Pantograph-catenary contact force provides the main basis for evaluation of current quality collection; however,the pantograph-catenary contact force is largely affected by the catenary irregularities.To analyze the c...Pantograph-catenary contact force provides the main basis for evaluation of current quality collection; however,the pantograph-catenary contact force is largely affected by the catenary irregularities.To analyze the correlated relationship between catenary irregularities and pantograph-catenary contact force,a method based on nonlinear auto-regressive with exogenous input(NARX) neural networks was developed.First,to collect the test data of catenary irregularities and contact force,the pantograph/catenary dynamics model was established and dynamic simulation was conducted using MATLAB/Simulink.Second,catenary irregularities were used as the input to NARX neural network and the contact force was determined as output of the NARX neural network,in which the neural network was trained by an improved training mechanism based on the regularization algorithm.The simulation results show that the testing error and correlation coefficient are 0.1100 and 0.8029,respectively,and the prediction accuracy is satisfactory.And the comparisons with other algorithms indicate the validity and superiority of the proposed approach.展开更多
A probabilistic method based on principle of maximum entropy was employed to analyze the randomness of contact force between geomembrane and granular material.The contact force distribution is exponential according to...A probabilistic method based on principle of maximum entropy was employed to analyze the randomness of contact force between geomembrane and granular material.The contact force distribution is exponential according to the proposed method and the grain size is the most important factor that affects the distribution of contact force.The proposed method is then verified by a series of laboratory experiments using glass beads and cobbles as granular material and a very thin pressure,indicating that film is firstly used in these experiments which give a reliable method to measure the contact force at each contact point.展开更多
Cold rotary forging is an advanced and complex metal forming technology with continuous local plastic deformation.Investigating the contact force between the dies and the workpiece has a great significance to improve ...Cold rotary forging is an advanced and complex metal forming technology with continuous local plastic deformation.Investigating the contact force between the dies and the workpiece has a great significance to improve the life of the dies in cold rotary forging.The purpose of this work is to reveal the contact force responses in cold rotary forging through the modelling and simulation.For this purpose,a 3D elastic-plastic dynamic explicit FE model of cold rotary forging is developed using the FE code ABAQUS/Explicit.Through the modelling and simulation,the distribution and evolution of the contact force in cold rotary forging is investigated in detail.The experiment has been conducted and the validity of the 3D FE model of cold rotary forging has been verified.The results show that: 1) The contact force distribution is complex and exhibits an obvious non-uniform characteristic in the radial and circumferential directions; 2) The maximum contact force between the upper die and the workpiece is much larger than that between the lower die and the workpiece; 3) The contact force evolution history is periodic and every period experiences three different stages; 4) The total normal contact force is much larger than the total shear contact force at any given time.展开更多
