Ship Moving Research Articles

RANS Computation of the Mean Forces and Moments, and Wave-Induced Six Degrees of Freedom Motions for a Ship Moving Obliquely in Regular Head and Beam Waves

Ship maneuvering performance in waves has attracted much attention in recent years. One of main research efforts for this problem has been devoted to the high-accuracy computation of hydrodynamic forces and moments, as well as wave-induced motions, for ships performing maneuvering motions in waves. The objective of this article is to present a numerical study on the computation of the mean forces and moments, and wave-induced six degrees of freedom motions for a ship moving obliquely in regular head and beam waves. The RANS (Reynolds-Averaged Navier-Stokes) solver based on OpenFOAM is used for this purpose. The RANS computations herein are carried out in a horizontal coordinate system. The numerical wave maker with prescribing values of flow variables on the domain boundaries is applied for the wave generation in the computational domain. However, in order to prevent wave reflection, relaxed zones adjacent to the wave maker boundaries are set up. A new program module is inserted into OpenFOAM to update the flow velocity and wave evaluation on the wave-maker boundaries and in the relaxed zones during the RANS computation. The mesh deformation method is employed to allow the ship to perform motions in space. However, a virtual spring system is attached to the ship so as to restrain the surge, sway and yaw, while heave, pitch and roll are completely free, so that the ship is able to oscillate periodically around a certain position in space. The computed mean forces and moments with the inertia effects agree fairly well with the experimental data, and the computed wave-induced motions are also in quite reasonable agreement with the experimental data. This study shows a very successful computation, as well as the procedure of the RANS results processing.

Numerical Simulation of a Polar Ship Moving in Level Ice Based on a One-Way Coupling Method

In most previous ice–ship interaction studies involving fluid effects, ice was taken as unbreakable. Building breakable level ice on water domain is still a big challenge in numerical simulation. This paper overcomes this difficulty and presents a numerical modeling of a ship moving in level ice on the water by using a one-way CFD-DEM (computational fluid dynamics-discrete element method) coupling method. The detailed numerical processes and techniques are introduced. The ice crack propagation process including radial and circular cracks have been observed. Numerical results are compared with previous experimental data and good agreement has been achieved. The results show that water resistance is an order of magnitude smaller than ice resistance during the ice-breaking process. Ice resistance shows strong oscillation along with ice failure process, which are affected by ship speed and ice thickness significantly.

Mini-Tsunami Made by Ship Moving Across a Depth Change

Abstract A ship moving across a shallow depth change, in water in a small or narrow space, may create a small tsunami, 0.5–1 km long, observed as a harbor wave on shore, where a wave height up to 1...

Research on Waterway Wireless Propagation Characteristics Based on Channel Measurement: Ship Moving Across vs. Moving Through

Zhang, J.; Li, C.; Shu, X., and Chen, W., 2020. Research on waterway wireless propagation characteristics based on channel measurement: Ship moving across vs. moving through. In: Zheng, C.W.; Wang, Q.; Zhan, C., and Yang, S.B. (eds.), Air-Sea Interaction and Coastal Environments of the Maritime and Polar Silk Roads. Journal of Coastal Research, Special Issue No. 99, pp. 99-104. Coconut Creek (Florida), ISSN 0749-0208.The safety of ship traffic in inland waterway is crucial and relies on wireless communications. Yet previous wireless communication studies have focused on coastal and vehicles on land. This manuscript present measurement and analyses ship-to-boat pontoon campaign investigating the wireless propagation channel at 5.9 GHz in inland waterway. Research explore in particular the effect of ship motion transverse to and parallel to a fixed boat pontoon. And study analyze the effects of line-of-sight and non-line-of-sight conditions, which typify “inland intelligent waterway” scenarios. Beside different motion conditions like moving transverse to and parallel to boat pontoon, research also explore channel metrics such as path loss, small-scale fading, and correlations of signal with ship motion. The research results show that the relative motion of ships in inland intelligent waterway communication cannot be ignored.

Research on Wash Wave in Shallow Water Caused by Ship Moving at High Speed

Based on the theory of shallow-water wave, the theoretical model was established for calculating wash wave caused by ship moving at subcritical and supercritical speed. Wave elevation and pressure variation were obtained by numerical simulation, and their features were analyzed. A measuring system of wash wave and pressure variation was developed, and wave elevation and pressure variation induced by a towed ship model were measured. A good agreement existed between the calculated with experimental results.

