Purpose-Rail corrugation is still one of the unsolved challenges in the railway industry,and the abnormal vibration and high-frequency noise caused by it constitute serious adverse effects on the operating environment...Purpose-Rail corrugation is still one of the unsolved challenges in the railway industry,and the abnormal vibration and high-frequency noise caused by it constitute serious adverse effects on the operating environment.How to control corrugation has been an important research theme,and understanding corrugation evolution features is the necessary prerequisite.This study aims to investigate the specific evolution characteristics of corrugation from the contact stick-slip perspective.Design/methodology/approach-The formation and development processes of corrugation are analyzed by using a self-designed scale-down test device.Specifically,the contact stick-slip characteristics under different creepage conditions are analyzed and the formation mechanism of corrugation is summarized.On the basis of corrugation formation,the trend of corrugation development is further emphasized to completely describe the whole process of corrugation evolution.Findings-The results show that,under the determined vertical load condition,the contact interface appears the creep force-creepage negative slope phenomenon in the transverse direction.The cause of short-pitch corrugation on the rail wheel surface under the smaller angles of attack may be related to the inherent vibration frequency of the test device,and the cause of corrugation on the rail wheel surface under the larger angles of attack is mainly related to the stick-slip vibration induced by contact creep saturation.Originality/value-This research explores the evolution characteristics of corrugation by adopting a selfdesigned scale-down test device,and elucidates the mechanism of corrugation in detail.展开更多
In earthquake-prone areas,mountain tunnels often suffer from seismic damage when traversing active fault zones.To capture the seismic behavior of mountain tunnel under the action of active faults motion,the rate and s...In earthquake-prone areas,mountain tunnels often suffer from seismic damage when traversing active fault zones.To capture the seismic behavior of mountain tunnel under the action of active faults motion,the rate and state friction(RSF)relation is introduced to define the stickeslip dynamic behavior of a fault.The RSF relation is implemented in the finite element methods(FEMs).Numerical simulations of triaxial patch tests indicate that the RSF method can effectively capture the stickeslip dynamics.To reproduce the seismic damage to Daliang tunnel caused by slip of the Lenglongling fault,a three-dimensional(3D)numerical model including tunnel structure and plates of the fault is established.Seismic waves triggered by fault slip are then reproduced using the model.The simulation results show that the waves are dissipated while travelling and that their amplitudes decrease with depth.The failure of the tunnel lining is captured,and its seismic responses,including the displacement and strain of the structure,are extracted for various fault strike angles.The simulations are consistent with the observations,and it indicates that the movement of the simulated tunnel structure adjacent to the fault surface is significantly greater than those in the foot wall and in the middle of the fault.This study has the potential to provide a more direct means of understanding the seismic action of infrastructure induced by earthquakes.Seismic waves are no longer needed as input to the numerical simulation and instead,the earthquakes are generated by directly modeling the stickeslip motion of the fault.展开更多
This work deals with super-harmonic responses and the stabilities of a gear transmission system of a high-speed train under the stick-slip oscillation of the wheel-set.The dynamic model of the system is developed with...This work deals with super-harmonic responses and the stabilities of a gear transmission system of a high-speed train under the stick-slip oscillation of the wheel-set.The dynamic model of the system is developed with consideration on the factors including the time-varying system stiffness,the transmission error,the tooth backlash and the self-excited excitation of the wheel-set.The frequency-response equation of the system at super-harmonic resonance is obtained by the multiple scales method,and the stabilities of the system are analyzed using the perturbation theory.Complex nonlinear behaviors of the system including multi-valued solutions,jump phenomenon,hardening stiffness are found.The effects of the equivalent damping and the loads of the system under the stick-slip oscillation are analyzed.It shows that the change of the load can obviously influence the resonance frequency of the system and have little effect on the steady-state response amplitude of the system.The damping of the system has a negative effect,opposite to the load.The synthetic damping of the system composed of meshing damping and equivalent damping may be less than zero when the wheel-set has a large slippage,and the system loses its stability owing to the Hopf bifurcation.Analytical results are validated by numerical simulations.展开更多
