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1.
Application of the extended Melnikov's method for single-degree-of-freedom vessel roll motion 总被引：2，自引：0，他引：2
Traditionally, when using Melnikov's method to analyze ship motions, the damping terms are treated as small. This is typically true for roll motion but not always true for other and/or multiple degrees of freedom. In order to apply Melnikov's method to other and/or multiple-degree-of-freedom motions, the small damping assumption must be addressed. In this paper, the extended Melnikov method is used to analyze ship motion without the constraint of small linear damping. Two roll motion models are analyzed here. One is a simple roll model with nonlinear damping and cubic restoring moment. The other is the model with biased restoring moment. Numerical simulations are investigated for both models. The effectiveness and accuracy of this method is demonstrated. 相似文献
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Maintenance and repair at the operational level is a critical function to comply with the standard of competence for officers in charge of an engineering watch in a manned/unmanned ship engine room. The human factor in ship maintenance especially deals with fulfilling of the required competency about dismantling, inspecting, repairing and reassembling equipment in accordance with manuals and good practice stated in STCW Code, as amended in 2010. This study extends the shipboard operation human reliability analysis (SOHRA) through the marine auxiliary machinery maintenance operations. The approach involves the determined marine-specific error producing conditions (EPC) and generic task type parameters to quantify generic error probability (GEP) values along with the subtasks of the maintenance operation. To acquire the EPC and GEP values, the real case study on heavy fuel oil (HFO) purifier overhauling considers different operating conditions on-board selected five ships in a dry bulk fleet. The case study shows that human error probability (HEP) values of tasks in maintenance operation change in regard to ship operating conditions. Consequently, the study contributes to the marine engineering field in improving the human factor in ship repair and maintenance operations. This approach is further extended by incorporating maintenance 4.0 requirements into ship operating environment to conduct scenario-based task analysis. 相似文献
4.
Hyeon Kyu Yoon Nam Sun Son Gyeong Joong Lee 《Oceanic Engineering, IEEE Journal of》2007,32(4):798-806
When a fast container ship or a naval vessel turns, accompanying roll motions occur. This roll effect must be considered in the horizontal equations of the motion of the ship to predict the maneuverability of the ship properly. In this paper, a new method for determining a model structure of the hydrodynamic roll moment acting on a ship and for estimating the hydrodynamic coefficients is proposed. The method utilizes a system identification technique with the data from sea trial tests or from free running model (FRM) tests. To obtain motion data that is applied to the proposed algorithm, an FRM of a large container ship was developed. Using this model ship, standard maneuvering tests were carried out on a small body of water out of doors. A hydrodynamic roll moment model was constructed utilizing the data from turning circle tests and a 20-20 zig-zag test. This was then confirmed through a 10-10 zig-zag test. It was concluded that a model structure of the hydrodynamic roll moment model could be established without difficulty through a system identification method and FRM tests. 相似文献
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This paper presents a potential based boundary element method for solving a nonlinear free surface flow problem for a ship moving with a uniform speed in finite depth of water. The free surface boundary condition is linearized by the systematic method of perturbation in terms of a small parameter up to third order. The surfaces are discretized into flat quadrilateral elements and the influence coefficients are calculated by Morino's analytical formula. Dawson's upstream finite difference operator is used in order to satisfy the radiation condition. The second order solution gives better result than the first or third order solution. So the present method with the second order solution can be adopted as a powerful tool for the hydrodynamic analysis of the thin ship in finite depth of water. 相似文献
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A study is conducted to estimate the accurate attitude of a ship's motion and the estimation is used to arrive at the corrections required for a farfield pattern of a coaxial circular array. The relevant analytical expression is developed for the computation of moving average filter weights to estimate the ship's attitude for beamsteerings at different sea conditions. Farfield patterns are presented for different steered directions for the coaxial circular array of the additive type, and the multiplicative array technique is also used for beamsteering for higher steering angles to observe its control on the sidelobes as well as for the main beamwidths. In order to introduce an adaptive filter to estimate the accurate attitude for stable sonar platform, an adaptive parameter is examined for bathymetric applications where nonstationary ship movement prevails. 相似文献
