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Problems with Contact resistance and Open boundaries

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Hi All,

I am attempting to make a simple model of a laser heating a material and then having heat flow across the boundary to a second material.

However I am having several problems.

1) I cannot figure out how to create thermal contact resistance (I know it has something to do with pairs of some kind but I cannot discover how to create these pairs.

2) I modeled the laser as an oblique cone however when I ran the simulation the cone is being heated while everything else is not, despite having open boundaries.

If anyone can offer suggestions or look at my model I would appreciate it.

Thank you,

John Haase

6 Replies Last Post 1 juin 2012, 14:05 UTC−4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 21 avr. 2011, 11:28 UTC−4
Hi

I cannot find back the example I believe existed in 3.5 but you could study , by analogy, the model library case:
Comsol Multiphysics - Electromagnetics - Thin film resistance

its a electric resistive and not thermal case, but very similar

For the basic physics without the contact though.

It's somewhat more complex when you add the contact as the contact area varies (as well as the pressure hence normally the thermal conductivity of the contact too, but that you must model yourself I believe, via your own equations)

The PAirs as you say. Is linked to the COMSOL Assembly mode (nothing to do with CAD assembly) you set that in the Geometry Finish node. But before, group (via a "Geometry - Boolean Operations - Compose") your geometries where you want to apply "Continuity" by default and leave only (if possible) the contact boundaries as separate items. In assembly mode, if two independent Domains (=volumes in 3D, surfaces in 2D) are adjacent with a common boundary this boundary will be de-doubled, one attached to the "left domain" the other to the "right domain". While in "union" mode the common boundary will be replaced by a shared boundary with full continuity of the physics applied to it. This is a fundamental concept in COMSOL that must be carefully studied and understood to take all the advantages of this tool

For boundaries that are de-doubled in assembly mode, and for which you want a "continuity" of the physics, you need to define an identity pair under "Definitions" and then apply a "Continuity Pair - Boundary Condition, specifically

--
Good luck
Ivar
Hi I cannot find back the example I believe existed in 3.5 but you could study , by analogy, the model library case: Comsol Multiphysics - Electromagnetics - Thin film resistance its a electric resistive and not thermal case, but very similar For the basic physics without the contact though. It's somewhat more complex when you add the contact as the contact area varies (as well as the pressure hence normally the thermal conductivity of the contact too, but that you must model yourself I believe, via your own equations) The PAirs as you say. Is linked to the COMSOL Assembly mode (nothing to do with CAD assembly) you set that in the Geometry Finish node. But before, group (via a "Geometry - Boolean Operations - Compose") your geometries where you want to apply "Continuity" by default and leave only (if possible) the contact boundaries as separate items. In assembly mode, if two independent Domains (=volumes in 3D, surfaces in 2D) are adjacent with a common boundary this boundary will be de-doubled, one attached to the "left domain" the other to the "right domain". While in "union" mode the common boundary will be replaced by a shared boundary with full continuity of the physics applied to it. This is a fundamental concept in COMSOL that must be carefully studied and understood to take all the advantages of this tool For boundaries that are de-doubled in assembly mode, and for which you want a "continuity" of the physics, you need to define an identity pair under "Definitions" and then apply a "Continuity Pair - Boundary Condition, specifically -- Good luck Ivar

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Posted: 1 decade ago 22 avr. 2011, 10:56 UTC−4
Ivar,

I attempted to do what I think you are saying, but when I do I get the error:

Fail to evaluate variable Jacobian

in addition a heat flux I am trying to model is locally reaching 10^4 K while the surrounding areas are remaining unaffected.

If you could take a look at my model I would be very appreciative.

Thank you,

John Haase
Ivar, I attempted to do what I think you are saying, but when I do I get the error: Fail to evaluate variable Jacobian in addition a heat flux I am trying to model is locally reaching 10^4 K while the surrounding areas are remaining unaffected. If you could take a look at my model I would be very appreciative. Thank you, John Haase


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Posted: 1 decade ago 22 avr. 2011, 16:10 UTC−4
Everyone,

I'm sorry about the triple post. I figured out that I needed to apply a conductive boundary and a thin thermally resistive layer.

However there is one more issue which I am having trouble with. I am trying to model a laser with a simple heat flux, however the laser interact beneath the surface and the problem I'm having is that when the area I want to affect is in a union there is only the top of the shape to select and when there is no union (and thereby an assembly) there is no heat transfer from that region.

If someone could take a look at my model I would appreciate it.

Thank you,

John Haase
Everyone, I'm sorry about the triple post. I figured out that I needed to apply a conductive boundary and a thin thermally resistive layer. However there is one more issue which I am having trouble with. I am trying to model a laser with a simple heat flux, however the laser interact beneath the surface and the problem I'm having is that when the area I want to affect is in a union there is only the top of the shape to select and when there is no union (and thereby an assembly) there is no heat transfer from that region. If someone could take a look at my model I would appreciate it. Thank you, John Haase


Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 23 avr. 2011, 08:16 UTC−4
Hi

its linked to the way you select the options in your union. If you do not keep the interior boundaries the two intersecting volumes will not coexist later. If you need just the surface shape, you can forget the interior boundaries, if you want to use a volumetric heat source penetrating into the material add the interior boundaries, you can do it the way I believe you are trying, but cutting out a small volume from the main one onto which you can apply a body heat source, not just a surface heat flux.

