Proceedings of the 9th International Conference

on Hydrodynamics (ICHD 2010)

October 11 – 15, 2010,Shanghai, China
Editors: Y. S. Wu, S. Q. Dai, H. Liu, L. D. Zhou, X. C. Yang

Naval Hydrodynamics, Ocean Engineering, and Coastal Engineering(26)

E1-1 Roll response of ship-hull sections in variable bathymetry regions by a hybrid BEM- vortex particle method

Kostas A. Belibassakis

Department of Naval Architecture, Technological Educational Institute of Athens, Ag. Spyridonos 12210, Athens, Greece

Abstract :

A non-linear, hybrid method has been developed with application to the problem of roll response of ship-hull sections of general  shape, floating in general bathymetry regions. Using  domain decomposition, the present method is based on boundary element formulation for the representation of the non-linear potential wave motion around the floating body, in combination with vortex particle method for the generation of vorticity in the boundary layer and numerical simulation of vorticity convection and viscous diffusion in subregions close to the solid boundary. Subsequently, hydrodynamic forces on the floating body are obtained by pressure integration, and the hydrodynamic coefficients (added mass, damping) are calculated. Numerical results are presented and compared with experimental data and other methods. It is shown that the present method provides results of reasonable accuracy, illustrating that the mixing of boundary integral methods and particle methods is a useful tool for the evaluation of ship-hull characteristics in rolling motion, where viscous effects associated with boundary layer separation could be significant.

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E1-2 Numerical simulations of wave-induced ship motions in regular oblique waves by a time domain panel method

Jing-pu Chen, De-xiang Zhu

China Ship Scientific Research Center, Shanghai 200011, China

Abstract :

Based on the method for ship motions in head waves, the numerical method for predicting ship motions in oblique waves is developed in this paper. The artificial spring model is adopted to control the numerical drifting in sway and yaw motions, while the empirical method is used for roll damping due to viscous effects. To validate present method, the simulated results of Flokstra container in oblique waves are compared with the experimental results.

E1-3 Prediction of excess resistance of ships by 3-D near field approach and its comparison with some alternative methods

N.M. Golam Zakaria, Mir Tareque Ali

Dept. of Naval Architecture and Marine Engineering, Bangladesh University of Engineering and Technology(BUET), Dhaka-1000, Bangladesh

Abstract :

Second-order forces have been widely investigated using 2-D methods since the early 60’s and more recently also using 3-D methods. The present work uses near field approach of 3-D Green Function method as well as some alternative 2-D methods for calculating the second order forces or excess resistance in waves. In this paper, results for excess resistance using both 3-D near field approach and 2-D methods are presented and compared with other published data and experimental measurement. The application of present 3-D approach to sea keeping problems of some complex geometry like Series 60 hull and a bulk carrier ship demonstrates that 3-D near field approach is valid in predicting added resistance of ship in waves and also provides better results in many cases particularly for blunt shaped slow speed vessel.

E1-4 Numerical simulation of a submerged gravity cage with the frame anchor system in irregular waves

Yun-peng Zhao, Tiao-jian Xu, Guo-hai Dong, Yu-cheng Li

State Key Lab of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China.

Abstract :

When typhoon or extreme wave conditions occur, submergence under water may be an effective way for the net cage to avoid the attack. In this paper, a numerical method is developed to simulate the hydrodynamic behavior of net cage, which has been verified in our previous paper. Herein, by the numerical model the mooring line force and cage motion are calculated when the net cage is both in floating and submerging conditions. According to the simulated results, it can be found that the decrease of the mooring line force and cage motion is obvious when the net cage is submerged. The results of this study will give a good reference for better knowledge of dynamic behavior of submersible net cage.

E1-5 Verification and validation of CFD predictions for a manoeuvring tanker

Lu Zou, Lars Larsson, Michal Orych

Department of Shipping and Marine Technology, Chalmers University of Technology, Gothenburg, Sweden.

Abstract :

This paper presents a study on the Verification and Validation (V&V) of CFD solutions for a tanker without appendages manoeuvring at varying drift angles and water depths. A steady state Reynolds Averaged Navier-Stokes solver is applied to solve the viscous flow around the ship neglecting the free surface, sinkage and trim. Discretization errors and uncertainties in hydrodynamic forces and moments are estimated through grid convergence studies. Validation is performed by comparison with model test data.

