一种网格环境下的密码计算模型

由于密码学和信息安全领域的许多问题最终都被转化为一个耗时的计算,其中许多计算需要利用多台异构的和地理分布的计算机协同,才能有效完成.密码算法的设计、分析和应用对于计算环境敏感,且依赖性较强,不同类型的算法和算法的不同实现模式对计算环境要求差异很大,而且到目前为止还不存在一种通用的分布式密码计算模型.为此,本文根据密码计算本身的需求,首先分别分析了密码算法设计、分析和应用的目标和特征,提出了相应的计算模式,给出了一种网格环境下的通用密码计算模型.进而讨论了密码计算任务分割策略,资源分配和负载平衡问题.最后给出了网格环境Globus Toolkit下的模型构架、实现与实验结果.

基于网格技术的密码学计算平台的设计

结合现有的网格技术、思想和密码计算的特点,分析了利用网格技术实现密码学计算的可行性,并结合J2EE开发方式的优势实现系统支持,最后提出了一种有效的、可行的密码计算网格平台构架.

关于网格计算授权机制的研究

分析了目前网格计算中最流行的安全机制GSI(Grid Security Infrastructure,网格安全基础设施)和基于GSI的CAS(Community Authorization Service,组织授权服务),提出了一种基于本地角色授权的、能够解决大规模VO(Virtual Organization,虚拟组织)的授权问题的方案.同GSI和CAS不同的是,本方案中的用户只需要进行本地认证就能够根据其在本地组织的角色来访问VO.

一种面向网格计算的分布式匿名协作算法

基于TCG提出的可信计算技术为网格协作安全性提出一种匿名分组身份验证算法,该算法可以非常可靠地解决网格计算平台之间的身份匿名验证问题.算法使用一个硬件模块TPM解决远程的身份验证,并通过TPM机制可以提供可靠的匿名验证和平台认证功能.算法中所有涉及的验证过程都是基于匿名机制实现的,除了实现匿名验证机制以外,算法还提供一套完整标记恶意网络实体的方法.提出了网格计算中虚拟分组的匿名认证平台架构,并在此架构基础上分成5步实现匿名验证算法,然后说明了算法在一种对等计算平台的应用实例,与GT2,GT3,GT4以及信任管理进行安全性的比较,并设计一个实验评价其性能.

基于移动代理的网格计算系统体系结构研究

本文针对物理链路可靠性低、容错性要求高、实体异构程度高的基础设施网格化需求，在系统分析当前主流的网格体系结构的基础上，研究了移动代理（PVM）系统的特性，根据移动代理的特点，提出了基于移动代理的四层网格计算模型MAGC(Mobile Agent Based Grid Computing)，描述了MAGC模型的层次结构，给出了MAGC模型的一个设计方案，分析了MAGC模型的特点，最后介绍了在Aglet平台下实现的原型系统。本文取得的成果主要包括： 第二章提出了基于移动代理的四层网格计算模型(MAGC)，说明了模型中每个层次的功能和层次之间的依赖关系。MAGC模型基于代码迁移，可以解决网络环境恶劣的条件下，网格系统的运行与部署问题。设计了MAGC模型的两个重要基础结构：作业机制和消息机制。设计了移动代理平台抽象层，使网格系统独立于具体的移动代理平台，从而具有一定的可移植性。 第三章在MAGC模型的基础上，进一步给出了MAGC模型的一个实现方案，阐述了MAGC模型中四个子层的功能和组件划分，对每层所包含的组件和组件实现的功能进行了描述，说明了系统的启动方式。 第四章基于MAGC模型构建了一个原型系统，原型系统以IBM开发的Aglets移动代理软件包为基础，实现了作业机制、消息机制和MAGC模型中的移动代理平台抽象层、系统服务层、API层、应用作业层四个子层。

一种非线性的分布式网格资源调价算法

针对网格环境下分布式异步动态调价算法存在均衡价格收敛过程缓慢、调价效率较低的缺点,提出了一种基于市场机制的非线性调价算法。该算法结合了当前超额需求和过去超额需求对资源价格变化的影响,较真实地刻画了需求变化后资源价格的波动过程。实验证明,非线性的调价算法明显地提高了价格收敛速度,降低了调价次数。

Computation of Viscous Incompressible Flow using Pressure Correction Method on Unstructured Chimera Grid

In this paper, a pressure correction algorithm for computing incompressible flows is modified and implemented on unstructured Chimera grid. Schwarz method is used to couple the solutions of different sub-domains. A new interpolation to ensure consistency between primary variables and auxiliary variables is proposed. Other important issues such as global mass conservation and order of accuracy in the interpolations are also discussed. Two numerical simulations are successfully performed. They include one steady case, the lid-driven cavity and one unsteady case, the flow around a circular cylinder. The results demonstrate a very good performance of the proposed scheme on unstructured Chimera grids. It prevents the decoupling of pressure field in the overlapping region and requires only little modification to the existing unstructured Navier–Stokes (NS) solver. The numerical experiments show the reliability and potential of this method in applying to practical problems.

Crypto-grid计算系统的设计与实现

简要介绍网格、密码计算特点和Crypto-grid的主要服务和组成,然后从系统需求、实现方法、主要功能模块、子任务计算实现等几个方面来剖析密码网格计算系统.

