How to Start Transient Response Calculations for Rotating Structures Without Causing Centrifugal Force Shocks

Abstract

In computer programs for transient response calculations often only homogeneous and not more complicated, inhomogeneous initial conditions can be considered. The initial conditions assumed here are the stresses or displacements generated by the centrifugal force field in rotating structures. Nevertheless, calculations can be started with homogeneous initial conditions. The system has then to be transferred to operating conditions in a precalculation by a suitable rotational speed characteristic. Only then can the actual simulation begin. The rotational speed characteristic must have the additional capability of establishing the inhomogeneous initial conditions in minimum time. Precise imitation of the long technical run-up procedure is undesirable because of high computer cost and numerical inaccuracy. Modal equations are taken as the basis for formulation of an optimization problem whose solution determines the optimum speed characteristic. For the technically important case where a single prevailing natural vibration has to be controlled, it is possible to state the solution explicitly. With several natural vibrations, the control must be determined numerically. The procedure is used in calculating the effects of bird strike on rotating turbine blades.