前置导管节能效果数值计算与分析

前置导管作为一种典型的船舶节能装置,被广泛地应用于商船。该文分别对带前置导管与不带前置导管的JBC(Japan Bulk Carrier)进行带桨与不带桨数值计算,研究前置导管的节能效果。文中数值计算采用的求解器为上海交通大学基于开源代码平台Open FOAM与重叠网格技术自主开发的求解器naoe-FOAM-SJTU。该文通过试验值和CFD计算值对前置导管的节能效果进行评估,表明数值模拟结果与试验值吻合较好。     

针对PRESENT分组密码算法的代数分析*

本文研究针对PRESENT分组密码的代数分析。通过使用S盒的表达式形式,构建出多轮PRESENT加密中的代数方程组。这种构建方程的方法被推广到具有小型S盒的典型SPN型分组密码算法的方程构建问题中。文中还对简化的PRESENT算法进行了攻击实验。采用MiniSAT作为攻击过程中的求解工具,对4轮、6轮PRESENT加密进行实际攻击。可以在一分钟之内恢复4轮加密的所有密钥,数小时内恢复6轮加密的密钥。并且通过引入了差分思想,首次将有效攻击轮数提高到8轮。     

Aerodynamic shape optimization using efficient evolutionary algorithms and unstructured CFD solver

An efficient evolutionary algorithm is presented for shape optimization of transonic airfoils. Several techniques have been used to improve the efficiency and convergence rate of the optimization Genetic Algorithm (GA). A new airfoil shape parameterization method is used which is capable of producing more efficient shapes at viscous flow conditions. A Real-Coded Population Dispersion (PD) Genetic Algorithm is developed in order to increase the robustness and convergence rate of the Genetic Algorithm. A Multi-Layer Perceptron Neural Network (NN) is utilized to reduce the huge computational cost of the objective function evaluation. Further improvement in the performance of NN is obtained by using dynamic retraining and normal distribution of the training data to determine well trained parts of the design space to NN. Using the above techniques, the total computational time of optimization algorithm is reduced up to 60% compared with the conventional GA.     

Higher order operator splitting methods via Zassenhaus product formula: Theory and applications

In this paper, we contribute higher order operator splitting methods improved by Zassenhaus product. We apply the contribution to classical and iterative splitting methods. The underlying analysis to obtain higher order operator splitting methods is presented. While applying the methods to partial differential equations, the benefits of balancing time and spatial scales are discussed to accelerate the methods.The verification of the improved splitting methods are done with numerical examples. An individual handling of each operator with adapted standard higher order time-integrators is discussed. Finally, we conclude the higher order operator splitting methods.     

塔机有限元分析求解器的快速求解技术

塔式起重机结构有限元分析中，静力方程求解器是分析程序的核心。随着塔机求解规模的增大及对求解速度的高要求．传统的直接求解器愈显不足，成为有限元分析中的瓶颈。目前较好的塔机有限元程序是用稀疏直接求解器．其中引入循环展开（100p—unmlling）技术改进工作性能，实践证明，它对内存或硬盘空间的需求量明显减少，求解速度得到显著提高。     

C语言与Python语言混合编程的接口设计

在开发用于电磁场工程中参数提取的求解器过程中，为兼顾计算效率和方便的界面设计，采用C语言和Python语言混合编程的开发手段。本文阐述了这两种语言在本求解器中的接口设计方案，从而实现了这两种语言的混合编程。     

Numerical and experimental analyses of hydrodynamic performance of a channel type planing trimaran

This paper studies the hydrodynamic performance of a channel type planing trimaran. A numerical simulation is carried out based on a RANS-VOF solver to analyze the hydrodynamic performance of the channel type planing trimaran. A series of hydrodynamic experiments in towing tank were carried out, in which both the running attitude and the resistance performance of the trimaran model were recorded. Some hydrodynamic characteristics of the channel type planning trimaran are shown by the results. Firstly, the resistance declines significantly, with the forward speed across the high-speed resistance peak due to the combined effects of the aerodynamic and hydrodynamic lifts. Secondly, the resistance performance is influenced markedly by the longitudinal positions of centre of the gravity and the displacements. Besides, the pressure distribution on the hull and the two-phase flow in the channel are discussed in the numerical simulations.     

Investigation of the NREL phase VI experiment with the incompressible CFD solver THETA

DLR's incompressible flow solver THETA is introduced for wind turbine applications on the isolated NREL phase VI Unsteady Aerodynamic Experiment rotor. The optimization of parameter settings for the prediction of attached and separated flows on the rotor is performed, including time step size, spatial discretization scheme, turbulence models and Chimera overset grid technique. Afterwards, a systematic study on the pressure distributions, rotor thrust and rotor torque for experimental series S, I and J is performed. The accuracy of results for wind velocities between 7 and 25 m s[[EQUATION1]], covering attached, partly separated and deep stalled flow conditions, is discussed. While good to excellent agreement between THETA sectional pressure distributions and the experimental reference data is achieved in attached flow and deep stall configurations, more efforts are needed to predict partly separated flow cases with comparable accuracy. A code‐to‐code comparison with DLR's compressible flow solver TAU enabled the quantification of differences in pressure prediction because of the use of incompressible and compressible flow solvers. Copyright © 2017 John Wiley & Sons, Ltd.     

Structure-adaptive parallel solution of sparse triangular linear systems

Solving sparse triangular systems of linear equations is a performance bottleneck in many methods for solving more general sparse systems. Both for direct methods and for many iterative preconditioners, it is used to solve the system or improve an approximate solution, often across many iterations. Solving triangular systems is notoriously resistant to parallelism, however, and existing parallel linear algebra packages appear to be ineffective in exploiting significant parallelism for this problem.     

SMT求解器理论组合技术研究

可满足模理论(SMT)求解器是计算机科学中用来判定一阶逻辑公式可满足性的程序,是许多形式化方法的验证引擎.理论求解器实现了SMT基于不同理论背景的求解过程,然而实际问题常以多个理论为背景.因此,本文重点介绍理论组合判定方法,概述SMT求解器的发展现状,并分析了几个主流SMT求解器理论组合判定关键技术.通过对照实验,评估...