To research the influence of asymmetric brake shoe forces(ABSF)induced by braking failure on the dynamic performance of six-axle locomotive,the static equilibrium model of three-axle bogie and dynamic model for locomo...To research the influence of asymmetric brake shoe forces(ABSF)induced by braking failure on the dynamic performance of six-axle locomotive,the static equilibrium model of three-axle bogie and dynamic model for locomotive are established.The coupling vibration equations of axle hung motor and wheelset are derived.For the air braking,the influence mechanism of ABSF on the wheel-rail asymmetric motion and force characteristics are discussed.It can be found that if the ABSF is applied in the front wheelset,all the wheelsets move laterally in the same direction.Once the ABSF occurs in the middle or rear one,other wheelsets may move laterally towards the opposite direction.The motion amplitude and direction of all wheelsets strictly depend on the resultant moment of suspension yawing moment and brake shoe asymmetric moment.For the asymmetric braking,the free lateral gap of axle-box could increase the wheelset motion amplitude,but could not change the moving direction.In both the straight line and curve,the ABSF may lead to wheelset misaligning motion,intensify the wheel-rail lateral dynamic interaction and deteriorate wheel-rail contact state.Especially for the steering wheelsets,the asymmetric braking increases the wheelset attack angle significantly,which forms the worst braking condition.展开更多
目的:对混合牙列儿童的咬合力和咬合接触进行测量分析,初步提供混合牙列个别正常[牙合]儿童咬合情况的基线数据。方法:采用横断面研究,共纳入20例混合牙列个别正常[牙合]儿童,其中男童12例,女童8例,年龄在6.5~9.8岁。使用Dental Prescal...目的:对混合牙列儿童的咬合力和咬合接触进行测量分析,初步提供混合牙列个别正常[牙合]儿童咬合情况的基线数据。方法:采用横断面研究,共纳入20例混合牙列个别正常[牙合]儿童,其中男童12例,女童8例,年龄在6.5~9.8岁。使用Dental PrescaleⅡ咬合分析系统进行牙尖交错位时咬合力和咬合接触的测量,包括全牙列最大咬合力(N)及咬合接触面积(mm^(2))、左右双侧最大咬合力及咬合接触面积、平均咬合压强(MPa)、最大咬合压强(MPa),并确定咬合力重心位置。对最大咬合力、平均咬合压强、咬合接触面积的性别差异进行分析,比较混合牙列个别正常[牙合]儿童咬合的双侧对称性,对咬合数据与年龄、身高、体质量、体重指数(body mass index,BMI)的相关性进行分析。结果:(1)20例混合牙列儿童在牙尖交错位时平均最大咬合力为(869.18±106.64)N,平均咬合接触面积为(25.19±2.89)mm^(2),平均咬合压强为(34.37±5.98)MPa,最大咬合压强中位数(P_(25),P_(75))为120(120,120)MPa;(2)左右双侧在最大咬合力、咬合接触面积、平均咬合压强、最大咬合压强上差异无统计学意义(P>0.05);(3)牙尖交错位时,12例男童和8例女童的平均咬合接触面积分别为(26.71±3.91)mm^(2)和(21.62±3.08)mm^(2),平均最大咬合力分别为(911.92±145.05)N和(769.47±116.45)N,差异有统计学意义(P<0.05),而平均咬合压强在男童和女童间差异无统计学意义(P>0.05);(4)牙尖交错位时的最大咬合力与年龄呈弱相关(r=0.219,P=0.046),与咬合接触面积呈极强的正相关(r=0.949,P<0.001),平均咬合压强、最大咬合压强、咬合接触面积与年龄、身高、体质量、BMI均无相关性;(5)20例混合牙列个别正常[牙合]儿童的咬合重心均位于磨牙区,最大咬合压强点有7例儿童仅位于第一恒磨牙区,有10例儿童在乳磨牙区和第一恒磨牙区均存在,有3例儿童仅位于乳磨牙区。结论:混合牙列个别正常[牙合]儿童在牙尖交错位时的最大咬合力、咬合接触面积、平均咬合压强、最大咬合压强双侧对称性良好;最大咬合力、咬合接触面积存在性别差异,男童大于女童;最大咬合力与咬合接触面积呈正相关。展开更多
基金Project(20120009110035)supported by Specialized Research Fund for the Doctoral Program of Higher Education of ChinaProject(2011BAG01B05)supported by National Key Technology Research and Development Program of ChinaProject(2011AA110501)supported by National High-tech Research and Development Program of China
文摘Pantograph-catenary contact force provides the main basis for evaluation of current quality collection; however,the pantograph-catenary contact force is largely affected by the catenary irregularities.To analyze the correlated relationship between catenary irregularities and pantograph-catenary contact force,a method based on nonlinear auto-regressive with exogenous input(NARX) neural networks was developed.First,to collect the test data of catenary irregularities and contact force,the pantograph/catenary dynamics model was established and dynamic simulation was conducted using MATLAB/Simulink.Second,catenary irregularities were used as the input to NARX neural network and the contact force was determined as output of the NARX neural network,in which the neural network was trained by an improved training mechanism based on the regularization algorithm.The simulation results show that the testing error and correlation coefficient are 0.1100 and 0.8029,respectively,and the prediction accuracy is satisfactory.And the comparisons with other algorithms indicate the validity and superiority of the proposed approach.
基金Project(51079047)supported by the National Natural Science Foundation of ChinaProject Funded by the Priority Academic Program of Jiangsu Higher Education Institutions,China
文摘A probabilistic method based on principle of maximum entropy was employed to analyze the randomness of contact force between geomembrane and granular material.The contact force distribution is exponential according to the proposed method and the grain size is the most important factor that affects the distribution of contact force.The proposed method is then verified by a series of laboratory experiments using glass beads and cobbles as granular material and a very thin pressure,indicating that film is firstly used in these experiments which give a reliable method to measure the contact force at each contact point.
