一种自组织网络DSR路由协议改进方法的研究

提出了一种基于缓冲器的DSR路由协议改进方案,对DSR的路由缓冲机制和路由缩短机制进行了改进,并在NS2中对改进协议和原DSR协议进行了对比仿真。仿真结果证明,改进的DSR协议在网络吞吐量、端到端时延、丢包率方面均优于原DSR协议。     

MAODV协议的QoS延伸

研讨了Ad Hoc网络中具有QoS约束的多播路由问题和网络模型,提出了一种基于延伸MAODV（Multicast Ad Hoc On-demand Distance Vector）多播路由协议的延时、带宽和包丢失率等度量的QoS多播路由协议。仿真实验显示该协议较好地改进b 端到端传输延时、带宽利用率和传输性能,为Ad Hoc网络QoS多播路由提供了一种新的有效途径。     

基于节点稳定性与跨层优化的MANET路由设计

针对移动自组织网络(MANET)中优化链路状态路由(OLSR)协议路由稳定性差和端到端延时高的问题,提出一种改进的OLSR路由协议。考虑MANET拓扑的移动性,通过优先选择平均相遇率较小、稳定性较高的中继节点构建移动拓扑,避免路由震荡。基于跨层技术,利用链路层共享的链路速率优化路由权值,从而提高路由性能。实验结果表明,与OLSR协议相比,改进协议在MANET网络中具有更好的网络稳定性及更低的端到端延时。     

自组织网络路由协议及仿真技术研究

自组织网络的路由协议是无线通信技术的重要核心部分。针对目前多数自组织网络协议设计的局限性,依据自组织网络结构和移动模型,研究自组织网络节点与临近节点之间的相对位置参数。依据其相对位置参数大小,提出自组织网络路由协议的改进算例。应用网络节点移动工具NS2仿真平台,基于网络端到端之间的延时时间判断,进行相应的网络路由协议改进前后的网络性能评价。仿真实验表明,改进后的无线自组织网络协议能够有效地提高网络性能。     

移动Adhoc网络分级安全路由SAODV协议研究

在移动Adhoc网络中,路由协议的安全性和开销已经成为一个重要的问题。SecureAODV（SAODV）协议作为Adhoc网络中一种流行的安全路由协议,其节点的签名验证过程和双签名机制限制了协议性能的提高。在对SAODV协议和A—SAODV协议比较分析的基础上提出了一种新的安全性改进方案,有效地引入了安全级别的概念,并对A--SAODV协议的自适应机制（AdaptiveReply Decision）进行了进一步优化。在NS2下的仿真结果表明,改进后的A—SAODV协议在缩短端到端延迟、提高吞吐量、增强安全等方面效果显著。     

基于Qualnet的Ad hoc路由协议性能分析

利用Qualnet仿真平台对移动自组网DSR和AODV路由协议的重要性能指标进行仿真测试,特别对不同暂停时间和业务发送时间下的抖动、吞吐量、端到端延时等参数进行了详细比较,对不同路由协议的实际应用和进一步性能改进提供数据参考.     

一种TEEN协议的节能型改进算法

在TEEN协议中,最高级簇头与基站之间采用单跳通信方式,网络能耗较大。为了降低无线传感器网络的能量消耗,提出一种TEEN协议的节能型改进算法。该算法借鉴平面路由协议Rumor的工作机制建立簇头与基站之间的通信路径,所有簇头与基站之间都采用多跳路由方式。与TEEN协议相比,该算法明显改善了网络能量消耗和网络生存时间,并使网络规模不再受到簇头通信半径的限制。     

容迟网络中传染路由协议优化

针对传染路由协议（EPI）的泛洪机制会造成容迟网络资源浪费的问题,提出将节点间的历史相遇信息引入传染路由协议的改进算法（EPI-HT）,以达到准确选择数据下一跳转发节点的目的。仿真结果表明,改进后的EPI-HT比EPI明显抑制了数据泛洪传输,可提高交付率,同时降低端到端时延。     

MANET中节点驻留时间对路由协议性能的影响

为了研究AODV,DSR和DSDV三种路由协议在MANET中运行恒定比特率FTP业务条件下的性能表现,使用NS仿真软件通过计算机仿真方法建立仿真模型,配置网络业务,运输层分别使用TCP协议和UDP协议对网络运行时的分组投递率和端到端时延等性能指标进行仿真分析。通过仿真分析发现,UDP通信时,DSR具有更高的分组投递率和更小的端到端时延;对于TCP传输而言,AODV比DSR和DSDV在分组投递率和端到端时延方面更有优势。所得结果对特定场合下MANET选择合适的路由协议具有指导意义,为进一步改进路由协议提供了参考依据。     

