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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

    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
  • 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
 

Experimental Analysis of an Air Washer

Hello World,   Today i will like tell you all about my 4th year project which was on the topic of experimental analysis of an air washer. In the recent sanario the peoples are slowly getting conscious about the beast(pollution) intended to destroy our beautiful sphere(earth). This pollution had drastically spread in our world drastically in few years. It is sad to say but we are only responsible for it. The careless burning of fossil fuels, heavy growth in industries and inventions without considering about the earth safety pushed of us into this undesirable situation.   But now the peoples are thinking about what they are doing and what they had done including the government which taken so many steps for the control on pollution. The scientist's also get conscious about their invention which will be in the favor the reducing pollution.     In India the refrigerants like R 22 is going to be banned in upcoming few years which is one of the major reason for the depletion of the ozone layer which causes global warming and some harmful skin disease's. These things created the requirement for the replacement of old cooling systems and introduction of the new inventions which are environment friendly.   My project was on the same concern me and my friends decided to try the project which can be the one of the substitute of the recent refrigeration system. On the suggestion of our professor we modified the air washer to not only work as an evaporative cooler but also can remove the sulphure dioxide from the air which is one of the gas responsible for green house effect.   In my project my team was using spray type air washer with the very simple design since it become easier to modify.                                                                                                                                                           The spray type air washers consists of a chamber or casing containing a spray nozzle system, a sink for removing the spray water as it falls. And an eliminator section for the removal of moisture in the air. A pump recirculates water at the rate higher than the evaporation rate.   Intimate contact between the spray water and the air flow causes heat and mass transfer between the air and the water. The air washer used in the industries has the basic use to clean air and control the properties of the air as per the requirement.   The air washer can perform two kinds of cooling: 1. Direct evaporative cooling 2.Indirect evaporative cooling   The direct evaporative cooling is done by the direct contact between sprayed water and the flowing air in the chamber. Where the indirect evaporative cooling is done by providing heat exchanger at the front of air washer. The syphon present in the heat exchanger is circulated by the cold water and the hot air is passed through the fins of the heat exchanger. Which causes heat exchange between air and water.   The indirect evaporative cooling was done in my project by the use of car radiator.
AIR WASHER SPECIFICATIONS
BLOWER                suction blower with 1HP, 3PHASE, 440 V and internal diameter 4 inch   NOZZLE SECTION                     the nozzle section consist of:-   1. 4 elbow joints (0.5 inch bore) 2. 3 distributors (0.5 inch bore) 3. 10 vertical pipes (0.5 inch bore & 50 cm length) 4. 10 holes on vertical pipe each (1 mm bore) 5. 5 holes on horizontal pipe each (1 mm bore)   All the components in the nozzle section are made up of PVC material.   The body of the air washer was made up of the aluminium composite pannel.  Two layers of simple cellulose pad was use in the eliminator section to absorb the moisture in the air.                                                                                                                                                                                                                                                                                                  The picture above will give you the brief and real understanding of the project.   The analysis was done with the following aims: 1. circulating the water at normal temperature and analyzing the changes in the property of the air 2. circulating hot water through air washer and analyzing the change in the properties of air 3. circulating chilled water through air washer and analyzing the changes in properties of air   I am providing some videos of working of my project i hope you will like it.   please give reviews on my publish and don't forget to follow. your reviews are precious to me and your following will motivate to share new views thank you.                                                                                               

saurabh kumar tiwari

saurabh kumar tiwari

 

