We consider the two-dimensional stochastic quasi-geostrophic equation ■=1/(R_e)△~2■-r/2△■+f(x,y,t)(1.1) on a regular bounded open domain D ■,where ■ is the stream function,F Froude Number (F≈O(1)),R_e Reynolds...We consider the two-dimensional stochastic quasi-geostrophic equation ■=1/(R_e)△~2■-r/2△■+f(x,y,t)(1.1) on a regular bounded open domain D ■,where ■ is the stream function,F Froude Number (F≈O(1)),R_e Reynolds number(R_e■10~2),β_0 a positive constant(β_0≈O(10^(-1)),r the Ekman dissipation constant(r≈o(1)),the external forcing term f(x,y,t)=-(dW)/(dt)(the definition of W will be given later)a Gaussian random field,white noise in time,subject to the展开更多
Method of testing for dynamic output forces from jet elements is studied, the handwidth is large in testing with this method. By establishing a model of the test system and simulating it, principles of how inherent fe...Method of testing for dynamic output forces from jet elements is studied, the handwidth is large in testing with this method. By establishing a model of the test system and simulating it, principles of how inherent features of the test system affect the dynamic force test are found out. Thus a theoretical foundation is given for the design and error modification to the actual test system.展开更多
The initiation of convective cells in the late morning of 24 June 2010 along the eastward extending ridge of the Dabie Mountains in the Anhui region, China, is studied through numerical simulations that include local ...The initiation of convective cells in the late morning of 24 June 2010 along the eastward extending ridge of the Dabie Mountains in the Anhui region, China, is studied through numerical simulations that include local data assimilation. A primary convergence line is found over the ridge of the Dabie Mountains, and along the ridge line several locally enhanced convergence centers preferentially initiate convection. Three processes responsible for creating the overall convergence pattern are identified. First, thermally-driven upslope winds induce convergence zones over the main mountain peaks along the ridge, which are shifted slightly downwind in location by the moderate low-level easterly flow found on the north side of a Mei-yu front. Second, flows around the main mountain peaks along the ridge create further convergence on the lee side of the peaks. Third, upslope winds develop along the roughly north-south oriented valleys on both sides of the ridge due to thermal and dynamic channeling effects, and create additional convergence between the peaks along the ridge. The superposition of the above convergence features creates the primary convergence line along the ridge line of the Dabie Mountains. Locally enhanced convergence centers on the primary line cause the initiation of the first convection cells along the ridge. These conclusions are supported by two sensitivity experiments in which the environmental wind （dynamic forcing） or radiative and land surface thermal forcing are removed, respectively. Overall, the thermal forcing effects are stronger than dynamic forcing given the relatively weak environmental flow.展开更多
Rail weld irregularities are one of the primary excitation sources for vehicle-track interaction dynamics in modern high-speed railways.They can cause significant wheel-rail dynamic interactions,leading to wheel-rail ...Rail weld irregularities are one of the primary excitation sources for vehicle-track interaction dynamics in modern high-speed railways.They can cause significant wheel-rail dynamic interactions,leading to wheel-rail noise,component damage,and deterioration.Few researchers have employed the vehicle-track interaction dynamic model to study the dynamic interactions between wheel and rail induced by rail weld geometry irregularities.However,the cosine wave model used to simulate rail weld irregularities mainly focuses on the maximum value and neglects the geometric shape.In this study,novel theoretical models were developed for three categories of rail weld irregularities,based on measurements of the high-speed railway from Beijing to Shanghai.The vertical dynamic forces in the time and frequency domains were compared under different running speeds.These forces generated by the rail weld irregularities that were measured and modeled,respectively,were compared to validate the accuracy of the proposed model.Finally,based on the numerical study,the impact force due to rail weld irrregularity is modeled using an Artificial Neural Network(ANN),and the optimum combination of parameters for this model is found.The results showed that the proposed model provided a more accurate wheel/rail dynamic evaluation caused by rail weld irregularities than that established in the literature.The ANN model used in this paper can effectively predict the impact force due to rail weld irrregularity while reducing the computation time.展开更多
Batteries power numerous technolo-gies,yet higher energy density de-mands push lithium cobalt oxide(Li-CoO_(2)referred as LCO)cathodes to higher voltages,triggering unwanted chemical reactions.In this work,we in-vesti...Batteries power numerous technolo-gies,yet higher energy density de-mands push lithium cobalt oxide(Li-CoO_(2)referred as LCO)cathodes to higher voltages,triggering unwanted chemical reactions.In this work,we in-vestigate how carbonate-based elec-trolytes degrade on deeply delithiated LCO surfaces via extensive reactive molecular dynamics simulations.These simulations unveil the forma-tion of characteristic gas products and unstable surface species,which can undermine the cathode structure and reduce battery performance.By examining different solvent composi-tions,the simulations reveal that partial fluorination reduces oxidative degradation and gas evolution,thus offering a route to improve interface stability.Overall,this study provides an atomic-level perspective on preventing unwanted reactions and guiding the design of safer and more robust battery systems for high-voltage applications.展开更多
Hydrocarbon distribution rules in the deep and shallow parts of sedimentary basins are considerably different, particularly in the following four aspects. First, the critical porosity for hydrocarbon migration is much...Hydrocarbon distribution rules in the deep and shallow parts of sedimentary basins are considerably different, particularly in the following four aspects. First, the critical porosity for hydrocarbon migration is much lower in the deep parts of basins： at a depth of 7000 m, hydrocarbons can accumulate only in rocks with porosity less than 5%. However, in the shallow parts of basins （i.e., depths of around 1000 m）, hydrocarbon can accumulate in rocks only when porosity is over 20%. Second, hydrocarbon reservoirs tend to exhibit negative pressures after hydrocarbon accumulation at depth, with a pressure coefficient less than 0.7. However, hydrocarbon reservoirs at shallow depths tend to exhibit high pressure after hydrocarbon accumulation. Third, deep reservoirs tend to exhibit characteristics of oil （-gas）-water inversion, indicating that the oil （gas） accumulated under the water. However, the oil （gas） tends to accumulate over water in shallow reservoirs. Fourth, continuous unconventional tight hydrocarbon reservoirs are distributed widely in deep reservoirs, where the buoyancy force is not the primary dynamic force and the caprock is not involved during the process of hydrocarbon