Wigley Hull Research Articles

A Computational Fluid Dynamics Method for Resistance Prediction of the Floating Hull of Wave Glider

The wave glider is a surface vehicle with an attached sub-surface wing system which propels the surface component forward, negating the need for a motor. Wave glider could be used for intelligence, surveillance, passive monitoring of marine life, monitoring exclusive economic zones for fishing and other economic resources that are important and useful to coastal countries. Monitoring of coastal waters normally requires large amounts of expensive surveillance. They can be used to find and research resources and fisheries at a fraction of the cost of other methods. Since the wave glider can either be programmed for a journey or to keep station, it is looked at as an alternative for expensive moored buoys. In this paper we present a method focused on the mesh generation to predict calm water resistance for the floating part of the wave glider (the hull). In this study a wigley hull form (4m) used as the floating hull has been investigated in order to predict the fluid flow of the ship using computational fluid dynamics (CFD). Calculations for total resistance are carried out for Froude numbers in the range of 0.10 to 0.40. Commercial CFD software fluent is used to investigate the fluid flow of wigley hull. Three different mesh sizes are used in this study to calculate the mesh effects. The results obtained from CFD calculations for total resistance are compared with the experimental results for accuracy of the solution parameters. The comparison shows a good agreement between experimental and CFD results. The method is evaluated by comparing the numerical predictions for wigley hull form (2m) with wigley hull form (4m) using the same mesh sizes under the same conditions in an attempt to design the floating hull of wave glider . The results obtained from CFD calculations are compared for accuracy of the solution parameters and the method is useful and acceptable.

Computation of Motion and Added Wave Resistance With the Panel-Free Method

Computations have been performed to predict motions and added wave resistances for ships at forward speeds. The radiation and diffraction problems of a ship with forward speed are solved with the panel-free method in the frequency domain. In this paper, the effect of the m-terms and forward-speed/zero-speed Green functions (GFs) on the solutions are investigated using two Wigley hull ships. Computed motions, hydrodynamic coefficients, and added wave resistances were compared with the experimental data.

A Rankine Panel Method for Added Resistance of Ships in Waves

A new Rankine panel method and an extended Reynolds-Averaged Navier–Stokes (RANS) solver were employed to predict added resistance in head waves at different Froude numbers of a Wigley hull, a large tanker, and a modern containership. The frequency domain panel method, using Rankine sources as basic flow potentials, accounts for the interaction of the linear periodic wave-induced flow with the nonlinear steady flow caused by the ship's forward speed in calm water, including nonlinear free surface conditions and dynamic squat. Added resistance in waves is obtained by the pressure integration method. The time domain RANS solver, based on a finite volume method, is extended to solve the nonlinear equations of the rigid body six-degrees-of-freedom ship motions. The favorable comparison of the panel and RANS predictions demonstrated that the Rankine method is suitable to efficiently obtain reliable predictions of added resistance of ships in waves. Comparable model test predictions correlated less favorably, although the overall agreement was felt to be acceptable, considering the difficulties associated with the procedures to obtain accurate measurements.

Viscous Flow Computation around the Wigley Hull with the Maneuvering Motion using the Inertial Coordinate System on the Non-inertial Grids

Computational Fluid Dynamics (CFD) technique for ship hydrodynamics has been well developed with advanced capabilities for resistance and propulsion, seakeeping, and maneuvering. The Authors’ laboratory (Laboratory 3 of Department of Naval Architecture and Ocean Engineering in Osaka University) specializes in resistance and propulsion field and has carried out several simulations based on the CFD code in non-inertial ship-fixed coordinates system. The purpose of this research is to transform the present computation code to the one in inertial coordinate and to investigate the flow field around the Wigley hull for several motions up to three degrees of freedom (3 DOF). The transformed code is simulated on the flat plate initially and the nature of the flow field is investigated and confirmed with the hydrodynamics theory. Then, the wigley hull motions are simulated in several ways such as; uniform motion, pure yaw and circular motion test. The features of the flow field and hydrodynamic forces acting on the hull are discussed based on the computed results. Finally, the propeller effect is implemented behind the wigley hull using the body-force concept by the quasi-steady infinite bladed Blade Element Theory and a propulsion characteristic is observed. The transformed computation code in inertial coordinate is found to be much easier to simulate the different kinds of maneuvering motions compared to the code in non-inertial system and this paper covers the detailed transformation steps and the discussions on the computation results of different motions.

