A rigid-flexible coupling finite element model of coupler for analyzing train instability behavior during collision

Rail vehicles generate huge longitudinal impact loads in collisions.If unreasonable matching exists between the compressive strength of the intermediate coupler and the structural strength of the car body,the risk of car body structure damage and train derailment will increase.Herein,a four-stage rigid-flexible coupling finite element model of the coupler is established considering the coupler buckling load.The influence of the coupler buckling load on the train longitudinal-vertical-hori-zontal buckling behavior was studied,and the mechanism of the train horizontal buckling instability in train collisions was revealed.Analysis results show that an intermediate coupler should be designed to ensure that the actual buckling load is less than the compressive load when the car body structure begins to deform plastically.The actual buckling load of the coupler and the asymmetry of the structural strength of the car body in the lateral direction are two important influencing factors for the lateral buckling of a train collision.If the strength of the two sides of the car body structure in the lateral direction is asymmetrical,the deformation on the weaker side will be larger,and the end of the car body will begin to deflect under the action of the coupler force,which in turn causes the train to undergo sawtooth buckling.

Numerical Modelling of Coupled Heat and Mass Transfer in Porous Materials: Application to Cinder Block Bricks

In this work, we present numerical modelling of coupled heat and mass transfer within porous materials. Our study focuses on cinder block bricks generally used in building construction. The material is assumed to be placed in air. Moisture content and temperature have been chosen as the main transfer drivers and the equations governing these transfer drivers are based on the Luikov model. These equations are solved by an implicit finite difference scheme. A Fortran code associated with the Thomas algorithm was used to solve the equations. The results show that heat and mass transfer depend on the temperature of the air in contact with the material. As this air temperature rises, the temperature within the material increases, and more rapidly at the material surface. Also, thermal conductivity plays a very important role in the thermal conduction of building materials and influences heat and mass transfer in these materials. Materials with higher thermal conductivity diffuse more heat.

Finite-difference model of land subsidence caused by cluster loads in Zhengzhou,China

Groundwater exploitation has been regarded as the main reason for land subsidence in China and thus receives considerable attention from the government and the academic community.Recently,building loads have been identified as another important factor of land subsidence,but researches in this sector have lagged.The effect of a single building load on land subsidence was neglected in many cases owing to the narrow scope and the limited depth of the additional stress in stratum.However,due to the superposition of stresses between buildings,the additional stress of cluster loads is greater than that of a single building load under the same condition,so that the land subsidence caused by cluster loads cannot be neglected.Taking Shamen village in the north of Zhengzhou,China,as an example,a finite-difference model based on the Biot consolidation theory to calculate the land subsidence caused by cluster loads was established in this paper.Cluster loads present the characteristics of large-area loads,and the land subsidence caused by cluster loads can have multiple primary consolidation processes due to the stress superposition of different buildings was shown by the simulation results.Pore water migration distances are longer when the cluster loads with high plot ratio are imposed,so that consolidation takes longer time.The higher the plot ratio is,the deeper the effective deformation is,and thus the greater the land subsidence is.A higher plot ratio also increases the contribution that the deeper stratigraphic layers make to land subsidence.Contrary to the calculated results of land subsidence caused by cluster loads and groundwater recession,the percentage of settlement caused by cluster loads in the total settlement was 49.43%and 55.06%at two simulated monitoring points,respectively.These data suggest that the cluster loads can be one of the main causes of land subsidence.

3D numerical simulation in acoustic-elastic coupled media with staggered-grid finite-difference method

Acoustic-elastic coupled media is often encountered in most marine explorations, and accurate simulation of acoustic-elastic coupled media is of great significance. At present, the study of acoustic-elastic coupled media still assumes that the solid of the acoustic-elastic coupled media is isotropic, but this assumption is not in accordance with the actual situation. In this paper, we derive the solid media of acoustic-elastic coupled media from isotropic media to anisotropic media, and propose an acoustic-elastic coupled medium based ontransverse isotropic media with vertical symmetric axes(VTI) to improve the accuracy of forward modeling. Based on the relationship between the Thomsen parameter and the coefficient matrix of the anisotropic elastic wave equation, we transform the Thomson parameter into a velocity model with anisotropic properties. We use a staggered grid finite difference method to simulate the propagation of a wavefield in a three-dimensional acoustic-elastic coupled media. We obtain the snapshots of the wave field when the solid of the acoustic-elastic coupled media is an isotropic medium and a VTI media. When the solid of the acoustic-elastic coupled media is considered VTI media, we can observe the qP wave and qS wave that cannot be observed in the isotropic medium from the wave field snapshot. We can also find that the seismic records obtained by the method we use are more realistic. The algorithm proposed in this paper is of great significance for high-precision ocean numerical simulation.