accumulation. Conversely, the majority of hydrocarbons in shallow regions accumulate in traps with complex structures. The results of this study indicate that two dynamic boundary conditions are primarily responsible for the above phenomena： a lower limit to the buoyancy force and the lower limit of hydrocarbon accumulation overall, corresponding to about 10%-12% porosity and irreducible water saturation of 100%, respectively. These two dynamic boundary conditions were used to divide sedimentary basins into three different dynamic fields of hydrocarbon accumulation： the free fluid dynamic field, limit fluid dynamic field, and restrain fluid dynamic field. The free fluid dynamic field is located between the surface and the lower limit of the buoyancy force, such that hydrocarbons in this field migrate and accumulate under the influence of, for example, the buoyancy force, pressure, hydrodynamic force, and capillary force. The hydrocarbon reservoirs formed are characterized as ＂four high,＂ indicating that they accumulate in high structures, are sealed in high locations, migrate into areas of high porosity, and are stored in reservoirs at high pressure. The basic features of distribution and accumulation in this case include hydrocarbon migration as a result of the buoyancy force and formation of a reservoir by a caprock. The limit fluid dynamic field is located between the lower limit of the buoyancy force and the lower limit of hydrocarbon accumulation overall; the hydrocarbon migrates and accumulates as a result of, for example, the molecular expansion force and the capillary force. The hydrocarbon reservoirs formed are characterized as ＂four low,＂ indicating that hydrocarbons accumulate in low structures, migrate into areas of low porosity, and accumulate in reservoirs with low pressure, and that oil（-gas）-water inversion occurs at low locations. Continuous hydrocarbon accumulation over a large area is a basic feature of this field. The restrain fluid dynamic field is located under the bottom of hydrocarbon accumulation, such that the entire pore space is filled with water. Hydrocarbons migrate as a result of the molecular diffusion force only. This field lacks many of the basic conditions required for formation of hydrocarbon reservoirs： there is no effective porosity, movable fluid, or hydrocarbon accumulation, and potential for hydrocarbon exploration is low. Many conventional hydrocarbon resources have been discovered and exploited in the free fluid dynamic field of shallow reservoirs, where exploration potential was previously considered to be low. Continuous unconventional tight hydrocarbon resources have been discovered in the limit fluid dynamic field of deep reservoirs; the exploration potential of this setting is thought to be tremendous, indicating that future exploration should be focused primarily in this direction.展开更多
Reclamation is one of the fastest-growing land use type developed in coastal areas and has caused degradation and loss of coastal wetlands as well as serious environmental problems. This paper was aimed at monitoring ...Reclamation is one of the fastest-growing land use type developed in coastal areas and has caused degradation and loss of coastal wetlands as well as serious environmental problems. This paper was aimed at monitoring the spatiotemporal patterns of coastal wetlands and reclamation in the Yangtze Estuary during the 1960s and 2015. Satellite images obtained from 1980 to 2015 and topography maps of the 1960 s were employed to extract changes of reclamation and coastal wetlands. Area-weight centroids were calculated to identify the movement trend of reclamation and coastal wetlands. The results show that from the 1960 s to 2015, the net area of natural wetlands declined by 574.3 km^2, while man-made wetlands and reclamation increased by 553.6 and 543.9 km^2, respectively. During the five study phases, the fastest areal change rate natural wetlands was –13.3 km^2/yr in the period of 1990–2000, and that of man-made areas was 24.7 km^2/yr in the same period, and the areal change rate of reclamation was 27.6 km^2/yr in the period of 2000–2010. Conversion of coastal wetlands mainly occurred in the Chongming Island, Changshu City and the east coast of Shanghai Municipality. Reclamation was common across coastal areas, and was mainly attributed to settlement and man-made wetlands in the Chongming Island, Lianyungang City and the east coast of Shanghai Municipality. Natural wetlands turned into farmlands and settlement, and man-made wetlands gained from reclamation of farmlands. The centroid of natural wetlands generally moved towards the sea, man-made wetlands expanded equally in all directions and inland, and the centroid of reclamation migrated toward Shanghai Municipality. Sea level rise, erosion-deposition changes, and reclamation activities together determine the dynamics of the Yangtze Estuary wetlands. However, reclamation activities for construction of ports, industries and aquaculture are the key causes for the dynamics. The results from this study on the dynamics of coastal wetlands and reclamation are valuable for local government to put forward sustainable land use and land development plans.展开更多
In current precision and ultraprecision machining practice,the positioning and control of actuation systems,such as slideways and spindles,are heavily dependent on the use of linear or rotary encoders.However,position...In current precision and ultraprecision machining practice,the positioning and control of actuation systems,such as slideways and spindles,are heavily dependent on the use of linear or rotary encoders.However,positioning control is passive because of the lack of direct monitoring and control of the tool and workpiece positions in the dynamic machining process and also because it is assumed that the machining system is rigid and the cutting dynamics are stable.In ultraprecision machining of freeform surfaces using slow tool servo mode in particular,however,account must be taken of the machining dynamics and dynamic synchronization of the cutting tool and workpiece positioning.The important question also arises as to how ultraprecision machining systems can be designed and developed to work better in this application scenario.In this paper,an innovative dynamics-oriented engineering approach is presented for ultraprecision machining of freeform surfaces using slow tool servo mode.The approach is focused on seamless integration of multibody dynamics,cutting forces,and machining dynamics,while targeting the positioning and control of the tool–workpiece loop in the machining system.The positioning and motion control between the cutting tool and workpiece surface are further studied in the presence of interfacial interactions at the tool tip and workpiece surface.The interfacial cutting physics and dynamics are likely to be at the core of in-process monitoring applicable to ultraprecision machining systems.The approach is illustrated using a virtual machining system developed and supported with simulations and experimental trials.Furthermore,the paper provides further explorations and discussion on implementation perspectives of the approach,in combination with case studies,as well as discussing its fundamental and industrial implications.展开更多
