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get certain elements of a mesh, then refine mesh there
Posted Jan 27, 2011, 4:53 a.m. EST Interfacing, Mesh Version 3.5a 2 Replies
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Hi,
i'm quite new to Comsol and i'm not sure if the following is possible to do with the software combined with Matlab:
There is a simple 2D square geometry with a mesh on it.
Now i want to get a list of certain elements of that mesh: The list should contain all triangles that are located on a circle on that 2D plane defined by an equation like (x-1)^2+(y-1)^2=0.5.
Then i need to refine the mesh around the mesh elements on the list.
I thought it might be possible to determine the triangles by checking if a triangle has nodes that are inside AND outside of the circle (or if one or two nodes exactly on it). This could be done by inserting the coordinates in (x-1)^2+(y-1)^2<=0.5 and checking it the equation holds. The problem is that i don't know how to start or if this approach is possible at all.
Thanks for any suggestions :)
i'm quite new to Comsol and i'm not sure if the following is possible to do with the software combined with Matlab:
There is a simple 2D square geometry with a mesh on it.
Now i want to get a list of certain elements of that mesh: The list should contain all triangles that are located on a circle on that 2D plane defined by an equation like (x-1)^2+(y-1)^2=0.5.
Then i need to refine the mesh around the mesh elements on the list.
I thought it might be possible to determine the triangles by checking if a triangle has nodes that are inside AND outside of the circle (or if one or two nodes exactly on it). This could be done by inserting the coordinates in (x-1)^2+(y-1)^2<=0.5 and checking it the equation holds. The problem is that i don't know how to start or if this approach is possible at all.
Thanks for any suggestions :)
2 Replies Last Post Jan 29, 2011, 5:11 a.m. EST
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Posted:
1 decade ago
In the matlab interface you can get the the node coordinates as
fem.mesh.p
The node numbers of the individual elements are stored in
fem.mesh.t
If x0,y0,r describes your circle,
vec1 = (fem.mesh.p(1,fem.mesh.t(1,:)) - x0).^2 + (fem.mesh.p(2,fem.mesh.t(1,:)) - y0).^2 < r^2;
, will give you a boolean vector for which nodes (1st local node in the elements) are inside your circle. You can construct
vec2 = (fem.mesh.p(1,fem.mesh.t(2,:)) - x0).^2 + (fem.mesh.p(2,fem.mesh.t(2,:)) - y0).^2 < r^2;
vec3 = (fem.mesh.p(1,fem.mesh.t(3,:)) - x0).^2 + (fem.mesh.p(2,fem.mesh.t(3,:)) - y0).^2 < r^2;
Corresponding to the 2nd and 3rd local node in the elements. I think
idx = find(and(vec1+vec2 + vec3 ~= 0, vec1+vec2 + vec3 ~= 3));
will give you the elements that have nodes both inside and outside the circle (as you suggested). You can then proceed to use the meshrefine command with this idx variable.
fem.mesh.p
The node numbers of the individual elements are stored in
fem.mesh.t
If x0,y0,r describes your circle,
vec1 = (fem.mesh.p(1,fem.mesh.t(1,:)) - x0).^2 + (fem.mesh.p(2,fem.mesh.t(1,:)) - y0).^2 < r^2;
, will give you a boolean vector for which nodes (1st local node in the elements) are inside your circle. You can construct
vec2 = (fem.mesh.p(1,fem.mesh.t(2,:)) - x0).^2 + (fem.mesh.p(2,fem.mesh.t(2,:)) - y0).^2 < r^2;
vec3 = (fem.mesh.p(1,fem.mesh.t(3,:)) - x0).^2 + (fem.mesh.p(2,fem.mesh.t(3,:)) - y0).^2 < r^2;
Corresponding to the 2nd and 3rd local node in the elements. I think
idx = find(and(vec1+vec2 + vec3 ~= 0, vec1+vec2 + vec3 ~= 3));
will give you the elements that have nodes both inside and outside the circle (as you suggested). You can then proceed to use the meshrefine command with this idx variable.
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Posted:
1 decade ago
Thank you so much for this elegant solution, this totally works for me :)
I use fem.mesh = meshrefine(fem,'tri',idx); to refine the mesh then.
I use fem.mesh = meshrefine(fem,'tri',idx); to refine the mesh then.