The multi-point dynamic aggregation(MPDA)problem is a challenging real-world problem.In the MPDA problem,the demands of tasks keep changing with their inherent incremental rates,while a heterogeneous robot fleet is re...The multi-point dynamic aggregation(MPDA)problem is a challenging real-world problem.In the MPDA problem,the demands of tasks keep changing with their inherent incremental rates,while a heterogeneous robot fleet is required to travel between these tasks to change the time-varying state of each task.The robots are allowed to collaborate on the same task or work separately until all tasks are completed.It is challenging to generate an effective task execution plan due to the tight coupling between robots abilities and tasks'incremental rates,and the complexity of robot collaboration.For effectiveness consideration,we use the variable length encoding to avoid redundancy in the solution space.We creatively use the adaptive large neighborhood search(ALNS)framework to solve the MPDA problem.In the proposed algorithm,high-quality initial solutions are generated through multiple problem-specific solution construction heuristics.These heuristics are also used to fix the broken solution in the novel integrated decoding-construction repair process of the ALNS framework.The results of statistical analysis by the Wilcoxon rank-sum test demonstrate that the proposed ALNS can obtain better task execution plans than some state-of-the-art algorithms in most MPDA instances.展开更多
Sandwich structures are vulnerable to multi-point impacts,and such impacts can result in a reduction in residual strength even catastrophic accident.Therefore,the multi-point impact behaviors of PMI foam sandwich stru...Sandwich structures are vulnerable to multi-point impacts,and such impacts can result in a reduction in residual strength even catastrophic accident.Therefore,the multi-point impact behaviors of PMI foam sandwich structure are investigated and studied using experimental and numerical coupled methods.Three impact energy levels and five Distances Between Impact Positions(DBIP)are considered in details,and representative impact characteristics are compared to reveal the association between Compression After Impact(CAI)strength and DBIP.Results indicate that the interference between the multi-point impact events has a dominant effect on CAI strength when DBIP is small,and the variation in bending stiffness induced by the boundary effect is the dominant factor affecting CAI strength when DBIP ranges from 20 mm to 60 mm.In addition,matrix damage represents the primary damage mode in multi-point impact,and the calculated ratio of energy absorbed by the top face sheet and honeycomb core,in relation to the total absorbed energy,serves as a clear indicator of the damage severity experienced by both components.This work is enlightening for the structural design of impact-resistant composites.展开更多
Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint ...Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint with a5-m wavelength range, leaving a significant knowledge gap in this field.Design/methodology/approach – In this study, the authors used the well-established inertial referencemethod (IR-method), and the state-of-the-art multi-point chord reference method (MCR-method). Two methodshave been applied in different types of rail straightness measurement trollies, respectively. These instrumentswere tested in a high-speed rail section within a certain region of China. The test results were ultimatelyvalidated through using traditional straightedge and feeler gauge methods as reference data to evaluate the railweld joint straightness within the 5-m wavelength range.Findings – The research reveals that IR-method and MCR-method produce reasonably similar measurementresults for wavelengths below 1 m. However, MCR-method outperforms IR-method in terms of accuracy forwavelengths exceeding 3 m. Furthermore, it was observed that IR-method, while operating at a slower speed,carries the risk of derailing and is incapable of detecting rail weld joints and low joints within the track.Originality/value – The research compare two methods’ measurement effects in a longer wavelength rangeand demonstrate the superiority of MCR-method.展开更多
Multi-point forming (MPF) is an advanced manufacturing technology for three-dimensional sheet metal parts. In this paper, the MPF integrated system is described that can form a variety of part shapes without the need ...Multi-point forming (MPF) is an advanced manufacturing technology for three-dimensional sheet metal parts. In this paper, the MPF integrated system is described that can form a variety of part shapes without the need for solid dies, and given only geometry and material information about the desired part. The central component of this system is a pair of matrices of punches, and the desired discrete die surface is constructed by changing the positions of punches though the CAD and control system. The basic MPF process is introduced and the typical application examples show the applicability of the MPF technology. Wrinkle and dimple are the major forming defects in MPF process, numerical simulation is a feasible way to predict forming defects in MPF. In conventional stamping, the mode to form sheet metal with blankholder is an effective way to suppress wrinkling; the same is true in MPF. A MPF press with flexible blankholder was developed, and the forming results indicated the forming stability of this technique. Based on the flexibility of MPF, varying deformation path MPF and sectional MPF were explored that cannot be realized in conventional stamping. By controlling each punch in real-time, a sheet part can be manufactured along a specific forming path. When the path of deformation in MPF is designed properly, forming defects will be avoided completely and lager deformation is achieved. A work piece can be formed section by section though the sectional MPF, and this technique makes it possible to manufacture large size parts in a small MPF press. Some critical experiments were performed that confirmed the validity of two special MPF techniques.展开更多
