Multi-Body Dynamics Modeling of Heavy Goods Vehicle-Rail Interaction

Based on the principle of vehicle-track coupling dynamics, SIMPACK multi-body dynamics software is used to establish a C80 wagon line-coupled multi-body dynamics model with 73 degrees of freedom. And the reasonableness of the line-coupled dynamics model is verified by using the maximum residual acceleration, the nonlinear critical speed of the wagon. The experimental results show that the established vehicle line coupling dynamics model meets the requirements of vehicle line coupling dynamics modeling.

Dynamics of perinuclear actin ring regulating nuclear morphology

Cells are capable of sensing and responding to the extracellular mechanical microenvironment via the actin skeleton.In vivo,tissues are frequently subject to mechanical forces,such as the rapid and significant shear flow encountered by vascular endothelial cells.However,the investigations about the transient response of intracellular actin networks under these intense external mechanical forces,their intrinsic mechanisms,and potential implications are very limited.Here,we observe that when cells are subject to the shear flow,an actin ring structure could be rapidly assembled at the periphery of the nucleus.To gain insights into the mechanism underlying this perinuclear actin ring assembly,we develop a computational model of actin dynamics.We demonstrate that this perinuclear actin ring assembly is triggered by the depolymerization of cortical actin,Arp2/3-dependent actin filament polymerization,and myosin-mediated actin network contraction.Furthermore,we discover that the compressive stress generated by the perinuclear actin ring could lead to a reduction in the nuclear spreading area,an increase in the nuclear height,and a decrease in the nuclear volume.The present model thus explains the mechanism of the perinuclear actin ring assembly under external mechanical forces and suggests that the spontaneous contraction of this actin structure can significantly impact nuclear morphology.

Machine learning molecular dynamics simulations of liquid methanol

As the simplest hydrogen-bonded alcohol,liquid methanol has attracted intensive experimental and theoretical interest.However,theoretical investigations on this system have primarily relied on empirical intermolecular force fields or ab initio molecular dynamics with semilocal density functionals.Inspired by recent studies on bulk water using increasingly accurate machine learning force fields,we report a new machine learning force field for liquid methanol with a hybrid functional revPBE0 plus dispersion correction.Molecular dynamics simulations on this machine learning force field are orders of magnitude faster than ab initio molecular dynamics simulations,yielding the radial distribution functions,selfdiffusion coefficients,and hydrogen bond network properties with very small statistical errors.The resulting structural and dynamical properties are compared well with the experimental data,demonstrating the superior accuracy of this machine learning force field.This work represents a successful step toward a first-principles description of this benchmark system and showcases the general applicability of the machine learning force field in studying liquid systems.

Spatial-temporal Dynamics and Driving Forces of Land Development Intensity in the Western China from 2000 to 2015

The change in land development intensity is an important perspective to reflect the variation in regional social and economic development and spatial differentiation.In this paper,spatial statistical analysis,Ordinary Least Squares(OLS),and Geographically weighted regression(GWR)methods are used to systematically analyse the spatial-temporal characteristics and driving forces of land development intensity for 131 spatial units in the western China from 2000 to 2015.The findings of the study are as follows:1)The land development intensity in the western China has been increasing rapidly.From 2000 to 2015,land development intensity increased by 3.4 times on average.2)The hotspot areas have shifted from central Inner Mongolia,northern Shaanxi and the Beibu Gulf of Guangxi to the Guanzhong Plain and the Chengdu-Chongqing urban agglomeration.The areas of cold spots were mainly concentrated in the Qinghai-Tibet Plateau,Yunnan,and Xinjiang.3)Investment intensity and the natural environment have always been the main drivers of land development intensity in the western China.Investment played a powerful role in promoting land development intensity,while the natural and ecological environment distinctly constrained such development.The effect of the economic factors on land development intensity in the western China has changed,which is reflected in the driving factor of construction land development shifting from economic growth in 2000 to economic structure,especially industrial structure,in 2015.

