Sam Farjamirad
  • Member for 3 years, 11 months
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3 answers
2 votes
121 views
Does gravity have any effect on metal casting?
Accepted answer
-3 votes

In theory yes! But how much difference does it make, it depends on the impurities, material, and of course size of the part. Right after filling the mold, the metal is still a fluid, it means the ...

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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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2 answers
0 votes
52 views
Position vector to Velocity vector
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If you only have a general postion vector that describes the path of the object, then it's impossible to derive the velocity vector. Here I try to demonstrate it: Since the point masses are ...

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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
44 views
Why large industrial units combine induction and synchronous motors?
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0 votes

As the name suggests, induction motors are inductive, it means they require inductive power input, or reactive power. The problem with reactive power consumption is, if you max the monthly limitation ...

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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?
Accepted answer
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
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
1 votes
45 views
Valve/Filter allowing through gas only, no liquid
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0 votes

What are you searching for is called: Thermostatic expansion valve or (TXV). You have one of those in your air conditioner. Because the compressor of AC's are designed to handel only vapour.

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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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4 answers
2 votes
710 views
When calculating a force, why do I get different result when I try to calculate via torque vs via sum of forces at an axis?
0 votes

The answer is you have more variables than the equations, look at the general form of the problem: We have in total five unknowns here and two equations of equilibrium: $$y-z-x=0$$ $$-z(d+e)+yd=0$$...

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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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2 answers
0 votes
113 views
Does the frequency of input voltage in induction motors have to be continuously altered?
-1 votes

But if we assume the motor starts from zero RPM, at what speed does the field rotate at this moment in time? The synchronous speed (rotating field speed) $\Omega_{sy}$ is independent of the rotor ...

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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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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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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
35 views
Simulating AC using DC
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0 votes

This is possible! The AC motors are designed to run with AC currents so this is not a very good idea. A very popular way to do it is PWM, it basically mimics a sin wave by switching between two states,...

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1 answers
0 votes
82 views
how to find the motor specification
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There are two masses here to accelerate, the target $10$ kg and the mass of the belt which is yet unknown(usually it is given as weight per meter), the total mass is $M$. I make some assumptions here:...

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3 answers
3 votes
101 views
Transferring energy generated by photovoltaic methods
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As stated before in the comments, natural and political challenges let you down to follow this project but electrical engineers and providers face another challenge, look the graph here onder: 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
1 votes
79 views
Phase response of a continuous transfer function
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0 votes

The plots are correct. This is how we do it on our heads in about a minute after years of practice. The magnitude: Consider the numerator and denominator separately. Numerator rise with a slope of $...

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1 answers
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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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2 answers
1 votes
84 views
Differential equation
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In general an infinite number of functions satisfy differential equations (DV). To obtain a specific solution a first order ODE must have an initial condition or constraint that specifies the value of ...

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2 answers
1 votes
55 views
MANUFACTURING PROCESS: ROLLING PROCESS
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There are many reasons behind, and many ways to justify why it is so. I'm trying to clarify it by using the conservation of the mass. 1- The density of the rolling material doesn't change, so its ...

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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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2 answers
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95 views
How to fix this gear
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First you need to get rid of the leftover cups and cones by grinding it to have a smooth surface. To get the best result you have to choose the same material but if you don't know the exact ...

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1 answers
2 votes
29k views
Inverter + Direct drive vs. Belt drive motor in washing machines?
Accepted answer
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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1 answers
0 votes
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
3 votes
103 views
LC oscillator circuit
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Yes, the frequency remains the same, why ? Suppose you replaced the capacitors with an equivalent capacitor but the rest of circuit remains the same, so the current and voltage oscillate with ...

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