Simulating Base-Shake Environmental Testing
In most military aircraft and spacecraft applications, each payload structure must be pre-tested on a shake table to insure that it can withstand the vibration environment that it will experience during flight. Shaker testing is done using a control PSD which is designed to realistically represent the floor motion of the aircraft during takeoff, in flight, or during landing. Qualification testing is typically done by mounting the test article on one or more shakers, and exciting it with a closed loop shaker testing system so that the base of the payload responds with the pre-specified control PSD. When a test vehicle is too massive to be tested by mounting it on shakers, it is impossible to perform a base-shake test on a shake table. So the question arises; “Are there other more convenient driving points from which to excite the structure which will simulate a base-shake test?” In this approach, we derive a frequency domain Transmissibility model which is used to calculate PSDs for convenient driving points as functions of the base-shake PSDs. These calculated PSDs would then used to control a shaker test that simulates the base-shake test. The Transmissibility model is validated by using an inverse calculation to calculate base-shake PSDs as functions of thenew driving point PSDs. Suitable driving points can then be chosen by comparing the calculated base-shake PSDs with the original pre-specified base-shake PSDs.
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