IMPLEMENTACIÓN DEL A.V.A

INTRODUCTION

A developed and well-maintained road network is imperative for the distribution of freight in the modern world. During transportation, both passengers and products are subjected to dynamic motion due to the irregular nature of pavement surfaces. This dynamic interaction is difficult to accurately predict due to the random and nonstationary nature of pavements and the complicated (and often nonlinear) dynamic characteristics of vehicles. Accurately characterising the dynamic motion generated by vehicles during transport would provide significant benefits to numerous fields.

One field of interest is in the development of protective packaging systems to prevent, or minimise, product damage occurring during the distribution phase. Often, the level of packaging used is far greater than required, resulting in excessive waste which is of significant environmental concern. Another is in evaluating the performance of heavy vehicles to prevent and minimise pavement damage. As a heavy vehicle passes over a pavement, dynamic forces are exerted onto the pavement and induce damage, resulting in rougher roads. The maximum allowable loads of heavy vehicles is constantly increasing, further emphasising the importance of designing suspension systems which are considered road-friendly. For both fields it is important to establish accurate estimates of the dynamic characteristics, namely the Frequency Response Function (FRF), of vehicles.

This thesis is focused on the development and validation of a practical technique to estimate the dynamic characteristics of road vehicles, namely the Frequency Response Function (FRF), using only in-service vibration response data. Currently, various methods are available to estimate the dynamic characteristics and are separated into two broad categories; response-only (transient) and excitation-response methods. There are numerous drawbacks associated with both types of approaches, such as cost and relevance. Furthermore, these approaches all require the vehicle to be removed from operation. The development of a practical method to estimate the dynamic characteristics using only response data measured during a vehicle’s normal operation would offer significant benefits to numerous industries.

Chapter 2 describes the background and impetus of the research undertaken in this thesis, primarily focused on the optimisation of protective packaging for products during transportation. The significance of vehicle ride quality and the use of protective packaging systems to prevent product damage are explained. The optimisation of protective packaging systems by simulating transportation vibration in the laboratory is also discussed. A history of quantifying pavement deterioration due to the passage of heavy vehicles, focused on establishing the road-friendliness of heavy vehicles, is presented.

Chapter 3 presents a comprehensive literature review related to vehicle-road interaction. The Chapter is divided into three main sections. The first section discusses the fundamental quarter car model commonly used in vehicle dynamic simulations and its dynamic characteristics. The second section of the literature review is focused on the nature of longitudinal pavement profiles and the development of various spectral models used to approximate them. A brief investigation into the statistical nature of longitudinal pavement profiles is also discussed. The third section describes the various experimental approaches and analysis techniques used to estimate the dynamic characteristics of vehicles. The section is separated into the three different categories; response-only (transient), excitation-response and in-service response methods.

Chapter 4 presents the principal hypothesis of the research and is supported by a number of sub- hypotheses. Chapter 5 describes the methodology of the research to be undertaken in this thesis. First, the design and configuration of an idealised, single-wheeled vehicle to validate the various experimental approaches is described. The general methodology to critically evaluate the current methods used to estimate the dynamic characteristics of vehicles (to determine the true FRF of the vehicle) is outlined, focusing on both response-only (transient) and excitation- response methods. The methodology for the in-service experiments is also presented and discusses important considerations that must be made, such as the selection of suitable roads for testing.

Chapter 6 presents an experimental evaluation of the various approaches currently available to estimate the dynamic characteristics of vehicles and determine the true FRF, if it exists, of the idealised vehicle. Both response-only (transient) and excitation-response methods are evaluated and compared using the prototype vehicle.

Chapter 7 is focused on the development and methodology of two analytical techniques to estimate the dynamic characteristics of vehicles using only in-service response data. The first approach is based on the fact that the transmissibility FRF of a quarter car vehicle tends towards one at low frequencies. Combining an assumed spectral function to represent the road elevation profile with the vibration response data, the approach aims to estimate both the dynamic characteristics of the vehicle and the road spectral properties. The second analytical method uses the random decrement technique to obtain the random decrement signature from the response of the vehicle, from which the dynamic characteristics may be estimated. The random decrement technique can be used to estimate the sprung mass mode dynamic characteristics or the FRF directly from the signature. An experimental evaluation to ascertain the optimum parameters of the random decrement signature for the estimation of the dynamic characteristics for both approaches is also presented.

Chapter 8 presents the results from a series of in-service experiments using the idealised vehicle. The first series of experiments were undertaken using the idealised vehicle; however inconsistencies were found and ultimately required the actual profile travelled by the vehicle to be known. The second series of in-service experiments were undertaken with the idealised vehicle instrumented as an inertial profilometer. An investigation into the minimum length of road required to obtain a sufficient estimate of the dynamic characteristics was undertaken using a Monte Carlo simulation. The Chapter closes with the estimation of the dynamic characteristics of in-service response data measured from two transport vehicles during normal operation. Chapter 9 concludes the thesis by outlining the main outcomes of the research and identifies future work that may be undertaken.