Comparative Assessment of Force Estimation in MIMO Tests

Dynamic testing of systems is most realistic of real-world conditions when multiple input and multiple output (MIMO) techniques are used. To replicate measured environmental conditions, a series of desired outputs on the system must be realized by inverting the frequency response functions (FRF) matrix for force estimation. Depending on the number of inputs and outputs, the type and number of solutions can vary significantly. Depending on the objective of the test, defining the target response can also vary, such as matching accelerations, stresses, or strains at various locations. In MIMO testing, both the auto spectra and cross spectra of the outputs affect the auto spectra of the inputs. Defining the most relevant outputs and the optimal input spectra is an ongoing challenge and has attracted recent attention. This research evaluates the errors associated with these variables on a linear multi-story frame fixed at the base. Three inputs are provided uniaxially with the use of suspended electrodynamic shakers, and up to nine output locations are instrumented with accelerometers. Results of tests are analyzed to guide improved MIMO testing.