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  • 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
    • 5,374 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
    • 27 comments
    • 2,266 views
  • 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
    • 4 comments
    • 961 views

Our community blogs

  1. Tema I

     

    La fabricación de piezas por maquinado

     

    1.1 Introducción

    Todo ingeniero debe tener una cultura general integral y, dentro de esta, como es lógico, una cultura de la profesión. Parte de la cultura del ingeniero mecánico consiste en conocer la historia de la ingeniería, y en el caso particular de este blog es importante comenzar por conocer muy brevemente la historia de las máquinas herramienta. Para ello se presentará  más adelante el anexo I, el cual trata sobre la Evolución de las máquinas herramienta [1].  

     

    La revolución industrial surgida con la máquina de vapor no hubiera sido posible si no se hubiera construido primero una máquina herramienta capaz de fabricar las piezas fundamentales del invento que sintetizó James Watt: la máquina de vapor. Por cierto, para que Watt llegara a su invento tuvo que haber otros que le precedieron e hicieron sus propios descubrimientos previos en el mismo campo de la energía del vapor de agua a presión, de modo que, como casi siempre ocurre, Watt recopiló esos conocimientos, los organizó, sistematizó, les añadió algo más y construyó, ayudado por Wilkinson y su mandrinadora, la primera máquina de vapor.

     

    Y antes de eso, y después de eso, siempre ha sido así. Sin máquinas herramienta no hay desarrollo posible. Las máquinas herramienta fabrican las piezas que se ven a diario sin que se les preste la debida atención: las del ómnibus que lleva a los pasajeros, las de la termoeléctrica o el grupo electrógeno que produce la electricidad, las del combinado lácteo que procesa la leche, las de los equipos que emplea el médico, las de los equipos que perforan para buscar o bombear petróleo desde las profundidades de la tierra, las del molino del central azucarero. Y como si todo esto fuera poco, las máquinas herramienta fabrican otras máquinas herramienta, se podría decir figuradamente que son las únicas máquinas que garantizan la continuidad de su especie.

     

    Nota:

    ¿Por qué “máquinas herramienta” y no “máquinas herramientas”? En la lengua castellana los sustantivos formados por dos sustantivos forman el plural solo con el primero de ellos. Así, otros ejemplos pueden ser: profesores guía; palabras clave; fresas madre. No obstante, en ocasiones se puede considerar que el segundo de los dos sustantivos hace función de adjetivo, y entonces sería “máquinas herramientas”. En este blog se prefiere la primera variante.

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    1. In a steam turbine, the ............ is allowed to rotate?

    2. Which valve controls the flow of steam into the turbine?        

    3. The blades in a ............... turbine are designed so that the pressure below the blade is always higher than the pressure above which causes them to move (or spin) as high velocity fluid flows through them.       

    4. Where in the steam path is the energy transferred from the steam to the turbine?       

     

    5. There is excessive corrosion on the turbine/driven unit train.  The carbon rings have been inspected and are clean, and do not need replacing.  What is the most probable cause of the corrosion?       

  2. Recently I was interviewed by a Mechanical Engineering student on the importance of communications. I’m approaching 40 years in engineering practice so the examples began to flow and the student’s 15 minute time estimate for the meeting quickly turned into two hours. The meeting itself was a lesson in communications. My awareness of the root cause, that I will describe below, I believe made the information more valuable.

    The student and I covered many issues on the topic of communications, but the emphasis of his questioning was the difference between communicating with other engineers versus business majors or the sales personnel. The root issue of communications I believe goes deeper and must be identified to minimize the occurrence.

    There have been many occurrences of communication problems in my life and not all involved engineering. In the past, I viewed each incident as individual and isolated events. Of late, I have come to the conclusion there are common causes. Here I address one that I think is more common than realized.

    Communication problems are often dismissed as the language, generational, or cultural gaps. These all contribute to the issue but are not the root cause of a large portion of communication problems. If fact, obvious language issues often result in precautions being taken to avoid miscommunications.

