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The transfer function of a impulse response

Posted 20 ott 2013, 09:17 GMT-4 Structural Mechanics Version 4.3b 10 Replies

Wang Qiang
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Hi all:
My problem as bellows:
1.A cantilever plate: the length 300mm, the width 200mm, the thickness 6mm; the clamped end
dimension : the length 60mm, the width 50mm, the thickness 6mm.(see Fig 1)
2. The Young’s modulus 56e9 Pa, the Poisson’s ration 0.3, the density 2646kg/m^3,the dampng parameter,Rayleigh damping,the mass damping parameter 300[1/s], the Stiffness damping parameter 3.2e-5[s] .
3. Simulation the transfer function in the frequency domain, giving a hammer impact force 100N to the
point 5, getting the acceleration response in the point 2. (See Fig 2)
How to get?
Details see the attchment!
For tips and ideas, I would be very grateful!
10 Replies Last Post 21 nov 2013, 21:34 GMT-5
Wang Qiang
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Posted: 1 decade ago 20 ott 2013, 20:35 GMT-4
Hi:
get some answers from the forum but I can not get final correct result. My process as follows:
1. First give step function;
2. Study in the time dependent;
How to do in the next step, I don’t know?
Can you please help me with this problem.
Thank you!
Hi: get some answers from the forum but I can not get final correct result. My process as follows: 1. First give step function; 2. Study in the time dependent; How to do in the next step, I don’t know? Can you please help me with this problem. Thank you!
Wang Qiang
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Posted: 1 decade ago 20 ott 2013, 22:27 GMT-4
Hi:
the transfer function should be X"/F solution in the frequency domain, to determine the frequency response function , However, how to get acceleration response of the frequency domain in output point and the force response of the frequency domain in the input point?
I really appreciate if you help me with this issue which has really killed me in past days.
Regards,
Hi: the transfer function should be X"/F solution in the frequency domain, to determine the frequency response function , However, how to get acceleration response of the frequency domain in output point and the force response of the frequency domain in the input point? I really appreciate if you help me with this issue which has really killed me in past days. Regards,
Wang Qiang
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Posted: 1 decade ago 22 ott 2013, 00:51 GMT-4
Hi:
This quension has troubled me some days,1 hope some one give me some advises.I made some work, but how to do in the next step, I dont know.
Thank you very much!
Hi: This quension has troubled me some days,1 hope some one give me some advises.I made some work, but how to do in the next step, I dont know. Thank you very much!
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago 23 ott 2013, 09:35 GMT-4
Dear Wang,

A frequency domain analysis (instead of the time dependent analysis) is best suited for getting the transfer functions that you need. Check out the COMSOL documentation and examples for more details.

Nagi Elabbasi
Veryst Engineering
Dear Wang, A frequency domain analysis (instead of the time dependent analysis) is best suited for getting the transfer functions that you need. Check out the COMSOL documentation and examples for more details. Nagi Elabbasi Veryst Engineering
Wang Qiang
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Posted: 1 decade ago 24 ott 2013, 10:07 GMT-4
Dear:Nagi Elabbasi
First, thank you very much for your reply! I take this case into account in a frequency domain analysis, but how to apply an impulse force in the frequency domain. The applied force should be as harmonic excitation in the frequency domain under normal conditions. The impulse force is not the harmonic excitation. If this structure is subjected to the harmonic excitation, so the transfer functions is easy to get, however it is not.
Hope that I get your detailed advises, thank you!
Dear:Nagi Elabbasi First, thank you very much for your reply! I take this case into account in a frequency domain analysis, but how to apply an impulse force in the frequency domain. The applied force should be as harmonic excitation in the frequency domain under normal conditions. The impulse force is not the harmonic excitation. If this structure is subjected to the harmonic excitation, so the transfer functions is easy to get, however it is not. Hope that I get your detailed advises, thank you!
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago 24 ott 2013, 13:51 GMT-4
Dear Wang,

You're welcome! You should multiply the harmonic response predicted from COMSOL with the Laplace transform of your impulse function.

Nagi Elabbasi
Veryst Engineering
Dear Wang, You're welcome! You should multiply the harmonic response predicted from COMSOL with the Laplace transform of your impulse function. Nagi Elabbasi Veryst Engineering
Wang Qiang
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Posted: 1 decade ago 25 ott 2013, 04:13 GMT-4
Dear:Nagi Elabbasi
Than you for your help!
How to carry out it in the COMSOL? It is best, if you give me some detailed steps. It may take you some time.
Thank you in advance!
Yours
Wang Qiang
Dear:Nagi Elabbasi Than you for your help! How to carry out it in the COMSOL? It is best, if you give me some detailed steps. It may take you some time. Thank you in advance! Yours Wang Qiang
Wang Qiang
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Posted: 1 decade ago 21 nov 2013, 08:15 GMT-5
Dear Nagi Elabbasi
I attach my module structural. Hope that getting your help.
If giving a sine sweep in the point 1, we get responsive acceleration in the point 2.
How to get frequency response function in point 1 and point 2?
Thanks in advance!
Dear Nagi Elabbasi I attach my module structural. Hope that getting your help. If giving a sine sweep in the point 1, we get responsive acceleration in the point 2. How to get frequency response function in point 1 and point 2? Thanks in advance!
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago 21 nov 2013, 13:30 GMT-5
Dear Wang,

Create a 1D Plot and add Point Graphs for the quantities you want to see. COMSOL should give you a plot of those quantities vs. frequency.

Nagi Elabbasi
Veryst Engineering
Dear Wang, Create a 1D Plot and add Point Graphs for the quantities you want to see. COMSOL should give you a plot of those quantities vs. frequency. Nagi Elabbasi Veryst Engineering
Wang Qiang
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Posted: 1 decade ago 21 nov 2013, 21:34 GMT-5
Dear Nagi Elabbasi
I am very grateful for you reply my question.
Now I give point 1 a sine sweep force F=1N, in the frequency domain, and get the acceleration response (m^2/s) in the point 2. In the theory, the frequency response function (g/N vs. frequency) is got by x..(omega)/F(omega).
In the results, I select the 1D plot , and right click select the point graph.
In the data, selection point 2, in the y-axis data, type solid.u_ttZ, so I get the curve of m^2/s vs. frequency.
Is this curve the frequency response function that I want?
If I give point 1 a sine sweep force F=8N, so the the frequency response function (g/N vs. frequency) is got by x..(omega)/8.
I am not sure.
How to get frequency response function under impulse excitation in point 1?
Please accept my heartfelt thanks and deepest gratitude!
Dear Nagi Elabbasi I am very grateful for you reply my question. Now I give point 1 a sine sweep force F=1N, in the frequency domain, and get the acceleration response (m^2/s) in the point 2. In the theory, the frequency response function (g/N vs. frequency) is got by x..(omega)/F(omega). In the results, I select the 1D plot , and right click select the point graph. In the data, selection point 2, in the y-axis data, type solid.u_ttZ, so I get the curve of m^2/s vs. frequency. Is this curve the frequency response function that I want? If I give point 1 a sine sweep force F=8N, so the the frequency response function (g/N vs. frequency) is got by x..(omega)/8. I am not sure. How to get frequency response function under impulse excitation in point 1? Please accept my heartfelt thanks and deepest gratitude!

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