Menu

Discussion Forum

New Discussion
Filtrer

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

pressure wave generation due to thermal expansion in fluid

Posted 26 avr. 2015, 17:11 UTC−4 Structural Mechanics Version 5.0 5 Replies

Yuankang Lu
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hi all,

I'm a beginner of COMSOL, and I m working on a laser-ultrasonic model. But I have encountered a problem and hope someone can help ;)

My model is relatively simple. a small block of metal is immerged in water and a laser is used to heat this metal. The metal will go through an thermo expansion because of the laser heating and generate pressure wave in water.

I split the model in two parts. In the first part, I use the module " Thermal stress" to simulate the thermal expansion of the metal. In the second part, I use an acoustic module "acoustic-solid interaction " to simulate the pressure wave generation and propagation in water.

The output of the first part, Thermal Stress, is displacement, while the input (or boundary conditions) of acoustic model is always pressure. I have some difficulty in setting the boundary conditions for the second part of my simulation.

Does anybody have some ideas? Any suggestions are welcomed ;) Thx
5 Replies Last Post 24 nov. 2015, 22:17 UTC−5
COMSOL Moderator

Hello Yuankang Lu

Your Discussion has gone 30 days without a reply. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help.

If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base.

Rijil Thomas
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 9 years ago 24 nov. 2015, 06:36 UTC−5
Hi,
May I ask, were you able to solve this problem? Even I have a similar problem and I wish to know how did you manage to solve it?
Especially, the boundary conditions you used for the first part to find displacement field.
Hi, May I ask, were you able to solve this problem? Even I have a similar problem and I wish to know how did you manage to solve it? Especially, the boundary conditions you used for the first part to find displacement field.
Nagi Elabbasi Facebook Reality Labs
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 9 years ago 24 nov. 2015, 12:35 UTC−5
Hi Rijil,

That’s an interesting problem. Thermal expansion (and heating) is usually slow enough that it does not create a significant pressure wave in a surrounding fluid.

Nagi Elabbasi
Veryst Engineering
Hi Rijil, That’s an interesting problem. Thermal expansion (and heating) is usually slow enough that it does not create a significant pressure wave in a surrounding fluid. Nagi Elabbasi Veryst Engineering
Rijil Thomas
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 9 years ago 24 nov. 2015, 13:11 UTC−5
Hi Nagi,
Correct me if I am wrong.
Isn't the same principle of heating and thermal expansion that is being obeyed in photoacoustics?
According to photoacoustics, from what I read, a sudden heating due to a very short laser pulse will cause heating and expansion producing pressure to surrounding medium.
Hi Nagi, Correct me if I am wrong. Isn't the same principle of heating and thermal expansion that is being obeyed in photoacoustics? According to photoacoustics, from what I read, a sudden heating due to a very short laser pulse will cause heating and expansion producing pressure to surrounding medium.
Nagi Elabbasi Facebook Reality Labs
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 9 years ago 24 nov. 2015, 13:57 UTC−5
Thanks Rijil, you are right. I was not aware of applications involving such a fast rate of change in temperature! So, going back to the original questions. The thermal boundary conditions for the thermal-structural part should in my opinion be a boundary heat flux (spatially varying if necessary) on the surface where the laser is applied to the metal. The structural boundary conditions depend on how the block is held in place. The surface of the solid block should be automatically detected by COMSOL as a shared structural-acoustic boundary. Therefore, COMSOL will set up the correct interface conditions relating water pressure to displacements/velocities/accelerations of the metal block. Depending on the geometry/loading/material properties there may be substantial heating of the water as well, in which case you need a thermoacoustic model of the water as well. COMSOL should again handle the thermal interface conditions between block and water. There is a good COMSOL Model Gallery example called “Photoacoustic Resonator” that you have probably seen already. It has some good details.

Good luck.

Nagi Elabbasi
Veryst Engineering
Thanks Rijil, you are right. I was not aware of applications involving such a fast rate of change in temperature! So, going back to the original questions. The thermal boundary conditions for the thermal-structural part should in my opinion be a boundary heat flux (spatially varying if necessary) on the surface where the laser is applied to the metal. The structural boundary conditions depend on how the block is held in place. The surface of the solid block should be automatically detected by COMSOL as a shared structural-acoustic boundary. Therefore, COMSOL will set up the correct interface conditions relating water pressure to displacements/velocities/accelerations of the metal block. Depending on the geometry/loading/material properties there may be substantial heating of the water as well, in which case you need a thermoacoustic model of the water as well. COMSOL should again handle the thermal interface conditions between block and water. There is a good COMSOL Model Gallery example called “Photoacoustic Resonator” that you have probably seen already. It has some good details. Good luck. Nagi Elabbasi Veryst Engineering
Rijil Thomas
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 9 years ago 24 nov. 2015, 22:17 UTC−5
Thank you Nagi for your response.
Can I clarify few more things?
In my case, it is a nanoparticle suspended in a medium. And I know the heat absorbed by the particle. So I modeled the particle in heat transfer physics as a heat source (W/m^3). Do I also need to give the heat flux which is in W/m^2 ? If so, how to convert heat source to heat flux?
Furthermore, it is suspended freely in medium. So how will the structural boundary condition be?
Thank you Nagi for your response. Can I clarify few more things? In my case, it is a nanoparticle suspended in a medium. And I know the heat absorbed by the particle. So I modeled the particle in heat transfer physics as a heat source (W/m^3). Do I also need to give the heat flux which is in W/m^2 ? If so, how to convert heat source to heat flux? Furthermore, it is suspended freely in medium. So how will the structural boundary condition be?

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content