基于动态网格细分的烟雾模拟

提出了一种基于动态网格细分的烟雾模拟方法,该方法主要采取图形设备上的动态网格管理对烟雾进行并行处理以达到泊松方程的迭代求解。为了实现高性能,利用高速缓存以提高存取权限和适应硬件的能力。实验结果表明,该方法能够实现比较快速的模拟,结果比较令人满意。     

Application of the method of manufactured solutions to the verification of a pressure-based finite-volume numerical scheme

The present study reports a numerical procedure based on a series of tests that make use of the method of manufactured solutions (MMS) and allow to evaluate the effective numerical performance with respect to the theoretical order of accuracy. The method is applied to a pressure-based finite volume numerical scheme suited to variable density flows representative of those encountered in combustion applications. The algorithm is based on a predictor-corrector time integration scheme that employs a projection method for the momentum equations. A physically consistent constraint is retained to ensure that the velocity field is solved correctly. The MMS application shows that the combination of this velocity constraint and the variable-coefficient Poisson solver is of fundamental importance to ensure both the numerical stability and the expected order of accuracy. Especially, the resort to an inner iteration procedure gives rise to undeniable improvements in terms of both the order of accuracy and error magnitude. The MMS applications confirm the interest of the method to conduct a preliminary check of the performance of any numerical algorithm applied to both fully incompressible and variable density flows. Finally, the analysis is ended by the application of the retained pressure-based finite-volume scheme to the numerical simulation of mixing layers featuring increasing values of the density contrast. The corresponding results shed some light onto the stability and robustness of the numerical scheme, important issues that are not addressed through MMS analyses.     

New numerical method for the solutions of the MCDF equations based on the CIP method

A new numerical method based on the constrained interpolation profile (CIP) method to solve the Multiconfiguration Dirac-Fock (MCDF) equations is presented. The radial wave functions are represented by the values and the spatial derivatives on an arbitrary grid system, and approximated by cubic polynomials. Owing to this representation, the values and the spatial derivatives of the effective charge distribution and inhomogeneous term are calculated using the previous cycle's wave functions. Then the homogeneous MCDF equations are integrated to obtain two linearly independent solutions, which are used to construct the Green function, by the adaptive stepsize controlled Runge-Kutta method controlling the truncation errors within a prescribed accuracy. The radial wave function is improved by taking the convolution of the Green function and the inhomogeneous term. The effectiveness of this numerical procedure is investigated after implementing it into the relativistic atomic structure code GRASP92.     

基于迭代网格划分和熵估计的稀疏轨迹预测

针对移动对象轨迹预测所面临的"数据稀疏"问题,即有效的历史轨迹空间不能覆盖所有可能的查询轨迹,提出了一种基于迭代网格划分和熵估计的稀疏轨迹预测算法(TPDS-IGP&EE).首先,对轨迹区域进行迭代网格划分并生成轨迹序列;然后,引入L-Z熵估计计算轨迹序列的熵值,在轨迹熵值的基础上进行轨迹综合形成新的轨迹空间;最后,结合子轨迹综合算法,进行稀疏轨迹预测.实验结果表明,当轨迹完整度达到90%以上,Baseline算法的查询覆盖率只有25%左右;而TPDS-IGP&EE算法几乎不受查询轨迹长度的影响,可以预测几乎100%的查询轨迹;并且TPDS-IGP&EE算法的预测准确率普遍高于Baseline算法4%左右;同时Baseline算法的预测时间非常长,达到100 ms,而TPDS-IGP&EE算法的预测时间(10 μs)几乎可以忽略不计.TPDS-IGP&EE算法能够有效地进行稀疏环境下的轨迹预测,具有更广的预测范围、更快的预测速度和较高的预测准确率.     

基于数字平方算法的APSK信号位定时误差估计方法

APSK高阶调制用于卫星通信时,信号受收发系统的时钟频差影响严重,同步算法也较为复杂。介绍了APSK的信号模型,在此基础上,采用一种数字平方算法估计位定时的误差。仿真结果表明,该方法能较好地估计出APSK信号位定时误差,且算法不受载波频偏的影响。通过仿真得出了算法性能与运算数据长度的关系。     

On numerical error in the finite element method

Various sources of errors, physical and numerical, in the finite element method are analysed. A new type of iterative improvement is introduced where the residual is calculated in single precision. The iteration scheme is analysed with respect to round-off errors and found to give significant improvement over existing direct approaches.     

