空中动态悬跨缆设计及极值疲劳分析

从工程实际问题出发,利用实测资料,对渤海上的一个连接FPSO与固定导管架平台的动态悬跨缆进行基本的线型设计.借助Orcaflex软件对动态缆响应进行非线性时域分析,在不同海况下对动态缆进行极值分析和疲劳分析,进而对其进行安全评估,指出管缆的危险区域.结果对类似的悬跨缆设计、分析以及对其危险区域的保护等工作有实际参考意义.     

单侧主缆刚度损伤悬索桥的模态分析及1∶1内共振

悬索桥缆索在长期服役状态下损伤很难避免,单侧主缆刚度损伤会使系统出现主梁竖弯与扭转自由度间的耦合,这可能会进一步对悬索桥的模态和大振幅下的非线性响应造成影响.为此,建立了考虑单侧主缆刚度受损的七自由度悬索桥横截面模型,模态分析发现单侧主缆刚度损伤会使得系统前两阶固有频率曲线由交叉变为跃迁,导致两个本身相互独立的模态发生耦合.以此为基础,考虑悬索桥主缆刚度有损伤和未损伤两种工况,运用拓展的增量谐波平衡法(EIHB)计算系统在内共振条件下的非线性振动.研究结果表明：单侧主缆刚度有损伤的悬索桥在外部简谐激励下发生1:1内共振,系统能量表现出明显的转移现象;竖向和扭转简谐激励下,有损伤的悬索桥较未损伤工况响应幅值有所减小,但出现了两个共振响应峰值,对激励频率更为敏感.数值结果与利用Runge-Kutta法计算得到的结果吻合一致,验证了EIHB法的准确性.     

生物医学信号时间属性及其分析研究的进展

与宇宙随着时间膨胀和大自然随着时间演化一样,表征生命体征的生物医学信号同样有很强的时效性,它随着时间不断地在变化着.因此,常用具有时间概念的时间序列信号来描述与分析.很久以来,借助各种传感器和电子测量仪器获取各种类型的生理时间序列信号,对其进行传统的方法分析与处理,同时认为生理系统为平稳的线性系统,进行时域、频域、时频变换分析以及统计学处理.人体(或高级动物)的生理系统是自然界中最复杂的系统.在对人体生物医学信号进行非线性动力学分析时,对时间属性的研究即是对时间复杂度参数(如熵值等)的研究.熵在增大,所有活体系都在耗散,现在研究的是远离平衡、非线性耗散系统中,时间上不可逆的动态演化.显然,在人们熟知的“生物钟”周期中,机体的生理状态每时每刻都不同,不同周期里的状态也各不相同,则通过非线性动力学分析表征生命体征的复杂度参数也各不相同.生物医学信号时间序列的非性线分析除了混沌分析、幂律分析、多重分形、熵分析等方法外,近期有学者对时间序列进行时间不可逆性分析,以期进一步揭示生命活动的非线性动力学系统本质.自然变更、生物进化、社会发展等都是无序的、不可逆的过程,研究其不可逆性正在引起空间、时间和动力学概念上的巨大变化.因此,序列的时间不可逆性分析提供了一种分析非线性动力学系统的新思路.     

非线性动态系统中迭代的同步数据协调与显著误差检测的支持向量回归方法

化工厂中过程数据的质量严重影响到来自例如性能监控, 在线优化和控制等活动所获得的效益和性能. 由于许多化工过程通常表现为非线性动态特性, 例如扩展卡尔曼滤波(EKF)和非线性动态数据协调(NDDR)等技术已经被发展出来改进数据的质量. 近期, 迭代非线性动态数据协调(RNDDR)技术已被提出, 该技术结合了EKF和NDDR技术的优点. 但是, RNDDR技术不能够处理具有显著误差的测量值. 本文中, 一种非线性动态系统中迭代的同步数据协调与显著误差检测的支持向量(SV)回归方法被提出. SV回归是一种经验风险和结构风险间的妥协, 并且对于数据协调来说, 其对随机误差和显著误差是鲁棒的．通过将结构风险取代RNDDR中的极大似然估计并使其最小化, 我们的方法不仅可以实现迭代非线性动态数据协调, 还可以同时实现显著误差检测. 本文中的非线性动态系统仿真结果显示出, 所提出的方法在迭代实时估计框架下, 对于非线性动态系统的同步数据协调和显著误差检测是鲁棒、稳定并且精确的. 该方法也可以提供更好的控制性能.     

