About Structure Constraints

In Native and FEM mode Structure, you can apply constraints in your model. While defining constraints for a Structure model, your goal is to fix portions of the model geometry so that the model cannot move, or can move only in a predetermined way. Your model's constraints, along with its loads, provide the software with the real-world conditions that it uses as the basis for analysis.

In constraining a Structure model, you are defining the extent to which your model can move in reference to a coordinate system. Thus, when you add constraints, you specify translational or rotational part movement. The software assumes that any unconstrained portion of your Structure model is free to move in all directions.

Use constraints for the following:

• Simulate real-world mounting—For example, you can constrain the radial and axial direction at a bolt hole to allow rotation about the hole. This requires a cylindrical coordinate system with the z-axis aligned with the hole's axis.

• Enforce displacements—For example, you can move a part by a specified distance into another in a contact analysis.

• Analyze a section of a cyclically symmetric model—The section simulates the behavior of the whole part, reducing meshing and analysis time. The geometry, materials, and loads must be cyclically symmetric. For example, if you want to analyze a section of a fan blade subject to pressure and centrifugal loading. It is worth noting that the symmetry surfaces need not be planar.

• Analyze a section of a reflective or planar symmetric model—Use this type of constraint to impose symmetry conditions.

• Eliminate rigid body motion—For all analyses, you should, at minimum, specify constraints to prevent rigid body motion. An insufficiently constrained model will give an error during run time. There are two exceptions to this rule:

◦ unconstrained modal analysis

◦ presence of spring-to-ground elements

Before applying constraints, see Guidelines for Structure Constraints. Every constraint is created as part of a constraint set. In Structure, you can use only one constraint set per analysis although you can combine multiple constraints into a single constraint set that is active during the analysis.

You can choose from the following constraint types:

• Displacement constraint—Create various entity-based constraint types.

• Planar, Pin, and Ball Constraints—Create a constraint along a planar, cylindrical, or spherical surface for 3D models.

• Symmetry constraint—Create cyclic or mirror symmetry constraints that allow you to take advantage of your model’s geometric symmetry. This command is not available in FEM mode.

For each of these three constraint types, you need to consider different factors and use different creation methods. To review information that is common to all three constraint types, see:

Creo Simulate applies the constraints you specify to all the entities that you select and places a constraint icon at each location.

For compressed solid parts in assemblies, Creo Simulate automatically adds a constraint between intersecting midsurfaces whenever possible. When Creo Simulate adds such a constraint, the constrained midsurfaces are forced to deform together during a run.

After you create a constraint, you can troubleshoot constraints, control constraint icon visibility, and place constraints on layers.

To create, edit, or delete constraint sets, click Home > Constraints > Constraint Sets to open the Constraint Sets dialog box.

If you are working in Thermal, see About Thermal Boundary Conditions for information on applying convection conditions, prescribed temperatures, or cyclic symmetry.