We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted...We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted to overcome the bending moment in the lateral friction movement. Besides some classical phenomena of stick-slip movement such as periodical slow increase of frictional force in sticking phase and a sudden drop when slipping, a special phenomenon that the contact area increases with the tangential force is observed, which was called junction growth by Tabor in 1959.Image processing methods are developed to observe the variation of the junction area. The results show that the center of the strongest contact region will keep sticking under the tangential force until the whole slipping, the strongest point undergoes three stages in one cycle, which are named as sticking stage, fretting stage, and cracking stage, respectively. The combined analysis reveals a physical process of stick-slip movement: the tangential force causes the increase of the real contact area, which reduces the pressure between the contact spots and finally leads to the slipping. Once slipping occurs,the real contact area drops to the original level resulting in the pressure increase to the original level, which makes the sticking happen again.展开更多
The shear behavior of granular materials plays an important role in understanding the occurrence of geological hazards. This study introduces the use of direct shear tests and acoustic emission(AE) technology on glass...The shear behavior of granular materials plays an important role in understanding the occurrence of geological hazards. This study introduces the use of direct shear tests and acoustic emission(AE) technology on glass beads to investigate the distributions features of AE during the stick-slip processes. Results show that the shearing behavior of granular samples was shown as a series of similar, periodic stick-slip events. Some AE features — energy and Root Mean Square(RMS) —showed significant spatial clustering. Combined with the distribution of AE in the stick-slip event, the AE signal can be divided into four types: 1. low-energy and highfrequency AE, which represent particle friction;2. highenergy and low-frequency AE, which represent structural failure, that is, the slip process;3. low-RMS and lowfrequency AE represent internal local failure;and 4.high-RMS and high-frequency AE caused by overall structure failure. The b-value representing the energy distribution of AEs is used to describe the changing of AE sources during shear process. In addition, the amount and energy of AE had a significant positive correlation with normal stress. The shear rate mainly affects the AE representing particle friction, and the faster the shear rate, the lower the incidence of these friction AEs. According to the time sequence of the occurrence of different types of AE, AE rate, b-value and local failure AE signal can be applied to the prediction or early warning of geological hazards.展开更多
This paper, using Karnopp's model of friction force and phase plane method, studies the stick-slip motion of the flexible drive mechanism. It is explained that a sudden drop of friction force is the essential sour...This paper, using Karnopp's model of friction force and phase plane method, studies the stick-slip motion of the flexible drive mechanism. It is explained that a sudden drop of friction force is the essential source of stick-slip motion when the sliding is impending. A new criterion for occurrence of stick-slip motion is established. The stick-slip region and the stable region in a parameter plane are separated by a critical parameter curve. Moreover, for the stick-slip motion of the flexible drive mechanism without viscous damping, a parameter expression is obtained. The results may be used in design of the flexible drive mechanism.展开更多
In this paper a new physical model for studying stick-slip is established. Based on the dynamics system of the model,the state equation of the system is presented. And simulation analysis on the influential factors of...In this paper a new physical model for studying stick-slip is established. Based on the dynamics system of the model,the state equation of the system is presented. And simulation analysis on the influential factors of stick-slip is carried out. The relationship between stiffness ( horizontal and normal) ,dampness,mass, difference of static and kinetic coefficients of friction,driving velocity,and amplitude in normal direction is analyzed and parameters of stick-slip are evaluated. Results show that stick-slip can be reduced by improving horizontal stiffness,decreasing dampness,reducing mass,cutting down the difference of static and kinetic coefficients of friction,properly choosing the vertical stiffness and properly inducting the normal oscillation.展开更多
When the machine tool is in the start-and stop-stages,the stick-slip phenomenon will be observed and highprecision positioning,machining accuracy and fretting feed will not be guaranteed. The most critical reason is t...When the machine tool is in the start-and stop-stages,the stick-slip phenomenon will be observed and highprecision positioning,machining accuracy and fretting feed will not be guaranteed. The most critical reason is that there is the difference between the dynamic and the static friction coefficients. Textures with different area ratios are fabricated on the surfaces of the upper PTFE-based composite and the friction tests are carried out on a reciprocating tribotester under the boundary lubrication and flat-on-flat contact conditions. The results show that there exists an optimal textured area ratio of 19.6% that can minimize the difference between the dynamic and the static friction coefficients.展开更多
