Publication news

ABS braking on rough terrain

Nico A. van der Merwe, P. Schalk Els, Vidas Žuraulis,

Journal of Terramechanics, Volume 80, 2018, Pages 49-57, ISSN 0022-4898,

Abstract: The performance of Anti-lock Brake Systems (ABS) for vehicles deteriorate on rough terrains, due to fluctuations in the angular wheel speeds and in the vertical loading conditions of the tyre caused by the terrain inputs. In this paper, ABS braking performance on non-deformable rough terrain is investigated by performing experiments and simulations using a testing trailer and a validated multi-body dynamics model. The trailer was constructed using a Land Rover Defender chassis and installed with standard Land Rover braking components including an ABS modulator. It was found in the ABS tests performed, while using a standard Bosch ABS algorithm, that the ABS algorithm failed to perform optimally due to oscillations and irregularities that were present in the measurement of angular wheel speeds. Good correlation is found between the tyre forces measured and the forces simulated using an FTire model in MSC ADAMS software. A powerful platform was created for future off-road ABS investigation and development using both experiments and a simulation platform.

Keywords: Anti-lock braking system; ABS; Rough terrain; ADAMS; FTire; Belgian paving

Comparison of simulation models NRMM and NTVPM for assessing military tracked vehicle cross-country performance

J.Y. Wong, P. Jayakumar, E. Toma, J. Preston-Thomas,

Journal of Terramechanics, Volume 80, 2018, Pages 31-48, ISSN 0022-4898

Abstract: Mobility of ground vehicles is an important issue for defence operations. In the United States and some other NATO countries, the NATO Reference Mobility Model (NRMM) is currently used to evaluate military ground vehicle mobility. The cross-country performance prediction module of NRMM is based on empirical relations established with test data primarily collected decades ago. It has inherent limitations, such as the uncertainty whether the empirical relations can be extrapolated beyond the test conditions upon which they were derived. This paper describes a comparison of the empirically-based NRMM with the physics-based Nepean Tracked Vehicle Performance Model (NTVPM) for assessing the cross-country performance of military tracked vehicles. It examines the soundness of the methodologies of NRMM and NTVPM, the adequacy of the vehicle design parameters and terrain characteristics that they take into account, the user friendliness of their operations, and the correlations between the measured cross-country performance of a notional tracked vehicle (an armoured personnel carrier) and that predicted by the two simulation models on sandy terrain, muskeg and snow-covered terrain. Based on the results of the evaluation, it appears that the physics-based NTVPM has potential as the basis for the development of the next generation simulation model for assessing the cross-country performance of military tracked vehicles.

Keywords: Coefficient of correlation; Coefficient of variation; Computer simulation models; Cross-country performance; Empirical models; Mean maximum pressure; Measured data; Physics-based models; Predicted performance; Tracked vehicles

Road profile reconstruction using connected vehicle responses and wavelet analysis

Zhiming Zhang, Chao Sun, Raj Bridgelall, Mingxuan Sun

Journal of Terramechanics, Volume 80, 2018, Pages 21-30, ISSN 0022-4898,

Abstract: Practitioners analyze the elevation profile of a roadway to detect localized defects and to produce the international roughness index. The prevailing method of measuring road profiles uses a specially instrumented vehicle and trained technicians, which usually leads to a high cost and an insufficient measurement frequency. The recent availability of probe data from connected vehicles provides a method that is cost-effective, continuous, and covers the entire roadway network. However, no method currently exists that can reproduce the elevation profile from multi-resolution features of the vehicle inertial response signal. This research uses the wavelet decomposition of the vehicle inertial responses and a nonlinear autoregressive artificial neural network with exogenous inputs to reconstruct the elevation profile. The vehicle inertial responses are a function of both the vehicle suspension characteristics and its speed. Therefore, the authors normalized the vehicle response models by the traveling speed and then numerically solved their inertial response equations to simulate the vehicle dynamic responses. The results demonstrate that applying the artificial neural network to the wavelet decomposed inertial response signals provides an effective estimation of the road profile.