Last Post -- Time to Hang It Up

Mechanics Corner
    A Journal of Applied Mechanics and Mathematics by DrD
    © Machinery Dynamics Research, 2017
Last Post
Time to Hang It Up    
This will be the final post of Mechanics Corner here on Mechanical Engineering Forums. It has run almost exactly two years, and there have been ups and downs along the way. In this final post, I want to reflect a bit on my original goals for the blog, and also on what has actually happened. When our host first proposed to me that I might write a blog for ME Forums, I was excited about it. About half of my career had been spent in engineering education, and I always loved working with students. It seemed like a way to get back to something that I had long enjoyed, and so I accepted his suggestion. A long time ago, back when I was about 14 or 15 years old, in Junior High School, my shop teacher mentioned, in an off-hand way in class, that various curves could be described mathematically. I’d never heard that before, but I thought immediately, “This has interesting possibilities.” Moving ahead a few years, I discovered that I wanted to study and build my career around was the area known as Applied Mechanics, although it was a time before I first heard that term. In my freshman physics class, I discovered the laws of motion, and thought to myself, “This is great stuff! I can use math to describe how things move!” All of that happened back in the 1950s, and I’m still doing the same thing today (some might say I am in a rut!). As a teacher, I taught mostly undergraduate engineering courses, although I taught my share of graduate courses as well. It was the undergraduate courses that I liked most, because I firmly believe that the economy of a nation is strongly dependent on the quality of the baccalaureate level engineers produced in that nation. Engineers with graduate degrees are valuable as well, but the vast majority of the national engineering workload falls to BS level engineers.    Thus, I envisioned Mechanics Corner as a sort of continuation of the several undergraduate courses I most enjoyed teaching — kinematics, dynamics of machines, vibrations, and mechanics of materials. For the most part, I have stuck to the plan, so that most of the technical posts I have made have dealt with problems that I considered suitable for undergraduate engineering students, say perhaps, junior level. I have posted a few topics from my industrial experience, but those have been situations that baccalaureate level engineers would be expected to handle. Now I knew it would not be exactly like continuing to teach my classes. In particular, you would not have any homework or tests, and I would not have any grading to do – a win-win, or so I thought. I did hope, that even with no assigned homework, readers would take an interest in the problems discussed, even to the point of working through the details for themselves (I was terribly naive, apparently!). I knew from my own experience that the only way I ever really learned a new idea was to get in and work with it, work some problems, make some numbers, plot some curves, until I really understood what it was all about. I’ll venture to say that nobody ever learned any technical material simply by reading only. In actual fact, in the early days, I had one or two folks say that they would in fact work through the problems, so I was encouraged. What I was not prepared for, however, was the fact that the vast majority never seemed to even read very carefully, much less work through the problems! The questions that have come, and there have been a few, have largely been about matters totally unrelated to the posts. The most common question has been, “Suggest a topic for my final project,” which relates to not a single post. Needless to say, that aspect of my vision was totally unfulfilled. But there is another side. I ventured to write a few “philosophical” articles, items dealing with academic integrity and cheating, with how to ask for help, with how to write a report or a paper, and various other matters. I really thought all of this would be considered obvious and trivial, so I was completely unprepared for the excitement that some of these articles generated. There were, in some cases, many, many comments, and people seemed to really be interested. I’m left to wonder: why? Are these ideas foreign to the culture of India and SE Asia? Are these things not all taught at home and in the public schools? I don’t know, but there was a lot of interest in these matters. But Mechanics Corner was intended to be primarily a technical blog, and there, it just did not excite the interest of the readership. As time passed, there was less and less interest. First, the comments dropped off to just about zero, and later, there were fewer and fewer who even bothered to “like” the articles. Finally, the number of reads has dropped to almost nothing (there may be no one left to read this final note). Well, there could hardly be any more clear indication that it is time to stop. I asked for opinions about this from some of the administrators, and was told that the blog was just over the heads of the readership. That makes me sad; that was never the intent. If it is true, I do not see how engineering has a very bright future among this readership. Even so, I wish all of you the best for your careers. I hope that you are able to find rewarding and beneficial work in which you will be happy and make a real contribution to your societies. To use an old cowboy metaphor perhaps familiar to many of you from Bollywood, “It is time to hang up the bridle and saddle, and say, ‘Adios’ (Adios is literally, “to God”).  

DrD

DrD

 

A Problem in Statics & Dynamics, #34

Mechanics Corner
    A Journal of Applied Mechanics and Mathematics by DrD, # 34
    © Machinery Dynamics Research, 2015
A Problem in Statics & Dynamics     
    
Introduction         A problem was recently posted on this Forum, requesting help, that has led me to consider a somewhat more general problem for this post. The scope of this post will include the original problem, although not by the method required there, but will also go beyond to a more general geometry. We begin here by stating the present problem; interested readers are invited to search back for the original problem posted 19 December, 2016, by iivii.
    