DYNAMICS OF SANDY DESERTIFICATION AND ITS DRIVING FORCES IN WESTERN JILIN PROVINCE

By establishing the interpreting elements, and applying supervised classification, the sandy desertific- ation was interpreted and the desertified land areas of the counties in the western Jilin Province in 1986 and in 2000 were obtained. Taking Tongyu and Qian’an as examples, the natural driving forces and man-made driving forces were analyzed. The paper comes the conclusions that the material sources and the warming and dry climate are the internal causes of potential land desertification; the irrational human activities, such as destroying forest and reclaiming the grassland, are the external causes of potential land desertification; while more rational human activities, such as planting trees and restoring grassland can reverse the land desertification. Furthermore, the countermeasures and suggestions for the development of agriculture and animal husbandry in the western Jilin Province are put forward.

Dynamic response in two-dimensional transversely isotropic thick plate with spatially varying heat sources and body forces

This paper deals with a two-dimensional （2D） problem for a transverselyisotropic thick plate having heat sources and body forces. The upper surface of the plate is stress free with the prescribed surface temperature, while the lower surface of the plate rests on a rigid foundation and is thermally insulated. The study is carried out in the context of the generalized thermoelasticity proposed by Green and Naghdi. The governing equations for displacement and temperature fields are obtained in the Laplace-Fourier transform domain by applying the Laplace and Fourier transforms. The inversion of the double transform is done numerically. Numerical inversion of the Laplace transform is done based on the Fourier series expansion. Numerical computations are carried out for magnesium （Mg）, and the results are presented graphically. The results for an isotropic material （Cu） are obtained numerically and presented graphically to be compared with those of a transversely isotropic material （Mg）. The effect of the body forces is also studied.

Mean Forces in Quantum Molecular Dynamics

Analytical forces are derived from Skyrme-type potentials.Comparisons aremade between the calculations by analytical formula and by difference method on po-tentials.Application of the analytical mean forces can save much CPU time and raisethe calculation accuracy.

Method of Testing of Dynamic Forces on Digital Jet Elements

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.

Dynamic Characteristics and Driving Forces of Wetland Landscapes in Northeast China

Dynamic characteristics and spatial-temporal distribution patterns of wetland landscapes in northeast China from 1986 to 2000 were quantitatively analyzed and studied by applying theories and methods of landscape ecology,Land Change Science,remote sensing and GIS techniques.Through analyzing the dynamic spatial-temporal change degree,direction and pattern of wetland within the study area,as well as the characteristics of landscape pattern change and landscape transformation,this study got the following results:area and patch amount of wetland in northeast China showed a decreasing trend as a whole in the past 15 years.In terms of dynamic landscape changes,although the annual decrease rate of the last 5 years was 28 times more than that of the first 10 years,the first 10 years was a period with relatively more drastic patch changes of wetland landscapes in northeast China.By reviewing the overall changes of wetland landscapes in northeast China,the following characteristics were summarized:expanding in certain periods but decreasing in the overall trend,shrinking in parts but expanding from boundaries,showing high fragmentation and so on.Study on its driving forces showed that a unique spatial pattern of wetland landscapes was formed with the dual intervention of natural and artificial factors.

A strategy for lightweight designing of a railway vehicle car body including composite material and dynamic structural optimization

Rolling stock manufacturers are finding structural solutions to reduce power required by the vehicles,and the lightweight design of the car body represents a possible solution.Optimization processes and innovative materials can be combined in order to achieve this goal.In this framework,we propose the redesign and optimization process of the car body roof for a light rail vehicle,introducing a sandwich structure.Bonded joint was used as a fastening system.The project was carried out on a single car of a modern tram platform.This preliminary numerical work was developed in two main steps:redesign of the car body structure and optimization of the innovated system.Objective of the process was the mass reduction of the whole metallic structure,while the constraint condition was imposed on the first frequency of vibration of the system.The effect of introducing a sandwich panel within the roof assembly was evaluated,focusing on the mechanical and dynamic performances of the whole car body.A mass saving of 63%on the optimized components was achieved,corresponding to a 7.6%if compared to the complete car body shell.In addition,a positive increasing of 17.7%on the first frequency of vibration was observed.Encouraging results have been achieved in terms of weight reduction and mechanical behaviour of the innovated car body.