    About 25 years ago I was among a group of technical people gathered for a seminar. While waiting for the speaker, conversations started within the group. Two people were carrying on an energetic conversation for 10-15 minutes consisting of acronyms -- just alphabet soup. Just prior to the speaker arriving, the two having the conversation realized each used a particular acronym for entirely different and unrelated meanings. Yet these two had conversed as if they were on the same subject. Imagine if the conversation had developed into a disagreement to the point of anger, and the instructor arrived before these two were able to define terms. Both would have left thinking badly of the other and maybe worse.

    In another situation I was just hired into a new position by a former coworker, now manager of a program. He asked that I do something which I immediately did. At our next meeting, the manger began to tell me how I should go about doing the task. I was fuming, to say the least. I was saying to myself, "what was wrong with the way I did it?" I fumed and fumed until I finally asked. The manager looked at me in astonishment and said “You did it? I am not use to anything getting done so fast around here.”

    One final example. A new VP of engineering admonished me for my poor design and release process causing many problems – no specifics were provided. I was shocked to the point of speechlessness, so I did not immediately ask for specifics that would have revealed the root cause of his dissatisfaction.

    I assumed my 2 + year old procedure had grown stale and caused problems. I printed a copy of my Design and Release Procedure and read it line for line, looking for something that was no longer correct. After failing to find any problems, I wrote in large red letters “Tell me what I need to change.” The boss was not at his desk, so I left it on his seat. Sometime later, a much more humble boss came to my office and asked if the release date on the procedure was correct – it was, and about 2 years old, so I said yes, and he left.

    All three examples have the same root cause. In each case one or both parties assumed implicitly that the other party knew something that in reality they did not.

    Case One: Each party assumed that a particular acronym meant the same to each of them.

    Case Two: I implicitly assumed the manger would know that I would quickly act on the simple assignment. We had worked together for 6 years prior, on a different program.

    Case Three: The VP had come to believe implicitly that there was no written process. In his mind, every problem that arose appeared to be a result of not having a process. I assumed he was talking directly to the written document that he did not know existed.

    As an independent Professional Engineer many of my clients are not engineers. What were once safe assumptions while working in an engineering office with other engineers, I learned quickly was no longer acceptable.

    Current technologies allow people from around the world to communicate with incredible ease. This has resulted in the root-cause I suggested above to run unchecked. When we write we need to be aware of generational, language, or cultural gaps as well as office jargon*. All can easily result in implicit assumptions of other people’s knowledge that are false.

    The first professional letter I wrote to be send outside the corporation was brought back to me by my supervisor. He called to my attention that office jargon has no place for a formal business letter. Here again, I was implicitly assuming the terms used every day in our group would be universally understood. It took me 40 years to “connect the dots.”**

    * Special words or expressions that are used by a particular profession or group and are difficult for others to understand.

    ** To understand the relationship between different ideas or experiences

  3. Mechanics Corner

    A Journal of Applied Mechanics and Mathematics by DrD, #36

     

    Base Acceleration Problem

    Introduction

    In a recent post (#35) I mentioned that I often participate in another forum called Physics Forums (PF). The problem that I want to discuss here is an elaboration on a problem that recently appeared at PF. I'm going to add a little bit of complexity to the problem (the problme as stated at PF was extremely simple) in order to make a particular point.

    123.png

    The system of interest is shown in Figure 1, a body with a single wing attached to one side. You might consider this to be one side of an airplane, or perhaps a stirring paddle used to mix paint. The mass of the wing is M, and the center of mass for the wing is at the point marked CM, a known distance u from the main body. We are told that the main body has an acceleration a sub z in the z-direction, and that the whole system is immersed in a viscous liquid such that the drag force is proportional to the square of the velocity in the z-direction. Our concern is with the connection between the wing and the main body. We need to determine the shear and bending moment on that connection due to z-direction motion.

