The early fatigue damage in the van-body of the semi-trailer is often caused by the unique mechanical characteristics and the dynamic impact of the loads.The traditional finite element method with static strength anal...The early fatigue damage in the van-body of the semi-trailer is often caused by the unique mechanical characteristics and the dynamic impact of the loads.The traditional finite element method with static strength analysis cannot support the fatigue design of van-body;thus,the dynamics analysis should be adopted for the endurance performance.The accurate dynamics model to describe the transient impacts of all kinds of uneven road and the proper system transfer functions to calculate the load transfer effects from tire to van-body are two critical factors for transient dynamics analysis.In order to evaluate the dynamic performance,the dynamics model of the trailer with the air suspension is brought forward.Then the analysis method of the power spectral density （PSD） is set up to study the transient responses of the road dynamic impacts.The transient responses transferred from axles to van-body are calculated,such as dynamic stress,dynamic RMS acceleration,and dynamic load factors.Based on the above dynamic responses,the fatigue life of van-body is predicted with the finite element analysis （FEA） method.Applying the test parameters of the trailer with air suspension,the simulation system with Matlab/Simulink is constructed to describe the dynamic responses of the impacts of the tested PSD of the vehicle axles,and then the fatigue life is predicted with FEA method.The simulated results show that the vibration level of the van-body with air suspension is reduced and the fatigue life is improved.The real vehicle tests on different roads are carried out,and the test results validate the accuracy of the simulation system.The proposed fatigue life prediction method is effective for the virtual design of auto-body.展开更多
A simple four-dimensional system with only one control parameter is proposed in this paper. The novel system has a line or no equilibrium for the global control parameter and exhibits complex transient transition beha...A simple four-dimensional system with only one control parameter is proposed in this paper. The novel system has a line or no equilibrium for the global control parameter and exhibits complex transient transition behaviors of hyperchaotic attractors, periodic orbits, and unstable sinks. Especially, for the nonzero-valued control parameter, there exists no equilibrium in the proposed system, leading to the formation of various hidden attractors with complex transient dynamics. The research results indicate that the dynamics of the system shows weak chaotic robustness and depends greatly on the initial states.展开更多
A reproducing kernel collocation method based on strong formulation is introduced for transient dynamics. To study the stability property of this method, an algorithm based on the von Neumann hypothesis is proposed to...A reproducing kernel collocation method based on strong formulation is introduced for transient dynamics. To study the stability property of this method, an algorithm based on the von Neumann hypothesis is proposed to predict the critical time step. A numerical test is conducted to validate the algorithm. The numerical critical time step and the predicted critical time step are in good agreement. The results are compared with those obtained based on the radial basis collocation method, and they axe in good agreement. Several important conclusions for choosing a proper support size of the reproducing kernel shape function are given to improve the stability condition.展开更多
We designed and evaluated a fluoride-based high concentration erbium/ cerium co-doped fiber amplifier. It is suitable for Metropolitan Area Networks due to faster transient, flatter (unfiltered) gain, smaller footprin...We designed and evaluated a fluoride-based high concentration erbium/ cerium co-doped fiber amplifier. It is suitable for Metropolitan Area Networks due to faster transient, flatter (unfiltered) gain, smaller footprint and gain excursion than its silica-based counterpart.展开更多
Although debates exist,marine reserves play an important role in fisheries management.Based on stable equilibrium state,theoretical frameworks of various systems suggest that fisheries management with the implementati...Although debates exist,marine reserves play an important role in fisheries management.Based on stable equilibrium state,theoretical frameworks of various systems suggest that fisheries management with the implementation of marine reserves has obvious advantage in achieving multiple goals such as improving the target fisheries yields as well as maintaining species persistence in comparison with strategy of traditional fishing effort control.More recently,ecologists pay attention to the transient dynamics of fisheries yields when marine reserves are established.Simulation results suggest that the relative advantages between different fisheries management strategies(the implementation of marine reserves vs.traditional fishing effort control)depend on not only life histories but also the measurement metrics of fisheries yields(measured by number vs.measured by weight).Further research on transient dynamic pattern of fisheries yields can help fishery managers adjust relevant policies at an appropriate ecological time scale to achieve both conservation and economic goals,which provide a theoretical foundation for adaptive marine reserve management.展开更多
Through adding a nonlinear self-feedback term in the evolution equations of neural network, we introduced a transiently chaotic neural network model. In order to utilize the transiently chaotic dynamics mechanism in o...Through adding a nonlinear self-feedback term in the evolution equations of neural network, we introduced a transiently chaotic neural network model. In order to utilize the transiently chaotic dynamics mechanism in optimization problem efficiently, we have analyzed the dynamical procedure of the transiently chaotic neural network model and studied the function of the crucial bifurcation parameter which governs the chaotic behavior of the system. Based on the dynamical analysis of the transiently chaotic neural network model, chaotic annealing algorithm is also examined and improved. As an example, we applied chaotic annealing method to the traveling salesman problem and obtained good results.展开更多