During the drilling process,stick-slip vibration of the drill string is mainly caused by the nonlinear friction gen-erated by the contact between the drill bit and the rock.To eliminate the fatigue wear of downhole dr...During the drilling process,stick-slip vibration of the drill string is mainly caused by the nonlinear friction gen-erated by the contact between the drill bit and the rock.To eliminate the fatigue wear of downhole drilling tools caused by stick-slip vibrations,the Fractional-Order Proportional-Integral-Derivative(FOPID)controller is used to suppress stick-slip vibrations in the drill string.Although the FOPID controller can effectively suppress the drill string stick-slip vibration,its structure isflexible and parameter setting is complicated,so it needs to use the cor-responding machine learning algorithm for parameter optimization.Based on the principle of torsional vibration,a simplified model of multi-degree-of-freedom drill string is established and its block diagram is designed.The continuous nonlinear friction generated by cutting rock is described by the LuGre friction model.The adaptive learning strategy of genetic algorithm(GA),particle swarm optimization(PSO)and particle swarm optimization improved(IPSO)by arithmetic optimization(AOA)is used to optimize and adjust the controller parameters,and the drill string stick-slip vibration is suppressed to the greatest extent.The results show that:When slight drill string stick-slip vibration occurs,the FOPID controller optimized by machine learning algorithm has a good effect on suppressing drill string stick-slip vibration.However,the FOPID controller cannot get the drill string system which has fallen into serious stick-slip vibration(stuck pipe)out of trouble,and the machine learning algorithm is required to mark a large amount of data on adjacent Wells to train the model.Set a reasonable range of drilling parameters(weight on bit/drive torque)in advance to avoid severe stick-slip vibration(stuck pipe)in the drill string system.展开更多
Purpose–Large displacement misalignment under the action of active faults can cause complex threedimensional deformation in subway tunnels,resulting in severe damage,distortion and misalignment.There is no developed ...Purpose–Large displacement misalignment under the action of active faults can cause complex threedimensional deformation in subway tunnels,resulting in severe damage,distortion and misalignment.There is no developed system of fortification and related codes to follow.There are scientific problems and technical challenges in this field that have never been encountered in past research and practices.Design/methodology/approach–This paper adopted a self-designed large-scale active fault dislocation simulation loading system to conduct a similar model test of the tunnel under active fault dislocation based on the open-cut tunnel project of the Urumqi Rail Transit Line 2,which passes through the Jiujiawan normal fault.The test simulated the subway tunnel passing through the normal fault,which is inclined at 608.This research compared and analyzed the differences in mechanical behavior between two types of lining section:the opencut double-line box tunnel and the modified double-line box arch tunnel.The structural response and failure characteristics of the open-cut segmented lining of the tunnel under the stick-slip part of the normal fault were studied.Findings–The results indicated that the double-line box arch tunnel improved the shear and longitudinal bending performance.Longitudinal cracks were mainly distributed in the baseplate,wall foot and arch foot,and the crack position was basically consistent with the longitudinal distribution of surrounding rock pressure.This indicated that the longitudinal cracks were due to the large local load of the cross-section of the structure,leading to an excessive local bending moment of the structure,which resulted in large eccentric failure of the lining and formation of longitudinal cracks.Compared with the ordinary box section tunnel,the improved double-line box arch tunnel significantly reduced the destroyed and damage areas of the hanging wall and footwall.The damage area and crack length were reduced by 39 and 59.3%,respectively.This indicates that the improved double-line box arch tunnel had good anti-sliding performance.Originality/value–This paper adopted a self-designed large-scale active fault dislocation simulation loading system to conduct a similar model test of the tunnel under active fault dislocation.This system increased the similarity ratio of the test model,improved the dislocation loading rate and optimized the simulation scheme of the segmented flexible lining and other key factors affecting the test.It is of great scientific significance and engineering value to investigate the structure of subway tunnels under active fault misalignment,to study its force characteristics and damage modes,and to provide a technical reserve for the design and construction of subway tunnels through active faults.展开更多
It is revealed in frictional experiments on medium-scale samples that period doubling bifurcation of stress drop for stick-slip occurs due to macroscopic heterogeneity of the sliding surface under conditions for typic...It is revealed in frictional experiments on medium-scale samples that period doubling bifurcation of stress drop for stick-slip occurs due to macroscopic heterogeneity of the sliding surface under conditions for typical stick-slip.The observed data show that the period doubling bifurcation of stress drop results from the alternate occurrence of strain release along the whole fault and along part of fault.This implies that complicated nonlinear behavior corresponds to clear physical implication in some cases.展开更多
