S175 Containership Research Articles

A rapid motion forecast strategy for ships in waves using seakeeping and maneuvering modules

This paper develops a new navigation assisted system for ships with time-varying wave disturbances. A new framework is presented using seakeeping and maneuvering modules to achieve the fast forecast of ship motions. S175 containership and KVLCC2 tanker are adopted to verify the seakeeping module. Based on the validated module, the heave, roll and pitch motions of a cruise ship in different conditions are calculated by using three-dimensional Rankine panel method. The horizontal surge, sway and yaw motions of ships can be rapidly evaluated by using MMG model considering the wave drift forces. Finally, the motion amplitudes of 6°-of-freedom can be forecasted rapidly by using seakeeping and maneuvering modules. The study provides the insight into the motions of ships in waves. It is of great engineering application value to evaluate the total ship motion amplitudes and to improve the safety of navigation of ships in waves.

Probabilistic surrogate-based optimization of ship hull-propulsor design with bi-level infill sampling technique

This work develops a new multi-level hull-propulsor optimization tool, systematically considering the full range of expected operating conditions. Different solvers with variable fidelities are used to evaluate hydrodynamic objective functions and constraints. The bi-fidelity surrogate model is applied to integrate the accuracy advantage of a medium-fidelity solver with the efficiency advantage of a low-fidelity solver. A bi-level technique of infill sampling integrated with a new version of multi-objective evolutionary algorithms is presented to enhance the effectiveness of the surrogate models. A ship velocity- and sea state-based joint probability density function is employed to take into account the real lifetime operational space. The well-known S175 containership, KP505 propeller and a MAN B&W marine engine are utilized as the initial hull-propulsor model. The final results show that the optimization framework is able to achieve some optimum hull-propulsor designs from the lifetime fuel consumption and energy efficiency design index points of view and to reduce the overall lifetime ownership cost significantly.

Numerical investigation of bottom slamming using one and two way coupled methods of S175 hull

Numerical simulations of bottom slamming are conducted for a S175 container ship hull using two-phase computational fluid dynamics (CFD) and potential flow solvers. Suitable combinations of these two different models are used for two different coupling strategies named one and two way coupling methods. Various parameters such as the incident wave steepness, wavelength and the forward speed (specified using the Froude number) in a head sea over a range are considered to investigate the slamming phenomenon based on the one way and the two way coupling methods. The overall analysis shows that for most of the cases, the prediction of the bottom slamming pressure from the one-way coupling method maintains a nearly steady difference with respect to that of the two way coupling method over the range of the input parameters and thus forms basis for a new empirical formulation to estimate the peak slamming pressure for a range forward speeds. The performance of this empirical formula is qualitatively discussed with respect to the prediction from the two way coupling method. It is observed that the derived analytical formulation gives reliable results and may be used for efficient estimation of bow slamming pressures at a relatively low computational cost.

Numerical study on mean wave drift forces and moment of ships using Rankine panel method in frequency domain

A three-dimensional frequency-domain seakeeping model based on the Rankine panel method is developed to compute the mean wave drift forces and moment acting on ships with forward speeds. Two different linearization models (the double-body and Neumann–Kelvin models) are applied to evaluate the mean wave drift forces and moment using a near-field method. In these models, the Rayleigh’s artificial friction is adopted in the free-surface boundary condition to suppress longer wave components in computational regions apart from the ship. A novel upwind difference scheme is introduced to calculate the first-order and second-order derivatives of the velocity potential on the free surface. Wigley I, Wigley III and S175 containership are adopted in numerical simulations to validate the effectiveness of the developed model. In the present study, the motion response amplitude operators in head, beam and oblique seas obtained using the two models are compared, and their contributions to the mean wave drift forces and moment are analyzed. Results show that in head seas, the pitch motions have significant effects on the surge-directional wave drift force Fx. In beam seas, the heave motions have the most effect on the mean wave drift forces and moment (Fx, Fy and Mz).

