Development and numerical validation of an improved prediction model for wheel-soil interaction under multiple operating conditions

Yonghao Du, Jingwei Gao, Lehua Jiang, Yuanchao Zhang
Journal of Terramechanics, Volume 79, 2018, Pages 1-21, ISSN 0022-4898, 
https://doi.org/10.1016/j.jterra.2018.04.005.

Abstract: This paper presents the establishment and validation of an improved model predicting tractive parameters of a lugged wheel under multiple operating conditions. During the basic straight driving wheel-soil interaction, the common-used equivalent radius theory and the bulldozing theory are combined to calculate the lug effects referring the traditional theories of soil stress distribution, while the bulldozing effect is reconsidered according to the work conservation. On the basis of the further prediction under multiple conditions including the inclination in three degrees of freedom and the turning driving, the numerical model using the discrete element method under each operating condition is separately established. Under such circumstances, the validation and analysis are conducted differing in sizes and driving parameters of the wheel. It is indicated that the improved model displays the better reasonability and precision in predicting lug effects of a heavy off-road wheel. This model is mostly accurate and sensitive to the variation of parameters under straight and inclining driving conditions, but demands further correction during low slipping of the turning condition. Generally, the improved model in this paper focuses on the prediction of drawbar pull and driving torque, but lacks precision in the tendency of sinkage.

Keywords: Wheel-soil interaction; Prediction model; Lug effects; Multiple operating conditions; Discrete element method
 

Interaction of a rigid beam resting on a strong granular layer overlying weak granular soil: Multi-methodological investigations

Zuhair Kadhim Jahanger, S. Joseph Antony, Elaine Martin, Lutz Richter
Journal of Terramechanics, Volume 79, 2018, Pages 23-32, ISSN 0022-4898,
https://doi.org/10.1016/j.jterra.2018.05.002.

Abstract: In the geotechnical and terramechanical engineering applications, precise understandings are yet to be established on the off-road structures interacting with complex soil profiles. Several theoretical and experimental approaches have been used to measure the ultimate bearing capacity of the layered soil, but with a significant level of differences depending on the failure mechanisms assumed. Furthermore, local displacement fields in layered soils are not yet studied well. Here, the bearing capacity of a dense sand layer overlying loose sand beneath a rigid beam is studied under the plain-strain condition. The study employs using digital particle image velocimetry (DPIV) and finite element method (FEM) simulations. In the FEM, an experimentally characterised constitutive relation of the sand grains is fed as an input. The results of the displacement fields of the layered soil based DPIV and FEM simulations agreed well. From the DPIV experiments, a correlation between the slip surface angle and the thickness of the dense sand layer has been determined. Using this, a new and simple approach is proposed to predict theoretically the ultimate bearing capacity of the layered sand. The approach presented here could be extended more easily for analysing other complex soil profiles in the ground-structure interactions in future.

Keywords: Granular mechanics; Bearing capacity; Layered soil; FEM; DPIV; Failure mechanism

A unified equation for predicting traction for wheels on sand over a range of braked, towed, and powered operations

George L. Mason, James M. Williams, Farshid Vahedifard, Jody D. Priddy
Journal of Terramechanics, Volume 79, 2018, Pages 33-40, ISSN 0022-4898,
https://doi.org/10.1016/j.jterra.2018.05.005.

Abstract: Vehicle traction between the wheel and the ground surface is a critical design element for on-road and off-road mobility. Adequate traction in dry sand relates to the vehicle’s ability to negotiate deserts, sand dunes, climb slopes, and ingress/egress along beaches. The existing traction equations predict values for only one mode of operation (braked, towed, or powered). In this article, we propose a unified algorithm for continuous prediction of traction over a range of braked, towed, and powered operations for wheels operating on sand. A database of laboratory and field records for wheeled vehicles, entitled Database Records for Off-road Vehicle Environments (DROVE), was used to develop the proposed algorithm. The algorithm employs the ratio of contact pressure to cone index as a primary variable to develop fitting parameters for a relationship between slip and traction. The performance of the algorithm is examined versus the measured data and is also compared against two alternative equations. The new equation showed higher correlation and lower error compared to the existing equations for powered wheels. The proposed equation can be readily implemented into off-road mobility models, eliminating the need for multiple traction equations for different modes of operation.

