evidently the Research Center in Waterloo was quite a shock for him, because JD encourages their engineers to get involved with the equipment, to get dirty, to drive tractors around, etc. As the 6 month period went by, the man began to eventually get into the "American way," that is, to get more personally involved with his work. He took those attitudes with him when he returned to India. The report came back to Waterloo from his manager in India that the man was a much, much better engineer after his 6 months in the US. Rather than standing aloft, he was getting into the machinery, getting dirty and working with the machinery. The point of this story is that, through the agency of international business, attitudes about work and many other matters are being changed. New ideas that work better are spread to areas in need of them, and there is progress around the world, one person at a time. We all benefit from this. DrD  

DrD

DrD

 

Why Designs Fail ?

With so much scientific tools, why do designs fail?

Why the unsinkable Titanic sank? Why did the thoroughly tested Columbia space shuttle burned out on return? Why Toyota had to call back thousands of cars designed by expert engineers?

Design might fails because somebody made a stupid mistake in his calculations, like in the old joke about the bridge that fell down because the engineer forgot to multiply by two. It might happen, but it is extremely rare. Most design failures happen because one specific mode of failure was never checked against, because it was never identified as risky.

The sad truth is that we cannot design anything to work. We can only try to find out if a certain design might fail in a certain specific way. This is one reason why we cannot send computers to design things. They are excellent in optimizations, when we tell them what parameter to optimize and for what mode of failure.

The Tacoma narrows bridge collapsed in 1940 because nobody thought that wind might arouse resonant vibrations in the bridge. It was OK for what it was designed for: for static loads. No computer would have suggested another mode of failure.

The Titanic sank because nobody asked what happens if the ship scratch its side on an iceberg. Had it been thought, maybe the designers would have ordered that it would be better to throw the engines to full back and bump into the iceberg head on! It would have been damaged badly, but it would not sink.

If only the designers of the Columbia would have only thought of the possibility of losing their thermal shield bricks on launch, the Columbia would have still be in service today. For a fact, once they identified the problem, they had no big difficulty to fix it.

The philosopher of science, Karl Popper, said that in order to be scientific a claim must be "falsifiable". Moreover, he suggested that a claim cannot be proved by repeating experiments with positive results. No matter how many times it passes a test, there is always a chance that one more test will prove it wrong. To prove a theory requires infinite number of successful tests. One failure is enough to disprove it.

So it is in our world of design. The failures described, all have shown that these designs were not perfect. They had errors embedded in them. And these errors are all the result of not being able to foresee the single mode of failure that could go wrong. No scientific calculation can help against an unidentified mode of failure.

What is the lesson to be learned? Be paranoid! Always look around searching for the mode of failure you might have missed.

I like to call rules by names. The name I gave this rule is "the law of the wild west".

It goes as follows:

The guy who kills you will be the one hiding behind the bush, that you failed to notice

Bumo

Bumo

 

Asking the correct questions for FMEA

An article appeared in an engineering forum entitled Why Designs Fail. As I thought about the article and the examples presented, the Titanic, Tacoma Bridge, etc., I realized mitigating the consequences of a failure are more important than preventing the failure. One of the subjects I did not learn in the classroom was Failure Mode and Effect Analysis (FMEA). I do not intend to cover the subject of FMEA but would like to emphasize one small portion. FMEA was introduced to me on my first job in the late 70's. One aspect of human nature needs to be over come when applying FMEA. Problems we do not expect to happen due to low probability, we tend to dismiss with no contingency if it occurs. FMEA forces you to separate probability from consequences. During my FMEA training I was told to ask what happens if a particular failure were to occur, without arguing over the probability, which is addressed separately.  Most homes have smoke detectors and many have fire extinguishers. These items provide early warning and a method to stop or at least slow the progression of a fire until help arrives. Few homes have precautions for an asteroid strike though the results will be far worst with little mitigation possible.   A different state of mind comes into play when you accept the sinking of a ship as a possibility. Expecting to foresee all the possible ways it could happen may be impossible. How a ship could fill with water is irrelevant once it happens. If the Titanic designers had asked themselves what would happen if the entire ship flooded, not worrying about the how, lives would have been saved. Perhaps the compartments would have been 100% isolated from each other or more lifeboats provided.

