Numerical Investigation of the Dynamics for Low Tension Marine Cables

This paper presents a numerical investigation into the dynamics of marine cables which are extensively used in offshore industry. In this numerical study, the Euler-Bernoulli beam model is adopted to develop the governing equations of the cable. Bending stiffness is considered to cope with the low tension problem in local area of towing cable, and thus a more accurate solution with the consideration of the axial elongation can be given.The derived strongly-coupled and nonlinear governing equations are solved by a second-order accurate, implicit,and large time step stable central finite difference method. The quadratically convergent Newton-Raphson iteration method is applied to solving the discrete nonlinear algebraic equations. Then a towed array sonar system(TASS)problem is studied. The numerical solutions agree reasonably well with the experimental data and the simulated results of the references. The specified program of the present paper shows great robustness with high efficiency.     

Dynamic Behavior of Two Part Towing Cable System During Turning

An improved numerical method is used to simulate the dynamic behavior of a two part towing cable systems during turnings. In U turns and full turns, periodical heave motions are found both for the towed vehicle and for the depressor. Periodic motions of the subsea units and of the cable surface tension are closely related to the turning parameters, such as turning velocity and turning radius. System parameters, such as length of the second cable and the vehicle hydrodynamics, also damp turning instability.     

Dynamic Effect Research of Cable-Lead-In Rod on Towed System

This paper aims to research the cable-lead-in rod effect on a towed system through mathematical modeling and numerical simulations. The rod dynamics, as a key part of this study, is modeled using the combination of cable node governing equations and kinematic constraint conditions. As the first attempt to analyze such a problem, the rod is simply treated as an elastic cable segment so as to be incorporated into the dynamics of the cable, and a set of algorithm is then proposed based on the kinematic constraint conditions to fully describe its motions. Meanwhile, the cable and the underwater vehicle are modeled by the traditional lumped mass method and the 6 degree-of-freedom maneuverability equations for submarines respectively; the coupling boundary conditions besides the rod dynamics are also given to form the whole system's model. Several numerical cases are performed to investigate the rod effect on the system in different maneuver situations. Some meaningful conclusions are drawn through comparative analysis.     

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.     

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.     

一种轻型可展军用桥梁的设计与动力学分析

为保障人员迅速跨越沟渠、谷地等人工或天然障碍,研制了一种新型的轻型可展军用桥梁.该桥采用剪式铰和套筒可展机构实现轴向展开,用电机牵引主动索,展开至设计位置后锁定成工作状态.分析了预应力索和加劲桁架机构在减小桥梁变形、提高承载力方面的作用;制作缩比模型并进行了展开试验验证.研究结果表明:预应力索的设置使桥梁挠度从1/114减小到1/386,加劲桁架使桥梁承载力提高35.1%;该结构形式能稳定展开并投入使用,模型试验结果与展开的仿真结果吻合.      

外激励作用下亚音速二维粘弹性壁板系统的混沌运动

为了研究壁板在亚音速气流和外激扰联合作用下的非线性运动特性,基于Hamilton原理,建立了外激励作用下亚音速粘弹性壁板的非线性运动方程,并采用Galerkin方法将其离散为常微分方程组,研究了系统的平衡点及其稳定性.利用Melnikov方法得到了壁板出现混沌运动时系统参数所满足的临界条件,分析了外激励幅值、频率及气流来流速度之间的临界关系,并与系统混沌运动的数值模拟结果进行了对比.结果表明:当无量纲动压值超过64.42时,壁板系统平衡点的个数及其稳定性均会发生改变;使用Melnikov方法确定的混沌运动临界参数与数值模拟结果相符,该方法可用于判定混沌运动是否发生.      