During the operation of magnetic liquid double suspension bearing(MLDSB),due to rotor resonance,assembly error and other factor,the vibration amplitude of the rotor in resonance state exceeds the original design clear...During the operation of magnetic liquid double suspension bearing(MLDSB),due to rotor resonance,assembly error and other factor,the vibration amplitude of the rotor in resonance state exceeds the original design clearance,resulting in the collision damage between the rotor and the stator,the rotor and the casing.This paper presents a method to simulate the influence of different factors on the dynamic characteristics of 5 degrees of freedom(DOF)rotor based on the dynamic model of MLDSB.Firstly,according to the second Lagrange equation,the dynamic equation of 5 DOF rotor is derived,and the mathematical model is established.Then,based on 5 DOF rotor dynamic equation,the rotor transient dynamic equation under collision state is obtained,and the rotor transient collision dynamic simulation model is established.Finally,the key influencing factors of rotor dynamic characteristics are extracted,and the influence mapping relationship of rotor displacement,axis locus and stress distribution under different factors is simulated by using ANSYS Workbench software.The experimental results show that this method can effectively reflect the influence of various factors on the dynamic characteristics of the rotor.This method can provide theoretical reference for the design and control of MLDSB.展开更多
The matrix expression for the 3 D transient dynamic boundary integral equation in Laplace transform space is obtained and the degenerative element method has been implemented to treat the kernel function over the sin...The matrix expression for the 3 D transient dynamic boundary integral equation in Laplace transform space is obtained and the degenerative element method has been implemented to treat the kernel function over the singular element. In the computer program BEMTDY the Koizumi′s numerical inversion method is used and three examples of the 3 D vibrated foundation under harmonic forces and the influence with both adjacent foundations are studied.展开更多
This paper investigates persistence of transient dynamics depending on parameters in spatially coupled ecological systems. We emphasis that the persistence time can be obtained by populations of species or Lyapunov ex...This paper investigates persistence of transient dynamics depending on parameters in spatially coupled ecological systems. We emphasis that the persistence time can be obtained by populations of species or Lyapunov exponents of transient dynamics. It is found that extreme sensitive dependence of persistence on parameters occurs commonly in ecological models. A non-zero uncertainty exponent is used to characterize the high sensitivity in a reasonable parameter region. The result of a small uncertainty exponent indicates a fractal structure of transient persistence in the two-dimensional parameter space. In spite of different methods of measurement, the fractal dimensions have a good consistency. Since populations of natural communities with many coupled oscillators are often affected by disturbance of migration rates, the large probability of error in estimating persistence of transients should be concerned.展开更多
This paper presents a numerical analysis of the dynamic transient behaviors of undersea cables.In this numerical study,the governing equations based on Euler-Bernoulli beam theory are adopted,and they can satisfy many...This paper presents a numerical analysis of the dynamic transient behaviors of undersea cables.In this numerical study,the governing equations based on Euler-Bernoulli beam theory are adopted,and they can satisfy many applications no matter what the magnitude of the cable tension is.The nonlinear coupled equations are solved by a popular central finite difference method,and the numerical results of transient behaviors are presented when several kinds of surrounding conditions,such as different towing speeds of surface vessel,different currents and waves with various frequencies and amplitudes,are exerted.Then a detailed comparison of the results,including the upper end tension and cable shape in time-domain,is made under the above external excitations,and finally the possible reasons for these are further explained.展开更多
A new method is developed to assess and analyze the dynamic performance of hydrostatic bearing oil film by using an amulets-layer dynamic mesh technique. It is implemented using C Language to compile the UDF program o...A new method is developed to assess and analyze the dynamic performance of hydrostatic bearing oil film by using an amulets-layer dynamic mesh technique. It is implemented using C Language to compile the UDF program of a single oil film of the hydrostatic bearing. The effects of key lubrication parameters of the hydrostatic bearing are evaluated and analyzed under various working conditions,i.e. under no-load,a load of 40 t,a full load of 160 t,and the rotation speed of 1r/min,2r/min,4r/min,8r/min,16r/min,32r/min. The transient data of oil film bearing capacity under different load and rotation speed are acquired for a total of 18 working conditions during the oil film thickness changing. It allows the effective prediction of dynamic performance of large size hydrostatic bearing. Experiments on hydrostatic bearing oil film have been performed and the results were used to define the boundary conditions for the numerical simulations and validate the developed numerical model. The results showed that the oil film thickness became thinner with the increase of the operating time of the hydrostatic bearing,both the oil film rigidity and the oil cavity pressure increased significantly,and the increase of the bearing capacity was inversely proportional to the cube of the change of the film thickness. Meanwhile,the effect of the load condition on carrying capacity of large size static bearing was more important than the speed condition. The error between the simulation value and the experimental value was 4.25%.展开更多
