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44 votes
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Why are engine blocks so robust apart from containing high pressure?

If you consider only the static forces then indeed the thickness might seem over-engineered. However, engine blocks are not statically loaded. They operate in the range of a few hundred to a few ...
NMech's user avatar
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15 votes

Why are engine blocks so robust apart from containing high pressure?

You need to consider that the complete engine block has to withstand the reciprocating forces generated by each of the pistons and con rods moving as well as the rotational forces from the rotating ...
Solar Mike's user avatar
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12 votes

Why are engine blocks so robust apart from containing high pressure?

The vibration, loading, and fatigue aspects have already been addressed, but a wide range of operating temperatures is another factor. A typical consumer engine can be deployed in anything from say -...
brichins's user avatar
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11 votes

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

It really depends on the problem and what you want to capture. Usually, in classes, it may be beneficial for the students at an initial stage to disregard gravity alltogether in order to simplify the ...
NMech's user avatar
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8 votes
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Stiffness of a cantilever beam

Stiffness is a murky term frequently used ambiguously in engineering. However, the most common definition of stiffness is the product of a beam's Young's Modulus $E$ (which is a function of its ...
Wasabi's user avatar
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7 votes

In vibration study, should the reference be necessarily the mean/equilibrium position?

It can be arbitrary. It just simplifies the mathematics significantly. However the end result should be the same.
NMech's user avatar
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6 votes

Three-phase versus single-phase operation of a generator

But I'm thinking it may be better (more efficient maybe? less vibration maybe?) to run it in three-phase mode, with the load balanced among the three hot terminals. Correct. Figure 1. The load is ...
Transistor's user avatar
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5 votes
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Can a thing resonate whilst exposed to white noise?

You won't get much resonance because the phase the thing is being driven with keeps changing. The resonant thing will act like a notch filter, so you are left with the frequencies near its resonance. ...
Olin Lathrop's user avatar
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5 votes
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How to simulate the Natural Frequencies of a Planetary Gearbox?

To obtain the modes shapes and resonant frequencies, you start from your equation of motion with no externally applied forces, which is indeed as you've stated. $$\mathbf M \mathbf{\ddot q} + \mathbf ...
Involute's user avatar
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5 votes

Which mode does get excited under action of dynamic loading?

Take the Fourier Transform of the time varying driving force, this will give the frequency content of the driving force. Multiple modes of vibration can be driven at once, and will superpose with each ...
Involute's user avatar
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5 votes
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Do internal / external stresses affect modal frequency?

Consider a small piece cut out of a structure that has non-zero internal stress. To maintain equilibrium, there must be some forces applied to the boundary of the piece. (Of course when it was part ...
alephzero's user avatar
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5 votes
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How do those "dipole-shaped" weights attached to sections of electrical power lines work?

According to the wiki, these are called Stockbridge dampers. The design is tuned for a specific length and one might also expect a specific mass/material. The weights are mounted on flexible arms, ...
fred_dot_u's user avatar
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4 votes

I want a shockproof table for a model train. That is, protection from physical jolts, not electrical volts

Build two tables. The outer table will have a hole in the middle and only hold the glass plate. There should be about 10 cm of free space between the tables. The train will be placed on the inner ...
jpa's user avatar
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4 votes
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Strategies for cable vibration: eigenvalues are suitable?

Mathematically, an eigenvalue analysis assumes the modal displacements are infinitesimally small, so the change in stiffness in the cable caused by the vibration is a second order effect which can be ...
alephzero's user avatar
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4 votes

What does 1 x rpm or 2 x rpm or 3 x rpm in vibration analysis mean?

RPM = revolutions per minute. In the context of vibration monitoring, 1 x rpm means a vibration frequency that is the same as the rotation speed (one vibration oscillation per revolution of the ...
alephzero's user avatar
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4 votes
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How can I measure the vibrations of a solid object?

An accelerometer is the correct choice, but the smartphone accelerometer gets its readouts smoothed out in software before being made accessible to userspace. It won't pick up such fine vibrations. ...
SF.'s user avatar
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4 votes

Resonance vs flutter

In flutter, the force applied to the structure depends on the deformation and velocity of the structure. Therefore, the force is necessarily at exactly the same frequency as the motion, though it may ...
alephzero's user avatar
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4 votes
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What is the difference between washer and O-ring, what are their advantages of one over the other?

An o-ring usually (but not always) has a round section and is made of a compressible material such as rubber, neoprene, silicon etc. A washer tends to have a square or rectangular section and is ...
Solar Mike's user avatar
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4 votes
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Why does the frequency of a bottle filling up changes?

Most acoustic vibrations of air more or less confined to a given geometry can be explained by two basic models. One is the one-dimensional treatment of the air in a tube, and the other is the lumped-...
ttonon's user avatar
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4 votes

Why are engine blocks so robust apart from containing high pressure?

The example picture does not show a very solid outter wall; what you see a gasket surface. A closer look will show a lot of variations in thickness, with a lot of ribbs, bulky parts (for mounting, and ...
Bassa's user avatar
  • 41
4 votes

Why are engine blocks so robust apart from containing high pressure?

No one has mentioned yet that there are structural loads placed on the block by other components. The first that comes to mind are the cylinder heads, and as it (they) are torqued, the block needs to ...
Mobius's user avatar
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4 votes
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Wierd faulty gearbox FFT

Vibrations are the manifestation of things occurring at some frequency. This can be one per rev from imbalance (nothing is ever perfectly balanced) in gears spinning, one per tooth from each tooth ...
Abel's user avatar
  • 1,353
4 votes

In vibration study, should the reference be necessarily the mean/equilibrium position?

So you need a point, "zero point" as you really want the amplitude of the displacement as the conditions vary. if you use a moving point to measure another moving point then you have to ...
Solar Mike's user avatar
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3 votes

Can a thing resonate whilst exposed to white noise?

The thing will vibrate at all frequencies. It will vibrate more (be amplified) at frequencies that are close to a natural frequency. Effectively, the system will act as a band pass filter (NOT a band ...
Daniel K's user avatar
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3 votes
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Why is the spin velocity of a gear irrelevant if perfectly balanced?

This depends greatly on the context. Here is a counter-example, a situation in which the spin velocity of the gear is relevant to the dynamics of the overall system, even if that velocity is constant....
Daniel K's user avatar
  • 2,646
3 votes

Why is the spin velocity of a gear irrelevant if perfectly balanced?

If the gear is not balanced then the center of mass will oscillate as it spins which will induce additional load on the shaft and create vibrations. This effect greatly depends on the speed of the ...
ratchet freak's user avatar
3 votes
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How do I represent equations of motion of a dynamic system in State Space?

Karlo mentioned to use the state space of $[q,\dot{q}]^T$ this allows you to write the system as a first order differential equation of state space. If $X$ were the state space, you could write $\dot{...
Orion Yeung's user avatar
3 votes
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Is a 3 Hz beat frequency from my neighbor's HVAC a sign of a malfunction?

A 3Hz pulsating hum-- noise that is getting louder and softer at 3Hz. Yes, I agree that would be quite annoying. Since this is a residential unit in the US, both the compressor and the fan are run ...
user1683793's user avatar
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3 votes

Measuring motor vibrations

Typically, motor vibration analyses and monitoring are done in the frequency domain, taking the time data and processing it into the frequency domain via subsequent FFT's. Roughly speaking, the ...
DLS3141's user avatar
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3 votes
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What does multiplicity of a multiple natural frequency mean?

"Multiplicity" usually refers to several different modes with the same natural frequency. For example, ignoring any fault conditions and tolerances, if there are several identical planet gears, each ...
alephzero's user avatar
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