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This paper addresses an important problem in ship control application—the robust stabilization of underactuated ships on a linear course with comfort. Specifically, we develop a multivariable controller to stabilize ocean surface ships without a sway actuator on a linear course and to reduce roll and pitch simultaneously. The controller adapts to unknown parameters of the ship and constant environmental disturbances induced by wave, ocean current and wind. It is also robust to time-varying environmental disturbances, time-varying change in ship parameters and other motions of the ship such as surge and heave. The roll and pitch can be made arbitrarily small while the heading angle and sway are kept to be in reasonably small bounds. The controller development is based on Lyapunov’s direct method and backstepping technique. A Lipschitz continuous projection algorithm is used to update the estimate of the unknown parameters to avoid the parameters’ drift due to time-varying environmental disturbances. Simulations on a full-scale catamaran illustrate the effectiveness of our proposed controller. 相似文献
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Donghoon Kang Vishwanath Nagarajan Yoshiaki Gonno Kazuhiko Hasegawa 《Ocean Engineering》2011,38(10):1184-1196
The inflow characteristics to each one of the rudders of single-propeller twin-rudder system are investigated. It is shown that this inflow is not parallel to ship's centerline. This may result in asymmetric maneuvering characteristic of the ship thereby reducing ship's maneuvering performance. For this purpose, a method of installing single-propeller twin-rudder system is proposed. This method is called “virtual zero rudder angle” arrangement. Here, each one of the twin-rudder is set at an angle corresponding to the inflow to the rudder. The improvement in ship's maneuvering characteristics with “virtual zero rudder angle” arrangement is investigated using experiments and numerical simulations for different ship types. It is shown that this arrangement may also improve ship's propulsion performance. 相似文献
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Thomas W. TreakleIII Dean T. Mook Stergios I. Liapis Ali H. Nayfeh 《Ocean Engineering》2000,27(12):1171
A method to evaluate the use of actively controlled moving weights on board ships to reduce roll motion is developed. The weights can simulate in principle anti-roll-tank systems, or they can be considered a possible anti-roll device in their own right. The ship, the moving weight, and the control device are considered components of a single dynamic system. The full eight-degree-of-freedom set of coupled governing equations for the complete dynamic system is derived. And a three-degree-of-freedom non-linear approximation for the roll motion only (MOTSIM) is derived from these eight equations. The reduced set of equations is used to determine the influence of various parameters and to evaluate control strategies. A PID controller is developed to command the position of the weight and a servomechanism model is used to predict its actual position. Then, the moving-weight system is incorporated into LAMP (Large–Amplitude–Motion Program), a computer code that integrates the governing equations of the sea and the motion of the ship interactively and simultaneously and predicts the motion of the ship in the time domain. A comparison of the results from the two simulations shows that there is fairly good correlation between the simple and complex models, but the simple model is a little optimistic in predicting the effectiveness of the moving-weight system. The results predict that the moving-weight system can be an excellent roll-suppressing device when the moving weight is as small as 1% of the displacement of the ship and the maximum distance the weight moves is as small as 15% of the half-beam. 相似文献
10.
The analytical method developed by Svendsen (1968) for a forced heave motion is extended to the general problem of wave induced heave, roll and sway motions of a long ship at a depth of water which is only slightly larger than the draught of the ship. This corresponds, for example, to the situation of a fully loaded ship in a harbour area.After linearization of the problem, the water motion is considered for each of the three individual motions and for the wave reflection-transmission problem for a fixed ship. The ensuing results for the forces on the ship are then synthesized to form the equations of motion, which are presented with all coefficients given, including mooring forces.Analytical and numerical results are given for the three components of motion, for the associated resonance frequencies, and for the hydrodynamic masses and moments of inertia. Finally, the assumptions used are analyzed and evaluated by comparison with measurements and with other results for a special case. 相似文献
11.