In this work,a comparative study is performed to investigate the influence of time-varying normal forces on the friction properties and friction-induced stick-slip vibration(FIV)by experimental and theoretical methods...In this work,a comparative study is performed to investigate the influence of time-varying normal forces on the friction properties and friction-induced stick-slip vibration(FIV)by experimental and theoretical methods.In the experiments,constant and harmonic-varying normal forces are applied,respectively.The measured vibration signals under two loading forms are compared in both time and frequency domains.In addition,mathematical tools such as phase space reconstruction and Fourier spectra are used to reveal the science behind the complicated dynamic behavior.It can be found that the friction system shows steady stick-slip vibration,and the main frequency does not vary with the magnitude of the constant normal force,but the size of limit cycle increases with the magnitude of the constant normal force.In contrast,the friction system under the harmonic normal force shows complicated behavior,for example,higher-frequency larger-amplitude vibration occurs and looks chaotic as the frequency of the normal force increases.The interesting findings offer a new way for controlling FIV in engineering applications.展开更多
In drilling field, stick-slip vibrations of the drill-string are the main reason for the failure of the drilling system. To suppress the undesired stick-slip vibrations, an observer-based state feedback control method...In drilling field, stick-slip vibrations of the drill-string are the main reason for the failure of the drilling system. To suppress the undesired stick-slip vibrations, an observer-based state feedback control method is proposed. The drilling system is described by a lumped parameter model including a Karnopp friction torque model. A state observer is designed to estimate the bit velocity in bottom hole and a state feedback controller is proposed to control the top drive velocity. By simulation, the performance of the control algorithm is demonstrated. Based on the control algorithm, a stick-slip vibration control system is developed. Test results show that the control system can effectively eliminate stick-slip vibrations of the drill-string and can be applied to the drilling field.展开更多
Since stick-slip actuators present the advantage of allowing long displacements(several centimeters or even more)at a high speed with an ultra high resolution(<5nm),a new type of stick-slip piezoelectric actuator i...Since stick-slip actuators present the advantage of allowing long displacements(several centimeters or even more)at a high speed with an ultra high resolution(<5nm),a new type of stick-slip piezoelectric actuator is proposed to attain sub-nanometer positioning accuracy.The actuator is composed of a slider and a tower-shaped stator using forced bending vibration in y-z plane to generate tangential vibration on the top of the driving foot.When excited by the sawtooth input voltage,driving foot of the stator is able to generate a tangential asymmetrical vibration on the top,and the slider is thus pushed to move.A prototype and its testing equipment are fabricated and described.Following that,the testing of vibration mode and mechanical characteristics as well as stepping characteristics are conducted.Experimental results show that under the condition that the sawtooth input voltage is400VP-Pand the pre-pressure is 6N.Velocity of the actuator reaches its maximum 1.2mm/s at the frequency of 8000 Hz and drops to its minimum 35nm/s at the frequency of 1Hz.When the excitation signal is the single-phase sawtooth stepping signal,the tower-shaped actuator can directionally move forward or backward step by step.And when excited by the sawtooth stepping signal with 1Hz and 300VP-Pduring 1cycle(200ms),the actuator has a minimum stepping distance of 22 nm.展开更多
For the smaller thrust,it is difficult to achieve 3Dtrans-scale precision positioning based on previous stick-slip driving.A large thrust trans-scale precision positioning stage is studied based on the inertial stick-...For the smaller thrust,it is difficult to achieve 3Dtrans-scale precision positioning based on previous stick-slip driving.A large thrust trans-scale precision positioning stage is studied based on the inertial stick-slip driving.The process of the movement is divided into two steps,i.e.,the″sliding″phase and the″stickness″phase.In the whole process,the kinematics model of the inertial stick-slip driving is established,and it reveals some factors affecting the velocity of inertial stick-slip driving.Furthermore,a simulation of movement is preformed by Matlab-Simulink software,and the whole process of the inertial stick-slip driving is displayed.After one experimental prototype is designed,the back and forth velocity is tested.Finally,the simulation verifies the accuracy of the kinematics model.展开更多
基金funded by the Science and Technology Research Project of Universities in Hebei Province(No.QN2025314)Youth Specialization Fund for State Key Laboratory(No.50110010766)Shanghai Key Laboratory of Rail Infrastructure Durability and System Safety(No.R202405).
