Petascale large eddy simulation of jet engine noise based on the truncated SPIKE algorithm

With the emergence of petascale computing platforms, high-fidelity computational aeroacoustics (CAA) simulation has become a feasible, robust and accurate tool that complements theoretical and empirical approaches in the prediction of sound levels generated by aircraft airframes and engines. Differentiating itself from the broader discipline of computational fluid dynamics, CAA is particularly challenging as it demands high accuracy, good spectral resolution, and low dispersion and diffusion errors from the underlying numerical methods. Large eddy simulation based on space-implicit high-order compact finite difference schemes has been shown to meet such stringent requirements. In this paper, we discuss a new, scalable parallelization scheme with a three-dimensional computational space partitioning. Unlike many traditional multiblock computational fluid dynamics (CFD) methods, our partitioning is non-overlapping. We use the truncated SPIKE algorithm to solve the governing equations accurately and limit one-sided biased differentiation to just the physical boundaries. We present experimental performance data collected on Kraken and Ranger, two near-petascale computing platforms.     

湍流模型对电源车车舱内流场及散热的影响

针对某静音型电源车车舱结构及其通风散热特点,建立了车舱内部计算流体力学(Computational Fluid Dynamics,CFD)仿真模型,通过设置各类解析条件,分别利用Standardk-ε,Realizablek-ε,Standardk-ω和SSTk-ω四种湍流模型仿真模拟了车舱内流场和车载柴油发电机组的温度场,并分别测试了两条垂直线的风速对流场仿真结果进行了评价,测试了柴油发电机组和消声器不同测点的温度值,分析了散热的仿真精度.结果表明:k-ε模型的数值模拟结果比k-ω模型更加贴近实测结果,表明Realizablek-ε模型的仿真精度最高,适合静音型电源车车舱结构.     

建筑物健康诊断两种风荷载传感器的设计与应用

介绍了建筑物风工程研究用的两种风荷载传感器. 种是采用MEMS技术的梁膜岛复合力敏结构压阻微差压敏感元件,用准齐平无应力微封装,适用于建筑物缩模风洞试验测试用的风荷载动态微型微压传感器.另一种是采用MEMS梁膜复合结构力敏芯片,考虑了减小雨水张力影响及冲击载荷伴生的振动影响及防雷保护而封装的复合风雨荷载,现场实测用的风荷载传感器,它们均在实验和应用中取得良好的应用效果.     

Effects of speed, load and damping on the dynamic response of railway bridges and vehicles

In this paper, the effects of various parameters influencing the dynamic response of railway bridges are investigated. A versatile and computationally efficient numerical model was developed for this purpose. The model incorporates three-dimensional multi-body train and finite element bridge subsystems. The corresponding equations of motion are integrated numerically by applying the Newmark’s method combined with a modified Newton-Raphson iterative procedure. The model was verified by comparisons with analytical and numerical solutions available in the literature and good agreement was found. A parametric analysis was carried out to establish the key variables influencing the dynamic response of railway bridges. The speed of the train, train-to-bridge frequency, mass and span ratios, as well as bridge damping were identified as significant variables. Vehicle damping was found to have negligible influence on bridge response. Particularly strong dynamic amplification was found for train with shortly and regularly spaced axles travelling at the critical speeds. Other general conclusions were drawn on the basis of the parametric study.     

A three-dimensional model of primary thrombus formation based on fluid dynamics and level sets

In this paper, a three-dimensional (3D) multiscale model is proposed for the formation process of a primary thrombus. In the model, blood plasma is modelled by Navier–Stokes equations in macroscale because the blood plasma is seen as a continuous viscous fluid. The adhesion and aggregation of platelets are the main physiological processes of primary thrombus formation. As platelets and the primary thrombus are seen as rigid solids, these physiological processes are modelled in microscale according to the force related to the distance between the two solid bodies. We use level sets to represent the growth of the primary thrombus in 3D, and the multiscale model is applied to the 3D simulation of the primary thrombus formation. From numerical observations, the appearance of the formation process shows that it was affected by the change of blood-flow velocities. We can conclude that the appearance of the primary thrombus affects vascular blood flow.     

