Separation-bubble flow solution using Euler/Navier-Stokes zonal approach with downstream compatibility conditions

An Euler/Navier-Stokes zonal scheme is developed to numerically simulate the two-dimensional flow over a blunt leading-edge plate. The computational domain has been divided into inner and outer regions where the Navier-Stokes and Euler equations are used, respectively. On the downstream boundary, compatibility conditions derived from the boundary-layer equations are used. The grid is generated by using conformal mapping and the problem is solved by using a compressible Navier-Stokes code, which has been modified to treat Euler and Navier-Stokes regions. The accuracy of the solution is determined by the reattachment location. Bench-mark solutions have been obtained using the Navier-Stokes equations throughout the optimum computational domain and size. The problem is recalculated with sucessive decrease of the computational domain from the downstream side where the compatibility conditions are used, and with successive decrease of the Navier-Stokes computational region. The results of the zonal scheme are in excellent agreement with those of the benchmark solutions and the experimental data. The CPU time saving is about 15%.     

交通高峰期路段交通流动力学模型

研究了交通高峰期交通流的动力学规律。为了解决交通高峰期交通堵塞的问题,从车辆数量守恒的思想出发,对交通高峰期的路段交通流规律进行了探讨,分析了交通流参数,建立了交通流运动微分方程,通过理论推导得出了路段的一维交通流动力学模型。通过仿真实验表明,此模型能反映交通流的基本特性,能够为交通部门在交通高峰期调节路网交通流提供理论依据。     

Development and application of an integrated traffic simulation and multi-driving simulators

Professional virtual reality experiment tools, including driving simulators and traffic simulators, have their strengths and weaknesses. The integration of the two simulators will enhance the ability of both traffic modeling and driving simulation and present a new area of applications. This paper develops, implements, and validates an experimental platform that integrated a traffic simulator with multiple driving simulators (TSMDS). As a connected multi-user framework that allows multiple drivers who are simultaneously handling many driving simulators, it not only allows driver behavior experiments to be more accurate, controlled, and versatile but also simulates special driving behavior or multi-vehicle interactions under more realistic traffic flow environments. To validate the performance of TSMDS, 27 drivers were recruited to attend the lane changing experiments at a recurring on-ramp bottleneck and left-turn experiments at a two-phase signalized intersection in Shanghai. Both experiments required several drivers to drive the TSMDS and fulfill several complicated lane changing/crossing behaviors through their interaction. The results show that both the participants’ response and lane changing/crossing data that were obtained from the experiment are consistent with the field observation, which confirms the validity of the integrated platform.     

On-line distributed prediction of traffic flow in a large-scale road network

For on-line traffic control at traffic control centers there is a need for fast computations of predictions of traffic flow over a short prediction horizon, say 30 min, to evaluate the impact of different scenarios for the purpose of on-line scenario selection. A novel approach is presented to predict the traffic flow in a large-scale traffic network in an asynchronous, parallel, and distributed way at two or more subnetworks combined with a consistency check at the network level within a reasonable-small computation time.     

PARAMICS—Parallel microscopic simulation of road traffic

This paper describes work done on the original PARAMICS project, which was developed for the Edinburgh Parallel Computing Centre to examine parallel microscopic road traffic simulation. The simulator, constructed originally for a Thinking Machines Connection Machine (CM-200), uses a data-parallel approach to simulate approximately 200,000 vehicles on 20,000 miles of roadway. More recent work has focused on the use of a message-passing paradigm, with a 256-node CRAY T3D as the target machine. The message-passing version of PARAMICS, PARAMICS-MP, is inherently scalable and can model many smaller networks on a broad range of platforms.An earlier version of this paper was presented at Supercomputing '94.     

基于OpenCL的并行方腔流加速性能分析*

本文提出了一种使用OpenCL技术对方腔流问题进行加速计算的方法。在计算方腔流问题时,本文将其转换为Ｎ-Ｓ方程通过空间有限差分和龙格库塔时间差分求解,并使用局部缓存等技术进行GPU优化。实验在Nvidia和ATI平台对所给算法进行评测。结果显示,OpenCL相对其串行版本加速约30倍左右。     

城市中观交通仿真的交通流车簇模型

为了解决城市交通仿真模型仿真速度和仿真精确度的平衡问题,针对城市交通流运行特征,同时考虑影响交通流运行的若干因素,如车辆数目、红绿灯控制等,提出一种中观交通仿真车辆群体模法.该模型结合了宏观模型和微观模型的优点,同时对应的交通流配流算法解决了传统模型的不足,城市交通仿真实验结果表明了车辆群体模型和分配算法的合理性和有效性.     

