计算机有限元仿真在钢缆在线定量检测中的应用

钢缆在线检测时,钢缆与检测设备之间相对运动,钢缆中产生的涡流严重影响缺陷定量检测的精度。采用电磁场有限元专业软件,选择二维轴对称柱坐标系,创建钢缆缺陷检测结构的几何实体模型,利用瞬态求解器数值计算了磁路磁力线分布和钢缆截面涡流分布。研究发现：随着速度的增加,磁路磁力线密度逐渐增加,涡流密度先增加后减小,磁力线和涡流的扩散方向与速度方向有关。研究结果与国外发表文献中的实验结果相符合,验证了有限元仿真在钢缆在线检测中的有效性。     

Analysis of target configurations under dead loads for cable-supported bridges

This paper presents a rigorous approach for analyzing the target configurations of cable-supported structures under dead loads by the Newton–Raphson method. A linearized equilibrium equation of a cable element, which includes the nodal coordinates and the unstrained element length as unknowns, is formulated using the analytical solution of an elastic catenary cable. An incremental equilibrium equation for a single cable is formed with the proposed equilibrium matrices of cable elements. The geometry of the target configuration of a cable-supported structure under dead loads is utilized to solve the incremental equilibrium equation. Detailed procedures to analyze the target configurations of suspension bridges and cable-stayed bridges are presented. The efficiency and the accuracy of the proposed method are demonstrated through numerical examples.     

Nonlinear elasto-plastic analysis of slack and taut cable structures

This paper presents the geometrically nonlinear analysis of the slack and taut cable structures considering the material inelasticity subjected to self-weight, pretension, and external loads. The finite element procedure is briefly summarized using the Lagrangian formulation associated with isoparametric interpolation polynomials and the Newton–Raphson iterative scheme with incremental load. The simple and efficient method to determine the initial equilibrium state of the slack cable systems under self-weight as well as support motions is presented using the penalty method. The numerical algorithm to evaluate the tangent modulus of elasticity of cable is presented based on the iterative scheme. The accuracy and reliability of the present study are verified by comparing the predictions with those generated by well-reported slack and taut cable structure problems. The effect of the yielding of cable segments on displacements and stresses of cable structures is investigated.     

小波变换用于钢丝绳断丝检测的研究

本文采用漏磁场探伤方法对钢丝绳断丝进行检测,该方法的原理是利用励磁磁场和缺陷(即钢丝断丝处)相互作用产生的漏磁场来检测钢丝绳断丝,并且利用霍尔元件能够准确地获取漏磁场信号.首次把声表面波式小波变换的重构器件应用于钢丝绳断丝检测中.发现声表面波器件的发射叉指换能器和接收叉指换能器的指条重叠包络均按照小波函数(如Morlet小波)包络设计时,从而得到声表面波器件的发射叉指换能器和接收叉指换能器的脉冲响应函数均等于小波函数,所以制作出了声表面波式小波变换的重构器件.该器件是一带通滤波器,其相对带宽是1.1%,所以该器件可有效滤除干扰信号.     

Cable installation simulation by using a multibody dynamic model

A major concern when installing the cables into the underground conduit is minimizing the tensile forces exerted on the cables as they are pulled. This knowledge makes it possible to avoid over conservative design practices and to achieve substantial saving during construction. A general computing algorithm of predicting the tensile force of the cable pulled through the underground conduit with an arbitrary configuration is presented in this paper, which is based on multibody system dynamic formulation. The presented multibody dynamic model for this problem consists of the cable, the underground conduit, and the interaction between the cable and the conduit. In this paper, the cable is modeled by the finite cable element based on an absolute nodal coordinate formulation. The interaction between the cable and the underground conduit is described by the Hertz contact theory. Numerical examples are presented to illustrate the effectiveness and efficiency of the proposed method for estimating the cable tension.     

