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。     

Towed cable behaviour during ship turning manoeuvers

The results of dynamic and steady-state cable simulations are used to show that a towed system can behave in either of two different ways on entering a turn. In a large radius turn the system maintains its straight-tow equilibrium configuration but in a slightly perturbed form. In a turn of small radius the system effectively collapses resulting in a large increase of fish depth and cable tension. A formula is included by which the approximate minimum radius of turn that does not precipitate collapse can be quickly calculated.Non-dimensional tables are presented giving details of the equilibrium configuration adopted by the cable when the ship maintains a circular course.Graphs are presented from which the time constants for the decay of lateral and longitudinal disturbances of 2-D cable profiles can be easily calculated. These can be used to estimate the time taken for a towed system to return to equilibrium following a manoeuvre.The derivation of the equations for the steady-state configurations and the time constants are included in appendices.     

Parameters influence on maneuvered towed cable system dynamics

The dynamic response of a towed cable system to ship maneuver is parametrically simulated. Three dimensionless parameters influence on towed cable system maneuverability is investigated. They are ratio of total length to turning radius R/L, ratio of cable mass to vehicle mass σ, and ratio of mass unit length to hydrodynamic force w/r. An oscillatory motion of towed vehicle is found in simulation of spiral towed courses. Features of this oscillation in different spiral courses are compared. The sharp turns, gradual turns and their transient states of towed cable dynamics for different course directions are discussed extensively. According to the characters of transient states and horizontal trajectories evolution of maneuvered cable system, the dynamic behaviors can be divided into three situations in Fig. 8 turning maneuvers. The behavior of towed cable system during a zigzag turning course is simulated in the end. Two ingredients of heave motion are found during small ratio of turning radii to length in this course. The primary damp to initial turning becomes weak and the response to alternative turns plays a more and more important role. The damping properties of the transient behavior in different maneuvers show a periodical invariance to σ during some turning maneuvers.     

A study of the ship induced roll-yaw motion of a heavy towed fish

The lateral motions of roll, yaw and sway of a heavy towed fish are investigated. Perturbation lateral ship motion propagates down the cable as a damped wave and non-dimensional tables are provided that allow the attenuation of the motion to be estimated. The tables are supplemented by a short BASIC computer program for calculations outside the tabular range.Three-dimensional dynamic simulation of the Bath Mk 3 Sonar Fish is used to establish the effects of fish weight, towstaff length and vertical fin size on the amplitude of rolling and yawing motion. It is shown that very careful adjustment of fin size can reduce the amplitude of yawing motion by a factor of about 3. It is also shown that attaching the cable to the fish with a towstaff free to pivot only in pitch improves the towing properties of the fish and reduces the amplitude of rolling motion.     

Study on the Configuration of Towed Flexible Cables

Based on the fundamental equation of flexible cable dynamics for a towed system, an easily solved mathematical model is set up in this paper by means of appropriate simplification. Several regular patterns of spatial motion of towed flexible cables in water are obtained through numerical simulation with the finite difference method, and then modification and verification by trial results at sea. A technical support is provided for the towing ship to maneuver properly when a flexible cable is towed. Furthermore, the relations between two towed flexible cables, which are towed simultaneously by a ship, are investigated. The results show that the ship towing two flexible cables is safe under the suggested arrangement of two winches for the towing system, and the coiling/uncoiling sequences of the cables as well as the suggested way of maneuvering.     

Dynamic modeling of cable towed body using nodal position finite element method

This paper analyses nonlinear dynamics of cable towed body system. The cable has been modeled and analyzed using a new nodal position finite element method, which calculates the position of the cable directly instead of the displacement by the existing finite element method. The newly derived nodal position finite element method eliminates the need of decoupling the rigid body motion from the total motion, where numerical errors arise in the existing nonlinear finite element method, and the limitation of small rotation in each time step in the existing nonlinear finite element method. The towed body is modeled as a rigid body with six degrees of freedom while the tow ship motion is treated as a moving boundary to the system. A special procedure has been developed to couple the cable element with the towed body. The current approach can be used as design tool for achieving improved directional stability, maneuverability, safety and control characteristics with the cable towed body. The analysis results show the elegance and robustness of the proposed approach by comparing with the sea trial data.     