JAG Engineering LLC

JAG Engineering LLC

 

#27 -- Analytical Design -- Part II

Mechanics Corner
    A Journal of Applied Mechanics and Mathematics by DrD, # 27
    © Machinery Dynamics Research, 2016
Analytical Design -- Part II      Introduction     In Part I of this series, the problem posed was to apply, as far as possible, the available knowledge of mathematics and science to the design of an Emergency Steam Shut-Off Valve, to be gravity driven as in the sketch below, Fig. 1. The inlet and outlet for the steam flow are both specified to be 0.85 m in diameter, so the valve plug will be a little bit greater than this amount in diameter. That suggest that, as a first approximation, L2 =0.85 m. Now, where do we go from here?
    

    Fig. 1  Proposed Gravity Actuated Emergency Steam Cut-Off Valve.     The draftsman's sketch has been redrawn to scale, and it appears that this is a workable geometry (we will have to investigate that further, but it is a place to start). Scaling his sketch in such a manner that L2 =0.85 m, the first estimate for the dimensions is
    L1 = 3.460 m
    L2 = 0.85 m
    L3 = 0.902 m
    L4 = 1.912 m
    D = 0.638 m
    These are only preliminary, subject to change as needed, but they give us a place to start the kinematic considerations.
    There are two issues of major importance to be address early on: 1.Will the plug enter straight into the valve seat without binding or impacting on an edge?
2.How long will it take for the plug to fall into place?     These two issues will be our initial concern.     AnalyticalDesign-Pt2.pdf

DrD

DrD

 

#26 -- Analytical Design -- Part I

Mechanics Corner
    A Journal of Applied Mechanics and Mathematics by DrD, # 26
    © Machinery Dynamics Research, 2016
Analytical Design -- Part I      Introduction     On ME Forums, there have been a number of questions raised about design. Many students are writing in asking for ideas for a senior design project, others are asking for help with a design problem, etc. There has been some discussion about "Just what is design?" That was definitely a question in the minds of many faculty at one school where I taught a number of years ago. The engineering accreditation board in the US is called ABET (Accrediting Board for Engineering and Technology), and just before I joined this particular faculty, ABET had denied the school accreditation "because they were not teaching nearly enough design." When the faculty heard that, they were shocked, and we spent several years getting everyone on board with what design is.
    I am not going to attempt to launch into a full scale discussion of what constitutes "design," but rather, with this post I am beginning a short series on one narrow aspect of design. Please understand that this is not the full scope of design, but simply a part of it.
    In most jurisdictions where engineering is defined legally, the definition will include something like, "being qualified to design," and will also speak of having a sufficient knowledge of mathematics and science to apply those fields to the engineer's work. With this series, I hope to show the application of mathematics and science to a typical design problem. The problem I have chosen is fairly typical of a first cut at a design, but it must not be taken to represent all such problems. The Problem     Suppose that you are a young engineer, working in the nuclear power industry. Because of our natural fear of uncontrolled nuclear energy, one of the constant concerns in the nuclear power industry is how the plant will handle various possible accidents, particular things like an earth quake, bomb strike, or airplane crash onto the nuclear reactor. Any of these events could cause a need to shut down the nuclear steam generation, and bring the whole plant to an orderly halt. We are not about to tackle the entire problem, but just one small part of it, stopping the flow of steam from the system.
    In the event of a catastrophic accident, it is not wise to rely on the ordinary control systems that function using electrical actuators, pneumatic systems, or in some cases, hydraulics. All of these energy systems are likely to be disrupted by the emergency, so what is left to actuate a steam valve? AnalyticalDesign-Pt1.pdf

DrD

DrD

 

Professional Societies -- Or Not?

