To obtain the performance characteristics of hydrodynamic tractor-retarder assembly under traction work condition,a numerical simulation model of flow channel was established and tetrahedron unstructured grids were ad...To obtain the performance characteristics of hydrodynamic tractor-retarder assembly under traction work condition,a numerical simulation model of flow channel was established and tetrahedron unstructured grids were adopted in the meshing stage.The racing rotating speed of the brake wheels was calculated by computational fluid dynamics（CFD） calculation and interpolation,and then accurate boundary condition was applied to the CFD simulation to study the pressure and velocity distribution of internal flow field in hydrodynamic tractor-retarder assembly.Finally,the original characteristics were calculated by CFD post-processing analysis.Comparison of experimental data and flow field analysis results showed that the calculation tolerance of the torque ratio K and the efficiency η was less than 5%,and the calculation tolerance of the pump torque coefficient λ was less than 10%.展开更多
Repeated Unit Cell（RUC）is a useful tool in micromechanical analysis of composites using Displacement-based Finite Element（DFE）method,and merely applying Periodic Displacement Boundary Conditions（PDBCs）to RUC is ...Repeated Unit Cell（RUC）is a useful tool in micromechanical analysis of composites using Displacement-based Finite Element（DFE）method,and merely applying Periodic Displacement Boundary Conditions（PDBCs）to RUC is almost a standard practice to conduct such analysis.Two basic questions arising from this practice are whether Periodic Traction Boundary Conditions（PTBCs,also known as traction continuity conditions）are guaranteed and whether the solution is independent of selection of RUCs.This paper presents the theoretical aspects to tackle these questions,which unify the strong form,weak form and DFE method of the micromechanical problem together.Specifically,the solution’s independence of selection of RUCs is dealt with on the strong form side,PTBCs are derived from the weak form as natural boundary conditions,and the validity of merely applying PDBCs in micromechanical Finite Element（FE）analysis is proved by referring to its intrinsic connection to the strong form and weak form.Key points in the theoretical aspects are demonstrated by illustrative examples,and the merits of setting micromechanical FE analysis under the background of a clear theoretical framework are highlighted in the efficient selection of RUCs for Uni Directional（UD）fiber-reinforced composites.展开更多
In the use of finite element methods to the planar elasticity problems,one diffculty is to overcome locking when elasticity constant λ→∞.In the case of traction boundary condition,another diffculty is to make the d...In the use of finite element methods to the planar elasticity problems,one diffculty is to overcome locking when elasticity constant λ→∞.In the case of traction boundary condition,another diffculty is to make the discrete Korn＇s second inequality valid.In this paper,a triangular element is presented.We prove that this element is locking-free,the discrete Korn＇s second inequality holds and the convergence order is two.展开更多
为解决牵引供电系统中存在的负序、谐波和无功等问题,设计了基于模块化多电平的铁路功率调节器(Modular Multilevel Converter-Railway Static Power Conditioner,MMC-RPC)的电流补偿控制策略。首先分析了MMC-RPC的基本结构和补偿原理,...为解决牵引供电系统中存在的负序、谐波和无功等问题,设计了基于模块化多电平的铁路功率调节器(Modular Multilevel Converter-Railway Static Power Conditioner,MMC-RPC)的电流补偿控制策略。首先分析了MMC-RPC的基本结构和补偿原理,针对采用低通滤波器提取瞬时功率中的直流成分时效果差、相移滞后等问题,设计了基于二阶广义积分器(SOGI)的直流分量提取器,可以更快速有效地获取直流量。然后采用比例复数积分(Proportional Complex Integral,PCI)控制器,控制M M C的输出电流,达到牵引供电系统电能质量综合治理的目的。最后进行了仿真验证,仿真结果表明该控制策略具有较好的负序、谐波补偿能力。展开更多
基金Supported by the National Key Laboratory of Vehicular Transmission (9140C3405020905)the National Natural Science Foundation of China(50905016)
文摘To obtain the performance characteristics of hydrodynamic tractor-retarder assembly under traction work condition,a numerical simulation model of flow channel was established and tetrahedron unstructured grids were adopted in the meshing stage.The racing rotating speed of the brake wheels was calculated by computational fluid dynamics（CFD） calculation and interpolation,and then accurate boundary condition was applied to the CFD simulation to study the pressure and velocity distribution of internal flow field in hydrodynamic tractor-retarder assembly.Finally,the original characteristics were calculated by CFD post-processing analysis.Comparison of experimental data and flow field analysis results showed that the calculation tolerance of the torque ratio K and the efficiency η was less than 5%,and the calculation tolerance of the pump torque coefficient λ was less than 10%.
文摘为解决铁路供电负序问题,同时兼顾无功补偿与谐波治理,由2个单相模块化多电平换流器(modular multilevel converter,MMC)背靠背连接构造铁路功率调节器(MMC-RPC),并直接接入牵引网。较传统RPC而言,取消了降压变压器,提高了直流电压,减小了直流端电流。针对铁路供电,分析单相系统的电压与功率间的数学模型,设计了一种无需系统角频率和电感参数的直接功率控制策略(direct power control,DPC)。以V/v牵引变为例,在Matlab/Simulink中搭建仿真模型,仿真结果验证了所提策略的有效性。
文摘Repeated Unit Cell（RUC）is a useful tool in micromechanical analysis of composites using Displacement-based Finite Element（DFE）method,and merely applying Periodic Displacement Boundary Conditions（PDBCs）to RUC is almost a standard practice to conduct such analysis.Two basic questions arising from this practice are whether Periodic Traction Boundary Conditions（PTBCs,also known as traction continuity conditions）are guaranteed and whether the solution is independent of selection of RUCs.This paper presents the theoretical aspects to tackle these questions,which unify the strong form,weak form and DFE method of the micromechanical problem together.Specifically,the solution’s independence of selection of RUCs is dealt with on the strong form side,PTBCs are derived from the weak form as natural boundary conditions,and the validity of merely applying PDBCs in micromechanical Finite Element（FE）analysis is proved by referring to its intrinsic connection to the strong form and weak form.Key points in the theoretical aspects are demonstrated by illustrative examples,and the merits of setting micromechanical FE analysis under the background of a clear theoretical framework are highlighted in the efficient selection of RUCs for Uni Directional（UD）fiber-reinforced composites.
文摘In the use of finite element methods to the planar elasticity problems,one diffculty is to overcome locking when elasticity constant λ→∞.In the case of traction boundary condition,another diffculty is to make the discrete Korn＇s second inequality valid.In this paper,a triangular element is presented.We prove that this element is locking-free,the discrete Korn＇s second inequality holds and the convergence order is two.
文摘为解决牵引供电系统中存在的负序、谐波和无功等问题,设计了基于模块化多电平的铁路功率调节器(Modular Multilevel Converter-Railway Static Power Conditioner,MMC-RPC)的电流补偿控制策略。首先分析了MMC-RPC的基本结构和补偿原理,针对采用低通滤波器提取瞬时功率中的直流成分时效果差、相移滞后等问题,设计了基于二阶广义积分器(SOGI)的直流分量提取器,可以更快速有效地获取直流量。然后采用比例复数积分(Proportional Complex Integral,PCI)控制器,控制M M C的输出电流,达到牵引供电系统电能质量综合治理的目的。最后进行了仿真验证,仿真结果表明该控制策略具有较好的负序、谐波补偿能力。
