A new mathematical hull-form with 10-shape parameters for evaluation of ship response in waves

This study presents a new mathematical hull-form that is expressed as an explicit function with 10 hull-form parameters, which is called the Matsui hull-form in this study. The proposed hull-form was developed by expanding the modified Wigley hull-form so that the following 10 hull-form parameters can be independently varied: main dimensions $$L$$ L , $$B$$ B , $$d$$ d , fineness coefficients $${C}_{b}$$ C b , $${C}_{\mathrm{m}}$$ C m , $${C}_{\mathrm{w}}$$ C w , second moment of waterplane area coefficient $${C}_{\mathrm{w}2}$$ C w 2 , longitudinal center of buoyancy LCB and floatation LCF, and a parameter $$\beta$$ β related to anterior–posterior asymmetry. The main purpose of this hull-form is that it is utilized for the following two objects: the first is the simple evaluation of the seakeeping performance and wave loads in the early ship designing stage without any detailed offset data, and the second is a systematical study on the influence of a ship’s dimensions on the ship response in waves. This paper presents the derivation of the Matsui hull-form and the applicability of the proposed hull-from was confirmed by comparing the ship response in waves with the actual ships. Moreover, a sensitivity analysis of the ship response in waves was conducted as an example of the application of the proposed hull-form.

Investigating the Effect of Heterogeneous Hull Roughness on Ship Resistance Using CFD

Research into the effects of hull roughness on ship resistance and propulsion is well established, however, the effect of heterogeneous hull roughness is not yet fully understood. In this study, Computational Fluid Dynamics (CFD) simulations were conducted to investigate the effect of heterogeneous hull roughness on ship resistance. The Wigley hull was modelled with various hull conditions, including homogeneous and heterogeneous hull conditions. The results were compared against existing experimental data and showed a good agreement, suggesting that the CFD approach is valid for predicting the effect of heterogeneous hull roughness on ship resistance. Furthermore, the local distributions of the wall shear stress and roughness Reynolds number on the hull surface were examined to assess the flow characteristics over the heterogeneous hull roughness.

Hydroelastic behaviour and analysis of marine structures

The numerical predictions of the hydroelasticity of floating bodies with and without forward speed are presented using a direct time domain approximation. Boundary-Integral Equation Method (BIEM) with three-dimensional transient free surface Green function and Neumman-Kelvin approximation is used for the solution of the hydrodynamic part and solved as impulsive velocity potential whilst Euler-Bernoulli beam approach is used for the structural analysis with analytically defined modeshapes. The hydrodynamic and structural parts are then fully coupled through modal analysis for the solution of the hydroelastic problem. A stiff structure is then studied assuming that contributions of rigid body modes are much bigger than elastic modes. A rectangular barge with zero speed and Wigley hull form with forward speed are used for the numerical analyses and the comparisons of the present ITU-WAVE numerical results for response amplitude operator, bending moment, shear force etc. show satisfactory agreement with existing experimental results.

An RBF-Based h-Adaptive Cartesian Grid Refinement Method for Arbitrary Single/Multi-Body Hull Modeling and Reconstruction

Complex single/multi-body structures are generally found in ship and ocean engineering. They have the smooth, sharp, concave, and convex surface features in common. Precise modeling of the structures is the basis of numerical simulation. However, the most widely used explicit modeling method requires considerable manual operations. The result is also difficult to reproduce. Therefore, this paper presents a Radial basis function (RBF) based hierarchical (h-) adaptive Cartesian grid method. The RBF is introduced for arbitrary implicit modeling over the Cartesian framework. Thanks to its natural properties, the RBF is easy to use, highly automated, and only needs a set of scatter points for modeling. The block-based h-adaptive mesh refinement (AMR) combined with the RBF aims to enhance the local grid resolution. It accelerates the calculation of intersecting points compared with the uniform Cartesian grid. The accuracy, efficiency, and robustness of the proposed method are validated by the simulation of the 3D analytical ellipsoidal surface and the unclosed conic surface. To select suitable parameters, we thoroughly investigated the uncertainty factors including sample points, RBF functions, and h-AMR grids. The simulation results of the single/multi-body Wigley hull and KCS hull forms verified the proper selection of the factors and the feasibility of our method to solve practical problems.

