Questions tagged [mechanical-engineering]

Questions within the problem domain of mechanical engineering. Mechanical Engineering can be a broad field; consider choosing more specific tags if they apply.

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1answer
663 views

What is the physical meaning of pulse rate and blood pressure, from a turbo machinery point of view?

Our hearts are peristaltic pumps, which has a periodic compression and expansion. The head developed can be taken as blood pressure. There are situation when the blood pressure is normal while the ...
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2answers
6k views

How Can I Determine Multiple Discharges from a Pipe Network? (Knowing the Inlet Conditions)

I have little/no experience with pipe networks and have been searching for a methodology to calculate the discharge from multiple outlets of an oil pipe network with a single inlet. As far as i can ...
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2answers
2k views

Why does filter efficiency decrease with thickness?

I understand that the most important parameters for a filter are basically pressure drop and thickness, both of which affect efficiency. However why does thickness cause a change in efficiency? I'm ...
8
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1answer
618 views

What does “tol” mean in a gear box?

In this NASA document, it is mentioned on page 221 (239 of the pdf) that a "23 tol gear box" was used. What does that mean? A google search for "23 tol gear box" (with quotes) comes up completely ...
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2answers
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How does the shape of CPU/GPU fan blades affect their performance and loudness?

I need to replace the fan on my graphics card. The original fan is exactly like this one but there is another fan that seems to be a new revision of the same model number from the same manufacturer (...
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4answers
460 views

Could house fires be prevented by increasing dryer vent speed?

In the US, clothes dryers are one of the leading causes of house fires: In 1998, CPSC estimates that there were approximately 15,600 clothes dryer fires resulting in 20 deaths, 370 injuries and $...
8
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1answer
172 views

Scale models of thermal plumes

I want to look at the thermal heat plume of a human in still air in a room. So I have a tank of water with a heating coil/cylinder in it. How do I calculate what the heat output of my heating coil ...
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1answer
4k views

Why don't we use principal maximum stresses when designing a structural element?

Consider a concrete column is under compression from top loading and also carries some shear stresses. If take a plane 2d element in the column with these stresses and rotate it to the point it gives ...
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2answers
2k views

Efficiency in a gas turbine or aircraft engine

Most modern aircraft engines, such as the one depicted below taken from Wikipedia, are composed of several compressor stages which are driven by a turbine (or several), and a combustion chamber in-...
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132 views

What is the name of this particular mechanical linear position switch made of perforated spring strip?

I'm writing a few elementary paragraphs about switches and switch technology, and I cannot for the life of me remember what a particular kind is called, to give it an honorable mention. Here is a ...
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1answer
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Contours of radial-flow impeller vane

I've been studying the design of turbopumps and their impellers, all the design equations and what-not; this question concerns the contours of the impeller vanes. I'm going to attempt to enter ...
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2answers
358 views

Could magnetic levitation transportation systems become a commonplace technology?

Magnetic levitation systems of transportation such as trains seem to be commonplace in early 2000's science fiction, and while some systems exist currently, they aren't exactly common. It seems to me ...
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1answer
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How can I calculate the stresses and limits for the physical lowering of in-service pipelines?

Sometimes underground pipelines are exposed due to vertical scour or lateral migration of streams (or other erosion). One option is to lower the (in-service) pipeline to a new depth that provides ...
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2answers
5k views

Not a good idea to rub two of the same material against each other?

I've read that it's not a good idea to rub two surfaces of the same material against each other, e.g., plastic against plastic, metal against metal. Plastic against metal is preferred. Why is this the ...
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2answers
13k views

Force required to crop/cut a mild steel bar

I have cropping/cutting wedges with a thickness of 4 mm cutting either side of a round mild steel bar (17.5 mm). Imagine two wedges being driven together with a round mild steel bar in the middle (...
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100 views

Moment equation from dynamics differs with equations from physics & statics. Where did I go wrong?

