Multibody analyses generally involve large rotations in static or transient dynamics analysis, so nonlinear geometric effects must be accounted for. To do so, issue the NLGEOM,ON command.

For faster convergence in a full transient dynamic analysis where mass elements such as MASS21 are used, issue the NROPT,UNSYM command. The command activates the Newton-Raphson option for solving the nonlinear equations in the analysis, necessary due to the nonsymmetric stiffness contribution resulting from gyroscopic effects.