Massless Cable for Real-time Simulation

A technique for real‐time simulation of hoisting cable systems based on a multibody nonideal constraint is presented. The hoisting cable constraint is derived from the cable internal energies for stretching and twisting. Each hoisting cable introduces two constraint equations, one for stretching and one for torsion, which include all the rigid bodies attached by the same cable. The computation produces the global tension and torsion in the cable as well as the resulting forces and torques on each attached body. The complexity of the computation grows linearly with the number of bodies attached to a given cable and is weakly coupled to the rest of the simulation. The nonideal constraint formulation allows stable simulations of cables over wide ranges of linear and torsional stiffness, including the rigid limit. This contrasts with lumped element formulations including the cable internal degrees of freedom in which computational complexity grows at least linearly with the number of cable elements – usually proportional to cable length – and where numerical stability is sensitive to the mass ratio between the load and the lumped elements.     

测井缆长的误差建模及应用

为提高测井电缆缆长测量精度,给光纤陀螺连续测斜仪提供高精度缆长信息,对基于光电编码器的缆长测量方法进行了详细误差分析并建立了缆长拉伸误差数学模型。构建了基于FPGA@虚拟仪器的缆长测量系统并应用拉伸误差模型进行拉伸误差的软件补偿．实现了测井缆长的高精度测量。最后刺ABAQUS有限元软件对测量结果进行了仿真验证,结果表明。经误差补偿后缆长测量相对误差低于0．3‰,满足测斜仪对缆长精度的要求。     

The efficiency of dynamic relaxation methods in static analysis of cable structures

Nine different schemes of dynamic relaxation method are compared in the paper. Schemes with viscous damping and schemes with kinetic damping are used. Kinetic damping with a peak in the middle of the time step and kinetic damping with the parabolic approximation of the peak are considered. They are also used in three different ways of cable approximation. The cable is approximated as a tension bar, a catenary and a parabolic cable element. The efficiency and stability of each method are compared to three selected 3D examples of cable structures and one existing structure. The effect of mass distribution along the structure is also of interest and is studied in the paper.     

The analysis of nonlinear cable net systems and their supporting structures

The analysis of large cable net systems is feasible only with the aid of high speed digital computers. However, even computerized design of cable nets requires careful formulation and the selection of efficient solution techniques. This paper describes the solution of a general integrated structural system which includes three-dimensional beam members and cable elements that is useful to the design engineer. This solution is used to analyze an example prestressed cable structure, and results are presented to demonstrate the efficiency and accuracy of different solution techniques and to illustrate the effect of variation of important parameters.NET 3 is the general solution program. Input includes: (1) cable sizes, weights, and stress-strain characteristics; (2) initial coordinate points and cable forces due to prestressing; (3) support conditions for the cable net; (4) applied loads; and (5) data for supporting structure. The initial shape and cable forces are computed with the aid of an auxilliary program, SHAPE, given the coordinates of the cable end points, the initial prestressing forces, and an initial interior coordinate. The cable stress-strain characteristics may be linear or nonlinear. The supporting structure may be replaced with equivalent spring stiffnesses or actual three-dimensional elements.The assumptions used in the solution are: (1) cable elements are straight between nodal points and have no flexural stiffnesses; (2) the roofing and decking provide no stiffness; (3) all loads are applied at the nodal points; and (4) all supporting structural elements are elastic. It should be noted that no displacements of the cable nodal points are neglected. Even at boundaries, the elastic stiffness can be considered. Temperature changes can be analyzed to determine their effect upon the structure.Cable net structures usually have many elements and require relatively large amounts of computer time. In addition many loading and geometric conditions must be considered. To be useful as a practical design tool, it was essential that the program be as efficient as possible and require a minimum of storage. The solution utilizes a variation of the Newton-Raphson method. Initially the tangent-modulus stiffness is used. At each iteration the change in the element force is compared with the change in element force for the previous iteration to determine if the convergence rate is within a prescribed value. If it is acceptable, the stiffness for the previous iteration is used; if unacceptable for any element, tangent stiffnesses for all elements are recalculated. This technique attempts to combine the best features of the Newton-Raphson and the modified Newton-Raphson methods by increasing convergence probability and decreasing solution time.To minimize storage requirements, NET 3 has the capability of utilizing tapes in the problem solution. The storage requirements are determined internally before the solution is initiated. If the required storage exceeds that alloted for the system of equations, the solution is effected through the use of tapes.Output for the cables includes nodal point displacements, nodal point forces, and element forces; for beam elements, forces and moments are given. The solution has been verified by comparison with results by other investigators.An elliptical shaped structure, 220 by 240 ft, has been analyzed with the program to investigate the influence of several parameters. The short direction cables were prestressed, and a uniform load of 40 psf was assumed. The variables investigated include: (1) initial prestress force; (2) degree of stiffness of supporting structure; (3) cable sizes; (4) sag-span ratio; and (5) temperature change.     

