Negative radius on element XXX
Negative radius on element XXX
(OP)
Hello,
I am doing coupled field electrostatics/structural analysis.
It means that I calculate an electrostatic force, then the displacement of the structure due to this force. After that I do a mesh morphing to calculate the new electrical field and electrostatic force, and so on until convergence occurs. I am doing this on a circular plate, so I used axisymmetrical modeling. I have large deflection, but for relatively small strain.
My problem arises with high tensions (i.e. large displacement) after some iterations, I can do the mesh morphing, but I can't solve the electrostatic problem anymore and I get this error message : "Negative Radius on Element XXX" (XXX being the number of an element situated on the axis of revolution of my rectangle (the rectangle, by rotation around the Y axis, creates a circular plate))
What I don't understand is that the element is not highly deformed and looks fine. I've tried to look in the help files for this error message, but the only reference I can find about "Negative Radius" is in the time bisection paragraph of the automatic time stepping chapter :
5 An illegal element distortion is detected (e.g., negative radius in an axisymmetric analysis)
But I don't see what is wrong with my element. It has move a lot from its original point (it's at the center of the plate), but is not distorted. I tried to unmesh the area and remesh it, but if I control the new mesh, I do have the same error coming.
Does anyone know what is causing this problem and how I could solve it?
Thanks in advance for your replies.
I am doing coupled field electrostatics/structural analysis.
It means that I calculate an electrostatic force, then the displacement of the structure due to this force. After that I do a mesh morphing to calculate the new electrical field and electrostatic force, and so on until convergence occurs. I am doing this on a circular plate, so I used axisymmetrical modeling. I have large deflection, but for relatively small strain.
My problem arises with high tensions (i.e. large displacement) after some iterations, I can do the mesh morphing, but I can't solve the electrostatic problem anymore and I get this error message : "Negative Radius on Element XXX" (XXX being the number of an element situated on the axis of revolution of my rectangle (the rectangle, by rotation around the Y axis, creates a circular plate))
What I don't understand is that the element is not highly deformed and looks fine. I've tried to look in the help files for this error message, but the only reference I can find about "Negative Radius" is in the time bisection paragraph of the automatic time stepping chapter :
5 An illegal element distortion is detected (e.g., negative radius in an axisymmetric analysis)
But I don't see what is wrong with my element. It has move a lot from its original point (it's at the center of the plate), but is not distorted. I tried to unmesh the area and remesh it, but if I control the new mesh, I do have the same error coming.
Does anyone know what is causing this problem and how I could solve it?
Thanks in advance for your replies.





RE: Negative radius on element XXX
Is your model constrained correctly? I'm thinking rigid body motion and that possibly one (or more) of your elements is/are displacing outside the "allowed zone" in axisymmetric XY space? Make sure your triad is plotted at the origin (/triad,orig) then change displacement scaling to 1:1 (/dscal,1,1) and then pldisp. Have you tried running with/without NLGEOM as well?
Cheers,
-- drej --
RE: Negative radius on element XXX
If I take a close look to the border element near Y=0, I can indeed see that they have a slight negative move on the x axis, which is indeed illegal, but what can I do against it?
Thanks for your help.
RE: Negative radius on element XXX
RE: Negative radius on element XXX
This shows that x component of the keypoints cannot be chosen randomly.
Hope this helps.