Experimental Dynamic Load Simulation by Means of Modal Force Combination

The increase of dimensions and recent advances in the lightweight design of space systems have led to the requirement of new structural dynamic qualification techniques. The paper presents a new concept called the Modal Force Combination (MFC) technique. The method replaces the base accleration commonly applied during structural dynamic qualification by having a set of forces act directly in a selected number of structural points. The forces compensate for the d'Alembert inertia forces which arise due to transient multi-axial base acceleration. The transient forcing functions are calculated by means of modal deformations and related model force distributions in order to obtain the same structual responses of the structure as would occur with base accleration. The MFC method offers two possibilities of performing a simulation: the energy method and the deflection method. Both versions were investigated experimentally. The essentials of the verification tests are presented. The results of experimental dynamic load simulation by means of modal force combination are compared with measurements from base excitation performed on DLR's multi-axis vibration simulator MAVIS in Göttingen, Germany. In conclusion, the state of the art of the development of the new qualification method is discussed