Methods for parallel computation of complex flow problems

This paper is an overview of some of the methods developed by the Team for Advanced Flow Simulation and Modeling (TAFSM) [http://www.mems.rice.edu/TAFSM/] to support flow simulation and modeling in a number of “Targeted Challenges”. The “Targeted Challenges” include unsteady flows with interfaces, fluid–object and fluid–structure interactions, airdrop systems, and air circulation and contaminant dispersion. The methods developed include special numerical stabilization methods for compressible and incompressible flows, methods for moving boundaries and interfaces, advanced mesh management methods, and multi-domain computational methods. We include in this paper a number of numerical examples from the simulation of complex flow problems.     

流量装置流量稳定性数值仿真评价方法研究

为了提高装置流量稳定性,提出基于计算流体动力学（ CFD）仿真,采用轴向动量数KU、旋流数KV 和不对称数KA ,分析管路不同截面位置的流场速度特征,利用多个截面位置的特征参数变化,评价装置管路的流量稳定性。对新建水装置流量稳定性进行数值仿真分析与实验测试,得出一致性结论。该方法可以在装置设计阶段,对流量稳定性进行评价,从而优化管路结构,提高装置流量稳定性。     

交通流多格点预估格子模型与数值仿真

考虑驾驶员对多格点交通流量预估效应,建立了新的交通流多格点预估格子模型。通过线性稳定性分析获得了改进模型的稳定性条件。通过非线性分析得到了扭结—反扭结密度波解,得到了交通流相空间的三个区域:稳定区域、亚稳定区域和不稳定区域。数值仿真验证了考虑驾驶员对多格点的预估效应,能够进一步提高交通流的稳定性。     

基于CFD仿真的切向涡轮流量传感器结构优化

为降低切向涡轮流量计的测量下限,以25 mm口径机械式热量表为例,利用计算流体动力学（ CFD）仿真软件对传感器内部三维流场进行研究,提出了提高传感器性能的10种结构改进方案,并通过CFD仿真对优化后的传感器性能进行预测,选择出最佳方案。结果表明：结构参数改进后,测量下限由0.07 m3/h降为0.035 m3/h。     

Automated adaptive cardiovascular flow simulations

We present an automatic adaptive procedure to perform blood flow simulations in the cardiovascular system. The procedure allows the user to start with subject-specific data collected through clinical measurements, like magnetic resonance imaging (MRI) data, and evaluate physiological parameters of interest, like flow distribution, pressure variations, wall shear stress, in an automatic and efficient manner. The process involves construction of geometric models of blood vessels, specification of flow conditions and application of an adaptive flow solver. The latter is based on incompressible Navier–Stokes equations using adaptive spatial discretization (meshing) techniques. In this article, we demonstrate the method on a model of a human abdominal aorta of a normal subject with geometry and flow rates assimilated from MRI data. The results obtained show that boundary layer mesh adaptivity offers a better alternative leading to more accurate predictions, especially for key physiological quantities like wall shear stress.     

并行计算在弧形翼弹数值仿真中的应用

在以MPICH技术构建的局域网集群系统下,利用并行计算程序进行了超声速弧形翼-身组合体的三维绕流流场数值仿真,得到了弧形翼射弹的流场信息;并且通过对不同数量网格在集群不同结点数目下的计算结果进行分析比较,得出了加速比和并行效率随结点数目变化的规律,发现大规模网格在加速比和并行效率方面性能优越,更适合集群系统的并行计算,同时验证了此集群系统在数值仿真应用中的有效性和优越性,为进行大规模科学工程计算提供了技术支持.     