The support of coal roadways is seriously affected by intense dynamic pressures.This can lead to problems with large deformation of the roof and the two side walls of coal roadways.Rapid convergence of the walls and r...The support of coal roadways is seriously affected by intense dynamic pressures.This can lead to problems with large deformation of the roof and the two side walls of coal roadways.Rapid convergence of the walls and roof,a high damage rate to the bolts and cables,or even abrupt roof collapse or rib spalling can occur during the service period of these coal roadways.Analyzing the main support measures used in China leads to a proposed new cable truss supporting system.Thorough study of the entire structure shows the superiority of this design for roadways suffering under dynamic pressure.A corresponding mechanical model of the rock surrounding the cable truss system is described in this paper and formulas for calculating pre-tightening forces of the truss cable,and the minimum anchoring forces,were deduced.The new support system was applied to a typical roadway affected by intensive dynamic pressure that is located in the Xinyuan Coal Mine.The results show that the largest subsidence of the roof was 97 mm,the convergence of the two sides was less than 248 mm,and the average depth of the loose,fractured layer was only 6.12 mm.This proves that the new support system is feasible and effective.展开更多
It has been found that the brittle material, monocrystalline silicon, can be machined in ductile mode in nanoscale cutting when the tool cutting edge radius is reduced to nanoscale and the undeformed chip thickness is...It has been found that the brittle material, monocrystalline silicon, can be machined in ductile mode in nanoscale cutting when the tool cutting edge radius is reduced to nanoscale and the undeformed chip thickness is smaller than the tool edge radius. In order to better understand the mechanism of ductile mode cutting of silicon, the molecular dynamics （MD） method is employed to simulate the nanoscale cutting of monocrystalline silicon. The simulated variation of the cutting forces with the tool cutting edge radius is compared with the cutting force results from experimental cutting tests and they show a good agreement. The results also indicate that there is silicon phase transformation from monocrystalline to amorphous in the chip formation zone that can be used to explain the cause of ductile mode cutting. Moreover, from the simulated stress results, the two necessary conditions of ductile mode cutting, the tool cutting edge radius are reduced to nanoscale and the undeformed chip thickness should be smaller than the tool cutting edge radius, have been explained.展开更多
The roll motions are influenced by significant viscous effects such as the flow separation.The 3D simulations of free decay roll motions for the ship model DTMB 5512 are carried out by Reynold averaged NavierStokes(RA...The roll motions are influenced by significant viscous effects such as the flow separation.The 3D simulations of free decay roll motions for the ship model DTMB 5512 are carried out by Reynold averaged NavierStokes(RANS) method based on the dynamic mesh technique.A new moving mesh technique is adopted and discussed in details for the present simulations.The purpose of the research is to obtain accurate numerical prediction for roll motions with their respective numerical/modeling errors and uncertainties.Errors and uncertainties are estimated by performing the modern verification and validation(V&V) procedures.Simulation results for the free-floating surface combatant are used to calculate the linear,nonlinear damping coefficients and resonant frequencies including a wide range of forward speed.The present work can provide a useful reference to calculate roll damping by computational fluid dynamics(CFD) method and simulate a general ship motions in waves.展开更多
The axial magnetic force, induced by the complicated flux linkage distribution from rotor magnet and stator slotted, is constructed by different relative heights and calculated by 3D finite element method (FEM) to ana...The axial magnetic force, induced by the complicated flux linkage distribution from rotor magnet and stator slotted, is constructed by different relative heights and calculated by 3D finite element method (FEM) to analyze the dynamic characteristics for a DVD spindle motor. The axial magnetic force is designed to provide an axial stiffness, and govern the natural frequency of the dynamic performance. According to the simulation results and experimental measurements, the dynamic behaviors are significantly improved with a variation of relative height of rotor magnet and stator slotted on a DVD spindle motor.展开更多
Negative step response experimental method is used in wrist force sensor＇s dynamic performance calibration. The exciting manner of negative step response method is the same as wrist force sensor＇s load in working. T...Negative step response experimental method is used in wrist force sensor＇s dynamic performance calibration. The exciting manner of negative step response method is the same as wrist force sensor＇s load in working. This experimental method needn＇t special experiment equipments. Experiment＇s dynamic repeatability is good. So wrist force sensor＇s dynamic performance is suitable to be calibrated by negative step response method. A new correlation wavelet transfer method is studied. By wavelet transfer method, the signal is decomposed into two dimensional spaces of time-frequency. So the problem of negative step exciting energy concentrating in the low frequency band is solved. Correlation wavelet transfer doesn＇t require that wavelet primary function be orthogonal and needn＇t wavelet reconstruction. So analyzing efficiency is high. An experimental bench is designed and manufactured to load the wrist force sensor orthogonal excitation force/moment. A piezoelectric force sensor is used to setup soft trigger and calculate the value of negative step excitation. A wrist force sensor is calibrated. The pulse response function is calculated after negative step excitation and step response have been transformed to positive step excitation and step response. The pulse response function is transferred to frequency response function. The wrist force sensor＇s dynamic characteristics are identified by the frequency response function.展开更多
Based on electromagnetics and mechanics, electromechanical coupled dynamic equations for the drive were developed. Using method of perturbation, free vibrations of the mechanical system under electric disturbance were...Based on electromagnetics and mechanics, electromechanical coupled dynamic equations for the drive were developed. Using method of perturbation, free vibrations of the mechanical system under electric disturbance were investigated. The forced responses of the mechanical system to mechanical excitation under electric disturbance were also presented. It is known that for the system with electric disturbance, as time grows, beat occurs. When electric disturbing frequency is near to the natural frequencies of the mechanical system or their integer multiple, resonance vibrations occur. The forced responses of the mechanical system to mechanical excitation under electric disturbance are compound vibrations decided by mechanical excitation, electric disturbance and parameters of the system. The coupled resonance vibration caused by electric disturbance and mechanical excitation was discussed as well. The conditions under which above coupled resonance occurs were presented. The results show that when the difference of the excitation frequency and the perturbation frequency is equal to some order of natural frequency, coupled resonance vibrations occur.展开更多