Assembly Drawing, with Dimensions   StatDynProb.pdf

DrD

DrD

 

What are hydraulic cylinders,working principles !!

Hydraulic cylinders haven’t really changed a lot over the years. The manufacturing processes are much more streamlined and the tolerances are much tighter, but for the most part cylinders are still the hard working push/pull tools they have always been. These things have literally shaped the world around us. Anything that gets lifted, pushed, hauled, dumped, dug, crushed, drilled or graded has gotten that way by some truck, crane, dozer or tractor using a hydraulic cylinder. But how do hydraulic cylinders work?
The amazing amount of force a cylinder exerts is due to the simple mechanical principle of pressure exerted on the surface area of the
piston . Simply put, the larger the diameter of the cylinder, the more it will lift. 

SK sharma

SK sharma

 

If There Is a Fastener There Will Be a Tool That Requires Access.

I get great satisfaction when working with my hands. When I do so I always ask why the item I am working on is as it is. One source of frustration I believe many have experienced it the lack of tool access. Sometimes n-1 fasteners are a breeze to access and the nth takes more time to remove than all the other combined. I don’t recall from my machine design class ever addressing this real world situation. I learned how to size bolts, bearings, and cross-sections but I don’t recall any mention of tool access. I learned there existed standards for tool access when I entered industry. In the auto industry one thing you tried to avoid was the need for special tool kits. These were not cheap and every automobile dealer and repair shop needs to purchase the special kits if they intend to make the particular repair. As much as this was avoided 30 years ago (and I assume still today) these special kits existed. While working in a different industry we were cleaning up a lab area. I came across an Allen Wrench (hex key) that did not make the usual 90 degree bend. It brought to mind the special kits I mentioned above. It had been modified to have a second bend nearly 90 degrees. I taped it to the wall in the design department with the following note. Do Not Design Anything That Needs a Tool Like This! There are reasons a lack of tool access happens. Parts designed for one application may have been created with adequate access. The same item is later used on a different application and the surrounding space is already accounted for. But there are cases where there simply is not enough thought applied or too many bean counters controlling the design function. As the Wyoming winter approaches there are things that need attention. Today two of those frustrations had to be addressed. I have a generator for times when power goes out and an ATV (all terrain vehicles) for snow removal. Both have batteries for starting. Battery removal is more difficult than it should be for both.The generator can be manually started but if needed when it is -20F (-29C) that can be quite an effort. For the ATV the battery is held in place with two screws and a padded flat metal bar across the width of the battery. This is an (n-1) example. One of the two screws has plenty of access and the other is under a plastic housing. What would make it more user friendly (for those who buy the products) would be to make the end of the retaining bar that is under the plastic housing, slip into a slot of some kind. The other end which is very accessible would use the one screw. This would eliminate one fastener, eliminate the captured nut or tapped hole (can’t see what is there) and make battery removal so much easier for little or no cost. My solution which could easily be incorporated at the factory was to cut a slot on the end of the bar with poor tool access. Doing so eliminated the need to remove the hidden fastener. Just loosen enough to slip the retaining bar out then back in. You can rotate the retainer but it must pass over the positive terminal and the bar is grounded to the frame. Better to remove it.  For the generator I speculate this is the multi application issue. The same design is sold with and without battery start. These options don’t come cheap and if as in the auto industry, have a handsome margin. So why punish the big spenders? The panel with all the outlets is welded to the frame. The panel extends quite a distance down to provide a billboard for the power rating. Behind the immovable plate lies the battery. Accessing the battery retainers and cables would be simple if the lower portion of the plate was either detachable or eliminated. Since I don’t transport the generator I leave the retainers off. Access to the cables is still more difficult than it need be. So for those who have not yet entered industry let these two examples provide food for thought when you are designing equipment. Many small improvements can be incorporated for little or no cost prior to production release of the design. Those about to enter industry seek out the senior engineers and ask for the standards books. Spend some time, even your own time, skimming through the manuals. They contain thousands of man-years of experience. Also spend time in the manufacturing and service facilities if possible. These efforts will provide an insight to what is not taught in class. Photo 1 Is a top down view of the battery retainer.  Photo 2 You can see the hidden fastener and the modification to the retainer. Photo 3 Is the generator. The bottom half of the battery can be seen. Photo 4 Is the side view of the battery. Photo 5 Shows the bottom half of the battery more clearly than photo 3.  