Numerical simulation of aircraft arresting process with an efficient full-scale rigid-flexible coupling dynamic model

The arresting process of carrier-based aircraft is widely recognized as a challenging task,characterized by the highest accident rate among all carrier-based aircraft operations.Dynamic simulation plays a crucial role in assessing the intricate responses of the arresting process,favoring the design of carrier-based aircraft.An efficient and accurate rigid-flexible coupling model for analyzing the dynamic response of the arresting process is proposed.By combining the dynamic characteristics of airframe,landing gear,arresting hook and arresting gear system,the rigid-flexible coupling dynamic model is established to reflect the relative motion of the coupling parts and arresting load.The dynamic model is verified through simulations of landing gear landing drops and by comparing the arresting simulation results with corresponding data in the US military standard.Additionally,simulations of the arresting process under different off-center distance and aircraft yaw angle are conducted to obtain the dynamic response of the aircraft during the arresting process.The result indicates that the rigid-flexible coupling dynamic model proposed is effective for analyzing the arresting dynamics response of carrier-based aircraft.The axial force of the arresting cable on both sides of the hook engagement point,pitch and yaw angle of aircraft are inconsistent under yaw and off-center arresting.The analysis method and obtained results provide valuable references for assessing the dynamic responses of carrier-based aircraft during arresting process and offer valuable in-sights in the design of carrier-based aircraft.

Simulation of Coupling Process of Flexible Needle Insertion into Soft Tissue Based on ABAQUS

In order to get to the desired target inside the body,it is essential to investigate the needle-tissue coupling process and calculate the tissue deformation.A cantilever beam model is presented to predicting the deflection and bending angle of flexible needle by analyzing the distribution of the force on needle shaft during the procedure of needle insertion into soft tissue.Furthermore,a finite element(FE)coupling model is proposed to simulate the needle-tissue interactive process.The plane and spatial models are created to relate the needle and tissue nodes.Combined with the cantilever beam model and the finite element needle-tissue coupling model,the simulation of needle-tissue interaction was carried out by the ABAQUS software.The comparing experiments are designed to understand the needle-tissue interactions,by which the same points in the experiments and simulation are compared and analyzed.The results show that the displacements in x and z directions in the simulation can accord with the experiments,and the deformation inside the tissue mainly occurs in the axial direction.The study is beneficial to the robot-assisted and virtual needle insertion procedure,and to help the physicians to predict the inside tissue deformation during the treatments.

Two-dimensional simulation on the rolling process of semi-solid 60Si2Mn by finite element method

The effect of various process variables on the law of metal flow for semi-solid rolling 60Si2Mn was studied by finite element method. Semi-solid 60Si2Mn can be described as compressible rigid visco-plastic porous material saturated with liquid. In terms of ther-mo-mechanical coupling condition, the distributions of stress, velocity and temperature were studied using software MARC. The simulation results show that the rigid visco-plastic model can accurately describe the semi-solid 60Si2Mn rolling process. The great deformation can achieve completely in view of low flow stress of semi-solid slurry.