In order to study the impacts of warhead geometry and initiation pattern on the lethality of aimable warhead, multi-point synchronous initiated hexagonal prism and cylindrical warheads were compared through numerical ...In order to study the impacts of warhead geometry and initiation pattern on the lethality of aimable warhead, multi-point synchronous initiated hexagonal prism and cylindrical warheads were compared through numerical simulation, combined with theoretical formulas of fragment decelera- tion and target plugging. Enhancements of fragment velocity, kinetic energy and density toward the target and target destructions were analyzed. The results show that hexagonal prism warhead can produce dense fragment beams and enhance average velocity and kinetic energy with asymmetric eight-point initiation by 24. 13% and 54. 52% respectively, which are higher than those of the isomet- ric or same weight cylindrical warhead. The effective fragments are still relatively concentrated in an area of 8 m × 2 m for the hexagonal prism warhead when the distance between warhead and target is 40 m.展开更多
The wheel-rail contact problems, such as the number, location and the track of contact patches, are very important for optimizing the spatial structure of the rails and lowering the vehicle-turnout system dynamics. Ho...The wheel-rail contact problems, such as the number, location and the track of contact patches, are very important for optimizing the spatial structure of the rails and lowering the vehicle-turnout system dynamics. However, the above problems are not well solved currently because of having the difficulties in how to determine the multi-contact, to preciously present the changeable profiles of the rails and to establish an accurate spatial turnout system dynamics model. Based on a high-speed vehicle-turnout coupled model in which the track is modeled as flexible with rails and sleepers represented by beams, the line tracing extreme point method is introduced to investigate the wheel-rail multiple contact conditions and the key sections of the blade rail, longer nose rail, shorter rail in the switch and nose rail area are discretized to represent the varying profiles of rails in the turnout. The dynamic interaction between the vehicle and turnout is simulated for cases of the vehicle divergently passing the turnout and the multi-point contact is obtained. The tracks of the contact patches on the top of the rails are presented and the wheel-rail impact forces are offered in comparison with the contact patches transference on the rails. The numerical simulation results indicate that the length of two-point contact occurrence of a worn wheel profile and rails is longer than that of the new wheel profile and rails; The two-point contact definitely occurs in the switch and crossing area. Generally, three-point contact doesn’t occur for the new rail profile, which is testified by the wheel-rails interpolation distance and the first order derivative function of the tracing line extreme points. The presented research is not only helpful to optimize the structure of the turnout, but also useful to lower the dynamics of the high speed vehicle-turnout system.展开更多
A multi-point flexible straightening process characterized by reciprocating bending is proposed.Specifically,the process is analyzed in terms of deformation mechanism and verified by numerical simulations and physical...A multi-point flexible straightening process characterized by reciprocating bending is proposed.Specifically,the process is analyzed in terms of deformation mechanism and verified by numerical simulations and physical experiments of the straightening of a series of metal profiles with different materials and initial shapes.Further,the relationship between the bending radius and the times of reciprocating bending required to unify the curvature is discussed,and the distribution of residual stress after straightening is analyzed.The results show that the reciprocating bending process can eliminate the difference of the initial curvature,make the curvature of each section tend to be uniform;the times of reciprocating bending to reach the uniform curvature decreases with the decrease of bending radius.The straightness of the straightened profile obtained from the experiment and simulation is less than 0.2%,demonstrating a good feasibility of this method.展开更多
A kind of third order multi-point boundary value problems, x＇＇＇（ ι） = f（ t, x （ t ）, x＂ （ t ）, x＇＇＇ （ t ） ） ＋ m 2 e（t）,t∈（0, 1）,x（0）=ax（ξ）,x＇（0）-0,x（l）= ^m2∑j=1 βjx（ηj）, fεC[0,...A kind of third order multi-point boundary value problems, x＇＇＇（ ι） = f（ t, x （ t ）, x＂ （ t ）, x＇＇＇ （ t ） ） ＋ m 2 e（t）,t∈（0, 1）,x（0）=ax（ξ）,x＇（0）-0,x（l）= ^m2∑j=1 βjx（ηj）, fεC[0, 1]×R^3, e（t）∈L^1[0, 1],a≥0, is considered, all theβj＇s have not the same sign, 0〈ξ〈 l, 0〈η1〈 η2〈… 〈ηm.2〈 1. By using the coincidence degree theory, some existence theorems for the problems at resonance are obtained.展开更多
In this paper, the principle of multi-point forming (MPF) technique is presented. One of the most serious defects, wrinkling, during the multi-point forming process of a shallow rectangle cup is discussed by means of ...In this paper, the principle of multi-point forming (MPF) technique is presented. One of the most serious defects, wrinkling, during the multi-point forming process of a shallow rectangle cup is discussed by means of numerical simulation on the shallow rectangle cup forming process. The effects of thickness, material of sheet metal and the pressure of the blank holder are investigated. Based on the simulation results, the reasons and control methods of wrinkling are pointed out. Moreover, the experiment on the multi-point die forming of the shallow rectangle cup by the MPF machine is done to validate the efficiency of the numerical simulation, and the result proves that the application of an elastic cushion in the forming can restrain wrinkling efficiently.展开更多
