主动式声纳列阵拖曳系统姿态数值计算

主动式声纳列阵拖曳系统是用于探测潜艇的新型声纳系统，为了准确探测潜艇的位置，必须首先预报声纳列阵的瓷态，本文通过对其三维力学模型的分析，得到该系统的运动微分方程，其中缆索的力学方程是基于Ablow和Milinazzo的模型，而对于拖体则运用六自由度空间运动方程模拟，结合边界条件，用有限差分法求解，通过对拖船的不同运动状态如匀速，变速和回转的计算，证明本文的方法对于预报声纳列阵的姿态是有效的。     

水下拖曳升沉补偿系统水动力数学模型研究

建立变缆长的水下拖曳升沉补偿系统水动力学偏微分方程组和边界条件.拖缆动力学模型基于Ablow and Schechter模型,拖体采用水下运载体六自由度方程模拟,运用有限差分法离散偏微分方程组和牛顿迭代法计算变缆长情况下拖体深度与拖缆各点张力的动态取值.数值计算结果表明采用收放拖缆的升沉补偿方法能够有效削弱母船升沉运动对拖体深度和拖缆张力的影响.     

On the motions of the underwater remotely operated vehicle with the umbilical cable effect

In this paper, a hydrodynamic model is developed to simulate the six degrees of freedom motions of the underwater remotely operated vehicle (ROV) including the umbilical cable effect. The corresponding hydrodynamic forces on the underwater vehicle are obtained by the planar motion mechanism test technique. With the relevant hydrodynamic coefficients, the 4th-order Runge–Kutta numerical method is then adopted to solve the equations of motions of the ROV and the configuration of the umbilical cable. The multi-step shooting method is also suggested to solve the two-end boundary-value problem on the umbilical cable with respect to a set of first-order ordinary differential equation system. All operation simulations for the ROV including forward moving, ascending, descending, sideward moving and turning motions can be analyzed, either with or without umbilical cable effect. The current effect is also taken into consideration. The present results reveal that the umbilical cable indeed significantly affects the motion of the ROV and should not be neglected in the simulation.     

Dynamic Analysis of Towed and Variable Length Cable Systems

Towed cable systems are frequently used in marine measurements where the length of the towed cable varies during launch and recovery. In this paper a novel method for modeling variable length cable systems is introduced based on the finite segment formulation. The variable length of the towed cable is described by changing the length of the segment near the towing point and by increasing or decreasing the number of the discrete segments of the cable. In this way, the elastic effects of the cable can be easily handled since geometry and material properties of each segment are kept constant. Experimental results show that the dynamic behavior of the towed cable is consistent between the model and the physical cable. Results show that the model provides numerical efficiency and simulation accuracy for the variable length towed system.     

波浪作用下刚性框架浮体及其锚绳运动数值模拟精度分析

由小尺度刚性杆件构成的复杂结构近年来多用于海洋平台建设和海洋监测浮标制作以及海洋增养殖人工浮鱼礁的设计。采用有限单元法和集中质量点法建立波浪作用下刚性框架浮体及其锚绳运动数值模型,探讨空间单元划分、时间离散步长、数据保存格式对刚性框架浮体和柔性锚绳运动模拟精度的影响,分别给出此三者之间的匹配关系。研究结果表明:框架浮体的单元划分可依据是否出水给定,单元的划分比建议取0.05;锚绳的单元划分与其上端连接的浮体浮力有关,当锚绳的拉力主要由上端浮体浮力产生时锚绳单元的划分影响较小,当锚绳的拉力主要由波浪力产生时锚绳单元的划分比建议取0.02;空间单元划分与时间离散步长存在匹配关系,通过减小时间步长来追求数值模拟精度时必须同时考虑保存运动物理量截断误差的影响。     

Nonlinear dynamics of an elastic cable during laying operations in rough sea

A numerical approach for predicting motion and tension of extensible marine cables during laying operations in a rough sea is presented here. The solution methodology consists of dividing the cable into straight elements, which must satisfy an equilibrium equation and compatibility relations. The system of nonlinear differential equations is solved by the Runge–Kutta method, taking the effect of regular and/or irregular waves into account explicitly.

Illustrative applications of the method are given for a typical cable laying ship. The results are presented as rms values of the cable dynamic tension and corresponding dynamic factor for two different types of cable and several values of cable stiffness. The effect of axial deformation on the maximum tension at the shipboard pulley location is highlighted.     

