Publication news

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,
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)

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,
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,  
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

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,
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,
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


Identification, design and kinematic analysis of an earthmoving mechanism

Yongjun Pan, Alfonso Callejo  Journal of Terramechanics, Volume 66, August 2016, Pages 27-39, ISSN 0022-4898,
Earthmoving mechanisms in motor graders are critical components for earthwork, compaction and re-handling, and yet they have not received much attention by mechanical engineering research in recent times. In this paper, a comprehensive analysis, from mechanism identification and innovative design to kinematic analysis, is presented. First, the mechanism analysis and synthesis method based on multibody system dynamics is carried out through the analysis of the system topology and connectivity. We conclude that the earthmoving multibody system is a spatial hybrid mechanism, which consists of a spatial parallel mechanism and a spatial serial mechanism. Second, a number of new spatial parallel mechanisms, which are advantageous with respect to the original one under certain conditions, are generated. The kinematic characteristics of the parallel mechanism family are investigated in terms of constraint equations formulated in natural coordinates. Third and last, kinematic simulations and optimization processes are carried out to evaluate the advantages of the presented spatial parallel mechanisms. Simulation results show that these mechanisms can provide better kinematic performance.  
Keywords: Motor grader; Earthmoving mechanism; Multibody systems; 3RRPS-S mechanism; Natural coordinates


Suitability of rubber track as traction device for power tillers

Showkat Rasool, Hifjur Raheman
Journal of Terramechanics, Volume 66, August 2016, Pages 41-47, ISSN 0022-4898,
Suitability of using rubber tracks as traction device in power tillers replacing pneumatic tires was studied using an experimental setup consisting of a track test rig for mounting a 0.80 m × 0.1 m rubber track and a loading device for applying different drawbar pulls. Tests were conducted in the soil bin filled with lateritic sandy clay loam soil at an average soil water content of 9% dry basis by varying the cone index from 300 to 1000 kPa. Data on torque, pull and Travel Reduction Ratio (TRR) were acquired using sensors and data acquisition system for evaluating its performance. Maximum tractive efficiency of the track was found to be in the range of 77–83% corresponding to a TRR of 0.12–0.045. The Net Traction Ratio (NTR) at maximum tractive efficiency was found to be between 0.49 and 0.36.

Using non-linear regression technique, a model for Gross Traction Ratio (GTR) was developed and it could predict the actual values with a maximum variation of 6% as compared to an average variation of 50% with Grisso’s model. Based on this model, tractive efficiency design curves were plotted to achieve optimum tractive performance of track for any given soil condition. 
Keywords: Track tester; Soil bin; Traction ratios; Travel Reduction Ratio; Tractive efficiency


Comparison of SPH simulations and cone index tests for cohesive soils

Christopher Goodin, Jody D. Priddy
Journal of Terramechanics, Volume 66, August 2016, Pages 49-57, ISSN 0022-4898,

The cone penetrometer test has been used for decades to quantify the soft soil mobility performance of ground vehicles. As physics-based methods for modeling soil are developed, it is necessary to validate these simulations against databases relating Cone Index (CI) to vehicle mobility. However, in order to make this comparison, the relationship between the engineering properties of the soil (density, bulk modulus) and the cone index must be determined. To that end, in this work, simulations of cone penetrometer tests in cohesive soil using the smoothed particle hydrodynamics (SPH) method are presented. Three dimensional simulations were conducted and compared to laboratory measurements of cone index in soft soil. The SPH model is parametrized using the elastic moduli of the soil (bulk and shear modulus), the soil density, and the soil cohesion. A novel method which includes skin friction is employed to calculate the forces exerted on the cone tip by the soil. The simulations give good agreement with the measurements, with a coefficient of determination R 2 = 0.76 . These results indicate that SPH may be viable for simulating soft soil in conditions relevant for vehicle mobility considerations.
Keywords: Cone index; SPH; Mohr–Coulomb

Tire compaction capacity rating on non-standard soil

Alexandr Grečenko
Journal of Terramechanics, Volume 66, August 2016, Pages 59-61, ISSN 0022-4898,
Tire Compaction Capacity rating system with its CC index was evolved to support the choice of proper tires for off-road vehicles or machines operating on crop producing land with aim to prevent harmful compaction of the ground. This system, fundamentally presented in the Journal of Terramechanics, Vol. 52/2014, is based on a great number of laboratory compaction tests in common clay–loam soil (here marked as standard soil). The presented article deals especially with more accurate application of numerical rating to sandy and clay soils (very different grain size) under the designation equivalent Compaction Capacity (eCC) index, however, is applicable to an arbitrary soil type. The features and practical use of eCC rating are explained and discussed in this technical note. 
Keywords: Soil compaction risk; Off-road tires; Tire equivalent compaction capacity index