Keywords: Off-road mobility; Sand; Traction; Vehicle Terrain Interface (VTI) model; Database Records for Off-road Vehicle Environments (DROVE)

UGV with a distributed electric driveline: Controlling for maximum slip energy efficiency on stochastic terrain

Mostafa A. Salama, Vladimir V. Vantsevich, Thomas R. Way, David J. Gorsich]

Journal of Terramechanics, Volume 79, October 2018, Pages 41-57, ISSN 0022-4898, https://doi.org/10.1016/j.jterra.2018.06.001.

Abstract: 
Energy saving has been a prominent concern of ground vehicle Original Equipment Manufacturers and research agencies for decades. The search for technological advances that can increase energy efficiency of vehicles has been a relentless quest. The framework of research on energy efficiency improvements has been considerably extended after the introduction of fully electric vehicles with electric motors that individually drive each wheel, i.e., In-Wheel Motors (IWM). Although incoming IWM vehicles can significantly decrease driveline power losses and, thus, improve vehicle energy efficiency compared to conventional mechanical driveline systems, one technical problem related to the vehicle-tire-terrain interaction needs to be addressed in fully electric terrain vehicles. These vehicles are still lacking strategies to manage power distribution between the drive wheels, which are not connected by a driveline system anymore, with the purpose to minimize slip power losses at all tires and maximize vehicle slip energy efficiency. Inappropriate power delivered to each of the wheels, which run in different stochastic terrain conditions, can deteriorate slip energy efficiency of a vehicle with four individually driven wheels. The research work presented in this article addresses the problem of wheel power distribution for an unmanned ground vehicle (UGV) with four IWMs.

Keywords: In-Wheel Motor UGV; Optimal wheel power distribution; Stochastic terrain condition; Slip energy efficiency; Inverse dynamics control

Performance of combined offset disc harrow (front active and rear passive set configuration) in soil bin

Ganesh Upadhyay, Hifjur Raheman

Journal of Terramechanics, Volume 78, 2018, Pages 27-37, ISSN 0022-4898,
https://doi.org/10.1016/j.jterra.2018.04.002.

Abstract: Soil bin investigations were initiated with combined offset disc harrow (CODH) which unites the benefits of powered discs and combination tillage together through a front active-rear passive set configuration. The proposed configuration may help to achieve timeliness in sowing, better crop residue handling with reduced tillage passes and improved engine power utilization of tractor. The effects of speed ratio (u/v), front gang angle (α), operating depth and cone index (CI) on its draft, torque and power requirement were studied and compared with its traditional passively driven mode at an average soil moisture of 9–10% (db) in sandy-clay loam soil. Optimum system settings were found out before further performance evaluation in the field. The substantially reduced draft requirement with CODH might help to reduce the wheel slippage and improve field productivity while increased power requirement might prevent the under-loading of tractor engine. Tillage quality was assessed considering CI values and found to be far superior compared to traditional mode. Optimum system settings were found at α of 35° and u/v ratio of 3.6 in terms of lowest power expenditure and better work quality with torque power expenditure of 60–70% in total power indicating improved utilization of engine power if operated with tractor power take-off (PTO).

Keywords: Draft; Torque; Passively driven mode; Speed ratio; Front gang angle
 

Probabilistic self-tuning approaches for enhancing performance of autonomous vehicles in changing terrains

Alvaro Javier Prado, Fernando A. Auat Cheein, Saso Blazic, Miguel Torres-Torriti,

Journal of Terramechanics, Volume 78, 2018, Pages 39-51, ISSN 0022-4898,
https://doi.org/10.1016/j.jterra.2018.04.001.