水下非均匀拖缆稳态动力学分析

水下拖缆物理参数不均匀会影响拖缆的动力特性,研究非均匀拖缆的参数变化对拖缆动力特性的影响有一定的工程实际意义。建立了拖曳系统运动的三维数学模型,推导出了水下非均匀拖缆的稳态运动控制方程,在首尾两端加上相应的定解条件,直接求得或使用嵌套二分法求得非均匀拖缆在端点的初始值,进而求解稳态动力学方程。借助文献中的拖缆—海底拖车系统算例,通过计算结果的对比,验证了数学模型及计算方法的正确性。通过四阶龙格库塔法进行数值仿真计算,得到了稳态解,分析了非均匀拖缆自身物理参数变化对缆绳系统稳态运动的影响。结果表明,非均匀拖缆的切向阻力系数、法向阻力系数、直径和密度变化会影响稳态缆形和张力分布,影响的程度各不相同。最后给出了两个尾拖船系统非均匀拖缆的稳态运动算例。     

基于有限元模型和模态参数的损伤识别

本文从特征值问题出发 ,结合结构系统的有限单元模型并引入单元损伤因子 ,导出了求解单元损伤因子的方程 ,从而可以确定结构的损伤位置和损伤程度。利用简支梁进行了数值模拟 ,建立了简支梁的有限单元模型 ,用不同单元弹性模量的降低来模拟各种不同的损伤工况 ,并对每种工况进行了损伤位置和损伤程度识别 ,数值模拟结果同实际情况吻合很好。     

Numerical simulation of longitudinal tackle oscillations when salvaging sunken vessels from deep water

A mathematical model is proposed for longitudinal oscillations of a tackle used for salvaging sunken vessels to the sea surface. The numerical approximation of the obtained model along the tackle rope length is accomplished by means of the finite-difference method. To implement this method, the transformation of independent coordinates is introduced into the constant step mesh. The integration with respect to time is carried out by the Φ-Wilson method. To solve the nonlinear systems of algebraic equations, iteration methods are used. There are examples of calculations for the vessel separation from the seabed and salvage from 1655 m depth when using various methods of controlling the winch shaft moment. The area of winch moment and heaving motion amplitude values that provide vessel emergency-free separation from seabed are calculated. It is shown that, with accuracy sufficient for practical use, the rope system of the tackle can be replaced in some cases by a single equivalent rope. Moreover, the rope mass can be neglected if it is considerably less than the mass of the vessel being salvaged. It is emphasized that the selection of the control of the velocity of salvage depends to a large extent on winch operation peculiarities.     

Degradation of rope properties under increasing monotonic load

This paper describes the development of a computational model to predict the response of synthetic-fiber ropes under both monotonic and cyclic loads. The model addresses the issue of damage to a rope cross-section and its effect on rope response. Isotropic damage is assumed and is therefore characterized by a scalar quantity known as the damage index. The damage index is used to quantify the amount of deterioration that takes place in a damaged rope throughout its loading history. For the current study, data obtained from static tension tests are used to determine the evolution relationship for the damage index. This relationship is based on the stiffness ratio between experimental data and simulation of rope response without any source of damage and is assumed to be described by an exponential equation. Numerical simulations of damaged rope behavior compare well with experimental results.     

Numerical Simulation of Dynamic Response of Supple Nets

1 .Introduction Owing to the decline of capture fisheries andsaturation of traditional inshorefarms ,sea cage cul-ture as a newtype of aquaculture is developingrapidlyin China .However ,cage culture is a highriskoperation.The practice is vulnerable to natural hazards ,such as strong tides ,storms and typhoons .So,it is necessaryto assess the behavior of a sea cage exposedto waves and current before the designandinstallation of the structure . Computer simulation,due to its many advantages ,ha…     

钢管脐带缆扭转平衡设计

钢管脐带缆包含多种螺旋缠绕的功能单元，其在外力载荷下会发生相对运动，而且钢管的刚度较大对扭转平衡有重要影响，因此，相对于普通电缆，钢管脐带缆在扭转平衡设计时更加困难。根据扭转平衡理论公式，采用控制变量法，以第二层铠装钢丝的绞合角度为变量进行扭转平衡设计。首先建立脐带缆缆芯有限元模型，对其施加拉伸载荷，结果显示缆芯出现了扭转，这证明不能将脐带缆缆芯视为一实心圆柱。其次建立不同绞合角度的脐带缆有限元模型，设置各功能单元的材料属性和摩擦系数，分析模型在拉伸载荷下的扭转角度，并将相同拉伸载荷下的扭转角度拟合为直线，从而得到钢管脐带缆在扭转平衡状态时的最优绞合角度。最后，采用试验方法对实物钢管脐带缆进行扭转平衡测试，测试结果显示在拉伸载荷下脐带缆单位长度扭转角度十分微小，这表明缆是扭转平衡的。因此验证了使用的有限元方法在钢管脐带缆扭转平衡设计中的有效性。     

