Negative Jacobians in mesh
Moderator: GiD Team
Negative Jacobians in mesh
Hi, I'm attempting to run a solver that requires zero or positive Jacobians for every element, but I keep getting negative Jacobians when I mesh. Is there a way to force non-negative Jacobians?
Re: Negative Jacobians in mesh
Unfortunately it is not possible to force non-negative jacobians.
After meshing a popup message will said that there are some negative jacobian elements.
You can only see from the Mesh->Mesh quality... window the distribution of element's quality ('minimum jacobian' is one of the criteria qualities), and a <Double>-click will select the elements with lower quality (below the x-value) to visually identify the wrong parts.
You must to change something in your geometry or the assigned mesh data (sizes, element type) or general meshing preferences in order to try to achieve a good mesh.
After meshing a popup message will said that there are some negative jacobian elements.
You can only see from the Mesh->Mesh quality... window the distribution of element's quality ('minimum jacobian' is one of the criteria qualities), and a <Double>-click will select the elements with lower quality (below the x-value) to visually identify the wrong parts.
You must to change something in your geometry or the assigned mesh data (sizes, element type) or general meshing preferences in order to try to achieve a good mesh.
Re: Negative Jacobians in mesh
Hi escolano, thanks for the quick reply. In a few cases, according to the shape quality and minimum Jacobian information provided in Mesh->Mesh quality, I could create a mesh with non-negative shape qualities and Jacobians. However, when I tried to run the simulation, the same error appeared: "element [####]: Jacobian<0". I then redefined and simplified some surfaces. The new mesh seems to work fine now.
Thanks for the tip about double clicking to see the elements below a threshold in Mesh->Mesh quality. However, that feature does not seem to work in my GiD version (v.12.0).
Thanks for the tip about double clicking to see the elements below a threshold in Mesh->Mesh quality. However, that feature does not seem to work in my GiD version (v.12.0).
Re: Negative Jacobians in mesh
You must double click over the rectangle area of the mesh quality graph,
then a vertical red line is showed on the graph and the elements with less quality are selected (and then drawn in red),
and you can move these elements to another layer with the button 'Send to Layer' of the lower-rigth corner of the window.
It must work also in your 12.0 version.
then a vertical red line is showed on the graph and the elements with less quality are selected (and then drawn in red),
and you can move these elements to another layer with the button 'Send to Layer' of the lower-rigth corner of the window.
It must work also in your 12.0 version.