一个基于备份路由的AODV路由协议

AODV路由协议每次在源节点只建立一条通向目的节点的路由,未能充分利用从中间节点或者目的节点返回的路由应答信息,针对这一问题,提出了一个改进的方法。在源节点处建立一条主路由的基础上,利用路由应答信息,建立一条备份路由,并且每次将最优的设为主路由,次优的设为备份路由。仿真结果表明,改进的协议和原协议相比,降低了端到端的延时,提高了包投递率     

Monte Carlo simulations of a single polystyrene chain in spherical confinement

We report on Monte Carlo simulations of a single coarse-grained polystyrene chain in spherical confinement. To this end we employ a variant of the freely rotating chain model, the parameters of which are chosen to mimic polystyrene in good solvent conditions. Entanglements are analyzed as a function of molecular weight and capsid radius to provide an educated guess about the structure of a single polystyrene chain in a miniemulsion droplet. We also show that significant knotting occurs first when the radius of the confining sphere falls below the chain?s radius of gyration.     

A Riccati equation approach to maximizing the stability radius of a linear system by state feedback under structured stochastic Lipschitzian perturbations

The object of this paper is to maximize the stability radius of a linear state space system by state feedback under Lipschitzian structured stochastic perturbations. The supermanl achievable stability radius is characterized via the resolution of a parametrized Riccati equation and a matrix inequality. The dependence on the parameters is investigated and the limiting behaviour is examined. An example illustrating the results is treated at the end of the paper.     

Introducing Radius of Torsure and Cylindroid of Torsure

Robotic path planning can involve the specification of the position and orientation of an end‐effector to achieve a desired task (e.g., deburring, welding, or surface metrology). Under such scenarios the end‐effector is instantaneously rotating and translating about a unique axis; the ISA. Alternately, the performance of direct contact mechanisms (viz., cam systems and gear pairs) are dependent on the surface geometry between two surfaces in direct contact. Determination of this geometry can entail the parametrization of a family of geodesics curves embedded within each surface. This parametrization is tantamount to an end‐effector rotating and translating about an ISA. In both scenarios there is a unique ISA for each geodesic embedded in a surface. Here, curvature and torsion of a spatial curve are coupled together to define an alternative definition for the radius‐of‐curvature of a spatial curve. This new definition is identified as radius of torsure to distinguish it from the classical definition for radius‐of‐curvature. Further, it is shown that the family of twists that corresponds to the pencil of geodesics coincident with a point on a surface defines a cylindroid: the cylindroid of torsure. An illustrative example is provided to demonstrate this difference. © 2003 Wiley Periodicals, Inc.     

An Automated Method to Calibrate Industrial Robots Using a Virtual Closed Kinematic Chain

This paper describes an industrial robot calibration algorithm called the virtual closed kinematic chain method. Current robot kinematic calibration methods use measurements of position and orientation of the end effector. The accuracy of these measurements is limited by the resolution of the measuring equipment. In the proposed method, a laser pointer tool, attached to the robot's end effector, aims at a constant but unknown location on a fixed object, effectively creating a virtual 7 DOFs closed kinematic chain. As a result, small variations in position and orientation of the end effector are magnified on the distant object. Hence, the resolution of observations is improved, increasing the accuracy of joint angle measurements that are required to calibrate the robot. The method is verified using both simulation and real experiments. It is also shown in simulation that the method can be automated by a feedback system that can be implemented in real time. The accuracy of the robot after using the proposed calibration procedure is measured by aiming at an arbitrary fixed point and measuring the mean and standard deviation of the radius of spread of the projected points. The mean and standard deviation of the radius of spread were improved from 5.64 and 1.89 mm to 1.05 and 0.587 mm, respectively.     

Correlation between machining direction,cutter geometry and step-over distance in 3-axis milling: Application to milling by zones

Computer-Aided Manufacturing (CAM) occupies an increasingly important role in engineering with all it has to offer in terms of new possibilities and improving designer/manufacturer productivity. The present study addresses machining of free-form surfaces on a 3-axis NC machine tool. There have recently been a large number of studies devoted to planning tool paths on free-form surfaces with various strategies being adopted. These strategies are intended to increase efficiency by reducing the overall length of machining. Often, the choice of the cutter is arbitrary and the work focuses on planning. In order to boost productivity, the present work offers assistance in choosing the cutting tool, the machining direction and cutting by surface zones, adopting a milling strategy by parallel planes. To do so, a comparison is made between milling using a spherical end milling cutter and a torus end milling cutter with the same outer radius. This comparison relates to the radius of curvature of the trace left by the cutter at the point of contact between the tool and the workpiece in relation to the direction of feed motion.     