文摘Purpose-Rail corrugation is still one of the unsolved challenges in the railway industry,and the abnormal vibration and high-frequency noise caused by it constitute serious adverse effects on the operating environment.How to control corrugation has been an important research theme,and understanding corrugation evolution features is the necessary prerequisite.This study aims to investigate the specific evolution characteristics of corrugation from the contact stick-slip perspective.Design/methodology/approach-The formation and development processes of corrugation are analyzed by using a self-designed scale-down test device.Specifically,the contact stick-slip characteristics under different creepage conditions are analyzed and the formation mechanism of corrugation is summarized.On the basis of corrugation formation,the trend of corrugation development is further emphasized to completely describe the whole process of corrugation evolution.Findings-The results show that,under the determined vertical load condition,the contact interface appears the creep force-creepage negative slope phenomenon in the transverse direction.The cause of short-pitch corrugation on the rail wheel surface under the smaller angles of attack may be related to the inherent vibration frequency of the test device,and the cause of corrugation on the rail wheel surface under the larger angles of attack is mainly related to the stick-slip vibration induced by contact creep saturation.Originality/value-This research explores the evolution characteristics of corrugation by adopting a selfdesigned scale-down test device,and elucidates the mechanism of corrugation in detail.
基金funded by the National Natural Science Foundation of China(Grant No.52178339,52090084,and 51938008)Shenzhen Natural Science Fund(Stable Support Plan Program Grant No.20220808150117002)。
文摘In earthquake-prone areas,mountain tunnels often suffer from seismic damage when traversing active fault zones.To capture the seismic behavior of mountain tunnel under the action of active faults motion,the rate and state friction(RSF)relation is introduced to define the stickeslip dynamic behavior of a fault.The RSF relation is implemented in the finite element methods(FEMs).Numerical simulations of triaxial patch tests indicate that the RSF method can effectively capture the stickeslip dynamics.To reproduce the seismic damage to Daliang tunnel caused by slip of the Lenglongling fault,a three-dimensional(3D)numerical model including tunnel structure and plates of the fault is established.Seismic waves triggered by fault slip are then reproduced using the model.The simulation results show that the waves are dissipated while travelling and that their amplitudes decrease with depth.The failure of the tunnel lining is captured,and its seismic responses,including the displacement and strain of the structure,are extracted for various fault strike angles.The simulations are consistent with the observations,and it indicates that the movement of the simulated tunnel structure adjacent to the fault surface is significantly greater than those in the foot wall and in the middle of the fault.This study has the potential to provide a more direct means of understanding the seismic action of infrastructure induced by earthquakes.Seismic waves are no longer needed as input to the numerical simulation and instead,the earthquakes are generated by directly modeling the stickeslip motion of the fault.
基金Project(U1234208)supported by the National Natural Science Foundation of ChinaProject(2016YFB1200401)supported by the National Key Research and Development Program of China
文摘This work deals with super-harmonic responses and the stabilities of a gear transmission system of a high-speed train under the stick-slip oscillation of the wheel-set.The dynamic model of the system is developed with consideration on the factors including the time-varying system stiffness,the transmission error,the tooth backlash and the self-excited excitation of the wheel-set.The frequency-response equation of the system at super-harmonic resonance is obtained by the multiple scales method,and the stabilities of the system are analyzed using the perturbation theory.Complex nonlinear behaviors of the system including multi-valued solutions,jump phenomenon,hardening stiffness are found.The effects of the equivalent damping and the loads of the system under the stick-slip oscillation are analyzed.It shows that the change of the load can obviously influence the resonance frequency of the system and have little effect on the steady-state response amplitude of the system.The damping of the system has a negative effect,opposite to the load.The synthetic damping of the system composed of meshing damping and equivalent damping may be less than zero when the wheel-set has a large slippage,and the system loses its stability owing to the Hopf bifurcation.Analytical results are validated by numerical simulations.
