TRACTIVE PERFORMANCE ANALYSIS ON RADIALLY DEPLOYABLE WHEEL CONFIGURATION OF LUNAR ROVER VEHICLE BY DISCRETE ELEMENT METHOD

With the consideration of volume constraint of launch vehicle and trafficability of rover vehicle on lunar regolith terrain, a new design of radially deployable wheel is presented. For the purpose of achieving the meso-mechanics and dynamical behavior of lunar soil particles as well as macro-parameters of tractive performance for radially deployable wheel, the interaction between two types of wheel configurations and lunar soil particles is analyzed by means of discrete element method. The network of contact forces, the displacement vector chart, and the deformation of lunar soil beneath wheels are plotted. The equations of soil thrust, motion resistance, drawbar pull and driven torque are derived in granular scale based on the coordinates transformation and algebraic summation. The calculated results show that there is sufficient traction for both 6-split and 12-split radially deployable wheels with 304 mm outspread diameter to negotiate lunar regolith terrain specified here; the value of drawbar pull enhances with the increase of split number of radially deployable wheel, however, the required driven torque increases simultaneously, therefore, the tractive efficiency decreases.

Coefficient of Engine Flexibility as a Basis for the Assessment of Vehicle Tractive Performance

The paper attempts to analyze full load characteristics of over 500 combustion engines. Using statistical tools, the author determined the value of the coe cient of flexibility. Engine flexibility is the capability of the engine to adapt to varying loads. Importantly, in the investigations, the author took into account the parameters calculated in the course of the investigations on a chassis dynamometer, i.e., actual, not taken from technical specifications of brand new vehicles. Di erent stages of operating wear allow a better characterization of the population. Subsequent utilization of the results in tractive calculations is more reliable. The engines were divided into in six groups, depending on the type of fuel system: fuel injected gasoline and turbocharged gasoline, spark ignition LPG, naturally aspirated diesel and turbocharged diesel. However, engines running on alternative fuels are characterized with a greater flexibility than the fuel injected base engines. Conformity of flexibility of fuel injected and LPG IV generation engines have been observed,which confirms the appropriateness of engine adaptation to alternative fueling. Gasoline engine supercharging allowed a reduction of the maximum engine speed of the maximum torque, which extends the range of analyzable speeds for flexibility and consequently, the flexibility as such.

Damage due to rolling in total knee replacement-The influence of tractive force

The femoral condyles of a knee prosthesis articulate with a combination of rolling and sliding on the tibial polyethylene plateau.Little is known about potential polyethylene damage due to rolling motion.Since rolling does not exclude the presence of tangential surface loads,this study sought to investigate the influence of tractive rolling on the wear of polyethylene.A“wheel-on-flat”apparatus,consisting of a metal wheel and a polyethylene flat,mimicked contact conditions present in total knee replacement.An increasingly tractive force under conditions of pure rolling was applied.It was found that under rolling kinematics a tangential surface load of up to 17%of the normal load could be transferred through the contact.Surface damage was dependent on the amount of tractive force and appeared more severe with higher forces.In the region of highest tractive force,wear features were identified that resembled perpendicular ridges on surfaces of retrieved tibial polyethylene devices.This suggests that tractive rolling may be a relevant wear mode in total knee replacement.

Comparing tractive performance of steel and rubber single grouser shoe under different soil moisture contents

Steel and rubber are two kinds of materials which are often used for the tracks of off-road vehicles.The objective of this study was to compare tractive performances of steel and rubber grouser shoes under different soil moisture contents.In this study,the tractive performance of single grouser shoe was predicted by soil parameters and three-dimensional shearing model.The soil used in this study was clay soil,and ten different soil moisture contents ranged from 8.58%to 54.36%were applied for investigation of soil parameters.For each soil moisture content,the penetration test,direct shearing test,density and soil moisture content measurement have been performed to obtain the required soil parameters.The experimental results showed that thrust and running resistance of steel single grouser shoe had similar trends to those of rubber single grouser shoe.The thrust of rubber single grouser shoe was always greater than that of steel single grouser shoe with the increase of soil moisture content,and as well as the running resistance.However,the traction of rubber single grouser shoe had a different trend to that of steel single grouser shoe.The traction of steel single grouser shoe was always greater than that of rubber single grouser shoe at any given moisture content except at the stage of less than 15%moisture content.From the experimental results,it can be concluded that the steel single grouser shoe performed better than rubber single grouser shoe in traction for the soil used in this study.