This article deals with the following second-order multi-point boundary value problem x″（t）=r（t,x（t）,x′（t））＋e（t）,t∈（0,1）x′（0）=m∑i=1aix′（ξi）,x（1）=n∑j=1βjx（ηj）, Under the resonance conditi...This article deals with the following second-order multi-point boundary value problem x″（t）=r（t,x（t）,x′（t））＋e（t）,t∈（0,1）x′（0）=m∑i=1aix′（ξi）,x（1）=n∑j=1βjx（ηj）, Under the resonance conditions m∑i=1ai=1,n∑j=1βj=1,n∑j=1βjηj=1 , by applying the coincidence degree theory, some existence results of the problem are established. The emphasis here is that the dimension of the linear operator is two. In this paper, we extend and improve some previously known results like the ones in the references.展开更多
To apply the multi-point forming technology to the field of tube processing,the process of multi-point forming for tube is studied.Numerical simulation for the process of multi-point forming for tube is achieved by us...To apply the multi-point forming technology to the field of tube processing,the process of multi-point forming for tube is studied.Numerical simulation for the process of multi-point forming for tube is achieved by using elastic-plastic FEM in ABAQUS.During simulation,reasonable coefficient of mass scaling and friction model of penalty function are used.The influence of several major technological parameters on the process is analyzed.When the tube diameter is 60 mm and the forming curvature radius is 1000 mm,the distortion rate of cross-section and the absolute forming error gradually decrease with the increasing of tube wall thickness;However,when the tube wall thickness is constant,the smaller the curvature radius,the larger the distortion rate of cross-section,but as to forming part,its absolute forming error becomes smaller.展开更多
In this paper, we consider the following multi-point boundary value problem of fractional differential equation D^α0＋u（t）=f（t,u（t）,D^α-10＋u（t）,D^α-20＋u（t）,D^α-30＋u（t）,t∈（0,1）,I^4-α0＋u（0）=0,D^...In this paper, we consider the following multi-point boundary value problem of fractional differential equation D^α0＋u（t）=f（t,u（t）,D^α-10＋u（t）,D^α-20＋u（t）,D^α-30＋u（t）,t∈（0,1）,I^4-α0＋u（0）=0,D^α-10＋u（t）=^n∑i=1αiD^α-10＋u（ξ1）,D^α-20＋u（1）=^n∑j=1D^α-20＋u（ηj）,D^α-30＋u（1）-D^α-30＋u（0）=D^α-20＋u（1/2）,where 3 〈 α ≤ 4 is a real number. By applying Mawhin coincidence degree theory and constructing suitable operators, some existence results of solutions can be established.展开更多
This paper is concerned with the existence of solutions for the following multipoint boundary value problem at resonance{(Φp (x'))' + f(t,x)=0,0 < t < 1,x' (0)=x'(ξ) x(1)=m-3 ∑i=1 βi x(η i),...This paper is concerned with the existence of solutions for the following multipoint boundary value problem at resonance{(Φp (x'))' + f(t,x)=0,0 < t < 1,x' (0)=x'(ξ) x(1)=m-3 ∑i=1 βi x(η i),where βi∈ R,m-3 ∑i=1 β i=1,0 < η 1 < η 2 < ··· < ηm-3 < 1,m-3 ∑i=1 βiηi=1,0 < ξ < 1.An existence theorem is obtained by using the extension of Mawhin's continuation theorem.Since almost all the multi-point boundary value problem at resonance in previous papers are for the linear operator without p-Laplacian by the use of Mawhin's continuation theorem,our method is new.展开更多
In this paper, we study the multiplicity of positive solutions for multi-point boundary value problem of Riemann-Liouville fractional differential equation with multi-terms fractional derivative in the boundary condit...In this paper, we study the multiplicity of positive solutions for multi-point boundary value problem of Riemann-Liouville fractional differential equation with multi-terms fractional derivative in the boundary conditions. By using the properties of the Green function and a generalization of the Leggett-Williams fixed point theorem due to the work of Bai and Ge, the sufficient conditions to guarantee the existence of at least three positive solutions are established. In the end of this paper, we have also given out the example to illustrate the wide range of potential application of our main results.展开更多
A Markov repairable system with history-dependent up and down states is presented. The state space of the repairable system is divided into three sets, which are up states, down states and changeable states.Using aggr...A Markov repairable system with history-dependent up and down states is presented. The state space of the repairable system is divided into three sets, which are up states, down states and changeable states.Using aggregated stochastic processes, we can get the multi-interval availability and multi-point availability for the Markov repairable system. Finally, numerical examples are given to illustrate the obtained results.展开更多
