Conflicting Coordinate Systems
You can specify displacement coordinate systems for mesh controls on points, edges, curves, and surfaces in FEM mode. Because these geometric entities are part of the definition for modeling entities such as constraints, rigid links, and weighted links, a conflict may arise between the various coordinate systems when you output to the NASTRAN solver.
There are several situations that may cause conflicts:
• A conflict may occur if you use the same or adjacent geometry to define two modeling entities. For example, if you define constraint a using a surface, and constraint b using an edge of that surface, a conflict could occur. In this case, the geometric precedence rules would respect constraint b over constraint a.
• A conflict may occur when coordinate systems are associated with two parts in an assembly. In this case, the assembly hierarchy of the part determines the precedence. You can view the assembly hierarchy in the Model Tree.
• A conflict may occur when coordinate systems are associated with a part or subassembly as well as a top-level assembly. In this case, you can suppress the part or subassembly coordinate system by using the Ignored Mesh Control option on the Mesh Control dialog box.
• A conflict may occur when coordinate systems associated with different entities, such as constraints and mesh controls, share a geometric entity or a node.
For example, suppose you define a constraint on a surface with a Cartesian coordinate system (coordinate system A), and you also define a displacement coordinate system (coordinate system B) for a mesh control on the same surface. If the axes for both coordinate systems are parallel, but coordinate system B is rotated with respect to coordinate system A so that the X and Y axes are interchanged, a conflict will occur. Of course, non-parallel axes will also cause a conflict.
Creo Simulate checks your displacement coordinate systems and attempts to resolve conflicts by using geometric and model-hierarchy precedence rules. If the software cannot resolve the conflicts, an error message appears and the output stops. You must resolve the conflict before the run can continue. When the software sets the displacement coordinate system for each node, it checks for conflicts in this order:
• Mesh controls — The software checks for conflicts between displacement coordinate systems used to define mesh controls and tries to resolve them using geometric and assembly precedence rules. An example of a non-resolvable conflict is a different displacement coordinate system assigned to surfaces that belong to the red and yellow sides of a shell pair. The geometric precedence rules are:
◦ A mesh control applied to a point overrides a mesh control applied to an edge or surface that contains that point.
◦ A mesh control applied to an edge overrides a mesh control applied to a surface that contains that edge.
• Rigid or weighted links— The software checks for conflicts between the coordinate systems associated with rigid or weighted links and tries to resolve them using geometric and assembly precedence rules.
• Mesh controls and rigid or weighted links — The software checks for conflicts between coordinate systems associated with links and displacement coordinate systems for mesh controls.
• Constraints — The software checks for conflicts between the coordinate systems associated with constraints and tries to resolve them using geometric and assembly precedence rules. If you apply a free and a fixed degree of freedom to the same node, the fixed constraint takes precedence over the free constraint. The presence of a fixed constraint also overrides the geometric precedence rules, so that a fixed constraint on a surface takes precedence over a free constraint on a point. A non-resolvable conflict may occur between partially fixed or partially free constraints on adjacent objects.
• Mesh controls, rigid or weighted links, and constraints — The software checks for conflicts between constraints and mesh controls, and between constraints and links.
Return to Displacement Coordinate System (FEM mode).