JAG Engineering LLC

JAG Engineering LLC

 

MACHINE DESIGN :- 40 POSSIBLE QUESTIONS

1. What are the differences between true stress, engineering stress, proof stress.
2. What do you men by factor of safety and what is its significance
3. What do you mean by Young’s modulus, modulus of rigidity and bulk modulus.
4. What do you mean by resilience.
5. What is pure torsion and what do you mean by flexural igidity.
6. What is the difference between endurance limit stree and endurance strength.
7. What do you understand by efficiency of riveted joint.
8. What is caulking and fullering in riveted joint.
9. What do you mean by stress conc. Factor and what are the methods to reduce stress conc.
10. Why stress conc. Is more serious in brittle materials. 11. What do you mean by fatigue .
12. Springs are subjected to which type of streses.
13. What are the difference between through bolt, tap bolt and stud.
14. What is check nut and what is the function of washer.
15. Cotter and knuckle joints take which type of load and where they are used.
16. What are the difference types of couplings and what is their function.
17. What is the function of key and which type of stress they are subjected to?
18. Generally shafts are subjected to which type of stress.
19. What are the difference types of mechanical drives and which is the best for different situations.
20. What is the function of a bush why it is phosphor bronze.
21. What are difference types of threads and which threads are used for power transmission and why.
22. Why the pulley arms are elliptical in cross section and it is made up of cast iron.
23. Why it is required to change the all V belt if one of them is broken.
24. Why V belts transmit more power than flat belts.
25. What is the meaning of 6*37 or 6*7 in a rope drive.
26. What do you mean by pinion sprocket and wheel sprocket and which one is used for driving shaft.
27. What is the function of flywheel and why its material is cast iron.
28. Why the leaf springs are laminated as reducing length.
29. What is the function of clutch and is the difference between uniform wear and uniform pressure.
30. Now a days which type of clutches are used in automobiles. 31. Why disc brake is more efficient than mechanical brake.
32. What is the function of bearings and what are the different types.
33. What is bearing characteristics number and bearing modulus.
34. What is the significance of the digits of a rolling contact bearing number 6304?
35. Which type of gear drive is used for perpendicular transmission of power?
36. Why helical gears transmit more power than spur gears.
37. What do you mean by different terms like back lash, pressure angle, circular pitch in a gear drive.
38. Why involute tooth profile is better than cycloid tooth profile?
39. What is interference in gear drive and how to avoid it?
40. What do you mean by law of gearing

saurabhjain

saurabhjain

 

Over Engineered or Over Designed?

I recall many years ago first hearing the term Over Engineered. It rang a sour note but I had not given it much thought. I still hear this said today about older equipment. For instance the DC Generators at Pratt Institute in Brooklyn NY have been in operation for over 100 years. http://inspectapedia.com/heat/Steam_Systems_Pratt_Milster.php I had the opportunity a few years ago to visit my alma mater. To my surprise and delight the Chief Engineer who provided the tour of the facility to my class in about 1977 was still on the job as was the equipment. But I digress. Over Engineered is often brought up when speaking about 1950’s vintage American automobiles. “They don’t build them like that anymore”. They don’t build them like that anymore because they don’t design like they use to. When I worked in the auto industry in the late 70’s and early 80’s engineering was in good part “seat of the pants” designing. A lot less analysis than one would expect. Two-D CAD was just getting introduced. There was extensive testing before production. What a lack of analysis left unknown, testing –often brutal testing- would reveal. If a component broke it was made stronger by adding more material or eliminating tight radii or other stress concentration features. Whether the rest of the system was just good enough or 10 times stronger than needed was an unknown. Over time components that never failed were targets for cost reduction. This also was not as analytical as it is likely today. Getting back to the subject of this blog, I would offer that the "weaker" a device is, the more it was engineered. Weaker, because it is designed closer to the expected loads. This of course is aside from shoddy design work.  For greater strength the addition of material will usually achieve this. For an item like the generators at Pratt added weight can also help with vibration. The penalties are the onetime cost of added material and greater shipment weight. Adding more material globally to a system such as a rocket, aircraft and to today’s automobile is forbidden. This requires much move engineering. I hope I have provided a better understanding of the term Over Engineered and realize it is really a misleading expression. Equipment back then was Over Designed because the factors of ignorance were much greater just a few decades ago.

