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 mes...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.展开更多
The paper attempts to analyze full load characteristics of over 500 combustion engines. Using statistical tools, the author determined the value of the coefficient of flexibility. Engine flexibility is the capability ...The paper attempts to analyze full load characteristics of over 500 combustion engines. Using statistical tools, the author determined the value of the coefficient 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. Different 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.展开更多
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...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.展开更多
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 s...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.展开更多
基金the Doctoral Program of Higher Education of China(No.20070006012)and Pre-research Project of China Academy of Space Technology.
文摘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.
基金financed from the funding allocated for science by the Ministry of Science and Higher Education–Poland
文摘The paper attempts to analyze full load characteristics of over 500 combustion engines. Using statistical tools, the author determined the value of the coefficient 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. Different 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.
文摘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.
文摘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.