基金Project supported by the National Natural Science Foundation of China(Grant No.11872033)the Beijing Natural Science Foundation,China(Grant No.3172017)
文摘We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted to overcome the bending moment in the lateral friction movement. Besides some classical phenomena of stick-slip movement such as periodical slow increase of frictional force in sticking phase and a sudden drop when slipping, a special phenomenon that the contact area increases with the tangential force is observed, which was called junction growth by Tabor in 1959.Image processing methods are developed to observe the variation of the junction area. The results show that the center of the strongest contact region will keep sticking under the tangential force until the whole slipping, the strongest point undergoes three stages in one cycle, which are named as sticking stage, fretting stage, and cracking stage, respectively. The combined analysis reveals a physical process of stick-slip movement: the tangential force causes the increase of the real contact area, which reduces the pressure between the contact spots and finally leads to the slipping. Once slipping occurs,the real contact area drops to the original level resulting in the pressure increase to the original level, which makes the sticking happen again.
基金funded by the National Nature Science Foundation of China Grants (41807278,41790432,U20A20112)the Strategic Priority Research Program of the Chinese Academy of Sciences Grant (No.XDA23090202)+2 种基金the Key Research Program of Frontier Sciences,Chinese Academy of Sciences Grant (No.QYZDY-SSWDQC006)support from the CAS Pioneer Hundred Talents Programthe China-Pakistan Joint Research Center on Earth Sciences。
文摘The shear behavior of granular materials plays an important role in understanding the occurrence of geological hazards. This study introduces the use of direct shear tests and acoustic emission(AE) technology on glass beads to investigate the distributions features of AE during the stick-slip processes. Results show that the shearing behavior of granular samples was shown as a series of similar, periodic stick-slip events. Some AE features — energy and Root Mean Square(RMS) —showed significant spatial clustering. Combined with the distribution of AE in the stick-slip event, the AE signal can be divided into four types: 1. low-energy and highfrequency AE, which represent particle friction;2. highenergy and low-frequency AE, which represent structural failure, that is, the slip process;3. low-RMS and lowfrequency AE represent internal local failure;and 4.high-RMS and high-frequency AE caused by overall structure failure. The b-value representing the energy distribution of AEs is used to describe the changing of AE sources during shear process. In addition, the amount and energy of AE had a significant positive correlation with normal stress. The shear rate mainly affects the AE representing particle friction, and the faster the shear rate, the lower the incidence of these friction AEs. According to the time sequence of the occurrence of different types of AE, AE rate, b-value and local failure AE signal can be applied to the prediction or early warning of geological hazards.
文摘This paper, using Karnopp's model of friction force and phase plane method, studies the stick-slip motion of the flexible drive mechanism. It is explained that a sudden drop of friction force is the essential source of stick-slip motion when the sliding is impending. A new criterion for occurrence of stick-slip motion is established. The stick-slip region and the stable region in a parameter plane are separated by a critical parameter curve. Moreover, for the stick-slip motion of the flexible drive mechanism without viscous damping, a parameter expression is obtained. The results may be used in design of the flexible drive mechanism.
文摘In this paper a new physical model for studying stick-slip is established. Based on the dynamics system of the model,the state equation of the system is presented. And simulation analysis on the influential factors of stick-slip is carried out. The relationship between stiffness ( horizontal and normal) ,dampness,mass, difference of static and kinetic coefficients of friction,driving velocity,and amplitude in normal direction is analyzed and parameters of stick-slip are evaluated. Results show that stick-slip can be reduced by improving horizontal stiffness,decreasing dampness,reducing mass,cutting down the difference of static and kinetic coefficients of friction,properly choosing the vertical stiffness and properly inducting the normal oscillation.
基金financially supported by the National Natural Science Foundation of China (No. 51675268)
文摘When the machine tool is in the start-and stop-stages,the stick-slip phenomenon will be observed and highprecision positioning,machining accuracy and fretting feed will not be guaranteed. The most critical reason is that there is the difference between the dynamic and the static friction coefficients. Textures with different area ratios are fabricated on the surfaces of the upper PTFE-based composite and the friction tests are carried out on a reciprocating tribotester under the boundary lubrication and flat-on-flat contact conditions. The results show that there exists an optimal textured area ratio of 19.6% that can minimize the difference between the dynamic and the static friction coefficients.