Keywords: Road roughness; Profile reconstruction; Vehicle response; Wavelet analysis; Neural network

Evaluating mobility vs. latency in unmanned ground vehicles

David J. Gorsich, Paramsothy Jayakumar, Michael P. Cole, Cory M. Crean, Abhinandan Jain, Tulga Ersal

Journal of Terramechanics, Volume 80, 2018, Pages 11-19, ISSN 0022-489

Abstract: As the penetration levels of unmanned ground vehicles (UGVs) in military applications increase, there is a growing need to evaluate their mobility across different latencies and various modes of operation ranging from pure teleoperation to full autonomy. State-of-the-art tools to evaluate mobility of ground vehicles do not address this need due to their not accounting for UGV technologies and the associated latencies. Although the trade-off between latency and performance has been thoroughly studied in the telerobotics literature and the results may qualitatively shed light onto the UGV domain, as well, a quantitative generalization is not possible due to the differences in context. Recognizing this gap, this paper presents a functional relationship between mobility and latency in high-speed, teleoperated UGVs under the context of path following. Specifically, data from human-in-the-loop simulations performed in this paper are combined with data from prior studies to span three vehicle types, three courses, and teleoperation latencies ranging from 0 s to 1 s. This combination yields for the first time a diverse data set for the context of path following in high speed, teleoperated UGVs. Based on this data set, empirical relationships are derived to quantify the trade-off between latency versus average speed and lane keeping error. These relationships can be used to establish a benchmark to evaluate the performance of autonomy-enabled UGV systems.

Keywords: Mobility; Latency; Unmanned ground vehicles; Teleoperation

Use of explicit finite-element formulation to predict the rolling radius and slip of an agricultural tire during travel over loose soil

Dror Rubinstein, Itzhak Shmulevich, Nicolay Frenckel,

Journal of Terramechanics, Volume 80, 2018, Pages 1-9, ISSN 0022-4898,

Abstract: Theoretically, there is zero slip between two bodies when there is no relative motion in their contact points. In the contact between a wheel and a surface, zero slip can be obtained only in the case of a single contact point. In this case, the wheel and the surface must be rigid. The theoretical zero-slip condition can’t be obtained in the contact between tire and terrain surface. In much of the scientific literature, two alternatives are suggested for a practical definition of the zero-slip condition: the point at which the gross traction force is equal to zero, or the point at which the net traction force is equal to zero. In the ASABE (2013), there is still no unique definition for the practical zero-slip condition. According to the definition of zero-slip condition, the rolling radius is not constant and depends on the slip. A detailed finite-element model using Lagrangian elements was built for each tire, taking into account the effect of all tire materials and their arrangement, lug shape, and inflation pressure. The soil model was built with Eulerian elements, which allow a large degree of deformation and flow of the soil. The initial verification experiments of the tire models were conducted by pressing the tires against a rigid plane. Each tire was examined under several different inflation pressures. Very good correlations were obtained between the experimental and model results. The verification test for the gross and net traction forces was performed in the soil-bin laboratory at the Technion. Special equipment was built, including a heavy dragging platform and a cell to hook the tire. This equipment allows control of the tire slip. The net traction force, gross traction force, and vertical load were measured in each test. Good correlations were obtained between the experimental and model results. Using the FEM model developed, some definitions for zero-slip condition were examined. The results indicate that the best criterion for zero-slip condition is definition of the point at which the gross traction force is equal to zero.

Keywords: Soil wheel interaction; Gross traction; Net traction; Finite element; Eulerian; Lagrangian; Zero slip

A method for deducing pressure–sinkage of tracked vehicle in rough terrain considering moisture and sinkage speed

Congbin Yang, Guang Yang, Zhifeng Liu, Huaxiong Chen, Yongsheng Zhao,

Journal of Terramechanics, Volume 79, 2018, Pages 99-113, ISSN 0022-4898,

Abstract: Tracked vehicles assume an important role in engineering and agriculture. Supporting-trafficability is the lifeline of tracked vehicles. The terrain characteristics is concerned with the relationships critical in defining the mobility of tracked vehicles. Conventional terramechanics models cannot accurately describe the relationship between tracks and soil. A major problem is that these models do not account for the water content in the soil and sinkage speed. Water content is an important factor affecting sinkage of vehicles, which in turn affects vehicles’ driving resistance. Increased driving resistance is a barrier to the mobility of an tracked vehicle. Considering sinkage speed is conducive to describe the trafficability of tracked vehicle moving at high speed. In this paper, the terrain characteristics to describe the relationship of the pressure/sinkage of four common soil types in Southwest China were measured using soil bin tests. We discuss characteristics like high sinkage speed, water content variation, and repeated loading, as well as the relationships of these major factors with the deformation of soil. We present a method to deduce the pressure-sinkage relationship for track shoes using the stress-displacement relationship model proposed by Bekker. The described method advances the study and understanding of track-terrain interaction in complex environments.