Corona discharge, as a common means to obtain non-equilibrium plasma, can generally obtain high-concentration plasma by increasing discharge points to meet production needs. However,the existing numerical simulation m...Corona discharge, as a common means to obtain non-equilibrium plasma, can generally obtain high-concentration plasma by increasing discharge points to meet production needs. However,the existing numerical simulation models used to study multi-point corona discharge are all calculations of small-scale space models, which cannot obtain the distribution characteristics of plasma in large space. Based on our previous research, this paper proposes a hybrid model for studying the distribution of multi-point discharge plasma in large-scale spaces, which divides the computational domain and computes separately with the hydrodynamic model and the ion mobility model. The simulation results are verified by a needle–ball electrode device. Firstly, the electric field distribution and plasma distribution of the needle electrodes with single tip and double tips are compared and discussed. Secondly, the plasma distribution of the needle electrode with the double tip at different voltages is investigated. Both computational and experimental results indicate that the charged particle concentration and current of the needle electrode with double tips are both twice as high as those of the needle electrode with a single tip. This model can extend the computational area of the multi-point corona discharge finite element model to the sub-meter(25 cm) or meter level, which provides an effective means to study the plasma distribution generated by multiple discharge points in large-scale space.展开更多
In general, the seismic response analysis in earthquake engineering assumes that the vibration parameters of the target and the contact surface of the external media are identical,i. e., single point input. However, e...In general, the seismic response analysis in earthquake engineering assumes that the vibration parameters of the target and the contact surface of the external media are identical,i. e., single point input. However, earthquake energy has an attenuation phenomenon in wave propagation,so a wide range of soil slopes and the external medium contact surface of different input points on motion are not identical. If we consider single point input only, it may not correspond with reality, so it is necessary to carry out research on multi-point input methods. Based on the 2-D slope model,single-point input and multi-point input are performed respectively to analyze and compare their similarities and differences in the perspectives of the characteristics of seismic response of soil layer and plastic zone distribution to provide a reference for the seismic design of slopes. The results show that in the perspective of soil seismic response analysis,the peak acceleration output and peak velocity output under multi-point input are greater than the peak values under single point input at the same monitoring point,the peak appearing time is also earlier than that of the single point input; in terms of the plastic zone distribution,the multi-point effect is manifested as the presence of more obvious tensile shear failures; in the perspective of safety coefficient,the safety coefficient under each multi-point input is smaller than that of single point input,a difference of about 7 % or so. In summary,multi-point input is more reasonable and practical than single point input,so multi-point input should be considered in seismic design.展开更多
A class of multi-point boundary value problems are studied.Easily verified suffcient conditions to guarantee the existence of at least one solutions of above mentioned BVPs are established.The examples are presented t...A class of multi-point boundary value problems are studied.Easily verified suffcient conditions to guarantee the existence of at least one solutions of above mentioned BVPs are established.The examples are presented to illustrate the main results.展开更多
Resource allocation is an important problem in ubiquitous network. Most of the existing resource allocation methods considering only wireless networks are not suitable for the ubiquitous network environment, and they ...Resource allocation is an important problem in ubiquitous network. Most of the existing resource allocation methods considering only wireless networks are not suitable for the ubiquitous network environment, and they will harm the interest of individual users with instable resource requirements. This paper considers the multi-point video surveillance scenarios in a complex network environment with both wired and wireless networks. We introduce the utility estimated by the total costs of an individual network user. The problem is studied through mathematical modeling and we propose an improved problem-specific branch-and-cut algorithm to solve it. The algorithm follows the divide-and-conquer principle and fully considers the duality feature of network selection. The experiment is conducted by simulation through C and Lingo. And it shows that compared with a centralized random allocation scheme and a cost greed allocation scheme, the proposed scheme has better per- formance of reducing the total costs by 13.0% and 30.6% respectively for the user.展开更多
To improve the quality of multi-point die forming, a new approach using discrete steel pads was proposed. The formability of three different multi-point die forming processes was analyzed through numerical simulation ...To improve the quality of multi-point die forming, a new approach using discrete steel pads was proposed. The formability of three different multi-point die forming processes was analyzed through numerical simulation and experiments. Numerical simulation and experimental results showed that the use of discrete steel pads in the multi-point forming process can substantially improve the stress–strain state on the plate and suppress dimple, straight-edge, and wrinkle defects. This analysis verified that the use of discrete steel pads in a multi-point forming process can effectively improve the quality and accuracy with which sheet metal is formed.展开更多
基金supported in part by the National Outstanding Youth Talents Support Program(No.61822304)the Basic Science Center Program of the NSFC(No.62088101)+2 种基金the Project of Major International(Regional)Joint Research Program of NSFC(No.61720106011)the Shanghai Municipal Science and Technology Major Project(No.2021SHZDZX0100)the Shanghai Municipal Commission of Science and Technology Project(No.19511132101).