Stochastic Inverse Identification of Nonlinear Roll Damping Moment of a Ship Moving at Nonzero‐Forward Speeds

The nonlinear responses of ship rolling motion characterized by a roll damping moment are of great interest to naval architects and ocean engineers. Modeling and identification of the nonlinear damping moment are essential to incorporate the inherent nonlinearity in design, analysis, and control of a ship. A stochastic nonparametric approach for identification of nonlinear damping in the general mechanical system has been presented in the literature (Han and Kinoshits 2012). The method has been also applied to identification of the nonlinear damping moment of a ship at zero‐forward speed (Han and Kinoshits 2013). In the presence of forward speed, however, the characteristic of roll damping moment of a ship is significantly changed due to the lift effect. In this paper, the stochastic inverse method is applied to identification of the nonlinear damping moment of a ship moving at nonzero‐forward speed. The workability and validity of the method are verified with laboratory tests under controlled conditions. In experimental trials, two different types of ship rolling motion are considered: time‐dependent transient motion and frequency‐dependent periodic motion. It is shown that this method enables the inherent nonlinearity in damping moment to be estimated, including its reliability analysis.

A Combined Control System With Roll Reduction and Track Keeping for the Ship Moving in Waves

In this paper, a hydrodynamic numerical model with a combined control system is developed to simulate a ship steering in waves. The combined control system includes the PD controller and the sliding mode controller. By way of the rudder operation, the PD controller integrated with a line-of-sight (LOS) guidance system is used to control the track keeping, whereas the sliding mode controller is mainly chosen to reduce the roll motion. Different heading angle, wave height, wavelength, and initial speed are selected to investigate the combined control ability of the autopilot system. From simulation results, we find that this combined control system indeed works well, either for the ship roll motion reduction or for the ship track keeping in waves.

Dead-Water Effects of a Ship Moving in Stratified Seas

A linearized theory is presented for the dead-water phenomena. A two-layer fluid model of finite depth is assumed and the solutions for both the wave resistance, as well as the interface and free-surface disturbances, are obtained in terms of Green’s function. Numerical solutions are given for the case of a semi-submersible slender-body (prolate spheroid) moving steadily on the free-surface.

On the Distribution of Cross Flow Drag over the Length of a Ship Moving Transversely

It is of importance to evaluate the ship manoeuvring motion, such as the berthing in a harbour, the drifting behaviour of a disabled ship. A significant part of the lateral hydrodynamic forces acting on a ship will be due to cross flow drag, as the ship's drift velocity becomes relatively larger compared to the ahead speed. For the prediction of ship manoeuvrability at larger drifting angles, it will be required to estimate the cross flow forces accurately.In this paper, a calculation is given to the longitudinal distribution of the cross flow drag coefficient over the length of ship moving transversely. The theoretical method on basis of vortex model developed by the authors is applied to the Wigley hull and a container ship hull.By comparing with the measured results of captive model tests, the prediction results agree well with model tests. Therefore, this method will be useful for practical prediction of cross flow forces acting on a ship moving laterally, taking into account the forms of the ship's cross sections

The Diffraction Forces for a Ship Moving in Oblique Seas

The diffraction problem of a fixed slender ship moving in incident waves is formulated. The waves are assumed to be of the same order as the beam of the ship and are from an oblique heading. The boundary value problem is linearized with respect to wave amplitude and solved by the method of matched asymptotic expansions. The oscillating forward-speed potential is solved to two orders of magnitude. The first order is just the zero-speed case while the second-order problem involves solving a boundary-value problem with a nonhomogeneous free-surface condition. The solution to this second-order problem is given in terms of three auxiliary potentials, each satisfying a separate part of the boundary conditions. For zero forward speed, the sectional exciting force is calculated and compared with the commonly used integrand of the Khaskind relations. The two give different values, but when integrated over the hull both show the same total exciting force. The pressure distribution on an ore carrier for both zero forward speed and an abbreviated form of the forward-speed case is given and compared with experiments.

Forces and Moments on a Ship Moving in a Shallow Channel

The method of matched asymptotic expansions is applied to the problem of a ship moving with constant velocity in a channel of rectangular cross section. The depth of the channel is presumed small so that a linearized shallow-water solution is developed. The ship is assumed to be slender and is replaced in the outer region by a distribution of sources and vortices. As in earlier theories for slender bodies translating in shallow water, the source strength is proportional to the change in cross-sectional area of the ship. An integral equation must be solved to find the vortex strength. Using the source and vortex strengths, expressions are developed for the side force, yaw moment, sinkage, and trim. Numerical results are presented which show good agreement with experimental results.

Hydrodynamic Pressure Field on a Slender Ship Moving Over a High-Frequency Wavy Shallow Bottom

The hydrodynamic pressure field for the unsteady subcritical potential flow of a slender ship moving over a wavy wall in shallow water is analyzed using perturbation techniques. For the case of wall wavelength much smaller than the ship length but larger than the transverse ship dimensions, a combination of the methods of matched asymptotic expansions and multiple scales is used to obtain the lowest-order effect of the bottom variation.

Swanhild; Four and Twenty; Grey Ship Moving; Mere England

Swanhild; Four and Twenty; Grey Ship Moving; Mere England