Improperly Constrained Springs, Beams, or Shells
Springs, beams, or shells that are connected to solids without properly constrained degrees of freedom can cause some problems. Solids have only translational degrees of freedom. Because solids have no rotational degrees of freedom, adjacent idealizations with unconstrained rotational degrees of freedom can cause an error.
When springs, beams, or shells are connected to solids, they are really only connected at the translational degrees of freedom. The rotational degrees of freedom remain loose. Make sure that the rotational degrees of freedom are either supported or constrained.
• For example, you can attach a network of beams or shells to a set of solids such that the connection has structural integrity without need for further constraints. If you attach only one end of a beam or only one edge of a surface to a solid, you may need to use links to weld the rotational degrees of freedom to the solid.
• If you attach a single spring directly to a solid, you must constrain the rotational degrees of freedom of the spring, as shown in the following illustration.
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