With the aid of different types of mechanoreceptors,human is capable of perceiving stimuli from surrounding environments and manipulating various objects dexterously.In this paper,a bio-inspired tactile fingertip is d...With the aid of different types of mechanoreceptors,human is capable of perceiving stimuli from surrounding environments and manipulating various objects dexterously.In this paper,a bio-inspired tactile fingertip is designed mimicking human fingertip in both structures and functionalities.Two pairs of strain gages and(Polyvinylidene Fluoride)PVDF films are perpendicularly arranged to simulate the Fast-Adapting(FA)and Slowly Adapting(SA)type mechanoreceptors in human hands,while silicones,Polymethyl Methacrylate(PMMA),and electronic wires are applied to mimic the skin,bone and nerve fibers.Both static and dynamic forces can be perceived sensitively.A preprocessing electric circuit is further designed to transform the resistor changes into voltages,and then filter and amplify the four-channel signals.In addition to strong robustness due to the embedded structure,the developed fingertip is found sensitive to deformations via a force test experiment.Finally,two robotic experiments explore its recognition ability of contact status and object surface.Excellent performance is found with high accuracy of 99.72%achieved in discriminating six surfaces that are ubiquitous in daily life,which demonstrates the effectiveness of our designed tactile sensor.展开更多
Spectrum and self-excite characters are the two significant characters of the dynamics of sea ice. The spectrum character of sea ice is mainly shown by the spectrum of ice force. The spectrum character of the sea ice ...Spectrum and self-excite characters are the two significant characters of the dynamics of sea ice. The spectrum character of sea ice is mainly shown by the spectrum of ice force. The spectrum character of the sea ice is its intrinsic attributes. When the spectrum of ice force from the dynamic response of ice and structure interaction are evaluated, the effect of dynamic character of the structure must be eliminated. In this paper, the ice force spectrum at Bohai Bay and Liaodong Bay is evaluated from the displacement and strain responses of a single degree and a multi-degree freedom structure. The evaluated ice force spectrum can be used to define the spectrum character of ice in the analysis of ice induced vibration.展开更多
To improve surface accuracy of the work-piece and obtain potentially valuable information,a dynamic milling force prediction model was proposed based on data mining.In view of the current dynamic milling force obtaine...To improve surface accuracy of the work-piece and obtain potentially valuable information,a dynamic milling force prediction model was proposed based on data mining.In view of the current dynamic milling force obtained through finite element simulation and analytical calculation,in the finite element modeling,the model built is inevitably different from the actual working conditions,and the analytical calculation is slightly cumbersome and complex,and a dynamic milling force prediction model based on data mining is proposed.The model was established using a combination of regression analysis and Radial Basis Function(RBF) neural network.Using data mining as a means,the internal relationship between milling force,cutting parameters,temperature,vibration and surface quality is deeply analyzed,and the influence of dynamic milling force changes on different situations is extracted and summarized by the methods of cluster analysis and correlation analysis.The results show that the proposed dynamic milling force model has a good prediction effect,ensures the production quality,reduces the occurrence of flutter,improves the surface accuracy of the work-piece,and provides a more accurate basis for the selection of process parameters.展开更多
To study the similitude laws for dynamic ice force model test which is a hot problem in ice mechanics.In this paper,a new modified similitude law for dynamic ice force model test is proposed based on ice-induced virbr...To study the similitude laws for dynamic ice force model test which is a hot problem in ice mechanics.In this paper,a new modified similitude law for dynamic ice force model test is proposed based on ice-induced virbration theory and two reasonable assumptions.And the new law is vertified with an ice-induced pier virbration example.The numerical calculation results show that,firstly,the error of frequency factor between test value and theory value is small as well as that of displacement and velocity;Secondly,the time scale completely meet the similitude relation,the waveforms anastomotic well,and the phenomenon of offset and omit do not occur;Thirdly,as the damping ratio between prototype and model is nearly equal,the improved similitude law will still be applied.Therefore,the new modified similitude law is feasible to study dynamic ice force model test and can provide reference for the ice mechanics.展开更多
Shock absorbers are main elements into construction of train wagons that secure protection from longitudinal forces which appear during transitional regimes of movement. Besides, development of new constructive soluti...Shock absorbers are main elements into construction of train wagons that secure protection from longitudinal forces which appear during transitional regimes of movement. Besides, development of new constructive solutions for shock absorbers is quite popular development of their working mathematical models. This paper presents modem shock absorber with elastic block made from polymer elements that increase quantity of absorbed energy. This is achieved by increasing the stiffness characteristic of polymer elastic block. The construction is relatively simple and technology used to create the construction is with more or less low price. If there is not enough elastic stiffness of the polymer block, there is a possibility for not meeting the UIC （International Union of Railways） norms for absorbed energy. Therefore, according to the mentioned characteristic, shock absorbers are divided into three groups. The mathematical model presented in this paper allows calculating the necessary elastic characteristic of the polymer block for a short time. Differential equation of movement of the shock absorber elements is presented in this paper. Force change of polymer block for various impact velocities participates in the differential equation of movement where initial velocity V0 and the current meaning of the velocity x are taken into consideration. The presented equation is solved by using program language MATLAB/Simulink by developing a simulation model.展开更多
In this paper the author has used the normalized Routh equations[1]to .solve the dynamic problems and establish the general method for. finding out the constraint forces and the variations of the state of motion for t...In this paper the author has used the normalized Routh equations[1]to .solve the dynamic problems and establish the general method for. finding out the constraint forces and the variations of the state of motion for the complicated system.展开更多
基金Foundation item:The work was supported in part by the NSFC(No.90511009).