     

    BaseAccelerationProblem-36.pdf

  4. Explain the term hot cracking & cold cracking in welding and how these can be taken care of ?

    crack.jpg

     

    1. You can answer this question.
    2. You can like the best answer.
    3. You can share the question
    4. You can get updates of new questions on Facebook linkedin twitter & google plus
  5. 1) How to make the spiral pipe

    20160317231239983998.jpg.9778d1356d79391fbc6b63a29f825461.jpg

    2) Accessory of the pipe (Use to connect the pipe and bring pipe up)

    image3.jpeg.d12b925fa9d23b3715ec5d2c9447403d.jpegScreenHunter_174.jpg.551777ac14159a0ce06b5875400cec78.jpg

    image5.jpeg.864b7bc57d8dd415526a8577d048f982.jpeg

    3) Application

    building1.thumb.gif.c7ff3fac9ceeac273998d71de45572c6.gif

    15c2.jpg.8c7f53292facec8378bf1a0267b70547.jpgHTB1t6zCHpXXXXcIXpXXq6xXFXXXQ.jpg.dbf1a989c7e5acf0620377c12ea8e321.jpg

    4) Drawing 

    Click Download drawing of Bridge foundation 3D ( reference drawing )

    Click Download catalogue of the product

     

    spsp-juctions-type.jpg

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    Mechanical Design and More

     

    Why Design?

    The new era is flooded with products - Virtual or Physical. And with no surprise, everything needs to be designed. We are doing it from long back, since we are bringing something new or may be inventing. Design is the medium which brings your thoughts into a physical (nowadays virtual) form.
     

    Virtual/Web design

    Remember the old days websites or software packages - They were largely comprised of text, and design layout did not exist much. While later versions had some design, they were still extremely basic, consisting mainly of tags for headers, paragraphs, and links. Visual considerations such as typography, imagery, and navigation were still things of the not-too distant future.
     
    vDoIT_Ui-ux.png
    pc: www.vdoit.in
     
    And now, we are into a new age where we look forward to User Interface and User Experience (UI/UX) designers to improve overall experience and usability of webisites and software packages.
     
    There is a whole world behind these two words!!
     
    Just take an example of one of the largest social networking website, Facebook - Who decides, where will be your cover pic and where should be the display pic be located in your wall. Not only this, there are whole lot of stuffs on each and every website. Simple placement and positions of the buttons will change the overall experience of the user. This is where UI/UX designer are working hard by understanding human nature and behavior of doing things when they are 'online'.
     
    uiuxusability.jpg
    pc: www.mockingbot.com

     

     
    Just to add, each and every thing which you look into a website, software package or mobile applications , be it a logo, buttons, stickers and the entire range of interface details which you see are being designed by someone - Designers. Imagine the vast amount of work involved in this!

     


    Physical/Mechanical design

    Being a Mechanical Design Engineer, this excites me more.
     
    When I say "Mechanical", does it restricts me to gears, bolts-nuts, cam-shaft, car/aerospace bodies and parts?
     
    Well not at all !
     
    Name a product around you which you think is not of 'mechanical' genre - Mobile phones, Television (its remote too), Refrigerators, Air conditioners and many more. Most of us would say these are electronics/electrical products. They are listed under 'Electronics' category in amazon and flipkart too.

     
     
     TV-fridge.jpg

    Now, understand this - All of these products are obviously being invented/reinvented by electrical or electronics engineers and their functionality depends on basic rules and principles of these engineering discipline, but their actual physical being is a work of physics and mathematics. When I say physics and mathematics, its basically mechanical design in broader sense.

    For instance, the electronic board inside a mobile phone or TV is work of electronics ( circuit design, voltage calculations, etc), but they never tell how the mobile phone should look or feel to the end user when they will hold it. Also, electrical engineer can not tell how a TV to be wall mounted, what should be the screen thickness, corners, etc. In more engineering sense, the entire design is actually work of a Mechanical Design engineer who designs the fits/forms and the look of the appliance. Obviously when I say 'look', it opens a whole new world which revolves around aesthetics.  Probably, I will talk about ergonomics and aesthetics some other time.

     

    The Design Sense

    Any design needs to fulfill certain requirements which comes from end users. But the real question is what inspires a designer to design something new or may be modify an existing product to something new and more usable. The designer must satisfy all what is required by the user and obviously the standards set upon it (and off course the laws of physics and mathematics). These all might drive the design and product structure but these can never drive how the product will look or feel to the user. At some instances the user might not be interested on how it looks, it should perform and that's all counts.
    Design.png
    pc: www.api-university.com

    The design sense of the designer plays an important role on how the product is being designed and what features are built to satisfy all the requirements. Be it a UI/UX designer or Mechanical designer, designing under requirements are achievable like solving a problem but developing a design sense is something which comes with time and experience. In a way its a work of art.
    design%2Bsense.png
    ps: www.designschool.canva.com

    How do we develop a design sense?