Optimizing the Seakeeping Performance of Ship Hull Forms Using Genetic Algorithm

Hull form optimization from a hydrodynamic performance point of view is an important aspect of ship design. This study presents a computational method to estimate the ship seakeeping in regular head wave. In the optimization process the Genetic Algorithm (GA) is linked to the computational method to obtain an optimum hull form by taking into account the displacement as design constraint. New hull forms are obtained from the well-known S60 hull and the classical Wigley hull taken as initial hulls in the optimization process at two Froude numbers (Fn=0.2 and Fn=0.3). The optimization variables are a combination of ship hull offsets and main dimensions. The objective function of the optimization procedure is the peak values for vertical absolute motion at a point 0.15LBP behind the forward perpendicular, in regular head waves.

An iterative Rankine BEM for wave-making analysis of submerged and surface-piercing bodies in finite water depth

A 3-D iterative Rankine Boundary Element Method (BEM) for seakeeping problem in time domain is developed in the framework of linear potential theory. Waves generated by both submerged and surface-piercing bodies moving at a constant forward speed in otherwise calm water, and the resultant steady wave pattern, wave profile and resistance are computed to validate this newly-developed code. A rectangular computational domain moving with the same forward speed as the body is introduced, in which an artificial damping beach is installed at an outer portion of the free surface except the downstream side for satisfying the radiation condition. The velocity potential on the ship hull and the normal velocity on the free surface are obtained directly by solving the boundary integral equation, with the Rankine source used as the kernel function. An iterative time-marching scheme is employed for updating both kinematic and dynamic free surface boundary conditions to stabilize the calculation. Extensive results including the wave patterns, wave profiles and wave resistances for a submerged spheroid and a Wigley hull with forward speed are presented to validate the efficiency of the proposed 3-D time-domain higher-order approach. Finally, the sensitivity of ship-generated waves to the water depth is investigated. Computed results show satisfactory agreement with the corresponding experimental data and other numerical solutions.

Nonlinear hull girder loads of a RoPax ship

Numerical and experimental studies of nonlinear wave loads are presented. A nonlinear time domain method has been developed and the theoretical background of the method are provided. The method is based on the source formulation expressed by means of the transient three-dimensional Green function. The time derivative of the velocity potential in Bernoulli's equation is solved with a similar source formulation to that of the perturbation velocity potential. The Wigley hull form is used to validate the calculation method in regular head waves. Model tests of a roll-on roll-off passenger ship with a flat bottom stern have been carried out. Model test results of ship motions, vertical shear forces and bending moments in regular and irregular head waves and calm water are given. The nonlinearities in ship motions and hull girder loads are investigated using the calculation method and the model test results. The nonlinearities in the hull girder loads have been found to be significant and the calculation method can predict the nonlinear loads for the model test ship.

A time-domain higher-order boundary element method for 3D forward-speed radiation and diffraction problems

A time-domain higher-order boundary element method for seakeeping analyses in the framework of linear potential theory is newly developed. Ship waves generated by two modified Wigley models advancing at a constant forward speed in calm water or incident waves and the resultant radiation and diffraction forces are computed to validate this code. A rectangular computational domain moving with the same forward speed as the ship is introduced, in which an artificial damping beach is installed at an outer portion of the free surface except the downstream side for satisfying the radiation condition. The velocity potential on the ship hull and the normal velocity on the free surface are calculated directly by solving the boundary integral equation. An explicit time-marching scheme is employed for updating both kinematic and dynamic free-surface boundary conditions, with an embedding of a second-order upwind difference scheme for the derivative in the x-direction to stabilize the calculation. Extensive results including the exciting forces, added mass and damping coefficients, wave profiles, and wave patterns for blunt Wigley and slender Wigley hulls with forward speed are presented to validate the efficiency of the proposed 3D time-domain approach. The corresponding physical tests of the radiation and diffraction problems in a towing tank are also carried out. Computed numerical results show good agreement with the corresponding experimental data and other numerical solutions.

Simulation of Viscous Flow around Surface Ship Using ANSYS-Fluent CFD Code

In this paper, numerical simulations have been carried out to determine the incompressible free surface flow around a Wigley hull form for which experimental results are available. A commercial viscous flow finite volume code using the two-phase Eulerian-Eulerian fluid approach has been used in this study. The simulation conditions are the ones for which experimental results exist. The shear stress transport (SST) turbulence model has been used in the viscous flow code. A structured grid was used with the viscous flow code for meshing the computational domain. The results compare well with the available experimental data, which make their complementary application useful for determining the total ship resistance.

