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Heat transfer and frequency sweep

Posted 31.08.2011, 19:41 GMT-4 Heat Transfer & Phase Change, Studies & Solvers, Structural Mechanics Version 4.1, Version 4.2 3 Replies

Kamala McNaul
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I would like to do something that I think is very simple.

I would like to see the effects of a boundary heat source on the resonant frequency of a device. It seems like I should be able to run a study with two steps - one to apply the heat source, and then a frequency domain sweep to see if the peak has shifted. It seems so straightforward, but I keep getting error messages... Failed to find a solution for the initial parameter. Singular matrix. There are X number of void equations.

Any ideas? Does anyone have a model that does this? Not sure where I'm going wrong. Thanks!
3 Replies Last Post 06.09.2011, 02:02 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 02.09.2011, 15:39 GMT-4
Hi

the singular matrix error means mostly that you do not have enough BC to fully define your model. when you add multiple physics you need to ensure that EACh physics have enough BCs.

Take a careful look, normally if you define the initial temperature as T and drive T with a parametrical sweep , I believe this should work. You might need to combine a stationary solver to perform the thermal case, ad than follow up, using previous solution as initial conditions with a frequency sweep (or a times series whatever you need)

--
Good luck
Ivar
Hi the singular matrix error means mostly that you do not have enough BC to fully define your model. when you add multiple physics you need to ensure that EACh physics have enough BCs. Take a careful look, normally if you define the initial temperature as T and drive T with a parametrical sweep , I believe this should work. You might need to combine a stationary solver to perform the thermal case, ad than follow up, using previous solution as initial conditions with a frequency sweep (or a times series whatever you need) -- Good luck Ivar
Kamala McNaul
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Posted: 1 decade ago 03.09.2011, 20:05 GMT-4
Hi Ivar-

You were right. I was missing a boundary condition. Thanks for the tip.

I still don't see any effect on the second study step, the frequency domain, from the first step, the stationary solver for the thermal case - I've set the initial values on the second step to be the solution from the first step, but it doesn't seem to be working. Is there a trick I'm missing? How can I get the temperature/stress from the first step to affect the frequency in the piezoelectric physics?
Hi Ivar- You were right. I was missing a boundary condition. Thanks for the tip. I still don't see any effect on the second study step, the frequency domain, from the first step, the stationary solver for the thermal case - I've set the initial values on the second step to be the solution from the first step, but it doesn't seem to be working. Is there a trick I'm missing? How can I get the temperature/stress from the first step to affect the frequency in the piezoelectric physics?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 06.09.2011, 02:02 GMT-4
Hi
there are two conditions

1) as you said that the second solver is reading the initial values from the first one (check again the "dependent variables tab of your second solver, try to use the "stored" solution and be sure COMSOl has added a stored solution from the first solver ;)

2) that your physics is really using theinitial values from the first calculations, normally the initial stress should be used in structural, perhaps check what the structural initial condition BC is pointing to

--
Good luck
Ivar
Hi there are two conditions 1) as you said that the second solver is reading the initial values from the first one (check again the "dependent variables tab of your second solver, try to use the "stored" solution and be sure COMSOl has added a stored solution from the first solver ;) 2) that your physics is really using theinitial values from the first calculations, normally the initial stress should be used in structural, perhaps check what the structural initial condition BC is pointing to -- Good luck Ivar

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