    When I say DESIGN is work of art, any art comes with time and needs passion. We may learn design tools but the design sense needs dedication. A musician can learn how to play a guitar but can only develop new tunes if he is passionate about it.
     
    Have you ever thought why a particular product is being made/designed the way it is? Let me take a few examples:
     
    1. Bulbs - The iconic shape that blazes in our minds as the quintessential light bulb served two purposes in the advent of lighting: it was easily manufactured using glass-blowing techniques, and its spherical shape was best for controlling heat and light emissions.
    bulb.jpg
     
     
    2. Golf balls - Are a golf ball's dimples just there for aesthetics?
    Try aerodynamics - They actually create turbulence in the layer of air surrounding a ball in flight, reducing the drag behind the ball.
     
    golfball.png
     
    Now we know why helmets for cyclists are designed with dimples. But why not aircraft or cars?

     
    helmet.jpg
    3. Manhole covers - Why they are always round?
    They are round almost all over the world, so that they cannot possibly fall through their own holes. Any shape other than a circle would be able to fit through in at least one way.
     
    manhole1.jpg
     
    Off course few designers took it as challenge, but I am sure they had to make some arrangement, may be a hatch.
     
    square_manhole.jpg
     
    So now you know why certain features are designed in these products and why it was a sensible approach.

    I will discuss a lot more about design - Design thinking, mechanical design approach and the process to build something new and off course the tools which are used. Log in to 

    Why Design?

    The new era is flooded with products - Virtual or Physical. And with no surprise, everything needs to be designed. We are doing it from long back, since we are bringing something new or may be inventing. Design is the medium which brings your thoughts into a physical (nowadays virtual) form.

    Virtual/Web design

    Remember the old days websites or software packages - They were largely comprised of text, and design layout did not exist much. While later versions had some design, they were still extremely basic, consisting mainly of tags for headers, paragraphs, and links. Visual considerations such as typography, imagery, and navigation were still things of the not-too distant future.
     
    vDoIT_Ui-ux.png
    pc: www.vdoit.in
     
    And now, we are into a new age where we look forward to User Interface and User Experience (UI/UX) designers to improve overall experience and usability of webisites and software packages.
     
    There is a whole world behind these two words!!
     
    Just take an example of one of the largest social networking website, Facebook - Who decides, where will be your cover pic and where should be the display pic be located in your wall. Not only this, there are whole lot of stuffs on each and every website. Simple placement and positions of the buttons will change the overall experience of the user. This is where UI/UX designer are working hard by understanding human nature and behavior of doing things when they are 'online'.
     
    uiuxusability.jpg
    pc: www.mockingbot.com
     
     
    Just to add, each and every thing which you look into a website, software package or mobile applications , be it a logo, buttons, stickers and the entire range of interface details which you see are being designed by someone - Designers. Imagine the vast amount of work involved in this!
     


    Physical/Mechanical design

    Being a Mechanical Design Engineer, this excites me more.
     
    When I say "Mechanical", does it restricts me to gears, bolts-nuts, cam-shaft, car/aerospace bodies and parts?
     
    Well not at all !
     
    Name a product around you which you think is not of 'mechanical' genre - Mobile phones, Television (its remote too), Refrigerators, Air conditioners and many more. Most of us would say these are electronics/electrical products. They are listed under 'Electronics' category in amazon and flipkart too.

     
     
     TV-fridge.jpg

    Now, understand this - All of these products are obviously being invented/reinvented by electrical or electronics engineers and their functionality depends on basic rules and principles of these engineering discipline, but their actual physical being is a work of physics and mathematics. When I say physics and mathematics, its basically mechanical design in broader sense.
    For instance, the electronic board inside a mobile phone or TV is work of electronics ( circuit design, voltage calculations, etc), but they never tell how the mobile phone should look or feel to the end user when they will hold it. Also, electrical engineer can not tell how a TV to be wall mounted, what should be the screen thickness, corners, etc. In more engineering sense, the entire design is actually work of a Mechanical Design engineer who designs the fits/forms and the look of the appliance. Obviously when I say 'look', it opens a whole new world which revolves around aesthetics.  Probably, I will talk about ergonomics and aesthetics some other time.