Numerical solution of the incompressible Navier-Stokes equations with an upwind compact difference scheme

A new finite difference method for the discretization of the incompressible Navier-Stokes equations is presented. The scheme is constructed on a staggered-mesh grid system. The convection terms are discretized with a fifth-order-accurate upwind compact difference approximation, the viscous terms are discretized with a sixth-order symmetrical compact difference approximation, the continuity equation and the pressure gradient in the momentum equations are discretized with a fourth-order difference approximation on a cell-centered mesh. Time advancement uses a three-stage Runge-Kutta method. The Poisson equation for computing the pressure is solved with preconditioning. Accuracy analysis shows that the new method has high resolving efficiency. Validation of the method by computation of Taylor's vortex array is presented.

A Multimoment Finite-Volume Shallow-Water Model On The Yin-Yang Overset Spherical Grid

A numerical model for shallow-water equations has been built and tested on the Yin-Yang overset spherical grid. A high-order multimoment finite-volume method is used for the spatial discretization in which two kinds of so-called moments of the physical field [i.e., the volume integrated average ( VIA) and the point value (PV)] are treated as the model variables and updated separately in time. In the present model, the PV is computed by the semi-implicit semi-Lagrangian formulation, whereas the VIA is predicted in time via a flux-based finite-volume method and is numerically conserved on each component grid. The concept of including an extra moment (i.e., the volume-integrated value) to enforce the numerical conservativeness provides a general methodology and applies to the existing semi-implicit semi-Lagrangian formulations. Based on both VIA and PV, the high-order interpolation reconstruction can only be done over a single grid cell, which then minimizes the overlapping zone between the Yin and Yang components and effectively reduces the numerical errors introduced in the interpolation required to communicate the data between the two components. The present model completely gets around the singularity and grid convergence in the polar regions of the conventional longitude-latitude grid. Being an issue demanding further investigation, the high-order interpolation across the overlapping region of the Yin-Yang grid in the current model does not rigorously guarantee the numerical conservativeness. Nevertheless, these numerical tests show that the global conservation error in the present model is negligibly small. The model has competitive accuracy and efficiency.

A Pressure-Correction Method And Its Applications On An Unstructured Chimera Grid

In this paper, an unstructured Chimera mesh method is used to compute incompressible flow around a rotating body. To implement the pressure correction algorithm on unstructured overlapping sub-grids, a novel interpolation scheme for pressure correction is proposed. This indirect interpolation scheme can ensure a tight coupling of pressure between sub-domains. A moving-mesh finite volume approach is used to treat the rotating sub-domain and the governing equations are formulated in an inertial reference frame. Since the mesh that surrounds the rotating body undergoes only solid body rotation and the background mesh remains stationary, no mesh deformation is encountered in the computation. As a benefit from the utilization of an inertial frame, tensorial transformation for velocity is not needed. Three numerical simulations are successfully performed. They include flow over a fixed circular cylinder, flow over a rotating circular cylinder and flow over a rotating elliptic cylinder. These numerical examples demonstrate the capability of the current scheme in handling moving boundaries. The numerical results are in good agreement with experimental and computational data in literature. (C) 2007 Elsevier Ltd. All rights reserved.

Fast Computing For Lurr Of Earthquake Prediction

The LURR theory is a new approach for earthquake prediction, which achieves good results in earthquake prediction within the China mainland and regions in America, Japan and Australia. However, the expansion of the prediction region leads to the refinement of its longitude and latitude, and the increase of the time period. This requires increasingly more computations, and the volume of data reaches the order of GB, which will be very difficult for a single CPU. In this paper, a new method was introduced to solve this problem. Adopting the technology of domain decomposition and parallelizing using MPI, we developed a new parallel tempo-spatial scanning program.

Sediment incipience in turbulence generated in a square tank by a vertically oscillating grid

The failure of hydraulic structures in many estuaries and coastal regions around the world has been attributed to sediment transport and local scour. The sediment incipience in homogenous turbulence generated by oscillating grid is studied in this paper. The turbulent flow is measured by particle tracer velocimetry (PTV) technique. The integral length scale and time scale of turbulence are obtained. The turbulent flow near the wall is measured by local optical magnification. The sediment incipience is described by static theory. The relationship of probability of sediment incipience and the turbulent kinetic energy were obtained experimentally and theoretically. The distribution of the turbulent kinetic energy near the wall is found to obey the power law and the turbulent energy is further identified as the dynamic mechanism of sediment incipience.

Euler Solution Using Adaptive Cartesian Grid With A Gridless Boundary Treatment

A quadtree-based adaptive Cartesian grid generator and flow solver were developed. The grid adaptation based on pressure or density gradient was performed and a gridless method based on the least-square fashion was used to treat the wall surface boundary condition, which is generally difficult to be handled for the common Cartesian grid. First, to validate the technique of grid adaptation, the benchmarks over a forward-facing step and double Mach reflection were computed. Second, the flows over the NACA 0012 airfoil and a two-element airfoil were calculated to validate the developed gridless method. The computational results indicate the developed method is reasonable for complex flows.