Friction In TimeDependent, Modal Studies

Fatemeh Delzendehrooy

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Hello,

I want to simulate a phononic metamatreial and I want to include the friction in my simualtion. Based on previous discussions I learned that friction cannot be integrated into Frequncy Domain study due to its nonlinear nature which cannot be captured in linear harmonic study. It was suggested to use time dependent. My target is to get tranmission loss vs frequncy. So my question is that can I use time-dependent modal study to integrate the nonlinear nature of friction or I should use general time-dependent study. In latter case, should I get the input/output displacmeemnt at probes for each frequncy to get the transmission loss? Is this simulation reliable?

Cheers


2 Replies Last Post 15.07.2024, 12:11 GMT-4
Henrik Sönnerlind COMSOL Employee

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Posted: 4 days ago 11.07.2024, 12:12 GMT-4
Updated: 4 days ago 12.07.2024, 02:29 GMT-4

You cannot have nonlinearities in a modal study, so you must use a standard Time Dependent study.

This kind of analysis, where you are forced to run periodic problems in time domain is computationally very expensive. For each frequency, you must time-step many periods until you reach a stabilized solution that is independent of the initial conditions.

You can get some improvement by trying approximate the initial conditions using a linear frequency domain study.

As an inspiration, take a look at this example:

https://www.comsol.com/model/download/1254561/bracket_general_periodic.pdf
https://www.comsol.com/model/download/1254561/bracket_general_periodic.mph

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Henrik Sönnerlind
COMSOL
You cannot have nonlinearities in a modal study, so you must use a standard Time Dependent study. This kind of analysis, where you are forced to run periodic problems in time domain is computationally very expensive. For each frequency, you must time-step many periods until you reach a stabilized solution that is independent of the initial conditions. You can get some improvement by trying approximate the initial conditions using a linear frequency domain study. As an inspiration, take a look at this example:

Fatemeh Delzendehrooy

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Posted: 6 hours ago 15.07.2024, 12:11 GMT-4

Thank you very much Henrik,

Im not clear about the initial conditions using a linear frequency domain study. Do you mean I need to find the band gaps from freuncy domain and just consider them? Im also using parameteric sweep to repeat the simulation for couple of frequncies. Also, Im running simulation for 2D problem using Time dependent and simplify the model as simple as possible for just one unit cell, but after one day it was progressoed for 7%. To capture the contact I refined my mesh as much as possible and reduced time step. I used columb friction and applied a sinosouidal displacement. Otherwise it cannot capture the contact. I can see that reciprocal of step size convergance graph remained constant and didnt changed. Hence, I guess that simulation is correct but only requires imporvement of solver configuration.

Thank you!

Thank you very much Henrik, Im not clear about the initial conditions using a linear frequency domain study. Do you mean I need to find the band gaps from freuncy domain and just consider them? Im also using parameteric sweep to repeat the simulation for couple of frequncies. Also, Im running simulation for 2D problem using Time dependent and simplify the model as simple as possible for just one unit cell, but after one day it was progressoed for 7%. To capture the contact I refined my mesh as much as possible and reduced time step. I used columb friction and applied a sinosouidal displacement. Otherwise it cannot capture the contact. I can see that reciprocal of step size convergance graph remained constant and didnt changed. Hence, I guess that simulation is correct but only requires imporvement of solver configuration. Thank you!

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