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How can I render a boundary acoustically invisible?

Posted Jan 31, 2020, 3:34 p.m. EST Acoustics & Vibrations Version 5.4 13 Replies

Mark Magro
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I have setup a geometry on comsol to investigate the transient behaviour of waves incident to it. I have modelled this by importing the geometry to comsol, surrounding it by a sphere and inserted a block to use as a plane wave radiation source that will be incident to one of the boundaries of the imported geometry.

I have set the boundaries of the geometry imported to sound hard, the sphere to exterior field calculation (which I think is the new name for perfectly matched layer) to avoid reflections. Set on of the boundaries of the block to plane wave radiation incident to the geometry opening.

The geometry opening consists of boundaries which I have assigned to sound soft boundary. Now the problem is that sound soft boundary reduces all incident pressure to 0 so I am never getting waves to enter the geometry. What boundary condtion should I assigned to this boundary in order to get waves to enter the imported geometry?

I have attached the project in order to understand better what I am talking about.

13 Replies Last Post Feb 3, 2020, 4:14 p.m. EST
Edgar J. Kaiser Certified Consultant
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Posted: 5 years ago Feb 1, 2020, 4:13 a.m. EST

Mark,

I guess no specific BC are required. Just assign suitable material properties and COMSOL will take care of continuity.

Cheers Edgar

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Mark, I guess no specific BC are required. Just assign suitable material properties and COMSOL will take care of continuity. Cheers Edgar
Mark Magro
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Posted: 5 years ago Feb 3, 2020, 1:08 a.m. EST

Hi, thank you for you reply. The thing is that when I added the physics (Pressure Acoustics, Transient), the boundaries I mentioned are assigned to sound hard boundaries by default and COMSOL does not let me disassign this boundary condition (remove form selectio button is greyed out). The only way I could remove it from sound hard boundary is by assigned it to another boundary type.

Hi, thank you for you reply. The thing is that when I added the physics (Pressure Acoustics, Transient), the boundaries I mentioned are assigned to sound hard boundaries by default and COMSOL does not let me disassign this boundary condition (remove form selectio button is greyed out). The only way I could remove it from sound hard boundary is by assigned it to another boundary type.
Edgar J. Kaiser Certified Consultant
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Posted: 5 years ago Feb 3, 2020, 3:59 a.m. EST

Something might be wrong in the geometry sequence or not everything is included in the physics. Difficult to say without seeing the model.

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Something might be wrong in the geometry sequence or not everything is included in the physics. Difficult to say without seeing the model.
Mark Magro
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Posted: 5 years ago Feb 3, 2020, 5:53 a.m. EST
Updated: 5 years ago Feb 3, 2020, 10:44 a.m. EST

Hi, I have attached it.

Hi, I have attached it.
Edgar J. Kaiser Certified Consultant
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Posted: 5 years ago Feb 3, 2020, 7:55 a.m. EST

Please attach an .mph file. I don't have the time to assemble 10 archives!

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Please attach an .mph file. I don't have the time to assemble 10 archives!
Mark Magro
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Posted: 5 years ago Feb 3, 2020, 7:58 a.m. EST

You only have to extract one file only by putting all files in the same folder... I couldn't upload the .mph file as it is larger the 5mb.

You only have to extract one file only by putting all files in the same folder... I couldn't upload the .mph file as it is larger the 5mb.
Edgar J. Kaiser Certified Consultant
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Posted: 5 years ago Feb 3, 2020, 8:05 a.m. EST

You can clear solutions and mesh.

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
You can clear solutions and mesh.
Mark Magro
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Posted: 5 years ago Feb 3, 2020, 8:36 a.m. EST
Updated: 5 years ago Feb 3, 2020, 4:15 p.m. EST

You are right. Totally forgot about that.

You are right. Totally forgot about that.
Edgar J. Kaiser Certified Consultant
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Posted: 5 years ago Feb 3, 2020, 12:04 p.m. EST

Mark,

only the spherical domain is included in Pressure Acoustics. Add all domains and those inner boundaries on the geometry import get continuous.

Cheers Edgar

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Mark, only the spherical domain is included in Pressure Acoustics. Add all domains and those inner boundaries on the geometry import get continuous. Cheers Edgar
Mark Magro
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Posted: 5 years ago Feb 3, 2020, 3:00 p.m. EST

Hi Edgar,

That seems to help but I am still struggling in getting the two geometires to interact.

I basically need to define the boundaries were continutity occurs. Do I need to set up boundary paris? How is that done?

Mark

Hi Edgar, That seems to help but I am still struggling in getting the two geometires to interact. I basically need to define the boundaries were continutity occurs. Do I need to set up boundary paris? How is that done? Mark
Edgar J. Kaiser Certified Consultant
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Posted: 5 years ago Feb 3, 2020, 3:19 p.m. EST

You shouldn't need pairs because the geometry is a union. You have to skip those internal sound soft boundaries of course.

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
You shouldn't need pairs because the geometry is a union. You have to skip those internal sound soft boundaries of course.
Mark Magro
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Posted: 5 years ago Feb 3, 2020, 4:02 p.m. EST

Hi Edgar,

I think I managed to model it as I needed.

I used an identity pair which paired the boundary at the interface to all the other boundaries.

I set up an interior sound hard boundary. I selected the rest (i.e. excluding the interface) of the internal geometry boundaries.

That did the trick.

Thanks for your help

Mark

Hi Edgar, I think I managed to model it as I needed. I used an identity pair which paired the boundary at the interface to all the other boundaries. I set up an interior sound hard boundary. I selected the rest (i.e. excluding the interface) of the internal geometry boundaries. That did the trick. Thanks for your help Mark
Edgar J. Kaiser Certified Consultant
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Posted: 5 years ago Feb 3, 2020, 4:14 p.m. EST

You are welcome.

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
You are welcome.

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