连续交通流模型的并行计算

为了降低连续交通流模型并行计算的实现难度,参考离散交通流模型并行计算的框架,提出了一套连续交通流模型并行计算的框架.该框架包括同步机制、基于网格的区域分解方法和边界缓冲模型,其中同步机制采用与离散交通流模型并行计算相同的主从结构的同步机制,基于网格的区域分解方法和边界缓冲模型分别用来实现任务的分解和提供仿真计算时所需的交互数据.实验中,选用了一个大规模路网进行验证,结果表明应用这一框架,可以方便地实现连续交通流模型的并行计算,提高连续交通流模型运算的速度,从而满足了智能交通系统中大规模交通路网实时、高效和动态仿真的需求.     

WENO格式与虚拟单元浸入边界法在笛卡尔网格中的应用

高精度有限差分WENO格式在结构网格上处理具有复杂几何外形绕流问题时较困难,而虚拟单元浸入边界法却是一种较新颖且对网格的要求较低的方法,适用于复杂几何外形边界的处理.为此,在笛卡尔网格上采用WENO格式以求解Euler守恒律方程,试图将两者有效结合起来,希望能在笛卡尔网格上处理具有复杂几何外形的物体绕流问题.最后,几个经典数值算例的结果验证了该方法的有效性.     

Study on complicated solid modeling and Cartesian grid generation method

A Cartesian grid generation method is developed in this study.Two kinds of solid modeling methods,CSG and STL models,are used for complicated solid modeling.The staircase boundary approximation is implemented to handle irregular geometries and the computational domain is discretized using a regular Cartesian grid.Using the edge-based integral slice algorithm,the models are sliced with a set of parallel planes to generate 2D slices information.The scan line filling technique is used to achieve grid generation after slicing.Two grid generation examples with a CSG model and a STL model are given to test the capability of the grid generation method.For grid displaying,a method is proposed to remove the hidden surfaces fasten based on the topology of orthogonal hexahedral grids.The parallelization of grid displaying is achieved by employing multi-threaded parallel technique.Parallel test results show that the parallel algorithm has the absolute advantage on speed compared to the serial algorithm.     

Numerical simulations of self-propelled swimming of 3D bionic fish school

Numerical simulations of self-propelled swimming of a three dimensional bionic fish and fish school in a viscous fluid are carried out. This is done with the assistance of a parallel software package produced for 3D moving boundary problems. This computational fluid dynamics package combines the adaptive multi-grid finite volume method, the immersed boundary method and VOF (volume of fluid) method. By using the package results of the self-propelled swimming of a 3D bionic fish and fish school in a viscous fluid are obtained. With comparison to the existing experimental measurements of living fishes, the predicted structure of vortical wakes is in good agreement with the measurements. Supported by the Key Project of National Natural Science Foundation of China (Grant No. 10532040)     

High performance parallel computing of large eddy simulation of the flow in a curved duct with square cross section

Large eddy simulation(LES) cooperated with a high performance parallel computing method is applied to simulate the flow in a curved duct with square cross section in the paper. The method consists of parallel domain decomposition of grids, creation of virtual diagonal bordered matrix, assembling of boundary matrix, parallel LDL^T decomposition, parallel solving of Poisson Equation, parallel estimation of convergence and so on. The parallel computing method can solve the problems that are difficult to solve using traditional serial compuling. Furthermore, existing microcnmputers can be fnlly used to resolve some large-scale problems of complex turbulent flow.     

带TVB限制器的RKDG方法与浸入边界方法在Euler方程中的应用

在求解Euler方程时,带TVB限制器的Runge-Kutta间断有限元(RKDG)方法是一种高精度、高并行效率的方法,而浸入边界方法是一种较新颖且对网格要求较低的方法,适用于处理复杂几何外形的边界.尝试了将上述2种方法结合起来求解Euler方程在笛卡尔网格上具有复杂几何外形的物体绕流问题,数个经典算例的数值结果验证了该方法的有效性.     

