Development of an Accurate Urban Modeling System Using CAD/GIS Data for Atmosphere Environmental Simulation

This paper presents an urban modeling system using CAD/GIS data for atmosphere environmental simulation, such as wind flow and contaminant spread in urban area. The CAD data is used for the shape modeling for the high-storied buildings and civil structures with complicated shape since the data for that is not included in the 3D-GIS data accurately. The unstructured mesh based on the tetrahedron element is employed in order to express the urban structures with complicated shape accurately. It is difficult to understand the quality of shape model and mesh by the conventional visualization technique. In this paper, the stereoscopic visualization using virtual reality (VR) technology is employed for the verification of the quality of shape model and mesh. The present system is applied to the atmosphere environmental simulation in urban area and is shown to be an useful planning and design tool to investigate the atmosphere environmental problem.     

Development of Simulation System for the Disaster Evacuation Based on Multi-Agent Model Using

This paper presents a simulation system for the disaster evacuation based on multi-agent model considering geographical information. This system consists of three parts, the modeling for the land and buildings using GIS data, the analysis of disaster evacuation using multi-agent model, and the visualization for the numerical results using the virtual reality technique. By introducing the numerical solver of the natural disaster to the present system, it is possible to evaluate not only the damage of structure but also the damage of human being. Furthermore, it is possible to investigate the appropriate evacuation route by the simulation. The Dijkstra algorithm is used to obtain shortest route to the refuge. In addition, the visualization using virtual reality technique is curried out to understand the feeling of refugee. The present system is applied to the evacuation analysis by the flood flow in urban area and is shown to be a useful tool to investigate the damage by natural disasters.     

An element by element spectral element method for elastic wave modeling

The spectral element method which combines the advantages of spectral method with those of finite element method, provides an efficient tool in simulating elastic wave equation in complex medium. Based on weak form of elastodynamic equations, mathematical formulations for Legendre spectral element method are presented. The wave field on an element is discretized using high?order Lagrange interpolation, and integration over the element is accomplished based upon the Gauss?Lobatto?Legendre integration rule. This results in a diagonal mass matrix which leads to a greatly simplified algorithm. In addition, the element by element technique is introduced in our method to reduce the memory sizes and improve the computation efficiency. Finally, some numerical examples are presented to demonstrate the spectral accuracy and the efficiency. Because of combinations of the finite element scheme and spectral algorithms, this method can be used for complex models, including free surface boundaries and strong heterogeneity.     

A new model for the grid size optimization of the finite element method --Based on its application to the water quality modeling of the topographically complicated river

The finite element method is one of the typical methods that are used for numerical water quality modeling of the topographically complicated river. In this paper, based on the principle of probability theory the probability density of pollutants is introduced. A new model for the grid size optimization based on the finite element method is developed with the incorporation of the maximum information entropy theory when the length of the grid is given. Combined with the experiential evaluation approach of the flow discharge per unit river width, this model can be used to determine the grid size of the finite element method applied to water quality modeling of the topographically complicated river when the velocity field of the river is not given. The calculating results of the application of the model to an ideal river testified the correctness of the model. In a practical case-the application of the model to the Xingjian River (the Hengyang section of the Xiangjiang River), the optimized width of the grid of the finite element method was gained and the influence of parameters was studied, which demonstrated that the model reflected the real situation of the pollutants in the river, and that the model had many excellent characteristics such as stabilization, credibility and high applicability in practical applications.     

Modeling of Busbars in High Power Neutral Point Clamped Three-Level Inverters

The busbars in high power neutral point clamped three-level inverters are modeled using the Maxwell Q3D Extractor software, which is based on the partial element equivalent circuits method. The equivalent circuits of the busbars and devices model are simulated in the electric simulator PSlM to analyze the effects of the parasitic inductance on the switching characteristics of the integrated gate commutated thyristor （IGCT） in different topology positions. The simulation results agree well with the measured impedance analyzer results and the IGCT test results, which proves the effectiveness of the modeling method for the large, complex busbars.     

Efficient and reproducible folding simulations of the Trp-cage protein with multiscale molecular dynamics

Folding simulations are often time-consuming or highly sensitive to the initial conformation of the simulation even for mini protein like the Trp-cage. Here, we present a multiscale molecular dynamics method which appears to be both efficient and insensitive to the starting conformation based on the testing results from the Trp-cage protein. In this method the simulated system is simultaneously mod- eled on atoms and coarse-grained particles with incremental coarsening levels. The dynamics of coarse-grained particles are adapted to the recent trajectories of finer-grained particles instead of fixed and parameterized energy functions as used in previous coarse-grained models. In addition, the compositions of coarse-grained particles are allowed to be updated automatically based on the coherence during its history. Starting from the fully extended conformation and other several different conformations of the Trp-cage protein, our method successfully finds out the native-like conformations of the Trp-cage protein in the largest cluster of the trajectories in all of the eight performed simulations within at most 10 ns simulation time. The results show that approaches based on multiscale modeling are promising for ab initio protein structure prediction.     

