Publication news

Generation of stochastic mobility maps for large-scale route planning of ground vehicles: A case study

Ramon Gonzalez, Paramsothy Jayakumar, Karl Iagnemma   
Journal of Terramechanics, Volume 69, February 2017, Pages 1-11, ISSN 0022-4898,  
This paper describes a simple and efficient methodology to generate a mobility map accounting for two sources of uncertainty, namely measurement errors (RMSE of a Digital Elevation Model) and interpolation error (kriging method). The proposed methodology means a general-purpose solution since it works with standard and publicly-available Digital Elevation Models (DEMs). The different regions in the map are classified according to the geometry of the surface (i.e. slope) and the soil type. A real USGS DEM demonstrates the suitability of the proposed methodology: (1) interpolation of a 26 × 40 -km2 DEM to a finer resolution (30-m to 20-m); (2) analysis of the number of random realizations to account for the variability of the data; (3) efficient computation time (4-million-point DEM requires less than 30 min to complete the whole process); (4) route planning using the stochastic mobility map (constraints in slope and soil properties). UNCLASSIFIED: Distribution Statement A. Approved for public release; distribution is unlimited. #27681    
Keywords: Stochastic conditional simulation; Geographical Information System (GIS); Next-Generation NATO Reference Mobility Model (NG-NRMM); Digital Elevation Model (DEM); Soil moisture


3D contact patch measurement inside rolling tyres

A. Glenn Guthrie, Theunis R. Botha, P. Schalk Els    
Journal of Terramechanics, Volume 69, February 2017, Pages 13-21, ISSN 0022-4898,  
This paper presents a novel method for capturing the 3D profile of the inside of a rolling off-road vehicle tyre at the tyre-road contact region. This method captures the contact region at all times as the vehicle negotiates obstacles. The system uses a pair of inexpensive digital cameras (capable of capturing up to 300 frames per second) and features a purely mechanical stabilisation system to ensure that the cameras capture the contact region at any wheel speed or vehicle acceleration.

The captured images are processed using 3D computer vision techniques using an open source computer vision library called OpenCV. Stereo image pairs are used to create clouds of 3D points showing the profile of the inside surface with good accuracy. Various obstacles were traversed with the deformed tyre profile being compared to the undeformed profile. The system improves on current measurement techniques used to measure the contact patch by capturing a large region of the contact patch, providing full 3D surface geometry, as well as remaining centred on the contact patch irrespective of wheel rotation. The system also enables other imaging techniques to be used such as digital image correlation to determine velocity profiles as well as strain measurements.    
Keywords: Computer vision; Stereography; Tyre deformation; Contact patch; Tyre footprint; Image correlation

Effectiveness evaluation of hydro-pneumatic and semi-active cab suspension for the improvement of ride comfort of agricultural tractors

Kyuhyun Sim, Hwayoung Lee, Ji Won Yoon, Chanho Choi, Sung-Ho Hwang  
Journal of Terramechanics, Volume 69, February 2017, Pages 23-32, ISSN 0022-4898,  
Advances have been made to agricultural tractors to improve their ride comfort. However, the ride comfort of tractors is relatively low compared to that of passenger vehicles. Many researchers have developed various types of suspension for tractors. While most studies have focused on the geometry of the suspension, few studies have been carried out on the development of a control algorithm for tractor suspension.

In this paper, to improve the ride comfort of an agricultural tractor, a hydro-pneumatic suspension model with a semi-active suspension control is developed with computer simulation, and the effectiveness of the suspension is evaluated before the vehicle is equipped with the suspension and placed into production.