基于温度场的电缆接头温度监测系统研究

针对电缆接头线芯的温度无法直接测量的问题,应用有限元法建立了电缆接头稳态温度场分布模型;利用ANSYS软件对其温度场分布进行了仿真分析,得到了电缆接头线芯温度和表面温度的关系;根据仿真结果,提出了一种基于温度场的电缆接头温度监测系统的设计方案,给出了系统中供电电源和数据处理的设计,为工程中监测电缆接头温度、电缆运行状况提供了理论依据。     

城市配网排管敷设三芯10kV电缆的温度场数值计算

在保证电力电缆运行可靠性的前提下最大限度提高其载流量,对于提高电缆的经济运行具有重要意义。本文以排管敷设方式下10kV交联聚乙烯电力电缆为研究对象,对其在稳态和暂态运行下的电缆整体温度场和载流量进行了研究。通过构造排管电缆温度场的控制方程和边界条件,分析排管内部空气热流场及排管周围环境温度场,建立排管电缆温度场域有限元计算模型。借助ANSYS分析软件,得到排管内部空气流场矢量分布和排管内部电缆整体温度场分布。与保守的IEC60287标准排管电缆载流量计算方法相比,载流量提高约为6%,可为电力生产厂家及电力部门计算地下电缆载流量提供重要依据。     

Vision-assisted profile inspection system of inhomogeneous flex circuits in hard disk drives

Previous contributors have identified flex circuit or cable vibrations to be problematic sources for decreasing operation accuracy of read/write head in hard disk drives. To reduce the vibrations from the flex cable, damper layer or piezo-electric (PZT) layer have been reported to be effective in controlling the cable’s dynamics. However, due to complexity in the largely deformed circuit with additional layer, it is quite difficult to come up with proper analytical model to depict cable’s profile. In this work, a vision system and detection method are proposed and examined with mock flex cables by sandwiching additional PZT film layer between two plastic laminates, causing the cable to be inhomogeneous along its free length direction. From the present investigation, close-to-real 2D geometry or say the profile of inhomogeneous flex cable can be obtained by image processing filters including standard deviation threshold of the captured flex cable image. To ensure reliability in obtaining the correct profile of the cable, three types of evaluation techniques were implemented on the flex cable’s image contour. The profile was used in constructing finite element mode from which natural frequencies were validated by experimental measurements. Study on the flex cable’s non-uniformity reveals that the PZT film near J-block joint stiffens and straightens the cable contour. Without bending the cable contour too much and destroying the mechanical design of flex cable, it was suggested by this work that PZT layer would be an appropriate control medium to eliminate the cable vibrations.     

Parametric study of free vibration of sagged cables

The finite element method is applied to the study of natural frequencies and modes of vibration of sagged cables. Extensional characteristics of the element are fully considered. The method is applied to a numerical example taken from the literature and which has previously been analysed by classical and other methods. The results obtained by the use of a straight element are compared with those obtained by the use of curved elements. Finally, a parametric study is conducted to determine the influence of various parameters on the spectrum of natural frequencies of a sagged cable and appropriate nondimensional curves are presented. These non-dimensional curves give an insight into the general characteristics of the sagged cable, and can be used to predict in-plane natural frequencies over a wide range of sag/span ratio.     

多档货运索道动力计算方法及结构冲击影响研究

根据多档索道工作索(承载索和牵引索)及运行小车的相互作用关系,基于有限质点法理论建立质点运动方程,构建了适用于多档货运索道整体结构的动力计算方法.在计算方法中,采用索滑移单元的方式模拟工作索与支架、载荷的滑移接触状态,并提出牵引索循环行进计算方法.应用构建的整体计算方法分析了载荷质量、牵引机牵引速度及承载索长度等主要影响因素作用下运行小车通过货运索道支架时的冲击动力响应,给出了承载索、牵引索及支架的张力变化情况,对实际工程中货运索道钢丝绳、支架等结构的动态冲击性能提出技术要求,可为多档货运索道的设计提供更加科学合理的参考依据.     