基金This research was funded by the National Natural Science Foundation of China(51974052)(51804061)the Chongqing Research Program of Basic Research and Frontier Technology(cstc2019jcyj-msxmX0199).
文摘During the drilling process,stick-slip vibration of the drill string is mainly caused by the nonlinear friction gen-erated by the contact between the drill bit and the rock.To eliminate the fatigue wear of downhole drilling tools caused by stick-slip vibrations,the Fractional-Order Proportional-Integral-Derivative(FOPID)controller is used to suppress stick-slip vibrations in the drill string.Although the FOPID controller can effectively suppress the drill string stick-slip vibration,its structure isflexible and parameter setting is complicated,so it needs to use the cor-responding machine learning algorithm for parameter optimization.Based on the principle of torsional vibration,a simplified model of multi-degree-of-freedom drill string is established and its block diagram is designed.The continuous nonlinear friction generated by cutting rock is described by the LuGre friction model.The adaptive learning strategy of genetic algorithm(GA),particle swarm optimization(PSO)and particle swarm optimization improved(IPSO)by arithmetic optimization(AOA)is used to optimize and adjust the controller parameters,and the drill string stick-slip vibration is suppressed to the greatest extent.The results show that:When slight drill string stick-slip vibration occurs,the FOPID controller optimized by machine learning algorithm has a good effect on suppressing drill string stick-slip vibration.However,the FOPID controller cannot get the drill string system which has fallen into serious stick-slip vibration(stuck pipe)out of trouble,and the machine learning algorithm is required to mark a large amount of data on adjacent Wells to train the model.Set a reasonable range of drilling parameters(weight on bit/drive torque)in advance to avoid severe stick-slip vibration(stuck pipe)in the drill string system.
基金funded by the High Speed Railway and Natural Science United Foundation of China[Award number:U1934213]and the General Program of National Natural Science Foundation of China[Award number:51878572].
文摘Purpose–Large displacement misalignment under the action of active faults can cause complex threedimensional deformation in subway tunnels,resulting in severe damage,distortion and misalignment.There is no developed system of fortification and related codes to follow.There are scientific problems and technical challenges in this field that have never been encountered in past research and practices.Design/methodology/approach–This paper adopted a self-designed large-scale active fault dislocation simulation loading system to conduct a similar model test of the tunnel under active fault dislocation based on the open-cut tunnel project of the Urumqi Rail Transit Line 2,which passes through the Jiujiawan normal fault.The test simulated the subway tunnel passing through the normal fault,which is inclined at 608.This research compared and analyzed the differences in mechanical behavior between two types of lining section:the opencut double-line box tunnel and the modified double-line box arch tunnel.The structural response and failure characteristics of the open-cut segmented lining of the tunnel under the stick-slip part of the normal fault were studied.Findings–The results indicated that the double-line box arch tunnel improved the shear and longitudinal bending performance.Longitudinal cracks were mainly distributed in the baseplate,wall foot and arch foot,and the crack position was basically consistent with the longitudinal distribution of surrounding rock pressure.This indicated that the longitudinal cracks were due to the large local load of the cross-section of the structure,leading to an excessive local bending moment of the structure,which resulted in large eccentric failure of the lining and formation of longitudinal cracks.Compared with the ordinary box section tunnel,the improved double-line box arch tunnel significantly reduced the destroyed and damage areas of the hanging wall and footwall.The damage area and crack length were reduced by 39 and 59.3%,respectively.This indicates that the improved double-line box arch tunnel had good anti-sliding performance.Originality/value–This paper adopted a self-designed large-scale active fault dislocation simulation loading system to conduct a similar model test of the tunnel under active fault dislocation.This system increased the similarity ratio of the test model,improved the dislocation loading rate and optimized the simulation scheme of the segmented flexible lining and other key factors affecting the test.It is of great scientific significance and engineering value to investigate the structure of subway tunnels under active fault misalignment,to study its force characteristics and damage modes,and to provide a technical reserve for the design and construction of subway tunnels through active faults.
文摘It is revealed in frictional experiments on medium-scale samples that period doubling bifurcation of stress drop for stick-slip occurs due to macroscopic heterogeneity of the sliding surface under conditions for typical stick-slip.The observed data show that the period doubling bifurcation of stress drop results from the alternate occurrence of strain release along the whole fault and along part of fault.This implies that complicated nonlinear behavior corresponds to clear physical implication in some cases.
