Sam Farjamirad
  • Member for 3 years, 11 months
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4 answers
13 votes
15k views
Why is oil used as the lubricant in power generators, while water is the most available, cheapest and accessible lubricant?
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58 votes

The whole point of lubrication is to keep the two surfaces almost apart. Water has low viscosity in comparison to oil-based lubricants, which means that it forms a thinner film (electrohydrodynamic ...

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1 answers
4 votes
177 views
What methods are there to test the flexural, tensile and compressive strength of concrete?
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8 votes

There are two methods to test flexural strength, three point and four point method. Three point method: and the corresponding moment line: four point load: and its moment line: The maximum ...

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1 answers
3 votes
59 views
What is the thermodynamic consideration so almost all air conditioners are installed on top?
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5 votes

The cold air has a higher density so it always settles down, by installing the AC on top, the cold air can interact faster with hotter air, so the cooling process is much faster. If you install the ...

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1 answers
2 votes
29k views
Inverter + Direct drive vs. Belt drive motor in washing machines?
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4 votes

There are tons of advantages and disadvantages, but I will mention only the relevant cons and pros. Indirect (belt) drive usually produces less noise in comparison to direct drive (continue power ...

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3 answers
3 votes
4k views
Moments of Fixed-Fixed Beam
4 votes

This is a statically indeterminate problem. I don't know what exactly you mean by moments develop at the fixed supports But I guess you mean if there exist any non-zero components of moment at the ...

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2 answers
3 votes
385 views
Swash Plate Pump Design
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3 votes

There exist three types of axial plunger pumps. 1- Rotating swash plate axiale plunger piston pumps: Usually for low-power systems, as the temperature rises above 120° C, it can degrade the fluid ...

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2 answers
1 votes
115 views
2nd Moment of Area of a ring
2 votes

You have done everything right! You calculated the polar moment of inertia $J$, which is the sum of second moment of areas $I_i$. But here you have a symmetric object so: $$J = I_x+I_y$$ and $$I_x=...

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1 answers
0 votes
111 views
How do I change the coordinate system from x-y to n-t or r-theta by using Matrix?
2 votes

The coordinate transformation of polar to cartesian is given by: $$\begin{pmatrix} r \\ \theta \end{pmatrix} = \begin{pmatrix} \cos\theta & \sin\theta \\ -\sin\theta & \cos\theta \end{pmatrix}...

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1 answers
1 votes
537 views
How do I find the vertical reaction forces?
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2 votes

There are multiple ways to solve this problem but I use the moment equilibrium around the points A and B. $$A_y 3l-q_0 4l^2=0$$ You can find the $A_y$ reaction force from the equation above and use ...

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3 answers
1 votes
172 views
Reaction Forces on a Beam
2 votes

Step one: Choose a right handed coordinate system. As you can see in my schematic: The $X$ axis lies along the beam: So, in $ZX$ plane, the counterclockwise moment is positive. Step 2: ...

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1 answers
0 votes
1k views
derivation of Young's modulus experiment formula
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2 votes

I try to tackel the problem in two different ways, as suggested in the comments. The first approach is based on Bernoulli beam theory, a set of differential equations, (if you want to know how drive ...

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1 answers
0 votes
1k views
Steady Non steady and Uniform Non Uniform flow
2 votes

The steady state refers to any phenomenon that is independent of time. Mathematically it means: $$\frac{\partial v}{\partial t} =0$$. Here is an example: Consider a fixed point in the atmosphere ...

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1 answers
0 votes
173 views
How to solve for moment with uniform distributed load
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2 votes

The resultant of distributed loads always acts on the centroid of the distributed load geometry, here the distributed load is uniform so its centroid lies half the way. If the distributed load varies ...

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2 answers
0 votes
108 views
A question on non-destructive testing and evaluation
2 votes

Yes, in material engineering they call it Thermography. By Radiating heat on the surface or infrared radiation we can map the temperature distribution. The heat transport throughout the material is ...