Mechanics Corner
    A Journal of Applied Mechanics and Mathematics by DrD
      Machinery Dynamics Research, (c)  2016
Professional Societies -- Or Not?
Introduction
    This post is written in response to questions raised by one of our regular participants, a young engineer in Australia. What I have to say here is based entirely on my own, very American, experience, and others may have different ideas. I would encourage a general discussion in the comments, so that we may see how various folks look at this question.
    The questioner asked, "... have you maintained a membership to such an organization for the purposes of networking and staying active in the engineering world?" I'd like to re-word the question just slightly to read, "What is the purpose for being in a professional society, and is it worth the costs?" My experience in this matter is limited strictly to American professional societies, but I suspect there will be some carry over to other nations as well.
What are we talking about?
    Before getting into the good and bad points, it is worthwhile to cite some examples of various professional societies, so that everyone will understand the kind of organizations are under consideration. Let me name a few that come to mind, just off the top of my head:
    ASME --- The American Society of Mechanical Engineers
    SAE --- Originally called the Society of Automotive Engineers, now legally simply SAE
    ASHRAE --- American Society of Heating, Refrigeration, and Air-conditioning Engineers
    NSPE --- National Society of Professional Engineers
    ASNE --- American Society of Naval Engineers
    SNAME --- Society of Naval Architects and Marine Engineers
    AIAA --- American Institute of Aeronautics and Astronautics
    IEEE --- Institution of Electrical and Electronic Engineers
    SME --- Society of Manufacturing Engineers
    ASCE --- American Society of Civil Engineers
    AIChE --- American Institute of Chemical Engineers
    IIE --- Institute of Industrial Engineers
    SAME --- Society of American Military Engineers
    SPE --- Society of Petroleum Engineers
    AWS --- American Welding Society
    This list is certainly not exhaustive; there are many more such organizations. As this brief list suggests, there is an organization for every interest! Let me talk a little bit about a few of these, the ones of which I am a member and one other that I am familiar with.
  ASME
    In many respects, ASME has long been the premier mechanical engineering society in the US. It first rose to prominence in the early 20th century when there was a nation-wide problem with boiler explosions. ASME took the lead in developing boiler standards, and today the ASME Boiler and Pressure Vessel Code is recognized world wide as a guide to safe design of such systems. Sales of the Code documents are a major source of income for the organization, and ASME is very active in many areas of Codes & Standards. It also published a number of technical journals, such as the Transaction of ASME, Journal of Applied Mechanics. They also organize and host many conferences around the country, and indeed around the world, on various topics of specialist interest.
    When I first joined ASME as a student in the early 1960s, it was a very membership oriented organization. Each year, when you paid your dues, you received five coupons that could be redeemed for technical papers that were available from ASME. At that time, the membership really ran the organization. Today, it has all changed. It is simply a business, run by a bunch of folks in New York, for their own benefit, and they simply do not care about the needs of the membership. If I want an ASME paper, I can buy it for about $25, exactly the same as anyone else can get it. There are ASME Student Sections at most American engineering schools, but ASME does little or nothing to support them. Over the years, I have attended many ASME functions, from local section meetings to national conferences. They are often well attended, and they are an opportunity to meet others in the field.
    I am a Life Member of ASME which simply means that I was foolish enough to pay dues for 30 years, and now I am exempt from further dues. I probably would not join ASME if I were starting today with what I know now.
 SAE
    SAE was originally known as the Society of Automotive Engineers, a fairly self-explanatory name. It has dropped the name to become simply SAE, and refers to itself as "the mobility society." It incorporates folks interested in mechanics, materials, fuels, lubricants, combustion, controls, electronics, etc., and deals with automobiles, trucks, ag machinery, boats, and aircraft. It is very, very broad, and almost any technical person can find a role in SAE. SAE, like ASME, also publishes many Codes and Standards, and organizes a number of technical meetings each year.
    One thing that I think is important about SAE is the way it supports engineering education. SAE sponsors, with significant amounts of money, many student design competitions in which undergraduates design, build, and test various real projects. One of the most popular of these is what is called the Mini-Baja Competition, a reference to the famous off-road racing done in Baja California (Lower Califormia, Mexico, a very primitive area located directly south of the US state of Califormia). Let me tell you a bit more about my own involvement with SAE.
    In the mid-1980s, I was teaching in a small engineering school in Wisconsin. I was in my office one afternoon when one of my former students burst in, eager to talk to me. Brad said, "Are you a member SAE?" to which I replied, "No, I am a member of ASME." He came back with "Well, would you be?" which really puzzled me. Why did he care whether I would join SAE or not? As the whole story came out, he was nearing graduation, and he wanted to do something of lasting value for the school. His idea was to organize a SAE Student Chapter and get them involved with the Mini-Baja race car competition. Such a group would need a faculty adviser, and he wanted me to be that adviser. To make a long story short, I joined SAE and we got approval to organize a Student Chapter and got started on the construction of a race car. I was amazed at the student enthusiasm, and also at the financial support we got from the Senior Section (the adult SAE Section in our area). Money poured in from the Senior Section, and we received a donated engine (everyone uses the same engine) and many items of donated hardware. We did not win that first year, but we did the next year, and I'm proud to say, the group continues to this day, doing very well year after year! A couple of years ago, I attended an SAE student competition where they were racing Formula I race cars. We had about 25 schools represented, coming from as far as 1000 miles away for the competition! This is a serious boost for engineering education, and a real service!
SNAME
    SNAME is the place where most naval engineering is focused. They publish a high quality series of technical journals, and deal with real marine engineering, including ships, off-shore platforms, ice-related problems, etc. I joined primarily because they are the only ones who seem to be concerned with a particular vibration problem that interests me. I have not solved that problem yet, but when I do, I'm sure I will publish the results in a SNAME journal. ASNE
    For contrast with SNAME, there is the American Society of Naval Engineers. I became aware of this organization when I worked for the US Navy, and found that it is mostly Navy officers, government big-shots, government contractors, and others, all pretending to be engineers. Their meetings (I went to several) are about as technical as a comic book. The only reason to be a member here is for the contacts one might make; the technical content is just about nil.
Summary
    So, back to the main question: Is it worth it?
    That depend entirely on your own goals and values. Are you interested in it for a social outlet? Are you interested in terms of community service? Are you hoping it may provide you a contact that could lead to a better job? Are you hoping to learn serious new engineering content? Before I would commit to one of these organization, I would try to investigate just how it fits into your own hopes.
    Most such organizations welcome visitors to your meetings, so you can probably visit a time or two and get some feel for the organization at your local level. Ask what does it do? What projects has it undertaken? Ask yourself if the meeting is well run and organized (I'd stay clear of disorganized groups; they are simply too boring for words!) Ask how often they meet, and what they do in their meetings. I have been on some really excellent field trips as part of various society meetings, and I have often taken students with me to these meeting where there was a field trip involved. I have also been to some really terrible meetings, with a dinner of rubberized chicken and a meandering, dull-as-dust speaker. They vary all over the map.
    I would suggest that every engineer should probably be a part of some such organization, but that should be chosen with real care. Check out prospects very carefully, find out what you might expect to get out of it, what you might expect to contribute, and what the financial cost is. Their can be real benefits, but not every possible choice leads to them. Make a wise choice!
    