    The Design Sense

    Any design needs to fulfill certain requirements which comes from end users. But the real question is what inspires a designer to design something new or may be modify an existing product to something new and more usable. The designer must satisfy all what is required by the user and obviously the standards set upon it (and off course the laws of physics and mathematics). These all might drive the design and product structure but these can never drive how the product will look or feel to the user. At some instances the user might not be interested on how it looks, it should perform and that's all counts.
    Design.png
    pc: www.api-university.com

    The design sense of the designer plays an important role on how the product is being designed and what features are built to satisfy all the requirements. Be it a UI/UX designer or Mechanical designer, designing under requirements are achievable like solving a problem but developing a design sense is something which comes with time and experience. In a way its a work of art.
    design%2Bsense.png
    ps: www.designschool.canva.com

    How do we develop a design sense?

    When I say DESIGN is work of art, any art comes with time and needs passion. We may learn design tools but the design sense needs dedication. A musician can learn how to play a guitar but can only develop new tunes if he is passionate about it.
     
    Have you ever thought why a particular product is being made/designed the way it is? Let me take a few examples:
     
    1. Bulbs - The iconic shape that blazes in our minds as the quintessential light bulb served two purposes in the advent of lighting: it was easily manufactured using glass-blowing techniques, and its spherical shape was best for controlling heat and light emissions.
    bulb.jpg
     
     
    2. Golf balls - Are a golf ball's dimples just there for aesthetics?
    Try aerodynamics - They actually create turbulence in the layer of air surrounding a ball in flight, reducing the drag behind the ball.
     
    golfball.png
     
    Now we know why helmets for cyclists are designed with dimples. But why not aircraft or cars?

     
    helmet.jpg
    3. Manhole covers - Why they are always round?
    They are round almost all over the world, so that they cannot possibly fall through their own holes. Any shape other than a circle would be able to fit through in at least one way.
     
    manhole1.jpg
     
    Off course few designers took it as challenge, but I am sure they had to make some arrangement, may be a hatch.
     
    square_manhole.jpg
     

    So now you know why certain features are designed in these products and why it was a sensible approach.

    I will discuss a lot more about design - Design thinking, mechanical design approach and the process to build something new and off course the tools which are used.

     

    Mechanical Design and More

     

     

  6. 58c0e1facf9a1_EffectofthetypeofmeshonaPipeflowproblem.thumb.jpg.1fdd8a463decca9320342da21a339a2f.jpg
     
     
    The project explains how the type of mesh can influence the results obtained for the mixing of flow in a pipe. The simulation is done on a cloud-based CAE platform called SimScale. The link to the project is here. This project is a part of the SimScale Professional Training on CFD (Computational Fluid Dynamics).
     
    ab25ab48061159.588d8513e593a.jpg
    The pipe flow geometry, originally uploaded by the SimScale Staff, available in the public projects.
     
    For this internal flow problem, a Hex-dominant parametric mesh is used. Two types of meshes are created for the problem - a coarse mesh ( which accommodates all the features of the geometry) and a fine mesh ( by increasing the fineness).
     
    d54ec048061159.588d8513e5e65.jpg
    Coarse mesh ( Fineness: 1-Very coarse)
     
    55c7a048061159.588d8513e635a.jpg
    Fine mesh ( Fineness : 4-Fine)
     
    The same type of analysis is performed for both the meshes (Fluid dynamics: Incompressible). Same boundary conditions and simulation controls are defined for both the meshes.
     
    53db0b48061159.588d8513e6863.jpg
    Simulation run: Coarse mesh
     
    c66e3948061159.588d8513e74ed.jpg
    Simulation run: Fine mesh
     
    The simulation results are post-processed (clip filter is used) to get the contour plot of the velocity flow field.
     
    ae485f48061159.588d8513e7a41.jpg
    Post-processor screenshot for coarse mesh
     
    d8894448061159.588d8513e8008.jpg
    Post-processor screenshot for fine mesh
     
    As revealed by the results the fines mesh captures specific physics (like flow separation and vorticities) more accurately. Isn't that expected? Well, not always!
     
     
     
    This blog was previously posted on Behance.

