Surface coat of 2D elements

Use the Surface Coat command to create a surface coating of 2D (shell) elements on top of existing 3D (solid) elements. You can use the options in the Surface Coat dialog box to control whether the software creates a surface coat of shell elements on either the free faces of selected solid elements or on an entire solid mesh. The resulting 2D mesh:

• Uses the nodes and the connectivity of the solid mesh on which it is defined.

• Can be linear or parabolic if the solid mesh is parabolic. For example, you can create a surface coating of either linear or parabolic quadrilateral elements on a mesh of parabolic quadrilateral elements. However, if the solid mesh is linear, then the resulting 2D mesh can only be linear.

• Is associated to the underlying 3D mesh and geometry if you select the Geometry option from the Mode list in the Surface Coat dialog box. If you delete or modify the 3D mesh or the geometry, the software first updates the 3D mesh and then updates the associated 2D surface coat mesh.

Note:

You can also create a coating mesh of 1D elements. For more information, see 1D element coating meshes.

When you use the Surface Coat command to create a 2D mesh around a model that contains both a hexahedral and a tetrahedral mesh, the software automatically detects and filters out any solid element free faces at the interface between those meshes. When you create a surface coat of shell elements on multiple 3D meshes that are not associated with any geometry, the software filters out internal shell elements that define a region that is separated by non-manifold element edges. The resulting 2D mesh contains only the envelope or outer skin that represents the union of all 3D meshes.

This example shows a simple model in which a hexahedral mesh is adjacent to a tetrahedral mesh. When you use the Surface Coat command to create a 2D mesh around both solid meshes, the software filters out the elements along the highlighted interface where the two mesh types meet.

Reasons to create a surface coat mesh

There are a number of different reasons why you might want to create a surface coating of 2D elements on your model. You can create a surface coating of 2D elements to:

• Model an actual surface coating on the underlying part.

• Add mass to your model.

• Facilitate post-processing in cases, for example, where you are chiefly interested in the stress results on the surface of the part. With this method, the solve time will be shorter and the size of the results file will be greatly reduced. Specifically, you can define a surface coat of 2D elements on an existing 3D mesh and then create a new group that contains just the 2D elements. When you specify the results to output from the analysis, you then request that the software only output stress results for the elements in the group. For example, if you are using Nastran as your solver, you can create a Structural Output Request modeling object and use the options on the Stress tab to request stress results only on the group of 2D elements. When you solve the model, the software only stores results for the 2D elements and not for the internal solid elements.

• Ensure that loads are correctly transferred between adjacent shell and solid meshes. For example, imagine a model that contains a thin rib that intersects the main body of a solid part. The rib is meshed with 2D elements, with 6 degrees-of-freedom each, while the part itself is meshed with 3D elements, with 3 degrees-of-freedom each. Suppose you need to apply a bending load to the end of the rib. To ensure that the moments transfer correctly from the 2D elements to the 3D elements, you can create a surface coating of 2D elements on the 3D elements that surround the location where the rib intersects the part.

• Help derive an appropriate acoustic mesh from an existing structural mesh. If the structural mesh is a solid mesh, you can use the Surface Coat command to first create a mesh of 2D elements on the surface of the 3D mesh. For more information, see Meshing for FEM acoustic analysis and Meshing for Acoustics BEM analysis.

• Create a 2D microphone mesh on the surface of a 3D fluid mesh. For more information, see Using microphone mesh to capture analysis results.

Where do I find it?

Application	Pre/Post
Prerequisite	A FEM file as the work part and displayed part
Command Finder	Surface Coat

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Surface coat of 2D elements, Simcenter 3D 2021.1 Series

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