J.-G. Dessureault 《Ocean Engineering》1976,3(2):99-111
“Batfish” is a streamlined vehicle developed to house fast-responding oceanographic sensors. It is towed behind a ship or small vessel and its depth is controlled from the vessel by a manually or automatically produced command signal. Variable-angle wings permit the vehicle to be lowered and a novel control surface, which eliminates the need for heavy ballast, assures lateral stability. There are two models: the standard and the wide-wing Batfish. The standard Batfish has collected temperature and conductivity data at depths of up to 200 m when towed at 10–25 km/hr, and the wide-wing Batfish at depths to 400 m when towed at 10–16km/hr. 相似文献
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Robust path-following of underactuated ships: Theory and experiments on a model ship 总被引：1，自引：0，他引：1
A method is proposed to design a new global controller that forces an underactuated ship to follow a reference path under disturbances induced by wave, wind and ocean-current. The controller is designed such that the ship moves on the path with an adjustable forward speed and its total velocity is tangential to the path. The ship under consideration is not actuated in the sway axis, and the mass and damping matrices are not assumed to be diagonal. Nonlinear damping terms are also included to cover both low- and high-speed applications. The new result is facilitated by choosing an appropriate origin of the body-fixed frame, designing a suitable filter of sway velocity, several nonlinear coordinate changes, the backstepping technique, and utilizing the ship dynamic structure. Experimental results on a model ship illustrate the effectiveness of the proposed method. 相似文献
14.
The ship routing problem can be known as a multi-objective problem. Since the operation strategy is influenced by ocean environments, e.g. wind, waves or ocean currents, it is therefore weather routed. In this study, the three-dimensional modified isochrone (3DMI) method utilizing the recursive forward technique and floating grid system for the ship tracks is applied to globally search for the optimum route. The proposed method considers two types of routing strategies, i.e. ETA (Estimated Time of Arrival) routing and FUEL (FUEL-saving) routing, with different constraints, such as land boundaries, significant wave heights, engine revolution speeds and roll responses. As a result, it is verified that the robustness of the proposed method appears to be a practical tool by adjusting the safety threshold for the trade-off of ship efficiency and economics. 相似文献
15.
GPU-Based DEM Simulations of Global Ice Resistance on Ship Hull During Navigation in Level Ice 总被引：1，自引：0，他引：1
The ice resistance on a ship hull affects the safety of the hull structure and the ship maneuvering performance in icecovered regions.In this paper,the discrete element method(DEM)is adopted to simulate the interaction between level ice and ship hull.The level ice is modeled with 3D bonded spherical elements considering the buoyancy and drag force of the water.The parallel bonding approach and the de-bonding criterion are adopted to model the freezing and breakage of level ice.The ship hull is constructed with rigid triangle elements.To improve computational efficiency,the GPU-based parallel computational algorithm was developed for the DEM simulations.During the interaction between the ship hull and level ice,the ice cover is broken into small blocks when the interparticle stress approaches the bonding strength.The global ice resistance on the hull is calculated through the contacts between ice elements and hull elements during the navigation process.The influences of the ice thickness and navigation speed on the dynamic ice force are analyzed considering the breakage mechanism of ice cover.The Lindqvist and Riska formulas for the determination of ice resistance on ship hull are employed to validate the DEM simulation.The comparison of results of DEM,Lindqvist,and Riska formula show that the DEM result is between those the Lindqvist formula and Riska formula.Therefore the proposed DEM is an effective approach to determine the ice resistance on the ship hull.This work can be aided in the hull structure design and the navigation operation in ice-covered fields. 相似文献
16.