In my dynamics class, we're being asked to solve the following problem: My Attempt: Since I'm given the initial velocity, final velocity, and distance, I solved for the acceleration of the plane ...
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1answer
2k views

Large deflection of a cantilever beam with distributed normal load

I have a strip of stainless steel encastree'd at one end to which is applied a constant pressure on one side, and I need to know what the deflection equation y = f(x) is at equilibrium. If the ...
8
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1answer
583 views

How do I best model a torque applied over a non-radial line?

I am looking to use FEA (specifically, Creo Simulate) to re-create the results of a static strength test on a part my company will be testing in our lab. Because the lab results are the ones we will ...
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1answer
4k views

What is the benefit of additional planetary gears?

A planetary gear is a gear that rotates not around an axle but around another gear known as a sun gear, or star gear. I have designed prototype systems in the past that used a single planetary gear ...
8
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1answer
272 views

Controlling hydraulic cylinders with variable delay

Electro-mechanical systems typically used in robots have very low delays and are quite simple to build servo controllers for. Hydraulic systems are much less common in robotics and have delay due to ...
8
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1answer
180 views

Water hammer and expansion waves

I was thinking about the relationship between water hammer and expansion waves. Pressure seems to drop across a surge wave travelling at the speed of sound in water hammer (after the fluid has been ...
8
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2answers
177 views

Can high alloy tool steels be quenched in brine?

It is will known that most of tool steels are quenched in oil to prevent cracking and distortion which appears when quenching in water due to non-uniform cooling caused by formation of insulating ...
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2answers
228 views

Heating circuit: Galvanized steel with press fitting vs welded steel pipes

What are the downsides for galvanized steel pipes + press fittings vs. welded steel pipes in a heating application? Diameter would be DN25/1". Background: The customer specifies only steel, only ...
8
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1answer
612 views

Air Conditioning Modes of Failure

I have a question about air conditioning and the probable modes of failure. I recently installed a Nest thermostat in my home. I've noticed that it seems to prefer to have the air conditioner's ...
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0answers
244 views

Forcing a part into “home position”

I have a design with two parts (at the moment): a fixed 10cm ring with vertical tracks a freely rotating block with a cut that may freely slide along that tracks: I'm trying to find a low profile ...
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7answers
6k views

Why do electric trains arc at high speeds?

When I watch videos of high speed trains I always see explosions of electricity near the top, or arcing. Why does that happen? I know that the Acela does it a lot but other high speed trains have it, ...
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5answers
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Would a centrifugal flyweight governor system slow down the descent of an object that is free falling down to the Earth's surface? (Revised design) [closed]

I am wondering if rotating flyweights would slow down the descent of a object that is free falling down to the Earth's surface. Please reference the conceptual drawing below: This drawing is showing ...
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4answers
308 views

Is radians a dimensionless quantity?

Quite often while calculating angular velocity we come across the quantity radians per second. How do I treat radian dimensionally?
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2k views

What are the common failure points of waterproof cases?

I am making a waterproof case for my Galaxy S5 and/or my Raspberry Pi. I plan to make the main body from (or at least decorate it with) wood, though I can use other, stronger materials where needed. ...
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4answers
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Does a diesel-like (ignition by compression) engine running on gaseous fuel exist?

I think, it could lead to, for example, very environment friendly and very efficient urban traffic. But I also think, it required very precise part construction. Do such things exist? At least in ...
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2answers
1k views

SOLIDWORKS - 3D Sketch of Trombone

My task is to create a 3D Sketch of a trombone like the one below My professor recommended defining the points 1-4 and putting a spline through them. I did that, but my resulting design looks weird. ...
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3answers
657 views

Can gravity be a driving force for a spring-mass system?

If a spring-mass system is undergoing free vibration (oscillating up and down), then does it imply that there is no gravity? My tutor always consider gravity when finding the Equation of Motion for ...
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3answers
8k views

What is Radial and Thickness Mode Vibration in a Piezo Electric Ceramic Disc Transducer?