Ultimate load carrying capacity of the Lu Pu steel arch bridge under static wind loads

This paper investigates the ultimate load carrying capacity of the Lu Pu Bridge under static wind loads through the spatial finite element model. Both geometric and material nonlinearities are involved in the analysis. The Lu Pu Bridge is a long-span half-through-type steel arch bridge with a 550 m-long central span under construction in Shanghai, China. This will be the longest central span of any arch bridge in the world. Three load combinations are used in the ultimate load capacity analysis of the bridge. Combination I: combined dead and live loads over the entire bridge. Combination II: combined dead and wind loads. Combination III: combined dead load, wind load and live load over the entire bridge. Ultimate load capacity of the bridge is first investigated under load combinations I and II. Attention is paid mainly to investigate the load capacity of the bridge under load combination III. In the case of load combination III, the influences of several parameters (i.e., loading sequence, three components of wind loads and wind loads of individual bridge element) on the ultimate load capacity of the bridge are discussed. It is concluded that wind loads result in significant reduction in the ultimate load capacity when applied wind loads become large.     

基于气象无人机GPS/DR组合导航的单步长测风方法研究

针对气象无人机GPS／DR组合导航的特点,提出了一种利用位置构成的矢量三角形关系进行风场测量的新方法,并提出了单步长风场测量,最后对测量结果进行了仿真,结果表明：采用单步长测量时风速变化频率较高,能够将风场高频信号的变化特点反映出来,测量精度较高,均方差为4m／s。可以作为气象无人机测风的一种新方法。     

Auto-CFD-NOW: A pre-compiler for effectively parallelizing CFD applications on networks of workstations

Computational Fluid Dynamics (CFD) applications are highly demanding for parallel computing. Many such applications have been shifted from expensive MPP boxes to cost-effective Networks of Workstations (NOW). Auto-CFD-NOW is a pre-compiler that transforms Fortran CFD sequential programs to efficient message-passing parallel programs running on NOW. Our work makes the following three unique contributions. First, this pre-compiler is highly automatic, requiring a minimum number of user directives for parallelization. Second, we have applied a dependency analysis technique for the CFD applications, called analysis after partitioning. We propose a mirror-image decomposition technique to parallelize self-dependent field loops that are hard to parallelize by existing methods. Finally, traditional optimizations of communication focus on eliminating redundant synchronizations. We have developed an optimization scheme which combines all the non-redundant synchronizations in CFD programs to further reduce the communication overhead. The Auto-CFD-NOW has been implemented on networks of workstations and has been successfully used for automatically parallelizing structured CFD application programs. Our experiments show its effectiveness and scalability for parallelizing large CFD applications. This work is supported in part by the China National Aerospace Science Foundation, and by the U.S. National Science Foundation under grants CCR-9812187, CCR-0098055, CCF-0325760, CCF 0514078, and CNS 0549006.     

CFD显式差分程序的自动并行技术研究

对CFD显式计算程序的自动并行技术作了研究和探讨,从应用的角度出发,充分利用显式差分的特点和模拟手工并行的过程,集中研究了区域划分,相关性分析以及同步通信与优化等自动并行的核心技术。     

冷弯薄壁型钢蒙古包风雪作用下仿真研究

冷弯薄壁型钢蒙古包是一种新型房屋结构,结构质量轻、柔性大的特点决定了其控制荷载为风荷载与积雪荷载.通过计算流体动力学(CFD)方法,将蒙古包的风荷载体型系数与现行规范进行对比.模拟得到屋面的风荷载分布与不均匀雪荷载分布,定义2种风向角,将风荷载与风雪荷载分别作用于冷弯薄壁型钢蒙古包刚架,分析不均匀雪荷载与不同风向角对刚...     