An optimal control algorithm for the semi-active suspension of the tractor is developed using a linear quadratic Gaussian. In the simulation, a hydro-pneumatic suspension system model is developed using SimulationX and is applied to a full vehicle model using MATLAB/Simulink. The suspension is assessed by experiments and simulations. The ride comfort using the ride comfort index according to ISO 2631 is evaluated by comparing a vehicle with a passive cab suspension to that with a hydro-pneumatic suspension applied with the semi-active control.  
Keywords: Agricultural tractor; Hydro-pneumatic suspension; Semi-active cab suspension; Ride comfort; Evaluation

Improvement of traction performance and off-road mobility for a vehicle with four individual electric motors: Driving over icy road

Dzmitry Savitski, Dmitrij Schleinin, Valentin Ivanov, Klaus Augsburg, Emilio Jimenez, Rui He, Corina Sandu, Phil Barber   
Journal of Terramechanics, Volume 69, February 2017, Pages 33-43, ISSN 0022-4898,  
To control speed and wheel slip for severe conditions of tire-surface interaction is a challenging task in the design of traction control system for electric vehicles with off-road capability. In this regard, the present paper focuses on a specific traction control for an electric vehicle with four individual in-wheel motors over icy road. The study demonstrates that a proper integration of the speed controller and wheel slip controller can essentially improve the mobility of the vehicle in the cases of acceleration and slope climbing. The paper discusses relevant case studies with particular attention given to the system architecture (sliding mode and PID control methods), extremum-seeking algorithm for maximum tire-road friction and corresponding slip value, and experimental validation of the tire model used in the controller with the help of the Terramechanics Rig in the Advanced Vehicle Dynamics Laboratory (AVDL) at Virginia Polytechnic Institute and State University.  
Keywords: Traction control; Speed control; Wheel slip control; Electric vehicle; Tire-ice interaction


Design and development of a new transformable wheel used in amphibious all-terrain vehicles (A-ATV)

Xiaolin Xie, Feng Gao, Chuan Huang, Wen Zeng   
Journal of Terramechanics, Volume 69, February 2017, Pages 45-61, ISSN 0022-4898,  
Conventional ground-wheeled vehicles usually have poor trafficability, low efficiency, a large amount of energy consumption and possible failure when driving on soft terrain. To solve this problem, this paper presents a new design of transformable wheels for use in an amphibious all-terrain vehicle. The wheel has two extreme working statuses: unfolded walking-wheel and folded rigid wheel. Furthermore, the kinematic characteristics of the transformable wheel were studied using a kinematic method. When the wheel is unfolded at walking-wheel status, the displacement, velocity and acceleration of the wheel with different slip rates were analyzed. The stress condition is studied by using a classic soil mechanics method when the transformable wheel is driven on soft terrain. The relationship among wheel traction, wheel parameters and soil deformation under the stress were obtained. The results show that both the wheel traction and trafficability can be improved by using the proposed transformable wheel. Finally, a finite element model is established based on the vehicle terramechanics, and the interaction result between the transformable wheel and elastic–plastic soil is simulated when the transformable wheel is driven at different unfold angles. The simulation results are consistent with the theoretical analysis, which verifies the applicability and effectiveness of the transformable wheel developed in this paper.  
Keywords: Transformable wheel; Soft terrain; Wheel-terrain interaction; Tractive performance


Predictability of boreal forest soil bearing capacity by machine learning

J. Pohjankukka, H. Riihimäki, P. Nevalainen, T. Pahikkala, J. Ala-Ilomäki, E. Hyvönen, J. Varjo, J. Heikkonen   
Journal of Terramechanics, Volume 68, December 2016, Pages 1-8, ISSN 0022-4898,  
In forest harvesting, terrain trafficability is the key parameter needed for route planning. Advance knowledge of the soil bearing capacity is crucial for heavy machinery operations. Especially peatland areas can cause severe problems for harvesting operations and can result in increased costs. In addition to avoiding potential damage to the soil, route planning must also take into consideration the root damage to the remaining trees. In this paper we study the predictability of boreal soil load bearing capacity by using remote sensing data and field measurement data. We conduct our research by using both linear and nonlinear methods of machine learning. With the best prediction method, ridge regression, the results are promising with a C-index value higher than 0.68 up to 200 m prediction range from the closest point with known bearing capacity, the baseline value being 0.5. The load bearing classification of the soil resulted in 76% accuracy up to 60 m by using a multilayer perceptron method. The results indicate that there is a potential for production applications and that there is a great need for automatic real-time sensoring in order to produce applicable predictions.  
Keywords: Terrain trafficability; Soil bearing capacity prediction; Forest harvesting; Machine learning; Open data