弯管内外表面腐蚀缺陷力学-电化学相互作用规律研究

为进一步研究弯管内外表面腐蚀缺陷力学-电化学(M-E)相互作用规律,建立基于多物理场耦合的弯管内外表面含腐蚀缺陷的三维模型,研究内压和缺陷几何形状对M-E相互作用规律及对弯管的影响。研究结果表明:当弯管内外表面存在腐蚀缺陷时,弯管内侧的M-E效应更强,增加应力和腐蚀的增长速率,使内侧更容易发生失效;当缺陷几何增长时,应力在缺陷长度和宽度方向上增长,腐蚀主要在缺陷长度方向上增长;外表面缺陷附近的应力和腐蚀增长规律基本一致,而内表面缺陷附近的应力增长较腐蚀增长更为复杂。研究结果可为含腐蚀缺陷弯管评估模型的完善以及管道系统完整性的管理提供理论参考。

不同制动工况下地铁车轮踏面磨耗研究

为研究不同制动方式对地铁车轮踏面磨耗的影响规律,联合ANSYS和SIMPACK软件,建立了车轮-闸瓦热机耦合有限元模型和含有柔性轮对的车辆动力学模型,同时考虑不同制动初速度和制动减速度对车轮踏面温度、踏面硬度、踏面与闸瓦间接触应力及制动距离的影响,分析了不同制动方式下车轮-闸瓦磨耗、车轮-钢轨磨耗和踏面总磨耗的变化规律。结果表明:踏面磨耗随着制动初速度的增大而增大;随着制动减速度的增大,车轮-闸瓦磨耗和总磨耗增大,车轮-钢轨磨耗减小;制动时踏面总磨耗主要受车轮-闸瓦磨耗影响。

不同季节影响下复合道面力学响应分析

为了研究复合道面在不同季节时的力学响应,以中原地区某机场改造项目为项目背景,借助三维有限元软件,建立了道面有限元模型,分析了复合道面在温度影响下的力学响应,并与机场监测数据进行对比,验证了模型的准确性。研究发现:大气温度所能影响的道面深度范围在0.56 m以内,和大气温度相比,道面面层温度峰值远大于气温峰值;道面内部不同结构层之间温度变化趋势相同,随着道面深度的加深,温度峰值逐渐递减,并且出现时间具有延迟现象;在不同季节,道面在相同机型作用下所产生的变形不同,说明温度对于道面的受力是有影响的,其中混凝土层在冬季时所产生的应变值比夏季所产生的减少约74%,变化比较明显。

SIMULATION OF SOLUTE TRANSPORT USING A COUPLING MODEL BASED ON FINITE VOLUME METHOD IN FRACTURED ROCKS

The discrete version of solute transport equation for porous matrix depicted with the continuum model and the discrete fractured-network model are derived for fractured rocks with the Finite Volume Method （FVM）. The two models are coupled according to the continuity condition of hydraulic head and concentration and the conservation of flow flux and mass flux in the contact plane between porous matrix and fractures. Numerical results show that the simulated concentration of the coupling model based on the FVM agrees well with that from analytical solution, which demonstrates that the coupling model can effectively be applied to the simulation of solute transport in fractured rocks.

大型风力机叶片前缘的雨滴冲击动力学响应机制

随着近年海上风力机设计的大型化,叶片前缘的雨蚀失效问题变得愈发突出,不仅影响机组的风能转化效率,对结构的稳定运行也构成潜在威胁。采用光滑粒子流体动力学(smooth particle hydrodynamics,SPH)法研究雨滴内部的本构关系,以有限元法(finite element method,FEM)建立叶片前缘的代表性体积单元(representative volume element,RVE)模型,两者相互耦合,研究雨滴在叶片表面形成的冲击响应过程。考虑自然降雨的实际工况,建立与降雨强度相关联的雨滴尺寸模型,以及雨滴的空间分布模型;通过单雨滴的冲击仿真,研究叶片表面冲击载荷以及雨滴内部的速度分布,从而解构雨滴冲击的物理过程,并通过冲击的应力、应变场分析,为潜在损伤区提供评价;建立多雨滴冲击的仿真模型,研究冲击应力场之间的耦合作用以及涂层表面的塑性应变累积效果。研究结果表明,水锤冲击是造成塑性应变累积的关键因素,虽然横向喷射阶段的应力响应幅值小并呈现一定的无序特征,但如果存在多雨滴耦合冲击的情况,则会在耦合区内出现应力峰值,并对叶片变形和失效存在潜在影响。

