Minimum Drives Spectral Density Matrix for MIMO Random Vibration Control Tests: Application Cases

The recent advances in excitation and vibration control systems are thrusting Multiple-Input-Multiple-Output (MIMO) vibration control tests at the attention of both industry and academia.
The straight answer to the question that might arise in the environmental engineers starting to look into the MIMO technology “why MIMO?” relies, without going into a more detailed “pro-and-cons”, in the definition of Environmental Testing itself. The goal of this type of tests is, in fact, to reproduce as closely as possible the vibration environment that a structure needs to withstand during its operational life. Despite the assumptions and the approximations allowing to perform a single axis test, a true vibration environment is however multi-axial.
Even if the evolution in testing equipment (shakers and controllers) and the increased complexity of items to be tested is such that this impressive practice is becoming more and more relevant, a full understanding of the process is still underway. The level of expertise needed to run these tests is the price to be paid to take into account the inter-axis interaction that makes this type of technology the best solution for high-fidelity environment replication.
The target that needs to be reached during the MIMO Random test is a full Spectral Density Matrix. Even if on one hand filling in this matrix with no a-priori knowledge of the cross-correlation between control channels is very challenging, on the other hand an ad-hoc choice of the cross-terms can bring interesting features. This work shows the possibility of obtaining a realizable target that minimizes the shakers’ required power without modifying the PSD levels set at the control points. The capability of the method is demonstrated on real tests application cases.