JAG Engineering LLC

JAG Engineering LLC

 

5 tips to survive a Seminar successfully!

Seminars have always been an important aspect of education. It's an opportunity to either gain knowledge on an unknown topic or develop ideas regarding something you already know.It's a place where you meet highly skilled persons and get to know their recent researches.You should attend at least a couple of seminars annually to keep yourself updated about the advancements taking place in your field. I've seen many people who keep avoiding seminars, although interested, just because they have never attended a seminar before. If this is your case, then I've only one thing to say "There's always a first time." Until and unless you attend a seminar, how can you overcome the fright?     Attending a seminar for the first time does not mean that you'll feel low or less confident than others. Here are a few tips that can make you seminar-ready. Here are a few tips that can help you get through a seminar and actually learn from it.   1. Know the Topic Usually there are no prerequisites to attend a seminar but ideally you should know something about the seminar you're going to attend.First know the topic, yes the topic. I've seen a lot of people coming for a seminar and asking what the topic is! Know the meaning of each term related to the topic, like definitions, some dates, names of some important people in that field, etc. If you still have some time and energy left, know who the speaker is and his background. You can look for his area of study, some research works, etc. So now that you know what you need to know, I'll suggest you some ways by which you can know it.( I just hope I didn't confuse you. Oops, I did! ) Now-a-days you can literally find everything on the web,sometimes even the details you need about the speaker from his research works. Now that you have the basic knowledge of the topic, you can consult the faculties if you feel like. You can find lot of details online but only after talking to the profs you get to know which information is relevant for the seminar you're going to attend.Knowing more never goes in vain, but off course you wouldn't like to clog your mind with so many points. If you feel it hard to remember all the points, you can make short notes and take it with you to the seminar. Just make sure your focus is on the speaker as soon as the seminar starts and not on these notes.        2. A proper attire it's never mandatory to wear formals for attending a seminar but avoid fancy dresses. Remember you're in the professional world, dress up like that. If you like make-ups go for it, but keep it light and simple. Just make sure you're comfortable with your look. In most of the cases, dressing up properly makes people feel confident.         3. Non-verbal communication People can communicate a lot of things even without uttering a single word, through their body gestures, eye movement, etc. ere lies the importance of non-verbal communication. You can put a smile on you face just to show that you're there to learn and not to oppose the idea the speaker is going to present. Nodding your head sometimes during the speech can also communicate a lot about you. It means you're listening and understanding the topic as well.         4. Be attentive It's not important to understand each and every part of the speech but at least you should get the essence of the speech. Just remember that the seminars are designed to provide you with a usable content on a variety of relevant subjects and keep you updated with the latest advancements in your field. So, try to gain as much knowledge as possible.         5. Asking Questions It's the best way to get you ideas about the topic reviewed by an experienced person, you'll get to know if you're on the right track. Speakers also encourage questions and it's a way of learning on their part too. But whenever you ask a question, make sure you know exactly what you need to know clearly. Frame the question in your mind first, you certainly don't want to stumble while asking.
At this moment, I certainly don't want to demotivate you, just remember that silence is better than asking "silly questions".   So the next time you're going for a seminar, you already now what to do and how to do!                        Happy "Seminar-ing" !  

