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Advances in Aircraft and Spacecraft Science
  Volume 7, Number 1, January 2020 , pages 79-90

A lower bound analytical estimation of the fundamental lateral frequency down-shift of items subjected to sine testing
Pietro Nali and Adriano Calvi

    The dynamic coupling between shaker and test-article has been investigated by recent research through the so called Virtual Shaker Testing (VST) approach. Basically a VST model includes the mathematical models of the test-item, of the shaker body, of the seismic mass and the facility vibration control algorithm. The subsequent coupled dynamic simulation even if more complex than the classical hard-mounted sine test-prediction, is a closer representation of the reality and is expected to be more accurate. One of the most remarkable benefits of VST is the accurate quantification of the frequency down-shift (with respect to the hard-mounted value), typically affecting the first lateral resonance of heavy test-items, like medium or large size Spacecraft (S/Cs), once mounted on the shaker. In this work, starting from previous successful VST experiences, the parameters having impact on the frequency shift are identified and discussed one by one. A simplified analytical system is thus defined to propose an efficient and effective way of calculating the lower bound frequency shift through a simple equation. Such equation can be useful to correct the S/C lateral natural frequency measured during the test, in order to remove the contribution attributable to the shaker in use. The so-corrected frequency value becomes relevant when verifying the compliance of the S/C w.r.t. the frequency requirement from the Launcher Authority. Moreover, it allows to perform a consistent post-test correlation of the first lateral natural frequency of S/C FE model.
Key Words
    vibration testing; seismic mass; frequency shift; Virtual Shaker Testing
Pietro Nali:Thales Alenia Space, Strada Antica di Collegno, 253, 10146, Turin, Italy

Adriano Calvi: European Space Agency ESA/ESTEC, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands

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