Boundary Conditions

Boundary conditions define how the model interacts with its environment. They are necessary to make the finite element problem well-posed.

Essential boundary conditions prescribe displacement values. Examples include fixed supports, rollers, symmetry constraints, and prescribed displacements. Natural boundary conditions prescribe forces or tractions, such as pressure and distributed surface loads.

A model must be sufficiently constrained to remove rigid body motion. Under-constrained models can produce singular stiffness matrices or unrealistic displacement fields. Over-constrained models can produce artificial stiffness and inaccurate stress concentrations.