Predicting the structures of complexes between phosphoinositide 3-kinase (PI3K) and romidepsin-related compounds for the drug design of PI3K/histone deacetylase dual inhibitors using computational docking and the ligand-based drug design approach

Predictions of the three-dimensional (3D) structures of the complexes between phosphoinositide 3-kinase (PI3K) and two inhibitors were conducted using computational docking and the ligand-based drug design approach. The obtained structures were refined by structural optimizations and molecular dynamics (MD) simulations. The ligands were located deep inside the ligand binding pocket of the p110α subunit of PI3K, and the hydrogen bond formations and hydrophobic effects of the surrounding amino acids were predicted. Although rough structures were obtained for the PI3K–inhibitor complexes before the MD simulations, the refinement of the structures by these simulations clarified the hydrogen bonding patterns of the complexes.     

Estimation of distribution and differential evolution cooperation for large scale economic load dispatch optimization of power systems

Economic Load Dispatch (ELD) is an important and difficult optimization problem in power system planning. This article aims at addressing two practically important issues related to ELD optimization: (1) analyzing the ELD problem from the perspective of evolutionary optimization; (2) developing effective algorithms for ELD problems of large scale. The first issue is addressed by investigating the fitness landscape of ELD problems with the purpose of estimating the expected performance of different approaches. To address the second issue, a new algorithm named “Estimation of Distribution and Differential Evolution Cooperation” (ED-DE) is proposed, which is a serial hybrid of two effective evolutionary computation (EC) techniques: estimation of distribution and differential evolution. The advantages of ED-DE over the previous ELD optimization algorithms are experimentally testified on ELD problems with the number of generators scaling from 10 to 160. The best solution records of classical 13 and 40-generator ELD problems with valve points, and the best solution records of 10, 20, 40, 80 and 160-generator ELD problems with both valve points and multiple fuels are updated in this work. To further evaluate the efficiency and effectiveness of ED-DE, we also compare it with other state-of-the-art evolutionary algorithms (EAs) on typical function optimization tasks.     

Three dimensional numerical simulations of long-span bridge aerodynamics, using block-iterative coupling and DES

The design of long-span bridges often depends on wind tunnel testing of sectional or full aeroelastic models. Some progress has been made to find a computational alternative to replace these physical tests. In this paper, an innovative computational fluid dynamics (CFD) method is presented, where the fluid-structure interaction (FSI) is solved through a self-developed code combined with an ANSYS-CFX solver. Then an improved CFD method based on block-iterative coupling is also proposed. This method can be readily used for two dimensional (2D) and three dimensional (3D) structure modelling. Detached-Eddy simulation for 3D viscous turbulent incompressible flow is applied to the 3D numerical analysis of bridge deck sections. Firstly, 2D numerical simulations of a thin airfoil demonstrate the accuracy of the present CFD method. Secondly, numerical simulations of a U-shape beam with both 2D and 3D modelling are conducted. The comparisons of aerodynamic force coefficients thus obtained with wind tunnel test results well meet the prediction that 3D CFD simulations are more accurate than 2D CFD simulations. Thirdly, 2D and 3D CFD simulations are performed for two generic bridge deck sections to produce their aerodynamic force coefficients and flutter derivatives. The computed values agree well with the available computational and wind tunnel test results. Once again, this demonstrates the accuracy of the proposed 3D CFD simulations. Finally, the 3D based wake flow vision is captured, which shows another advantage of 3D CFD simulations. All the simulation results demonstrate that the proposed 3D CFD method has good accuracy and significant benefits for aerodynamic analysis and computational FSI studies of long-span bridges and other slender structures.     

基于TL_Sheduling的异构集群负载均衡算法的研究与应用

异构环境下"集群系统"负载均衡技术的关键是实现进程的跨平台迁移,对于进程的跨平台迁移所带来的困难和开销是巨大的.在传统进程迁移算法基础上,充分考虑节点对提交作业的适应性,提出一种新的TL-Scheduling负载均衡算法,能够控制作业提交到适合它执行的节点上,该算法可以有效提高系统负载均衡和作业执行效率.在其基础上,研究设计了基于XML业务流程模板的卫星作业调度系统,使得作业调度系统更加实用化.     

