Wednesday, November 25, 2015

FEA : Shell Element Normals, Assign Material Side orientation in Thinshell Meshing, | Ansys , Hypermesh, Solidworks, Nastran NX

Checking Shell Element Normals in thin shell meshing

All shell elements have a normal (perpendicular) that defines the top and bottom of the mid surface meshing.
If we create,copy or move elements, shell normals may have a chance to change their different directions. During Post Processing and Optimization, it is necessary that the elements should have consistent tops and bottoms. All perpendiculars must point the same direction.

Shell normals and material orientation are independent of one another.Usually the pre-processing softwares have two tools for controlling shell element normals.

  • Shell Element Normals (Meshing task) lets you change shell element normals on a model that doesn't contain underlying geometry.
  • Material Side (Modeling task) lets you specify shell element normals on a model that contains underlying geometry.

Using Shell Element Normals

To use Shell Element Normals, select a "base element" with the desired orientation. Starting at that element, the command shifts the shell normals of the elements adjoining the base element until every element in the model is aligned.

For example, let us consider a sheet metal car bracket has been created in one quarter and then duplicated downward by reflecting. As a result, the shells normals of the lower half point in the opposite direction. By choosing a base element in the upper half, the command adjusts the lower elements until they're all pointing in the same direction.

Using Material Side

We can use Material Side in the Modeling task to control the direction of shell element normals when we mesh surfaces. Once you assign a material side to a surface, the mesh generator uses the material side's direction as the direction of the element normals.

We can't modify the material side for surfaces that make up a volume.

If we don't set the material side before you mesh surfaces, the mesh generator would automatically assigns a consistent direction for element normals. For example, let us consider of a mesh is generated on a non-manifold part and a manifold part where the software assigned the element normals.

If we use material Side and then mesh the part, the element normals point in the direction of the material side. Here, we should use Material Side to control the shell element normals on a non-manifold part and a manifold part .