Verification of RANS solvers with manufactured solutions

This paper discusses code verification of Reynolds-Averaged Navier Stokes (RANS) solvers with the method of manufactured solutions (MMS). Examples of manufactured solutions (MSs) for a two-dimensional, steady, wall-bounded, incompressible, turbulent flow are presented including the specification of the turbulence quantities incorporated in several popular eddy-viscosity turbulence models. A wall-function approach for the MMS is also described. The flexiblity and usefulness of the MS is illustrated with calculations performed in three different exercises: the calculation of the flow field using the manufactured eddy-viscosity; the calculation of the eddy-viscosity using the manufactured velocity field; the calculation of the complete flow field coupling flow and turbulence variables. The results show that the numerical performance of the flow solvers is model dependent and that the solution of the complete problem may exhibit different orders of accuracy than in the exercises with no coupling between the flow and turbulence variables.     

基于Web Service的数值计算网格平台研究

在自强2000高性能集群计算机应用环境中使用NetSolve时,发现该系统存在一些问题。针对这些问题,结合Web Service技术提出了一种应用于高性能计算的网格系统,对该系统的体系结构进行了探讨。该系统有效地把高性能计算资源和网格技术结合在一起,取得了良好的应用效果。     

基于地标被动观测的飞航导弹INS误差估计方法

针对飞航导弹惯导系统(INS)单独使用时存在位置和速度估计误差发散的问题,以INS误差作为状态量,以导弹相对于地标的观测序列和高度表辅助INS估计信息解算的伪观测序列构造观测量,从便于工程实现的角度,提出一种迭代求解算法。迭代求解过程主要包括：利用平均去噪的思想降低测量噪声的影响、估计INS水平通道的位置和速度误差、对观测方程进行更新。仿真结果验证了所提出方法的有效性。     

Remarks on a posteriori error estimation for inaccurate finite element solutions

Usually, error estimators for adaptive refinement require exact discrete solutions. In this paper, we show how inaccurate solutions (e.g., iterative approximations) can be used, too. As a side remark we characterise iterative solution schemes that are particularly suited to producing good approximations for error estimators. This work was supported by Deutsche Forschungsgemeinschaft (Project Ha 1324/9).     

基于P-Tree的网格资源定位方法

网格环境中,如何高效准确地定位分布在不同结点上的资源一直是研究的热点.在研究P-Tree定位方法的基础上,通过分析网格资源的发布和查询过程,针对现有网格资源具有多维属性的特点,运用数值范围属性支持的多维属性定位方法的思想,提出了基于范围查询的多维属性定位方法.分析和模拟实验结果表明,该方法能够在较小的通信开销下有效实现资源定位并具有良好的可扩展性.最后,指出下一步研究的方向.     

An efficient error estimation method for antenna distortions in space based radar

The phased array antenna plays an important role in determining the performance achievable in a space based radar system. However, the array position errors caused by the antenna distortions in the complex cosmic vacuum environment will distort the antenna pattern, which significantly degrades the performance of the radar systems. Most of the conventional estimation methods are proposed based on the random position errors without the consideration of the distortion character for spaceborne arrays, resulting in a large estimation error. In this paper, to address this issue, an efficient array error estimation method is proposed to compensate the antenna distortion errors. In the proposed method, the initial sensor positions can be obtained based on the measured results from the units distributed over the array surface. Then the distortion model parameters can be estimated by solving an optimization problem. Based on this, the sensor positions can be corrected with high accuracy at the lth iteration. In this way, the proposed method can improve the accuracy and the robustness of the estimation simultaneously. Several simulated results are presented to validate the proposed method for the position error estimation in a space based radar system.     

Fast robust estimation of prediction error based on resampling

Robust estimators of the prediction error of a linear model are proposed. The estimators are based on the resampling techniques cross-validation and bootstrap. The robustness of the prediction error estimators is obtained by robustly estimating the regression parameters of the linear model and by trimming the largest prediction errors. To avoid the recalculation of time-consuming robust regression estimates, fast approximations for the robust estimates of the resampled data are used. This leads to time-efficient and robust estimators of prediction error.     

Code verification for governing equations with arbitrary functions using adjusted method of manufactured solutions

A new, adjusted approach to code verification using the method of manufactured solutions is presented. It is applicable for the physical problems, represented by mathematical models that include partial differential governing equations, which contain one or more functions that can vary from case to case. For the verification of such codes it has to be presumed that the varying functions are arbitrary and that is why this adjusted method is called the MMS-A. The aim of the new approach is further simplification of the existing methods that can become complex, time consuming and less convenient in general, when used for problems with arbitrary functions. With some additional programming the MMS-A can also be used for verifying codes, in which it is difficult to access the right-hand side of the governing equations (black box codes). In the present article the new method is described in detail and it is compared to the original method of manufactured solutions. It is demonstrated that using the MMS-A, the additional source term can be omitted. The use of the MMS-A is shown through examples that display the effectiveness of the new method.     

