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It's amazing. There is a super easy criterion to know whether that can be useful. How many points can be plotted in a frequency range (Delta F) where Delta F is -3 dB frequency band around a peak ? Does this number depend on the peak frequency ? Does this number depend on sampling time (Delta...

It could be very useful in experimental modal analysis. Does the method work with short-duration time signal ?

Do you have Actran for Nastran ?

I have got the second edition of the book. The chapter 30 is "Theory of vibration isolation" and the equation is in the section "Rigidly connected coulomb damper"

The formula has been extracted from the "SHOCK AND VIBRATION HANDBOOK" from Harris & Crede, chapter 30.

Hi, So you need a formula between the two kind of damping... Et voila! ξfriction=(2η/π)2(1-ω2/ω02)2/(ω2/ω02[ω4/ω04-(4η/π)2])

Hi IRstuff, It's funny to read your sentense "Sounds like you should be talking to the manufacturer" for a non-native English speakers as me. You use the words "sounds" and "talking" (reminiscent of crosstalk) to say something which has nothing to do with sound and crosstalk. Freud would tell...

Wow, it's a subtle question. Suppose that Ai are the experimental mode shapes (a set of vector). Their amplitude can be very low. So the modal masses can also be very low. This is not good. When modal mass is normalized, something doesn't change : the Eigen frequency . Because an Eigen...

Why do you say that acoustic pressure is proportional to the plate displacement ? Plate Velocity = j * omega * Displacement From Acoustic point of view, Air Velocity is proportional to Delta Pressure / Delta X. Since there is equality between Acoustic Velocity and plate Velocity, we get that ...

What is the main difference between normal and complex modes ? The way the phase is taken into account. With normal modes, the phase exists, but it doesn't matter. Why ? Because the phase is either 0° or 180°. So the amplitude of the mode at each point is given by +something (0°) or -something...

Other standards : GAM EG13, STANAG 4370

When complex values appear, it means that damping is taken into account. Imaginary part of a complex eigenfrequency is related to damping value (damping loss factor). Imaginary part of a complex eigenvector means that mode is not normal (mode is not a stationary wave).

If this is an acoustic problem, then a nearing model could be the Helmholtz resonator with no neck...

Let's take an example. Let's suppose a beam, simply supported, length = L, etc.. Let's consider the 3 first modes (N=3) The modal response is something like this : P(x) = A1*sin(pi*x/L) + A2*sin(pi*2*x/L) + A3*sin(pi*3*x/L). (Sum of the 3 modes) You can imagine P(x) (for all x) as just 1 point...

You're not a gentleman. When you write some lousy messages, I say to myself : " This guy is just an idiot" but I don't write it to the entire community.

When doing modal analysis, you change of space. In modal analysis, the primary space is NOT the space-time. You have to have a little bit imagination. If you understand this, modal analysis will have no secret for you. In modal analysis, the space is NOT the 3d space. A point is NOT given by...

Greg, you annoy me with your "nonsense". Various methods of counting have been proposed in the literature, leading to different results and therefore (for some) to errors in the calculation of the fatigue lives. They are peak count, range-restricted peak count, level-restricted peak count...

You have to get first a time signal of your random vibration input spectrum. Then you need an algorithm to count every time the signal passes through zero. Divide the number, given by your counter, by 2 to get the number of cycles.

One word about "tapered peak". As you can see, tapering decreases with peak number. It means that the damping is certainly viscous or hysteretic. You can try to verify for each peak if (Delta f)/f = Constant ( where f is the frequency of the peak and Delta f is the passband located at...

The question is more complex than one might think. First, you have to know if you work with a random or a deterministic signal. For random signal, things are complicated... Listen to me very well, it's very important : We can say nothing about ONE random signal!! This is perfectly...