resonance

[Guido]

Hello everyone,

I press that I am not a mechanical designer and not professionally use softwares fem.

I want to understand something.

If I perform a modal analysis of a simple structure such as a beam bound to an extreme I get the resonance frequencies, for example, from 1 to 20° with indication of the "displacement".

can you explain why the dispacement, which if I have not understood badly represents the "setting" remains +/- constant on all frequencies, 20° included?
should not be attenuated as you move away from 1st?

Sorry for the question, but I would like to understand what is the behaviour of a metal structure, solicited impulsively, as it moves away from the 1st resonance frequency.

Thank you

guide

 

[Matteo]

vibration modes are represented with normal movements.
a modal analysis does not have a "strengthening" (in fact they are called "their own ways" to vibrate): what you see in the representation of the movements is the "how" vibrates the system for a certain frequency, has no quantitative value.

ps: the modal analyses solve them with the sharp calculator (see profile) ?

 

[Guido]

Thank you, matteo.

If I wanted to simulate the behaviour of the usual beam that was pressed with different frequencies, how should I move?
I mean, if you want to check out the "thing."

greetings
guide

 

[volaff]

but the beam is loaded by a forceful or you want to study the "natural ways of vibrating" i.e. by imposing a small shift and seeing the resonance frequencies?

 

[Matteo]

Thank you, matteo.

If I wanted to simulate the behaviour of the usual beam that was pressed with different frequencies, how should I move?
I mean, if you want to check out the "thing."

greetings
guide

that is a "frequency response analysis" for the "mathematic" part I refer you to wikipedia (http://it.wikipedia.org/wiki/risposta_in_frequenza), for definition in fem environment depends on the software you use: I can give you a hand with prom (creosim), swx simulation or neinastran even though the basic concepts are always the same.

 

[Guido]

Thanks, guys.

In practice, I need to assess the extent of vibration (moving) if the beam is urged by an impulsive force, depending on whether it is exciting it at the 1st freq. resonance or ....for example 10°.

In fact, the test I did not provide for any force applied.

use fusion with solver neinastran, but they are really at first arms and I don't know how to set the possible force to apply.

if someone wanted to try, the beam consists of a square profile (boxed) 60x60mm with 3mm thickness and is 1000mm long. bound to an extreme and completely free to the extreme opposite. the impulsive force is applied on the free end in any direction (but not along the axis of the beam:smile.

from the modal analysis, I accidentally go, I found the first freq. at 55hz and the tenth at 1740hz (always random). I would now like to apply a force, for example, of 100n with freq. of 55hz and simulate the response of the beam in terms of displacement and then to 1740hz to make the same verification.

It is a purely educational exercise that has no practical purpose, at least in my case. Maybe someone can even tell me... look at the freq. of 55hz happens this and to 1740hz happens this other...." simply calculating or according to a rule known... but I do not know!

Thank you.

guide

 

[luigi.paiano]

If you have to do an impulsive analysis it is useless that you calculate ways because you should consider so many, you should face the problem with a direct resolver otherwise you would make excessive mistakes.
As for the practical part I honestly do not know how to do, but someone here will know how to use these methods (it seems to be called mewmark method).
Then why do you talk about impulsive force and say you turn on one frequency? with a nom pulse excited only one frequency, theoretically the excites all (in practice instead excited up to a f dependent from the uphill time)

 

[Matteo]

Thanks, guys.

In practice, I need to assess the extent of vibration (moving) if the beam is urged by an impulsive force, depending on whether it is exciting it at the 1st freq. resonance or ....for example 10°.

In fact, the test I did not provide for any force applied.

use fusion with solver neinastran, but they are really at first arms and I don't know how to set the possible force to apply.

if someone wanted to try, the beam consists of a square profile (boxed) 60x60mm with 3mm thickness and is 1000mm long. bound to an extreme and completely free to the extreme opposite. the impulsive force is applied on the free end in any direction (but not along the axis of the beam:smile.

from the modal analysis, I accidentally go, I found the first freq. at 55hz and the tenth at 1740hz (always random). I would now like to apply a force, for example, of 100n with freq. of 55hz and simulate the response of the beam in terms of displacement and then to 1740hz to make the same verification.

It is a purely educational exercise that has no practical purpose, at least in my case. Maybe someone can even tell me... look at the freq. of 55hz happens this and to 1740hz happens this other...." simply calculating or according to a rule known... but I do not know!

Thank you.

guide

that unfortunately, I collaborated with a company that markets infusions (promising software) until 2 years ago, now for various reasons I no longer work on software products. if you can be useful we can compare the results obtained with other solutors: send me the "data" to this matteochiocciolacaedevice.net address, then we continue on the forum.