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Solving Helmholtz Equation in 2 Domains

Posted 8 janv. 2021, 06:18 UTC−5 Modeling Tools & Definitions, Studies & Solvers, Equation-Based Modeling Version 5.5 4 Replies

Oran Meir
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Hello all, I'm trying to simulate Light-Tissue Interaction by solving the RTE in the Diffusion Approx. The stationary form it takes is similar to the Helmholtz Equation. I've managed to get excellent results for a homogenous 3D block with isotropic optical properties. Now I'm trying to simulate 2 layers of material with different (still isotropic) optical properties. The solution propegates nicely in the first layer, but isn't going throguh to the second layer. My method: Setting up a 3D block with 2 layer Setting the Helmholtz Eq. for each layer with different coefficients. As can bee seen in the photos attached, the fluence doesn't go to the second domain.

I would appreciate some help, Oran

4 Replies Last Post 28 juin 2021, 04:40 UTC−4
Robert Koslover Certified Consultant
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Posted: 5 years ago 8 janv. 2021, 22:15 UTC−5

The pictures are a start, but I suggest you post your .mph file to the forum. I think that will make it easier for anyone here who wants to help to figure out what is really going on in your model.

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Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
The pictures are a start, but I suggest you post your .mph file to the forum. I think that will make it easier for anyone here who wants to help to figure out what is really going on in your model.
Oran Meir
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Posted: 5 years ago 29 janv. 2021, 05:04 UTC−5

SOLVED

The issue was I had to define Dirichlet BC as a Continuity condition at the domains interface. Without it the second equatuin didn't have any values to calculate.

Best regards, Oran

SOLVED The issue was I had to define Dirichlet BC as a Continuity condition at the domains interface. Without it the second equatuin didn't have any values to calculate. Best regards, Oran
Chironjeet Chaki
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Posted: 4 years ago 27 juin 2021, 00:15 UTC−4
Updated: 4 years ago 27 juin 2021, 00:16 UTC−4

Hi Oran, May I know how did you apply Dirichlet BC as a Continuity condition at the domains interface? A snapshot would be really helpful for me in the comsol setting. I'm doing the similar thing. Hope you help me.

Thanks a lot...

Hi Oran, May I know how did you apply Dirichlet BC as a Continuity condition at the domains interface? A snapshot would be really helpful for me in the comsol setting. I'm doing the similar thing. Hope you help me. Thanks a lot...
Oran Meir
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Posted: 4 years ago 28 juin 2021, 04:40 UTC−4

Hi Oran, May I know how did you apply Dirichlet BC as a Continuity condition at the domains interface? A snapshot would be really helpful for me in the comsol setting. I'm doing the similar thing. Hope you help me.

Thanks a lot...

Hi Chaki,

There's 2 options to solve this issue:

1) Define 2 Helmholtz equations within the same component. assuming your variable us , then in the second equation u define Dirichlet BC with prescribed value of . what happens is that it will take the value obatined from the first equation and apply it as continuity. unfortunately I did not use this method so I don't have pictures for you. 2) Using only 1 Helmholtz equation, you can define its parameters as variables. What I did is to define and as a step function that varies in the theoretical boundary, without actualy define a geometric doundary. that solver will handle it.

I hope you will find this helpful

>Hi Oran, >May I know how did you apply Dirichlet BC as a Continuity condition at the domains interface? A snapshot would be really helpful for me in the comsol setting. I'm doing the similar thing. Hope you help me. > >Thanks a lot... Hi Chaki, There's 2 options to solve this issue: 1) Define 2 Helmholtz equations within the same component. assuming your variable us u, then in the second equation u define Dirichlet BC with prescribed value of u. what happens is that it will take the value obatined from the first equation and apply it as continuity. unfortunately I did not use this method so I don't have pictures for you. 2) Using only 1 Helmholtz equation, you can define its parameters as variables. What I did is to define \mu_{a} and D as a step function that varies in the theoretical boundary, without actualy define a geometric doundary. that solver will handle it. I hope you will find this helpful

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