High Resolution Ship Hydrodynamics Simulations in Open Source Environment

The numerical simulation of wake and flee-surface flow around ships is a complex topic that involves multiple tasks： the generation of an optimal computational grid and the development of numerical algorithms capable to predict the flow field around a hull. In this paper, a numerical framework is developed aimed at high-resolution CFD simulations of turbulent, free-surface flows around ship hulls. The framework consists in the concatenation of ＂tools＂, partly available in the open-source finite volume library OpenFOAM. A novel, flexible mesh-generation algorithm is presented, capable of producing high-quality computational grids for free-surface ship hydrodynamics. The numerical frame work is used to solve some benchmark problems, providing results that are in excellent agreement with the experimental measures.

SHIP HYDRODYNAMICS BASIC RESEARCH IN THE UNITED STATES

An overview of basic research on ship hydrodynamics in the United States ispresented. The focus is on leading edge research of high scientific interest bUt with ship hydrodynamics applicability. The research topic areas are briefly discussed, representative highlights from recent research are presented, and scientific hurdles to improved ship hydrodynamics technology are delineated. The purpose of the paper is to stimulate international cooperation in solving the basic research problems of common interest to all hydrodynamicists.

Computation of Ship Hydrodynamic Interaction Forces in Restricted Waters using Potential Theory

A computer code based on the double-body potential flow model and the classic source panel method has been developed to study various problems of hydrodynamic interaction between ships and other objects with solid boundaries including the seabed. A peculiarity of the proposed implementation is the application of the so-called ＂moving-patch＂ method for simulating steady boundaries of large extensions. The method is based on an assumption that at any moment just the part of the boundary （＂moving patch＂） which lies close to the interacting ship is significant for the near-field interaction. For a specific case of the fiat bottom, comparative computations were performed to determine optimal dimensions of the patch and of the constituting panels based on the trade-off between acceptable accuracy and reasonable efficiency. The method was applied to estimate the sway force on a ship hull moving obliquely across a dredged channel. The method was validated for a case of ship-to-ship interaction when tank data were available. This study also contains a description of a newly developed spline approximation algorithm necessary for creating consistent discretizations of ship hulls with various degrees of refinement.

Numerical Prediction of Hydrodynamic Forces on A Berthed Ship Induced by A Passing Ship in Different Waterway Geometries

An investigation has been conducted to quantify the effect of waterway geometry on the form and magnitude of forces and moment experienced by a berthed ship due to a passing ship.By using the dynamic mesh technique and solving the unsteady RANS equations in conjunction with a RNG k？ε turbulence model,numerical simulation of the three-dimensional unsteady viscous flow around a passing ship and a berthed ship in different waterway geometries is conducted,and the hydrodynamic forces and moment acting on the berthed ship are calculated.The proposed method is verified by comparing the numerical results with existing empirical curves and a selection of results from model scale experiments.The calculated interaction forces and moment are presented for six different waterway geometries.The magnitude of the peak values and the form of the forces and moment on the berthed ship for different cases are investigated to assess the effect of the waterway geometry.The results of present study can provide certain guidance on safe maneuvering of a ship passing by a berthed ship.

Test Series Results of Varying Yaw and Roll Angles of Trimaran Amas

This paper illustrates the reasons behind the research strategy that has led to a new generation of trimaran hulls by minimizing the hull＇s drag-design approach. The objective of this study was to search for the optimal side-hull yaw and roll angle to minimize induced drag of trimarans a^d so to investigate the differences in the performance results of a trimaran hull. Specifically, this research has been based on a critical analysis of the diversity of ama yaw and roll angles and outriggers positioning. Then, the paper will be comparing the results of the test series of the yaw and roll angles of trimaran areas. Design and towing tank test of a scaled trimaran model will be illustrated and compared along with some key and relevant results. The term ＂ama＂ is a word in the Polynesian and Micronesian languages to describe the outrigger part of a canoe to provide stability.

Calculation of ship motions in steep waves with restoring and Froude-Krylov forces on an adaptive panel mesh with Gauss and analytic integration methods

The impulse response method is a frequently used method to calculate ship seakeeping behavior.In this paper,the restoring and Froude-Krylov calculation is conducted with constant evaluation of panel pressures as well as Gauss quadrature and an analytical integration.The applied panel grid is coarsened by an adaptive algorithm which is based on a normal vector condition.The comparison of methods is based on grid convergence studies which are followed by a verification of forces with computational fluid dynamics(CFD)results on the fixed duisburg test case in waves.Validations with experimental results in head,oblique and following waves show that all integration methods are accurate.The exact integration is numerically sensitive in some cases.Gauss quadrature is highly accurate;however,the additional effort is not beneficial since the geometrical accuracy has-stronger influence on the force amplitudes than the integration method.Adaptive grid coarsening reduces the simulation time and is accurate up to a level,where the panel length comes close the wavelength.The added resistance at the investigated Froude number of 0.05 shows higher uncertainty levels,this applies to the results of both the numerical methods and model tests.

10th International Workshop on Ship and Marine Hydrodynamics(IWSH 2017)

The 10th International Workshop on Ship and Marine Hydrodynamics （IWSH 2017） will be held in Keelung, Taiwan, China on November 5-8, 2017. It will be a platform for engineers and researchers to keep abreast of the current scientific and technological advancements in hydrodynamics of marine, ship and ocean engineering and other related fields, including theoretical, numerical and experimental aspects.