施工隧道负离子除尘效率的主要影响因素

为研究施工隧道内粉尘颗粒粒径、颗粒浓度、通风风速和负离子系统工作电压、纵向安装位置对负离子系统粉尘降除效率的影响，依据调研和实测选取隧道计算参数，建立隧道及负离子系统三维模型，采用RNG k-ε双方程湍流模型，并通过动量方程附加电场力源项的方法求解电流场，利用拉格朗日法求解粉尘颗粒的运动轨迹，用SIMPLE算法对颗粒运动与电场流场进行离散相和流体相相间耦合的数值模拟计算，并将模拟结果和隧道现场抽样试验结果对比分析. 研究结果表明:隧道粉尘粒径越大，浓度越大，风速越低，负离子系统工作电压越高，系统纵向安装位置越偏于上风口，负离子系统除尘效率越高；两组现场抽样试验与对应数值模拟所得的除尘效率分别为41.2%、56.7%和38.2%、51.1%，误差分别为15.5%和12.9%. 考虑施工隧道大空间复杂环境的影响，通过数值模拟的方法来研究负离子系统除尘效率及其与主要影响因素的关系是可行的.      

Direct algorithms for steady-state solution of long slender marine structures

The steady state solution of long slender marine structures simply indicates the steady motion response to the excitation at top of the structure.It is very crucial especially for deep towing systems to find out how the towed body and towing cable work under certain towing speed.This paper has presented a direct algorithm using Runge-Kutta method for steady-state solution of long slender cylindrical structures and compared to the time iteration calculation;the direct algorithm spends much less time than the time-iteration scheme.Therefore, the direct algorithm proposed in this paper is quite efficient in providing credible reference for marine engineering applications.     

用于柔索振动控制的索型动态吸振器

研究一类用于控制柔索在谐波激励下的主模态振动的索型动态吸振器．控制索（动态吸振索）与被控索（主索）具有相同的边界条件，并用均匀分布的线性弹簧和阻尼器与主索相联结．因为在相同边界条件下，主索和吸振索具有相同的特征函数，所以在主索的模态坐标下，系统的运动方程等同于具有两质量块的二自由度系统的运动方程．     

Cable Sliding at Supports in Cable Structures

To develop an effective numerical method for the cable sliding problem in cable structures，two-node catenary cable element was built to model the cables based on analytical solution of elastic catenary．Cooperated with Newton method，continuation method Was used to solve the nonlinear equations．This approach is more efficient than using Newton method only and has a wider range to select initial values for the process to converge．The relationship between the tension on a cable segment and its unstrained length was derived and used to calculate the unbalanced cable tensions at the supports．An example is presented to show the correctness and efficiency of the proposed method．     

基于离散势能场的行人路径规划算法研究

复杂二维场景中的行人路径规划是行人仿真研究体系中微观仿真服务的关键性问题之一。针对该问题提出基于离散势能场的路径规划算法，给出总体算法的流程，并针对离散势能场的生成算法、离散路径的合理化方法等关键环节进行详细论述，最后经算例证明该算法具有一定的有效性，同时存在一定的局限性。     

In-plane Auto-Parametric Vibration of Inclined Cables under Random Transverse Excitation

In-plane auto-parametric stochastic vibration of inclined cables subjected to Gaussian white noise in transverse bridge orientation is investigated. Based on Newton＇s laws of motion and Galerkin＇s modal truncation principle, the influences of geometry nonlinearity induced by sag and large displacement of cables and the initial equilibrium state are taken into account. Meanwhile, the three-dimensional non-linear differential equations of inclined cables for coupling vibration are deduced, equivalent stochastic linearization method is applied to derive the 14-dimensional first-order nonlinear differential equations of state vectors, and the Runge-Kutta integration method is utilized to obtain the root mean square （RMS） response. Results show that when the transverse random excitation imposed on the stayed cable exceeds a critical value, the in-plane transverse vibration of the cable are excited due to tim auto-parametric nonlinear coupling, and the critical value of random excitation increases with the damping ratio. In this motion, the cable response possesses non-stationary characteristics, even though the loading keeps stationary.     