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E2-1 A study on the sloshing effect on the motion of 2d boxes in regular waves

Dong-young Lee, Hang S. Choi, Odd M. Faltinsen

Department of Naval Architecture and Ocean Engineering, Seoul National University, Kwanak-ro 599, Sillim-dong, Kwanak-ku, Seoul 151-744, Korea

Abstract :

In this paper, we present a fundamental study on the sloshing effect for the sway motion of two boxes in two dimensions. First, we carry out experiments for two boxes of the same size and also different size in regular waves with different filling ratios, where the boxes are firmly connected each other. The sway motion is measured by a non-contact video camera. The measured motion is compared with numerical results obtained by using a computer program constructed based on the single-dominant multi-modal method. Good agreements are in general found, but clear discrepancies can also be observed at some incident wave frequencies. The friction on the tank rail and the locally resonated fluid motion between two boxes are regarded as main error sources. Therefore, it is necessary to clarify these error sources to predict more accurately.

E2-2 A comparative study on the fatigue life of mooring systems with different composition

Jun Sik Han, Yun Ho Kim, Young Jun Son, Hang S. Choi

Department of Naval Architecture & Ocean Engineering, Seoul National University, Kwanak-ro 599, Sillim-dong, Kwanak-ku, Seoul, Korea.

Abstract :

In this paper, two different types of the mooring system for a FPSO are considered, which is supposed to be installed in Gulf of Mexico. One system consists of 16 mooring lines (four by four) and another one consists of 12 mooring lines (four by three). It is designed that the static system stiffness are almost the same. Then two mooring systems are analyzed from the viewpoint of the extreme load and the fatigue life. A time-domain computational code is used in order to determine the extreme tension, while the spectral method is implemented for estimating the fatigue life. In the extreme dynamic load case, two mooring systems have almost the same results. In consequence, the fatigue life differs only slightly.

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E2-3 Numerical simulation of the structure of propeller’s tip vortex and wake

Fang-wen Hong, Shi-tang Dong

China Ship Scientific Research Center, Wuxi, China.

Abstract :

By means of numerical simulation, the evolvement of tip vortex and vortical trailing wake of a propeller were studied in details. From upstream of leading edge up to downstream of trailing edge, the tip vortices region extends rapidly and becomes sizable, which reason is that the transport of vortices between trailing wake and tip vortex takes place. The trailing wake region or the tip vortex region, each consists of sub-regions. The direction of the vortices in one of the sub-regions is opposite to that of the other sub-region. Each sub-region is structured with vortex layers of varying strength. The trailing wake possesses significant thickness and the tip vortex region occupies sizable space. The present analysis also show that within certain distance downstream from tailing edge, although the size and the configuration of the vortices region varies with going backwards, the total vortices flux through each station almost remains constant.

E2-4 Towards a fully 3D domain-decomposition strategy for water-on-deck phenomena

Giuseppina Colicchio, Marilena Greco, Claudio Lugni, Odd Magnus Faltinsen

CeSOS, Center of Excellence for Ships and Ocean Structures, Trondheim, Norway; INSEAN, The Italian Ship Model Basin, Rome, Italy.

Abstract :

A numerical approach has been used to analyze the water shipping caused by head sea waves for a FPSO ship at rest. A 3D Domain-Decomposition (DD) strategy is used, where a linear potential-flow seakeeping analysis of the vessel is coupled with a local nonlinear rotational-flow investigation for the prediction of water-ondeck phenomena. The Navier-Stokes solver is applied in the region close to the ship bow. It combines a finite-difference spatial algorithm with a predictor-corrector time scheme. The sea and ship surfaces are tracked with a Level-Set (LS) technique and a hybrid Eulerian-Lagrangian algorithm. The inner solver receives the initial and boundary conditions in terms of velocity, pressure,  sea-surface location and ship motions and provides the loads due to the nonlinear waveship interaction (including green-water loads) to the seakeeping method. Here the inner solver and its implementation within the DD are described in detail. Preliminary results in terms of water-on-deck occurrence are discussed and compared against 3D water-on-deck experiments.