Landscape pattern dynamics of water body in Kaifeng city in the 20th century

Landscape spatial pattern mainly refers to the distribution of patches, which are different in size and shape in space owing to the interaction of various ecological activities. In landscape ecology study, landscape pattern has been one of the key study areas. Water body landscape plays an important role in the development history of a city, but at present city water body landscape in many cities has been destroyed, hence protecting water body in the city is becoming more and more important. In order to protect city water body landscape reasonably, the precondition is to probe the dynamics of water body landscape. Based on historical data and remote sensing data, six indexes including patch number, patch area, landscape dominance index, fractal dimension, patch density and connectivity index etc. were used to analyze landscape pattern dynamics of water body in Kaifeng city since the end of the Qing Dynasty (in the 20th century). The results showed: (1) Since the end of the Qing Dynasty, landscape area of water body in Kaifeng city increased first and then decreased from 1898 to 2002AD; the landscape dominant degree had the same changing tendency with the area. (2) Patch number of water body landscape in Kaifeng city had an increase from 1898 to 2002, but maximum area of patch, minimum area of patch and average area of patch decreased, which resulted in an increase in landscape fragment degree. (3) Connectivity index decreased and fractal dimension increased from 1898 to 2002. The reasons for these changes were the repeated overflows and flooding of the Yellow River and the influence of human activities.

A comprehensive comparative investigation of frictional force models for dynamics of rotor−bearing systems

Vibrations of a rotor-bearing system(RBS)can be affected by the frictional forces between the components of the inherent bearings.Thus,an in-depth investigation of the influences of the frictional moments of the bearings on the vibrations of the RBS can be helpful for understanding the vibration mechanisms in the rotating machinery.In this study,an improved dynamic model of a RBS considering different frictional force models is presented.A comparative investigation on the influences of the empirical and analytical frictional force models on the vibration characteristics of the RBS is proposed.The empirical frictional force models include Palmgren’s and SKF’s models.The analytical frictional force model considers the rolling friction caused by the radial elastic material hysteresis,slipping friction between the ball and races,viscosity friction caused by the lubricating oil,and contact friction between the ball and cage.The influences of the external load and rotational speed on the vibrations of the RBS are analyzed.The comparative results show that the analytical frictional force model can give a more reasonable method for formulating the effects of the friction forces in the bearings on the vibrations of the RBS.The results also demonstrate that the friction forces in the bearings can significantly affect the vibrations of the RBSs.

Effects of unsteady deformation of flapping wing on its aerodynamic forces

Effects of unsteady deformation of a＇flapping model insect wing on its aerodynamic force production are studied by solving the Navier-Stokes equations on a dynamically deforming grid. Aerodynamic forces on the flapping wing are not much affected by considerable twist, but affected by camber deformation. The effect of combined camber and twist deformation is similar to that of camber deformation. With a deformation of 6% camber and 20% twist （typical values observed for wings of many insects）, lift is increased by 10% - 20% and lift-to-drag ratio by around 10% compared with the case of a rigid fiat-plate wing. As a result, the deformation can increase the maximum lift coefficient of an insect, and reduce its power requirement for flight. For example, for a hovering bumblebee with dynamically deforming wings （6% camber and 20% twist）, aerodynamic power required is reduced by about 16% compared with the case of rigid wings.

EXACT SOLUTION TO THE PROBLEM OF A HALF-PLANE CRACK IN A TRANSVERSELY ISOTROPIC PIEZOELECTRIC BODY SUBJECTED TO ANTISYMMETRIC TANGENTIAL POINT FORCES

An exact and complete solution of the problem of a half-planecrack in an infinite transversely isotropic piezoelectric body ispresented. The upper and lower crack faces are assumed to be loadedantisym- metrically by a couple of tangential point forces inopposite directions. The solution is derived through a lim- itingprocedure from that of a penny-shaped crack. The expressions for theelectroelastic field are given in terms of elementary functions.Finally, the numerical results of the second and third mode stressintensity factors k_2 and k_3 of piezoelectric materials and elasticmaterials are compared in figures.

