Initial Results from Experimental Dynamic Load Simulation by means of Modal Force Vectors.

Kurzfassung

Increase of size and recent advances in lightweight design of space systems have led to the requirement of new approaches to structural dynamic testing techniques. The paper gives a brief survey of different qualification methods based on single-axis and multi-axis testing. A new concept called the modal force combination (MFC) method is proposed, in which the base excitation of a spacecraft due to various load events can be simulated by a set of forces acting directly in specially selected structural points. The forces compensate for the d'Alembert's inertia forces arising due to the transient multi-axial base accelration. The forcesare specially conditioned by a series expansion of so-called modal force distribution so that they produce the same deformations and accelerations in the structure as would occur by base excitation. Two versions of the MFC concept are presented in the paper. The first uses arbitrary orthogonal force vectors in the vicinity of the resonance frequencies, and the second is based on transfer functions.Initial experimental results are presented, taken from an applicationof the technique on a three-dimensional test structure. The results of experimental dynamic load simulation by means of modal force vectors are compared with measurements from base excitation performed on DLR's multi-axis vibration simulator MAVIS 2. In conclusion, the presented MFC versions are discussed.