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Journal of Terramechanics, Vol. 48, Issue 1

ISTVS Award Announcement, Journal of Terramechanics, Volume 48, Issue 1, February 2011, Pages 1-2, ISSN 0022-4898, 10.1016/S0022-4898(10)00095-9.

V.N. Nguyen, S. Inaba
Effects of tire inflation pressure and tractor velocity on dynamic wheel load and rear axle vibrations
Journal of Terramechanics, Volume 48, Issue 1, February 2011, Pages 3-16, ISSN 0022-4898, 10.1016/j.jterra.2010.09.001.
Abstract: The objective of this study was to evaluate the effects of agricultural tire characteristics on variations of wheel load and vibrations transmitted from the ground to the tractor rear axle. The experiments were conducted on an asphalt road and a sandy loam field using a two-wheel-drive self-propelled farm tractor at different combinations of tractor forward speeds of approximately 0.6, 1.6 and 2.6 m/s, and tire inflation pressures of 330 and 80 kPa. During experiments, the vertical wheel load of the left and right rear wheels, and the roll, bounce and pitch accelerations of the rear axle center were measured using strain-gage-based transducers and a triaxial accelerometer. The wavelet and Fourier analyses were applied to measured data in order to investigate the effects of self-excitations due to non-uniformity and lugs of tires on the wheel-load fluctuation and rear axle vibrations. Values for the root-mean-square (RMS) wheel loads and accelerations were not strictly proportional and inversely proportional to the forward speed and tire pressure respectively. The time histories and frequency compositions of synthesized data have shown that tire non-uniformity and tire lugs significantly excited the wheel load and accelerations at their natural frequencies and harmonics. These effects were strongly affected by the forward speed, tire pressure and ground deformation.
Keywords: Dynamic wheel load; Vibration; Tire non-uniformity; Tire lug; Wavelet analysis; Fourier analysis

Hiroshi Nakashima, Yasuyuki Shioji, Taizo Kobayashi, Shigeru Aoki, Hiroshi Shimizu, Juro Miyasaka, Katsuaki Ohdoi
Determining the angle of repose of sand under low-gravity conditions using discrete element method
Journal of Terramechanics, Volume 48, Issue 1, February 2011, Pages 17-26, ISSN 0022-4898, 10.1016/j.jterra.2010.09.002.
Abstract: This study is a comparative investigation of data, collected through experimental and numerical means, related to the flow of sand particles through a hopper under low-gravity conditions. During a parabolic airplane flight simulating low-gravity conditions, we determined effects of gravity on the angle of repose of sand pile particles by flowing dry sand from a hopper. The gravity effects on the angle of repose of the sand were negligible. Two-dimensional discrete element method (DEM) was used to simulate the angle of repose. Results were compared to observations made during the low-gravity experiments. Effects of varying parameters such as the friction coefficient and coefficient of rolling friction were determined by running various DEM simulations. Moreover, the effect of the elemental radius on the angle of repose was investigated using DEM. The angle of repose is influenced by certain changes in the friction coefficient and rolling friction values, but the elemental radius has only a negligible effect on the angle of repose within the range of variation. Results show that the DEM model used for this study might be applicable to determine terramechanical interactions under lunar surface gravity conditions, provided that parameters are adjusted and an extended period of simulation is achieved.
Keywords: Angle of repose; Sand; Low-gravity; DEM; Friction coefficient; Rolling friction; Element radius

