Experimental Comparison of Maximum Length Sequence (MLS) and Impact Hammer Methods to Evaluate Vibration Transfer Functions in Soil

Abstract

The purpose of this paper is to test the validity of a pseudo binary sequence based method which is spectrally flat, and which is called MLS (for Maximum Length Sequences) to assess the differences in the level of vibration between different accelerometers, and evaluate key parameters that can be changed to improve the results. Before checking the validity of the MLS method, a description of the site where the test took place and a comparison of three different methods to setup accelerometers in soil are given. Measurements are also used to compute the improvement of signal to noise ratio as a function of the number of hits. Comparison between the impact hammer and MLS method is then analyzed. The main aspects of the signal processing used to analyze MLS and impact hammer signals are presented. Some information on the type of device used in the study and the primary characteristics of measured impulse responses are also presented. A comparison of mitigation at different distances between the MLS method (fixed parameters) and impact hammer method is then given. A parametric study is then performed on each MLS key parameter: MLS order, number of means, number of impulse responses analyzed, influence of background noise and linear behavior of the electrodynamic shaker. Finally, the variation of soil properties measured with the MLS and impact hammer methods over five days is given.KeywordsLinear Feedback Shift RegisterOctave BandImpact HammerMaximum Length SequenceVibration MitigationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.