     

     

     

     

     

     

     

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    Recent Entries

    boiler.thumb.jpg.e337153387408b1c1d3b910b196ba2ea.jpg

    • The boiler system comprises a feed-water system, steam system, and fuel system. The feed-water system supplies treated water to the boiler and regulate it automatically to meet the steam demand. Various valves and controls are provided to access for maintenance and monitoring.
    • The steam system heats and vaporizes the feed water and controls steam produced in the boiler. Steam is directed through a piping system to the application. Throughout the system, steam pressure is regulated using valves and monitored with steam pressure gauges.
    • The fuel system consists of all equipment used to supply of fuel to generate the necessary heat. The equipment required in the fuel system depends on the type of fuel used in the system.

    Boilers Classification:

    There are a large number of boiler designs, but boilers can be classified according to the following criteria:

    1. According to Relative Passage of water and hot gases:

    • Water Tube Boiler: A boiler in which the water flows through some small tubes which are surrounded by hot combustion gases, e.g., Babcock and Wilcox, Stirling, Benson boilers, etc.
    • Fire-tube Boiler: The hot combustion gases pass through the boiler tubes, which are surrounded by water, e.g., Lancashire, Cochran, locomotive boilers, etc.

    2. According to Water Circulation Arrangement:

    • Natural Circulation: Water circulates in the boiler due to density difference of hot and water, e.g., Babcock and Wilcox boilers, Lancashire boilers, Cochran, locomotive boilers, etc.
    • Forced Circulation: A water pump forces the water along its path, therefore, the steam generation rate increases, Eg: Benson, La Mont, Velox boilers, etc.

    3. According to the Use:

    • Stationary Boiler: These boilers are used for power plants or processes steam in plants.
    • Portable Boiler: These are small units of mobile and are used for temporary uses at the sites.
    • Locomotive: These are specially designed boilers. They produce steam to drive railway engines.
    • Marine Boiler: These are used on ships.

    4. According to Position of the Boilers:

    • Horizontal, inclined or vertical boilers

    5. According to the Position of Furnace

    • Internally fired: The furnace is located inside the shell, e.g., Cochran, Lancashire boilers, etc.
    • Externally fired: The furnace is located outside the boiler shell, e.g., Babcock and Wilcox, Stirling boilers, etc.

    6. According to Pressure of steam generated

    • Low-pressure boiler: a boiler which produces steam at a pressure of 15-20 bar is called a low-pressure boiler. This steam is used for process heating.
    • Medium-pressure boiler: It has a working pressure of steam from 20 bars to 80 bars and is used for power generation or combined use of power generation and process heating.
    • High-pressure boiler: It produces steam at a pressure of more than 80 bars.
    • Sub-critical boiler: If a boiler produces steam at a pressure which is less than the critical pressure, it is called as a subcritical boiler.
    • Supercritical boiler: These boilers provide steam at a pressure greater than the critical pressure. These boilers do not have an evaporator and the water directly flashes into steam, and thus they are called once through boilers.

    7. According to charge in the furnace.

    • Pulverized fuel,
    • Supercharged fuel and
    • Fluidized bed combustion boilers.
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    hello All,

     i am working as a design engineer and i am working on sheet metal structures. i am looking at the calculations to decide on the thickness of sheet metal to carry a particular load.

    i calculated the sectional modulus of the design based on the cross sectional area of sheet metal and it is well within the sectional modulus of material. I would like to know werher the approach is right or are there other calculations which i should do before deciding the thickness?.

    request to suggest on the above

    please find the image below for reference

    2017-03-03_08h02_02.png

    2017-03-03_08h04_02.png

  7. ADENIJI

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    What are the classifications of engine? 

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  8. Many research and development have been conducted  to meet society needs for safer vehicles. Particularly, occupant protection system such as air bags, developed and introduced in order to reduce occupant injuries in crashes, are currently installed in most vehicles making significant contribution to safety.

     

    Meanwhile, many studies have been made into the development of active safety technologies that help to avoid crash accidents. Unfortunately the current situation is that the active safety technologies are not sufficient spread. Adaptive cruise control has been commercialized since 1995, but its primary use has not been convincing.Some audible warning system  are also being offered, but have not yet reached widespread use.