Abstract: Motion controllers usually require a tuning stage to ensure an acceptable performance of the vehicle during operation in challenging scenarios. However, such tuning stage is a time consuming process for the programmer and often is based on intuition or heuristic approaches. In addition, once tuned, the vehicle performance varies according to the nature of the terrain. In this work, we study the use of well-known probabilistic techniques for self-tuning trajectory tracking controllers for service units based on the idea of saving both vehicle’s resources and human labour force time. The proposed strategies are based on Monte Carlo and Bayesian approaches to find the best set of gains to tune the controller both off-line and on-line, thus enhancing the controller performance in the presence of changing terrains. The approaches are implemented and validated on a skid-steer mini-loader vehicle usually used for mining purposes. Implementation details and both simulation and empirical results are included in this work, showing that when using our approaches, effort can be saved up to 30% and tracking errors reduced up to 75%.

Keywords: Trajectory tracking control; Auto-tuning; Industrial machinery; Wheel-terrain interaction

State of the knowledge of vegetation impact on soil strength and trafficability

Wendy L. Wieder, Sally A. Shoop

Journal of Terramechanics, Volume 78, 2018, Pages 1-14, ISSN 0022-4898,
https://doi.org/10.1016/j.jterra.2018.03.006.

Abstract: Researchers in a variety of fields have studied using vegetation to alter or reinforce soils. However, using vegetation for soil preservation in long-term land management of military training areas used for off-road vehicle maneuvers is more recent. Much of the work reported in the literature deals with trees and larger shrubs, appropriate for slope and bank stabilization. Other research efforts are for agricultural or forestry applications and involve crops, and again, large trees. This review discusses the issue of vegetation and its effect on a variety of soil strength parameters. It also reviews work regarding the effect of vehicle operations on vegetation and conversely the effect of vegetation on vehicle performance, or trafficability. The reviewed test methods and proposed soil strength models, based on a variety of soil properties, provide a basis for continuing work on models to evaluate areas used for off road military vehicle operations.

Keywords: Trafficability; Soil strength; Terrain; Impact; Mobility; Biomass; Vegetation
 

FE-DEM with interchangeable modeling for off-road tire traction analysis

Kenta Nishiyama, Hiroshi Nakashima, Taiki Yoshida, Hiroshi Shimizu, Juro Miyasaka, Katsuaki Ohdoi

Journal of Terramechanics, Volume 78, August 2018, Pages 15-25, ISSN 0022-4898, https://doi.org/10.1016/j.jterra.2018.03.005.

Abstract: This study examines a new finite element/discrete element method (FE-DEM) with interchangeable modeling between FEM and DEM for tire traction analysis. In the method, named iFE-DEM, the soil in a soil bin is modeled initially by FEM except for the region under or near the tire, which is modeled using DEM. When the FEM tire model starts to travel over DEM soil elements, the updated tire location will activate new conversion of modeling from FEM to DEM so that the zone of influence around the contact interface between tire and soil can be analyzed continuously using DEM. Those mobilized DEM elements rearward of the tire might be converted again to FEM elements by assuming that the effect of the stress state in DEM generated by tire travel might be negligible. The computational time for two-dimensional iFE-DEM analysis of a slip of 40% using the smallest region of initial DEM under the tire could be reduced to 23% of that obtained using DEM only soil modeling.

Keywords: FEM; DEM; Interchangeable modeling; Soil-wheel system; Traction performance

Experimental study of a tracked mobile robot’s mobility performance

Weidong Wang, Zhiyuan Yan, Zhijiang Du

Journal of Terramechanics, Volume 77, 2018, Pages 75-84, ISSN 0022-4898
https://doi.org/10.1016/j.jterra.2018.03.004.

Abstract: This paper proposes an experimental method of predicting the traction performance of a small tracked mobile robot. Firstly, a track-terrain interaction model based on terramechanics is built. Then, an experimental platform of the tracked robot is established, on which the measurement methods of the parameters that influencing the accuracy of the prediction model are introduced and the data post-processing are improved, including drawbar pull, slip ratio, sinkage, track deformation and so on. Based on the experimental data, several key terrain parameters are identified. With the tracked robot platform, the drawbar pull-slip ratio relationship is tested, and the effects on drawbar pull considering different kinds of terrain and the influence of the grousers are analyzed as well. The research results provide a reference for the experimental study on the traction performance of small tracked robots.

Keywords: Tracked mobile robot; Terrain–track interaction; Drawbar pull; Tractive performance; Experimental study