RANS Simulation of the Flow Around a Ship Advancing in Shallow Water

This paper simulates the viscous flow about a ship advancing in calm water of different water depths using Reynolds-Averaged Naiver-Stokes (RANS) method. A Wigley hull is taken as the study object, and the hull is free in sinkage and trim in the simulations. The fluid domain is discretized into hexahedral structured grids. The overset grid method and the deforming grid method are applied in different cases to capture the ship’s sinkage and trim motion. The grid independence analysis and validation of numerical method are carried out under deep water condition. Then, systematic simulations are carried out under shallow water condition at different ship speeds. The resistance performance and the wave pattern characteristics are compared with deep water condition to demonstrate the shallow water effect. Furthermore, resistance coefficient results under water depth-to-draft ratios of 2.0 and 1.5 are presented and compared. All simulations show great consistency with the theoretical and other potential theory based numerical results.

3D Numerical Simulations of Green Water Impact on Forward-Speed Wigley Hull Using Open Source Codes

A series of CFD RANS simulations are presented for Wigley hulls of two freeboard heights progressing with forward speed in waves. Free surface effects are captured using the Volume of Fluid (VOF) method embedded in open source software OpenFOAM. Comparisons of heave, pitch motions and added resistance of the first Wigley model against the experiments of Kashiwagi (2013) confirm the numerical validity of the hydrodynamic modelling approach. Further simulations for the lower-freeboard Wigley model reveal that the highest green water impact on decks appears in way of λ / L = 1.3 and at the highest instantaneous pitch amplitude where the water propagates far downstream and across the deck. The simulations also demonstrate that the green water events are associated with air bubble entrapment.

A parametric morphing method for generating structured meshes for marine free surface flow applications with plane symmetry

This article introduces a method for morphing a parametric, rectangular and structured 3D template mesh such that it embodies: (1) a given (half) hull surface properly aligned with a pre-defined air-water interface zone, (2) a high-quality boundary layer region near the hull, and (3) a smooth transition of the mesh to the template mesh structure away from the hull. The performance of the proposed method is successfully validated on three widely studied benchmark cases, namely the parabolic Wigley hull, the Series 60 hull and the DTMB 5415 combatant hull. The proposed automated mesh generation method is useful in shape optimization for computational fluid dynamics, among others. Highlights A new method for creating structured meshes for marine CFD applications is presented. The proposed method is parametric and thus fully programmable. The method includes an automatic resolution of CAD geometry errors. The resulting meshes are strictly orthogonal near the inter-phase zone and the hull. The main application of the proposed method is in CFD-based shape optimization.

The influence of numerical parameters in the finite-volume method on the Wigley hull resistance

The equations discretization errors are often overlooked compared to the spatial discretization errors. This article presents the results of the influence of various equations discretization schemes in computational fluid dynamics on the prediction of the ship resistance and wave elevation on the hull. For the analysis, steady flow around a model of the Wigley hull is numerically predicted by employing a finite-volume method solver based on Reynolds-averaged Navier–Stokes equations and the volume-of-fluid method. Six momentum discretization schemes, three multi-fluid discretization schemes and three gradient schemes, are used in the analysis. The results show that the choice of discretization schemes has a significant influence on the results of wave elevation and resistance force in the case of the flow around the Wigley hull. In conclusion, second-order discretization schemes should be used for the resistance evaluation, in order to properly capture the non-linear effects.

Experimental hydrodynamic analysis of trimaran-pentamaran with variation transom non-transom on mainhull and sidehull

One of the most essential aspects of ship is its resistance. There much have been done researches to analyze the reduction of resistance in order to get a good performance; yet the multihull is still one of interesting researches to get the rightest configuration, as to produce minimum resistance. This research is experimental study to obtain the lowest resistance with configuration consisting of stagger, clearance and trim of pentamaran. The pentamaran are performing as a trimaran formation by using Wigley hull with combinations transom on main hull and non-transom on side hulls. Its purpose is also to determine the destructive effects caused by wave interference. The research test conducted on stagger (a ratio of distance of stern main hull to stern side hull to main hull length)-positioning variations of 0.35 and 0.4. As for clearance (a ration of distance centerline of main hull to centerline of side hull to main hull width)-positioning variations, they exceed 1.05; 1.20; 1.35; and 1.50. The trim variations researched are 0°; 0.5 °; and 1.0 °. The result of this study was presented by tables and graphs of resistance components of side hull on stagger-clearance and trim condition.