Tania Alam

Tania Alam

 

BUE formation during machining

What is a BUE? BUEs are built-up edges formed due to the accumulation of work-piece material against the rake face of the tool. How are BUE formed? During machining, the upper layer of the work-piece metal experiences a large shear force as it comes in contact with the tool-tip and an amount of the metal gets welded to the tool-tip. This is due to work hardening of the metal layer. The metal adhered to the tool becomes so hard that it is difficult to remove.     Why are BUE formed? BUE formation is common under a few conditions which are : Low cutting speed  Work hardeneability of work piece material High feed rate Low rake angle Lack of cutting fluid Large depth of cut In which materials is it observed easily?   BUE formation is usually noticed in alloys such as Steel rather in pure metals.It is also observed in soft materials like soft pure Alumunium, hot rolled low carbon steel. What are the effects of BUE? There are a few basic effects caused by the BUE formation like : Change in tool geometry Change in rake steepness Reduction in contact area between the chip and the cutting tool. What are the advantages of BUE? BUE formation can have a few advantages on the cutting tool and ease of machining like : Slight increase in tool life Reduction in power demand. What are the disadvantages of BUE? The count of disadvantages is actually more than the advantages it has on the machining process. Poor surface finish  Problems in dimensional control of the process Leads to flank wear (damaging the flank face)       How can the BUE formation be prevented?  BUE formation is a common machining problem but there's a soluion to every problem.Here are a few prevention steps to reduce BUE formation Increasing cutting speed Use of cemented carbide tool in place of HSS tool Introduction of free machining materials ( loaded or resulphurized steel) Application of an appropriate lubricant at low cutting speed   P.S. - Suggestions are always welcomed.

Tania Alam

Tania Alam

 

Types of Kinematic pairs

When two links (or elements) in a machine are in contact with each other, they form a pair. When the relative motion between these two links is completely or partially constrained, then the links are said to form a kinematic pair.
In simple words, a kinematic pair or simply a pair is a joint of two links having relative motion between them. 
 
Kinematic pairs can be classified on the basis of:   1) Nature of contact between the pairing elements 
(a) Lower pair – surface or area contact between the members of the pair
There are 6 types of lower pairs
I. Revolute pair (R)
II. Prismatic pair (P)
III. Screw or helix pair (H)
IV. Cylindrical pair (C)
V. Spherical or globular pair (G)
VI. Planar pair or Ebony (E)                 (b) Higher pair – point or line contact between the members of the pair 
Examples of line contact – 
I. Tooth gears 
II. Ball and roller bearings 
III. Wheel rolling on a surface                  
Examples of point contact – 
I. Cam and follower pair                
(c) Wrapping pair – similar to higher pair, but there are multiple point contacts, one body wraps over the other, comprises of belts, chains, etc. Examples – A belt driven pulley                        
2) Nature of mechanical constraint 
(a) Form or Self closed pair – the contact between the two bodies is maintained by geometric form
Examples – Screw pair (lower pair)         (b) Forced closed pair – the contact between the two bodies is maintained by application of external force
Examples – Ball and roller bearings         
(c) Open pair – links are not help together mechanically, contact due to the force gravity or some spring action.
Examples – Cam and follower pair        
3) Nature of relative motion of one link to the other in the pair 
(a) Sliding pair – sliding motion
Examples – Rectangular rod in a rectangular hole in a prism     
(b) Turning pair – turning or revolving motion
Examples – Circular shaft revolving inside a bearing     
(c) Rolling pair – rolling motion
Examples – Ball and roller bearings      
(d) Screw or Helical pair – both turning and sliding motion
Examples – Lead screw and nut of a lathe     
(e) Spherical pair – one link is in the form of a sphere and can turn inside a fixed link
Examples – Ball and socket joint P.S. ~ Suggestions are always welcomed.