Call For Paper The 9th International Workshop on Ship and Marine Hydrodynamics

In 1999,the first International Workshop on Ship Hydrodynamics was successfully held in Wuhan,China.Then it was held in Wuhan,Shanghai,Zhenjiang,Harbin,Seoul in subsequent every two years.These Conferences had drawn a variety of international delegates including scientists,engineers and researchers with a common interest in ship hydrodynamics.

Application of Method of Fundamental Solutions in Solving Potential Flow Problems for Ship Motion Prediction

A novel panel-free approach based on the method of fundamental solutions (MFS) is proposed to solve the potential flow for predicting ship motion responses in the frequency domain according to strip theory. Compared with the conventional boundary element method (BEM), MFS is a desingularized, panel-free and integration-free approach. As a result, it is mathematically simple and easy for programming. The velocity potential is described by radial basis function (RBF) approximations and any degree of continuity of the velocity potential gradient can be obtained. Desingularization is achieved through collating singularities on a pseudo boundary outside the real fluid domain. Practical implementation and numerical characteristics of the MFS for solving the potential flow problem concerning ship hydrodynamics are elaborated through the computation of a 2D rectangular section. Then, the current method is further integrated with frequency domain strip theory to predict the heave and pitch responses of a containership and a very large crude carrier (VLCC) in regular head waves. The results of both ships agree well with the 3D frequency domain panel method and experimental data. Thus, the correctness and usefulness of the proposed approach are proved. We hope that this paper will serve as a motivation for other researchers to apply the MFS to various challenging problems in the field of ship hydrodynamics.

Fundamental problems in hydrodynamics of ellipsoidal forms

In this study, we tackle with one single effort, three fundamental problems in ship hydrodynamics, namely the attraction force exerted on a single ship moving rectilinearly close and parallel to a rigid wall（berthing）, the determination of the associated added-mass coefficients（maneuvering） and finally evaluating the forces exerted on a ship in a two-ship crossing scenarios. The novelty of the present approach relies on using Weinblum’s proposition to assimilate the ship’s hull by an ＂equivalent＂ tri-axial ellipsoid, as well as the employment of ellipsoidal harmonics expansion techniques.

Liutex-based centripetal force field model for improving the resistance and wake performances of JBC ship sailing in calm water

For complex aerodynamic and hydrodynamic problems,the analysis of vortex is very important.The Liutex method is an eigenvalue-based method which is local,accurate,and unique,which can give an accurate definition of vortex,so the control of vortex can be implemented and effectively guaranteed.Based on Liutex method,two methodologies of centripetal force model and counter-rotation force model were proposed to illustrate the vortex dynamics and possibly strengthen or weaken the vortices.In this paper,the Liutex-based centripetal force model is applied by adding a source term to the Navier-Stokes equations.In order to investigate the influence of the constructed Liutex force model on the 3-dimensional flow around a slow-fat ship,the calm-water drag calculation result of JBC ship is regarded as the initial flow field,and the new resistance and wake performances of the ship are obtained after applying the centripetal force model to the flow field with different strengths.Several views of the comparisons of the new steady flow fields are shown,and the parametric study results indicate that the Liutex-based centripetal force model can effectively change the resistance and wake performances of the JBC ship,which provides a new idea and theoretical basis for the comprehensive hydrodynamic performance optimization of the ship hull.

Sensitivity Analysis of the Hydrodynamic Coefficients in 4 Degrees of Freedom Ship Manoeuvring Mathematical Model

The S-type test is simulated based on a ship manoeuvring mathematical model of 4 degrees of freedom(4-DOF);simultaneously,sensitivity analysis of the hydrodynamic coefficients in the mathematical model is implemented by using an indirect method.The mathematical model is simplified by omitting the coefficients of smaller sensitivity according to the results of sensitivity analysis.The 10°/10° zigzag test and 35° turning circle manoeuvre are simulated with the original and the simplified mathematical models.The comparison of the simulation results shows the effectiveness of the sensitivity analysis and the validity of the simplified model.

AN ORDINARY DIFFERENTIAL EQUATION FOR THE 2D TRANSIENT FREE-SURFACE GREEN FUNCTIONS

Based on the Laplace transform an ordinary differential equation for the two-dimensional time-domain free-surface Green function in ship hydrodynamics is presented. The results for 2D Green function and its horizontal derivative are fifth-order ODEs and the vertical derivative satisfies a fourth-order ODE. All of these results may be used to accelerate the numerical computations for the time-domain BEM in marine hydrodynamics.

Optimization of the roll motion of box-shaped hull section with anti-rolling sloshing tanks and fins in beam waves

With the development of ocean engineering and demand for safety of the ship and offshore structures, the transportation and storage of liquid have become an important issue nowadays. Furthermore, in order to improve the hydrodynamic performances of the ship and offshore structures, the anti-rolling liquid tanks are often taken into consideration. The internal-external coupling flow effect is vital for the ship and liquid tank designs, especially when the external wave frequency is close to the natural frequency of liquid tanks with a certain filling ratio, large amplitude motions may occur, which is dangerous to some extent. In this paper, the simulation-based-design method is introduced at first, and the verification of the numerical calculation of internal-external coupling flow with liquid tanks is done then. Finally, the filling ratio of the anti-rolling liquid tank and the installation angle of the anti-rolling fins are optimized to reduce the roll motion amplitude of the hull section to the greatest extent under the combined action of the two anti-rolling devices. Optimization results show that the roll motion amplitude of box-shaped hull section can be successfully reduced by reasonably designing the two anti-rolling devices, which can be a reference to the future design of the fishing ship and other ships with anti-rolling devices.