Extracting fixed base modal models from vibration tests on flexible tables.
a acceleration dof degree of freedom H Frequency response function f Applied force FE Finite Element FRF Frequency Response Function Φc The mode shape matrix of the bare table at dof to be constrained Subscripts c degree of freedom at locations to be constrained f dof at free locations t dof at tip of the slip table s dof at the classic shaker input location on the slip table i any other dof not including t or s
Determination of Effective Masses and Modal Masses from Base- Driven Tests.
This paper deals with the identification of effective masses and modal masses from base-driven tests. When preforming a base-driven test with an elastomechanical structure, the structural responses can be related to the base accelerations and a modal identification of the structure can be accomplished. If, in addition, the base forces are measured, it is possible to determine the effective and modal masses of the structure. Here, the required equations describ- ing the dynamic behaviour are first developed and discussed.An analytical vibration system with simulated measurement errors is usedfor demonstrating the identification. In addition, a method to improve the accuracy of the identified parameters is shown.Based on the encouraging results, the application to real test data is en- visaged for further investigations.
Structural modification utilizing beam elements
A method for analyzing the effects of sophisticated beam-type structural modifications to a structure with a known modal database is presented. The modification technique integrates the dual modal space modification method with the transfer matrix method to perform general beam modifications. Consideration is given to two examples: one demonstrates the performance of the modification scheme when a severe structural change is made, while the other demonstrates a change to a complex structure.