    DrD is a retired Professor of Mechanical Engineering in the USA. He can be reached for comments, questions, or requests through the ME Forum message system.. Be sure to check back soon at www.http://mechanical-engineering.in/forum/blog/206-mechanics-corner/ for more articles.

DrD

DrD

 

War Stories

Mechanics Corner
    A Journal of Applied Mechanics and Mathematics by DrD
    © Machinery Dynamics Research, 2016
War Stories -- Dr. Jack Levedahl Today I want to tell a few war stories, war stories in the literal sense of the word, in that they all relate in one way or another to World War II. They all center on my friend Dr. Jack Levedahl, a most excellent mechanical engineer and adventurer. Jack was an elderly man when I first met him about 15 years ago, and he has since passed on, but I remember him with great fondness and respect. Jack grew up in a Swedish American family in Aurora, Illinois, southwest of Chicago. He grew up hunting small game in the fields around the town and tinkering in the machine shop his family ran. At the time that World War II began for the US, Jack was a mechanical engineering student at MIT. When the US entered the war, Jack dropped out of college and joined the US Army Air Force, as it was then called. Jack became a pilot and flew the North American P-51, the finest propeller driven fighter the US has ever built. The P-51 was originally designed for an American-made Continental Lycoming engine, but that didn't have enough umph! It wasn't long before the design was revised to include a Rolls-Royce Merlin engine with about 1600 hp. This gave the P-51 a top speed of around 450 mph, the fastest mass produced aircraft of WW II. It was quite a excellent machine! The Merlin engine was a marvelous design, but it was not easy to build. In England, the Brits built these engines one-by-one, essentially by hand, hand fitting all the bearings and other precision parts. There was simply no possibility that Rolls-Royce could supply engines at the rate needed by the US Army Air Force. For that reason, the design was licensed to the Packard automobile company in the US. Packard engineers reworked the design, loosening tolerances wherever possible, and came up with an engine that could be mass-produced. This produced an engine that was in many ways superior to the handmade engines from the UK. The Rolls-Royce engines were like a fine watch, but they had practically no truly interchangeable parts. This made field repairs extremely difficult and time-consuming. The Packard built engines ran a little more noisily, but they all had fully interchangeable parts and could be repaired with ease. This last proved to be a great benefit in the theater of war. When Jack had completed his training, he was sent to the Mediterranean where he was based on Sicily, flying missions north up the Italian peninsula. Gradually the Allied effort was driving the Germans back, and they were retreating back toward Germany. Jack told me in some detail about one such mission. Jack said that he and his wing man were attacking a German train headed north through the Brenner Pass into Austria. This was not an ordinary train but rather was an armored train. It carried on board a number of antiaircraft cannons, capable of firing at attacking aircraft. As they bored in on the train, Jack said his wing man was hit and went down, but he got through and shot-up the locomotive, causing the boiler to explode. I visited Jack in his apartment in Annapolis, Maryland one day where I saw a strip of aluminum about 15 inches wide and about 7 feet long hanging over a wide doorway. It was literally torn to pieces, with large gaping holes gouged through it, rather clearly the work of large bullets (probably 30 mm cannon fire). I asked Jack what the piece of metal was. He replied, "Oh, that was the canopy fairing from my plane. That was right behind me in the cockpit." When he had returned from one of his missions with his plane shot full of holes, the aircraft mechanics had salvage this one piece for him for a souvenir. When I asked if there had been anything else between him and the bullets he explained that there was an aluminum armor plate, about 1/2 inch thick behind his seat and that was all. When he had completed 50 missions, Jack was mustered out of the Army Air Force, even though the war was continuing. He did not want to leave, but there was a rule that if you survived to complete 50 missions you had to be retired. Not too many pilots survived 50 missions, so it wasn't a problem for very many people. Reluctantly, Jack returned to the US and enrolled again in MIT where he finished his degree. He went on and got a master's degree as