Tania Alam

Tania Alam

 

Types of Hydraulic Turbines

Turbines are machines which convert fluid energy to mechanical energy. When the fluid used is water, they are called hydraulic turbines.  Hydraulic turbines may be classified on the basis of four characteristics :       On the basis of the type of energy at the turbine inlet Impulse turbine total head of the incoming fluid is converted in to a large velocity head at the exit of the supply nozzle ( entire available energy of the water is converted in to kinetic energy.) water entering the runner of a reaction turbine has only kinetic energy the rotation of runner or rotor (rotating part of the turbine) is due to impulse action Flow regulation is possible without loss Unit is installed above the tailrace Casing has no hydraulic function to perform, because the jet is unconfined and is at atmospheric pressure. Thus, casing serves only to prevent splashing of water. It is not essential that the wheel should run full and air has free access to the buckets. eg - Pelton wheel turbine ( efficient with a large head and lower flow rate.)     Reaction or Pressure turbine the penstock pipe feeds water to a row of fixed blades through casing that convert a part of the pressure energy into kinetic energy before water enters the runner water entering the runner of a reaction turbine has both pressure energy and kinetic energy the rotation of runner or rotor (rotating part of the turbine) is partly due to impulse action and partly due to change in pressure over the runner blades Water leaving the turbine is still left with some energy (pressure energy and kinetic energy)  It is not possible to regulate the flow without loss Unit is entirely submerged in water below the tailrace Casing is absolutely necessary, because the pressure at inlet to the turbine is much higher than the pressure at outlet. Unit has to be sealed from atmospheric pressure. Water completely fills the vane passage.  eg - Francis and Kaplan turbines ( efficient with medium to low heads and high flow rates )           On the basis of the direction of flow through the runner Tangential flow turbine   Direction of flow is along the tangent of the runner  eg - Pelton wheel turbine.     Radial flow turbine   Direction of flow is in radial direction radially inwards or centripetal type, eg- old Francis turbine radially outwards or centrifugal type, eg -Fourneyron turbine           Axial flow turbine   Direction of flow is parallel to that of the axis of rotation of the runner the shaft of the turbine is vertical, lower end of the shaft is made larger which is known as hub (acts as runner)   eg - Propeller turbine ( vanes are fixed to the hub and they are not adjustable )        Kaplan turbine (vanes on hub are adjustable )     Mixed flow turbine   Water flows through the runner in the radial direction but leaves in a direction parallel to the axis of rotation of the runner  eg- Modern Francis turbine.               On the basis of the head at the turbine inlet High head turbine net head varies from 150m to 2000m or even more small quantity of water required eg -: Pelton wheel turbine.   Medium head turbine net head varies from 30m to 150m moderate quantity of water required eg -: Francis turbine. Low head turbine net head less than 30m large quantity of water required eg -: Kaplan turbine.   On the basis of the  specific speed of the turbine Before getting into this type, one should know what the specific speed of a turbine is. It defined as, the speed of a geometrically similar turbine that would develop unit power when working under a unit head (1m head).
  Low specific speed turbine specific speed is less than 50. (varying from 10 to 35 for single jet and up to 50 for double jet )  eg -: Pelton wheel turbine.
  Medium specific speed turbine specific speed varies from 50 to 250 eg -: Francis turbine
  High specific speed turbine specific speed more than 250 eg -: Kaplan turbine       References : 1. Course contents on NPTEL website 2. A textbook of Fluid Mechanics and HydraulicMachines - R.K. Bansal 3. Fluid Mechanics: Including Hydraulic Machines - A.K. Jain 7 hours, 59 minutes ago

Tania Alam

Tania Alam

 

Advanced Polynomial Curve Fitting

Mechanics Corner
    A Journal of Applied Mechanics & Mathematics by DrD, #33
    © Machinery Dynamics Research, 2016
Advanced Polynomial Curve Fitting
    The use of polynomials to fit engineering data is a common engineering practice. In school, we learn that "A data set consisting of n data points ((x_{i},y_{i}), i=1,2,3,…n) can be exactly fitted with a polynomial of degree n-1. Thus three data points can be fitted exactly with a quadratic expression, four data points can be fitted exactly with a cubic expression, and so on. If this approach is pursued much further, something ugly appears: while a polynomial of degree n-1 will pass exactly through n data points, for large values of n, it will oscillate wildly in between the data points. Since one of the most common reason for using a polynomial fit in the first place is for interpolation -- to be able to estimate a function value at locations between the known data points -- this wild oscillation is devastating. It is at this point that least squares fitting is usually introduced to give an approximate fit using a much lower order polynomial. A different approach is employed here. AdvancedPolynomialCurveFitting.pdf