文摘We consider the two-dimensional stochastic quasi-geostrophic equation ■=1/(R_e)△~2■-r/2△■+f(x,y,t)(1.1) on a regular bounded open domain D ■,where ■ is the stream function,F Froude Number (F≈O(1)),R_e Reynolds number(R_e■10~2),β_0 a positive constant(β_0≈O(10^(-1)),r the Ekman dissipation constant(r≈o(1)),the external forcing term f(x,y,t)=-(dW)/(dt)(the definition of W will be given later)a Gaussian random field,white noise in time,subject to the
文摘Method of testing for dynamic output forces from jet elements is studied, the handwidth is large in testing with this method. By establishing a model of the test system and simulating it, principles of how inherent features of the test system affect the dynamic force test are found out. Thus a theoretical foundation is given for the design and error modification to the actual test system.
基金primarily supported by the National Natural Science Foundation of China(Grant Nos.41375061,41130964 and 41461164008)the National Program on Key Basic Research project(973)(Grant Nos.2013CB430103 and 2012CB417200)the Special Public Sector Research of China(Grant No.GYHY201006004)
文摘The initiation of convective cells in the late morning of 24 June 2010 along the eastward extending ridge of the Dabie Mountains in the Anhui region, China, is studied through numerical simulations that include local data assimilation. A primary convergence line is found over the ridge of the Dabie Mountains, and along the ridge line several locally enhanced convergence centers preferentially initiate convection. Three processes responsible for creating the overall convergence pattern are identified. First, thermally-driven upslope winds induce convergence zones over the main mountain peaks along the ridge, which are shifted slightly downwind in location by the moderate low-level easterly flow found on the north side of a Mei-yu front. Second, flows around the main mountain peaks along the ridge create further convergence on the lee side of the peaks. Third, upslope winds develop along the roughly north-south oriented valleys on both sides of the ridge due to thermal and dynamic channeling effects, and create additional convergence between the peaks along the ridge. The superposition of the above convergence features creates the primary convergence line along the ridge line of the Dabie Mountains. Locally enhanced convergence centers on the primary line cause the initiation of the first convection cells along the ridge. These conclusions are supported by two sensitivity experiments in which the environmental wind （dynamic forcing） or radiative and land surface thermal forcing are removed, respectively. Overall, the thermal forcing effects are stronger than dynamic forcing given the relatively weak environmental flow.
基金supported by Natural Science Foundation of China(52178441)the Scientific Research Projects of the China Academy of Railway Sciences Co.,Ltd.(Grant No.2022YJ043).
文摘Rail weld irregularities are one of the primary excitation sources for vehicle-track interaction dynamics in modern high-speed railways.They can cause significant wheel-rail dynamic interactions,leading to wheel-rail noise,component damage,and deterioration.Few researchers have employed the vehicle-track interaction dynamic model to study the dynamic interactions between wheel and rail induced by rail weld geometry irregularities.However,the cosine wave model used to simulate rail weld irregularities mainly focuses on the maximum value and neglects the geometric shape.In this study,novel theoretical models were developed for three categories of rail weld irregularities,based on measurements of the high-speed railway from Beijing to Shanghai.The vertical dynamic forces in the time and frequency domains were compared under different running speeds.These forces generated by the rail weld irregularities that were measured and modeled,respectively,were compared to validate the accuracy of the proposed model.Finally,based on the numerical study,the impact force due to rail weld irrregularity is modeled using an Artificial Neural Network(ANN),and the optimum combination of parameters for this model is found.The results showed that the proposed model provided a more accurate wheel/rail dynamic evaluation caused by rail weld irregularities than that established in the literature.The ANN model used in this paper can effectively predict the impact force due to rail weld irrregularity while reducing the computation time.
基金support from the National Key Research and Development Program of China(No.2022YFB2502200)the Natural Science Foun-dation of Jiangsu Province(BK20230065)+2 种基金the Key Laboratory of Functional Nano&Soft Materials,the Collaborative Innovation Center of Suzhou Nano Sci-ence&Technology,the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)the 111 Project,Joint International Research Laboratory of Carbon-Based Functional Materials and Devices,Yue Liu acknowledges support from the National Natural Science Foundation of China(22303058)the Natural Science Foundation of Jiangsu Province(BK20230475).
文摘Batteries power numerous technolo-gies,yet higher energy density de-mands push lithium cobalt oxide(Li-CoO_(2)referred as LCO)cathodes to higher voltages,triggering unwanted chemical reactions.In this work,we in-vestigate how carbonate-based elec-trolytes degrade on deeply delithiated LCO surfaces via extensive reactive molecular dynamics simulations.These simulations unveil the forma-tion of characteristic gas products and unstable surface species,which can undermine the cathode structure and reduce battery performance.By examining different solvent composi-tions,the simulations reveal that partial fluorination reduces oxidative degradation and gas evolution,thus offering a route to improve interface stability.Overall,this study provides an atomic-level perspective on preventing unwanted reactions and guiding the design of safer and more robust battery systems for high-voltage applications.