文摘The multi-point dynamic aggregation(MPDA)problem is a challenging real-world problem.In the MPDA problem,the demands of tasks keep changing with their inherent incremental rates,while a heterogeneous robot fleet is required to travel between these tasks to change the time-varying state of each task.The robots are allowed to collaborate on the same task or work separately until all tasks are completed.It is challenging to generate an effective task execution plan due to the tight coupling between robots abilities and tasks'incremental rates,and the complexity of robot collaboration.For effectiveness consideration,we use the variable length encoding to avoid redundancy in the solution space.We creatively use the adaptive large neighborhood search(ALNS)framework to solve the MPDA problem.In the proposed algorithm,high-quality initial solutions are generated through multiple problem-specific solution construction heuristics.These heuristics are also used to fix the broken solution in the novel integrated decoding-construction repair process of the ALNS framework.The results of statistical analysis by the Wilcoxon rank-sum test demonstrate that the proposed ALNS can obtain better task execution plans than some state-of-the-art algorithms in most MPDA instances.
基金Supported by the National Key R&D Program of China(2023YFB3709602,2023YFB3709603)National Natural Science Foundation of China(12372141)the Key R&D Program in Shaanxi Province(2024GH-ZDXM-27).
文摘Sandwich structures are vulnerable to multi-point impacts,and such impacts can result in a reduction in residual strength even catastrophic accident.Therefore,the multi-point impact behaviors of PMI foam sandwich structure are investigated and studied using experimental and numerical coupled methods.Three impact energy levels and five Distances Between Impact Positions(DBIP)are considered in details,and representative impact characteristics are compared to reveal the association between Compression After Impact(CAI)strength and DBIP.Results indicate that the interference between the multi-point impact events has a dominant effect on CAI strength when DBIP is small,and the variation in bending stiffness induced by the boundary effect is the dominant factor affecting CAI strength when DBIP ranges from 20 mm to 60 mm.In addition,matrix damage represents the primary damage mode in multi-point impact,and the calculated ratio of energy absorbed by the top face sheet and honeycomb core,in relation to the total absorbed energy,serves as a clear indicator of the damage severity experienced by both components.This work is enlightening for the structural design of impact-resistant composites.
文摘Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint with a5-m wavelength range, leaving a significant knowledge gap in this field.Design/methodology/approach – In this study, the authors used the well-established inertial referencemethod (IR-method), and the state-of-the-art multi-point chord reference method (MCR-method). Two methodshave been applied in different types of rail straightness measurement trollies, respectively. These instrumentswere tested in a high-speed rail section within a certain region of China. The test results were ultimatelyvalidated through using traditional straightedge and feeler gauge methods as reference data to evaluate the railweld joint straightness within the 5-m wavelength range.Findings – The research reveals that IR-method and MCR-method produce reasonably similar measurementresults for wavelengths below 1 m. However, MCR-method outperforms IR-method in terms of accuracy forwavelengths exceeding 3 m. Furthermore, it was observed that IR-method, while operating at a slower speed,carries the risk of derailing and is incapable of detecting rail weld joints and low joints within the track.Originality/value – The research compare two methods’ measurement effects in a longer wavelength rangeand demonstrate the superiority of MCR-method.
