3. Frequency Based Spatial Damping Identification—Theoretical and Experimental Comparison

This research compares spatial damping identification methods, both theoretically and experimentally. In contrast to the commonly used damping methods (modal, proportional) the spatial damping information improves structural models with a known location of the damping sources. The real case robustness of full FRF matrix and local equation of motion methods were tested against: modal and spatial incompleteness, differences in viscous and hysteretic damping models and the effect of damping treatments. To obtain accurate results, a careful analysis of measurements in terms of reciprocity in the raw measurements, and in terms of how to preserve symmetry has to be done. It was found that full FRF matrix needs to be symmetrisized due to small deviations in reciprocity before the damping identification. Full frequency response function (FRF) matrix methods (e.g.: Lee-Kim) can identify the spatial damping if spatial and modal incompleteness are carefully evaluated, but the measurement effort increases with second order and, consequently, the size of the FRF matrix.