Accurate numerical method for the solutions of the Schrödinger equation and the radial integrals based on the CIP method

A new accurate numerical method based on the constrained interpolation profile (CIP) method to solve the Schrödinger wave equation for bound and free states in central fields and to calculate radial integrals is presented. The radial wave equation is integrated on an arbitrary grid system by the adaptive stepsize controlled Runge-Kutta method controlling the truncation errors within a prescribed accuracy. For the continuum orbitals in the highly oscillating region, the non-linear radial wave equation in the phase-amplitude representation is used. In the evaluation of the derivatives of the radial wave function, the potential energy is approximated by the CIP method. In addition, the radial integrals encountered in the computation of various atomic process are accomplished with the CIP method using the values and their analytical derivatives at the grids. This numerical procedure can be extended in a straightforward way to solve the Dirac wave equation.     

基于AGWL网格工作流模型的服务质量估算研究

针对ASKALON网格工作流管理系统中缺乏对服务质量组合方面的研究,基于AGWL网格工作流模型,提出了一种网格工作流服务质量的估算算法。该算法的主要特点是:1)基于AGWL语言;2)可扩展的QoS度量;3)多维全局QoS度量。最后,用仿真实验验证了该算法的可行性。     

基于分组误差的快速分数像素运动估计算法

H.264是最新一代的视频编码标准,它支持高精度分数像素运动估计。当在整数运动估计中采用快速算法后,分数像素的运动估计可能成为制约快速运动估计算法性能的瓶颈。根据匹配准则的目标函数在最优运动矢量的附近都是单调递增这一假设,提出一种基于分组误差的快速分数像素运动估计算法。实验结果表明该算法不但能够有效降低分数像素运动估计的计算量,而且还能保持较小的率失真性能损失。     

A service process optimization method based on model refinement

Due to the limited functionality of a single Web service, a group of Web services often need to be linked together, working as an integrated service process, to provide value-added functions. One of the key issues in modeling such an integrated service process, in addition to the functions it can provide, is the assurance of service quality. As Web services have become increasingly popular, a number of Web services with similar functions but different qualities can be readily found on the Internet. Which services you select to combine into an integrated service process severely impacts the quality of that service process. The quality of a service process is also subject to its structure. In the paper, a refinement method for quality optimization of a service process model is proposed. The refinement method takes into account the selection of Web services and the structure of the service process simultaneously. More specifically, in this method, a service process model is transformed into a process structure tree for quality calculation and then a genetic algorithm is applied to refine the service process model for quality optimization. The method, together with the experiment results, is discussed in detail in the paper. The experiment results show this method can optimize the quality of the service process by applying refinement method according to the requirements.     

基于最小均方误差估计的噪声相关UKF设计

传统Unscented卡尔曼滤波器(UKf)要求系统噪声和量测噪声必须是互不相关的.针对此局限性,研究了一类带相关噪声的非线性离散系统UKF设计方法.基于最小均方误差估计和正交变换,给出了噪声相关UKF滤波递推公式,并采用Unscented变换(UT)来计算系统状态的后验分布.所设计的UKF有效解决了传统UKF在噪声相关条件下非线性滤波失效的问题,拓展了UKF的应用范围.最后,仿真实例表明了所设计UKF的有效性.     

A grid workflow Quality-of-Service estimation based on resource availability prediction

Accurate estimation of workflow Quality of Service (QoS) enhances the efficiency of scheduling algorithms. The availability and performance variations of Grid computing resources have made this estimation a great challenge. Most workflow QoS estimation algorithms are based on static performance of resources. In this paper, based on resources availability prediction, we propose an algorithm called WQE for estimating the QoS of a Grid workflow. WQE consists of two phases: resource monitoring and analysis and workflow QoS computation. In the first phase, two prediction algorithms are proposed to stochastically predict the availability state of resources. In the second phase, the QoS of each activity is estimated based on the host availability prediction result. The QoS of basic structures is computed by aggregating the QoS of their operands. Using a tree structure corresponding to the workflow, the QoS of basic structures is used to compute the total QoS of the workflow. The simulation results on Notre Dame University trace showed that the proposed method has higher estimation accuracy in comparison with HEFT.