建筑绕流风场的并行化数值模拟

本文从建筑绕流风场数值模拟问题的功能并行性出发,依据重新排序的并行化原则。建立了三处理机Ｔｒａｎｓｐｕｔｅｒ并行系统基于ＳＩＭＰＬＥＣ算法的一种所谓方程分离并行策略,对该策略的求解步骤,数据通讯并行效率等进行了分析,并与区域分裂并行策略作了比较。文末给出了计算实例,计算结果表明方程分离策略的并行粒度大,数据通讯简单,收敛性较好,采用该策略可获得较高的并行效率。     

Numerical investigation of particle saltation in the bed-load regime

This paper numerically investigates particle saltation in a turbulent channel flow having a rough bed consisting of 2–3 layers of densely packed spheres.In this study,we combined three the state-of-the-art technologies,i.e.,the direct numerical simulation of turbulent flow,the combined finite-discrete element modelling of the deformation,movement and collision of the particles,and the immersed boundary method for the fluid-solid interaction.Here we verify our code by comparing the flow and particle statistical features with the published data and then present the hydrodynamic forces acting on a particle together with the particle coordinates and velocities,during a typical saltation.We found strong correlation between the abruptly decreasing particle stream-wise velocity and the increasing vertical velocity at collision,which indicates that the continuous saltation of large grain-size particles is controlled by collision parameters such as particle incident angle,local rough bed packing arrangement,and particle density,etc.This physical process is different from that of particle entrainment in which turbulence coherence structures play an important role.Probability distribution functions of several important saltation parameters and the relationships between them are presented.The results show that the saltating particles hitting the windward side of the bed particles are more likely to bounce off the rough bed than those hitting the leeside.Based on the above findings,saltation mechanisms of large grain-size particles in turbulent channel flow are presented.     

区域分解并行有限元计算方法研究

按照区域分解算法“分而治之”的思想,研究了在普通PC机群上实现大规模并行有限元计算的方法.针对PC机群的特点,有限元计算数据采用分布式存储策略,方程组的求解采用并行预处理共轭梯度算法.采用C++语言及MPI消息传递接口开发了基于PC机群的并行有限元计算程序,利用6台计算机对247871个单元的有限元模型进行了并行求解,并行加速比达到5.26.验证了程序的可靠性和高效性.     

Splitting extrapolation based on domain decomposition for finite element approximations

Splitting extrapolation based on domain decomposition for finite element approximations is a new technique for solving large scale scientific and engineering problems in parallel. By means of domain decomposition, a large scale multidimensional problem is turned to many discrete problems involving several grid parameters The multi-variate asymptotic expansions of finite element errors on independent grid parameters are proved for linear and nonlin ear second order elliptic equations as well as eigenvalue problems. Therefore after solving smaller problems with similar sizes in parallel, a global fine grid approximation with higher accuracy is computed by the splitting extrapolation method.     

双互易杂交边界点法参数及域内节点分布

为了解决双互易杂交边界点法推广应用中存在的障碍和缺点,如自由参数过多、域内节点数量及分布无规律可循等缺点,选取不同的有代表性的算例,分别研究双互易杂交边界点法自由参数的选择、自由参数与精度之间的关系、域内节点的布置数量和位置与精度之间的关系等.通过理论分析和数值实验得出：子域半径的较佳取值为0.85,子域半径与形状参数的最佳比值为1.0～1.3;当域内节点数量与边界节点数量接近时,计算效率达到最大;域内节点宜较多地布置在平行于梯度大的方向上.     

Monte Carlo simulation for simultaneous particle coagulation and deposition

The phenomena of simultaneous particle coagulation and deposition are of great ubiq- uity and of key importance in nature and various engineering applications, including the precipitation and downfall of rain, ice, snowflakes, fog and hail, the scavenging of fly ashin electrostatic precipitator of power plant, the transplantation of fume in smoke flue of pulverized coal-fired plant, nuclear reactor analysis modeling aerosol’s diffusion and deposition when blasting, the suspension and sedimenta…     

混合并行技术在FDTD计算中的应用研究

为提高网络环境下细粒度并行FDTD计算的性能,引入局域网两层并行能力的概念,发展了一种高性能的混合并行FDTD算法。在该算法中,通过利用MPI与OpenMP多线程技术,在传统域分解FDTD算法基础上,实现了数据与任务的两层并行化。作为算法实现的应用,对一种常见的车载隐藏式印刷天线进行了模拟研究。计算在不同数量的PC机上执行,并与传统的网络并行FDTD算法进行了比较。数值结果表明,当域分解粒度较小时,该混合并行方法能够有效地提高局域网并行FDTD的算法性能。     

