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Posted Nov 10, 2011, 6:39 a.m. EST RF & Microwave Engineering, Geometry, Mesh, Parameters, Variables, & Functions Version 4.2a 11 Replies

Lasse Murtomäki
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I try to do a basic thing: subtract a block from a sphere in order to make a truncated sphere. But the difference operator vanishes both objects. In an old version (3.5a) it still works. If the block makes only a dent in the sphere, it works OK, so why not for an entire polar cap?

I also have tried to make a swept mesh from the surface of an outer sphere to an inner one. It is impossible because Comsol nags that only one surface á domain is allowed. If I define a layer for the outer sphere, it is divided into 8 domains (lower and upper quadrants), and a swept mesh is possible domain by domain.

Making a 2d drawing on the Work Plane and revolving it produces a truncated sphere, but now the outer sphere is again one single domain, and swept mesh is no more possible. I have also tried to use Split and Delete Entity operators in various ways, but have not found a solution. On-line manuals do not help, really.

Are there changes in the drawing operations in version 4.2?
11 Replies Last Post Mar 31, 2012, 2:03 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 10, 2011, 7:32 a.m. EST
Hi

I have no problems subtracting a block from a sphere, even making multiple caps. But I might not use the same shapes as you. But I do not see how to sweep from a sphere to a sphere. Indeed COMSOL cuts parts into their hemisphere/blocks in certain cases to handle curved shapes. Several CAD tools do it like that, but others not ;)

Things have changed, I agree, it took me some days to get used to the new interface, but then I now highly prefer it from the v3.5 one

--
Good luck
Ivar
Hi I have no problems subtracting a block from a sphere, even making multiple caps. But I might not use the same shapes as you. But I do not see how to sweep from a sphere to a sphere. Indeed COMSOL cuts parts into their hemisphere/blocks in certain cases to handle curved shapes. Several CAD tools do it like that, but others not ;) Things have changed, I agree, it took me some days to get used to the new interface, but then I now highly prefer it from the v3.5 one -- Good luck Ivar
Lasse Murtomäki
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Posted: 1 decade ago Nov 10, 2011, 7:45 a.m. EST
Really, it is nothing weird I am trying: a plain sphere with the radius of 8 mm from which I want to remove a cap of the height of 6 mm, leaving a truncated sphere with the height of 10 mm. Please look at the file.
Really, it is nothing weird I am trying: a plain sphere with the radius of 8 mm from which I want to remove a cap of the height of 6 mm, leaving a truncated sphere with the height of 10 mm. Please look at the file.

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Lasse Murtomäki
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Posted: 1 decade ago Nov 10, 2011, 7:53 a.m. EST
To reply your swept mesh questions: here it is.
To reply your swept mesh questions: here it is.
John H.
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Posted: 1 decade ago Nov 10, 2011, 12:57 p.m. EST
For what it's worth, I can confirm that the model you posted, "sphere_and_block.mph", produces an empty geometry, and I agree that this is not the expected behavior. It seems that the Comsol geometry kernel has a problem with the "layered sphere" you defined. Looks like a bug to me, as nothing in the documentation indicates that this operation is not supported.

