Converting a Slip Table Random Vibration Test to a Fixed Base Modal Analysis

Abstract

Validation of finite element models using experimental data with unknown boundary conditions proves to be a significant obstacle. For this reason, the boundary conditions of an experiment are often limited to simple approximations such as free or mass loaded. This restriction means that vibration testing and modal analysis testing have typically required separate tests since vibration testing is often conducted on a shaker table with unknown boundary conditions. If modal parameters can be estimated while the test object is attached to a shaker table, it could eliminate the need for a separate modal test and result in a significant time and cost savings. This research focuses on a method to extract fixed base modal parameters for model validation from driven base experimental data. The feasibility of this method was studied on an Unholtz-Dickie T4000 shaker and slip table using a mock payload and compared with results from traditional modal analysis testing methods.

Appendices

Appendix 1 Unconstrained Mode Shapes on Seismic Mass

Fig. A1.1

Rigid X on seismic

Fig. A1.2

Rigid Y on seismic

Fig. A1.3

Twist about Z on seismic

Fig. A1.4

Rigid Z on seismic

Fig. A1.5

Twist about Y on seismic

Fig. A1.6

Twist about X on seismic

Fig. A1.7

Elastic mode 1 on seismic

Fig. A1.8

Elastic mode 2 on seismic

Fig. A1.9

Elastic mode 3 on seismic

Fig. A1.10

Elastic mode 4 on seismic

Appendix 2 Unconstrained Mode Shapes on Shaker Table

Fig. A2.11

Rigid fore-aft on shaker table

Fig. A2.12

Lateral mode of shaker table

Fig. A2.13

Vertical mode of shaker table

Fig. A2.14

Elastic 1 on shaker table

Fig. A2.15

Elastic 2 on shaker table

Fig. A2.16

Elastic 3 on shaker table

Fig. A2.17

Elastic 4 on shaker table