Liang Ding, Haibo Gao, Zongquan Deng, Keiji Nagatani, Kazuya Yoshida
Experimental study and analysis on driving wheels’ performance for planetary exploration rovers moving in deformable soil
Journal of Terramechanics, Volume 48, Issue 1, February 2011, Pages 27-45, ISSN 0022-4898, 10.1016/j.jterra.2010.08.001.
Abstract: Planetary rovers are different from conventional terrestrial vehicles in many respects, making it necessary to investigate the terramechanics with a particular focus on them, which is a hot research topic at the budding stage. Predicting the wheel–soil interaction performance from the knowledge of terramechanics is of great importance to the mechanical design/evaluation/optimization, dynamics simulation, soil parameter identification, and control of planetary rovers. In this study, experiments were performed using a single-wheel testbed for wheels with different radii (135 and 157.35 mm), widths (110 and 165 mm), lug heights (0, 5, 10, and 15 mm), numbers of lugs (30, 24, 15, and 8), and lug inclination angles (0°, 5°, 10°, and 20°) under different slip ratios (0, 0.1, 0.2, 0.3, 0.4, 0.6, etc.). The influences of the vertical load (30 N, 80 N, and 150 N), moving velocity (10, 25, 40, and 55 mm/s), and repetitive passing (four times) were also studied. Experimental results shown with figures and tables and are analyzed to evaluate the wheels’ driving performance in deformable soil and to draw conclusions. The driving performance of wheels is analyzed using absolute performance indices such as drawbar pull, driving torque, and wheel sinkage and also using relative indices such as the drawbar pull coefficient, tractive efficiency, and entrance angle. The experimental results and conclusions are useful for optimal wheel design and improvement/verification of wheel–soil interaction mechanics model. The analysis methods used in this paper, such as those considering the relationships among the relative indices, can be referred to for analyzing the performance of wheels of other vehicles.
Keywords: Terramechanics; Planetary exploration rover; Wheel performance; Dimension; Lug; Slip ratio; Performance indices

Hualin Fan, Fujun Liu, Han Long
Locomotion of vehicles on hinged road mats
Journal of Terramechanics, Volume 48, Issue 1, February 2011, Pages 47-55, ISSN 0022-4898, 10.1016/j.jterra.2010.09.003.
Abstract: In this paper, the hinged road-mat construction is modeled as a cable structure, and based on the equivalent cable theory the sinkage of the roadway is evaluated. Neglecting details of the interaction between tires and road mats, works caused by the traction, resistance, and drawbar pulling are defined to build a new work criterion to evaluate the mobility of vehicles on the hinged road mats. Mobility diagrams, related to coefficient of adhesion, terrain deformation, beam width, and fastening force, are developed to evaluate the locomotion of vehicles and further guide the design of hinged road mats. The presented method compares well with the field terramechanical experiments of the hinged road mats, thus verifying the validity of equivalent cable modeling and work criterion for hinged road mats.
Keywords: Locomotion; Hinged road mats; Traction work criterion

A. Abo Al-kheer, A. El-Hami, M.G. Kharmanda, A.M. Mouazen
Reliability-based design for soil tillage machines
Journal of Terramechanics, Volume 48, Issue 1, February 2011, Pages 57-64, ISSN 0022-4898, 10.1016/j.jterra.2010.06.001.
Abstract: Using classical design methods for tillage machines does not completely guarantee a safety and satisfactory performance, due in part to the randomness of tillage forces. This randomness is derived from the variability in soil engineering properties and the variations in tool design parameters and operational conditions. In this paper, a reliability-based design approach was developed, for the first time, by integrating the randomness of tillage forces into the design analysis of tillage machines, aiming at achieving reliable machines. The proposed approach was based on the uncertainty analysis of basic random variables and the failure probability of tillage machines. The failure probability was estimated according to two performance criteria related to the structural design requirement and the quality of tillage operation. Two reliability methods, namely the Monte Carlo simulation technique and the first-order reliability methods were used for this purpose. This approach was implemented for the design of a chisel plough shank.

The results showed that there were many values of the shank dimensions that guaranteed the required reliability level. However, in order to achieve the best design solution from an economic point of view, minimizing the volume of the shank structure was integrated into the reliability-based design approach. This led to the reduction of the initial volume of the shank structure by 6.86%. It was concluded that integrating the economical constraint into the reliability-based design approach can lead to optimal designs of tillage tools that ensures the required reliability level at low cost.
Keywords: Reliability-based design; Tillage machines; Tillage forces; Failure probability