Towed underwater PIV measurement for free-surface effects on turbulent wake of a surface-piercing body

In the present study, a towed underwater particle image velocimetry (PIV) system was validated in uniform flow and used to investigate the free-surface effects on the turbulent wake of a simple surface-piercing body. The selected test model was a cylindrical geometry formed by extruding the Wigley hull's waterplane shape in the vertical direction. Due to the constraints of the two-dimensional (2D) PIV system used for the present study, the velocity field measurements were done separately for the vertical and horizontal planes. Using the measured data at several different locations, it was possible to identify the free-surface effects on the turbulent wake in terms of the mean velocity components and turbulence quantities. In order to provide an accuracy level of the data, uncertainty assessment was done following the International Towing Tank Conference standard procedure.

Towed underwater PIV measurement for free-surface effects on turbulent wake of a surface-piercing body

In the present study, a towed underwater particle image velocimetry (PIV) system was validated in uniform flow and used to investigate the free-surface effects on the turbulent wake of a simple surface-piercing body. The selected test model was a cylindrical geometry formed by extruding the Wigley hull's waterplane shape in the vertical direction. Due to the constraints of the two-dimensional (2D) PIV system used for the present study, the velocity field measurements were done separately for the vertical and horizontal planes. Using the measured data at several different locations, it was possible to identify the free-surface effects on the turbulent wake in terms of the mean velocity components and turbulence quantities. In order to provide an accuracy level of the data, uncertainty assessment was done following the International Towing Tank Conference standard procedure.

Comparative study on computation of ship added resistance in waves

Recently, the design of commercial ships that produce less greenhouse gas has been of great interest in naval architecture fields. Ship designers are asked to find optimum hull forms with minimum resistance in ocean waves. An accurate computation of added resistance, therefore, is getting more important for the prediction of power increase in random ocean waves. This study focuses on a comparison of the computational results of added resistance on ships in waves. To calculate added resistance, three different numerical approaches are applied: the strip method, the Rankine panel method, and the Cartesian grid method, which solves the Euler equation. In order to predict added resistance, near- and far-field approaches are adopted in the strip and Rankine panel methods, while added resistance is calculated directly in the Cartesian grid method. The computational results are validated by comparing them with experimental data on Wigley hulls, Series 60 hulls, and the S175 containership, and show reasonable agreements for all models. The study is extended to the analysis of added resistance in short wavelengths; therefore, the established asymptotic methods for short waves are examined.

An evolutionary optimization technique applied to resistance reduction of the ship hull form

Hull form optimization from a hydrodynamic performance point of view is an important aspect of ship design. This paper presents a computational method to estimate the ship resistance (viscous & wave) in calm-water. In the optimization process the evolution strategy (ES) technique is linked to the computational method to obtain an optimum hull form by taking into account the displacement as design constraint. For allowing the large variation of hull form during optimization process the hull surface is represented by NURBS. New hull forms are obtained from the well-known S60 hull and the classical Wigley hull taken as initial hulls in the optimization process at Fn=0.316. The optimization variables are a combination of ship hull offsets and main dimensions. The benchmark results for two test cases indicate that the total resistance of optimized hulls is reduced significantly.DOI: http://dx.doi.org/10.3329/jname.v10i1.12927

Ship hull form optimization by evolutionary algorithm in order to diminish the drag

This study presents a numerical method for optimizing hull form in calm water with respect to total drag which contains a viscous drag and a wave drag. The ITTC 1957 model-ship correlation line was used to predict frictional drag and the corrected linearized thin-ship theory was employed to estimate the wave drag. The evolution strategy (ES) which is a member of the evolutionary algorithms (EAs) family obtains an optimum hull form by considering some design constraints. Standard Wigley hull is considered as an initial hull in optimization procedures for two test cases and new hull forms were achieved at Froude numbers 0.24, 0.316 and 0.408. In one case the ES technique was ran for the initial hull form, where the main dimensions were fixed and the only variables were the hull offsets. In the other case in addition to hull offsets, the main dimensions were considered as variables that are optimized simultaneously. The numerical results of optimization procedure demonstrate that the optimized hull forms yield a reduction in total drag.

Numerical Solution of Body-Exact Problem in the Time Domain

Motions of a floating body in waves are computed in the time domain by solving the body-exact problem with the panel-free method and exact geometry. In the present study, the body boundary condition is imposed on the instantaneous wetted surface exactly at each time step. The free surface boundary is assumed linear so that the time-domain Green function can be applied. The body geometry is represented by NonUniform Rational B-Spline surfaces. At each time step, the instantaneous wetted surface is obtained by trimming the entire body surface. With the panel-free method, the body-exact problems are solved without involving repanelization of the wetted hull surface at each time step. Validation studies have been carried out for a submerged sphere, a flared body, and a Wigley hull. The hydrodynamic forces on the submerged sphere undergoing large-amplitude motion were computed and compared with analytical solutions. For the flared body oscillating in a free surface and the Wigley hull in waves, numerical results were compared with experimental data and solutions by other numerical methods.