The geometry sequence worked as expected as soon as I switched to the Parasolid geometry kernel, the one that ships with any of the CAD import modules.
For what it's worth, I can confirm that the model you posted, "sphere_and_block.mph", produces an empty geometry, and I agree that this is not the expected behavior. It seems that the Comsol geometry kernel has a problem with the "layered sphere" you defined. Looks like a bug to me, as nothing in the documentation indicates that this operation is not supported. The geometry sequence worked as expected as soon as I switched to the Parasolid geometry kernel, the one that ships with any of the CAD import modules.
Dennis Brown
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Posted: 1 decade ago Nov 10, 2011, 2:34 p.m. EST
I think there is a bug in the s/w. I played with the sphere layer thickness and the object seems to disappear between 0.822 and 0.823mm. On the upside if you were to create one sphere with 8mm radius and a second one at 7.5mm radius, you be ok when you do the difference operation. Looks like it is something funky with the layer feature.
I think there is a bug in the s/w. I played with the sphere layer thickness and the object seems to disappear between 0.822 and 0.823mm. On the upside if you were to create one sphere with 8mm radius and a second one at 7.5mm radius, you be ok when you do the difference operation. Looks like it is something funky with the layer feature.
Lasse Murtomäki
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Posted: 1 decade ago Nov 10, 2011, 3:52 p.m. EST
May I add that the objects vanish also without the layer!
May I add that the objects vanish also without the layer!
John H.
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Posted: 1 decade ago Nov 11, 2011, 3:07 a.m. EST
On my system, the objects disappear for a layer thickness between 0.743 and 0.744 mm. Funny thing...
On my system, the objects disappear for a layer thickness between 0.743 and 0.744 mm. Funny thing...
John H.
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Posted: 1 decade ago Nov 11, 2011, 3:07 a.m. EST
When I remove the layer, everything works as expected: I get the cut-off sphere. I can also make the layered structure using the sequence Dennis described. Not surprisingly so. If it wasn't for the layers, this geometry operation is extremely common in any Comsol model.
When I remove the layer, everything works as expected: I get the cut-off sphere. I can also make the layered structure using the sequence Dennis described. Not surprisingly so. If it wasn't for the layers, this geometry operation is extremely common in any Comsol model.
Shoval Zoran
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Posted: 1 decade ago Nov 13, 2011, 9:15 a.m. EST
could it be that comsol just has problems with dealing with very small sizes? it appeared to me once that while I could mesh a domain when it was in meters, changing it to mm made it impossible to mesh. I'm using 4.2 here.
could it be that comsol just has problems with dealing with very small sizes? it appeared to me once that while I could mesh a domain when it was in meters, changing it to mm made it impossible to mesh. I'm using 4.2 here.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 13, 2011, 2:47 p.m. EST
Hi

do not forget there are a few geoemtry absolute and relative precision values to be checked/adapted,
these might be involved in your issue.
See the geometry tab

--
Good luck
Ivar
Hi do not forget there are a few geoemtry absolute and relative precision values to be checked/adapted, these might be involved in your issue. See the geometry tab -- Good luck Ivar
Glenston Miranda
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Posted: 1 decade ago Mar 31, 2012, 2:03 a.m. EDT

Hi

do not forget there are a few geoemtry absolute and relative precision values to be checked/adapted,
these might be involved in your issue.
See the geometry tab

--
Good luck
Ivar


Hi,

I have a strange error occurring for the mesh based on the geometry that i have built.
The model's big so ive used swept meshes to reduce the no of elements.

I want to keep the no of elements to within 1 million to solve on a 16 GB system.

The default size is 1250 micrometer based on the minumum wavelength/6.
Been struggling with this for quite some time.

Any kind of help would be greatly appreciated.
Ive attached the model in this post.

Mapped1 and Swept 1 are for domain 8 which is one arm of the spiral. This mesh builds successfully.
Mapped2 and Swept 2 for domain 7 which is another arm of the spiral shows an error.
This is strange as both the arms are identical in geometry and in the mesh settings.
Error on inverted element found is

Regards
Glenston
[QUOTE] Hi do not forget there are a few geoemtry absolute and relative precision values to be checked/adapted, these might be involved in your issue. See the geometry tab -- Good luck Ivar [/QUOTE] Hi, I have a strange error occurring for the mesh based on the geometry that i have built. The model's big so ive used swept meshes to reduce the no of elements. I want to keep the no of elements to within 1 million to solve on a 16 GB system. The default size is 1250 micrometer based on the minumum wavelength/6. Been struggling with this for quite some time. Any kind of help would be greatly appreciated. Ive attached the model in this post. Mapped1 and Swept 1 are for domain 8 which is one arm of the spiral. This mesh builds successfully. Mapped2 and Swept 2 for domain 7 which is another arm of the spiral shows an error. This is strange as both the arms are identical in geometry and in the mesh settings. Error on inverted element found is Regards Glenston

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