Continuum Modeling and Simulation of Robotic Appendage Interaction With Granular Material

Legged locomotion has advantages when one is navigating a flowable ground or a terrain with obstacles that are common in nature. With traditional terra-mechanics, one can capture large wheel–terrain interactions. However, legged motion on a granular substrate is difficult to investigate by using classical terra-mechanics due to sharp edge contact. Recent studies have shown that a continuum simulation can serve as an accurate tool for simulating dynamic interactions with granular material at laboratory and field scales. Spurred by this, a computational framework based on the smoothed particle hydrodynamics (SPH) method has been developed for the investigation of single robot appendage interaction with a granular system. This framework has been validated by using experimental results and extended to study robot appendages with different shapes and stride frequencies. The mechanics’ results are expected to help robot navigation and exploration in unknown and complex terrains.

Efficient evaluation of bridge deformation for running safety of railway vehicles using simplified models

The running safety of high-speed trains over bridges is a great concern in bridge design. Typically, the running safety of vehicles is evaluated by vehicle–track simulations that are computationally expensive and unfamiliar to bridge designers. This study investigates simplified vehicle–track models for assessing the running safety of vehicles on deformed bridges. Four types of simplified vehicle models along with four types of simplified wheel–track models are investigated. The predicted wheel–rail forces are compared with those simulated by the detailed vehicle–track program. In these simulations, typical bridge deformations are taken as excitations to the dynamic system. It is found that omitting the rail vibration leads to large wheel–rail response errors. The wheel–rail constraint model gives similar wheel–rail responses to those obtained by the Hertz contact model. A vehicle–track model with five degrees-of-freedom is adequate for assessing wheel–rail forces. Furthermore, an analytical solution to the wheel–rail forces running over an angular rotation was obtained. These simplified vehicle–track models provide an efficient way to assess the running safety of vehicles on deformed bridges when using probabilistic or optimal analyses that require a large number of simulations.

Investigation on Derailment of Empty Wagons of Long Freight Train during Dynamic Braking

The derailments of empty wagons of long freight trains frequently occurred around the world, which caused tremendous losses every year. Aiming at an actual derailment of empty wagons on straight line during dynamic braking, the field investigation was conducted to find the reasons of the accident. According to the investigation results, the large coupler yaw angle and coupler force, the special connection mode by drawbars, as well as the poor conditions of wheel treads and flanges were supposed to be responsible for the accident. The simulaiton model composed of 3 C80-type gondolas, and two RFC-type drawbars is established, the accuracy of which is validated by the field experimental test. When the wheel-rail friction coefficient is set to be 0.7 and the coupler forces are set to be 350 kN with a coupler yaw angle of 7 degrees, the simulation results are consistent with the field investigation results. Simulation results indicate that the coupler yaw angle, coupler force, and wheel-rail friction coefficient have significant influences on the derailment. The increasing coupler yaw angle and coupler force will increase the risk of derailment. For the wagon units adopting the drawbars, the riskiest wagon changes from the middle wagon to the front one as the lateral components of the coupler forces increase. A large wheel-rail friction coefficient can raise the risk of derailment. However, an overlarge friction coefficient will decrease the derailment risk. According to the field investigation and simulation results, the wheel-rail friction coefficients should be limited below 0.5 to ensure the running safety of empty wagons. Besides, the operations of the train should be optimized to avoid large coupler yaw angle and coupler force.

Research of Element Segregation to Large Wheel Hub Hardness and Mechanical Properties

This paper focused on the Cu alloy elements macro segregation of large squeeze casting wheel hub, analysed element segregation on the wheel axle, wheel arm and wheel rim. Three positions on the hardness and mechanical properties were tested, researched the influence of element segregation on the hardness and mechanical properties.

A Finite Element Model of Roll-Over Protective Structures for Wheel Loader Frame

ROPS is an effective way to reduce casualty rate in the rolling accident. This paper introduces the design of a cab to strengthen safety-ROPS large wheel loader method. The finite element model, it's a ROPS rear, absorbers and supporting structure frame of the safety-cabs, was created. Force and displacement boundary conditions obtained in accordance with the international standard ISO3471:2008-The large deformation elastic-plastic finite element analysis, horizontal, vertical and ROPS vertical load cases of performance testing and the corresponding lab for investigation. The test results show that the design can meet the requirements of ISO3471 ROPS: 2008. Test results differences and simulation and welded joint of the fracture analysis on the reason.