海洋非黏结柔性管道接头密封结构分析

介绍海洋非黏结柔性管道接头的常见密封结构,用Abaqus对接头的密封特性进行数值分析,研究密封圈的密封性能对不同密封结构参数的灵敏度,得到密封结构参数变化对接头密封结构的密封性能和力学性能影响的一般规律.结果表明密封结构的主要设计参数为密封圈的锥角和曲率半径以及加载位移等.     

Efficient circular arc interpolation based on active tolerance control

In this paper, we present an efficient sub-optimal algorithm for fitting smooth planar parametric curves by G¹ arc splines. To fit a parametric curve by an arc spline within a prescribed tolerance, we first sample a set of points and tangents on the curve adaptively as well as with enough density, so that an interpolation biarc spline curve can be with any desired high accuracy. Then, we construct new biarc curves interpolating local triarc spirals explicitly based on the control of permitted tolerances. To reduce the segment number of fitting arc spline as much as possible, we replace the corresponding parts of the spline by the new biarc curves and compute active tolerances for new interpolation steps. By applying the local biarc curve interpolation procedure recursively and sequentially, the result circular arcs with no radius extreme are minimax-like approximation to the original curve while the arcs with radius extreme approximate the curve parts with curvature extreme well too, and we obtain a near optimal fitting arc spline in the end. Even more, the fitting arc spline has the same end points and end tangents with the original curve, and the arcs will be jointed smoothly if the original curve is composed of several smooth connected pieces. The algorithm is easy to be implemented and generally applicable to circular arc interpolation problem of all kinds of smooth parametric curves. The method can be used in wide fields such as geometric modeling, tool path generation for NC machining and robot path planning, etc. Several numerical examples are given to show the effectiveness and efficiency of the method.     

Discrete-time optimal regulator with closed-loop poles in a prescribed region

This paper is concerned with the problem of designing discrete-time optimal control systems with closed-loop poles in a prescribed region of stability. First, by utilizing the property of the Riccati equation with Q being zero, we develop a method for allocating poles in a disc with centre at the origin of the complex plane and with radius less than 1. Secondly, we deal with pole placement in a disc which is in the unit disc and also contacts the point 1 + j0 of the complex plane. To this end, a bilinear transformation and continuous-time regulator results are employed. In each case, the radius of the disc can be specified as a design parameter, and the weighting matrices of the performance index are obtained to fulfil the desired pole allocations. The design procedures are also illustrated by numerical examples.     

一种图像的连续性边缘提取方法

图像边缘提取是图像处理领域的重要环节,边缘提取的连续性显得尤为重要,其结果可以作为语义分割、测量的基础,为此提出一种图像的连续性边缘提取方法。首先采用卡尼(Canny)算法完成图像的边缘检测,得到粗分割结果。由于该类算法采用算子进行操作,不可避免地产生非连续性区域,因此利用两类模板对粗分割结果进行形态学膨胀操作,连续性边缘采用小半径膨胀,边缘末端采用大半径膨胀,以此构成一幅膨胀图连接这些非连续性区域。最后,将该膨胀图作为平均曲率运动(MCM)方程嵌入函数u的初始值,通过引入g函数在原图中进行迭代求解,完成图像边缘的连续性提取。实验结果验证了算法的实用性与有效性。     

End mill design and machining via cutting simulation

This paper describes a design process for an end mill. A solid model of the designed cutter is constructed together with the computation of the cutter’s geometry, wheel geometry, and wheel positioning data for fabricating end mills with the required cutter geometry. The main idea of the process is to use the cutting simulation method to obtain the machined shape of an end mill by using Boolean operations between a given grinding wheel and a cylindrical workpiece (raw stock). The major design parameters of a cutter, such as rake angle and inner radius, can be verified by interrogating the section profile of its solid model. This study investigates the relationship between various dimensional parameters and proposes an iterative approach to obtain the required geometry of a grinding wheel and cutter location (CL) data for machining an end mill that satisfies the design parameters. This research was implemented using a commercial computer aided design (CAD) system with API function programming and is currently used by a commercial tool maker in Korea. It can eliminate the need to produce a physical prototype during the design stage and can be used in virtual cutting tests and analyses.