I am trying to use a Piezo Electric Ceramic Disc Transducer for ultrasonic sensing measurements for fluid levels. A Piezo Ceramic Disc with a Resonant frequency of 215 KHz or 1 MHz is under ...
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2answers
910 views

Creating smooth shaft resistance

I am trying to emulate the resistance of a hand wheel which moves a table via a series of shafts and chains which turn an acme screw. I am switching to a CNC system that will allow the user to keep ...
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5answers
7k views

How can I improve traction on a wheeled vehicle yet reduce friction?

This is inspired by a project I undertook for my Physics class last year; I'd like to apply it in the future. Background: For the project, I and a few classmates were required to build a small car ...
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5answers
411 views

How can we prevent/detect hydrogen embrittlement?

There has recently been a series of high profile bolt failures on 'The Cheesegrater' in London, which have been attributed to hydrogen embrittlement. What can engineers do to ensure that hydrogen ...
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1answer
2k views

Modeling Transient Heat Transfer between two 1-D materials

I have been working on creating a 1-D model of a material with a layer of heat resistant material stuck to it. For this I have been trying to use the implicit finite-differential method. The equations ...
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2answers
7k views

Interpretation of shear flow/shear center of L-profile

I have calculated the shear flows and center of an L shaped profile. I assume they are correctly calculated (I followed the same steps as during the lectures for an I shaped profile). However, I have ...
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2answers
285 views

Modelling splashing water in FEA

I'm running an FEA on a vessel that has a "splashing water" effect with vibrations. The problem I'm really coming up against is what kind of Young's Modulus and Poisson's ratio to use for the fluids? ...
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4answers
4k views

How does a diesel internal combustion engine start even though there are no spark plugs?

I was just wondering how a diesel engine starts, given that there are no spark plugs. How does it build up 'momentum' for that first explosion in the cylinder? Does it have something to do with the ...
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2answers
115 views

Traction mechanisms for a robot in confined spaces

I'd like to build an exploratory robot that can fit within confined spaces1. What traction mechanisms should I consider to propel a robot along the inside of a 4" pipe? The pipe to be traversed will ...
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3answers
3k views

Why use non-dimensional coefficients?

Aerospace engineering textbooks make frequent use of non-dimensional coefficients like $C_L$, $C_D$ and a whole host of others. Usually, for equations of motion, it is preferred to replace variables ...
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3answers
471 views

Information regarding plastic hinges that can hold the position

I am trying to find some information regarding the design of plastic hinges that can move freely but also hold a position in any degree, like in this little camera: https://www.kickstarter.com/...
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1answer
1k views

How is fuel mixed with air in a jet engine?

I am working on an idea that involves a jet engine, but I don't quite know how the fuel system works. In a combustion engine like that in a car, you have nozzles that spray the fuel into the piston ...
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2answers
200 views

What is this pan-tilt system called?

Based on the description of friend I drew this small example of a specific pan-tilt mechanism I'd like more information on, but as I'm not an engineer I don't really know what terms to use and can't ...
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3answers
243 views

What is “flow instability” in porous media?

Pressure drop across a porous medium can be described by the Forchheimer extension to Darcy’s law: $$-\frac{dp}{dx} = \frac{\mu}{K_1}\cdot v + \frac{\rho}{K_2}\cdot v^2$$ where $K_1$ and $K_2$ are ...
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1answer
2k views

What is this pressure gauge on the London Underground measuring?

I noticed this pressure gauge on the Piccadilly Line of London Underground yesterday. It was located on the side of a row of seats. Close-up of the gauge at hand: click for larger version of image ...
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2answers
2k views

Why do some high speed trains have long noses, while others do not?

Why do some high speed trains like the Shinkansen E5 and E6, have really long noses while other trains, like the Eurostar and Javelin, have shorter noses? How does the shape of the nose affect the ...
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2answers
121 views

Adding a lubricant to an already lubricious material, how is CoF affected?

I have a dry film moly-graphite lubricant (CoF=.075) and a lubricious CVD coating (CoF=.05). The CoF of each of these lubricious materials was determined using the same ASME standardized test. The ...
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3answers
1k views

Compound gear system ratio

This might be a stupid question, but I'm new to mechanics, so please bear with me. Suppose I have a compound gearing system defined in the image below (not to scale). The green gear is the driving ...

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