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Controlling the Geometry Shape Order - How to Always Get Isoparametric Elements!
Posted Jan 29, 2020, 10:28 a.m. EST Version 5.5 1 Reply
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Hi Everyone,
I still have a question concerning the above post. Here are the details again:
I am trying to simulate a simple MBB problem (with filleted corners) using the Solid Mechanics interface. I am playing around with the Geometry Shape Order option, I am trying to make sure I always get isoparamteric elements, given that the mesh discretization is quadratic with triangular elements. But so far the Geometry Shape Order keeps changing on its own depending on the mesh density, even though I explicitly set it to quadratic. For instance, at coarse meshes, the Geometry Shape Order jumps to cubic. For a very fine mesh, the Geometry Shape Order jumps down to linear! How can I make sure I get isoparametric elements? Is there a way to fix the Geometry Shape Order?
Additional Important Info: 1. I figure out the used Geometry Shape Order by extracting a numerical result at Lagrange points using the "LiveLink to Matlab" module which gives the number and coordinates of the Lagrange points. As far as I know, Lagrange points determine the Geometry Shape Order. 2. The Geometry Shape Order can be manipulated through the "LiveLink with Matlab" module through the "sorder" option. It's still 2 for quadratic but it gives a different result as stated above.
Any help is greatly appreciated.
Sincerely, Mohamed Abdelhamid
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Hi Mohamed,
If you have a single physics interface, like Solid Mechanics, there is no need to touch the settings for the geometry shape order at all. It is the same as the discretization order for the displacement field as long as the default setting Automatic is used. This ensures isoparametric elements.
If there are several physics interfaces in the model, with conflicting discretization orders, Automatic is still usually the best choice, but you can make a manual override. Most users will never experience a need for changing the settings for the geometry shape function order.
The geometry shape function order used is printed in the Log window, so there is no need to use indirect methods to infer it.
The number of mesh elements does not change shape function orders, neither for the geometry or the dependent variables. What you have been looking at is probably the grid used for visualization, which as a default is coarser (per element) if there are many elements in the model.
Regards,
Henrik
Henrik Sönnerlind
COMSOL