A Practical Method for Estimating Ground Vehicle Frequency Response Function from Response Data

摘要

This paper describes the investigation of a practical method for estimating the Frequency ResponseFunction (vibration transmissibility) of ground vehicles using only vibration response data. The approach relieson the fact that the elevation of road surfaces (longitudinal profile), which is random, can be characterisedby a well-defined spectral function such as that used by the International Standards Organisation. Thepaper shows that, if a vehicle is driven on a road with a random elevation profile at a known constant speed,an approximate relationship between the average Power Spectral Density of the vertical response vibrationsand the transmissibility of the vehicle for the vertical vibration mode can be derived. An initial series of experimentswas undertaken to test the hypothesis by comparing results obtained from field data with transmissibilitymeasurement made under controlled conditions using a servo-hydraulic vibration test rig. Field datawas obtained by driving the test vehicle at predetermined constant speeds along various stretches of roadwhile continuously recording the vertical acceleration in line with the rear axle. Measurements of vehiclelimited white noise for displacement, velocity and acceleration) as well as various excitation severities (overallroot-mean-square level) in order to establish the influence, if any, of nonlinearities in the system. Resultsfrom these preliminary experiments show that the commonly used exponent for the spectral characteristics ofpavement is not always valid for finite road lengths. The mathematical model relating the vertical responsepower spectral density of a vehicle to its transmissibility was further developed to enable the extraction of theoptimum spectral exponent. This is achieved using vibration response data for a single vehicle travelling onthe same road at two or more predetermined speeds. Results from further experiments show that reasonablyaccurate estimates of vehicle transmissibility can be obtained notwithstanding the simplified approach andnonlinearities of the system. The method affords a practical and economical means for estimating the frequencyresponse characteristics of ground vehicles.