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Computing Volume of a Cavity
Posted Dec 29, 2020, 8:22 a.m. EST Structural & Acoustics, General, Bioengineering Version 5.4 6 Replies
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I am currently working on mechanical modeling of the heart; in my simulation I need to compute the volume change of the left cavity under applying a pressure load to it. I know that for such a purpose I should use the integral operator in the definition tab under component coupling. I used this operator and selected the boundaries that I wanted to be integrated, as shown in the picture(intop1) that I attached here, after that I defined a variable named (LV_Volume) and used the operator intop1 to evaluate the volume as shown in the picture (Variable_LV_Volume) that I attached, but the variable computes the surface area not the volume of the boundary. What expression should I use for the intop1 operator to compute the Volume of the boundary? Thank you in advance for any help that might be provided by anyone.
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Caveat: I'm just making a wild guess here, and your model may have other issues, but... In regard to Intop1, where it says Geometric entity level, I see that you have selected Boundary. Consider clicking the little down arrow there and choose Domain instead. And then select the appropriate domain(s), which in a 3D problem, are generally volume(s). Good luck.
-------------------Scientific Applications & Research Associates (SARA) Inc.
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Caveat: I'm just making a wild guess here, and your model may have other issues, but... In regard to Intop1, where it says Geometric entity level, I see that you have selected Boundary. Consider clicking the little down arrow there and choose Domain instead. And then select the appropriate domain(s), which in a 3D problem, are generally volume(s). Good luck.
Dear Dr. Koslover,
Thank you for responding to my question. Unfortunately, the part that I want to compute the volume is boundary and if I specify Geometry Entity Level as domain the interested parts cannot be selected. Also, in regard to your Caveat what do you mean by other issues in my model?
I am new in COMSOL and appreciate any help,
Thank you
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You might want to upload your model to the forum. If you cannot select the domain(s) for which you want to compute the volume, then this hints to me that you have created a surface model, not a a volume model. I'm an RF guy and I don't really know anything about how to model a heart, but it seems strange to me that you wouldn't include the enclosed volume as part of your computational domain. Did you exclude it by accident? Are you, perhaps, trying to model the heart without including any of the blood within it? Even so, it should have a thickness to it. If your model includes surfaces but no domains, then you have not defined your geometry properly. Hmm. By some chance, did you create your geometry with a different tool and then import it into Comsol Multiphysics? If so, the format and import process could have thrown away your volumes and left only surfaces. And that would be a problem. But I'm just guessing, so I suggest you upload your model to the forum so others can take a look at it.
-------------------Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
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Bottom line: an open surface does not define a volume. A closed one does and that volume can be computed by a surface integral via Gauss's theorem (a.k.a. the divergence theorem). You can go that route if you first ensure your cavity forms a closed boundary; this does not seem to be currently the case judging by the screenshot you attached earlier.
Jeff
-------------------Jeff Hiller
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You might want to upload your model to the forum. If you cannot select the domain(s) for which you want to compute the volume, then this hints to me that you have created a surface model, not a a volume model. I'm an RF guy and I don't really know anything about how to model a heart, but it seems strange to me that you wouldn't include the enclosed volume as part of your computational domain. Did you exclude it by accident? Are you, perhaps, trying to model the heart without including any of the blood within it? Even so, it should have a thickness to it. If your model includes surfaces but no domains, then you have not defined your geometry properly. Hmm. By some chance, did you create your geometry with a different tool and then import it into Comsol Multiphysics? If so, the format and import process could have thrown away your volumes and left only surfaces. And that would be a problem. But I'm just guessing, so I suggest you upload your model to the forum so others can take a look at it.
My geometry has one domain and that is the whole geometry, I have created the geometry from medical images in a software named MIMICS and then imported the IGES format of the geometry to COMSOL Multiphysics. As you can see from the picture (Geometry) that is attached, my model has volume and it is not a surface model. I am trying to model the heart without including any of the blood within it and the effect of the blood is considered by a time varying pressure load over the cavities.
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Bottom line: an open surface does not define a volume. A closed one does and that volume can be computed by a surface integral via Gauss's theorem.
Jeff
via Gauss's theorem.
Dear jeff
In this book https://link.springer.com/book/10.1007/978-3-642-54801-7 in Chapter 8 Problems, mentioned an expression for surface integral via Gauss's theorem that computes the volume of cavity boundaries for a 2-Dimensional axisymmetric geometry in COMSOL Multiphysics but in my case the geometry is 3-Dimensional and that expression doesn’t work.
Is there any other way that I can compute the volume of the cavity?
Thank you