The specialized equipment utilized in long-line tunnel engineering is evolving towards large-scale,multifunctional,and complex orientations.The vibration caused by the high-frequency units during regular operation is ...The specialized equipment utilized in long-line tunnel engineering is evolving towards large-scale,multifunctional,and complex orientations.The vibration caused by the high-frequency units during regular operation is supported by the foundation of the units,and the magnitude of vibration and the operating frequency fluctuate in different engineering contexts,leading to variations in the dynamic response of the foundation.The high-frequency units yield significantly diverse outcomes under different startup conditions and times,resulting in failure to meet operational requirements,influencing the normal function of the tunnel,and causing harm to the foundation structure,personnel,and property in severe cases.This article formulates a finite element numerical computation model for solid elements using three-dimensional elastic body theory and integrates field measurements to substantiate and ascertain the crucial parameter configurations of the finite element model.By proposing a comprehensive startup timing function for high-frequency dynamic machines under different startup conditions,simulating the frequency andmagnitude variations during the startup process,and suggesting functions for changes in frequency and magnitude,a simulated startup schedule function for high-frequency machines is created through coupling.Taking into account the selection of the transient dynamic analysis step length,the dynamic response results for the lower dynamic foundation during its fundamental frequency crossing process are obtained.The validation checks if the structural magnitude surpasses the safety threshold during the critical phase of unit startup traversing the structural resonance region.The design recommendations for high-frequency units’dynamic foundations are provided,taking into account the startup process of the machine and ensuring the safe operation of the tunnel.展开更多
The allocation of annual growth in biomass to primary plant organs is a central theme in ecology due to its role in developing ecological theories and agricultural applications.Classic theories have significantly impr...The allocation of annual growth in biomass to primary plant organs is a central theme in ecology due to its role in developing ecological theories and agricultural applications.Classic theories have significantly improved our understanding of biomass allocation patterns influenced by various factors.However,increasing contrasting observations cannot be explained by classic theories.Recently,transient dynamic theory can resolve the problem.Here,we provide empirical evidence describing transient variations of biomass allocated to stems for four crop species(i.e.corn,soybean,flax,and wheat)in single and mixed systems.We show that plant ontogeny and increasing intraspecific competition promote variations in stem mass fractions.However,variations in stem mass fractions are reduced under strong interspecific competition.Plants with large total biomass have relatively stable stem mass fractions.These findings provide empirical foundations for integrating transient dynamics into general theoretical frameworks of biomass allocation patterns and may stabilize agricultural crop yields.展开更多
Effective detection schemes for spatiotemporal light fields hold significant importance in the study of highdimensional spatiotemporal nonlinear systems.We propose a compact seven-core fiber spatiotemporal mapping sys...Effective detection schemes for spatiotemporal light fields hold significant importance in the study of highdimensional spatiotemporal nonlinear systems.We propose a compact seven-core fiber spatiotemporal mapping system(SCF-SMS)to investigate the transient dynamics within a spatiotemporal mode-locked(STML)fiber laser.By utilizing this system,we observed intriguing transient phenomena during STML processes,including beating dynamics and spatiotemporal soliton state transition dynamics.In the beating dynamics,two channels corresponding to distinct spatial sampling points exhibited different transient behaviors.Conversely,during the spatiotemporal soliton state transition dynamics,the transition processes of two channels were asynchronous,with observable discrepancies before and after the transitions.Compared with existing spatiotemporal light field acquisition methods,the SCF-SMS enables more compact spatiotemporal mapping within STML fiber lasers.This real-time,synchronous system for spatiotemporal soliton information measurement facilitates an in-depth study of nonlinear dynamical phenomena in STML fiber lasers.展开更多
This paper proposes a new dynamic model for the study of friction-induced self-excited vibration of a disc brake system,where the pad’s motions in both radial and circumferential/tangential directions are included,wh...This paper proposes a new dynamic model for the study of friction-induced self-excited vibration of a disc brake system,where the pad’s motions in both radial and circumferential/tangential directions are included,which is in stark contrast to the previous studies that normally consider the pad’s motion in the tangential/circumferential direction only.The non-smooth dynamics of the system including three different states of motion,i.e.,stick,slip and separation,is investigated.Both the linear stability analysis and the transient dynamic analysis are performed.The numerical results in the linear stability analysis indicate that the inclusion of pad’s radial motion in the present brake model significantly expands the ranges of operating parameters for dynamic instability than the brake model with only circumferential/tangential motion for the pad.For the transient dynamic analysis,two different methods,i.e.,the time integration method and the shooting method,are employed for the calculation of steady-state response.The accuracy and efficiency of the shooting method are subsequently examined.The numerical results show rich bifurcation behaviours of the steady-state response in the present brake model with the variations of brake pressure N_(0) and disc speedΩ,and that k_(ir)(the stiffness of the inclined spring in the radial direction)is a key parameter for controlling the occurrence of chaotic vibration in the system.展开更多