Computer simulation of flow fields for quenching medium

Using finite element method (FEM), the complex flow fields of quenching medium in a quenching tank are calculated for the cases with and without a work-piece in it. The influence of the flow homogenization device on the flow fields is studied. The computer simulation results are in consistency with the actual measurement results. According to the simulated results, the structure of the quenching tank and the flow homogenization device are optimized and more uniform flow fields are obtained.     

Finite Element Simulation of Metal Quenching

The evolution of the phase transformation and the resulting internal stresses and strains in metallic parts during quenching were modeled numerically. The numerical simulation of the metal quenching process was based on the metallo-thermo-mechanical theory using the finite element method to couple the temperature, phase transformation, and stress-strain fields. The numerical models are presented for the heat treatment and kinetics of the phase transformation. The finite element models and the phase transition kinetics accurately predict the distribution of the microstructure volume fractions, the temperature, the distortion, and the stress-strain relation during quenching. The two examples used to validate the models are the quenching of a small gear and of a large turbine rotor. The simulation results for the martensite phase volume fraction, the stresses, and the distortion in the gear agree well with the experimental data. The models can be used to optimize the quenching conditions to ensure product quality.     

CALCULATION AND MEASUREMENT OF DYNAMIC EXPANSION OF ROVING FLYER

Roving flyer is an important part of roving frame. Its dynamic expansions affect the quality of rove greatly. The expansions are calculated by means of the general program SAP84 based on finite element method in this paper. Its measuring principle and usage are also described. The results of calculating and measuring are identical. The method presented in the paper is effective for studying the properties of roving flyer.     

Simulation on Dynamic Bending Features of Fabric Based on Fluid-Solid Interaction Technique

This paper is devoted to the two-dimensional nonlinear modeling of the fluid-solid interaction (FSI) between fabric and air flow, which is based on the Automatic Incremental Dynamic Nonlinear Analysis (AIDNA)-FSI program in order to study the dynamic bending features of fabrics in a specific air flow filed. The computational fluid dynamics (CFD) model for flow and the finite element model (FEM) for fabric was set up to constitute an FSI model in which the geometric nonlinear behavior and the dynamic stress-strain variation of the relatively soft fabric material were taken into account. Several FSI cases with different time-dependent wind load and the model frequency analysis for fabric were carried out. The dynamic response of fabric and the distribution of fluid variables were investigated. The results of numerical simulation and experiments fit quite well. Hence, this work contributes to the research of modeling the dynamic bending behavior of fabrics in air field.     

基于随机扩展方法的致密油储层裂缝建模研究

现有的储层裂缝建模方法大多忽略了储层裂缝扩展历史与裂缝属性随机分布特征之间的本质关系,所建裂缝模型多为不考虑断裂尖端扩展历史的静态模型,因而不可能给出有效的区域裂缝信息。针对裂缝建模难题,提出了基于裂缝扩展反演模型的裂缝建模方法。首先,基于裂缝扩展规律,采用扩展有限元方法,利用模拟退火技术,建立裂缝扩展反演模拟模型;然后,采用克里金模型和断裂力学模拟系统,综合构造和成像测井裂缝解释资料,构建多场趋势克里金估计模拟模型。选取大情字井地区青山口组扶余致密油层作为实验区,建立了该区块的裂缝扩展模型和裂缝分布模型。实验表明,构建的基于随机扩展有限元模拟的裂缝建模方法可以克服现有裂缝建模方法的不足,可提高裂缝性油藏的表征精度。     

面向流体流动的计算机模拟

针对流体系统的特点,研究了模拟流体流动的格子自动机方法。对流可视化技术的现状、方法和可视化系统的设计进行了分析和探索。考察了几种典型的流动现象,得到了与实验较为一致的结论。研究结果表明：在目前条件下,立足于格子自动机这种具有极度并行性的新型流体计算模型,结合科学计算可视化技术,利用计算机来解决流体流动问题的计算机模拟方法是一条值得深入探索的研究途径。     

