On the non-Gaussian nature of random vehicle vibrations

This paper presents one of the outcomes of a research project concerned with the development of a method for synthesizing, under controlled conditions in the laboratory, the random vibrations generated by road transport vehicles. It addresses some of the deficiencies and limitations of current random vibration synthesis methods used for evaluating and validating the performance of packaging systems. The paper deals with the development of a technique for decomposing non-stationary random vibration signals into constituent Gaussian elements. The hypothesis that random non-stationary vehicle vibrations are essentially composed of a sequence of zero-mean random Gaussian processes of varying standard deviations is tested and the paper reveals that the variations in the magnitude of the vibrations are the cause of the leptokurtic, non-Gaussian nature of the process. It is shown how non-stationary vibration signals can be systematically decomposed into these independent random Gaussian elements by means of a numerical curve-fitting procedure. The paper describes the development of the algorithm which is designed to automatically extract the parameters of each constituent Gaussian process namely the RMS level and the Vibration Dose. The validity of the Random Gaussian Sequence Decomposition (RGSD) method was tested using a set of road vehicle vibration records and was found to be capable of successfully extract the Gaussian estimates as well as the corresponding Vibration Doses. Validation was achieved by comparing the sum of these Gaussian estimates against the PDF of the original vibration record. All validation cases studied show that the RGSD algorithm is very successful in breaking-down non-stationary random vibration records into their constituent Gaussian processes. Finally, the significance and relevance of this technique with respect to the synthesis of non-stationary vibrations for package evaluation and validation purposes is highlighted