Analysis and Numerical Simulation of Rolling Contact between Sphere and Cone

In non-conforming rolling contact, the contact stress is highly concentrated in the contact area. However, there are some limitations of the special contact model and stress model used for the theoretical study of the phenomenon, and this has prevented in-depth analysis of the associated friction, wear, and failure. This paper is particularly aimed at investigating the area of rolling contact between a sphere and a cone, for which purpose the boundary is determined by the Hertz theory and the geometries of the non-conforming surfaces. The phenomenon of stick-slip contact is observed to occur in the contact area under the condition of no-full-slip（Q 〈 μ·P）. Using the two-dimensional rolling contact theory developed by CARTER, the relative positions of the stick and slip regions and the distribution of the tangential force over the contact area are analyzed. Furthermore, each stress component is calculated based on the Mc Ewen theory and the idea of narrow band. The stress equations for the three-dimensional rolling contact between the sphere and the cone are obtained by the principle of superposition, and are used to perform some numerical simulations. The results show that the stress components have a large gradient along the boundary between the stick and slip regions, and that the maximum stress is inversely proportional to the contact coefficient and proportional to the friction coefficient. A new method for investigating the stress during non-classical three-dimensional rolling contact is proposed as a theoretical foundation for the analysis of the associated friction, wear, and failure.

Traction Potential Analysis of Self-Propelled Seafloor Trencher Based on Mechanical Measurements in Bentonite Soil

Shear stress-displacement relationship model of soil is very important to predict the tractive performance of tracked vehicle. Most shear stress-displacement models were proposed for terrestrial field.However,they are not suit for soft seafloor with flow surface and high water content. Based on comprehensive analysis of seafloor soil shear deformation and track segment shear tests,a new empirical model of shear stressdisplacement relationship for saturated soft-plastic soil(SSP model) was proposed. To validate the SSP model and evaluate potential tractive force of self-propelled seafloor trencher,a test platform,where track segment shear test and drawbar pull test can be performed in seafloor soil substitute(bentonite water mixture),was built. Series of shear tests were carried out. Test results show that the SSP model can describe the mechanical behavior of track segment in seafloor soil substitute with good approximation. Through analyzing the main external forces,including environmental loads from seafloor soil and sea current applied to seafloor tracked trencher during the trenching process in a straight line,drawbar pull analysis model was deduced with the SSP model. A scale test model of seafloor tracked trencher was built,and the verification tests for drawbar pull analysis model were designed and carried out. Results of verification tests indicate that the drawbar pull analysis model was feasible and effective. The drawbar pull tests also indicated that the SSP model is valid from another side.

Feasibility of implementation of intelligent simulation configurations based on data mining methodologies for prediction of tractor wheel slip

This paper deals with implementation of intelligent simulation configurations for prediction of tractor wheel slip in tillage operations.The effects of numeral variables of forward speed(2,4,and 6 km/h)and plowing depth(10,20,and 30 cm),and nominal variable of tractor driving mode(two-wheel drive(2WD)and four-wheel drive(4WD))on tractor rear wheel slip were intelligently simulated utilizing data mining methodologies of artificial neural network(ANN)and adaptive neuro-fuzzy inference system(ANFIS).Neuro-fuzzy potential of the ANFIS simulation framework against neural ability of the ANN simulation framework was apprised.Results confirmed higher efficiency of the best configuration of the ANFIS simulation framework with satisfactory statistical performance criteria of coefficient of determination(0.981),root mean square error(1.124%),mean absolute percentage error(1.515%),and mean of absolute values of prediction residual errors(1.135%)than that of the ANN simulation framework.Physical perception obtained from the ANFIS simulation results demonstrated that the wheel slip increased nonlinearly with increment of forward speed and plowing depth,while it decreased as tractor driving mode changed from the 2WD to 4WD.Therefore,the best configuration of the ANFIS based intelligent simulation framework implemented in this study can be used for further relevant studies of tractor rear wheel slip as a reference.

PPG Ranked 28th among 100 Recognized Enterprises for Contribution to China's 30 Years of Reform and Opening-up

In the recently announced "Honor and Re-sponsibility-q 2008 Multinational Corporation’s Contribution to China",PPG Industries(NYSE:PPG)ranked 28th of 100 enterprises winning an