Publication news

Terrain classification using ToF sensors for the enhancement of agricultural machinery traversability

Francisco Yandun Narváez, Eduard Gregorio, Alexandre Escolà, Joan R. Rosell-Polo, Miguel Torres-Torriti, Fernando Auat Cheein
In Journal of Terramechanics, Volume 76, 2018, Pages 1-13, ISSN 0022-4898


Ground properties influence various aspects of mobile machinery navigation including localization, mobility status or task execution. Excessive slipping, skidding or trapping situations can compromise the vehicle itself or other elements in the workspace. Thus, detecting the soil surface characteristics is an important issue for performing different activities in an efficient, safe and satisfactory manner. In agricultural applications, this point is specially important since activities such as seeding, fertilizing, or ploughing are carried on within off-road landscapes which contain a diversity of terrains that modify the navigation behaviour of the vehicle. Thus, the machinery requires a cognitive capability to understand the surrounding terrain type or its characteristics in order to take the proper guidance or control actions. This work is focused on the soil surface classification by implementing a visual system capable to distinguish between five usual types of off-road terrains. Computer vision and machine learning techniques are applied to characterize the texture and color of images acquired with a Microsoft Kinect V2 sensor. In a first stage, development tests showed that only infra-red and RGB streams are useful to obtain satisfactory accuracy rates (above 90%). The second stage included field trials with the sensor mounted on a mobile robot driving through various agricultural landscapes. These scenarios did not present illumination restrictions nor ideal driving roads; hence, conditions can resemble real agricultural operations. In such circumstances, the proposed approach showed robustness and reliability, obtaining an average of 85.20% of successful classifications when tested along 17 trials within agricultural landscapes.

Keywords: Agricultural robotics; Terrain classification; Pattern recognition

2D FE–DEM analysis of contact stress and tractive performance of a tire driven on dry sand

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

Journal of Terramechanics, Volume 74, 2017, Pages 25-33, ISSN 0022-4898,

Normal and tangential stresses acting over a contact interface of a tire driven on dry sand were investigated to expand the applicability of our model incorporating 2D FE–DEM with proportional–integral–derivative (PID) control. A simple averaging method for contact reaction was introduced: computational segments were defined over the lower half part of the tire circumference that translates without rotation with the tire; then the contact stresses were calculated segment by segment. For the analysis, it was assumed that the tire was in rigid contact mode and that it would travel on the model sand terrain in stationary condition. The integration of normal and tangential contact stresses with respect to the angle of rotation was then applied to calculate the vertical contact load, gross tractive effort, net traction, and running resistance of the tire by parametric (or semi-empirical) analysis. The result of tractive performance obtained through the parametric analysis was found to be similar to the result of tractive performance obtained directly using FE–DEM analysis. A forward shift of the consistent angle of rotation for maximum normal contact stress and that for maximum tangential contact stress with the increase of slip from 22% was also observed in the FE–DEM result.

Keywords: Soil–wheel system; Normal contact stress; Tangential contact stress; Traction performance; DEM; FEM

Influence of atmosphere on lunar rover performance analysis based on soil parameter identification

Masataku Sutoh, Sachiko Wakabayashi, Takeshi Hoshino

Journal of Terramechanics, Volume 74, December 2017, Pages 13-24, ISSN 0022-4898,
Abstract: Abstract  

This paper outlines an analysis of the traveling performance of a lunar rover. The analysis is in the form of numerical simulations and it uses soil properties, identified in vacuum, and mechanics of wheel-based travel. The wheel-to-ground contact model and soil parameters are determined first so they could be used in the numerical simulation. A soil test device is introduced and the soil parameters are identified from plate-pressing and shear tests. Finally, numerical simulations are conducted using the parameters identified and their results are discussed along with those of the traveling tests conducted in vacuum. The soil tests indicated that the wheel sinkage into the ground can increase in vacuum and that the shear stress acting beneath the wheel in vacuum is almost the same as that in the atmosphere. Because of these trends, the simulations and traveling tests showed that the traveling performance of the wheel can decrease in vacuum. Although it has been widely considered that the vacuum environments enhance the traveling performance of the wheel, this study confirmed that it is not always the case.

