High-resolution finite difference schemes using curvilinear coordinate grids for DNS of compressible turbulent flow over wavy walls

Direct numerical simulations of compressible turbulent flow over wavy wall geometries have been carried out by solving N–S equations on general curvilinear coordinates. A 6th order WENO scheme with minimized dispersion and controllable dissipation is employed to compute the inviscid fluxes, a 4th order central difference scheme is applied to compute the viscous fluxes, and a 6th order conservative compact scheme is used for computing the geometrical metrics. An implicit LU-SGS method is used for time integration to improve computational efficiency over the explicit schemes such as the Runge–Kutta approach. The validity and applicability of the present algorithm is confirmed by comparing our results with laboratory experimental measurements and DNS results in the literature.     

Meshfree simulations of spall fracture

Shock wave induced spall fracture is a complex multiscale phenomenon, and it is a challenge to build a constitutive and computational model that can capture essential features of the spall fracture. In this work, we present a computational micro-mechanics model to simulate spall fracture by utilizing the multiscale micro-mechanics theory proposed by Wright and Ramesh [36] and a RKPM meshfree method. The focus of this work is to develop and demonstrate a simulation tool that is capable of simulations of spall fracture in engineering application. First, based on a well-known empirical formula, we relate the macroscale spall strength to the kinematics of micro void growth in a Representative Volume Element (RVE). The connection between micro void growth and overall kinematics of the RVE is made through the conservation of mass in the micro to macro transition process. Second, we develop a set of meshfree void growth algorithms that is tailored to represent kinematics of void nucleation, growth and coalescence, and these algorithms retain the conservation of mass, momentum, and energy during simulations of ductile spall fracture. Third, based on the Johnson–Cook model, we developed a meshfree computational formulation, and we have carried out simulations of the spall fracture of a Ti–6Al plate under impact loads to validate the model. From the simulation, we find that the interaction between the first two inelastic wave pulses plays an important role in the mechanism of spall fracture. The numerical results show that the proposed method can capture some features of the spall fracture, and it may be used to simulate the spall fracture in engineering applications.     

Motion regularization for matting motion blurred objects

This paper addresses the problem of matting motion blurred objects from a single image. Existing single image matting methods are designed to extract static objects that have fractional pixel occupancy. This arises because the physical scene object has a finer resolution than the discrete image pixel and therefore only occupies a fraction of the pixel. For a motion blurred object, however, fractional pixel occupancy is attributed to the object’s motion over the exposure period. While conventional matting techniques can be used to matte motion blurred objects, they are not formulated in a manner that considers the object’s motion and tend to work only when the object is on a homogeneous background. We show how to obtain better alpha mattes by introducing a regularization term in the matting formulation to account for the object’s motion. In addition, we outline a method for estimating local object motion based on local gradient statistics from the original image. For the sake of completeness, we also discuss how user markup can be used to denote the local direction in lieu of motion estimation. Improvements to alpha mattes computed with our regularization are demonstrated on a variety of examples.     

多频连续波雷达数据实时压缩算法设计

随着测试参数种类增加,测试环境越来越复杂,海量雷达数据与有限存储容量之间的矛盾日益明显,实时数据采集与压缩技术可以缓解这一矛盾的加剧.雷达数据采集系统采取了基于FPGA的LZW实时无损压缩算法.该算法能够实现追求采集信号精度的同时减低算法难度,已成功应用于某飞行测试实验,性能指标满足应用要求.     

基于SoPC的网络入侵检测中模式匹配系统设计

设计了一种基于FPGA的模式匹配系统,通过Verilog HDL语言实现系统主体;采用开源的Snort规则,选用由“异或”运算组成的适合FPGA处理的HashMem函数进行模式匹配;通过软件预处理找出Snort中的冲突模式串进行单独匹配从而用硬件方法解决冲突.硬件电路采用DM9000A网络控制器接收网络数据.实验结果显...     

贪婪算法在构建物流网络中的应用

分析了目前我国物流产业发展的现状,提出了如何利用Dijkstra算法在一个物流网络的各个节点之中,找出适合作为物流中心的节点。然后根据实际情况的需要,提出了一种经过改进的并行Prim算法。根据这一算法可以在整个物流网络当中找出两条以上的物流送货线路,从而提高物流运输的工作效率并在一定程度上减少物流产生的损耗。     

中空纤维支撑液膜处理含铜废水的数值模拟

处理含重金属离子的废水在环保和资源综合利用中备受关注,为了从微观机理上研究支撑液膜传质特性,建立中空纤维支撑液膜萃取铜离子的传质微分方程和有限差分法离散方程,并用Matlab迭代求解,得到铜离子在萃取过程中管内浓度轴向与径向的分布.分别模拟不同操作条件下的铜离子萃取情况,符合实验数据.表明在一定范围内,纤维管径增大、管...     

模糊自调整PID的精馏塔参考模型解耦控制研究

一个现代化的化工企业,精馏塔生产装置种类和数目为数众多,生产目的也多种多样。精馏塔控制方法的改良可以引起显著经济效益的变化,同时可以使生产过程更加节能环保,因此,化工企业存在着精馏过程控制算法的改良问题。精馏过程约占工业总能耗的1/3,其节能控制潜力很大。精馏塔温度控制系统是典型的多输入多输出耦合系统。针对多输入多输出耦合系统,为使其解耦控制与主回路控制达到相互独立,本文在分析与总结模糊逻辑、PID控制等优点的基础上,设计了一种参数自调整模糊PID控制器,并将其与多变量参考模型解耦控制方法结合,实现了精馏塔温度控制系统的解耦控制。参考模型回路由控制器和被控对象的模型两部分组成。模糊PID解耦控制器的引入,使控制与解耦功能分别由2个不同的控制器独立完成,最后将该算法应用于化工精馏塔温度控制模型中。由仿真结果可知,本文方法可以使实际输出结果很好的跟踪目标结果,从仿真图可得出,该方法可以较好的实现动态和静态解耦,解耦控制效果比较理想。进而可以将该方法用于实际的化工生产过程中,具有一定的实用价值。     

基于互斥角色约束的SSOD策略实现研究

静态职责分离（SSOD）是保证计算机安全的重要策略。在基于角色的权限控制(RBAC)中直接基于互斥角色约束（2-2 SMER）实现最简单的SSOD策略（2-n SSOD）是困难的。通过对互斥角色的权限分配进行约束,研究并证明了基于2-2 SMER实现2-n SSOD策略的充分条件,此充分条件和现有研究相比具有更弱的约束力,支持更灵活的权限分配。进一步给出了实现2-n SSOD策略的授权管理操作规则,以确保权限的动态管理始终满足此充分条件,维持系统对2-n SSOD策略的满足状态。最后,通过应用实例说明了实现2-n SSOD策略方法的有效性和可行性     

C＋＋语言程序设计中学生工程能力的培养

本文通过C＋＋语言程序设计的实习,提出了目前存在的问题。通过分析其理论实践意义、具体解决方案和具体实施过程,论述了如何将学生工程能力的培养贯穿于C＋＋语言程序设计的教学中。