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, http://dx.doi.org/10.1016/j.jterra.2016.09.003.
http://www.sciencedirect.com/science/article/pii/S0022489816300477  
Abstract:  
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, http://dx.doi.org/10.1016/j.jterra.2016.09.002.
http://www.sciencedirect.com/science/article/pii/S0022489816300465  
Abstract:  
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, http://dx.doi.org/10.1016/j.jterra.2016.10.002.
http://www.sciencedirect.com/science/article/pii/S0022489816300520  
Abstract: 
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

The test and simulation of ABS on rough, non-deformable terrains

Wietsche Clement William Penny, Pieter Schalk Els
Journal of Terramechanics, Volume 67, October 2016, Pages 1-10, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.05.001.
http://www.sciencedirect.com/science/article/pii/S0022489816300258
Abstract:
It is well known that the performance of many antilock braking systems (ABS) deteriorate on rough, non-deformable surfaces due to a number of factors such as axle oscillations, wheel speed fluctuations and deficiencies in the algorithms. Rough terrain excitation further contribute to dynamic tyre effects such as loss of vertical contact and poor contact patch generation that leads to reduced longitudinal force generation. In this study, a slightly modified version of the Bosch ABS algorithm is implemented in Matlab/Simulink using co-simulation with a validated full vehicle ADAMS model that incorporate a valid high-fidelity FTire model. A non-ABS test vehicle is fitted with a commercial ABS modulator controlled by an embedded computer. The co-simulation model is validated with vehicle test data on both smooth and rough terrains. Initial results show that wheel speed fluctuations on rough terrain cause inaccuracies in the estimation of vehicle velocity and excessive noise on the derived rotational acceleration values. This leads to inaccurate longitudinal slip calculation and poor control state decisions respectively. It is concluded that, although the correlation is not yet as desired, the combined use of a simulation model and test vehicle can be a useful tool in the research of ABS braking on rough terrains. 
Keywords: Anti-lock Braking System; Rough terrain; Bosch algorithm; Simulating ABS; ADAMS; FTire

Parameterisation, validation and implementation of an all-terrain SUV FTire tyre model

Hans-Rudolf B. Bosch, Herman A. Hamersma, P. Schalk Els
Journal of Terramechanics, Volume 67, October 2016, Pages 11-23, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.06.001.
http://www.sciencedirect.com/science/article/pii/S002248981630026X  
Abstract: 
This paper focuses on the parameterisation, validation and implementation of an FTire model of a Michelin LTX A/T2 235/85R16 tyre. This tyre is designed for both on- and off-road use and is commonly used on all wheel drive SUVs. Quasi-static laboratory and dynamic field tests were conducted to acquire parameterisation and validation test data for the FTire model. Quasi-static parameterisation tests include acquiring vertical tyre stiffness over a flat plate and cleats, tyre footprint sizes and shapes, longitudinal, lateral and torsional tyre stiffness for various tyre normal loads, as well as vibrational tyre responses. Dynamic parameterisation tests include dynamic cleat test data. An Adams model of the tyre testing equipment is implemented to simulate the FTire model and validate it against dynamic validation test results. Finally, the model is implemented on a fully nonlinear multi-body dynamics model of a Land Rover Defender. It is found that the FTire model is able to predict the lateral tyre behaviour well on a smooth road surface. The vertical and longitudinal tyre behaviour on a smooth road surface and on a rough surface are predicted accurately. 
Keywords: FTire; Static tyre tests; Dynamic tyre tests; Tyre model parameterisation; Tyre model simulation; Tyre model validation

Improved sinkage algorithms for powered and unpowered wheeled vehicles operating on sand

George L. Mason, Farshid Vahedifard, Joe D. Robinson, Isaac L. Howard, George B. McKinley, Jody D. Priddy
Journal of Terramechanics, Volume 67, October 2016, Pages 25-36, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.07.001.
http://www.sciencedirect.com/science/article/pii/S0022489816300271
Abstract:  
Modeling and simulation of vehicles in sand is critical for characterizing off-road mobility in arid and coastal regions. This paper presents improved algorithms for calculating sinkage (z) of wheeled vehicles operating on loose dry sand. The algorithms are developed based on 2737 tests conducted on sand with 23 different wheel configurations. The test results were collected from Database Records for Off-road Vehicle Environments (DROVE), a recently developed database of tests conducted with wheeled vehicles operating in loose dry sand. The study considers tire diameters from 36 to 124 cm with wheel loads of 0.19–36.12 kN. The proposed algorithms present a simple form of sinkage relationships, which only require the ratio of the wheel ground contact pressure and soil strength represented by cone index. The proposed models are compared against existing closed form solutions defined in the Vehicle Terrain Interface (VTI) model. Comparisons suggest that incorporating the proposed models into the VTI model can provide comparable predictive accuracy with simpler algorithms. In addition to simplicity, it is believed that the relationship between cone index (representing soil shear strength) and the contact pressure (representing the applied pressure to tire-soil interface) can better capture the physics of the problem being evaluated.  
Keywords: Vehicle off-road mobility; Sand; Traction; Sinkage; Vehicle Terrain Interface (VTI); Database Records for Off-road Vehicle Environments (DROVE)