考虑气体的渗流应力耦合模型在黄壁庄水库中的应用

目前建立的多孔介质耦合模型通常认为气体是不可压缩的,无法描述气体的输运过程,无法反映气体对水体入渗和固体变形的影响。为了描述多孔介质中固液气三相的渗流应力耦合过程,基于多孔介质理论和有效应力原理,提出了一种耦合了改进守恒水平集(ICLS)方法并考虑气体可压缩性的固液气三相渗流应力耦合模型。将该方法应用于黄壁庄水库坝前冒泡现象的渗流应力耦合分析中,模拟了水位骤升后,固体变形、水体入渗和气体运移过程,及其耦合效应。计算结果表明,该方法能够简单直观的描述水气两相的运移过程及渗流应力耦合过程,且模拟结果与实际观测结果基本一致。

C型钢缀板柱的有限元模拟方法研究

缀板柱以其制造简便、稳定性高且价格低廉的优势,在工程钢结构中得到了广泛应用,如何准确模拟缀板与立柱之间的连接情况,是工程结构有限元模拟时的重要问题。文章采用有限元软件ANSYS,研究C型钢缀板柱中缀板与立柱之间连接情况的有限元模拟问题,通过对比单元整体建模与节点耦合建模的模拟结果,分析了节点耦合连接方法的模拟原理并提出了使用时的注意事项。计算分析表明:整体建模模拟效果较好但不便于模型修改和精细化模拟,节点耦合便于修改但需要考虑耦合方法和连接面积。文章提出的简化统一耦合方法模拟效果好,适应性强,对于工程实践中的有限元模拟工作具有一定指导意义。

A Coupling Model of the Discontinuous Deformation Analysis Method and the Finite Element Method

Neither the finite element method nor the discontinuous deformation analysis method can solve problems very well in rock mechanics and engineering due to their extreme complexities. A coupling method combining both of them should have wider applicability. Such a model coupling the discontinuous deforma- tion analysis method and the finite element method is proposed in this paper. In the model, so-called line blocks are introduced to deal with the interaction via the common interfacial boundary of the discontinuous deformation analysis domain with the finite element domain. The interfacial conditions during the incre- mental iteration process are satisfied by means of the line blocks. The requirement of gradual small dis- placements in each incremental step of this coupling method is met through a displacement control proce- dure. The model is simple in concept and is easy in numerical implementation. A numerical example is given. The displacement obtained by the coupling method agrees well with those obtained by the finite ele- ment method, which shows the rationality of this model and the validity of the implementation scheme.

基于双向流固耦合的旋翼振动响应及噪声仿真分析

为精确预估流固耦合效应对旋翼桨叶振动响应及噪声计算的影响,本文建立了计算流体力学(Computational fluid dynamics,CFD)模型和高精度结构有限元模型,基于弱流固耦合方法完成了旋翼单向及双向流固耦合计算,并采用基于Kirchhoff方法对FW⁃H方程进行求解,分析了旋翼近场旋转噪声。首先,基于地面模态分析试验对桨叶结构有限元模型进行高精度建模,同时完成旋翼旋转状态的CFD计算,并采用两种网格映射方式和四点插值法进行流场与结构的数据传递,完成了旋翼单向稳态及单向瞬态流固耦合分析。然后采用双向弱流固耦合方法计算结构动响应及非定常流场,分析比较单、双向流固耦合计算方法下桨叶振动响应的差异。最后,基于单、双向流固耦合计算得到桨叶表面的时变气动压强,计算旋翼旋转噪声,分析比较单、双向流固耦合计算方法的旋转噪声大小及分布特征。结果表明,文中基于高精度桨叶模型及双向流固耦合方法计算出的桨叶动响应及噪声分布符合悬停旋转噪声规律,可为未来桨叶结构设计、强度校核及噪声预估提供参考。