Numerical investigations on seakeeping and added resistance in head waves based on nonlinear potential flow methods

A fully nonlinear potential flow (FNPF) method and a body-exact (BE) method based on the time-domain desingularized-Rankine panel (DRP) method have been developed to compute the motion responses and added resistance for ships traveling in regular head waves. In the present methods, the disturbed wave potential is separated from the incident potential, and the boundary value problem (BVP) for the disturbed potential is established in each method. To validate the present FNPF and BE methods, different hull forms are adopted, including two Wigley hulls and the S-175 containership. The results of radiation, diffraction, and free motion simulations are presented and systematically compared with the experimental data and linear solutions using the double-body (DB) and Neumann–Kelvin (NK) methods. Through comparison, we demonstrate that the present FNPF method can accurately predict the motion responses and added resistance of ships. For the ships with large flare angles, the FNPF and BE methods give better predictions of peak motion responses than those using DB and NK. In addition, the FNPF method can well predict the added resistance, and has significant advantages over the other numerical methods at high forward speed (Fn=0.3). The analyses also confirm that, compared with the heave and pitch motions, the added resistance and the total wave elevations are more sensitive to the incident wave amplitude. The dimensionless added resistance decreases with the increase of incident wave amplitude, which is mainly driven by the total wave elevations along the waterline in the bow region. As the incident wave amplitude increases, the 1st harmonic amplitudes of the heave and pitch motions and the total wave elevations in the bow region decrease, while the 2nd harmonic amplitudes increase.

Numerical investigations on nonlinear motions of ships sailing in large-amplitude waves based on hybrid HOBEM

This paper presents a nonlinear numerical approach based on hybrid higher-order boundary element method (HOBEM) to investigate the wave-induced motion responses of ships with forward speed. The radiation and diffraction forces in time domain are determined by convolution of the impulsive response functions computed from frequency-domain hydrodynamic data of the hybrid method using a combination of Rankine source and translating-pulsating Green's function. In its numerical implementation, steady flow effects are included in the inner domain encompassing the ship, 9-node bi-quadratic curvilinear elements are employed to discretize the boundaries and analytical quadrature formulas are derived to calculate the influence coefficients related to the Green's function over the control surface so as to improve the accuracy, efficiency and stability. Meanwhile, the nonlinear incident wave force and hydrostatic restoring force are calculated over the instantaneous wetted surface of the ship hull during the motion process to capture the nonlinear properties. Based on the method, a numerical program is developed to predict and analyze the motion response of a modified Wigley hull and a non-wall-sided S175 containership advancing in waves with different amplitudes and heading angles. By comparing the present computed results with experimental data and other numerical solutions, it is found that the nonlinear calculations can produce more accurate motion responses in large-amplitude waves with strong nonlinearity. And the present nonlinear method based on hybrid HOBEM is of higher accuracy and better stability than traditional nonlinear methods based on three-dimensional pulsating source (3DP) and translating-pulsating source (3DTP), especially for S175 with large flare near the waterline.

Prediction of the maneuvering behavior of a containership in a seaway

This study investigated the turning maneuver performance of a containership in regular waves using a two-time scale formulation. This article also presents a ship motion program, coupled with a 3-degree of freedom (3-DOF) maneuvering solver, whereby the seakeeping problem is solved with the forward speed considered in the computations. Captive tests were simulated in a computational fluid dynamics (CFD) environment to obtain the maneuvering derivatives. A near-field analysis was performed to obtain the effective wave force, which was the second-order mean drift force in this analysis. The proposed method was used to estimate the turning circle maneuver performance of the S-175 containership in both calm water and waves of different wavelengths. Ultimately, the simulation results showed high consistency with experimental data.

CFD investigation on the hydrodynamic loads and motions when ship maneuvers in regular and irregular waves

To explore and predict the ship maneuverability in the regular and irregular waves, the zigzag tests, the turning tests, and the course-keeping tests for the model-scale S175 containership under various wave conditions are simulated. The simulations are performed using a structured overset Unsteady Reynolds Averaged Navier-Stokes (URANS) solver with a moving grid. A body force method is adopted to predict the propeller forces. The simulation results are validated by the free-running experiments with satisfactory accuracy, which indicates that the present simulation strategy is effective and reliable. The hydrodynamic loads on the hull and the rudder together with the ship motion characteristics during the maneuvers in waves are obtained. It is concluded that the ship motions and hydrodynamic loads increase with the increase of the wavelength when the wave height is kept constant. The variation trends and magnitudes for low-frequency components of the self-propulsion factors in waves are similar to those in the calm water condition except obvious high-frequency fluctuations due to the wave effect. For the zigzag tests under the long-crested and short-crested irregular waves, the time histories of the yaw and rudder angle are similar. For the turning tests, the amplitude of roll motion in waves is much larger compared with that of the zigzag tests under the same wave condition, and the drift of the trajectory due to the wave is obvious. The current course keeping simulation can be an alternative tool to predict course keeping maneuvers in waves. Furthermore, flow visualizations are presented for providing a better understanding of the wave effect on free-running ship maneuvers.