Keywords: Supporting-trafficability; Tracked vehicle; Rough terrain; Pressure-sinkage relationship; Terramechanics

Estimation of terramechanics parameters of wheel-soil interaction model using particle filtering

Shamrao, Chandramouli Padmanabhan, Sayan Gupta, Annadurai Mylswamy

Journal of Terramechanics, Volume 79, 2018, Pages 79-95, ISSN 0022-4898,


Abstract: Accurate estimation of the parameters affecting the wheel-soil interaction terramechanics of an extraterrestrial rover is key to the success of its mission. Traditional approaches to estimating the relevant parameters based on laboratory tests lead to predictions that show significant deviation from experimental observations. The objective of this article is to apply dynamic Bayesian estimation techniques on the measurements from simple single wheel tests to estimate the terramechanics parameters. This ensures that the parameter estimation takes into account the scatter that invariably exists in physical measurements. A mathematical model for a rigid wheel driven on a dry (0% moisture content) granular soil medium is considered to model the planetary regolith. It is demonstrated that adopting Bayesian techniques for terramechanics parameter estimation leads to good predictions for the drawbar pull, torque and the wheel sinkage. This bypasses the need for using more complex models which in turn require additional parameters to be estimated.

Keywords: Wheel-soil interaction; Dynamic Bayesian estimation; Particle filter; Single wheel test; Bevameter

Determination of in-situ engineering properties of soil using an inverse solution technique and limited field tests

Qingsong Zhang, Shrini K. Upadhyaya, Qingxi Liao, Xuan Li

Journal of Terramechanics, Volume 79, 2018, Pages 69-77, ISSN 0022-4898,

Abstract: The goal of this research is to develop a response surface based inverse solution technique to determine in-situ engineering properties of soil for use in mobility and traction prediction models from the force displacement data generated by a cone penetrometer device. The nonlinear elasto-plastic behavior of soil was characterized by a six-parameter constitutive model – two elastic parameters (i.e., bulk modulus, K and the Poisson’s ratio, υ), three plastic parameters (i.e., angle of internal friction φ, cohesion c, and soil hardening parameter λ), and one soil physical condition parameter (i.e. initial void ratio, e∗). Soil failure was represented by the Drucker-Prager yield criterion and associated flow rule. LS-DYNA FEM software package was used to model the soil-cone interaction problem. FEM simulations were conducted for a set of soil properties properly selected within the defined parameter space. The analysis of FEM simulations indicated that the cone penetration force-displacement curves could be represented by two piecewise smooth functions – a parabola followed by a straight line. The coefficients of these two curves were used to create fourth order response surfaces using a stepwise multiple linear regression technique. The results showed both cohesion and soil hardening parameter could be predicted using this methodology.

Keywords: Finite element modeling; Machine-soil interaction; Nonlinear behavior; Optimization

Assessment of the side thrust for off-road tracked vehicles based on the punching shear theory

Sung-Ha Baek, Gyu-Beom Shin, Choong-Ki Chung,

Journal of Terramechanics, Volume 79, 2018, Pages 59-68, ISSN 0022-4898,


Abstract: The track system is generally applied for heavy off-road vehicles. While moving on the off-road, the track system horizontally transmits an engine torque to the soil-track interface, resulting in slip displacement and an associated soil thrust acting as a traction force. As soil thrust is developed on the bottom and the side of the track system (hereinafter referred to as “bottom thrust” and “side thrust”, respectively), it is imperative to evaluate both the bottom thrust and the side thrust to assess the off-road tracked vehicle’s performance. Unlike the bottom thrust, however, the mechanisms of the side thrust have not been fully understood. To address this, this study aimed to evaluate the side thrust for off-road tracked vehicles. A new mechanism for the side thrust was theoretically investigated based on the punching shear theory. A series of model track experiments were conducted on a model track system with silty sand. From the experiment results, the shapes of the failure surface were observed, and the side thrust was measured for verification purposes. Particular attention was given to the development of a side thrust prediction model for the heavy off-road tracked vehicles based on the proposed mechanism.

Keywords: Off-road tracked vehicle; Track system; Tractive performance; Side thrust; Model track experiment; Soil-track interaction; Punching shear theory