C.R. Mehta, Karan Singh, M.M. Selvan
A decision support system for selection of tractor–implement system used on Indian farms
Journal of Terramechanics, Volume 48, Issue 1, February 2011, Pages 65-73, ISSN 0022-4898, 10.1016/j.jterra.2010.05.002.
Abstract: The selection of tractor and its matching implements has now become very difficult in India because of availability of variety of tractor models ranging from 10 to 45 kW. To overcome the problem of matching of tractor–implement system, an expert system modelling approach leading to decision support system (DSS) was adopted to make the step wise decision. The application of DSS was demonstrated in the paper to select either an implement to match the tractor or to select a tractor to match the implement under different soil and operating conditions. The DSS leading to computer software developed in Visual Basic™ programming provided the intuitive user interfaces by linking databases such as specifications of tractors and implements, tractor performance data, soil and operating conditions, to support the decision on selection of tractor–implement system. The programme calculates working width of implement based on input data for the most critical field operation and helps in selection of a suitable implement having width nearer to the calculated value among the commercially available implements. The software calculates the required drawbar power of the tractor based on draft and working speed of the selected implement. Finally, the PTO power requirement of a tractor is calculated by the software. Based on calculated PTO power, the software suggests available makes and models of tractor/machinery from the compiled data bank. The developed DSS was tested with a case study to demonstrate the flexibility of the software. The DSS can be used effectively in selection of a tractor or an implement of particular size from various makes and models of commercially available tractors and implements.
Keywords: Decision support system; Tractor; Matching implements; Drawbar power; PTO power

X. Potau, M. Comellas, M. Nogués, J. Roca
Comparison of different bogie configurations for a vehicle operating in rough terrain
Journal of Terramechanics, Volume 48, Issue 1, February 2011, Pages 75-84, ISSN 0022-4898, 10.1016/j.jterra.2010.06.002.
Abstract: Conventional wheeled vehicles have serious mobility limitations in rough terrain while walking vehicles have inherent drawbacks such as a high number of DOF and actuators, control complexity and low energy efficiency. Vehicles that passively fit the position of multiple wheels to maintain contact with the ground can be a good solution to this problem. The present work aims to comparatively quantify the ability of overcoming obstacles that is achieved by using different configurations of vehicles with bogies. Different configurations of vehicles facing obstacles when climbing along ramps of different longitudinal slope have been modeled. Further analyses have been done in order to investigate the influence of the position of the center of gravity and obstacle traversing speed. Different asymmetrical bogie configurations have also been proposed to further improve the obstacle surmounting capacity of the 4-axle vehicle. The results show a clear improvement in the ability to overcome obstacles when using bogies. Compromise solutions can be found for the obstacle traversing speed and position of the center of gravity. Asymmetrical bogie geometry can provide an improvement in the obstacle surmounting ability, although vehicle application has to be taken into account to find the best solution.
Keywords: Off-road; Rough terrain; Bogie; Traction; Obstacle surmounting; Parametrical model; Four axle

R.H. King, P. Van Susante, M.A. Gefreh
Analytical models and laboratory measurements of the soil–tool interaction force to push a narrow tool through JSC-1A lunar simulant and Ottawa sand at different cutting depths
Journal of Terramechanics, Volume 48, Issue 1, February 2011, Pages 85-95, ISSN 0022-4898, 10.1016/j.jterra.2010.07.003.
Abstract: Excavation equipment for developing NASA’s lunar outpost must be carefully designed to reduce launch cost, minimize operation cost, and enhance reliability. Excavation equipment requires knowledge of the stresses and strains in the equipment caused by the forces experienced during excavation. The types of excavation anticipated indicate that blade tools would move the most material. There are several analytical models available to predict forces from blade tools interacting with soil; however, it is not clear which if any, can predict lunar excavation forces precisely enough. Consequently, we measured the forces to push narrow (2.5-cm wide) square and round rods through a control material, Ottawa sand, and JSC-1A lunar mare regolith simulant at different cut depths in a controlled laboratory setting. The measurement results were compared with the forces predicted by eight analytical models. The Zeng, Luth and Wismer, and the Qinsen and Suren models fit the measurements best, considering that our study was limited to pushing stimulant and sand with small rods. The results show that depth of cut has a dramatic effect on the soil–tool interaction forces. Consequently, lunar missions should use a series of shallow cuts to reduce equipment size and power requirements.
Keywords: Excavation-force measurement; Excavation-force models; Lunar outpost; Lunar simulant