文摘Multi-point forming (MPF) is an advanced manufacturing technology for three-dimensional sheet metal parts. In this paper, the MPF integrated system is described that can form a variety of part shapes without the need for solid dies, and given only geometry and material information about the desired part. The central component of this system is a pair of matrices of punches, and the desired discrete die surface is constructed by changing the positions of punches though the CAD and control system. The basic MPF process is introduced and the typical application examples show the applicability of the MPF technology. Wrinkle and dimple are the major forming defects in MPF process, numerical simulation is a feasible way to predict forming defects in MPF. In conventional stamping, the mode to form sheet metal with blankholder is an effective way to suppress wrinkling; the same is true in MPF. A MPF press with flexible blankholder was developed, and the forming results indicated the forming stability of this technique. Based on the flexibility of MPF, varying deformation path MPF and sectional MPF were explored that cannot be realized in conventional stamping. By controlling each punch in real-time, a sheet part can be manufactured along a specific forming path. When the path of deformation in MPF is designed properly, forming defects will be avoided completely and lager deformation is achieved. A work piece can be formed section by section though the sectional MPF, and this technique makes it possible to manufacture large size parts in a small MPF press. Some critical experiments were performed that confirmed the validity of two special MPF techniques.
文摘In order to study the impacts of warhead geometry and initiation pattern on the lethality of aimable warhead, multi-point synchronous initiated hexagonal prism and cylindrical warheads were compared through numerical simulation, combined with theoretical formulas of fragment decelera- tion and target plugging. Enhancements of fragment velocity, kinetic energy and density toward the target and target destructions were analyzed. The results show that hexagonal prism warhead can produce dense fragment beams and enhance average velocity and kinetic energy with asymmetric eight-point initiation by 24. 13% and 54. 52% respectively, which are higher than those of the isomet- ric or same weight cylindrical warhead. The effective fragments are still relatively concentrated in an area of 8 m × 2 m for the hexagonal prism warhead when the distance between warhead and target is 40 m.
基金supported by National Natural Science Foundation of China (Grant Nos. 51175032, U1134201)National Basic Research Program of China (973 Program, Grant No. 2011CD711104)
文摘The wheel-rail contact problems, such as the number, location and the track of contact patches, are very important for optimizing the spatial structure of the rails and lowering the vehicle-turnout system dynamics. However, the above problems are not well solved currently because of having the difficulties in how to determine the multi-contact, to preciously present the changeable profiles of the rails and to establish an accurate spatial turnout system dynamics model. Based on a high-speed vehicle-turnout coupled model in which the track is modeled as flexible with rails and sleepers represented by beams, the line tracing extreme point method is introduced to investigate the wheel-rail multiple contact conditions and the key sections of the blade rail, longer nose rail, shorter rail in the switch and nose rail area are discretized to represent the varying profiles of rails in the turnout. The dynamic interaction between the vehicle and turnout is simulated for cases of the vehicle divergently passing the turnout and the multi-point contact is obtained. The tracks of the contact patches on the top of the rails are presented and the wheel-rail impact forces are offered in comparison with the contact patches transference on the rails. The numerical simulation results indicate that the length of two-point contact occurrence of a worn wheel profile and rails is longer than that of the new wheel profile and rails; The two-point contact definitely occurs in the switch and crossing area. Generally, three-point contact doesn’t occur for the new rail profile, which is testified by the wheel-rails interpolation distance and the first order derivative function of the tracing line extreme points. The presented research is not only helpful to optimize the structure of the turnout, but also useful to lower the dynamics of the high speed vehicle-turnout system.
基金financially supported by the National Natural Science Foundation of China(No.52005431)the National Natural Science Foundation of Hebei Province,China(No.E2020203086)the National Major Science and Technology Project of China(No.2018ZX04007002).
文摘A multi-point flexible straightening process characterized by reciprocating bending is proposed.Specifically,the process is analyzed in terms of deformation mechanism and verified by numerical simulations and physical experiments of the straightening of a series of metal profiles with different materials and initial shapes.Further,the relationship between the bending radius and the times of reciprocating bending required to unify the curvature is discussed,and the distribution of residual stress after straightening is analyzed.The results show that the reciprocating bending process can eliminate the difference of the initial curvature,make the curvature of each section tend to be uniform;the times of reciprocating bending to reach the uniform curvature decreases with the decrease of bending radius.The straightness of the straightened profile obtained from the experiment and simulation is less than 0.2%,demonstrating a good feasibility of this method.
文摘A kind of third order multi-point boundary value problems, x＇＇＇（ ι） = f（ t, x （ t ）, x＂ （ t ）, x＇＇＇ （ t ） ） ＋ m 2 e（t）,t∈（0, 1）,x（0）=ax（ξ）,x＇（0）-0,x（l）= ^m2∑j=1 βjx（ηj）, fεC[0, 1]×R^3, e（t）∈L^1[0, 1],a≥0, is considered, all theβj＇s have not the same sign, 0〈ξ〈 l, 0〈η1〈 η2〈… 〈ηm.2〈 1. By using the coincidence degree theory, some existence theorems for the problems at resonance are obtained.