Simulation studies of the response of deeply towed vehicle to various towing ship maneuvers

The behavior of a long cable towed at slow speeds through the ocean depends in a complex fashion on the path followed by the towing ship relative to the water. A cable simulation program was used to characterize the response of the cable by using idealized towing ship maneuvers as input to the program. The response of the cable was noted and it was found that the behavior of the cable was strongly dependent on the fundamental period of the towing vessel maneuvers. Sinusoidal deviations of the towing ship from a straight towing track resulted in delayed and reduced excursions of the towed vehicle from the tract; the estimated response ratio varied from 0·002 to 0·800, depending both on the period of the deviations (periods ranged from 5·5 to 4·0 hr) and on the towing depth (2 or 6 km). The ship's speed was 3 km/hr. The time lag between ship motion and vehicle response was approximately 0·5 hr for the shallow case and 1·3 hr for the deep case. Simulations runs of a low dragk (faired) cable showed that the behavior of the vehicle when towed at a depth of 6 km was similar to that obtained with a conventional cable at 2 km depth. The response of the towed vehicle to a right-angle turn of the towing ship was investigated and a generalized model of the response developed. The effects of a controllable side force on the towed vehicle were also simulated and it was noted that a deviation (2-hr period) of the towed vehicle from a straight-line track could be reduced from 40 to 2 m by impressing a side force on the vehicle with an average magnitude of 150 newtons (30 lb).     

The adjustment of fin size to minimise the ship induced pitching motion of a towed fish

The hydrodynamic forces and moments that act on a towed fish are described and related to fundamental static and dynamic towing characteristics. It is shown that, when the fin height is reduced almost to the point giving neutral stability in pitch, the fish maintains almost constant pitch attitude while it is forced to heave or surge by ship motion transmitted down the cable.Wind tunnel tests provide the necessary hydrodynamic data for a computer simulation in two dimensions of the Bath Mk 3 sonar fish towed on faired cable. The results show that the magnitude of the pitch attitude variations of the fish can be greatly reduced by decreasing the fin size, with further reduction being possible by correctly locating the pointwhere the cable is attached to the fish. It is also shown that decreasing the fin size reduces the magnitude of the tension variations in the cable, thereby lowering the probability that the cable will go slack.These results generalise to a large class of towed systems using either or bare cable, and a formula is included by which the magnitude of the ship-inducing pitching motion of a fish can be estimated, given the necessary hydrodynamic data.Possible difficulties associated with towing a low stability fish are considered and a method is included for assessing the minimum stability likely to be necessary to achieved satisfactory towing behaviour.     

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。     

Investigation on a two-part underwater manoeuvrable towed system

A hydrodynamic model of a two-part underwater manoeuvrable towed system is proposed in which a depressor is equipped with active horizontal and vertical control surfaces, and a towed vehicle is attached to the lower end of a primary cable. In such a system the towed vehicle can be manoeuvred in both vertical and horizontal planes when it is towed at a certain velocity and the coupling effect of excitations at the upper end of the primary cable and disturbances of control manipulations to the towed vehicle can be reduced. In the model the hydrodynamic behavior of an underwater vehicle is described by the six-degrees-of-freedom equations of motion for submarine simulations. The added masses of an underwater vehicle are obtained from the three-dimensional potential theory. The control surface forces of the vehicle are determined by the wing theory. The results indicate that with relative simple control measures a two-part underwater manoeuvrable towed system enables the towed vehicle to travel in a wide range with a stable attitude. The method in this model gives an effective numerical approach for determining hydrodynamic characteristics of an underwater vehicle especially when little or no experimental data are available or when costs prohibit doing experiments for determining these data.     

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.     

Numerical Simulation of Dynamic Response of Towed Systems

In this paper,the dynamic response of undersea -+towed systems is numerically simulated.Atwo body towed system is especially considered in detail.The factors influencing the heave oftowed-bodies,such as the weight of the towed-body(in sea water),the length and the weight(in sea water)per unit length of the cable between towed-bodies and towing ship,are investigated in detail.Calculationsshow that the two-body towed system can greatly increases the stability of the towed system.     

A hydrodynamic model of a two-part underwater towed system

A three-dimensional model of a two-part underwater towed system is studied. In the model, the governing equations of cables are established based on the Ablow and Schechter method. The boundary conditions for the two-part underwater towed system are derived. The six-degrees-of-freedom equations of motion for submarine simulations are adopted to predict the hydrodynamic performance of a towed vehicle. The established governing equations for the system are then solved using a central finite difference method. In this paper several algorithms are used to solve this special form of finite difference equations. The results in this paper indicate that the two-part underwater towed system improves the dynamic behavior of the towed vehicle and is an easy way to decouple the towing ship motion from the towed vehicle. Because the model uses an implicit time integration, it is stable for large time steps and is an effective algorithm for simulation of a large-scale underwater towed system.     