基金supported by the National Basic Research Program of China (Grant No: 2011CB201100)
文摘Hydrocarbon distribution rules in the deep and shallow parts of sedimentary basins are considerably different, particularly in the following four aspects. First, the critical porosity for hydrocarbon migration is much lower in the deep parts of basins： at a depth of 7000 m, hydrocarbons can accumulate only in rocks with porosity less than 5%. However, in the shallow parts of basins （i.e., depths of around 1000 m）, hydrocarbon can accumulate in rocks only when porosity is over 20%. Second, hydrocarbon reservoirs tend to exhibit negative pressures after hydrocarbon accumulation at depth, with a pressure coefficient less than 0.7. However, hydrocarbon reservoirs at shallow depths tend to exhibit high pressure after hydrocarbon accumulation. Third, deep reservoirs tend to exhibit characteristics of oil （-gas）-water inversion, indicating that the oil （gas） accumulated under the water. However, the oil （gas） tends to accumulate over water in shallow reservoirs. Fourth, continuous unconventional tight hydrocarbon reservoirs are distributed widely in deep reservoirs, where the buoyancy force is not the primary dynamic force and the caprock is not involved during the process of hydrocarbon accumulation. Conversely, the majority of hydrocarbons in shallow regions accumulate in traps with complex structures. The results of this study indicate that two dynamic boundary conditions are primarily responsible for the above phenomena： a lower limit to the buoyancy force and the lower limit of hydrocarbon accumulation overall, corresponding to about 10%-12% porosity and irreducible water saturation of 100%, respectively. These two dynamic boundary conditions were used to divide sedimentary basins into three different dynamic fields of hydrocarbon accumulation： the free fluid dynamic field, limit fluid dynamic field, and restrain fluid dynamic field. The free fluid dynamic field is located between the surface and the lower limit of the buoyancy force, such that hydrocarbons in this field migrate and accumulate under the influence of, for example, the buoyancy force, pressure, hydrodynamic force, and capillary force. The hydrocarbon reservoirs formed are characterized as ＂four high,＂ indicating that they accumulate in high structures, are sealed in high locations, migrate into areas of high porosity, and are stored in reservoirs at high pressure. The basic features of distribution and accumulation in this case include hydrocarbon migration as a result of the buoyancy force and formation of a reservoir by a caprock. The limit fluid dynamic field is located between the lower limit of the buoyancy force and the lower limit of hydrocarbon accumulation overall; the hydrocarbon migrates and accumulates as a result of, for example, the molecular expansion force and the capillary force. The hydrocarbon reservoirs formed are characterized as ＂four low,＂ indicating that hydrocarbons accumulate in low structures, migrate into areas of low porosity, and accumulate in reservoirs with low pressure, and that oil（-gas）-water inversion occurs at low locations. Continuous hydrocarbon accumulation over a large area is a basic feature of this field. The restrain fluid dynamic field is located under the bottom of hydrocarbon accumulation, such that the entire pore space is filled with water. Hydrocarbons migrate as a result of the molecular diffusion force only. This field lacks many of the basic conditions required for formation of hydrocarbon reservoirs： there is no effective porosity, movable fluid, or hydrocarbon accumulation, and potential for hydrocarbon exploration is low. Many conventional hydrocarbon resources have been discovered and exploited in the free fluid dynamic field of shallow reservoirs, where exploration potential was previously considered to be low. Continuous unconventional tight hydrocarbon resources have been discovered in the limit fluid dynamic field of deep reservoirs; the exploration potential of this setting is thought to be tremendous, indicating that future exploration should be focused primarily in this direction.
基金Under the auspices of National Program on Key Basic Research Project(No.2013CB430401)
文摘Reclamation is one of the fastest-growing land use type developed in coastal areas and has caused degradation and loss of coastal wetlands as well as serious environmental problems. This paper was aimed at monitoring the spatiotemporal patterns of coastal wetlands and reclamation in the Yangtze Estuary during the 1960s and 2015. Satellite images obtained from 1980 to 2015 and topography maps of the 1960 s were employed to extract changes of reclamation and coastal wetlands. Area-weight centroids were calculated to identify the movement trend of reclamation and coastal wetlands. The results show that from the 1960 s to 2015, the net area of natural wetlands declined by 574.3 km^2, while man-made wetlands and reclamation increased by 553.6 and 543.9 km^2, respectively. During the five study phases, the fastest areal change rate natural wetlands was –13.3 km^2/yr in the period of 1990–2000, and that of man-made areas was 24.7 km^2/yr in the same period, and the areal change rate of reclamation was 27.6 km^2/yr in the period of 2000–2010. Conversion of coastal wetlands mainly occurred in the Chongming Island, Changshu City and the east coast of Shanghai Municipality. Reclamation was common across coastal areas, and was mainly attributed to settlement and man-made wetlands in the Chongming Island, Lianyungang City and the east coast of Shanghai Municipality. Natural wetlands turned into farmlands and settlement, and man-made wetlands gained from reclamation of farmlands. The centroid of natural wetlands generally moved towards the sea, man-made wetlands expanded equally in all directions and inland, and the centroid of reclamation migrated toward Shanghai Municipality. Sea level rise, erosion-deposition changes, and reclamation activities together determine the dynamics of the Yangtze Estuary wetlands. However, reclamation activities for construction of ports, industries and aquaculture are the key causes for the dynamics. The results from this study on the dynamics of coastal wetlands and reclamation are valuable for local government to put forward sustainable land use and land development plans.
基金The authors are grateful for Ph.D.Scholarship funding support from Brunel University London and the UKEPSRC.
