3D Spring Support

A 3D spring support can be applied to nodes, edges or surfaces of a model.

What Does a 3D Spring Support Do?

• An edge or surface 3D spring support applies elastic boundary elements to each node on the edge or surface.
• A 3D spring support applies a stiffness to a node to resist either translation or rotation in or about a global direction. A new node is actually added to the model. The specified degree of freedom is restricted on this new node. An element is created between this node and the node on the model to which the 3D spring support is applied. This element is oriented along the global axis that the 3D spring support is applied along. This element acts like a translational or torsional spring, depending on the type of support specified (translation or rotation). The stiffness value refers to the stiffness of this spring. The magnitude of the translation or rotation of the node on the model depends on this value. A high stiffness allows very little, or no, movement of the node. A low stiffness allows the node to move considerably.
• You can fix the translation or rotation in all three global directions in the same dialog box and in a single application of the constraint. However, a separate boundary element is applied to the model node for each activated direction. For example, if you create a translational 3D spring support and check the boxes for X and Y in the Constrained section, two nodal spring supports are actually created. One acts along the X direction and the second acts along the Y direction.
• You can view the force or moment present in the nodal 3D spring support, which is based on the spring equation, F=kX. The greater the boundary displacement, the greater the spring force. In the Results environment, use the Linear Results Menu pull-out menu. Each degree of freedom that is constrained with a nodal 3D spring support is represented with a separate nodal boundary element. Therefore, you can see the forces and moments broken down into the global X, Y, and Z components.

Tip: 3D spring supports are a convenient means of providing static stability to a model that otherwise has no physical constraints. Three nodes not in a straight line – restrained in X, Y, and Z translation – fully fix the model from rigid body translation and rotation. Since the spring supports tie the model to the ground, set the stiffness to a small value so that a minimum amount of load is transferred through the springs. An appropriate stiffness can be estimated by recalling that the stiffness K = Force/displacement. So if it is suitable to transfer 10 lbs of load through the springs and the nodes are expected to deflect 0.01 inch, a small stiffness can be as large as 1000 lb/inch. The point is to create static stability (or equilibrium) without producing reaction forces at the 3D spring supports that are large enough to significantly distort the results.

How to Apply 3D Spring Supports

If you have nodes, edges or surfaces selected, you can right-click in the display area and select the Add pull-out menu. Select the Nodal 3D Spring Supports, Edge 3D Spring Supports or Surface 3D Spring Supports command. You can also click the Setup Constraints 3D Spring Support ribbon command. Edge 3D spring supports can only be applied to parts that originated from CAD solid models or 2D Mesh Generation.

Activate the check boxes for all of the global directions along which you want the translation or rotation to be resisted. Determine if you want the 3D spring support to resist translation or rotation of the node by selecting the appropriate radio button in the Type section. Specify the stiffness of the elastic boundary element in the Stiffness field.

Note: See the comments under the Application of Loads and Constraints at Duplicate Vertices heading on the Loads and Constraints page for information about how nodal loads are applied at duplicate vertices.