Nonparametric modeling of ship maneuvering motion in waves based on Gaussian process regression

A robust and easy-to-operate method based on Gaussian process regression (GPR) is proposed for nonparametric modeling of ship maneuvering in waves. The wave parameters that are difficult to measure are not needed when identifying the dynamic model. In order to extract the wave effect from the ship motion data, the black-box model is modified relative to that used for calm water case. Taking the KCS container ship and the S-175 container ship as study objects, the nonparametric models based on GPR are identified by utilizing the experimental data of turning circle maneuver of KCS model and zigzag maneuvers of S-175 model in regular waves. Using the identified nonparametric models, turning circle maneuver of KCS model and zigzag maneuvers of S-175 model in regular waves are predicted, and the prediction results are compared with the model test data to verify the proposed method of nonparametric modeling and to evaluate the performances of the identified nonparametric models. It shows that the trajectory of turning circle maneuver and the heading angle of zigzag maneuvers are well predicted, indicating that the nonparametric model based on GPR with the modified black-box model can predict the maneuvering motion in regular waves accurately.

Comparative Study on Predicting Ship Maneuvering in Waves Using a Quasi-Steady Method and a Time Domain Approach

_ Numerical prediction of ship maneuvering in waves was considered in this article. The wave drift loads, computed using the potential flow theory, were added into the mathematical modeling group (MMG) equations to account for the effect of waves on the ship maneuvering. Two numerical methods were tested for dealing with the coupled maneuvering-seakeeping problem, namely a time domain approach and a quasi-steady method. For the former approach, a time domain seakeeping computation was conducted that parallels to the maneuvering simulation. For the later one, it is assumed that at each time of the maneuvering process, the wave-ship interaction is in a time harmonic status and, therefore, the wave drift loads could be evaluated using a frequency domain computation. Turning maneuvers of the S-175 container ship in regular waves were numerically tested. The results of the quasi-steady method and the time domain approach show good agreements, which proved the validity of the quasi-steady assumption. The wave drift loads during the turning process were also presented, demonstrating the significant effect of the added resistance on the maneuvering prediction, in contrast to the less remarkable effects of the lateral wave drift force and the wave drift yaw moment. Introduction Ship maneuverability is typically predicted under calm water condition. This provides valuable information at the ship design stage. However, an actual seagoing ship usually maneuvers in waves. To reliably assess a ship’s navigation safety and total performance in a seaway, it is deemed important to understand the maneuvering behavior of a ship in waves. Indeed, ship maneuverability in waves has been increasingly investigated in recent years. Although the physical experiment is still regarded as the most reliable way to investigate ship maneuverability in waves, there are more and more studies providing practical mathematical models of ship maneuvering prediction. Generally, a mathematical model that is suitable for investigating the maneuvering of a ship in waves has to encapsulate the traditional theories of calm water maneuvering and forward-speed seakeeping.

Numerical study on added resistance of ships based on time-domain desingularized-Rankine panel method

Three-dimensional time-domain desingularized-Rankine panel (DRP) method has been developed to compute the added resistance for ships traveling in regular head waves using the near-field and middle-field approaches. To validate the present computational model, different hull forms are adopted, including two Wigley hulls, the S-175 containership and the KVLCC2 tanker. By systematically comparing the present results with the experimental data, it is demonstrated that the near-field and middle-field approaches based on a double-body linearization can accurately predict the added resistance of ships at Fn⩽0.25. The components and distribution of added resistance are compared and discussed. It is found that the maximum contribution on the added resistance comes from the waterline integral, and in long waves it occurs at the most forward part of the waterline. The analyses also confirm that, in intermediate waves and in the near-resonant wavelength of added resistance, the pitch motions have more significant effects on the added resistance than the heave motions. Furthermore, the interaction between the diffraction and the pitch-induced radiation components is the primary contributor to the added resistance in intermediate waves, except from the diffraction component.