文摘In current precision and ultraprecision machining practice,the positioning and control of actuation systems,such as slideways and spindles,are heavily dependent on the use of linear or rotary encoders.However,positioning control is passive because of the lack of direct monitoring and control of the tool and workpiece positions in the dynamic machining process and also because it is assumed that the machining system is rigid and the cutting dynamics are stable.In ultraprecision machining of freeform surfaces using slow tool servo mode in particular,however,account must be taken of the machining dynamics and dynamic synchronization of the cutting tool and workpiece positioning.The important question also arises as to how ultraprecision machining systems can be designed and developed to work better in this application scenario.In this paper,an innovative dynamics-oriented engineering approach is presented for ultraprecision machining of freeform surfaces using slow tool servo mode.The approach is focused on seamless integration of multibody dynamics,cutting forces,and machining dynamics,while targeting the positioning and control of the tool–workpiece loop in the machining system.The positioning and motion control between the cutting tool and workpiece surface are further studied in the presence of interfacial interactions at the tool tip and workpiece surface.The interfacial cutting physics and dynamics are likely to be at the core of in-process monitoring applicable to ultraprecision machining systems.The approach is illustrated using a virtual machining system developed and supported with simulations and experimental trials.Furthermore,the paper provides further explorations and discussion on implementation perspectives of the approach,in combination with case studies,as well as discussing its fundamental and industrial implications.
基金provided by the National Basic Research Program of China (No. 2010CB226802)the Fundamental Research Funds for the Central Universities (No. 2010YZ02)the State Key Laboratory of Coal Resources and Safe Mining (No.SKLCRSM 10B08)
文摘The support of coal roadways is seriously affected by intense dynamic pressures.This can lead to problems with large deformation of the roof and the two side walls of coal roadways.Rapid convergence of the walls and roof,a high damage rate to the bolts and cables,or even abrupt roof collapse or rib spalling can occur during the service period of these coal roadways.Analyzing the main support measures used in China leads to a proposed new cable truss supporting system.Thorough study of the entire structure shows the superiority of this design for roadways suffering under dynamic pressure.A corresponding mechanical model of the rock surrounding the cable truss system is described in this paper and formulas for calculating pre-tightening forces of the truss cable,and the minimum anchoring forces,were deduced.The new support system was applied to a typical roadway affected by intensive dynamic pressure that is located in the Xinyuan Coal Mine.The results show that the largest subsidence of the roof was 97 mm,the convergence of the two sides was less than 248 mm,and the average depth of the loose,fractured layer was only 6.12 mm.This proves that the new support system is feasible and effective.
基金Selected from Proceedings of the 7th International Conference on Frontiers of DesignManufacturing(ICFDM'2006).
文摘It has been found that the brittle material, monocrystalline silicon, can be machined in ductile mode in nanoscale cutting when the tool cutting edge radius is reduced to nanoscale and the undeformed chip thickness is smaller than the tool edge radius. In order to better understand the mechanism of ductile mode cutting of silicon, the molecular dynamics （MD） method is employed to simulate the nanoscale cutting of monocrystalline silicon. The simulated variation of the cutting forces with the tool cutting edge radius is compared with the cutting force results from experimental cutting tests and they show a good agreement. The results also indicate that there is silicon phase transformation from monocrystalline to amorphous in the chip formation zone that can be used to explain the cause of ductile mode cutting. Moreover, from the simulated stress results, the two necessary conditions of ductile mode cutting, the tool cutting edge radius are reduced to nanoscale and the undeformed chip thickness should be smaller than the tool cutting edge radius, have been explained.
基金the National Natural Science Foundation of China(No.51579147)
文摘The roll motions are influenced by significant viscous effects such as the flow separation.The 3D simulations of free decay roll motions for the ship model DTMB 5512 are carried out by Reynold averaged NavierStokes(RANS) method based on the dynamic mesh technique.A new moving mesh technique is adopted and discussed in details for the present simulations.The purpose of the research is to obtain accurate numerical prediction for roll motions with their respective numerical/modeling errors and uncertainties.Errors and uncertainties are estimated by performing the modern verification and validation(V&V) procedures.Simulation results for the free-floating surface combatant are used to calculate the linear,nonlinear damping coefficients and resonant frequencies including a wide range of forward speed.The present work can provide a useful reference to calculate roll damping by computational fluid dynamics(CFD) method and simulate a general ship motions in waves.
文摘The axial magnetic force, induced by the complicated flux linkage distribution from rotor magnet and stator slotted, is constructed by different relative heights and calculated by 3D finite element method (FEM) to analyze the dynamic characteristics for a DVD spindle motor. The axial magnetic force is designed to provide an axial stiffness, and govern the natural frequency of the dynamic performance. According to the simulation results and experimental measurements, the dynamic behaviors are significantly improved with a variation of relative height of rotor magnet and stator slotted on a DVD spindle motor.
基金National Hi-tech Research and Development Program of China(863 Program,No.2001AA42330).
文摘Negative step response experimental method is used in wrist force sensor＇s dynamic performance calibration. The exciting manner of negative step response method is the same as wrist force sensor＇s load in working. This experimental method needn＇t special experiment equipments. Experiment＇s dynamic repeatability is good. So wrist force sensor＇s dynamic performance is suitable to be calibrated by negative step response method. A new correlation wavelet transfer method is studied. By wavelet transfer method, the signal is decomposed into two dimensional spaces of time-frequency. So the problem of negative step exciting energy concentrating in the low frequency band is solved. Correlation wavelet transfer doesn＇t require that wavelet primary function be orthogonal and needn＇t wavelet reconstruction. So analyzing efficiency is high. An experimental bench is designed and manufactured to load the wrist force sensor orthogonal excitation force/moment. A piezoelectric force sensor is used to setup soft trigger and calculate the value of negative step excitation. A wrist force sensor is calibrated. The pulse response function is calculated after negative step excitation and step response have been transformed to positive step excitation and step response. The pulse response function is transferred to frequency response function. The wrist force sensor＇s dynamic characteristics are identified by the frequency response function.