New Derivation of Ordinary Differential Equations for Transient Free-Surface Green Functions

Based on the Laplace transform, a direct derivation of the ordinary differential equations for the three-dimensional transient free-surface Green function in marine hydrodynamics is presented. The results for the 3D Green function and all its spatial derivatives are a set of fourth-order ordinary differential equations, which are identical with that of Clement (1998). All of these results may be used to accelerate numerical computation for the time-domain boundary element method in marine hydrodynamics.     

Dynamic response simulation of a heavy cargo suspended by a floating crane based on multibody system dynamics

In this paper, the dynamic response simulation of heavy cargo suspended by a floating crane is performed. The dynamic equations of the motions of the floating crane and the heavy cargo must be considered by the coupled equations because the floating crane and the heavy cargo are connected by wire ropes and provide force and a moment for each other. Hence, the dynamic equations of motion are set up for considering the 6-degrees-of-freedom floating crane and the 6-degrees-of-freedom cargo based on multibody system dynamics. The nonlinear terms in the equations of motion are considered. In addition, the nonlinear hydrostatic force, the linear hydrodynamic force, the wire rope force, and the mooring force are considered as the external forces. Finally, we estimate the motion of the floating crane and the heavy cargo and also calculate the tension of the wire rope between the two.     

Wave propagation in a transversely isotropic porous ocean bottom

Abstract

The equations of wave motion are considered in this article for three-layered medium which consists of liquid and porous layers with finite depth and solid half-space such as ocean bed. By virtue of scalar potential functions for each layer, complicated differential equations of layers are reduced to ordinary differential equations. An analytical method is applied to determine the Green’s functions of media based on an arbitrary shaped time-harmonic excitation at the interface of liquid and porous layers. A Mathcad code is provided to compute the complex integrals. Displacement and stress fields of three layers are discussed. Comparing with special cases, existing answers represent the validity of the proposed method. Numerical results are carried out for circular patch, ring and point loads, and the effects of various parameters on the behavior of the system are plotted. Finally, the achieved results were under discussion.     

Mathematical modeling of spatial vibrations of lengthy hose structures

Spatial vibrations of hose constructions are considered with points of fastening under non-stationary kinematic actions. A model of hard rigid string is accepted as a computational model. The finite-difference method for the solution of equations of motion was used. A computational algorithm and a FORTRAN program were developed. The algorithm takes into account physical, geometrical and exploitative peculiarities of the constructions: bending stiffness, non-uniformity, geometrical non-linearity, conditions of fastening, internal/external hydrodynamics and internal dissipation of energy by friction between construction elements. It does not put any restraints on the initial form of construction, displacements and parameters of actions.As an example of practical application, a dynamics analysis of mooring utility systems under rough seas and wind loads was performed. Transient and steady-state modes of vibration were studied. Extreme generalized tensions and displacements of the construction were obtained as a function of roughness parameters, wind velocity and wind orientation, and geometrical and physical parameters of the construction.     

波浪作用下缆船拖带系统非线性运动数值模拟

基于船舶操纵性运动方程和拖缆的三维动力学运动方程,提出了被拖点位置匹配的方法,建立了拖船—拖缆—被拖船系统整体非线性拖带动力学模型。为了考察被拖船航向稳定性与横向稳性的关系以及波浪载荷作用的影响,被拖船采用水平面四自由度运动方程,并引入了波浪的作用力和力矩。拖船采用PD控制方法较真实地模拟了拖船航向改变的运动过程。对一个拖船—拖缆—被拖船系统(5 000 t的拖船和3 000 t的被拖船)在时域内进行了规则波浪作用下拖带运动的模拟,计算结果表明被拖带船舶在波浪中运动呈现运动稳定、不稳定和临界状态3种可能的特性。根据模拟计算结果,认为波浪中拖带航向稳定是被拖带船舶保持稳性的必要条件。     

Numerical simulation of undersea cable dynamics

A fully three-dimensional code has been written to compute the motion of a towed cable. The code is based on a robust and stable finite difference approximation to the differential equations derived from basic dynamics. A 3500-ft (1.07 km) cable pulled at 18.5 knots (34.3 km hr⁻¹) through a circular turn of 700 yd (0.64 km) radius has been computed in about half of the real time of the maneuver. The computed displacements are close to the measured ones; the changes in depth are within 2%.