基于非结构网格求解三维D'Alembert介质中声波方程的并行加权Runge-Kutta间断有限元方法

间断有限元方法(Discontinuous Galerkin method,简称DGM)在求解地震波动方程时具有低数值频散、网格剖分灵活等优点,因此,为适应数值模拟对模拟精度和复杂地质结构的要求,本文提出一种新的加权Runge-Kutta间断有限元(weighted Runge-Kutta discontinuous ...     

基于MPI环境的并行程序设计

MPI(Message Passing Interface)是消息传递并行程序设计的标准之一,概述了MPI的概念和组成,着重介绍了支持并行程序设计的消息传递接口(MPI)以及在MPI环境下的并行程序设计方法,并给出一个MPI并行程序设计实例,说明了MPI的程序设计流程和主从并行计算流程,由此提出了一个Master/Slave结构的设计模式。     

THE BEIJING AREA MESOSCALE NWP SYSTEM AND ITS APPLICATION

Significant progress has been made on the development of mesoscale numerical weather prediction(NWP)system for Beijing area,as a joint project of the National Meteorological Center(NMC)andthe Beijing Meteorological Bureau(BMB).On the basis of the non-hydrostatic mesoscale model PSU/NCAR MM5,a mesoscale NWP system for Beijing area(BJ-MM5V.1)has been developed on thecomputer IBM/SP2 MPP with 24 nodes at NMC.As a two-way nested grid model two grids arechosen with 45 and 15km grid length respectively,and 23 levels in the vertical.It takes 2 hours and20 minutes to make a 36h forecast,which satisfies the time requirement for the operational use.Inaddition to the routine data received from GTS at NMC,the enhanced observations over Beijingregion are used for the objective analyses.This system was put into semi-operational use during thesummer of 1997 to test its performance.The forecast products,hourly rainfalls and all of themeteorological elements needed,are provided to the forecasters at BMB for use.It is identified fromthe test results that the system is robust and has pretty good ability to forecast the spatial andtemporal distribution of the precipitation for the local heavy rainfalls.     

平行盾构隧道施工对既有隧道影响的数值分析

采用三维有限元方法对平行盾构隧道施工进行模拟,分析新隧道动态掘进时既有隧道位移、变形和内力的变化规律。模型中考虑了盾构机与管片衬砌相互作用,管片衬砌结构的横观各向同性性质。计算结果表明,既有隧道在盾构机附近主要产生纵向上的不均匀沉降和侧移,在盾构机后方主要产生横断面内的旋转。新隧道的修建还将使既有隧道受到“侧向加载“效应,使其横断面内的弯矩减小,轴力增大,且左、右侧受力不再对称。既有隧道纵向受力出现先受压、后受拉的特征,且在远离新隧道侧将出现最不利应力状态。分析表明盾构机顶进力、注浆压力和地层损失对既有隧道的影响较大,施工中应严格控制,而顶进反力的影响相对较小。该工作为类似工程的施工提供参考。     

大型洞室群软岩置换方案优化的并行实现

并行计算己成为求解大规模岩土工程问题的一种强大趋势 。 以水布娅大型洞室群软岩置换方案优化为例 , 探讨了方案优化中的并行计算问题,分析了并行计算中的编程模式 、 任务划分 、负载平衡和编程方法等问题,在 W id n o w s 环境下的 PC 机群上成功实现了软岩置换方案优化的并行计算,并获得了近乎线性的加速比 , 从而大大提高了方案优化的计算速度和效率 , 为岩土工程计算并行化思路提供了重要参考 。     

基于并行遗传算法的地震属性优化研究

系统介绍了遗传算法各步的改进策略。首先,产生多样化的初始群体,引入五进制的编码策略提高搜索速度,然后采用无退还随机选择机制防止收敛早熟,采取两点交叉及多点变异方案以扩大模型空间的搜索范围和保持个体的多样性。另外,为了保证算法的收敛,使用了代间隙技术。最后,按照并行算法设计原则给出改进后的并行遗传算法的算法描述,并通过运用改进的并行遗传算法解决了非线性、多参数、多极值的地震属性优化的实际问题。     

Effect of NAPL exposure on the wettability and two‐phase flow in a single rock fracture

