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Multiple Loads With Different Frequencies In Frequency Domain Study

Posted Aug 28, 2021, 7:25 a.m. EDT Acoustics & Vibrations, Studies & Solvers Version 5.6 8 Replies

Tommaso Botti
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Hi, I'm trying to evaluate the Transmission Loss on a glass panel when subjected to two different loads at the same time. In particular one is a boundary load representing an incident acoustic wave and has to be swept in frequency from 35 Hz to 4000 Hz; the other one is an edge load with a fixed frequency of 100 kHz that causes the propagation of a plane wave on the surface of the panel. I have to evaluate the Transmission Loss as a function of frequency (in the range 35-4000 Hz) considering both loads. To do so I have to perform a frequency domain study but the problem is that I want to vary the frequency of the boundary load only (from 35 Hz to 4000 Hz), while I want to keep the frequency of the edge load fixed at 100 kHz and consider both their contributions. Does anyone know a way to do it?

Thank you in advance, Tommaso

8 Replies Last Post Sep 6, 2021, 12:40 p.m. EDT
Mark Cops Triton Systems, Inc.
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Posted: 3 years ago Aug 28, 2021, 8:34 p.m. EDT

For a linear system both loads can be simulated separately the system response can be appropriately summed.

For a linear system both loads can be simulated separately the system response can be appropriately summed.
Tommaso Botti
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Posted: 3 years ago Aug 29, 2021, 7:11 a.m. EDT

Thank you for your reply. The problem is that I have to keep the frequency of one load fixed to 100kHz. So if I do the two studies separately when I combine them the range from 35 to 4000Hz remains unchanged (this is the one due to the other load which varies in this range). How can I evaluate how the Transmission Loss changes in this range of interest (35-4000 Hz) due to the presence of the load at 100kHz together with the one with frequency from 35 to 4000Hz? Thank you,

Tommaso

Thank you for your reply. The problem is that I have to keep the frequency of one load fixed to 100kHz. So if I do the two studies separately when I combine them the range from 35 to 4000Hz remains unchanged (this is the one due to the other load which varies in this range). How can I evaluate how the Transmission Loss changes in this range of interest (35-4000 Hz) due to the presence of the load at 100kHz together with the one with frequency from 35 to 4000Hz? Thank you, Tommaso
Edgar J. Kaiser Certified Consultant
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Posted: 3 years ago Aug 29, 2021, 8:00 a.m. EDT

Tommaso,

the straigthforward move is to do a time dependent study. But that comes at a price because you need to resolve the 100 kHz wave in time and space and you need to run it long enough to see the dynamic steady state. Can the problem be reduced to 2D?

Cheers Edgar

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Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Tommaso, the straigthforward move is to do a time dependent study. But that comes at a price because you need to resolve the 100 kHz wave in time and space and you need to run it long enough to see the dynamic steady state. Can the problem be reduced to 2D? Cheers Edgar
Dave Greve
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Posted: 3 years ago Aug 29, 2021, 12:51 p.m. EDT

Unless there is a nonlinearity that leads to a failure of superposition, a time dependent analysis will lead to the same result as summing the two solutions- but at a considerable computational cost.

Now if superposition holds- summing the frequency dependent solutions is the way to go.

Unless there is a nonlinearity that leads to a failure of superposition, a time dependent analysis will lead to the same result as summing the two solutions- but at a considerable computational cost. Now if superposition holds- summing the frequency dependent solutions is the way to go.
Edgar J. Kaiser Certified Consultant
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Posted: 3 years ago Aug 29, 2021, 1:14 p.m. EDT
Updated: 3 years ago Aug 29, 2021, 1:17 p.m. EDT

Just wondering how you would do that practically in this case. The two signals are applied on different boundaries leading to totally different excitation modes. We need to assume that the 100 kHz excitation affects the lower frequency signal. That is actually what Tommaso wants to find out as I understand it.

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Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Just wondering how you would do that practically in this case. The two signals are applied on different boundaries leading to totally different excitation modes. We need to assume that the 100 kHz excitation affects the lower frequency signal. That is actually what Tommaso wants to find out as I understand it.
Dave Greve
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Posted: 3 years ago Aug 29, 2021, 2:03 p.m. EDT

The question is HOW the two waves interact. Suppose a lower-frequency wave has high amplitude and it deforms the plate signfiicantly. Then propagation of the higher-frequency wave will be different (and modulated by the low-frequency wave). But this probably requires a LOT of displacement, far more than is likely in most physical situations.

In the non-destructive testing world there are some researchers who use harmonic or mixing wave generation to detect cracks. In these case the cracks provide the nonlinear behavior that results in wave mixing.

In the absence of a nonlinear interaction (caused by large displacements, cracks, or other phenomena) the waves do not interact.

The question is HOW the two waves interact. Suppose a lower-frequency wave has high amplitude and it deforms the plate signfiicantly. Then propagation of the higher-frequency wave will be different (and modulated by the low-frequency wave). But this probably requires a LOT of displacement, far more than is likely in most physical situations. In the non-destructive testing world there are some researchers who use harmonic or mixing wave generation to detect cracks. In these case the cracks provide the nonlinear behavior that results in wave mixing. In the absence of a nonlinear interaction (caused by large displacements, cracks, or other phenomena) the waves do not interact.
Edgar J. Kaiser Certified Consultant
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Posted: 3 years ago Aug 29, 2021, 4:15 p.m. EDT

Well, I think Tommaso got a few hints to consider. It really depends on what this is about in detail.

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Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Well, I think Tommaso got a few hints to consider. It really depends on what this is about in detail.
Tommaso Botti
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Posted: 3 years ago Sep 6, 2021, 12:40 p.m. EDT

First of all thank you for your replies. I'm trying to do the superposition of effects by doing: -a frequency domain study at 100kHz with the edge load only - a frequency domain study in the range 35-4000Hz with only the boundary load My question is how can I sum the responses properly in Comsol?

First of all thank you for your replies. I'm trying to do the superposition of effects by doing: -a frequency domain study at 100kHz with the edge load only - a frequency domain study in the range 35-4000Hz with only the boundary load My question is how can I sum the responses properly in Comsol?

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