Dynamic phenomena occurring on the ultrafast time scales are inherently difficult to image.While pump–probe techniques have been used for decades,probing nonrepeatable phenomena precludes this form of imaging.Additio...Dynamic phenomena occurring on the ultrafast time scales are inherently difficult to image.While pump–probe techniques have been used for decades,probing nonrepeatable phenomena precludes this form of imaging.Additionally,many ultrafast phenomena,such as electron dynamics,exhibit low amplitude contrast in the optical wavelength range and thus require quantitative phase imaging.To better understand the underlying physics involved in a plethora of ultrafast phenomena,advanced imaging techniques must be developed to observe single events at an ultrafast time scale.Here,we present,to the best of our knowledge,the first ptychographic imaging system capable of observing ultrafast dynamics from a single event.We demonstrate ultrafast dynamic imaging by observing the conduction band electron population from a 2-photon absorption event in ZnSe pumped by a single femtosecond pulse.We verify experimental observations by comparing them to numeric solutions of a nonlinear envelope equation.Our imaging method represents a major step forward in ultrafast imaging,bringing the capabilities of ptychography to the ultrafast regime.展开更多
The mechanism of a retracting cantilevered beam has been investigated by the invariant and energy-based analysis. The time-varying parameter partial differential equation governing the transverse vibrations of a beam ...The mechanism of a retracting cantilevered beam has been investigated by the invariant and energy-based analysis. The time-varying parameter partial differential equation governing the transverse vibrations of a beam with retracting motion is derived based on the momentum theorem. The assumed-mode method is used to truncate the governing partial differential equation into a set of ordinary differential equations (ODEs) with time-dependent coefficients. It is found that if the order of truncation is not less than the order of the initial conditions, the assumed-mode method can yield accurate results. The energy transfers among assumed modes are discussed during retraction. The total energy varying with time has been investigated by numerical and analytical methods, and the results have good agreement with each other. For the transverse vibrations of the axially retracting beam, the adiabatic invariant is derived by both the averaging method and the Bessel function method. (C) 2016 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.展开更多
A low velocity impact response study has been carried out on glass fibre composite laminates, made up of regular aircraft grade epoxy (GFRP) and shape memory polymer (GF-SMP). Under various impact loading intensities ...A low velocity impact response study has been carried out on glass fibre composite laminates, made up of regular aircraft grade epoxy (GFRP) and shape memory polymer (GF-SMP). Under various impact loading intensities (4J, 6J, 12J), the responses are measured by a network of PZT (Lead Zirconate Titanate) sensors. A signal analysis methodology is subsequently developed to process the very high frequency (60 MHz) sampled data. In two frequency bands, namely 0 - 2000 Hz and 0 - 100 KHz, the results are examined and the transient dynamic behaviours of the composite laminates are evaluated. It is observed that both the laminates have generated the high frequency structural waves (0 - 100 KHz), which can be exploited to examine the BVID. However, GF-SMP laminate has shown some advantage in terms of energy dissipation in the structural frequency band (<2000 Hz). Further, the GF-SMP laminate has demonstrated its capability to generate very high frequency structural waves, which could carry the damage information like BVID due to impact event to nearby sensors for impact event monitoring and health assessment.展开更多
In order to describe and control the stress distribution and total deformation of bladed disk assemblies used in the aeroengine, a highly efficient and precise method of probabilistic analysis which is called extremum...In order to describe and control the stress distribution and total deformation of bladed disk assemblies used in the aeroengine, a highly efficient and precise method of probabilistic analysis which is called extremum response surface method(ERSM) is produced based on the previous deterministic analysis results with the finite element model(FEM). In this work, many key nonlinear factors, such as the dynamic feature of the temperature load, the centrifugal force and the boundary conditions, are taken into consideration for the model. The changing patterns with time of bladed disk assemblies about stress distribution and total deformation are obtained during the deterministic analysis, and at the same time, the largest deformation and stress nodes of bladed disk assemblies are found and taken as input target of probabilistic analysis in a scientific and reasonable way. Not only their reliability, historical sample, extreme response surface(ERS) and the cumulative probability distribution function but also their sensitivity and effect probability are obtained. Main factors affecting stress distribution and total deformation of bladed disk assemblies are investigated through the sensitivity analysis of the model. Finally, compared with the response surface method(RSM) and the Monte Carlo simulation(MCS), the results show that this new approach is effective.展开更多
For the high-speed gasoline engine turbocharger rotor, due to the heterogeneity of multiple parts material, manufacturing and assembly errors, running wear in impeller and uneven carbon of turbine, the random unbalanc...For the high-speed gasoline engine turbocharger rotor, due to the heterogeneity of multiple parts material, manufacturing and assembly errors, running wear in impeller and uneven carbon of turbine, the random unbalance usually can be developed which will induce excessive rotor vibration, and even lead to nonlinear vibration accidents. However, the investigation of unbalance location on the nonlinear high-speed turbocharger rotordynamic characteristics is less. In order to discuss the rotor unbalance location effects of turbocharger with nonlinear floating ring bearings（FRBs）, the realistic turbocharger of gasoline engine is taken as a research object. The rotordynamic equations of motion under the condition of unbalance are derived by applied unbalance force and nonlinear oil film force of FRBs. The FE model of turbocharger rotor-bearing system is modeled which includes the unbalance excitation and nonlinear FRBs. Under the conditions of four different applied locations of unbalance, the nonlinear transient analyses are performed based on the rotor FEM. The differences of dynamic behavior are obvious to the turbocharger rotor systems for four conditions, and the bifurcation phenomena are different. From the results of waterfall and transient response analysis, the speed for the appearance of fractional frequency is not identical and the amplitude magnitude is different from the different unbalance locations, and the non-synchronous vibration does not occur in the turbocharger and the amplitude is relative stable and minimum under the condition 4. The turbocharger vibration and non-synchronous components could be reduced or suppressed by controlling the applied location of unbalance, which is helpful for the dynamic design, fault diagnosis and vibration control of the high-speed gasoline engine turbochargers.展开更多