Vehicle-wet snow interaction: Testing, modeling and validation

Jonah H. Lee, Daisy Huang    
Journal of Terramechanics, Volume 67, October 2016, Pages 37-51, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.08.001.
http://www.sciencedirect.com/science/article/pii/S0022489816300301  
Abstract: Abstract
For a vehicle interacting with snow, whether dry or wet, uncertainties exist in the mechanical properties of snow, and in the interfacial properties between the tires of the vehicle and snow. For dry snow, these uncertainties have been studied recently using methods within a statistical framework employing a simple stochastic tire-snow interaction model and several validation metrics. Wet snow is more complicated and much less studied than dry snow, especially for tire-snow interaction. In this paper, the authors used a physical tire-snow interaction model and a similar statistical framework as was used to analyze dry snow, and presented results of calibration and validation of the interaction model for wet snow in conjunction with new test data based on a single test run with the assumption that it would provide needed sampling points for statistical analysis. Four local and global statistical validation metrics were used to assess the physical and statistical models with good results. Comparison between wet and dry snow, based on a single test run, shows that the former has a lower interfacial coefficient of friction, and a higher drawbar pull than the latter.  
Keywords: Wet snow; Dry snow; Drucker–Prager; Drawbar pull; Torque; Validation metrics; Calibration; Stochastic; Uncertainties; Friction

A tire–ice model (TIM) for traction estimation

Anudeep K. Bhoopalam, Corina Sandu, Saied Taheri
Journal of Terramechanics, Volume 66, August 2016, Pages 1-12, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.02.003.
http://www.sciencedirect.com/science/article/pii/S0022489816000215
Abstract: 
Increased traffic safety levels are of highest importance, especially when driving on icy roads. Experimental investigations for a detailed understanding of pneumatic tire performance on ice are expensive and time consuming. The changing ambient and ice conditions make it challenging to maintain repeatable test conditions during a test program. This paper presents a tire–ice contact model (TIM) to simulate the friction levels between the tire and the ice surface. The main goal of this model is to predict the tire–ice friction based on the temperature rise in the contact patch. The temperature rise prediction in the contact patch is based on the pressure distribution in the contact patch and on the thermal properties of the tread compound and of the ice surface. The contact patch is next classified into wet and dry regions based on the ice surface temperature and temperature rise simulations. The principle of thermal balance is then applied to compute the friction level in the contact patch. The tire–ice contact model is validated by comparing friction levels from simulations and experimental findings. Friction levels at different conditions of load, inflation pressure, and ice temperatures have been simulated using the tire–ice contact model and compared to experimental findings. 
Keywords: Tire–ice model; Tire–ice friction

Modeling, calibration and validation of tractive performance for seafloor tracked trencher

Meng Wang, Chao Wu, Tong Ge, Zhi Min Gu, Yuan Hong Sun
Journal of Terramechanics, Volume 66, August 2016, Pages 13-25, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.03.001
http://www.sciencedirect.com/science/article/pii/S0022489816000227
Abstract: 
Shear stress–displacement model is very important to evaluate the tractive performance of tracked vehicles. A test platform, where track segment shear test and plate load test can be performed in bentonite–water mixture, was built. Through analyzing existing literatures, two shear stress–displacement empirical models were selected to conduct verification tests for seafloor suitability. Test results indicate that the existing models may not be suitable for seafloor soil. To solve this problem, a new empirical model for saturated soft-plastic soil (SSP model) was proposed, and series shearing tests were carried out. Test results indicate that SSP model can describe mechanical behavior of track segment with good approximation in bentonite–water mixture. Through analyzing main external forces applied to test scaled model of seafloor tracked trencher, drawbar pull evaluation functions was deduced with SSP model; and drawbar pull tests were conducted to validate these functions. Test results indicate that drawbar pull evaluation functions was feasible and effective; from another side, this conclusion also proved that SSP model was effective. 
Keywords: Shear stress–displacement; SSP model; Tractive performance; Drawbar pull; Seafloor tracked trencher