动态海缆机械性能有限元分析

为探究动态海缆在剧烈交变环境载荷下的疲劳寿命,基于环境载荷响应,开展动态海缆系统的整体分析。基于有限元方法,研究海水中悬浮的动态海缆在服役过程中承受的极端载荷,分析破断力和侧压力工况,提取关键部位的应力、应变分布并进行校核。研究结果可为动态海缆材料选型、结构优化以及疲劳分析和测试提供理论依据。     

Transient thermal analysis of underground power cables using two dimensional finite element method

Microsystem Technologies - This paper introduces the finite element method is used for predicting the temperature distribution in underground cable, using arch-shaped finite elements with...     

基于弱磁探测技术的高压海底电缆精确定位系统设计

高压海底电缆具有耐腐蚀、抗冲击性能好和电气寿命长等优点,是海上输电系统的重要组成部分,为保证海底输电系统正常运行,设计并开发了基于弱磁探测技术的高压海底电缆精确定位系统。装设海底弱磁探测器作为弱磁探测技术的执行元件,改装高压海底电缆精确定位器。根据高压海底电缆的组成结构、电力学工作原理以及磁场分布特征,构建高压海底电缆及其磁场等效模型。采集高压海底电缆的实时状态数据,利用弱磁探测技术获取高压海底电缆周围的磁信号,通过信号特征匹配与坐标计算,得出高压海底电缆精确定位结果。通过系统测试实验得出结论：与传统定位系统相比,优化设计系统定位静态电缆的平均误差降低约10.82m,定位动态电缆的平均误差降低了11.37m,表明了所设计系统在定位精度方面具有明显优势。     

基于视频相位的拉索振动检测

作为斜拉桥的重要受力构件,斜拉索的振动检测对桥梁健康监测具有关键作用.在实验室理想条件下,传统的空间相位振动检测算法能够实现结构振动的高精度测量,然而在实际场景下,环境因素如车辆、风激励以及拉索与地面的角度等会对测量结果造成较大的误差,因此其不适用于实际场景下的拉索振动检测.针对此问题,本文提出了一种基于方向自适应复可控滤波器的拉索振动频率检测算法,用于实现在真实场景下拉索振动的精确测量.首先,利用拉索的直线特性检测拉索位置,并确定拉索主振方向;其次根据拉索的振动方向特性,设计方向自适应复可控滤波器组,对视频的每一帧图像进行分解处理,得到不同尺度同一方向的相位谱和幅度谱,并对拉索边缘区域相位进行增强;最后将每一帧图像处理得到的不同尺度的空间相位进行平均,按时间顺序排列生成相位序列,对提取到的相位序列进行傅里叶变换得到拉索振动主频频率.通过与加速度传感器测量结果比较,证明本文算法鲁棒性较高,能够满足真实场景下桥梁拉索振动测量的应用需求.     

基于索-梁结构的斜拉桥非线性振动仿真研究

本文建立了索-梁结构的有限元模型,对斜拉桥线性和非线性振动问题进行研究.首先对结构进行模态分析,发现结构振动表现出全局模态,局部模态以及混合模态,且索梁两者之间固有频率相互影响,对低阶频率影响较大,对高阶频率影响较小.其次,应用有限元软件对索-梁结构的自由振动和强迫振动进行仿真研究.结果表明：整个自由振动过程中频率有先增大后减小的趋势,且最终小于真实频率;在强迫振动中,观察到了丰富的非线性振动现象,包括索的亚谐波共振和内共振,与以往的实验和理论研究结果定性上得到验证;为斜拉桥全桥非线性动力学分析提供参考.     

Geometrical nonlinearities on the static analysis of highly flexible steel cable-stayed bridges

An evaluation of the importance of geometrically nonlinear effects on the structural static analysis of steel cable-stayed bridges is presented. A finite element model is analyzed using linear, pseudo-linear and nonlinear methods. The pseudo-linear approach is based on the modified elastic modulus. The nonlinear analysis involves cable sag, large displacement and beam-column effects. The results confirm that both cable sag and large displacement originate the most important nonlinear effects in those structures. Beam-column effects are irrelevant for service loads. Both the pseudo-linear approach and the modified modulus element prove to be very limited or even inappropriate.