基金supported by National Natural Science Foundation of China (Grant No. 50905092)
文摘The early fatigue damage in the van-body of the semi-trailer is often caused by the unique mechanical characteristics and the dynamic impact of the loads.The traditional finite element method with static strength analysis cannot support the fatigue design of van-body;thus,the dynamics analysis should be adopted for the endurance performance.The accurate dynamics model to describe the transient impacts of all kinds of uneven road and the proper system transfer functions to calculate the load transfer effects from tire to van-body are two critical factors for transient dynamics analysis.In order to evaluate the dynamic performance,the dynamics model of the trailer with the air suspension is brought forward.Then the analysis method of the power spectral density （PSD） is set up to study the transient responses of the road dynamic impacts.The transient responses transferred from axles to van-body are calculated,such as dynamic stress,dynamic RMS acceleration,and dynamic load factors.Based on the above dynamic responses,the fatigue life of van-body is predicted with the finite element analysis （FEA） method.Applying the test parameters of the trailer with air suspension,the simulation system with Matlab/Simulink is constructed to describe the dynamic responses of the impacts of the tested PSD of the vehicle axles,and then the fatigue life is predicted with FEA method.The simulated results show that the vibration level of the van-body with air suspension is reduced and the fatigue life is improved.The real vehicle tests on different roads are carried out,and the test results validate the accuracy of the simulation system.The proposed fatigue life prediction method is effective for the virtual design of auto-body.
基金supported by the National Natural Science Foundation of China(Grant No.51277017)the Natural Science Foundation of Jiangsu Province,China(Grant No.BK2012583)the Fundamental Research Funds for the Central Universities of China(Grant No.NS2014038)
文摘A simple four-dimensional system with only one control parameter is proposed in this paper. The novel system has a line or no equilibrium for the global control parameter and exhibits complex transient transition behaviors of hyperchaotic attractors, periodic orbits, and unstable sinks. Especially, for the nonzero-valued control parameter, there exists no equilibrium in the proposed system, leading to the formation of various hidden attractors with complex transient dynamics. The research results indicate that the dynamics of the system shows weak chaotic robustness and depends greatly on the initial states.
基金Project supported by the Western Transport Technical Project of Ministry of Transport of China(No. 2009318000046)
文摘A reproducing kernel collocation method based on strong formulation is introduced for transient dynamics. To study the stability property of this method, an algorithm based on the von Neumann hypothesis is proposed to predict the critical time step. A numerical test is conducted to validate the algorithm. The numerical critical time step and the predicted critical time step are in good agreement. The results are compared with those obtained based on the radial basis collocation method, and they axe in good agreement. Several important conclusions for choosing a proper support size of the reproducing kernel shape function are given to improve the stability condition.
文摘We designed and evaluated a fluoride-based high concentration erbium/ cerium co-doped fiber amplifier. It is suitable for Metropolitan Area Networks due to faster transient, flatter (unfiltered) gain, smaller footprint and gain excursion than its silica-based counterpart.
基金supported by the Basic Research Program of Shanxi Province(grant 20210302124141)the National Natural Science Foundation of China(grant 32101235)to R.F.C.
文摘Although debates exist,marine reserves play an important role in fisheries management.Based on stable equilibrium state,theoretical frameworks of various systems suggest that fisheries management with the implementation of marine reserves has obvious advantage in achieving multiple goals such as improving the target fisheries yields as well as maintaining species persistence in comparison with strategy of traditional fishing effort control.More recently,ecologists pay attention to the transient dynamics of fisheries yields when marine reserves are established.Simulation results suggest that the relative advantages between different fisheries management strategies(the implementation of marine reserves vs.traditional fishing effort control)depend on not only life histories but also the measurement metrics of fisheries yields(measured by number vs.measured by weight).Further research on transient dynamic pattern of fisheries yields can help fishery managers adjust relevant policies at an appropriate ecological time scale to achieve both conservation and economic goals,which provide a theoretical foundation for adaptive marine reserve management.
文摘Through adding a nonlinear self-feedback term in the evolution equations of neural network, we introduced a transiently chaotic neural network model. In order to utilize the transiently chaotic dynamics mechanism in optimization problem efficiently, we have analyzed the dynamical procedure of the transiently chaotic neural network model and studied the function of the crucial bifurcation parameter which governs the chaotic behavior of the system. Based on the dynamical analysis of the transiently chaotic neural network model, chaotic annealing algorithm is also examined and improved. As an example, we applied chaotic annealing method to the traveling salesman problem and obtained good results.