文摘In this paper, the principle of multi-point forming (MPF) technique is presented. One of the most serious defects, wrinkling, during the multi-point forming process of a shallow rectangle cup is discussed by means of numerical simulation on the shallow rectangle cup forming process. The effects of thickness, material of sheet metal and the pressure of the blank holder are investigated. Based on the simulation results, the reasons and control methods of wrinkling are pointed out. Moreover, the experiment on the multi-point die forming of the shallow rectangle cup by the MPF machine is done to validate the efficiency of the numerical simulation, and the result proves that the application of an elastic cushion in the forming can restrain wrinkling efficiently.
基金Supported by the NSF of Jiangsu Province(BK2008119)the NSF of the Education Department of Jiangsu Province (08KJB110011)+1 种基金Innovation Project of Jiangsu Province Postgraduate Training Project(CX07S 015z)the Qinglan Program of Jiangsu Province (QL200613)
文摘This article deals with the following second-order multi-point boundary value problem x″（t）=r（t,x（t）,x′（t））＋e（t）,t∈（0,1）x′（0）=m∑i=1aix′（ξi）,x（1）=n∑j=1βjx（ηj）, Under the resonance conditions m∑i=1ai=1,n∑j=1βj=1,n∑j=1βjηj=1 , by applying the coincidence degree theory, some existence results of the problem are established. The emphasis here is that the dimension of the linear operator is two. In this paper, we extend and improve some previously known results like the ones in the references.
基金Sponsored by the Specific Targeted Research Projects,the 6th Framework Project,EU(Grant No.AST5-CT-2006-030877)
文摘To apply the multi-point forming technology to the field of tube processing,the process of multi-point forming for tube is studied.Numerical simulation for the process of multi-point forming for tube is achieved by using elastic-plastic FEM in ABAQUS.During simulation,reasonable coefficient of mass scaling and friction model of penalty function are used.The influence of several major technological parameters on the process is analyzed.When the tube diameter is 60 mm and the forming curvature radius is 1000 mm,the distortion rate of cross-section and the absolute forming error gradually decrease with the increasing of tube wall thickness;However,when the tube wall thickness is constant,the smaller the curvature radius,the larger the distortion rate of cross-section,but as to forming part,its absolute forming error becomes smaller.
基金Supported by the National Natural Science Foundation of China(Grant No.11071001)the Natural Science Foundation of Anhui Province(Grant No.1208085MA13)211Project of Anhui University(Grant No.KJTD002B)
文摘In this paper, we consider the following multi-point boundary value problem of fractional differential equation D^α0＋u（t）=f（t,u（t）,D^α-10＋u（t）,D^α-20＋u（t）,D^α-30＋u（t）,t∈（0,1）,I^4-α0＋u（0）=0,D^α-10＋u（t）=^n∑i=1αiD^α-10＋u（ξ1）,D^α-20＋u（1）=^n∑j=1D^α-20＋u（ηj）,D^α-30＋u（1）-D^α-30＋u（0）=D^α-20＋u（1/2）,where 3 〈 α ≤ 4 is a real number. By applying Mawhin coincidence degree theory and constructing suitable operators, some existence results of solutions can be established.
文摘This paper is concerned with the existence of solutions for the following multipoint boundary value problem at resonance{(Φp (x'))' + f(t,x)=0,0 < t < 1,x' (0)=x'(ξ) x(1)=m-3 ∑i=1 βi x(η i),where βi∈ R,m-3 ∑i=1 β i=1,0 < η 1 < η 2 < ··· < ηm-3 < 1,m-3 ∑i=1 βiηi=1,0 < ξ < 1.An existence theorem is obtained by using the extension of Mawhin's continuation theorem.Since almost all the multi-point boundary value problem at resonance in previous papers are for the linear operator without p-Laplacian by the use of Mawhin's continuation theorem,our method is new.
基金Supported by the National Natural Science Foundation of China(Grant No.11171220)the Hujiang Foundation of China(Grant No.B14005)
文摘In this paper, we study the multiplicity of positive solutions for multi-point boundary value problem of Riemann-Liouville fractional differential equation with multi-terms fractional derivative in the boundary conditions. By using the properties of the Green function and a generalization of the Leggett-Williams fixed point theorem due to the work of Bai and Ge, the sufficient conditions to guarantee the existence of at least three positive solutions are established. In the end of this paper, we have also given out the example to illustrate the wide range of potential application of our main results.
基金the National Natural Science Foundation of China(No.71371031)
文摘A Markov repairable system with history-dependent up and down states is presented. The state space of the repairable system is divided into three sets, which are up states, down states and changeable states.Using aggregated stochastic processes, we can get the multi-interval availability and multi-point availability for the Markov repairable system. Finally, numerical examples are given to illustrate the obtained results.
