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general and cartesian infinite elements
Posted 8 juin 2012, 14:16 UTC−4 Geometry Version 4.2a 5 Replies
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I have trouble understating how Cartesian infinite elements works.
Let's say, I design a sphere with radius 10, and position 0,0,0. I also add a layer with thickness 2m.
Therefore, the center of this object is at 0,0,0, and I can assign this center at the infinite elements by using type: spherical and as center 0,0,0.
Now if I design a block with 10x10x10 and position corner at 0,0,0, layer thickens 2 m, the center of the object is 5,5,5.
1) When I use Cartesian type infinite elements, what is considered as center?
2) If I change the type to general, I can understand the scaling direction (some areas are extent to x, some to x,y, some to x,z etc). But what is coordinate at interface? I remember that comsol 3.5 had as coordinates, the center of the domain. How could I use the general type, with blocks?
Thanks in advance.
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I do not believe you need to define any centre for cartesian PMLs, but you should not apply cartesian PML on a spherical or cylindrical outer geoemetrical shape, that will not work well.
Use the spherical or cylindrical PMLs on corresponding shaped geometries such that a wave emerging from "the centre" will hit the PML surfaces as close as possible in a "parallel" field way (perpendicular propagation)
This will alsways be the case, more or less, for a cartesian type independent where the source is in the volume
Another trick I have learnt about the PML or infinite elements: use the layer feature of the outer air/vacuum geometrical shape, then mesh the central part and mesh the PML is to use the advanced layer with a sweep mesh (or a few sweep meshes in cartesian) such that these PML region meshes have the type of "onion shells", and do not use regular thets (it works too, but I find less efficient. I mostly use about layer thickness of 1/10 of the total air size and at least 3 wavelengths, whatever is greatest, I tend to optimise both if possible
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Good luck
Ivar
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Thanks for the reply.
I am trying with the spherical elements, but I still have no luck. The "anomalous" body, should extented in infinity.
Any ideas?
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but you have GND on the external shell so I do not believe you can get cte charge all the way out, and anyhow it's not good practive (was in v3.5, perhaps that have chaned in v4?) to change the "material" and BCs of the PMLs.
And your cylinder is violating the spherical symmetry.
But have you tried with a cylinder type PML and geometry shape ?
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Good luck
Ivar
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I am trying to duplicate a comsol 3.5 model, where the cylinder was extending to infinity. This is something I cannont do with version 4? If not, then what is an alternative way besides extending the domain far far away?
I have two options for the infinite elements, where for these cylinders I have assigned cylindrical BC. In both cases, I have the same issues.
P.S.
(see this thread www.comsol.com/community/forums/general/thread/25481/)
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if you want a constant distribution, what about considering a cylindrical volume with symmetry conditions at the end caps ?
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Good luck
Ivar