Direct numerical simulation of turbulent flows with chemical reaction

Results from full turbulence simulations incorporating the effects of chemical reaction are compared with simple closure theories and used to reveal some physical insights about turbulent reacting flows. Pseudospectral methods for homogeneous turbulent flows with constant physical and thermal properties in domains as large as 64³ Fourier modes were used for these simulations. For the case of nonpremixed flows involving a two-species, second-order, irreversible chemical reaction, it is found that the scalar dissipation microscale is only a weak function of the reaction rate and that chemical reaction contributes very little to the decay of the variance of the reactant concentration. Examination of local values of the velocity and concentration fields shows that the local reaction rate is highest in regions of the greatest rates of strain and that vorticity tends to align with the reaction zone. Finally, difficulties associated with the evaluation of multipoint pdf's and with the archival of time-dependent data from the threedimensional simulations are described.Presented at the Second Nobeyama Workshop on Fluid Mechanics and Supercomputers, Nobeyama, Japan (September 1987).     

连续交通流可视化仿真

在大型城市的交通态势模拟中,宏观模型相比于微观模型,具有效率高,物理意义明确的优点,但缺乏车辆在各个时刻的细节描述。为了使宏观模型的交通模拟的显示更加直观,结合微观模型的更新方式,提出了基于宏观模型的可视化方法。通过道路上的车辆初始密度得到所有车辆的初始位置和速度;根据宏观路段速度更新车辆信息,使得宏观路段密度值与微观车辆所构成的车辆流密度相符。该方法能够给出宏观模型中车辆在各个时刻的运动情况,并添加了微观上的细节。以实例证明了该方法的可行性。     

热电薄膜型气体流量传感器的热模拟分析

利用有限元分析工具ANSYS/FLOTRAN ,模拟并分析了一个基于薄膜结构的热电型气体流量传感器的温度场。并具体地分析了在气体流量通道入口处气体的流向角度对传感器输出信号以及气体流动状态的影响。将最终的模拟计算结果与实验数据进行比较 ,发现二者基本吻合。利用此热学模型来模拟和分析此类传感器 ,不但可以减少大量的模拟分析过程而且可以降低计算的复杂度 ,另外也为此类传感器的设计和验证提供了一个非常简单而有效的方法和依据。     

交通诱导预测控制仿真研究

将动态交通分配实施过程纳入预测控制框架下以满足实时交通诱导的目的,提出一种交通诱导预测控制算法．该算法是在滚动时域基础上进行的,包括实时交通分配、交通流模拟运行及评价以及进化最佳路径３ 个重要环节．仿真结果表明,交通诱导预测控制是一种良好的计算机控制方法学,其优化过程预先考虑了目前交通分配对未来路网的影响,因而可有效地防范交通拥堵,实现考虑反馈的路网交通流实时分配优化,同时为出行者提供最佳路径．     

Multi space reduced basis preconditioners for parametrized Stokes equations

We introduce a two-level preconditioner for the efficient solution of large scale saddle-point linear systems arising from the finite element (FE) discretization of parametrized Stokes equations. This preconditioner extends the Multi Space Reduced Basis (MSRB) preconditioning method proposed in Dal Santo et al. (2018); it combines an approximated block (fine grid) preconditioner with a reduced basis (RB) solver which plays the role of coarse component. A sequence of RB spaces, constructed either with an enriched velocity formulation or a Petrov–Galerkin projection, is built. Each RB coarse component is defined to perform a single iteration of the iterative method at hand. The flexible GMRES (FGMRES) algorithm is employed to solve the resulting preconditioned system and targets small tolerances with a very small iteration count and in a very short time. Numerical test cases for Stokes flows in three dimensional parameter-dependent geometries are considered to assess the numerical properties of the proposed technique in different large scale computational settings.     

基于序贯蒙特卡洛算法的交通流事件重构

针对交通数据重构应用性差、缺乏对交通事件重构的研究等问题,结合交通流非线性非高斯的特点,提出一个基于序贯蒙特卡洛方法的交通流堵塞事件重构模型。该模型不断同化道路上的传感器数据,使仿真中的交通状态不断逼近真实路况,通过分析仿真数据以探测真实路网中存在的堵塞事件。模型能够对探测到的堵塞进行多粒子模拟来实现对真实道路上堵塞事件的重构。实验结果表明,该模型能够推测并重构出道路上的堵塞事件,对堵塞起始位置重构的平均误差为17m,对堵塞范围重构的平均覆盖率为82%。