Study on nonlinear heave and pitch motions of conventional and tumblehome hulls in head seas

The broadside of the tumblehome hull is inclined inward, while that of the conventional hulls is inclined outward. As a result of the geometric shape, the tumblehome hull has distinct motion characteristics compared to the conventional hulls. In this study, the nonlinear heave and pitch motion responses of a tumblehome hull are investigated experimentally and numerically. A series of model experiments at various wave slopes is performed to validate the nonlinear motion responses in head sea conditions. As a numerical approach, a time-domain B-spline 3-D Rankine panel method (RPM) and computational fluid dynamics (CFD) are adopted. During the nonlinear motion computation, a weakly-nonlinear method is applied to the RPM to consider the geometric properties of the tumblehome hull above the waterline. The S175 containership is selected as the comparative model. It is a conventional-shaped hull, and the relevant experimental results are available. For the conventional hull, the magnitudes of the motion transfer functions of the heave and pitch motions decrease as the wave slope increased. For the tumblehome hull, an opposite trend is observed in both the experimental and numerical results. The magnitudes of the motion transfer functions increase as the wave slope increased. The increase and decrease in the nonlinear motion responses are discussed.

THE INFLUENCE OF FORWARD SPEED AND NONLINEARITIES ON THE DYNAMIC BEHAVIOUR OF A CONTAINER SHIP IN REGULAR WAVES

The aim of this paper is to compare the heave and pitch motions for the S175 containership, travelling in head regular waves, obtained from frequency domain linear and time domain partly nonlinear potential flow analyses. The frequency domain methods comprise the pulsating and the translating, pulsating Green’s function methods, with the relevant source distribution over the mean wetted surface of the hull. The time domain method uses the radiation and diffraction potentials related to the mean wetted surface, implemented using Impulse Response Functions (IRF), whilst the incident wave and restoring actions are evaluated on the instantaneous wetted surface. The calculations are carried out for a range of Froude numbers, and in the case of the partly nonlinear method for different wave steepness values. Comparisons are made with available experimental measurements. The discussion focuses on the necessity for a nonlinear approach for predicting the radiation potential and the possible numerical methods for its formulation.

NON LINEAR ANALYSIS OF SHIP MOTIONS AND LOADS IN LARGE AMPLITUDE WAVES

A non linear time domain formulation for ship motions and wave loads is presented and applied to the S175 containership. The paper describes the mathematical formulations and assumptions, with particular attention to the calculation of the hydrodynamic force in the time domain. In this formulation all the forces involved are non linear and time dependent. Hydrodynamic forces are calculated in the frequency domain and related to the time domain solution for each time step. Restoring and exciting forces are evaluated directly in time domain in a way of the hull wetted surface. The results are compared with linear strip theory and linear three dimensional Green function frequency domain seakeeping methodologies with the intent of validation. The comparison shows a satisfactory agreement in the range of small amplitude motions. A first approach to large amplitude motion analysis displays the importance of incorporating the non linear behaviour of motions and loads in the solution of the seakeeping problem.

Uncertainty analyses on the CFD–FEA co-simulations of ship wave loads and whipping responses

In this paper, a fluid–structure interactions method which fully couples CFD and FEA solvers in a two-way manner is used to estimate ship wave loads and hydroelastic responses. The global motions, wave loads, and springing and whipping loads on a standard S175 containership model evaluated by the CFD–FEA coupling method are comprehensively investigated and related verification and validation studies are conducted. Verification and uncertainty analyses on the influence of fluid grid density, time step, fluid domain size, fluid viscosity and hull structural element number on the results of ship responses by the CFD–FEA coupling method are systematically conducted. The CFD–FEA co-simulated results of ship wave loads are further comprehensively compared with a series of existing results of S175 ship by potential flow theory, CFD simulation and tank model experiment as a benchmark and validation study. This study is the first specialized attempt of uncertainty analysis and benchmark study of ship motions, wave loads and hydroelastic responses predicted by CFD–FEA coupling method, which will provide valuable information regarding relative accuracy of the novel method used for wave loads prediction and hydroelastic analysis.

Numerical simulation of a vessel’s manoeuvring performance in regular waves

ABSTRACT This paper deals with the numerical simulation of a ship’s manoeuvring performance in regular waves. This is made possible by employing the time-domain code ELIGMOS, which adopts a hybrid formulation to couple seakeeping and manoeuvring contributions. The first and steady second-order wave-induced forces are incorporated, implementing a multidimensional interpolation scheme to account for their dependency on the instantaneous heading and forward speed values. Two methods have been adopted for the calculation of the added resistance regarding the size of the wavelength (short or long wave seas), namely a far and a near-field one, using the hydrodynamic software NEWDRIFT+ and NEWDRIFT v.7. Low-frequency hydrodynamic manoeuvring forces are incorporated by adopting the expressions suggested by the Japanese MMG (Manoeuvring Modelling Group) method. Validation of the suggested methodology is attempted through the comparison of numerical simulations of turning circle tests in calm water and in regular waves with available experimental evidence for the S-175 container ship.