Surface‐wetting properties are an important cause of changing the groundwater and two‐phase fluid flows. Various factors affecting the surface wettability were investigated in a parallel‐walled glass fracture with non‐aqueous phase liquid (NAPL) (gasoline, diesel, trichloroethylene, and creosote) wetted surfaces. First, the effect of the duration of NAPL exposure on wettability change was considered at pre‐wet fracture surfaces using the various NAPL species, and the result showed that the surface became hydrophobic after the exposure time of NAPL exceeded 2000 min. Second, the initial wetting state of the surface affected the timing when the wettability change begins as well as the extent of the wettability change in an NAPL‐wetted rock fractures. Under the dry condition, the wettability change was completed within a very short time of exposure to NAPL (~5 min), and then it finally reached the intermediate and weakly NAPL wetting (contact angle of 118°). Under the pre‐wet condition, a relatively long time of exposure (~5000 min) was needed to observe the obvious change of the surface wettability, which was changed up to strongly NAPL wetting (contact angle of 142°). Third, the wettability changed by NAPL exposure was stable and maintained for a long time, regardless of water flushing rate and temperature. Finally, the wettability change by the exposure of NAPL on parallel fracture surfaces was evaluated at various groundwater flow velocities. Result showed that groundwater flow velocity has an important impact upon measured contact angle. Although fracture surfaces were exposed to NAPL at the low groundwater flow velocity, the wettability was not changed from hydrophilic to hydrophobic when the contact time between NAPL and mineral surfaces was not sufficient owing to the pulse‐type movement of NAPL. This implies that the variation of exposure pattern due to groundwater flow on the wettability change can be an important factor affecting the wettability change of fracture surface and migration behaviour at natural fractured rock aquifers in case of NAPL spill. Copyright © 2015 John Wiley & Sons, Ltd.     

Porting of a wildfire risk and fire spread application into a cloud computing environment

Effective wildfire management is an essential part of forest firefighting strategies to minimize damage to land resources and loss of human lives. Wildfire management tools often require a large number of computing resources at a specific time. Such computing resources are not affordable to local fire agencies because of the extreme upfront costs on hardware and software. The emerging cloud computing technology can be a cost- and result-effective alternative. The purpose of this paper is to present the development and the implementation of a state-of-the-art application running in cloud computing, composed of a wildfire risk and a wildfire spread simulation service. The two above applications are delivered within a web-based interactive platform to the fire management agencies as Software as a Service (SaaS). The wildfire risk service calculates and provides daily to the end-user maps of the hourly forecasted fire risk for the next 112 hours in high spatiotemporal resolution, based on forecasted meteorological data. In addition, actual fire risk is calculated hourly, based on meteorological conditions provided by remote automatic weather stations. Regarding the wildfire behavior simulation service, end users can simulate the fire spread by simply providing the ignition point and the projected duration of the fire, based on the HFire algorithm. The efficiency of the proposed solution is based on the flexibility to scale up or down the number of computing nodes needed for the requested processing. In this context, end users will be charged only for their consumed processing time and only during the actual wildfire confrontation period. The system utilizes both commercial and open source cloud resources. The current prototype is applied in the study area of Lesvos Island, Greece, but its flexibility enables expansion in different geographical areas.     

面向复杂城市场景的Sort-First并行绘制系统中负载平衡与性能分析

在高精度建模方法越来越丰富的背景下,三维城市场景往往具有较大的场景规模和较高的复杂性,因此,当单台计算机难以满足实时绘制的需求时,多采用更加适合超高分辨率大屏幕显示的Sort-First方式进行并行绘制。针对现有研究性能量化分析的缺乏,及自适应负载平衡方法的缺陷,本文通过Sort-First并行绘制系统的加速比模型,分析绘制节点数、显示分辨率、网络传输速度、任务划分等因素对系统性能的影响,以及将绘制时间和传输时间的和作为反馈,对现有负载平衡策略进行了改进。本文给出了系统达到最高加速比,即负载完全均衡理想情况下的一个量化的必要条件。最后,基于Sort-First的并行绘制实验验证上述分析。实验结果表明:本文的改进加强了各节点的负载平衡性,在一定程度上提高了性能。     

基于GPU的SIFT特征点快速匹配

影像匹配是计算机视觉及数字摄影测量的核心问题,基于特征的SIFT匹配算法由于其较强的匹配能力和良好的健壮性成为研究的热点.但SIFT算子的多量性及提取特征点维度较高的特点,直接影响了匹配速度.因此,本文利用GPU强大的并行处理能力,就SIFT特征点匹配在GPU上的设计与实现进行了详细的介绍,并通过对比实验说明利用GPU对SIFT特征点进行匹配所带来的优势.