Check the number of domains you end up with it varies from 2 to 3, Inspect the same way your boundaries.
In "assembly mode" you have two overlapping boundaries for the adjacent interfaces (be aware volumes that penetrate are nut cut !) This allows to apply specific physics on the de-doubled boundaries, or identify pairs and decide yourself how you couple them (to be done for all physics applicable !)

--
Good luck
Ivar
Hi its linked to the way you select the options in your union. If you do not keep the interior boundaries the two intersecting volumes will not coexist later. If you need just the surface shape, you can forget the interior boundaries, if you want to use a volumetric heat source penetrating into the material add the interior boundaries, you can do it the way I believe you are trying, but cutting out a small volume from the main one onto which you can apply a body heat source, not just a surface heat flux. Check the number of domains you end up with it varies from 2 to 3, Inspect the same way your boundaries. In "assembly mode" you have two overlapping boundaries for the adjacent interfaces (be aware volumes that penetrate are nut cut !) This allows to apply specific physics on the de-doubled boundaries, or identify pairs and decide yourself how you couple them (to be done for all physics applicable !) -- Good luck Ivar

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Posted: 1 decade ago 1 juin 2012, 11:03 UTC−4
Hi Ivar,
I have a geometry with multiple interfaces but I only want one interface to be de-doubled and the rest 'unionized'. Can this be done? Thank you.


EH


Hi

I cannot find back the example I believe existed in 3.5 but you could study , by analogy, the model library case:
Comsol Multiphysics - Electromagnetics - Thin film resistance

its a electric resistive and not thermal case, but very similar

For the basic physics without the contact though.

It's somewhat more complex when you add the contact as the contact area varies (as well as the pressure hence normally the thermal conductivity of the contact too, but that you must model yourself I believe, via your own equations)

The PAirs as you say. Is linked to the COMSOL Assembly mode (nothing to do with CAD assembly) you set that in the Geometry Finish node. But before, group (via a "Geometry - Boolean Operations - Compose") your geometries where you want to apply "Continuity" by default and leave only (if possible) the contact boundaries as separate items. In assembly mode, if two independent Domains (=volumes in 3D, surfaces in 2D) are adjacent with a common boundary this boundary will be de-doubled, one attached to the "left domain" the other to the "right domain". While in "union" mode the common boundary will be replaced by a shared boundary with full continuity of the physics applied to it. This is a fundamental concept in COMSOL that must be carefully studied and understood to take all the advantages of this tool

For boundaries that are de-doubled in assembly mode, and for which you want a "continuity" of the physics, you need to define an identity pair under "Definitions" and then apply a "Continuity Pair - Boundary Condition, specifically

--
Good luck
Ivar


Hi Ivar, I have a geometry with multiple interfaces but I only want one interface to be de-doubled and the rest 'unionized'. Can this be done? Thank you. EH [QUOTE] Hi I cannot find back the example I believe existed in 3.5 but you could study , by analogy, the model library case: Comsol Multiphysics - Electromagnetics - Thin film resistance its a electric resistive and not thermal case, but very similar For the basic physics without the contact though. It's somewhat more complex when you add the contact as the contact area varies (as well as the pressure hence normally the thermal conductivity of the contact too, but that you must model yourself I believe, via your own equations) The PAirs as you say. Is linked to the COMSOL Assembly mode (nothing to do with CAD assembly) you set that in the Geometry Finish node. But before, group (via a "Geometry - Boolean Operations - Compose") your geometries where you want to apply "Continuity" by default and leave only (if possible) the contact boundaries as separate items. In assembly mode, if two independent Domains (=volumes in 3D, surfaces in 2D) are adjacent with a common boundary this boundary will be de-doubled, one attached to the "left domain" the other to the "right domain". While in "union" mode the common boundary will be replaced by a shared boundary with full continuity of the physics applied to it. This is a fundamental concept in COMSOL that must be carefully studied and understood to take all the advantages of this tool For boundaries that are de-doubled in assembly mode, and for which you want a "continuity" of the physics, you need to define an identity pair under "Definitions" and then apply a "Continuity Pair - Boundary Condition, specifically -- Good luck Ivar [/QUOTE]

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 1 juin 2012, 14:05 UTC−4
Hi

as often yes and no, what you can do is to group a series of geometrical objects and make an (or several) explicit union(s) between these, then when you exit in Assembly mode the dedoubled boundaries will only be applie between the last full objects.

So if you end up with two union onjects, each conaining many sub onbjects, and these two objects have one common boundary, then in assembly mode this common border will be dedoubled with an "up" and "down" side. You will notice this if you click on it you first catch one, then the other

--
Good luck
Ivar
Hi as often yes and no, what you can do is to group a series of geometrical objects and make an (or several) explicit union(s) between these, then when you exit in Assembly mode the dedoubled boundaries will only be applie between the last full objects. So if you end up with two union onjects, each conaining many sub onbjects, and these two objects have one common boundary, then in assembly mode this common border will be dedoubled with an "up" and "down" side. You will notice this if you click on it you first catch one, then the other -- Good luck Ivar

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