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1 answers
0 votes
285 views
How to calculate the torque of 4 wheeled vehicle before slipping
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2 votes

Before start to solve the problem, i like to use your assumption about load distribution. And i assume you found the static coefficient of friction. Notice there is a difference between static and ...

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2 answers
1 votes
272 views
Difference between phase and grain in a material
2 votes

A phase can be defined as as a homogeneous portion of a system that has uniform physical and chemical characteristics, so every pure material. grain is defined as an individual crystal in a ...

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1 answers
1 votes
2k views
What is the use of v notch in Izod charpy test
2 votes

The point is to promote the condition of brittle fracture. The notch here acts as a stress riser and favours the crack propagation. This test is designed for any material, if you already know that ...

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1 answers
1 votes
243 views
How can I couple two small parallel shafts offset a short distance from each other?
2 votes

The first option is Oldham coupling, you say ' I have less than a cubic centimetre of space between the shafts in which to place the coupling mechanism.', so i recommend Oldham coupling. They require ...

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2 answers
4 votes
481 views
How to determine tensile strength while the normalised tensile strength is known?
2 votes

The tensile strength is diameter dependent. How greater the diameter, how longer it takes to discharge the heat, so, the time it takes to cool down the material (here is steel) has an impact on the ...

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1 answers
2 votes
36 views
Fourier serie signal approximation
1 votes

If you already know the explicit form of the function $f(x)$, then it's possible to find the periode by solving this equation $f(x) = f(x+P)$. If you have a graphical representation of the function (...

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2 answers
2 votes
109 views
How does an air-bearing "pre-load" work?
1 votes

The reason is to prevent instability. What is instability? Let's have look at a simple shaft-journal bearing system. Here is an ideal system wherein a shaft is rotating clockwise inside a journal ...

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3 answers
2 votes
65 views
How to make a choice between rolling element bearing and journal (plain) bearing?
1 votes

It’s difficult to say when we should select the rolling element bearing or the other one, sometimes we have to consider the upsides and downsides of each to decide. Also the working condition and the ...

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1 answers
3 votes
459 views
Thevenin equivalent impedance in laplace domain
1 votes

The $\frac{4}{s}$ is a current source so it's open when you calculate the Thévenin equivalent, so no current flows thorough the 3 Ohm resistor however $\frac{12}{s}$ is a voltage source so it's a ...

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1 answers
0 votes
283 views
What do the short parallel lines mean in a symmetrical value?
1 votes

Those short parallel lines have absolutely no meaning in terms of information relating to the part, but we put them on the drawing to identify the line of symmetry. They are always at the right angles ...

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1 answers
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65 views
Approach to solve a frictional problem?
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1 votes

I'm trying to approach the problem at the high school level. The vertical force is proportional to the tangential force acting at the other end of the rod, the ratio of these two is called the ...

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2 answers
2 votes
603 views
Why is the unit for torsional twist in radians?
1 votes

The results of twist angle is indeed dimensionless, but so are radians! The radian is defined as the ratio of arc length to radius length, so both arc length and radius length have the same unit, ...

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1 answers
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86 views
Contradictory result for mass balance
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1 votes

The results are correct and not contradictory at all, but the way you interpret the problems is not totally correct. For mass or impulse balance, you have to first define a control volume. I define ...

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1 answers
2 votes
104 views
Resolution of forces and state of stress at a point
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1 votes

Sort of. When you resolve a vector into its component, you have to choose a coordinate system, resolving the vectors into components is the same as projecting the original vector on the coordinate ...

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1 answers
0 votes
152 views
90 degree pivot steering system to allow vehicles to move sideways
1 votes

Technically yes you can design it here is an example, however designers have to develop a locking system to prevent the back wheels while the car moves in a curve otherwise the car starts spinning ...

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1 answers
0 votes
63 views
Shear force requirement
1 votes

I use to build a very simple model first, then try to expand it. Here i try to find the minimum, force require to cut the wire, by using Tresca criterion: Yielding starts when the maximum shear ...

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