     

    Toyota Motors corporation has explored the possibility of producing an active safety system employing Intelligent Transport System (ITS) technologies,through participation in the Advanced Safety Vehicle (ASV) projects started in 1991 and led by ministry of land , infrastructure and transport.

     

    Critical basis ITS technologies for application to ASV includes a surround monitoring sensor and an obstacle determination algorithm which combines information from the surround monitoring sensor with other information to identify obstacles with which the vehicle is likely to actually crash.

     

    The sensors and crash determination algorithm for an active safety system should be capable of reliably determining that  a crash will not occur in non-crash situation. Advanced technologies are required to make these predictions and judgments correctly while also taking into account the driver's operation and behavior and this has hampered widespread of active safety systems.

     

    Pre-crash safety system has been developed which operates only when it is judged that a crash cannot be avoided by most drivers under normal driving conditions. Determining unavoidable crashes is restricted to a short time period immediately before the crash so as to improve the reliability of the judgement. In addition the pre-crash system is made with a mechanism and system that will not place the driver and the running vehicle in an unsafe condition even if the system is operated unnecessarily. As a result the world's first commercial system has been achieved.

     

     

     

     

     

     

     

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  9. 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. 

    Cylinder cutaway.png

    hydraulic.jpg

  10. .This is a lecture video I had given, for introduction and basics of this topic. I hope this will work out well with young undergrads and seniors can brush up too.

  11.  

    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?

     

    Seminar.jpg

     

    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.

      

    ohrdXaUq7HZlu.gif
     
     
    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.

     

    6kcYyQEX5nVRe.gif
     
     
      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.

     

    lMxlHF5sJ63NS.gif
     
     
      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.

     

    100YmlniUkSv84.gif
     
     
      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".

    26BRAk0i9RZkElSRW.gif

     

    So the next time you're going for a seminar, you already now what to do and how to do!

     

    gTNSX6N7vcKOY.gif
     
                       Happy "Seminar-ing" !

     

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    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.
    xm93ki.pngbue-mit.gif

    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 :
    1. Low cutting speed 
    2. Work hardeneability of work piece material
    3. High feed rate
    4. Low rake angle
    5. Lack of cutting fluid
    6. 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.

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    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. 
     

    Material Science and Engineering (1).jpg


    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)  

     
     

    Types of Lower pair

     
     
     
     
     

    (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    

     gear-a04.jpg   spherical_roller_bearing.jpg   wheel-contact-with-road-rolling-friction

     
     
     


    Examples of point contact  
    I. Cam and follower pair      

     cam_follower_wht.gif

     
     
     
     


    (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      

              belts40a77c7ac4ffe4ef3972ee9f2eb89d757.p

     
     

      
    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)    

     

     screw_conn.gif

    (b) Forced closed pair – the contact between the two bodies is maintained by application of external force
    Examples – Ball and roller bearings       

    220px-BallBearing.gif 


    (c) Open pair – links are not help together mechanically, contact due to the force gravity or some spring action.
    Examples – Cam and follower pair
     snlcam4.gif
     
     
     


    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  

      image20.png


    (b) Turning pair – turning or revolving motion
    Examples – Circular shaft revolving inside a bearing  

      Fig75bushedbearing.jpg
    (c) Rolling pair – rolling motion
    Examples – Ball and roller bearings    

     self-aliging-ball-bearing-596.jpg


    (d) Screw or Helical pair – both turning and sliding motion
    Examples – Lead screw and nut of a lathe  

      Locknut.jpg


    (e) Spherical pair – one link is in the form of a sphere and can turn inside a fixed link
    Examples – Ball and socket joint

    ball-and-socket-joint-1623_1.jpg

    P.S. ~ Suggestions are always welcomed.
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    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 :
     
     
    Material Science and Engineering (1).jpg
     
    • 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.)

     
    _PHgp4.gif
     
    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 )

     
    atE2tr.gif
     
     
     
     
    • 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.

     
    pelton turbine.gif
     
    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
    Stay_guide_vanes.png       Reaction.gif
     
    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 )

     

    Turbofan3_Labelled.gif

     
    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.

     
    borgwarner-efr-7163-turbo-3-content-11.j     bD24ct.gif
     
     
     
    • 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
  12. 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

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