基金Supported by the National Natural Science Foundation of China(No.52075468)。
文摘During the operation of magnetic liquid double suspension bearing(MLDSB),due to rotor resonance,assembly error and other factor,the vibration amplitude of the rotor in resonance state exceeds the original design clearance,resulting in the collision damage between the rotor and the stator,the rotor and the casing.This paper presents a method to simulate the influence of different factors on the dynamic characteristics of 5 degrees of freedom(DOF)rotor based on the dynamic model of MLDSB.Firstly,according to the second Lagrange equation,the dynamic equation of 5 DOF rotor is derived,and the mathematical model is established.Then,based on 5 DOF rotor dynamic equation,the rotor transient dynamic equation under collision state is obtained,and the rotor transient collision dynamic simulation model is established.Finally,the key influencing factors of rotor dynamic characteristics are extracted,and the influence mapping relationship of rotor displacement,axis locus and stress distribution under different factors is simulated by using ANSYS Workbench software.The experimental results show that this method can effectively reflect the influence of various factors on the dynamic characteristics of the rotor.This method can provide theoretical reference for the design and control of MLDSB.
文摘The matrix expression for the 3 D transient dynamic boundary integral equation in Laplace transform space is obtained and the degenerative element method has been implemented to treat the kernel function over the singular element. In the computer program BEMTDY the Koizumi′s numerical inversion method is used and three examples of the 3 D vibrated foundation under harmonic forces and the influence with both adjacent foundations are studied.
基金supported by the National Natural Science Foundation of China (11172233 and 10932009)the Fundamental Research Fund of Northwestern Polytechnical University (JC20110269)
文摘This paper investigates persistence of transient dynamics depending on parameters in spatially coupled ecological systems. We emphasis that the persistence time can be obtained by populations of species or Lyapunov exponents of transient dynamics. It is found that extreme sensitive dependence of persistence on parameters occurs commonly in ecological models. A non-zero uncertainty exponent is used to characterize the high sensitivity in a reasonable parameter region. The result of a small uncertainty exponent indicates a fractal structure of transient persistence in the two-dimensional parameter space. In spite of different methods of measurement, the fractal dimensions have a good consistency. Since populations of natural communities with many coupled oscillators are often affected by disturbance of migration rates, the large probability of error in estimating persistence of transients should be concerned.
基金the National High Technology Research and Development Program (863) of China(No. 2008AA092301-1)the National Natural Science Foundation of China(No. 50909061)the Ph.D. Programs Foundation of Ministry of Education of China(No. 20070248103)
文摘This paper presents a numerical analysis of the dynamic transient behaviors of undersea cables.In this numerical study,the governing equations based on Euler-Bernoulli beam theory are adopted,and they can satisfy many applications no matter what the magnitude of the cable tension is.The nonlinear coupled equations are solved by a popular central finite difference method,and the numerical results of transient behaviors are presented when several kinds of surrounding conditions,such as different towing speeds of surface vessel,different currents and waves with various frequencies and amplitudes,are exerted.Then a detailed comparison of the results,including the upper end tension and cable shape in time-domain,is made under the above external excitations,and finally the possible reasons for these are further explained.
基金Supported by the National Natural Science Foundation of China(No.51005063,51375123)National Science and Technology Cooperation Projects of China(No.2012DFR70840)
文摘A new method is developed to assess and analyze the dynamic performance of hydrostatic bearing oil film by using an amulets-layer dynamic mesh technique. It is implemented using C Language to compile the UDF program of a single oil film of the hydrostatic bearing. The effects of key lubrication parameters of the hydrostatic bearing are evaluated and analyzed under various working conditions,i.e. under no-load,a load of 40 t,a full load of 160 t,and the rotation speed of 1r/min,2r/min,4r/min,8r/min,16r/min,32r/min. The transient data of oil film bearing capacity under different load and rotation speed are acquired for a total of 18 working conditions during the oil film thickness changing. It allows the effective prediction of dynamic performance of large size hydrostatic bearing. Experiments on hydrostatic bearing oil film have been performed and the results were used to define the boundary conditions for the numerical simulations and validate the developed numerical model. The results showed that the oil film thickness became thinner with the increase of the operating time of the hydrostatic bearing,both the oil film rigidity and the oil cavity pressure increased significantly,and the increase of the bearing capacity was inversely proportional to the cube of the change of the film thickness. Meanwhile,the effect of the load condition on carrying capacity of large size static bearing was more important than the speed condition. The error between the simulation value and the experimental value was 4.25%.
基金Smart Integration Key Technologies and Application Demonstrations of Large Scale Underground Space Disaster Prevention and Reduction in Guangzhou International Financial City([2021]–KJ058).
文摘The specialized equipment utilized in long-line tunnel engineering is evolving towards large-scale,multifunctional,and complex orientations.The vibration caused by the high-frequency units during regular operation is supported by the foundation of the units,and the magnitude of vibration and the operating frequency fluctuate in different engineering contexts,leading to variations in the dynamic response of the foundation.The high-frequency units yield significantly diverse outcomes under different startup conditions and times,resulting in failure to meet operational requirements,influencing the normal function of the tunnel,and causing harm to the foundation structure,personnel,and property in severe cases.This article formulates a finite element numerical computation model for solid elements using three-dimensional elastic body theory and integrates field measurements to substantiate and ascertain the crucial parameter configurations of the finite element model.By proposing a comprehensive startup timing function for high-frequency dynamic machines under different startup conditions,simulating the frequency andmagnitude variations during the startup process,and suggesting functions for changes in frequency and magnitude,a simulated startup schedule function for high-frequency machines is created through coupling.Taking into account the selection of the transient dynamic analysis step length,the dynamic response results for the lower dynamic foundation during its fundamental frequency crossing process are obtained.The validation checks if the structural magnitude surpasses the safety threshold during the critical phase of unit startup traversing the structural resonance region.The design recommendations for high-frequency units’dynamic foundations are provided,taking into account the startup process of the machine and ensuring the safe operation of the tunnel.