多自由度非线性系统动态参数化模型建模方法研究

针对多自由度非线性系统的动态模型辨识问题,基于NARX(Non-linear Autoregressive with Exogenous inputs)模型的建模方法,考虑系统的物理设计参数,建立非线性系统动态参数化模型.首先,根据系统输入、输出数据建立系统不同参数下的NARX模型,并通过EFOR(Extended Forward Orthogonal Regression)算法对不同参数下NARX模型进行修正,以统一辨识得到的系统模型结构.随后,建立NARX模型系数与物理设计参数间的函数关系,得到多自由度非线性系统的动态参数化模型.以单输入、单输出两自由度非线性系统为例,根据数值仿真结果,对系统的动态参数化模型建模过程进行说明.最后,以带非线性涂层阻尼的悬臂梁作为试验对象,建立其动态参数化模型以反映其动力学特性.试验结果表明,非线性系统动态参数化模型能准确预测多自由度非线性系统的输出响应,为非线性系统的分析与优化设计提供了理论基础.     

针对执行器非光滑反向间隙-饱和的柔性立管边界控制

研究了针对执行器非光滑反向间隙-饱和约束特性的深海柔性立管系统振动控制和全局稳定问题.为了实现控制效果和品质,引入辅助系统和函数设计边界控制策略,以抑制立管系统振动并消除混合的反向间隙-饱和输入非线性影响.采用严格的分析且无需求助于模型降阶,所研发的控制器确保闭环系统在Lyapunov意义下的一致有界稳定性.通过选取恰当的设计参数,仿真结果验证了所设计控制器的控制性能.能.     

基于确定学习理论和Lempel-Ziv复杂度的非线性系统动态特征提取

对非线性系统产生的非线性非平稳信号进行有效的特征表达是特征提取领域重要且困难的问题.本文基于确定学习理论和Lempel-Ziv复杂度（LZ复杂度）提出一种新的非线性系统动态特征提取方法.新方法将从系统的动力学轨迹中提取特征.通过确定学习理论对产生回归轨迹的非线性动力学系统的未知系统动态进行局部准确建模/辨识,1）使用LZ复杂度对辨识得到的动力学轨迹进行特征表达,并提出时间复杂度和空间复杂度两个指标组成时空LZ复杂度,从时间域和空间域的角度刻画系统动力学轨迹的复杂程度.2）对提出的动态特征提取方法进行敏感度分析,定量评价系统的动态特征指标相对于系统从周期轨迹到混沌轨迹的参数变化敏感程度.3）通过数值仿真和实验分析以验证动态特征提取的有效性.与从系统状态轨迹中提取特征相比,本文提出的动态特征提取方法可以从系统内在动态的角度对原系统进行更好的表达.     

自适应神经模糊推理系统及其参数分析

该文介绍了自适应神经模糊推理系统的结构原理和推理方法,针对典型非线性系统,借助matlab中ANFIS的功能讨论训练次数、隶属度函数的数目及类型对自适应神经模糊推理系统(ANFIS)的直接影响,为后续对动态非线性系统的进一步研究打下了基础。     

带有死区输入和未建模动态的神经网络控制

针对一类具有死区非线性输入和未建模动态的非线性系统,提出一种自适应神经网络控制方法。该方法将后推技术和动态面技术结合,克服了计算复杂性问题,放宽了动态不确定性的假设,取消了神经网络逼近误差有界。借助中值定理和Young’s不等式,保证整个设计只需一个自适应参数,且控制增益只需存在一个上、下界。理论分析证明闭环系统所有信号半全局一致终结有界。仿真结果验证所提方案的有效性。     

利用SVR的非线性动态系统Wiener模型补偿

提出一种新的利用支持向量回归机(SVR)的非线性动态系统维纳(Wiener)模型补偿方法.首先,将非线性动态系统用Wiener模型描述成线性动态子环节和非线性静态增益;再设计结构上与之对应的Wiener补偿器,并进一步将其变换为可用SVR辨识的线性中间模型;最后,通过关系矩阵将中间模型的估计值转换为Wiener补偿器的实际参数.用实际压力响应系统的动态标定实验数据进行测试,结果表明,与最小二乘方法比较,所提方法建立的Wiener补偿器具有更强的抗干扰能力.因此,该研究为非线性动态系统补偿又提供了一种可选方法.     