共享内存系统中高效并行FDTD计算方案

针对电大问题的FDTD仿真,在共享内存系统中提出一种不交换数据的并行FDTD计算方案。该方案利用共享内存系统的通用多核处理器架构,直接读取并行场域边界面的数据实现并行计算,采用自主开发的多线程技术实现FDTD的并行计算。通过数值仿真测试,提出了最大并行计算效率的区域划分方式,并验证了所提出的方案是一种理想的基于共享内存系统的并行FDTD计算方案。     

Coupled GIMP and CPDI material point method in modelling blast-induced three-dimensional rock fractureOA

Three-dimensional rock fracture induced by blasting is a highly complex problem and has received considerable attention in geotechnical engineering. The material point method is firstly applied to treat this challenging task. Some inherent weaknesses can be overcome by coupling the generalized interpolation material point(GIMP) and the convected particle domain interpolation technique(CPDI). For the media in the borehole, unchanged GIMP-type particles are used to guarantee a homogenous blast pre...     

Surface-particle-emulsion heat transfer model between fluidized bed and horizontal immersed tube

A mathematical model, surface-particle-emulsion heat transfer model, is presented by considering voidage variance in emulsion in the vicinity of an immersed surface. Heat transfer near the surface is treated by dispersed particles touching the surface and through the emulsion when the distance from the surface is greater than the diameter of a particle. A film with an adjustable thickness which separates particles from the surface is not introduced in this model. The coverage ratio of particles on the surface is calculated by a stochastic model of particle packing density on a surface. By comparison of theoretical solutions with experimental data from some References, the mathematical model shows better qualitative and quantitative prediction for local heat transfer coefficients around a horizontal immersed tube in a fluidized bed.     

多孔介质方腔自然对流的直接数值模拟

为了研究多孔介质方腔的自然对流传热,通过在方腔内布置固体颗粒的方式来模拟多孔介质结构,并采用虚拟区域方法求解多孔介质中的流场和温度场,分析了固体颗粒的数目、布置方式和形状对传热效率的影响.在高Rayleigh数下,多孔介质方腔自然对流的传热主要是通过壁面附近热对流产生的环流.通过直接数值模拟研究发现：当保持Rayleigh数和固体体积分数不变时,随着模拟多孔介质的颗粒数目的增加,壁面平均Nusselt数随之减小,即传热效率降低,进一步的流场分析表明规则排列时最外排颗粒到壁面距离对于传热效率有重要的影响;当固体颗粒数目和体积分数相同时,颗粒随机布置在高Rayleigh数时比颗粒规则布置有更高的传热效率,而颗粒形状对于传热效率的影响则不大.     

Non—equilibrium Segregation of boron on grain boundary in Fe—30% Ni alloy

The moving boundary non-equilibrium segregation during recrystallization and the influence of pre-deformation in Fe-30% Ni Alloy at 1000℃ was investigated by the PTA9Particle tracking autoradiography)technique,optical and electron microscopy.The results indicated that intensity of bron segregation on moving boundary after different deformation is concerned with the pre-deformation degree and the moving speed of the boundary,The TEM(transmission electron microscopy)result showd that the dislocation density nearby the moving boundary increase obviously.The phenomena are discussed by the widening grain boundary mechanism.     

高维Kramers系统平均首次离出时间的渐近分析

讨论了布朗粒子从高维Kramers系统稳定平衡点的吸引域离出的平均首次离出时间。主要运用奇异摄动渐近展开、局部坐标变换、边界层展开方法,同时结合系统对应的伴随方程,得出平均首次离出时间的渐近表达式。     

考虑单侧接触结构-介质动力相互作用的边界元分析

应用时域边界元法研究了结构 -介质动力相互作用问题。假设摩擦遵守库仑定理。当入射波足够强时界面会出现局部滑移、分离。由于边界上的区域 (滑移、分离和粘着 )是未知的 ,所以本问题实际上是个复杂的边界非线性问题。为了确定未知区域 ,我们应用了一种有效的迭代技术。