Performance evaluation of a wire mesh wheel on deformable terrains

Han Huang, Jianqiao Li, Baichao Chen, Baoguang Wu, Meng Zou   
Journal of Terramechanics, Volume 68, December 2016, Pages 9-22, ISSN 0022-4898,  
Because of the unique lunar environment, a suitable wheel for lunar rover decides the rover’s trafficability on deformable terrains. The wire mesh wheel (hereinafter referred to as WMW) has the advantages of light weight and superior stability, been widely adopted for lunar rovers. But a comprehensive research on performance of WMW on deformable terrains has not been conduct. This paper would provide particular study on a type WMW, including quasi-static pressure-sinkage test and driving performance. A novel pressure-sinkage model for the WMW on deformable soils was presented. In order to investigate the sinkage characteristics of the WMW, tests were performed using a single-wheel testbed for the WMW with different loads and velocities. The effects of load and velocity on sinkage were analyzed, and the relationship between real and apparent sinkage was presented. The research on traction performance of WMW under different slip ratios (0.1–0.6) was also conducted, contrast tests were proceed by using a normal cylindrical wheel (hereinafter referred to as CW). The traction performance of WMW is analyzed using performance indices including wheel sinkage, drawbar pull, driving torque, and tractive efficiency. The experimental results and conclusions are useful for optimal WMW design and improvement/verification of wheel–soil interaction mechanics model.  
Keywords: Wire mesh wheel; Pressure sinkage; Traction performance; Simulant regolith; Terramechanics


An efficient method for increasing the accuracy of mobility maps for ground vehicles

Ramon Gonzalez, Paramsothy Jayakumar, Karl Iagnemma   
Journal of Terramechanics, Volume 68, December 2016, Pages 23-35, ISSN 0022-4898,  
This paper presents an efficient method for increasing the accuracy of one key step regarding the process of determining a mobility map. That is, the interpolation of the original Digital Elevation Model (DEM) to a finer resolution before running multi-body-dynamics simulations. Specifically, this paper explores the use of fractal dimension and elevation range metrics for increasing the accuracy and reducing the computation time associated with the spatial interpolation ordinary kriging method. The first goal is to ensure the stationary variogram requirement. The second goal is to reduce kriging error or variance in the new predicted values. A novel segmentation-based approach has been proposed to divide the regions of interest into segments where stationarity is ensured. Empirical investigation based on real DEMs indicates the generality of the segmentation approach when natural and man-made terrains are considered. The proposed method leads to a more efficient computation burden and to more accurate results than the traditional approach.  
Keywords: Mobility prediction; NATO Reference Mobility Model (NRMM); Variogram; K-means; Man-made environment


Traveling and abrasion characteristics of wheels for lunar exploration rover in vacuum

Masataku Sutoh, Sachiko Wakabayashi, Takeshi Hoshino   
Journal of Terramechanics, Volume 68, December 2016, Pages 37-49, ISSN 0022-4898,  
This paper investigates the traveling and abrasion characteristics of rigid wheels for a lunar exploration rover at atmospheric pressure and in a vacuum. For this investigation, a traveling test system that enables the wheel to continuously travel over a long distance was developed. Using this system, tests on traveling performance and abrasion were conducted with the wheel on a lunar regolith simulant surface. In the initial tests, various wheels traveled over different ground conditions and their performances were evaluated based on the relationship between the drawbar pull and slippage. In the later tests, a wheel with grousers traveled a distance of 3 km and the abrasion was analyzed at various intervals. From the traveling performance tests, it was found that for a soft ground condition, the traveling performance of the wheels in vacuum was slightly lower than that in atmosphere. This indicates that ground tests performed in atmosphere overestimate the actual performance on the lunar surface. The abrasion tests suggested that the scratching of wheels occurs more easily in vacuum than in atmosphere. These experiments confirmed that the abrasion of the wheels do not cause any critical problem for a traveling distance of up to 3 km in a simulated lunar environment.  
Keywords: Lunar exploration; Wheel; Vacuum; Slippage; Abrasion; Long-distance travel