Improving Simulations of Vegetation Dynamics over the Tibetan Plateau:Role of Atmospheric Forcing Data and Spatial Resolution

The efficacy of vegetation dynamics simulations in offline land surface models(LSMs)largely depends on the quality and spatial resolution of meteorological forcing data.In this study,the Princeton Global Meteorological Forcing Data(PMFD)and the high spatial resolution and upscaled China Meteorological Forcing Data(CMFD)were used to drive the Simplified Simple Biosphere model version 4/Top-down Representation of Interactive Foliage and Flora Including Dynamics(SSiB4/TRIFFID)and investigate how meteorological forcing datasets with different spatial resolutions affect simulations over the Tibetan Plateau(TP),a region with complex topography and sparse observations.By comparing the monthly Leaf Area Index(LAI)and Gross Primary Production(GPP)against observations,we found that SSiB4/TRIFFID driven by upscaled CMFD improved the performance in simulating the spatial distributions of LAI and GPP over the TP,reducing RMSEs by 24.3%and 20.5%,respectively.The multi-year averaged GPP decreased from 364.68 gC m^(-2)yr^(-1)to 241.21 gC m^(-2)yr^(-1)with the percentage bias dropping from 50.2%to-1.7%.When using the high spatial resolution CMFD,the RMSEs of the spatial distributions of LAI and GPP simulations were further reduced by 7.5%and 9.5%,respectively.This study highlights the importance of more realistic and high-resolution forcing data in simulating vegetation growth and carbon exchange between the atmosphere and biosphere over the TP.

Poroelastodynamic responses and elastic moduli of a transversely isotropic porous cylinder under forced deformation test

Existing transversely isotropic poroelastodynamics solutions are limited to infinite domains and without experimental validation. Furthermore, there is a lack of analytical simulations for the elastic moduli dispersion of fluid-saturated porous cylinders. To address these three limitations and investigate the mechanisms of moduli dispersion, we present the analytical solutions of the poromechanical responses and the elastic moduli dispersion of a transversely isotropic, fluid-saturated, finite porous cylinder subjected to a forced deformation test. Through an example, we demonstrate the effects of loading frequency, boundary conditions, and material's anisotropy, dimension, and permeability on the responses of pore pressure,force, displacement, and dynamic elastic moduli of the cylinder. The specimen's responses are significantly influenced by the frequency of the applied load, resulting in a drained state at low frequencies and an undrained state at high frequencies. At high frequencies, the sample behaves identically for an open or a closed lateral boundary, and permeability has insignificant effects. The dynamic elastic moduli are mainly controlled by the loading frequency and the ratio of the sample's radius to its height. Lastly,we show excellent matches between the newly derived analytical solution and laboratory measurements on one clay and two shale samples from Mont Terri.

A New Dynamics Analysis Model for Five-Axis Machining of Curved Surface Based on Dimension Reduction and Mapping

The equipment used in various fields contains an increasing number of parts with curved surfaces of increasing size.Five-axis computer numerical control(CNC)milling is the main parts machining method,while dynamics analysis has always been a research hotspot.The cutting conditions determined by the cutter axis,tool path,and workpiece geometry are complex and changeable,which has made dynamics research a major challenge.For this reason,this paper introduces the innovative idea of applying dimension reduction and mapping to the five-axis machining of curved surfaces,and proposes an efficient dynamics analysis model.To simplify the research object,the cutter position points along the tool path were discretized into inclined plane five-axis machining.The cutter dip angle and feed deflection angle were used to define the spatial position relationship in five-axis machining.These were then taken as the new base variables to construct an abstract two-dimensional space and establish the mapping relationship between the cutter position point and space point sets to further simplify the dimensions of the research object.Based on the in-cut cutting edge solved by the space limitation method,the dynamics of the inclined plane five-axis machining unit were studied,and the results were uniformly stored in the abstract space to produce a database.Finally,the prediction of the milling force and vibration state along the tool path became a data extraction process that significantly improved efficiency.Two experiments were also conducted which proved the accuracy and efficiency of the proposed dynamics analysis model.This study has great potential for the online synchronization of intelligent machining of large surfaces.

