网络常见故障的分类诊断

网络故障极为普遍,故障种类也十分繁杂。如果把网络故障的常见故障进行归类查找,那么无疑能够迅速而准确的查找故障根源,解决网络故障。文章主要就网络常见故障的分类诊断进行了阐述。     

中国服装出口与绿色贸易壁垒

1、前言 纺织工业是中国出口创汇支柱性产业,也是外向依存度很高的行业.2001年中国纺织品出口创汇520.8亿美元,占全国出口商品总额的20.7%,其中服装出口约占纺织品出口总额的60%,即312亿美元.     

水面船舶操纵性敏感性分析

以两种水面船舶为研究对象,采用三自由度的常系数船舶操纵运动方程为数学模型,通过计算机仿真来考察水动力系数、舵的整流系数以及螺旋桨伴流系数对船舶操纵性的影响。结果用敏感性指数表示,仿真Z形操舵试验和船舶回转试验进行敏感性分析。分析表明,在船舶回转试验中,对船舶操纵性的回转性能影响较大的是线性水动力系数及舵整流系数;在Z形操舵试验中,线性水动力系数、舵整流系数、螺旋桨伴流系数、非线性水动力系数Nr′|r|以及附加质量(附加惯性矩)my、JZZ对超越角影响较大,其它系数依船型不同对超越角影响不同。从数据对比上看,这两种船的系数对超越角的影响普遍大于对回转直径的影响。不同船型的系数对超越角的影响相差很大。     

Steady state analysis of towed marine cables

Efficient numerical schemes were presented for the steady state solutions of towed marine cables. For most of towed systems, the steady state problem can be resolved into two-point boundary-value problem, or initial value problem in some special cases where the initial values are available directly. A new technique was proposed and attempted to solve the two-point boundary-value problem rather than the conventional shooting method due to its algorithm complexity and low efficiency. First, the boundary conditions are transformed into a set of nonlinear governing equations about the initial values, then bisection method is employed to solve these nonlinear equations with the aid of 4th order Runge-Kutta method. In common sense, non-uniform (sheared) current is assumed, which varies in magnitude and direction with depth. The schemes are validated through the DE Zoysa's example, then several numerical examples are also presented to illustrate the numerical schemes.     

中国服装出口与绿色贸易壁垒

2006年2月财政部颁布的《企业会计准则第7号——非货币性资产交换》借鉴了FAS153《非货币性资产交换》,对原有的非货币性交易准则进行了较大的修改,引入了公允价值作为计价基础,构成了一个公允价值和账面价值并存的计价模式。本文试图分析我国新旧准则的变化以及其与国外的处理方式的异同。     

拖航系统操纵运动仿真

采用MMG分离式船舶运动数学模型以及拖缆的悬链线模型,构建了由拖船——拖缆——被拖船组成的拖航系统操纵运动模型。通过数值计算,对该系统进行了操纵运动模拟仿真。主要的仿真项目包括拖航系统改变航向和受到小扰动时的运动。在此基础上研究了影响拖航系统航行性能的诸多因素,这些因素主要有:拖缆的长度、拖航速度、被拖船的拖航点位置。针对浅水效应给予拖航系统的影响以及通过改变PD控制参数改善拖航系统航向稳定性进行的初步探讨,得到了一系列有益的结论。     

A study on dynamic response of cable-seabed interaction

A numerical method is developed to investigate the dynamic response of cable-seabed interaction in this paper. The motion of cable is described by the Lumped Parameter Method, while the seabed, unlike the prevailing simplified model of elastic foundation, is modeled as an irregular continuous rigid surface with rebound and friction existing, and the forces exerted by the seabed consist of normal counterforce and isotropic tangential Coulomb friction resistance. To describe the detailed dynamic response, two coefficients are introduced by analogy with the theory of rigid body collision with friction. The cable-seabed kinematic and dynamic contact conditions are formulated subsequently, and are used to incorporate the seabed effect into the cable dynamics to produce a set of ordinary differential governing equations. In this paper, we employ 4th order Runge-Kutta method to solve these equations. Several simulation cases are presented to illustrate the seabed effect. The results show that friction and impact have a prominent influence on the statics and dynamics of the cable.     

Regularization method and immune genetic algorithm for inverse problems of ship maneuvering

Ship maneuverability, in the field of ship engineering, is often predicted by maneuvering motion group MMG) mathematical model. Then it is necessary to determine hydrodynamic coefficients and interaction force coefficients of the model. Based on the data of free running model test, the problem for obtaining these coefficients is called inverse one. For the inverse problem, ill-oposedness is inherent, nonlinearity and great computation happen,and the computation is also insensitive, unstable and time-consuming. In the paper, a regnlarization method is introduced to solve ill-posed problem and genetic algorithm is used for nonlinear motion of ship maneuvering. In addition, the immunity is applied to solve the prematurity, to promote the global searching ability and to increase the converging speed. The combination of regnlarization method and immune genetic algorithm(RIGA) applied in MMG mathematical model, showed rapid converging speed and good stability.     

A study of maneuvering control for an air cushion vehicle based on back propagation neural network

A back propagation (BP) neural network mathematical model was established to investigate the maneuvering control of an air cushion vehicle (ACV). The calculation was based on four-freedom-degree model experiments of hydrodynamics and aerodynamics. It is necessary for the ACV to control the velocity and the yaw rate as well as the velocity angle at the same time. The yaw rate and the velocity angle must be controlled correspondingly because of the whipping, which is a special characteristic for the ACV. The calculation results show that it is an efficient way for the ACV's maneuvering control by using a BP neural network to adjust PID parameters online.     

基于轨道交通网络特点的K最短路算法研究

城市轨道交通网络发展带来出行路径选择的复杂性,为了科学掌握线路客流,组织运输,合理引导乘客路径选择,需要开展轨道多路径算法研究;同时,随着生活节奏加快,要求算法高效,注重路径获取的实时性。针对轨道网络特征,将站点之间K最短路搜索转化为线路换乘组合搜索,降低搜索空间复杂度,并利用杭州轨道交通网络进行案例验证。算法明显提升轨道网络K最短路搜索效率,能够更快速响应轨道交通实际运行变化,有助于提升今后轨道交通出行服务应用。