On the effect of wind direction and urban surroundings on natural ventilation of a large semi-enclosed stadium

Natural ventilation of buildings refers to the replacement of indoor air with outdoor air due to pressure differences caused by wind and/or buoyancy. It is often expressed in terms of the air change rate per hour (ACH). The pressure differences created by the wind depend - among others - on the wind speed, the wind direction, the configuration of surrounding buildings and the surrounding topography. Computational Fluid Dynamics (CFD) has been used extensively in natural ventilation research. However, most CFD studies were performed for only a limited number of wind directions and/or without considering the urban surroundings. This paper presents isothermal CFD simulations of coupled urban wind flow and indoor natural ventilation to assess the influence of wind direction and urban surroundings on the ACH of a large semi-enclosed stadium. Simulations are performed for eight wind directions and for a computational model with and without the surrounding buildings. CFD solution verification is conducted by performing a grid-sensitivity analysis. CFD validation is performed with on-site wind velocity measurements. The simulated differences in ACH between wind directions can go up to 75% (without surrounding buildings) and 152% (with surrounding buildings). Furthermore, comparing the simulations with and without surrounding buildings showed that neglecting the surroundings can lead to overestimations of the ACH with up to 96%.     

液压制动螺纹插装集成阀动态特性仿真与研究

研究单个螺纹插装结构参数对集成阀系统的综合动态影响,为明确液压制动系统动态响应特性,采用功率键合图法建立了履带底盘液压制动螺纹插装集成阀控制系统的键图模型,根据图元之间的关系,选定状态变量,导出了系统数学模型,MATLAB软件上仿真求解系统状态方程组.对比试验曲线与仿真数据,结果相吻合,验证了系统模型和仿真算法的正确性.分析仿真结果,得到螺纹插式梭动阀阀芯球直径、进出油口直径和螺纹插式减压阀复位弹簧刚度、进出油口直径对系统的压力稳定值和稳定时间的综合影响规律.     

移动副速度对空气轴承影响的CFD仿真分析

研究空气轴承优化控制问题,针对高速移动副空气轴承对空气轴承气膜特性会影响定位精度特点,空气轴承采用非结构化网格实现了多节流器气膜的耦合,设计的密度可控的非均匀网格划分方案克服了最大最小尺寸比偏大给实际带来的困难。根据FLUENT用三维双精度耦合隐式标准k-ε粘性湍流两方程模型,仿真得到了不同移动副速度时,阵列多节流器耦合后的质量流量、气膜压强分布和速度分布,为辨识高速移动副时多节流器耦合的气膜数学模型提供了详实数据。当增大移动副速度时,耗气量减小但气膜承载力增加,为高速移动副空气轴承的优化设计提供了依据。     

大规模并行粒子模拟中基于主从架构的负载平衡策略研究与实现

粒子方法作为一种直观而且普适的模拟方法,在化工、材料、生物等领域得到了广泛的应用。本文采用主从(Master／Slave)并行模型,基于正交递归对分法(recursive coordinate bisection,RCB)和规则网格,设计出一种适用于具有多种复杂粒子的粒子系统并行模拟的负载平衡方法。应用该方法,在集群系统上采用离散元方法模拟了某钢铁公司滚筒系统。模拟采用4个节点,根据是否利用负载平衡模块分别进行测试,计算结果分析表明采用本文的负载平衡策略,计算效率提高了约14％。本文的算法具有较好的通用性,可以方便地应用于其它粒子方法的大规模并行计算问题。     

基于逆运动学和动力学的虚拟人行走仿真

在计算机上模拟真实人行走是计算机仿真的一个基本问题。人体行走是一种伴随着碰撞、摩擦和滑动的复杂的系统运动,为了实现模拟的逼真性,需要着重在运动控制上进行研究。首先对人体行走进行分析并建立了简单的人体模型,然后详细给出行走过程中关节点位置的数学描述,最后采用逆运动学求解雅可比矩阵的方法并结合动力学知识,运用VC＋＋．NET和OpenGL为编程工具以骨架模型实现了虚拟人行走。