Node and element association during morphing

After you morph a mesh, you can control the association between nodes, the elements connected to those nodes, and the polygon geometry.

• Use the Node Association command to associate the orphan nodes in a mesh to nearby polygon geometry within a specified tolerance. This command controls only the geometry association between a node and geometry. It does not change the location of a node. The software also tries to associate any elements connected to the nodes to the appropriate geometry, if possible.

• Use the Manual Node Association command to manually associate any orphan nodes in a mesh to nearby polygon geometry. For more information, see Manually associating nodes to geometry.

• Use the Node Dissociation command to remove the association between a node and the polygon geometry. This command is useful for cases in which the association between a node and the geometry is incorrect, such as when a node is associated to the wrong edge. The Node Dissociation command also disassociates any elements that are connected to the dissociated nodes from the geometry.

Node association in 3D meshes

You can associate an orphan 3D mesh to a solid body if:

• The mesh is not more than 110% of the size of the body in the X, Y, or Z directions.

• The mesh and the body are of similar size, and the distance between the centroid of the mesh and the centroid of the body does not exceed 10% of the mesh size in the X, Y, or Z directions. This means that there cannot be too much of an offset distance between the mesh and body

Note that:

• If a single mesh corresponds to a single body, the software treats the association of the nodes to the body in isolation. This means it considers the exterior nodes of the mesh as candidates for association to vertices, edges, and faces of the body, even if those nodes are shared with another mesh.

• Multiple, smaller meshes can be associated to a single body. In this case, the software associates the shared, interior nodes between the separate meshes to the body.

Association rules for elements and their midnodes

How the software associates an element to the geometry depends on the element’s order.

Element order	Association
1D	If both corner nodes are associated to an edge, including a vertex on the edge, the software associates the element to the edge.
2D	If all corner nodes are associated to a face, including an edge on the face or vertex on the edge, the software associates the element to the face.
3D	If all corner nodes are associated to a body, including an edge on the face or vertex on the edge, the software associates the element to the body.

The software associates the midnodes on the elements after it has associated all of the corner nodes. The table below details how midnodes are associated.

Association for corner node 1	Association for corner node 2	Association for mid-node
Vertex	Vertex	The edge between the two vertices
Vertex	Edge	Edge
Vertex	Face	Face
Edge	Edge	Edge
Edge	Face	Face
Face	Face	Face
Vertex/Edge/Face/Body	Body	Body
Vertex/Edge/Face/Body	Orphan—no association	Orphan—no association

Automatically associating nodes

When you use the Node Association command, the software tries to determine the best possible geometry association (vertex, edge, or face) for every external node.

• If the appropriate geometry is selected and it is within the distance tolerance of the node, the node is associated to that geometry.

• If the appropriate geometry is not within the tolerance, the node remains an orphan, with no association.

Note:

When you automatically associate nodes, you should use a progressively higher Distance Tolerance value.

Partial associativity

The morphing process can result in a model in which the mesh is only partially associated to the underlying geometry. A FEM file is fully associated when all nodes in the existing meshes are properly associated to the appropriate underlying edge, face, or body. Proper association is defined as follows:

• For edges, all nodes located on that edge must be associated with the edge, and the nodes at the ends of the edge must be associated with the underlying vertices.

• For faces, all edges that comprise the face must be properly associated, and all nodes that lie on the face are associated to the face.

• For bodies, all faces that comprise the body must be properly associated, and all nodes that lie inside the body must be associated with the body.

A mesh that is partially associated to the geometry can cause issues when geometry-based boundary conditions are defined on that geometry. For example, the value of a force defined on a polygon edge may not be correctly applied during a solve if the element edges along that polygon edge are not fully associated.

You can check your model for partially associated geometry by right-clicking on a FEM or Assembly FEM in the Simulation Navigator and choosing Report Association. Use this command to generate a list of all partially associated bodies in the information window.

When you export or solve a model, the Model Setup Check issues a warning if it finds a geometry-based boundary condition applied to an edge or face where the mesh is partially associated.

Where do I find it?

Application	Pre/Post
Prerequisite	A FEM file as the work part and displayed part
Command Finder	Node Association or Node Dissociation

Learn more

Morphing a mesh

Automatically morphing a mesh

Manually morphing a mesh

Morphing a revolved mesh

Comparing the manual morphing node distribution methods

Manually associating nodes to geometry

Quick links

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

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Node and element association during morphing, Simcenter 3D 2021.1 Series

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