基金supported by National Natural Science Foundation of China (Nos.52207158 and 51821005)the Fundamental Research Funds for the Central Universities (HUST: No.2022JYCXJJ012)the National Key Research and Development Program of China (Nos.2016YFC0401002 and 2016YFC0401006)。
文摘Corona discharge, as a common means to obtain non-equilibrium plasma, can generally obtain high-concentration plasma by increasing discharge points to meet production needs. However,the existing numerical simulation models used to study multi-point corona discharge are all calculations of small-scale space models, which cannot obtain the distribution characteristics of plasma in large space. Based on our previous research, this paper proposes a hybrid model for studying the distribution of multi-point discharge plasma in large-scale spaces, which divides the computational domain and computes separately with the hydrodynamic model and the ion mobility model. The simulation results are verified by a needle–ball electrode device. Firstly, the electric field distribution and plasma distribution of the needle electrodes with single tip and double tips are compared and discussed. Secondly, the plasma distribution of the needle electrode with the double tip at different voltages is investigated. Both computational and experimental results indicate that the charged particle concentration and current of the needle electrode with double tips are both twice as high as those of the needle electrode with a single tip. This model can extend the computational area of the multi-point corona discharge finite element model to the sub-meter(25 cm) or meter level, which provides an effective means to study the plasma distribution generated by multiple discharge points in large-scale space.
基金funded by the Program of China Earthquake Science Data Sharing Platform and the Youth Fund(17404031570521)
文摘In general, the seismic response analysis in earthquake engineering assumes that the vibration parameters of the target and the contact surface of the external media are identical,i. e., single point input. However, earthquake energy has an attenuation phenomenon in wave propagation,so a wide range of soil slopes and the external medium contact surface of different input points on motion are not identical. If we consider single point input only, it may not correspond with reality, so it is necessary to carry out research on multi-point input methods. Based on the 2-D slope model,single-point input and multi-point input are performed respectively to analyze and compare their similarities and differences in the perspectives of the characteristics of seismic response of soil layer and plastic zone distribution to provide a reference for the seismic design of slopes. The results show that in the perspective of soil seismic response analysis,the peak acceleration output and peak velocity output under multi-point input are greater than the peak values under single point input at the same monitoring point,the peak appearing time is also earlier than that of the single point input; in terms of the plastic zone distribution,the multi-point effect is manifested as the presence of more obvious tensile shear failures; in the perspective of safety coefficient,the safety coefficient under each multi-point input is smaller than that of single point input,a difference of about 7 % or so. In summary,multi-point input is more reasonable and practical than single point input,so multi-point input should be considered in seismic design.
基金Supported by the Science Foundation of Educational Committee of Hunan Province（08C794）
文摘A class of multi-point boundary value problems are studied.Easily verified suffcient conditions to guarantee the existence of at least one solutions of above mentioned BVPs are established.The examples are presented to illustrate the main results.
基金Supported by the National Science and Technology Major Project (No.2011ZX03005-004-04)the National Grand Fundamental Research 973 Program of China (No.2011CB302-905)+2 种基金the National Natural Science Foundation of China (No.61170058,61272133,and 51274202)the Research Fund for the Doctoral Program of Higher Education of China (No.20103402110041)the Suzhou Fundamental Research Project (No.SYG201143)
文摘Resource allocation is an important problem in ubiquitous network. Most of the existing resource allocation methods considering only wireless networks are not suitable for the ubiquitous network environment, and they will harm the interest of individual users with instable resource requirements. This paper considers the multi-point video surveillance scenarios in a complex network environment with both wired and wireless networks. We introduce the utility estimated by the total costs of an individual network user. The problem is studied through mathematical modeling and we propose an improved problem-specific branch-and-cut algorithm to solve it. The algorithm follows the divide-and-conquer principle and fully considers the duality feature of network selection. The experiment is conducted by simulation through C and Lingo. And it shows that compared with a centralized random allocation scheme and a cost greed allocation scheme, the proposed scheme has better per- formance of reducing the total costs by 13.0% and 30.6% respectively for the user.
文摘To improve the quality of multi-point die forming, a new approach using discrete steel pads was proposed. The formability of three different multi-point die forming processes was analyzed through numerical simulation and experiments. Numerical simulation and experimental results showed that the use of discrete steel pads in the multi-point forming process can substantially improve the stress–strain state on the plate and suppress dimple, straight-edge, and wrinkle defects. This analysis verified that the use of discrete steel pads in a multi-point forming process can effectively improve the quality and accuracy with which sheet metal is formed.
