Crack propagation path in two-directionally graded composites was investigated by the finite element method.A graded extended finite element method(XFEM)was employed to calculate displacement and stress fields in crac...Crack propagation path in two-directionally graded composites was investigated by the finite element method.A graded extended finite element method(XFEM)was employed to calculate displacement and stress fields in cracked graded structures.And a post-processing subroutine of interaction energy integral was implemented to extract the mixed-mode stress intensity factors(SIFs).The maximum hoop stress(MHS)criterion was adopted to predict crack growth direction based on the assumption of local homogenization of asymptotic crack-tip fields in graded materials.Effects of material nonhomogeneous parameters on crack propagation paths were also discussed in detail.It is shown that the present method can provide relatively accurate predictions of crack paths in two-directionally graded composites.Crack propagates in the decreasing direction of effective Young′s modulus.The shape and steepness of property gradient perpendicular to the crack surface have great influences on crack paths.Through redesigning material property reasonably,crack growth in graded material can be changed to improve mechanical behaviours of cracked structures.展开更多
In the case of electric or tram traction vehicles, the energy for propulsion purposes, as well as all other purposes, is processed and delivered via traction substations. Knowledge of the course of traction substation...In the case of electric or tram traction vehicles, the energy for propulsion purposes, as well as all other purposes, is processed and delivered via traction substations. Knowledge of the course of traction substation loading, especially at the stage of its design, is an extremely important issue because of the choice of the processing equipment of the main circuit or protection devices. In the range of investigations of railway traction substation B in vicinity of Cracow （Poland）, the measurements of current load in hours 4：00 a.m.-8：00 p.m. were realized. The measurements for the analysis were chosen from those realized between 6：00 a.m.-8：00 a.m. （the morning rush time）. Due to the sampling of 2 h summit with a frequency of 2 kHz, the recorded data set contains 1.44 ~ 107 elements. Therefore, the necessary transformation of data was to lower frequency 1 Hz, 10 Hz and 50 Hz. The results of the analysis presented below indicate the effect of such conduct on the obtained results for the parameters of time series models. In view of the unsatisfactory effects of the polynomial approximation, there is a need to seek a more efficient approximation method for achieving the optimum compatibility with the measured process. Continued research should lead to the formulation of procedures, which will determine an acceptable accuracy of the expected variability of traction substation loads.展开更多
Electric trains typically travel across the railway networks in an inter-provincial,inter-city and intra-city manner.The electric train generally serves as a load/source in tractive/brake mode,through which power netw...Electric trains typically travel across the railway networks in an inter-provincial,inter-city and intra-city manner.The electric train generally serves as a load/source in tractive/brake mode,through which power networks and railway networks are closely coupled and mutually influenced.Based on the operational mode of rail trains and the characteristics of their load power,this paper proposes a coordinated optimal decisionmaking method of demand response for controllable load of rail trains and energy storage systems.First,a coordinated approach of dynamically adjusting the load of the controllable rail train in considering the driving comfort and energy storage battery is designed.Secondly,under the time conditions that satisfy the train’s operational diagram,the functional relationship between the train speed and the load power is presented.Based on this,in considering the constraints of the train’s arrival time,driving speed,motor power,and driving comfort,the capacity of energy storage batteries and other constraints,an optimization model for demand response in managing the traction power supply system under a two-part price and time-of-use(TOU)price is proposed.The objective is to minimize the energy consumption costs of rail transit trains,and optimize the speed trajectory of rail trains,the load power of traction system,and the output of energy storage batteries.展开更多
基金supported by the Fundamental Research Funds for the Central Universities(No.NS2016003)
文摘Crack propagation path in two-directionally graded composites was investigated by the finite element method.A graded extended finite element method(XFEM)was employed to calculate displacement and stress fields in cracked graded structures.And a post-processing subroutine of interaction energy integral was implemented to extract the mixed-mode stress intensity factors(SIFs).The maximum hoop stress(MHS)criterion was adopted to predict crack growth direction based on the assumption of local homogenization of asymptotic crack-tip fields in graded materials.Effects of material nonhomogeneous parameters on crack propagation paths were also discussed in detail.It is shown that the present method can provide relatively accurate predictions of crack paths in two-directionally graded composites.Crack propagates in the decreasing direction of effective Young′s modulus.The shape and steepness of property gradient perpendicular to the crack surface have great influences on crack paths.Through redesigning material property reasonably,crack growth in graded material can be changed to improve mechanical behaviours of cracked structures.
文摘In the case of electric or tram traction vehicles, the energy for propulsion purposes, as well as all other purposes, is processed and delivered via traction substations. Knowledge of the course of traction substation loading, especially at the stage of its design, is an extremely important issue because of the choice of the processing equipment of the main circuit or protection devices. In the range of investigations of railway traction substation B in vicinity of Cracow （Poland）, the measurements of current load in hours 4：00 a.m.-8：00 p.m. were realized. The measurements for the analysis were chosen from those realized between 6：00 a.m.-8：00 a.m. （the morning rush time）. Due to the sampling of 2 h summit with a frequency of 2 kHz, the recorded data set contains 1.44 ~ 107 elements. Therefore, the necessary transformation of data was to lower frequency 1 Hz, 10 Hz and 50 Hz. The results of the analysis presented below indicate the effect of such conduct on the obtained results for the parameters of time series models. In view of the unsatisfactory effects of the polynomial approximation, there is a need to seek a more efficient approximation method for achieving the optimum compatibility with the measured process. Continued research should lead to the formulation of procedures, which will determine an acceptable accuracy of the expected variability of traction substation loads.
基金This work was supported in part by the National Natural Science Foundation of China(71931003)the Science and Technology Projects of Hunan Province and Changsha City(2018GK4002,2019CT5001,2019WK2011,2019GK5015 and kq1907086).
文摘Electric trains typically travel across the railway networks in an inter-provincial,inter-city and intra-city manner.The electric train generally serves as a load/source in tractive/brake mode,through which power networks and railway networks are closely coupled and mutually influenced.Based on the operational mode of rail trains and the characteristics of their load power,this paper proposes a coordinated optimal decisionmaking method of demand response for controllable load of rail trains and energy storage systems.First,a coordinated approach of dynamically adjusting the load of the controllable rail train in considering the driving comfort and energy storage battery is designed.Secondly,under the time conditions that satisfy the train’s operational diagram,the functional relationship between the train speed and the load power is presented.Based on this,in considering the constraints of the train’s arrival time,driving speed,motor power,and driving comfort,the capacity of energy storage batteries and other constraints,an optimization model for demand response in managing the traction power supply system under a two-part price and time-of-use(TOU)price is proposed.The objective is to minimize the energy consumption costs of rail transit trains,and optimize the speed trajectory of rail trains,the load power of traction system,and the output of energy storage batteries.