多胞子弹冲击泡沫夹芯梁的动力学响应分析

为了研究均匀/梯度多胞子弹冲击泡沫夹芯梁的耦合响应过程和多胞子弹对夹芯梁的加载效果,对该冲击过程开展了理论分析、数值模拟和试验研究:通过将泡沫夹芯梁等效为单梁以简化分析,基于多胞子弹的冲击波模型和泡沫夹芯梁的等效单梁响应模型,构建了多胞子弹冲击泡沫夹芯梁的耦合分析模型,给出了冲击过程中各响应阶段的控制方程,并结合龙格-库塔方法对方程进行了数值求解;基于三维Voronoi技术,开展了均匀/梯度多胞子弹冲击泡沫夹芯梁的细观有限元模拟;在多胞子弹的冲击测试平台上进行了试验研究,结合高速摄影技术获取了多胞子弹和泡沫夹芯梁的速度响应。结果表明:耦合分析模型可以准确地预测多胞子弹和泡沫夹芯梁的速度历程曲线以及多胞子弹产生的冲击压强;在初始动量相同但密度分布或初速度不同的多胞子弹冲击下,同一构型的泡沫夹芯梁展现出不同的力学响应,这说明多胞子弹的加载不能简单地等效为脉冲加载,多胞子弹与夹芯梁之间的耦合效应不可忽略;相较于均匀多胞子弹,梯度多胞子弹的冲击压力波形更加尖锐,在其衰减过程中展现出更强的非线性特征。

车辆服役环境对高速列车轴箱轴承温度的影响分析

构建考虑轴箱表面散热及轴承内部传热的功率损耗模型,分析轴箱轴承在不同服役环境下的载荷;综合考虑轴箱表面空气流场对流换热的影响,建立精细化轴箱轴承温度模型,分析不同服役环境对轴箱轴承温度分布和温度特性的影响,并通过轴承试验台验证模型的有效性。研究结果表明:当车辆速度由220 km/h增至300 km/h时,轴承的总摩擦力矩增大11.4%;当车轮多边形阶数由16阶增加到22阶时,摩擦力矩平均增大2.8%;轴箱轴承最高温度出现在内圈与滚动体接触的区域,最低温度出现在轴上且接近环境温度;当车速由220 km/h增加到300 km/h时,轴承的最高温度上升9.2℃,各节点处温度均有一定程度增加,当车轮多边形阶数由16阶增加到22阶时,最高温度平均升高1.1%;当多边形深度幅值由10 dB增加到18 dB时,最高温度平均升高1.4%。

基于刚柔耦合模型的某车载高炮火控诸元修正方法研究

针对车载高炮射击时车体姿态对射击精度的影响问题,提出了一种基于刚柔耦合模型修正火炮射击诸元的方法。以某车载高炮为研究对象,通过建立其刚柔耦合模型对车体姿态进行预测,火控系统将获取的射击方向上的车体姿态响应实时分解到沿车头方向和垂直于车头方向,经过纵、横倾及车向反变换后由载车不稳定坐标系转换为载车地理系下,再经滤波与解相遇问题求解得到地理系下的目标诸元,随后将地理系下的目标诸元通过纵、横倾及车向变换后得到载车不稳定系下的火炮射击诸元,从而将修正后的瞄准诸元提供给火炮。为验证修正方法的可行性与适用性,以另一型车载炮为对象进行了试验验证,试验结果表明:经诸元修正后的火炮射击精度得到明显改善,火炮射击初期高低和方位弹丸脱靶量均值分别减小了53.1%和41.3%,修正效果显著,研究可为车载高炮火控射击诸元修正提供一种新思路。

基于损伤模型的混凝土冻融循环过程数值模拟研究

冻融损伤是寒区混凝土主要破坏方式之一,冻融过程是混凝土材料逐渐破坏演变的过程。引入损伤理论建立了混凝土水热力损伤耦合模型,该模型可以模拟混凝土冻融过程中水的相变、孔隙水压等变化过程,通过累积损伤真实反映破坏过程。通过与相关文献中的试验数据对比,验证了模型的准确性,并研究了中心最低温度、降温速率以及初始孔隙率对混凝土试件冻融损伤的影响规律。结果表明:随着试件中心最低温度的降低、降温速率的增大和初始孔隙率的增大,混凝土的累积损伤值逐渐增大;损伤区虽然从混凝土试件四周逐渐向内发展,但在降温速率和初始孔隙率过大时,最大损伤区和裂缝却出现在棱角附近的试样内部,并向外部扩展,该结果解释了棱柱体混凝土冻融破坏后棱角最先掉落的现象。