MODEL-REDUCTION TOOLS FOR NONLINEAR STRUCTURAL DYNAMICS

Three mode types are proposed for reducing nonlinear dynamical system equations, resulting from finite element discretizations: tangent mode s, modal derivatives, and newly added static modes. Tangent modes are obtained from an eigenvalue problem with a momentary tangent stiffness matrix. Their derivatives with respect to modal coordinates contain m uch beneficial reduction information. Three approaches to obtain modal derivatives are presented, including a newly introduced numerical way . Direct and reduced integration results of truss examples show that t angent modes do not describe the nonlinear system sufficiently well, w hereas combining tangent modes with modal derivatives and/or static mo des provides much better reduction results.