Nonlinear adaptive control of an underwater towed vehicle

This paper addresses the problem of simultaneous depth tracking and attitude control of an underwater towed vehicle. The system proposed uses a two-stage towing arrangement that includes a long primary cable, a gravitic depressor, and a secondary cable. The towfish motion induced by wave driven disturbances in both the vertical and horizontal planes is described using an empirical model of the depressor motion and a spring-damper model of the secondary cable. A nonlinear, Lyapunov-based, adaptive output feedback control law is designed and shown to regulate pitch, yaw, and depth tracking errors to zero. The controller is designed to operate in the presence of plant parameter uncertainty. When subjected to bounded external disturbances, the tracking errors converge to a neighbourhood of the origin that can be made arbitrarily small. In the implementation proposed, a nonlinear observer is used to estimate the linear velocities used by the controller thus dispensing with the need for costly sensor suites. The results obtained with computer simulations show that the controlled system exhibits good performance about different operating conditions when subjected to sea-wave driven disturbances and in the presence of sensor noise. The system holds promise for application in oceanographic missions that require depth tracking or bottom-following combined with precise vehicle attitude control.     

Experimental investigation on a two-part underwater towed system

An experimental set-up is developed and proved to be effective for laboratory study of an underwater towed system. The experimental technique gives a practical method for monitoring the kinematic and dynamic performance of an underwater towed system in a ship towing tank. Both the theoretical and experimental results in the investigation indicate that the hydrodynamic response of a towed vehicle to the wave induced motion of a towing ship can be significantly reduced by applying a two-part tow method. A comparison of the numerical and experimental results in the investigation demonstrates that the numerical simulation results are close to the experimental data, overall agreement between experimental and theoretical results is satisfactory. The results qualitatively verify the mathematical model of a two-part underwater towed system proposed by Wu and Chwang [Wu, J., Chwang, A.T., 2000. A hydrodynamic model of a two-part underwater towed system. Ocean Engineering 27 (5), 455–472].     

A metamodel-based towed system simulation

The objective of this exercise was the development of a computer simulation of a US Navy towed system (towed body and line array) capable of near real-time predictive capabilities. The purpose of the computer simulation was to be able to determine the lateral motion of the towed body in response to ship maneuvers. The theoretical approach was to develop a spatial-domain computer simulation of each of the towed system components treated as a system, and then develop a “metamodel” of the response by using simple algebraic expressions. At-sea trials were conducted aboard US Navy vessels to verify the simulation and fine-tune its performance.     

关于变深声纳(VDS)拖缆拖体系统漂移的研究

变深声纳（ＶＤＳ）拖航中，拖缆拖体系统偏离拖船纵中剖面的现象称为漂移。本文针对为解决某变深声纳拖缆拖体系统拖航时出现的严重漂移，介绍了漂移的危害，分析了漂移产生的原因，解决漂移的方法和试验研究结果。     

Vibration induced in towed linear underwater array cables

Towed linear arrays of hydrophones are used in various applications, for example, seismic prospecting. Tow cable vibration is capable of causing output in the towed array system. Since one of the factors limiting acoustic sensitivity is self-noise, the general objective of this analysis is to investigate the nature of longitudinal and transverse cable vibrations, with the aim of minimizing vibration transmitted to the array. The equations of transverse cable motion are derived and solved for a single-póint excitation and for distributed-vortex excitation. The response to vortex-shedding excitation along the first 150 ft of array-end cable is quantitatively evaluated and compared with actual tow-trial measurements. Two types of longitudinal vibration are analyzed, one caused by direct excitation along the cable axis, and one caused indirectly by transverse cable vibration. Fluid drag and hysteretic damping are included in the analysis.     

海洋测量水下拖曳设备的位置计算方法研究

针对海洋测量水下拖曳设备位置确定问题,综合考虑拖缆受力、海流影响以及水下拖体的运动性质,建立了水下拖曳设备的位置计算模型,并仿真计算分析了测量船在不同航行状态下拖曳设备位置确定的规律,探讨了不同海流效应对拖曳设备位置确定的影响。仿真计算结果表明,在海洋动态环境作用下,拖缆各方向的偏移明显呈曲线形状,非简单几何运算所确定。测船各方向的运动均可对水下拖体的位置在相应方向产生一定影响,而水下拖体位置的变化量小于测船拖点位置的变化量。海流对水下拖曳设备定位可造成数米的偏差,需进行相应改正。建议可考虑采取船载式ADCP实时测流辅助水下拖曳设备定位的工作模式。     

A motion-compensated launch/recovery crane

Oceanographic instrumentation towed from a surface platform is normally subjected to unwanted vertical motion imparted by the rolling, heaving, and pitching of the platform. This motion can cause severe shock-loading conditions in the tow cable and induces unplanned depth variations that reduce the instruments' resolution. This article discusses a unique motion-compensation system for use with towed instrumentation that eliminates shock loading and minimizes depth variation. The system is operational in sea states as high as 5 and effectively decouples 96% of the vessel's motion.