CFRP索斜拉桥面内自由振动的多索梁模型及模态分析

为研究斜拉桥中索与梁、索与索之间的耦合振动问题,建立了斜拉桥的单梁-多索力学模型.考虑索的初始垂度引起的几何非线性因素的影响,将多索梁模型分段处理,基于索、梁经典的面内振动的微分方程,通过索、梁连接处的动态平衡条件,建立多索梁模型面内振动理论.以双索梁为例,应用分离变量法,结合边界条件,求解双索斜拉梁模型平面内自由振动的特征值问题.同时,建立双索梁的有限元模型,有限元所得结果与本文理论研究吻合良好.最后对CFRP索梁模型的各项相关重要参数进行分析,并将本文理论与课题组前期成果进行对比分析.研究表明,CFRP索能极大改善双索梁模型的基本动力学性能.增大拉索轴向刚度能明显提高模型的低阶频率,而梁弯曲刚度的提高对其高阶频率的提高比较明显.     

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。     

多索-单梁耦合结构的动力学建模及非线性特性研究

Long span cable-stayed bridges usually use dense cable systems, and the vibration frequencies of cables are very close, and there may be a frequency doubling relationship between cables. Therefore, there may be mutual coupling vibration between cables. Cable is an important load-bearing component of cable-stayed bridges, and it is very important to study the dynamic characteristics of multi cable single beam. In this paper, considering the boundary conditions of cable girder, cable tower and tower girder and the connection conditions at the connection points, based on Hamilton variational principle, the differential equations of motion of multi cable single beam structures are established. After dimensionless treatment ？ the reduced differential equation of motion is obtained according to the method of separating variables. In this paper, two adjacent cables are taken into account to analyze the dynamic behavior of double cable single beam coupling structure under different working conditions. It is found that, different from the "frequency turn" phenomenon in previous data, in this paper, the two frequency curves do not separate rapidly at the place where the frequency values are close, but continue to keep parallel and close to each other within a relatively small parameter range, and then separate rapidly. Finally, the nonlinear characteristics of the double cable single beam coupling structure are studied, and the structure is dis-cretized with two degrees of freedom and one degree of freedom respectively. It is found that the single mode assumption of the structure can reflect the nonlinear characteristics of the structure in the non resonant region, but in the resonant region, the nonlinear characteristics of the structure will jump, so it is more accurate to apply the two degree of freedom mode theory to research. © 2023 Journal of Dynamics and Control. All rights reserved.     

Dynamic Load Carrying Capacity of Flexible Cable Suspended Robot: Robust Feedback Linearization Control Approach

In this paper dynamic load carrying capacity (DLCC) of a cable robot equipped with a closed loop control system based on feedback linearization, is calculated for both rigid and flexible joint systems. This parameter is the most important character of a cable robot since the main application of this kind of robots is their high load carrying capacity. First of all the dynamic equations required for control approach are represented and then the formulation of control approach is driven based on feedback linearization method which is the most suitable control algorithm for nonlinear dynamic systems like robots. This method provides a perfect accuracy and also satisfies the Lyapunov stability since any desired pole placement can be achieved by using suitable gain for controller. Flexible joint cable robot is also analyzed in this paper and its stability is ensured by implementing robust control for the designed control system. DLCC of the robot is calculated considering motor torque constrain and accuracy constrain. Finally a simulation study is done for two samples of rigid cable robot, a planar complete constrained sample with three cables and 2 degrees of freedom and a spatial unconstrained case with six cables and 6 degrees of freedom. Simulation studies continue with the same spatial robot but flexible joint characteristics. Not only the DLCC of the mentioned robots are calculated but also required motors torque and desired angular velocity of the motors are calculated in the closed loop condition for a predefined trajectory. The effectiveness of the designed controller is shown by the aid of simulation results as well as comparison between rigid and flexible systems.     

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.     