Trim Optimization of Ship by a Potential-Based Panel Method

A surface panel method for a boundary-value problem with the free surface is proposed to predict ship wave resistance under different trim conditions based on a so-called double-model solution. The free surface boundary condition is linearized with respect to the oncoming flow and computed by a four-point finite difference scheme. Sample computation for Wigley hull is carried out to demonstrate the effectiveness and the robustness of the method. A hull model is taken into account at two different displacements with respect to trim conditions of lower wave resistance. It is demonstrated by calculation and experiment that the wave resistance under the trim conditions provided by the proposed method is lower than that under the initial conditions.

직교격자 기반 수치기법을 이용한 선박의 대변위 운동해석

In this study, a Cartesian-grid method based on finite volume approach is applied to simulate the ship motions in large amplitude waves. Fractional step method is applied for pressure-velocity coupling and TVD limiter is used to interpolate the cell face value for the discretization of convective term. Water, air, and solid phases are identified by using the concept of volume-fraction function for each phase. In order to capture the interface between air and water, the tangent of hyperbola for interface capturing (THINC) scheme is used with weighed line interface calculation (WLIC) method which considers multidimensional information. The volume fraction of solid body embedded in the Cartesian grid system is calculated using a level-set based algorithm, and the body boundary condition is imposed by a volume weighted formula. Numerical simulations for the two-dimensional barge type model and Wigley hull in linear waves have been carried out to validate the newly developed code. To demonstrate the applicability for highly nonlinear wave-body interactions such as green water on the deck, numerical analysis on the large-amplitude motion of S175 containership is conducted and all computational results are compared with experimental data.

A stable and adaptive semi-Lagrangian potential model for unsteady and nonlinear ship-wave interactions

We present an innovative numerical discretization of the equations of inviscid potential flow for the simulation of three dimensional unsteady and nonlinear water waves generated by a ship hull advancing in water. The equations of motion are written in a semi-Lagrangian framework, and the resulting integro-differential equations are discretized in space via an adaptive iso-parametric collocation Boundary Element Method, and in time via adaptive implicit Backward Differentiation Formulas (BDF) with variable step and variable order. When the velocity of the advancing ship hull is non-negligible, the semi-Lagrangian formulation (also known as Arbitrary Lagrangian Eulerian formulation, or ALE) of the free surface equations contains dominant transport terms which are stabilized with a Streamwise Upwind Petrov-Galerkin (SUPG) method. The SUPG stabilization allows automatic and robust adaptation of the spatial discretization with unstructured quadrilateral grids. Preliminary results are presented where we compare our numerical model with experimental results on the case of a Wigley hull advancing in calm water with fixed sink and trim.

Hydroelasticity of marine vessels advancing in a seaway

An important branch of hydroelasticity deals with the dynamic interactions between elastic structures and ocean waves. While the modal superposition method has been the primary approach in hydroelastic analysis of marine vessels, we present a directly coupled approach in the frequency domain with a rigorous treatment of the vessel forward speed. The formulation adopts a translating coordinate system with the free surface boundary conditions accounting for the double-body flow around the vessel and the radiation condition taking into account the Doppler shift of the scattered waves. A boundary element model, based on the Rankine source formulation, describes the potential flow and the hydrodynamic pressure on the vessel. A finite element model relates the vessel response to the hydrodynamic pressure through a kinematic and a dynamic boundary condition on the wetted hull surface. This direct coupling of the structural and hydrodynamic systems leads to an equation of motion in terms of the nodal displacement of the finite elements. The results are evaluated against predictions from a seakeeping model with forward speed and the modal superposition method at zero speed. A parametric study of a Wigley hull shows that forward speed introduces new resonance modes, which amplify the elastic response of the vessel in a seaway.

Free surface flow around a ship model using an interface-capturing method

A free surface, turbulent flow code around ship hulls using the Slightly Compressible Flow formulation is used for simulating the flow around a Wigley hull. The code uses finite differences and the numerical scheme was marched in time using the 2nd order explicit Runge–Kutta method. Turbulent flows were simulated using the Baldwin–Lomax turbulence model. The grid is generated using an algebraic grid generator. The free surface treatment method is an interface-capturing one, on a fixed grid on which the kinematic free surface equation is solved. Several boundary conditions were implemented and their behavior was assessed. The flow conditions are the ones for which experimental and numerical results exist. The results show very good agreement with the experimental results.