移动最小二乘微分求积法解Helmholtz方程

用一种新型的数值方法--移动最小二乘微分求积法（MLSDQ）求解二维Helmholtz方程。MLSDQ方法是一种直接将微分方程离散的方法，它是将未知函数的各阶偏导数在离散点处的值用域内各配点的函数值加权组合来表示，权系数则直接用移动最小二乘Galerkin法中的形函数求导得到，通过MLSDQ技术将Helmholtz方程和相应的边界条件转化成为一组关于各配点位势的线性代数方程组，求解这组代数方程，便可得到各配点的位势，通过求解几个具有精确解的算例，讨论了方法的收敛性和数值精度，结果表明：该方法较适合于求解小波数的Helmholtz方程,对高波数的方程，需要设置大量的域内配点才能有较好的数值结果。     

车辆-轨道系统耦合高频振动的研究

车辆-轨道垂向耦合振动是车辆-轨道耦合动力学主要研究课题.建立了车辆-轨道垂向耦合Timoshenko梁高频振动模型,运用快速积分方法编制仿真程序,对扁疤激励情况下的轮轨垂向高频振动进行系统仿真与分析,并与Eu ler梁模型仿真结果进行比较.结果表明,车辆速度与车轮扁疤的长度对轮轨系统振动有很大的影响;在高频情况下,进行振动与噪声的研究时,建议使用Timoshenko梁模型.     

大跨度斜拉桥拉索无应力长度的计算方法比较

推导了用抛物线理论与悬链线理论计算斜拉索无应力长度的公式 ,以南京长江二桥南汊斜拉桥为例 ,分析了用悬链线与抛物线理论计算斜拉索无应力长度的差别 .通过比较 ,认为对大跨度斜拉桥 ,用抛物线理论计算拉索无应力长度 ,完全可以满足精度要求     

单车荷载作用下T型刚构桥车致振动响应研究

根据车辆-桥梁结构振动特性,研究单车移动荷载作用下,T型刚构桥考虑桥面不平顺影响时桥梁振动响应及冲击特性。通过将T型刚构桥离散为三维梁单元有限元模型,车辆简化为九自由度整车模型（考虑车辆俯仰及侧翻）,桥面不平顺激励采用实测和数值模拟（根据国标GB／T7031—86给定功率谱密度曲线采用三角级数叠加法模拟）两种激励;以车轮与桥面相互接触处保持不脱离为条件,建立车辆与桥梁耦舍振动方程,利用模态综合法并结合Newmark—β数值积分方法进行迭代求解。以乔木湾乐安河T型刚构桥为工程背景,研究了单车荷载下,最不利位置处的冲击系数随桥梁结构阻尼、行车速度、桥面不平顺及车辆特性的变化关系,并将数值模拟结果与实测结果对比。研究结果表明,实测冲击系数与数值模拟的冲击系数较好吻合,乐安河大桥冲击系数满足04《桥规》要求。     

悬臂浇注施工斜拉桥的误差控制方法

在预应力混凝土(PC)斜拉桥悬臂施工中,为了减小索力及线形误差,分析了误差原因及其控制现状,提出了模型误差及悬浇效应误差的控制方法。结合三维实体等参元和板壳单元的优点,构造了适用于复杂桥梁结构空间分析的实体退化单元,建立了离散钢筋模型。根据挂篮牵索锚固点处的变形协调条件,推导出牵索索力随混凝土浇筑的增量计算公式,建立了悬浇过程中各工况下挂篮前端标高控制的计算公式。应用结果表明:在悬浇施工过程,牵索索力控制精度达到了3%,成桥索力控制精度达到5%,悬臂端标高误差控制在1 cm内,因此,提出的控制方法可实现PC斜拉桥悬浇过程各工况下索力及线形的准确预测。     

大跨度斜拉桥索与桥面耦合振动分析

为探讨大跨度斜拉桥拉索与桥面耦合振动特性,建立了拉索与桥面耦合振动模型,并用数值仿真方法分别对桥面与拉索的频率比、拉索倾角、桥面与拉索质量比对拉索与桥面耦合振动的影响进行了分析.结果表明:拉索不仅在桥面与其频率比为1时会产生共振,而且在频率比为1/2和2时也会产生共振;随着拉索倾角和桥面与拉索质量比的增大,桥面与拉索的频率比为1时,拉索的共振振幅减小,而桥面与拉索的频率比为1/2和2时,共振振幅将明显增大.     

机车柴油机凸轮磨损的数值模拟

基于离散数学理论和计算机技术,提出了一种数值模拟方法,以柴油机凸轮机构为研究对象,针对光面磨损失效形式,给出了数值模拟模型,提出了具体的算法方案并编写了通用程序,实现了磨损寿命的预测,为柴油机整机系统磨损过程数值模拟奠定了基础。