基于降阶模型的斜拉索振动的半主动神经网络控制

根据模态降阶理论,获得了斜拉索-阻尼器系统的降阶模型,有效地缩减了系统的自由度.根据ER/MR阻尼器特性和主动控制中LQG控制理论,建立了面向速度剪切的半主动LQG控制方法,并获得了很好的控制效果.本文设计了神经网络的观测器,使用的传感器数目大大减少,根据智能控制理论,设计了神经网络控制器,并提出采用该神经网络作斜拉索半主动控制的控制算法.振动仿真的结果表明,经过离线训练后的神经网络观测器和控制器,有效地抑制了斜拉索的振动.     

A novel scheme for large deflection analysis of suspended cables made of linear or nonlinear elastic materials

This paper presents a new approach to investigate the static response of horizontal and inclined suspended cables with deformable cross-section, made of general linear or nonlinear elastic materials, and subjected to vertical concentrated and distributed loads. The proposed technique also includes large sag and extensibility effects, and is based on an original finite difference scheme combined to a nonlinear least squares numerical solution. The mathematical formulation is developed for various loading cases, and an innovative computational strategy is used to transform the resulting nonlinear system of equations into a scaled nonlinear least squares problem. The numerical scheme is programmed and its application illustrated through examples highlighting the effects of coupling between the tension in a cable and the deformation of its cross-section as well as the use of cables made of neo-Hookean materials. The results obtained are in excellent agreement with analytical solutions when available. The proposed technique can be easily programmed and constitutes a valuable tool for large deflection analysis of suspended cables made of nonlinear elastic materials.     

Vibration analysis of cable-driven parallel manipulators

A cable-driven parallel manipulator is a manipulator whose end-effector is driven by a number of parallel cables instead of rigid links. Since cables always have more flexibility than rigid links, a cable manipulator bears a concern of possible vibration. Thus, investigation of vibration of cable manipulators caused by cable flexibility is important for applications requiring high system stiffness or bandwidth. This paper provides a vibration analysis of general 6-DOF cable-driven parallel manipulators. Based on the analysis of the natural frequencies of the multibody system, the study demonstrates that a cable manipulator can be designed stiff enough for special applications like the cable-manipulator based hardware-in-the-loop simulation of contact dynamics. Moreover, under an excitation, a cable may vibrate not only in its axial direction, but also in its transversal direction. The paper also analyzes the vibration of cable manipulators caused by cable flexibilities in both axial and transversal directions. It is shown that the vibration of a cable manipulator due to the transversal vibration of cables can be ignored comparing to that due to the axial flexibility of cables.     

Rain–wind induced vibrations – phenomenology,mechanical modelling and numerical analysis

The simultaneous appearance of rain and wind at cables of cable stayed bridges and hangars of arch bridges may induce varying oscillations with large amplitudes. These phenomena are identified as rain–wind induced vibrations. The paper presents a possible fluid-mechanical interpretation of rain–wind induced vibrations. Based on this interpretation a mechanical model is deduced, in order to enable numerical investigations. The complex system of nonlinear differential equations is analysed concerning the stability of solutions. Rain–wind induced vibrations exist only within a certain range of wind velocity. The lower limit of the critical velocity range is determined for various cable inclinations and angles of incidence. Furthermore, a fluid mechanical interpretation is given for the existence of the upper limit of critical velocity. The approximation of the upper limit velocities and the determination of the critical cable diameters can be derived from established fluid-mechanical correlations. The numerical investigations show that rain–wind induced oscillations occur on vertical cables, too. For the Faro–Falster Bridge, the numerical vibration analysis is carried out for the cables parallel and perpendicular to the wind direction. The analysis of the vibration frequencies is demonstrated for the Dömitz Bridge.     

海上横向补给系统多体动力学建模与仿真分析

海上横向补给是目前舰船补给的主要方式,通过接收船与发送船之间架设的恒张力高架索进行货物转运.本文利用多体动力学理论建立了海上横向补给系统的动力学模型.该系统由舰船、货物、滑轮以及高架索组成,对舰船、货物和滑轮采用刚体假设,对高架索采用几何精确梁理论进行建模.基于赫兹理论建立了滑轮与高架索之间的接触模型.为提升计算效率,针对恒张力索的特点提出了一种简化的力元模型,并通过与精确模型的对比验证了该简化模型的准确性.利用简化模型,对复杂海况下的补给作业进行了全过程动力学仿真,分析了船舶运动、补给距离、张紧力对转运过程的影响.结果表明在海况条件恶劣、补给距离长、张紧力过小时,无法保证转运过程安全作业.