共查询到20条相似文献，搜索用时 15 毫秒
1.
The dynamic behavior of a towed cable system that results from the tow ship changing course from a straight-tow trajectory to one involving steady circular turning at a constant radius is examined. For large-radius ship turns, the vehicle trajectory and vehicle depth assumed, monotonically and exponentially, the large-radius steady-state turning solution of Chapman [Chapman, D.A., 1984. The towed cable behavior during ship turning manoeuvers. Ocean Engineering 11, 327–361]. For small-radius ship turns, the vehicle trajectory initially followed a corkscrew pattern with the vehicle depth oscillating about and eventually decaying to the steady-state turning solution of Chapman (1984). The change between monotonic and oscillatory behavior in the time history of the vehicle depth was well defined and offered an alternate measure to Chapman's (1984) critical radius for the transition point between large-radius and small-radius behavior. For steady circular turning in the presence of current, there was no longer a steady-state turning solution. Instead, the vehicle depth oscillated with amplitude that was a function of the ship-turning radius and the ship speed. The dynamics of a single 360° turn and a 180° U-turn are discussed in terms of the transients of the steady turning maneuver. For a single 360° large-radius ship turn, the behavior was marked by the vehicle dropping to the steady-state turning depth predicted by Chapman (1984) and then rising back to the initial, straight-tow equilibrium depth once the turn was completed. For small ship-turning radius, the vehicle dropped to a depth corresponding to the first trough of the oscillatory time series of the steady turning maneuver before returning to the straight-tow equilibrium depth once the turn was completed. For some ship-turning radii, this resulted in a maximum vehicle depth that was greater than the steady-state turning depth. For a 180° turn and ship-turning radius less than the length of the tow cable, the vehicle never reached the steady-state turning depth. 相似文献
2.
D.A. Chapman 《Ocean Engineering》1984,11(1):23-64
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. 相似文献
3.
P. J. Wingham 《Ocean Engineering》1977,4(2):57-74
The relationship between the depth and trail attained by a towed submerged vehicle and the magnitude and direction of the forces on it has been examined theoretically, for cases involving faired cables.It is shown that when the body force is varied the body in equilibrium moves on an almost circular path as if the cable were straight, and that depth changes depend primarily upon the change in the component of the body force that acts at right angles to the line joining the top and bottom of the cable.Examples are given which demonstrate that for bodies towed at large depression angles the use of water brakes is more effective in changing depth than the use of lifting wings.The data is presented so that a rapid preliminary assessment can be made of any proposed system to obtain the best combination of speed and scope for achieving a given depth with a body having known lift and drag coefficients. 相似文献
4.
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. 相似文献
5.
Numerical simulation of undersea cable dynamics 总被引：7，自引：0，他引：7
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%. 相似文献
6.
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。 相似文献
7.
波浪作用下缆船拖带系统非线性运动数值模拟 总被引：1，自引：0，他引：1
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。 相似文献
8.
For accurate prediction of the deformation of cable in the towed system, a new finite element model is presented that provides a representation of both the bending and torsional effects. In this paper, the cubic spline interpolation function is applied as the trial solution. By using a weighted residual approach, the discretized motion equations for the new finite element model are developed. The model is calculated with the computation program complier by Matlab. Several numerical examples are presented to illustrate the numerical schemes. The results of numerical simulation are stable and valid, and consistent with the mechanical properties of the cable. The model can be applied to kinematics analysis and the design of ocean cable, such as mooring lines, towing, and ROV umbilical cables. 相似文献
9.
10.
Dynamic Analysis of Towed and Variable Length Cable Systems 总被引：2，自引：3，他引：2
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. 相似文献
11.
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. 相似文献
12.
A three-dimensional dynamic analysis of a towed system 总被引：1，自引：0，他引：1
Joël V. Sanders 《Ocean Engineering》1982,9(5):483-499
The three-dimensional configuration of a towed cable-body system during prescribed towship maneuvers is determined. Bending resistance and inertia terms are not retained in the towing model; methods are described for ascertaining when these effects are negligible. A physical finite difference formulation is employed to develop the discretized equations of motion, and the system configuration is advanced in time using a Runge-Kutta recurrence algorithm. The response of a reference towed system to a typical maneuver is presented graphically. 相似文献
13.
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. 相似文献
14.
Hae-Hoon Park 《Ocean Engineering》1993,20(2)
An indirect tension measurement method of a towing cable in midwater or a buoy cable is proposed using underwater acoustic positioning systems, etc., to give the in-water cable tension. The most simple and traditional cable tension measurement method is to apply a mechanical tension meter at the one end of the cable, but the method has limits in the aspects of continuous monitoring and manual operation. However, the technique in this study is to apply the Pode's analysis of the equilibrium configuration and tension of a flexible twine, in which the cable tension is given as a function of the geometric positions of both ends of the cable. A set of nonlinear integral equations is formulated and solved numerically by the Newton-Raphson method. Then the inclination angles and the tensions at the lower and the upper ends of the cable could be obtained. The derived method enables us to track a towed object, to measure the tension of a towing cable or a buoy cable and is also applicable to the remotely operated vehicle (ROV) tethered to a mother ship. 相似文献
15.
16.
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). 相似文献
17.
主动式声纳列阵拖曳系统姿态数值计算 总被引：2，自引：1，他引：2
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。 相似文献
18.
水下拖曳升沉补偿系统水动力数学模型研究 总被引：4，自引：2，他引：2
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. 相似文献
19.
D.A. Chapman 《Ocean Engineering》1982,9(3):189-220
Digital computer simulation in two dimensions of a neutrally-stable fish towed on a faired cable has been used to investigate the response of the fish to disturbances in the ship motion. The numerical methods used are described broadly, excluding mathematical detail, and selected results are presented which indicate typical behaviour of the system.The free oscillations of the fish-cable system and its response to deterministic and random ship disturbances are investigated. This reveals the dynamic principles governing the motion and allows the formulation of simple rules to give a first approximation to the magnitude of the fish response. It is shown that, provided resonances of the ship and fish-cable system do not coincide, the overall amplitude of motion of the fish is proportional to the sine of the angle made by the top of the cable with the horizontal. Formulae are given for calculating approximately the resonant frequencies of the towed system. 相似文献
20.
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. 相似文献