基金Project(51075350)supported by the National Natural Science Foundation of China
文摘Based on electromagnetics and mechanics, electromechanical coupled dynamic equations for the drive were developed. Using method of perturbation, free vibrations of the mechanical system under electric disturbance were investigated. The forced responses of the mechanical system to mechanical excitation under electric disturbance were also presented. It is known that for the system with electric disturbance, as time grows, beat occurs. When electric disturbing frequency is near to the natural frequencies of the mechanical system or their integer multiple, resonance vibrations occur. The forced responses of the mechanical system to mechanical excitation under electric disturbance are compound vibrations decided by mechanical excitation, electric disturbance and parameters of the system. The coupled resonance vibration caused by electric disturbance and mechanical excitation was discussed as well. The conditions under which above coupled resonance occurs were presented. The results show that when the difference of the excitation frequency and the perturbation frequency is equal to some order of natural frequency, coupled resonance vibrations occur.
基金funded by National Natural Science Foundation of China under Grant No.52205009Natural Science Foundation of Jiangsu Province under Grant No.BK20210233Open Foundation of the State Key Laboratory of Fluid Power and Mechatronic Systems.
文摘With the aid of different types of mechanoreceptors,human is capable of perceiving stimuli from surrounding environments and manipulating various objects dexterously.In this paper,a bio-inspired tactile fingertip is designed mimicking human fingertip in both structures and functionalities.Two pairs of strain gages and(Polyvinylidene Fluoride)PVDF films are perpendicularly arranged to simulate the Fast-Adapting(FA)and Slowly Adapting(SA)type mechanoreceptors in human hands,while silicones,Polymethyl Methacrylate(PMMA),and electronic wires are applied to mimic the skin,bone and nerve fibers.Both static and dynamic forces can be perceived sensitively.A preprocessing electric circuit is further designed to transform the resistor changes into voltages,and then filter and amplify the four-channel signals.In addition to strong robustness due to the embedded structure,the developed fingertip is found sensitive to deformations via a force test experiment.Finally,two robotic experiments explore its recognition ability of contact status and object surface.Excellent performance is found with high accuracy of 99.72%achieved in discriminating six surfaces that are ubiquitous in daily life,which demonstrates the effectiveness of our designed tactile sensor.
基金This Project is financially supported by National Natural Foundation of China
文摘Spectrum and self-excite characters are the two significant characters of the dynamics of sea ice. The spectrum character of sea ice is mainly shown by the spectrum of ice force. The spectrum character of the sea ice is its intrinsic attributes. When the spectrum of ice force from the dynamic response of ice and structure interaction are evaluated, the effect of dynamic character of the structure must be eliminated. In this paper, the ice force spectrum at Bohai Bay and Liaodong Bay is evaluated from the displacement and strain responses of a single degree and a multi-degree freedom structure. The evaluated ice force spectrum can be used to define the spectrum character of ice in the analysis of ice induced vibration.
基金Supported by Gansu Science and Technology Program(21YF5GA080)。
文摘To improve surface accuracy of the work-piece and obtain potentially valuable information,a dynamic milling force prediction model was proposed based on data mining.In view of the current dynamic milling force obtained through finite element simulation and analytical calculation,in the finite element modeling,the model built is inevitably different from the actual working conditions,and the analytical calculation is slightly cumbersome and complex,and a dynamic milling force prediction model based on data mining is proposed.The model was established using a combination of regression analysis and Radial Basis Function(RBF) neural network.Using data mining as a means,the internal relationship between milling force,cutting parameters,temperature,vibration and surface quality is deeply analyzed,and the influence of dynamic milling force changes on different situations is extracted and summarized by the methods of cluster analysis and correlation analysis.The results show that the proposed dynamic milling force model has a good prediction effect,ensures the production quality,reduces the occurrence of flutter,improves the surface accuracy of the work-piece,and provides a more accurate basis for the selection of process parameters.
基金Sponsored by the National Natural Science Foundation of China(Grant No.50678033)
文摘To study the similitude laws for dynamic ice force model test which is a hot problem in ice mechanics.In this paper,a new modified similitude law for dynamic ice force model test is proposed based on ice-induced virbration theory and two reasonable assumptions.And the new law is vertified with an ice-induced pier virbration example.The numerical calculation results show that,firstly,the error of frequency factor between test value and theory value is small as well as that of displacement and velocity;Secondly,the time scale completely meet the similitude relation,the waveforms anastomotic well,and the phenomenon of offset and omit do not occur;Thirdly,as the damping ratio between prototype and model is nearly equal,the improved similitude law will still be applied.Therefore,the new modified similitude law is feasible to study dynamic ice force model test and can provide reference for the ice mechanics.
文摘Shock absorbers are main elements into construction of train wagons that secure protection from longitudinal forces which appear during transitional regimes of movement. Besides, development of new constructive solutions for shock absorbers is quite popular development of their working mathematical models. This paper presents modem shock absorber with elastic block made from polymer elements that increase quantity of absorbed energy. This is achieved by increasing the stiffness characteristic of polymer elastic block. The construction is relatively simple and technology used to create the construction is with more or less low price. If there is not enough elastic stiffness of the polymer block, there is a possibility for not meeting the UIC （International Union of Railways） norms for absorbed energy. Therefore, according to the mentioned characteristic, shock absorbers are divided into three groups. The mathematical model presented in this paper allows calculating the necessary elastic characteristic of the polymer block for a short time. Differential equation of movement of the shock absorber elements is presented in this paper. Force change of polymer block for various impact velocities participates in the differential equation of movement where initial velocity V0 and the current meaning of the velocity x are taken into consideration. The presented equation is solved by using program language MATLAB/Simulink by developing a simulation model.
文摘In this paper the author has used the normalized Routh equations[1]to .solve the dynamic problems and establish the general method for. finding out the constraint forces and the variations of the state of motion for the complicated system.