Driving forces and their relative contributions to hydrocarbon expulsion from deep source rocks: A case of the Cambrian source rocks in the Tarim Basin

To thoroughly understand the dynamic mechanism of hydrocarbon expulsion from deep source rocks,in this study,five types of hydrocarbon expulsion dynamics(thermal expansion,hydrocarbon diffusion,compaction,product volume expansion,and capillary pressure difference(CPD))are studied.A model is proposed herein to evaluate the relative contribution of different dynamics for hydrocarbon expulsion using the principle of mass balance,and the model has been applied to the Cambrian source rocks in the Tarim Basin.The evaluation results show that during hydrocarbon expulsion from the source rocks,the relative contribution of CPD is the largest(>50%),followed by compaction(10%-40%),product volume expansion(5%-30%),and thermal expansion(2%-20%).The relative contribution of diffusion to hydrocarbon expulsion is minimal(<10%).These results demonstrate that CPD plays an important role in the hydrocarbon expulsion process of deep source rocks.The hydrocarbon expulsion process of source rocks can be categorized into three stages based on the contribution of different dynamics to the process:the first stage is dominated by compaction and diffusion to expel hydrocarbons,the second stage is dominated by product volume expansion and CPD,and the third stage is dominated by product volume expansion and CPD.This research offers new insights into hydrocarbon exploration in tight oil and gas reservoirs.

Dynamic performance of six-axle locomotive subjected to asymmetric brake shoe forces

To research the influence of asymmetric brake shoe forces(ABSF)induced by braking failure on the dynamic performance of six-axle locomotive,the static equilibrium model of three-axle bogie and dynamic model for locomotive are established.The coupling vibration equations of axle hung motor and wheelset are derived.For the air braking,the influence mechanism of ABSF on the wheel-rail asymmetric motion and force characteristics are discussed.It can be found that if the ABSF is applied in the front wheelset,all the wheelsets move laterally in the same direction.Once the ABSF occurs in the middle or rear one,other wheelsets may move laterally towards the opposite direction.The motion amplitude and direction of all wheelsets strictly depend on the resultant moment of suspension yawing moment and brake shoe asymmetric moment.For the asymmetric braking,the free lateral gap of axle-box could increase the wheelset motion amplitude,but could not change the moving direction.In both the straight line and curve,the ABSF may lead to wheelset misaligning motion,intensify the wheel-rail lateral dynamic interaction and deteriorate wheel-rail contact state.Especially for the steering wheelsets,the asymmetric braking increases the wheelset attack angle significantly,which forms the worst braking condition.

The influence of AAR coupler features on estimation of in-train forces

Inadequate management of large in-train forces transferred through coupler systems of a railway train leads to running and structural failures of vehicles.Understanding these phenomena and their mitigation requires accurate estimation of relative motions and in-train forces between vehicle bodies.Previous numerical studies have ignored inertia of coupling elements and the impacts between couplers.Thus,existing models underestimate the additional dynamic variations in in-train forces.Detailed multi-body dynamic models of two AAR(Association of American Railroads)coupler systems used in passenger and freight trains are developed,incorporating coupler inertia and various slacks.Due to the modeling and simulation com-plexities involved in a full train model,with such details of coupler system,actual longitudinal train dynamics is not studied.A system comprising only two coupling units,inter-connecting two consecutive vehicles,is modeled.Considered system has been fixed at one end and an excitation force is applied at the other end,to mimic a relative force transmission through combined coupler system.Simulation results obtained from this representative system show that,noticeable influence in in-train forces are expected due to the combined effect of inertia of couplers and intermittent impacts between couplers in the slack regime.Maximum amplitude of longitudinal reaction force,transferred from draft gear housing to vehicle body,is expected to be significantly higher than that predicted using existing models of coupler system.It is also observed that the couplers and knuckles are subjected to significant longitudinal and lateral contact forces,due to the intermittent impacts between couplers.Thus,accurate estimation of draft gear reaction force and impact forces between couplers are essential to design vehicle and coupler components,respectively.