基金Project(51105287)supported by the National Natural Science Foundation of ChinaProject(2012BAA08003)supported by the Key Research and Development Project of New Products and New Technologies of Hubei Province,ChinaProject(2013M531750)supported by China Postdoctoral Science Foundation
文摘Cold rotary forging is an advanced and complex metal forming technology with continuous local plastic deformation.Investigating the contact force between the dies and the workpiece has a great significance to improve the life of the dies in cold rotary forging.The purpose of this work is to reveal the contact force responses in cold rotary forging through the modelling and simulation.For this purpose,a 3D elastic-plastic dynamic explicit FE model of cold rotary forging is developed using the FE code ABAQUS/Explicit.Through the modelling and simulation,the distribution and evolution of the contact force in cold rotary forging is investigated in detail.The experiment has been conducted and the validity of the 3D FE model of cold rotary forging has been verified.The results show that: 1) The contact force distribution is complex and exhibits an obvious non-uniform characteristic in the radial and circumferential directions; 2) The maximum contact force between the upper die and the workpiece is much larger than that between the lower die and the workpiece; 3) The contact force evolution history is periodic and every period experiences three different stages; 4) The total normal contact force is much larger than the total shear contact force at any given time.
基金Projects(52072249,51605315)supported by the National Natural Science Foundation of ChinaProject(E2018210052)supported by the Natural Science Foundation of Hebei Province,ChinaProject(TPL1707)supported by the Open Funds for the State Key Laboratory of Traction Power,China。
文摘To research the influence of asymmetric brake shoe forces(ABSF)induced by braking failure on the dynamic performance of six-axle locomotive,the static equilibrium model of three-axle bogie and dynamic model for locomotive are established.The coupling vibration equations of axle hung motor and wheelset are derived.For the air braking,the influence mechanism of ABSF on the wheel-rail asymmetric motion and force characteristics are discussed.It can be found that if the ABSF is applied in the front wheelset,all the wheelsets move laterally in the same direction.Once the ABSF occurs in the middle or rear one,other wheelsets may move laterally towards the opposite direction.The motion amplitude and direction of all wheelsets strictly depend on the resultant moment of suspension yawing moment and brake shoe asymmetric moment.For the asymmetric braking,the free lateral gap of axle-box could increase the wheelset motion amplitude,but could not change the moving direction.In both the straight line and curve,the ABSF may lead to wheelset misaligning motion,intensify the wheel-rail lateral dynamic interaction and deteriorate wheel-rail contact state.Especially for the steering wheelsets,the asymmetric braking increases the wheelset attack angle significantly,which forms the worst braking condition.
文摘目的:对混合牙列儿童的咬合力和咬合接触进行测量分析,初步提供混合牙列个别正常[牙合]儿童咬合情况的基线数据。方法:采用横断面研究,共纳入20例混合牙列个别正常[牙合]儿童,其中男童12例,女童8例,年龄在6.5~9.8岁。使用Dental PrescaleⅡ咬合分析系统进行牙尖交错位时咬合力和咬合接触的测量,包括全牙列最大咬合力(N)及咬合接触面积(mm^(2))、左右双侧最大咬合力及咬合接触面积、平均咬合压强(MPa)、最大咬合压强(MPa),并确定咬合力重心位置。对最大咬合力、平均咬合压强、咬合接触面积的性别差异进行分析,比较混合牙列个别正常[牙合]儿童咬合的双侧对称性,对咬合数据与年龄、身高、体质量、体重指数(body mass index,BMI)的相关性进行分析。结果:(1)20例混合牙列儿童在牙尖交错位时平均最大咬合力为(869.18±106.64)N,平均咬合接触面积为(25.19±2.89)mm^(2),平均咬合压强为(34.37±5.98)MPa,最大咬合压强中位数(P_(25),P_(75))为120(120,120)MPa;(2)左右双侧在最大咬合力、咬合接触面积、平均咬合压强、最大咬合压强上差异无统计学意义(P>0.05);(3)牙尖交错位时,12例男童和8例女童的平均咬合接触面积分别为(26.71±3.91)mm^(2)和(21.62±3.08)mm^(2),平均最大咬合力分别为(911.92±145.05)N和(769.47±116.45)N,差异有统计学意义(P<0.05),而平均咬合压强在男童和女童间差异无统计学意义(P>0.05);(4)牙尖交错位时的最大咬合力与年龄呈弱相关(r=0.219,P=0.046),与咬合接触面积呈极强的正相关(r=0.949,P<0.001),平均咬合压强、最大咬合压强、咬合接触面积与年龄、身高、体质量、BMI均无相关性;(5)20例混合牙列个别正常[牙合]儿童的咬合重心均位于磨牙区,最大咬合压强点有7例儿童仅位于第一恒磨牙区,有10例儿童在乳磨牙区和第一恒磨牙区均存在,有3例儿童仅位于乳磨牙区。结论:混合牙列个别正常[牙合]儿童在牙尖交错位时的最大咬合力、咬合接触面积、平均咬合压强、最大咬合压强双侧对称性良好;最大咬合力、咬合接触面积存在性别差异,男童大于女童;最大咬合力与咬合接触面积呈正相关。