基金The authors would like to acknowledge the support from the National Natural Science Foundation of China(11672052 and 51822508)111 Project(B20008)and Natural Science Foundation of Zhejiang province(LQ22E050012).
文摘In this work,a comparative study is performed to investigate the influence of time-varying normal forces on the friction properties and friction-induced stick-slip vibration(FIV)by experimental and theoretical methods.In the experiments,constant and harmonic-varying normal forces are applied,respectively.The measured vibration signals under two loading forms are compared in both time and frequency domains.In addition,mathematical tools such as phase space reconstruction and Fourier spectra are used to reveal the science behind the complicated dynamic behavior.It can be found that the friction system shows steady stick-slip vibration,and the main frequency does not vary with the magnitude of the constant normal force,but the size of limit cycle increases with the magnitude of the constant normal force.In contrast,the friction system under the harmonic normal force shows complicated behavior,for example,higher-frequency larger-amplitude vibration occurs and looks chaotic as the frequency of the normal force increases.The interesting findings offer a new way for controlling FIV in engineering applications.
文摘In drilling field, stick-slip vibrations of the drill-string are the main reason for the failure of the drilling system. To suppress the undesired stick-slip vibrations, an observer-based state feedback control method is proposed. The drilling system is described by a lumped parameter model including a Karnopp friction torque model. A state observer is designed to estimate the bit velocity in bottom hole and a state feedback controller is proposed to control the top drive velocity. By simulation, the performance of the control algorithm is demonstrated. Based on the control algorithm, a stick-slip vibration control system is developed. Test results show that the control system can effectively eliminate stick-slip vibrations of the drill-string and can be applied to the drilling field.
基金supported by the Natural Science Foundation of China(Nos.51375224,51275235)the Re-search Fund for Young Teachers of Jinling Institute of Technology(No.Jit-b-201318)
文摘Since stick-slip actuators present the advantage of allowing long displacements(several centimeters or even more)at a high speed with an ultra high resolution(<5nm),a new type of stick-slip piezoelectric actuator is proposed to attain sub-nanometer positioning accuracy.The actuator is composed of a slider and a tower-shaped stator using forced bending vibration in y-z plane to generate tangential vibration on the top of the driving foot.When excited by the sawtooth input voltage,driving foot of the stator is able to generate a tangential asymmetrical vibration on the top,and the slider is thus pushed to move.A prototype and its testing equipment are fabricated and described.Following that,the testing of vibration mode and mechanical characteristics as well as stepping characteristics are conducted.Experimental results show that under the condition that the sawtooth input voltage is400VP-Pand the pre-pressure is 6N.Velocity of the actuator reaches its maximum 1.2mm/s at the frequency of 8000 Hz and drops to its minimum 35nm/s at the frequency of 1Hz.When the excitation signal is the single-phase sawtooth stepping signal,the tower-shaped actuator can directionally move forward or backward step by step.And when excited by the sawtooth stepping signal with 1Hz and 300VP-Pduring 1cycle(200ms),the actuator has a minimum stepping distance of 22 nm.
基金supported by the National Natural Science Foundation of China(No.51175358)the Natural Science Foundation of Jiangsu Province (No.BK20140345)+2 种基金Colleges and Universities Natural Science Foundation of Jiangsu Province (No.14KJB460025)the National Science Foundation for Post-Doctoral Scientists of China (No.2014M551651)the Natural Science Foundation of Jiangsu Province for Post-Doctoral Scientists (No. 1401073C)
文摘For the smaller thrust,it is difficult to achieve 3Dtrans-scale precision positioning based on previous stick-slip driving.A large thrust trans-scale precision positioning stage is studied based on the inertial stick-slip driving.The process of the movement is divided into two steps,i.e.,the″sliding″phase and the″stickness″phase.In the whole process,the kinematics model of the inertial stick-slip driving is established,and it reveals some factors affecting the velocity of inertial stick-slip driving.Furthermore,a simulation of movement is preformed by Matlab-Simulink software,and the whole process of the inertial stick-slip driving is displayed.After one experimental prototype is designed,the back and forth velocity is tested.Finally,the simulation verifies the accuracy of the kinematics model.
