Off-Road Mobility and Terramechanics: Theory into Practice - J. Y. Wong

This is the 2022 William H. Milliken Lecture Award presented by Prof. J. Y. Wong at the ASME IDETC-CIE Conference, 2022. It is also uploaded on the ISTVS Resource Initiative page: istvs.notion.s...
Abstract: A wide range of human endeavors, such as farming, natural resources exploration and exploitation, and defense operations, involve locomotion over unprepared terrain and wheeled or tracked off-road vehicles are commonly used. On highly deformable terrain, the thrust generated by the wheels or tracks may not be able to overcome the motion resistance and this would lead to immobilization. To predict off-road mobility, the understanding of the mechanics of vehicle-terrain interaction, which has now become known as terramechanics, is essential.
There are three basic issues in terramechanics: the measurement and characterization of terrain behavior; the elucidation of the mechanics of vehicle-terrain interaction; and the establishment of the relationships among mobility, vehicle design, and terrain characteristics. The aim of terramechanics is to provide guiding principles for the rational development and design of terrestrial off-road vehicles and extraterrestrial rovers in various operating environments. This lecture reviews the current status and future prospects of terramechanics.
A common technique for measuring the response of terrain to vehicular loadings uses a device known as the bevameter (conceived by Dr. M.G. Bekker, a pioneer in terramechanics). From measurements, parameters for characterizing terrain behavior are derived and they have become known as the Bekker-Wong (B-W) terrain parameters. They are adopted in the 2020 Standards of the International Society for Terrain-Vehicle Systems.
Using the B-W parameters to characterize terrain behavior, the mechanics of vehicle running gear (wheel or track)-terrain interaction is elucidated. As a result, an analytical framework has been established and computer simulation models for performance and design evaluation of wheeled and tracked vehicles have been developed. A representative model for tracked vehicles is presented. Its basic features have been substantiated with field test data. The model has been employed to assist off-road vehicle manufacturers in many countries in the development of new products, as well as governmental agencies in the evaluation of vehicle candidates from the procurement perspective. An example of the applications of the model to the development of a high-mobility version of a tracked armored vehicle is presented.
With mankind's increasing interest in the exploration of the universe, manned or unmanned rovers have been deployed to the Moon and Mars for surface exploration. To assess the potential of a simulation model originally developed for terrestrial wheeled vehicles for evaluating the mobility of future generations of extraterrestrial rovers with flexible wheels, a study was conducted to use the model for predicting the performance of a wire-mesh, flexible wheel for the manned Lunar Roving Vehicle used in the NASA Apollo Program, and the results are encouraging. Methods have also been developed for predicting the performances of rovers and their wheels on extraterrestrial surfaces under various gravities from the test results obtained on earth under earth's gravity. The basic features of these methods have been substantiated with test data.
Prospects for further developments of terramechanics are discussed. Applications of computational methods, such as the discrete element method (DEM) and the finite element method (FEM) to the analysis of the mechanics of vehicle-terrain interaction are reviewed. Challenges and opportunities in the field are indicated.
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