Characterization and synthesis of random acceleration vibration specifications

摘要

Random acceleration vibration specifications for subsystems, i.e. instruments,udequipment, are most times based on measurement during acoustic noise tests on system level, i.e. a spacecraft and measured by accelerometers, placed in the neighborhood of the interface between spacecraft and subsystem. Tuned finite element models can be used to predict the random acceleration power spectral densities at other locations than available via the power spectral density measurements of the acceleration. The measured and predicted power spectral densities do represent the modal response characteristics of the system and show many peaks and valleys. The equivalent random acceleration vibration test specification is a smoothed, enveloped, peak-clipped version of the measured and predicted power spectral densities of the acceleration spectrum.udThe original acceleration vibration spectrum can be characterized by a different number response spectra: Shock Response Spectrum (SRS) , Extreme Response Spectrum (ERS), Vibration Response Spectrum (VRS), and Fatigue Damage Spectrum (FDS). An additional method of non-stationary random vibrations is based on the Rayleigh distribution of peaks. The response spectra represent the responses of series of SDOF systems excited at the base by random acceleration,udboth in time and frequency domain. The synthesis of equivalent random acceleration vibration specifications can be done in a very structured manner and are more suitable than equivalent random acceleration vibrationudspecifications obtained by simple enveloping. In the synthesis process Miles’ equation plays a dominant role to invert the response spectra into equivalent random acceleration vibration spectra. A procedure is proposed to reduce the number of data point in the response spectra curve by dividing the curve in a numbers of fields. The synthesis to an equivalent random acceleration spectrum is performed on a reduced selected set of data points. The recalculated responseudspectra curve envelops the original response spectra curves. A real life measured random acceleration spectrum (PSD) with quite a number of peaks andudvalleys is taken to generate, applying response spectra SRS, ERS, VRS, FDS and the Rayleigh distribution of peaks, equivalent random acceleration vibration specifications. Computations are performed both in time and frequency domain.