An inverse hull design approach in minimizing the ship wave 总被引：1，自引：0，他引：1
The Levenberg–Marquardt Method (LMM) and a panel code for solving the wave-making problem are utilized in an inverse hull design problem for minimizing the wave of ships. A typical catamaran is selected as the example ship for the present study. The hull form of the catamaran is described by the B-spline surface method so that the shape of the hull can be completely specified using only a small number of parameters (i.e. control points). The technique of parameter estimation for the inverse design problem is thus chosen. The LMM of parameter estimation, which is the combination of steepest descent and Newton’s methods, has been proven to be a powerful tool for the inverse shape design problem. For this reason it is adopted in the present study.In the present studies, the inverse hull design method can not only be applied to estimate the hull form based on the known wave data of the target ship but can also be applied to estimate the unknown hull form based on the reduced wave height. The optimal hull forms of minimizing wave for a typical catamaran in deep water at service speed and at the critical speed of shallow water are estimated, respectively. Moreover, a new hull form with the combining feature of the optimal hull forms for deep water and shallow water is performing well under both conditions. The numerical simulation indicates that the hull form designed by inverse hull design method can reduce the ship wave significantly in comparison with the original hull form. 相似文献
17.
《中国海洋工程》1998,(1)
A quasi-steady time domain method is developed for the prediction of dynamic behavior of amooring system under the environmental disturbances,such as regular or irregular waves,winds and cur-rents.The mooring forces are obtained in a static sense at each instant.The dynamic feature of the moor-ing cables can be obtained by incorporating the extended 3-D lumped-mass method with the known shipmotion history.Some nonlinear effects,such as the influence of the instantaneous change of the wettedhull surface on the hydrostatic restoring forces and Froude-Krylov forces,are included.Thecomputational results show a satisfactory agreement with the experimental ones. 相似文献
18.
This study introduces a method of calculating a capsizing rate of a ship. The phenomenon ‘capsizing’ is described as a jump of local equilibrium point from that near the upright position of a ship to what describes the upside-down attitude of the capsized ship; the rate of occurrence of such jumps was calculated. The potential function corresponding to the roll restoring moment have two potential wells located at the roll displacement angle 0 and 180°, respectively. A nonlinear Fokker–Planck equation for the joint probability density function of roll angle and velocity was solved. The excitation to the ship was assumed to be a combination of a regular harmonic wave and a white noise process. 相似文献
19.
When a ship model test is performed in a tank, particularly when the tank is small and the ship model is relatively large, the blockage effect will inevitably occur. With increased ship model scale and speed, the blockage effect becomes more obvious and must be corrected. In this study, the KRISO 3600 TEU Container Ship(KCS) is taken as a model and computational fluid dynamics techniques and ship resistance tests are applied to explore the mechanism and correction method of the blockage effect. By considering the degrees of freedom of the sinkage and trim, the resistance of the ship model is calculated in the infinite domain and for blockage ratios of 1.5%, 1.8%, 2.2%, and3.0%. Through analysis of the free surface, pressure distribution, and flow field around the ship model, the action law of the blockage effect is studied. The Scott formula and mean flow correction formula based on the average cross sectional area are recommended as the main correction methods, and these formulas are improved using a factor for the return flow velocity correction based on comparison of the modified results given by different formulas. This modification method is verified by resistance test data obtained from three ship models with different scale ratios. 相似文献
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远海浮式结构物与供应船旁靠系泊特性研究 总被引：1，自引：0，他引：1
针对远海浮式结构物与供应船进行旁靠作业时,水动力干扰、两船的相对运动、旁靠系缆系统和护舷系统的受力特征等问题开展研究。建立各船的有限元模型,设计出两船旁靠连接缆系统,选取合适的系泊缆和护舷参数。研究表明:浮式结构物和供应船的横荡、纵荡方向存在一定的同步性或跟随性,幅值相差不大,其它方向的运动并不存在明显的同步特征;供应船的各自由度运动幅值均比浮式结构物偏大;旁靠护舷的受力时历出现了明显的低频效应,说明护舷的受力较大程度上受船体低频慢漂运动的影响;浮式结构物对供应船的水动力干扰较大,当浮式结构物在供应船的上风位置时,表现为屏蔽效应,供应船的运动较小;在其背风位置时,运动加剧,出现多次共振、峰值放大现象,供应船对浮式结构物的水动力性能几乎无影响,因此,供应船从浮式结构物的下风口一侧靠泊作业将更有利于船舶的安全性能。这些研究结论可为实际工程操作提供参考。 相似文献