well. Jack told me that one day about 1947 or 1948, he encountered a German-speaking man on the streets of Milwaukee, Wisconsin. The man was asking, in German, for directions to Mader’s, a famous German restaurant in Milwaukee. Jack spoke some German and was able to communicate with him, so he walked the visitor a few blocks over to the restaurant where they had a meal together. It turned out that the visitor was a famous mechanical engineering professor from the University of Aachen in Germany. He invited Jack to come to Aachen to study with him, and that's where Jack did his doctoral work. During the time that he was studying in Germany in the postwar period, Jack said that many of his fellow students were former German army personnel. One day, in a graduate student bull session, one of the other students described what he had done during the war. He explained that he had been a gunner on an armored train. He said that all came to an end one particular day in the Brenner Pass when his train was attacked by two American P-51s. He went on to say that he had shot down one of the attacking aircraft, but the other one got through and destroyed the locomotive of his train. It was a bit strange for Jack to have to tell him that he was the one who got through and blew up the locomotive! For many years after the war Jack was a research engineer for the U.S. Navy, working on a variety of projects. It was in that capacity that I encountered him when I worked for the U.S. Navy in a similar situation at the end of my working career. The Navy had a program for its research personnel that was called "Scientist-to-Sea" in which research engineers were allowed to sail on US naval ships under certain circumstances. Jack and I signed up for one of these cruise opportunities, and we sailed together from New York harbor down to Pascagoula, Mississippi on the destroyer Roosevelt, DDG-80. It was a marvelous eight days at sea, and we were free to explore the ship from stem to stern, talking to anyone and everyone and asking any question. So imagine two elderly men, acting like two kids, roaming the ship and asking to be let into out-of-the-way places such as the chain locker for the anchor chain and the steering gear compartment at the stern of the ship. We would go together and look in a section of the ship, and then we would return to the state room that we shared. There we would discuss what we saw, and frequently disagree about exact details of what we had seen. When we disagreed, we would get up and return to that part of the ship to take a second look, and thrash out just how each ship system worked. It was a grand experience for me, to be able to explore this fascinating mechanical system called a destroyer and continually discuss parts of it with this highly experienced and vastly knowledgeable mechanical engineer. I miss him greatly!

DrD

DrD

 

#25 -- A Textbook Statics Problem

Mechanics Corner
    A Journal of Applied Mechanics and Mathematics by DrD, # 25
    © Machinery Dynamics Research, 2016
A Textbook Statics Problem      Introduction     In the course of each day, I visit many web sites, always keeping an eye out for interesting engineering problems. The problem that is discussed here is one such that came from an American site (more about that web site later). The problem was presented as a simple statics problem, and the poster was asking for help in the solution. There were several replies with suggestions, but no one seemed to be able to really put their finger on the difficulty. As it turns out, this problem presents multiple difficulties, and offers an opportunity to look at several matters of interest to this readership.
    The question was posed with a hand drawing comparable to that shown in Fig. 1 here.
    
  
    Fig. 1  Schematic Drawing as Given     The person posting this problem implied, without ever clearly stating it, that the problem is to find Fex when the applied load T=100 N as indicated. He says, "So it's been a while since I've done FBDs, and what seems like a simple problem is causing me grief. ... Can someone tell me what I've done wrong here? I seriously was looking at this all day and was just scratching my head." Can any readers relate to the dilemma of this poster?
    Just looking at the sketch, it seems like a reasonable problem. When the load T is applied, it will tend to rotate the crank ABC in a clockwise direction, straightening the joint at C. This will push the roller at E against the wall, developing the reaction force Fex. There is no friction at either D or E, so what is the difficulty? TextbokStaticsProb.pdf

DrD

DrD

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