Keywords: Lunar exploration; Rover; Traveling performance; Vacuum; Soil parameter identification

Creating 3D models of tractor tire footprints using close-range digital photogrammetry

Amaneh E. Kenarsari, Stanley J. Vitton, John E. Beard,

Journal of Terramechanics, Volume 74, 2017, Pages 1-11, ISSN 0022-4898,

Abstract: Close-range digital photogrammetry is utilized to construct the 3D models of an agricultural tire footprint. These models were then analyzed to obtain the tire footprint depth, area and volume. The procedure of using the photogrammetry technique for developing 3D models of a tire footprint on soil as well as an assessment of the accuracy of the 3D models are discussed in this paper. Testing was conducted using a tractor tire in a large soil bin in a lab to generate a single tire footprint along with a rolling tire test to simulate a longer tire rut. Our experiments showed that the close-range digital photogrammetry provides an efficient and accurate method to assess the depth and volume of the tire footprint in soil.
Keywords: Photogrammetry; Tire footprint; 3D models; Large scale laboratory tests

Modeling of share/soil interaction of a horizontally reversible plow using computational fluid dynamics

Lin Zhu, Jia-Ru Ge, Xi Cheng, Shuang-Shuang Peng, Yin-Yin Qi, Shi-Wu Zhang, De-Quan Zhu

Journal of Terramechanics, Volume 72, 2017, Pages 1-8, ISSN 0022-4898
Abstract: The horizontally reversible plow (HRP) is currently widely used instead of the regular mold-board plow due to its high operational performance. Soil pressure during HRP tillage generally has adverse effects on the plow surface, especially on either the plowshare or the plow-breast. This effect eventually shortens the tool’s service life. For this reason, this investigation used a three-dimensional (3D) computational fluid dynamics (CFD) approach to characterize the share/soil interaction and thus assess the effects of different tillage conditions on the interaction. To achieve this goal, a 3D model of the plowshare was first constructed in the commercial software SolidWorks, and soil from Xinjiang, China, was selected and subsequently characterized as a Bingham material based on rheological behaviors. Finally, 3D CFD predictions were performed using the control volume method in the commercial ANSYS code Fluent 14.0 in which the pressure distributions and patterns over the share surface were addressed under different tillage speeds in the range of 2–8ms−1 and at operational depths ranging from 0.1 to 0.3m. The results show that the maximum pressure appeared at the share-point zone of the plowshare and that the increase in soil pressure was accompanied by either higher tool speed or greater operational depth. The calculated results qualitatively agreed with the preliminary experimental evidence at the same settings according to scanning electron microscopy (SEM). Once again, the CFD-based dynamic analysis in this study is demonstrated to offer great potential for the in-depth study of soil-tool interactions by simulating realistic soil matter.
Keywords: Soil-share interaction; Computational fluid dynamics (CFD); Tillage speed; Operational depth; Horizontally reversible plow (HRP)

Application of the FEM/DEM and alternately moving road method to the simulation of tire-sand interactions

Chun-Lai Zhao, Meng-Yan Zang

Journal of Terramechanics, Volume 72, 2017, Pages 27-38, ISSN 0022-4898,
Abstract: The three-dimensional finite-discrete element method (FEM/DEM) is applied to the simulation of tire-sand interactions, where the tire is discretized into hexahedron finite elements and sand is modeled by using the discrete element method. The feasibility and effectiveness of the method are proven by comparing the simulation results with the current reported results. Since long test roads are usually required for investigating tire running behaviors, which lead to large-scale simulation models and time consuming problems, the alternately moving road method is proposed to handle this problem. It can simulate tire running behaviors on an arbitrary length sand road with a constant road length value. The numerical model of a lug tire running on a bisectional road with fine and coarse sand is established to verify the feasibility of the method.