DrD

DrD

 

Braced Cantilever

Mechanics Corner
    A Journal of Applied Mechanics and Mathematics by DrD, # 32
    © Machinery Dynamics Research, LLC, 2015
Braced Cantilever Introduction     Anyone who has actually gotten into machine design is familiar with this difficulty. Consider the situation where a project is well advanced, many plans have been made, and it is all based on the assumption of the adequacy of one particular part. When you finally get to the detailed analysis of that part, the calculations show that it is not adequate. What can you do?
    To make the problem much more concrete, consider the cantilever beam shown in Figure 1. It supports a weight W at the free end, and when someone finally makes the calculation, the tip deflection, δ, is unacceptably large. The whole system design has been developed on the assumed adequacy of that cantilever, and there is no room to put in a beam with a larger section to give more stiffness. What can be done?     Any of countless machine design texts, mechanics of materials texts, etc., give the formula for the end deflection, δ=(WL³)/(3EI)     where
    E= Young's modulus for the beam material
    I= area moment of inertia for the beam cross section
    L= length of the beam
    W= tip load value
    While we can argue that someone should have checked this earlier, finger-pointing does not fix the problem.   BracedCantilever.pdf

DrD

DrD

 

What is the name of this mechanism.

good morning Someone could tell me what the name of this mechanism or how can I find a way to design it. It is a shaft that moves in a straight line vertically and along the way makes a 180 ° worst shaft never leaves his line of action . these links you can see the operation of the mechanism     Thank you Imagenes del giro.docx

Daniel Barco

Daniel Barco

 

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

DrD

DrD

 

Where is this?

Does anyone recognize where this video is shot? Is it a group of students at a school (what school?), or is it an industrial site (what company)? I am anxious for someone to locate this for me, please. DrD   Saurabh Jain, our host, has identified this location for me, and that is much appreciated. When I watched the video, I was aghast at all those nearly bare feet in a machine shop! I can appreciate that in Indian culture, the simple sandals are socially quite acceptable, but from a safety perspective, this is an absolute horror. Think of all the opportunities for something to drop on a foot, a tool, a machine part, sparks, etc.   Some years ago (quite a few years ago), I worked in a steel mill. We were required to wear hard hats and steel toed shoes at all times in the mill. And these were not just any old steel toed shoes. These shoes came up ankle high, and had massive steel toes and an additional steel plate, called a metatarsal plate, that came up over the top of the foot almost to the ankle. Each shoe weighed 4 lb, and it was very tiring simply to walk around wearing them. But, .... and this is the key part .... they added much to our safety. Even today, in my advanced old age, I have a pair of steel toed boots (but not metatarsal plates) for when I go into an industrial environment.   What is shown in this video is actually a cautionary tale, a warning of just about everything not to do from a safety perspective. Take heed! Be warned, or you could easily loose all your toes on one foot of the other.   DrD  

DrD

DrD

 

Did I Go to School to Make Copies?

I did not write the linked article. I should have since you will not learn this in school. When we finish 4 or more years of an ME education we are all wound up. We have been working at a pace which would kill us if tried it indefinitely. What shocked me when I entered industry was the trivia that engineers must be involved with. Perhaps like a soldier, you train to fight, but you don't do it 8-12/hr per day for 30 years. I don't know if the following article is accurate for small companies but it is for large corporations. I recall being bored and asked my supervisor for more work. He looked at me for a second or two then asked if I could make him a copy of some document. I said to him if this is what I get when I ask for more work I will eventually stop asking. My suggestion to young engineers is to keep in mind what one of my ME professors told us. “The best thing you can do is to get a job that keeps you as busy as I did.” I don't know if that is possible but I would keep that in mind. The article suggests too much complacency in my opinion. I think you need to know what is coming but don’t settle for making copies.

JAG Engineering LLC

JAG Engineering LLC

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