Slamming and green water loads on a ship sailing in regular waves predicted by a coupled CFD–FEA approach

A numerical simulation method is presented by integrating Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) solvers to predict ship wave loads and slamming loads taking into account hydroelastic effects. The interest of this study mainly lies in the slamming and green water pressures acting on a flexible ship investigated by the coupled CFD–FEA method. Firstly, verification and sensitivity analysis of the wave loads and slamming pressures on the S175 containership evaluated by the coupled CFD–FEA method is conducted by comparing the results using different mesh sizes and time step schemes. Discussion on the effect of hydroelasticity on impact pressures is also conducted. Then a comprehensive analysis on the global motions, wave loads, slamming and green water pressures of the ship in different regular wave conditions is undertaken. Finally, a simplified bow flare and bottom slamming pressure estimation method based on the seakeeping data of incident wave and ship global motions are proposed, which can reduce the computational burden of the two-way fluid-structure interaction simulations when impact pressure is concerned.

A CFD–FEA two-way coupling method for predicting ship wave loads and hydroelastic responses

This paper presents a co-simulation method for numerical prediction of nonlinear hydroelastic response of ship advancing in severe wave conditions. Two-way coupling of CFD and FEA solvers is applied where the external fluid pressure exported from the CFD simulation is used to derive the structural responses in the FEA solver and the structural deformations are fed back into the CFD solver to deform the mesh. Violent free surface flow such as slamming and green water on deck is well captured by the RANS and VOF techniques in the CFD solver. The nonlinear whipping and springing responses can be accurately simulated by the structural solver through the dynamic 3D FEA of the hull. By conducting co-simulations with a standard S175 containership, the developed fully coupled method was proved to be capable and reliable in accurate simulating almost all the physical characteristics of interests within the scope of ship seakeeping and hydroelasticity, which include large-amplitude motions, accelerations, wave loads, slamming loads, green water loads and whipping and springing responses of the hull in waves.

Viscous fluid–flexible structure interaction analysis on ship springing and whipping responses in regular waves

A two-way fluid structure interaction (FSI) of CFD–FEA numerical method is adopted to predict ship motions, wave loads and hydroelastic responses in regular waves. In the FSI algorithm, the external fluid loads obtained from the CFD model and the motions and structural deformations obtained from the FEA model are exchanged between each other in an iteratively staggered implicit coupling regime in time domain. The motions, vertical accelerations and wave loads including springing and whipping responses of a flexible S175 container ship under different regular wave conditions predicted by the FSI co-simulation method are systematically analyzed. High order hull girder vertical vibrations of up to 12th order harmonic springing and up to 4-node whipping responses have been successfully reproduced, which indicates that the CFD–FEA co-simulation method is reliable and capable in simulating ship nonlinear hydroelastic responses in waves. Moreover, some complex flow phenomena such as slamming, green water on deck, wave breaking and splashing have also been well reproduced from the CFD simulation. It is believed that the present FSI method will exhibit significant advantage over the traditional ways used for ship seakeeping and hydroelasticity analyses.

Numerical prediction of ship motion and slamming load characteristics in cross wave

When waves from two weather systems converge at a certain sea area, cross waves can be produced. It is important to have a better understanding of the motion characteristics of ship in cross sea to ensure its navigation safety. In this paper, the motion responses of a S175 container ship hull in cross sea is first analyzed based on CFD technique using RANS method. VOF method is used to model and capture the free surface and overset grid technique is adopted to simulate ship motions in waves. Verifications on ship motion by the numerical method have been conducted for time step- and grid-independent studies. According to the motion results by numerical simulation, typical conditions are chosen for further investigation of slamming pressure on bow area and green water on deck. It is found that vertical motion responses of ship induced by cross waves can be quite large and the ship experienced obvious roll–pitch-coupled motion. Severe bow slamming and green water under cross sea state are also observed. The bow flare slamming pressure on the baseline can be quite large in symmetric cross wave. Asymmetrical slamming impacts occurred when the ship sails in an asymmetric cross wave field.