Nonlinear Static Analysis Types

Small displacement analysis cannot handle all the nonlinearities specified in the previous section. In such cases, Large displacement analysis can be used. Currently, small displacement analysis is used by default and large displacement analysis can be activated (LGDISP), if required.

Small Displacement Analysis

In small displacement analysis the sources of nonlinearity are restricted to contact, GAP elements, and MATS1 elastic-plastic material. Geometric nonlinearities, follower loads, and large strain elasto-plasticity cannot be handled by small displacement analysis. As a typical guideline, small displacement analysis should be limited to small strains (some 5 percent strain) in both translation and rotation. There is no update of gap/contact element locations or orientation due to the deformations. They remain the same throughout the nonlinear computations. The orientation may change, however, due to geometry changes in optimization runs.

Large Displacement Analysis

Large Displacement Nonlinear Static Analysis (LGDISP) is used for the solution of problems wherein the load response relationship is nonlinear and large structural displacements are involved. The source of this nonlinearity can be attributed to multiple system properties, for example, materials, geometry, nonlinear loading and constraints. Currently, in OptiStruct the large displacement capabilities include large strain elasto-plasticity (MATS1), hyperelasticity of polynomial form (MATHE), contact with small tangential motion, deformation dependent loads (follower loads), and rigid body constraints.