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Presenter: Dr. Ramin Sedaghati, NRC Research Fellow, Canadian Space Agency
Supervisor:

Date: Fri, August 17, 2001
Time: 11:00:00 - 00:00:00
Place: EOW 430

ABSTRACT

Abstract:

The main goal of random vibration testing of a space structure is to ensure that the structure will survive the launch environment. Ideally, the input acceleration and forces to the structure during a vibration test would be the same, plus sometimes a known acceptable margin, as those encountered during the flight. However, because of the high complexity associated with such attempts due partly to the statistical nature of the launch environment, and to controller limitation (especially for older versions), this ideal situation is not really practical and has been replaced by testing procedures which often generates high vibrations at certain critical frequencies of the test article.

The traditional practice for specifying the input excitation for vibration testing is to envelop the launch interface acceleration spectra obtained normally from analytical methods such as couple load analysis, which is based on finite element models of both the test article and the mounting structure. The penalty of overtesting with conventional vibration test appears in design and performance compromises, as well as in the high costs and schedule overruns associated with recovery from artificial test failures, which would have not occurred during the flight.

In today's very competitive global market, there is a definite need for testing advanced space hardware with state-of-the-art technologies, instead of with the traditional approach, which has very high design margin with respect to flight environment. An improved random vibration test approach has been developed and implemented at NASA Jet Propulsion Laboratory (JPL), in the nineties. The approach is called Force Limited Vibration (FLV) testing. It has been used since its implementation in several space missions and has been validated with system level acoustic test and flight data.

Although the basic ideas behind FLV have been in the literature for several decades, it is the advent of new triaxial force sensors for a completely different market, which made its implementation easily available. In addition of controlling the input acceleration, the FLV testing measures and limits the reaction forces between the test article and the shaker through real time notching of the input acceleration. This seminar discusses the overtesting problem associated with traditional vibration testing. Some of the key features of the FLV testing are outlined. Some of the results in demonstrating the FLV testing by applying it to simple test articles are presented.