基金supported by the National Natural Science Foundation of China(grant 32225032,32101235)the National Key Research and Development Program of China(2023YFF0805600)the Top Leading Talents in Gansu Province to J.D.
文摘The allocation of annual growth in biomass to primary plant organs is a central theme in ecology due to its role in developing ecological theories and agricultural applications.Classic theories have significantly improved our understanding of biomass allocation patterns influenced by various factors.However,increasing contrasting observations cannot be explained by classic theories.Recently,transient dynamic theory can resolve the problem.Here,we provide empirical evidence describing transient variations of biomass allocated to stems for four crop species(i.e.corn,soybean,flax,and wheat)in single and mixed systems.We show that plant ontogeny and increasing intraspecific competition promote variations in stem mass fractions.However,variations in stem mass fractions are reduced under strong interspecific competition.Plants with large total biomass have relatively stable stem mass fractions.These findings provide empirical foundations for integrating transient dynamics into general theoretical frameworks of biomass allocation patterns and may stabilize agricultural crop yields.
基金National Natural Science Foundation of China(12274238,62205159,61835006)Natural Science Foundation of Tianjin Municipality(19JCZDJC31200)Special Project for Cooperation in Basic Research of Beijing,Tianjin and Hebei(21JCZXJC00010)。
文摘Effective detection schemes for spatiotemporal light fields hold significant importance in the study of highdimensional spatiotemporal nonlinear systems.We propose a compact seven-core fiber spatiotemporal mapping system(SCF-SMS)to investigate the transient dynamics within a spatiotemporal mode-locked(STML)fiber laser.By utilizing this system,we observed intriguing transient phenomena during STML processes,including beating dynamics and spatiotemporal soliton state transition dynamics.In the beating dynamics,two channels corresponding to distinct spatial sampling points exhibited different transient behaviors.Conversely,during the spatiotemporal soliton state transition dynamics,the transition processes of two channels were asynchronous,with observable discrepancies before and after the transitions.Compared with existing spatiotemporal light field acquisition methods,the SCF-SMS enables more compact spatiotemporal mapping within STML fiber lasers.This real-time,synchronous system for spatiotemporal soliton information measurement facilitates an in-depth study of nonlinear dynamical phenomena in STML fiber lasers.
基金supported by the Hong Kong Innovation and Technology Commission(Project No.MRP/030/21 under PiH/026/23)The Chinese University of Hong Kong(Project ID:3134167)the Research Grants Council(Project No.CUHK14211823)of Hong Kong Special Administrative Region,China.
文摘This paper proposes a new dynamic model for the study of friction-induced self-excited vibration of a disc brake system,where the pad’s motions in both radial and circumferential/tangential directions are included,which is in stark contrast to the previous studies that normally consider the pad’s motion in the tangential/circumferential direction only.The non-smooth dynamics of the system including three different states of motion,i.e.,stick,slip and separation,is investigated.Both the linear stability analysis and the transient dynamic analysis are performed.The numerical results in the linear stability analysis indicate that the inclusion of pad’s radial motion in the present brake model significantly expands the ranges of operating parameters for dynamic instability than the brake model with only circumferential/tangential motion for the pad.For the transient dynamic analysis,two different methods,i.e.,the time integration method and the shooting method,are employed for the calculation of steady-state response.The accuracy and efficiency of the shooting method are subsequently examined.The numerical results show rich bifurcation behaviours of the steady-state response in the present brake model with the variations of brake pressure N_(0) and disc speedΩ,and that k_(ir)(the stiffness of the inclined spring in the radial direction)is a key parameter for controlling the occurrence of chaotic vibration in the system.
基金funded through the Air Force Office of Scientific Research(FA9550-22-1-0495)the Los Alamos National Laboratory。
文摘Dynamic phenomena occurring on the ultrafast time scales are inherently difficult to image.While pump–probe techniques have been used for decades,probing nonrepeatable phenomena precludes this form of imaging.Additionally,many ultrafast phenomena,such as electron dynamics,exhibit low amplitude contrast in the optical wavelength range and thus require quantitative phase imaging.To better understand the underlying physics involved in a plethora of ultrafast phenomena,advanced imaging techniques must be developed to observe single events at an ultrafast time scale.Here,we present,to the best of our knowledge,the first ptychographic imaging system capable of observing ultrafast dynamics from a single event.We demonstrate ultrafast dynamic imaging by observing the conduction band electron population from a 2-photon absorption event in ZnSe pumped by a single femtosecond pulse.We verify experimental observations by comparing them to numeric solutions of a nonlinear envelope equation.Our imaging method represents a major step forward in ultrafast imaging,bringing the capabilities of ptychography to the ultrafast regime.
