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How to set a material's density is anisotropic ?

Posted 26 mar 2012, 10:04 GMT-4 Acoustics & Vibrations, Materials Version 4.2, Version 4.2a 11 Replies

Jiajun Ji
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hi, I'm new in comsol
I'm trying to define a material ,but its density is anisotropic , I don't know how to do with it.
could anybody please help me with this?
11 Replies Last Post 20 gen 2015, 01:47 GMT-5
Jaap Verheggen
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Posted: 1 decade ago 26 mar 2012, 11:00 GMT-4
What do you mean with density anisotropic?
Does it vary with location, thickness, ...
What do you mean with density anisotropic? Does it vary with location, thickness, ...
Edgar Kaiser
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Posted: 1 decade ago 26 mar 2012, 11:42 GMT-4
Normally you talk about anisotropy in case directions are involved. E.g. anisotropic Youngs Modulus. This could be expressed by matrices or tensors.
You probably mean non-uniform density. In this case you need to find a function that describes the density, probably as a function of location in space, find a suitable coordinate system and use this function as your expression for the density in the domain of interest.

Cheers
Edgar
Normally you talk about anisotropy in case directions are involved. E.g. anisotropic Youngs Modulus. This could be expressed by matrices or tensors. You probably mean non-uniform density. In this case you need to find a function that describes the density, probably as a function of location in space, find a suitable coordinate system and use this function as your expression for the density in the domain of interest. Cheers Edgar
Jiajun Ji
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Posted: 1 decade ago 27 mar 2012, 05:17 GMT-4
it means that the material in different direction has different density
it means that the material in different direction has different density
Jiajun Ji
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Posted: 1 decade ago 27 mar 2012, 05:20 GMT-4

What do you mean with density anisotropic?
Does it vary with location, thickness, ...


it means density vary with direction
[QUOTE] What do you mean with density anisotropic? Does it vary with location, thickness, ... [/QUOTE] it means density vary with direction
Jiajun Ji
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Posted: 1 decade ago 27 mar 2012, 05:57 GMT-4

Normally you talk about anisotropy in case directions are involved. E.g. anisotropic Youngs Modulus. This could be expressed by matrices or tensors.
You probably mean non-uniform density. In this case you need to find a function that describes the density, probably as a function of location in space, find a suitable coordinate system and use this function as your expression for the density in the domain of interest.

Cheers
Edgar


I'm doing acoustic cloaking with comsol .I know that ρ in r-direction is r/(r-R) and ρ in φ-direction is (r-R)/r. I don't know how to set these two function in material density. could you help me with this?
[QUOTE] Normally you talk about anisotropy in case directions are involved. E.g. anisotropic Youngs Modulus. This could be expressed by matrices or tensors. You probably mean non-uniform density. In this case you need to find a function that describes the density, probably as a function of location in space, find a suitable coordinate system and use this function as your expression for the density in the domain of interest. Cheers Edgar [/QUOTE] I'm doing acoustic cloaking with comsol .I know that ρ in r-direction is r/(r-R) and ρ in φ-direction is (r-R)/r. I don't know how to set these two function in material density. could you help me with this?
Jaap Verheggen
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Posted: 1 decade ago 27 mar 2012, 06:55 GMT-4
I have difficulties understanding how a material can have a different density depending on the direction.
Does that mean it weighs different depending on how you hold it?

Location I understand, but not direction.
I have difficulties understanding how a material can have a different density depending on the direction. Does that mean it weighs different depending on how you hold it? Location I understand, but not direction.
Jiajun Ji
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Posted: 1 decade ago 27 mar 2012, 07:58 GMT-4

I have difficulties understanding how a material can have a different density depending on the direction.
Does that mean it weighs different depending on how you hold it?

Location I understand, but not direction.


I'm doing acoustic cloaking with comsol . It shows that density in r-direction is r/(r-R) and density in φ-direction is (r-R)/r. I don't know how to set these two function in material density.
[QUOTE] I have difficulties understanding how a material can have a different density depending on the direction. Does that mean it weighs different depending on how you hold it? Location I understand, but not direction. [/QUOTE] I'm doing acoustic cloaking with comsol . It shows that density in r-direction is r/(r-R) and density in φ-direction is (r-R)/r. I don't know how to set these two function in material density.

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Alireza Bayat
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Posted: 1 decade ago 19 apr 2012, 23:01 GMT-4
Did you get your answer?
Did you get your answer?
Edgar Kaiser
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Posted: 1 decade ago 20 apr 2012, 06:26 GMT-4

I think this citation shows how to define the local density as a function of r and phi. This is what you must implement in COMSOL. So the density is a function of location and the location is in turn a function of the coordinates r and phi.

I think this citation shows how to define the local density as a function of r and phi. This is what you must implement in COMSOL. So the density is a function of location and the location is in turn a function of the coordinates r and phi.
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago 20 apr 2012, 08:48 GMT-4
I am not familiar with cloaking, but it seems that the density you need is really anisotropic (different in different directions) and not just non-homogeneous (varies with locations). What you need for that is density implemented as a tensor instead of a scalar. I have not seen that implemented before for density, but this is how an anisotropic thermal expansion coefficient, or thermal conductivity are implemented. It can be done by modifying the inertia terms in the COMSOL equations. Very interesting!

Nagi Elabbasi
Veryst Engineering
I am not familiar with cloaking, but it seems that the density you need is really anisotropic (different in different directions) and not just non-homogeneous (varies with locations). What you need for that is density implemented as a tensor instead of a scalar. I have not seen that implemented before for density, but this is how an anisotropic thermal expansion coefficient, or thermal conductivity are implemented. It can be done by modifying the inertia terms in the COMSOL equations. Very interesting! Nagi Elabbasi Veryst Engineering
Ravi Masna
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Posted: 9 years ago 20 gen 2015, 01:47 GMT-5
if you have an image describing your anisotropic density distribution with respect to x and y then you can do it.
definition-functions-image (import image)
and you can ascribe it for your density distribution as f(x,y) for 2d
care should be taken for coordinate values.
if you have an image describing your anisotropic density distribution with respect to x and y then you can do it. definition-functions-image (import image) and you can ascribe it for your density distribution as f(x,y) for 2d care should be taken for coordinate values.

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