Keywords: Finite element method; Discrete element method; Terramechanics; Computational mechanics; Tire-sand interactions

A high-fidelity approach for vehicle mobility simulation: Nonlinear finite element tires operating on granular material

Antonio Recuero, Radu Serban, Bryan Peterson, Hiroyuki Sugiyama, Paramsothy Jayakumar, Dan Negrut  

Journal of Terramechanics, Volume 72, August 2017, Pages 39-54, ISSN 0022-4898,  
Assessing the mobility of off-road vehicles is a complex task that most often falls back on semi-empirical approaches to quantifying the vehicle–terrain interaction. Herein, we concentrate on physics-based methodologies for wheeled vehicle mobility that factor in both tire flexibility and terrain deformation within a fully three-dimensional multibody system approach. We represent the tire based on the absolute nodal coordinate formulation (ANCF), a nonlinear finite element approach that captures multi-layered, orthotropic shell elements constrained to the wheel rim. The soil is modeled as a collection of discrete elements that interact through contact, friction, and cohesive forces. The resulting vehicle/tire/terrain interaction problem has several millions of degrees of freedom and is solved in an explicit co-simulation framework, built upon and now available in the open-source multi-physics package Chrono. The co-simulation infrastructure is developed using a Message Passing Interface (MPI) layer for inter-system communication and synchronization, with additional parallelism leveraged through a shared-memory paradigm. The formulation and software framework presented in this investigation are proposed for the analysis of the dynamics of off-road wheeled vehicle mobility. Its application is demonstrated by numerical sensitivity studies on available drawbar pull, terrain resistance, and sinkage with respect to parameters such as tire inflation pressure and soil cohesion. The influence of a rigid tire assumption on mobility is also discussed.  
Keywords: Mobility; Off-road vehicle dynamics; Nonlinear finite element; ANCF; Discrete element method; Chrono; Co-simulation; High-performance computing


Calculating fractal parameters from low-resolution terrain profiles

Christopher Goodin, Maria Stevens, Francisco J. Villafañe Rosa, Burney McKinley, Burhman Q. Gates, Phillip J. Durst, George L. Mason, Alex Baylot

Journal of Terramechanics, Volume 72, August 2017, Pages 21-26, ISSN 0022-4898,

Driver comfort on rough terrain is an important factor in the off-road performance of wheeled and tracked ground vehicles. The roughness of a terrain has typically been quantified by the U.S. Army as the root-mean-square elevation deviation (RMS) of the terrain profile. Although RMS is an important input into many mobility calculations, it is not scale invariant, making it difficult to estimate RMS from low resolution terrain profiles. Fractal parameters are another measure of roughness that are scale invariant, making them a convenient proxy for RMS. While previous work found an empirical relationship between fractal dimension and RMS, this work will show that, by including the cutoff length, an analytic relationship between fractal properties and RMS can be employed. The relationship has no free parameters and agrees very well with experimental data - thus providing a powerful predictive tool for future analyses and a reliable way to calculate surface roughness from low-resolution terrain data in a way that is scale invariant. In addition, we show that this method applies to both man-made ride courses and natural terrain profiles.  
Keywords: Fractal dimension; RMS; Surface roughness


A coupled sliding and rolling friction model for DEM calibration

Zamir Syed, Mehari Tekeste, David White

Journal of Terramechanics, Volume 72, August 2017, Pages 9-20, ISSN 0022-4898,

The accuracy of dense Discrete Element Method (DEM) simulations is sensitive to initial density, contact orientation, particle size and shape, and interparticle interaction parameters including contact stiffness, cohesion, coefficients of friction, and coefficients of restitution. Although studies have characterized the effects of individual particle interaction parameters on mechanical responses of loaded granular material, research combining DEM parameters for calibration is scarce. Robust DEM calibration methodology combining sliding and rolling friction coefficients was developed and validated to predict bulk residual soil strength of initially dense DEM particle assemblies. 
Keywords: Coupled sliding and rolling friction coefficients; Discrete element method; Soil