基于GWO改进神经网络的风致输电杆塔响应计算方法

针对基于有限元方法的风致输电杆塔仿真模型存在模型参数设置复杂、响应速度低下等问题,本文提出了一种结合杆塔仿真计算与机器学习的杆塔应力快速计算方法,实现了风致输电杆塔仿真模型的高效运算。本文首先利用有限元仿真分析10~35 m/s风速0~90°风向下输电杆塔的应力结果,将其作为神经网络训练样本;分析杆塔本征参数及气象因素对杆塔应力结果的影响,提出一种基于风速、风向和塔材类型等因素的特征值选取方法;利用GWO优化算法提高神经网络准确度,建立基于GWO-BPNN的杆塔风致应力计算模型,计算速度可达建模仿真的10倍以上。在准确率上,基于数据集划分训练集及验证集,模型准确率在98%以上,将计算结果与实际杆塔受灾情况相比情况一致。本模型可用于输电线路防风预警,致力于输电线路防灾减灾。     

电接触合金材料导电率的三维有限元分析

提出了一种计算多相合金电导率的数值模拟方法，采用有限元技术模拟电流流过导体时具有分布特征的电流场，各单元的组分随机产生以模拟实现的合金，通过计算全部单元中的总损耗来确定合金材料的等效电导率，在建立标量电位分析三维电流场有限元分析模型的基础上，以CuCr和AgW等合金为例计算了不同组分时电接触合金材料的电导率，并探讨了气孔率对电导率的影响，给出了不同组分时的电流场分布，计算结果与标准值的比较证明了模型的有效性。     

基于三维表面模型的注射成型充填模拟

充填模拟的计算机软件在预测复杂薄壁型腔的流动行为方面已经比较准确。现行的数值方法都是采用基于中性层的有限元／有限差分法,但中性层模型的引入使得模拟软件在应用中具有极大的局限性。本采用表面模型取代中性层模型,通过附加在壁厚方向上的边界条件来保证同一截面上对应表面的协调流动,这一创新使由现行的模具设计CAD系统产生的型腔模型可以直接应用于CAE软件,突破了原有软件的建模瓶颈。最后应用实例论证了本算法的合理性与可靠性。     

Advances in biomolecular surface meshing and its applications to mathematical modeling

In the field of molecular modeling and simulation, molecular surface meshes are necessary for many problems, such as molecular structure visualization and analysis, docking problem and implicit solvent modeling and simulation. Recently, with the developments of advanced mathematical modeling in the field of implicit solvent modeling and simulation, providing surface meshes with good qualities efficiently for large real biomolecular systems becomes an urgent issue beyond its traditional purposes for visualization and geometry analyses for molecular structure. In this review, we summarize recent works on this issue. First, various definitions of molecular surfaces and corresponding meshing methods are introduced. Second, our recent meshing tool, TMSmesh, and its performances are presented. Finally, we show the applications of the molecular surface mesh in implicit solvent modeling and simulations using boundary element method (BEM) and finite element method (FEM).     

基于向量式有限元法的风力发电机组一体化仿真分析

大型风电机组为强非线性刚柔耦合的周期时变多体系统,传统有限元方法不能解决叶片转动过程中由于刚体位移而导致的刚度矩阵奇异问题,向量式有限元法可有效考虑叶片的几何非线性和大变形运动、塔架的弹性变形、气动载荷等因素.基于MATLAB平台编制空间梁系结构求解程序,选取悬臂梁受端部集中动荷载和欧拉梁绕定轴转动两个典型算例验证程序的正确性.建立包含机舱、轮毂、叶片和塔架在内的风电机组一体化仿真分析模型,根据机组静止状态下自由振动响应,用模态参数识别方法提取了机组的自振频率,计算结果与传统有限元法吻合.采用谐波叠加法和本征正交分解法相结合的方式,运用B样条曲面插值策略,模拟生成风电机组在正常运行状态下的风速时程.采用向量式有限元法对正常运行状态下的风电机组进行风振响应分析,较好地反映了重力对叶片内力周期性变化的影响以及叶片与塔架的共同作用.     

混凝土骨料有限元模型自动生成方法

针对圆形、椭圆形、多边形三种剖面形状的骨料夹杂分别给出了混凝土的二维有限元建模方法,为细观结构研究提供了全自动的建模工具．提出了一种新的以面积为标度的任意两椭圆骨料侵入的判别准则,有效地克服了椭圆形骨料几何模型生成中的效率瓶颈问题;提出了综合考虑边数、形状、尺寸等随机特性的多边形骨料生成方法,并简单有效地保证了多边形骨料为凸的性质,使所建的随机几何模型能够更好地模拟人工骨料和再生骨料;对生成的几何模型,运用改进的推进波前法一次性生成所有骨料的有限元网格,为进一步的复合材料细观结构和宏观力学性能的多尺度计算打下了基础．最后用几个算例验证了算法的有效性。