4.8 Conclusions The six shaker input simulation was able to nearly replicate the results of an acoustic test environment up to about 3500 Hz. The match from 3500 to 4000 Hz was not very good. The element by element square of the absolute value of the FRF matrix was used with the target acceleration autospectra to calculate six voltage autospectra used for the input voltage to the shaker amplifiers in the inverse problem. Tikhonov regularization was utilized to reduce these inputs. Cross spectra were not needed for this method. Reduction of the force requirement was achieved by increasing the Tikhonov constant without a significant reduction in accuracy of matching the 37 internal target acceleration responses. The inverse problem was also calculated for 12 of the original 37 target autospectra with only a small reduction in accuracy of the simulation. Some additional reduction in the required forces appeared available based on the location of the shaker attachment. For the 4000 Hz bandwidth, it was found that the shakers could produce about three times the rated force input when attached to hard points of a structure. At soft structural force connection locations, the maximum force was limited by the amplifiers in the cases we tested. The slip force of the stingers and set screws was characterized to provide a degree of protection for the shakers and the test article. Notice. This manuscript has been authored by Sandia Corporation under Contract No. DE-AC04-94AL85000 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. Acknowledgments The acoustic test was performed by Eric Stasiunas and Ryan Schultz. Anthony Gomez was the primary technologist involved in the data acquisition along with the authors. Jerry Cap was the prime motivator who was able to get the testing programmed and funded. Diane Callow provided a huge portion of the logistic support in terms of writing the test plan and getting the testing approved to meet the operational and safety requirements. Bill Fladung from ATA engineering showed us how to input user defined time histories into the VTI source modules. 0 500 1000 1500 2000 2500 3000 3500 4000 10-2 10-1 100 101 102 103 104 Calculation of Floor Sum of PSDs Frequency - Hz Acoustic Truth Test MIMO Calculation with c=0.1 Fig. 4.12 Calculated sum of PSDs match for 6 floor mounted shakers and Tikhonov c value of 0.1 40 R.L. Mayes and D.P. Rohe
RkJQdWJsaXNoZXIy MTMzNzEzMQ==