基金supported by the National Natural Science Foundation of China (Nos. 11322214, 11172010, 11290152 and 11402007)supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada, the Canada Research Chair (CRC) Program+1 种基金the Bizkaia Talent Grant under the Basque Government through the BERC 2014–2017 ProgramSpanish Ministry of Economy and Competitiveness MINECO:BCAM Severo Ochoa excellence accreditation SEV-2013-0323
文摘The mechanism of a retracting cantilevered beam has been investigated by the invariant and energy-based analysis. The time-varying parameter partial differential equation governing the transverse vibrations of a beam with retracting motion is derived based on the momentum theorem. The assumed-mode method is used to truncate the governing partial differential equation into a set of ordinary differential equations (ODEs) with time-dependent coefficients. It is found that if the order of truncation is not less than the order of the initial conditions, the assumed-mode method can yield accurate results. The energy transfers among assumed modes are discussed during retraction. The total energy varying with time has been investigated by numerical and analytical methods, and the results have good agreement with each other. For the transverse vibrations of the axially retracting beam, the adiabatic invariant is derived by both the averaging method and the Bessel function method. (C) 2016 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.
文摘A low velocity impact response study has been carried out on glass fibre composite laminates, made up of regular aircraft grade epoxy (GFRP) and shape memory polymer (GF-SMP). Under various impact loading intensities (4J, 6J, 12J), the responses are measured by a network of PZT (Lead Zirconate Titanate) sensors. A signal analysis methodology is subsequently developed to process the very high frequency (60 MHz) sampled data. In two frequency bands, namely 0 - 2000 Hz and 0 - 100 KHz, the results are examined and the transient dynamic behaviours of the composite laminates are evaluated. It is observed that both the laminates have generated the high frequency structural waves (0 - 100 KHz), which can be exploited to examine the BVID. However, GF-SMP laminate has shown some advantage in terms of energy dissipation in the structural frequency band (<2000 Hz). Further, the GF-SMP laminate has demonstrated its capability to generate very high frequency structural waves, which could carry the damage information like BVID due to impact event to nearby sensors for impact event monitoring and health assessment.
基金Projects(51375032,51175017,51245027)supported by the National Natural Science Foundation of China
文摘In order to describe and control the stress distribution and total deformation of bladed disk assemblies used in the aeroengine, a highly efficient and precise method of probabilistic analysis which is called extremum response surface method(ERSM) is produced based on the previous deterministic analysis results with the finite element model(FEM). In this work, many key nonlinear factors, such as the dynamic feature of the temperature load, the centrifugal force and the boundary conditions, are taken into consideration for the model. The changing patterns with time of bladed disk assemblies about stress distribution and total deformation are obtained during the deterministic analysis, and at the same time, the largest deformation and stress nodes of bladed disk assemblies are found and taken as input target of probabilistic analysis in a scientific and reasonable way. Not only their reliability, historical sample, extreme response surface(ERS) and the cumulative probability distribution function but also their sensitivity and effect probability are obtained. Main factors affecting stress distribution and total deformation of bladed disk assemblies are investigated through the sensitivity analysis of the model. Finally, compared with the response surface method(RSM) and the Monte Carlo simulation(MCS), the results show that this new approach is effective.
基金Supported by National Natural Science Foundation of China(Grant Nos.51575176,51375162)Scientific Research Foundation of Hunan Provincial Education Department of China(Grant No.15B085)Postgraduate Innovation Foundation of Hunan University of Science and Technology,China(Grant No.S140020)
文摘For the high-speed gasoline engine turbocharger rotor, due to the heterogeneity of multiple parts material, manufacturing and assembly errors, running wear in impeller and uneven carbon of turbine, the random unbalance usually can be developed which will induce excessive rotor vibration, and even lead to nonlinear vibration accidents. However, the investigation of unbalance location on the nonlinear high-speed turbocharger rotordynamic characteristics is less. In order to discuss the rotor unbalance location effects of turbocharger with nonlinear floating ring bearings（FRBs）, the realistic turbocharger of gasoline engine is taken as a research object. The rotordynamic equations of motion under the condition of unbalance are derived by applied unbalance force and nonlinear oil film force of FRBs. The FE model of turbocharger rotor-bearing system is modeled which includes the unbalance excitation and nonlinear FRBs. Under the conditions of four different applied locations of unbalance, the nonlinear transient analyses are performed based on the rotor FEM. The differences of dynamic behavior are obvious to the turbocharger rotor systems for four conditions, and the bifurcation phenomena are different. From the results of waterfall and transient response analysis, the speed for the appearance of fractional frequency is not identical and the amplitude magnitude is different from the different unbalance locations, and the non-synchronous vibration does not occur in the turbocharger and the amplitude is relative stable and minimum under the condition 4. The turbocharger vibration and non-synchronous components could be reduced or suppressed by controlling the applied location of unbalance, which is helpful for the dynamic design, fault diagnosis and vibration control of the high-speed gasoline engine turbochargers.