E2-5 Numerical study of planing vessels in waves

Hui Sun, Odd M. Faltinsen

Centre for Ships and Ocean Structures, Department of Marine Technology, Norwegian University of Science and Technology, Trondheim, Norway.

Abstract :

The performance of planing vessels in waves is investigated numerically by assuming linear regular incident waves in head sea. A 2D+t theory is presented to perform nonlinear time domain simulations of a prismatic planing boat in incident waves. A Boundary Element Method is employed to solve the initial boundary value problems in two-dimensional (2D) cross-planes. A simplified theory is also applied. The added mass and damping coefficients used in the latter theory are determined from the numerical simulation of forced oscillations. The wave induced heave and pitch motions calculated by these two methods are compared with the experiments by Fridsma [1].

E3-1 RANS prediction of the KVLCC2 tanker in head waves

G.B. Deng, P. Queutey, M. Visonneau

E.M.N, L.M.F-UMR6598, Ecole Centrale de Nantes 1, Rue de la Noe, Nantes, France.

Abstract :

The present study is devoted to the computation of the KVLCC2 tanker in head wave with free heave and pitch motion. A RANS solver using finite-volume discretization and free-surface capturing approach is employed for the computation. Free ship motion is captured with a mesh deformation approach. Three different wave lengths (0.6Lpp, 1.1Lpp and 1.6Lpp) are computed. We focus on numerical uncertainty estimation in this paper. For each test case, three different meshes and at least three different time steps have been used to access both time and spatial discretization error. Additional computations with different setups aimed at identifying different numerical discretization errors will also be performed. It is demonstrated thatspecial attention needs to be paid to time discretization. To keep the same time accuracy, time step needs to be reduced on fine mesh for such kind of unsteady free-surface computation involving important pitch or roll motion.

E3-2 Theoretical analysis of wave and structure interaction around a composite-type coastal structure - a case study of a seawall and detached breakwaters

Masato Ichikawa , Takehisa Saitoh , Guo-ping Miao

Nishimatsu Construction Co., Ltd, 1-20-20 Toranomon, Minato-ku, Tokyo 105-8401, Japan

Abstract :

This study presents a theoretical method for analyzing flow fields around a composite-type coastal structure. A dividing region method, extended from previous work [1],[2],[3]is adopted, and the case composed of a seawall and detached breakwaters is the focus for a fundamental stage of this topic. Laboratory experiments are also conducted to examine the validity of this method. Theoretical results of water surface elevation around the composite-type structure agree well with the experimental results and the validity of this method is confirmed.

E3-3 Calculation of ship squat in restricted waterways by using a 3D panel method

Jian-xi Yao , Zao-jian Zou

School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China

Abstract :

A panel method is applied to calculate the sinkage and trim of a ship sailing in a shallow channel. The hull surface, free surface and channel wall surfaces are discretized into panels on which Rankine sources of constant strengths are distributed. An iterative scheme is used to deal with the nonlinear boundary conditions on free surface. The boundary condition on water bottom is satisfied by the method of images, whereas the radiation condition is satisfied by raised panels above free surface. The vertical force and pitching moment are obtained by integrating the hydrodynamic pressure over the hull surface, and the sinkage and trim are calculated according to dynamic equilibrium. Numerical calculations are performed for Series 60 (CB=0.6) ship. The numerical results are in good agreement with experimental data.

 

E3-4 A numerical comparison of end-plate effect propellers and conventional propellers

Hsun-jen Cheng, Yi-chung Chien, Ching-yeh Hsin, Kuan-kai Chang, Po-fan Chen

Department of Systems Engineering and Naval Architecture, National Taiwan Ocean University, Keelung, China

Abstract :

Unconventional propellers with end-plate effects such as Kappel propellers get designers’ attention due to the environmental concerns and energy saving problems. The computations have been carried out to compare the Kappel propellers and the conventional propellers, and the emphasis is put on the scale effects and the structural performance. The scale effect is first investigated, and the computational results show that the Kappel propeller has a larger scale effect than the conventional propeller. The structural analysis is then made, and the comparisons of the Kappel propeller and the conventional propeller show that the Kappel propeller suffers from a stronger stress concentration near the tip.

 

E3-5 Application of the adjoint method to the propeller designs

Ching-yeh Hsin, Kuan-chen Chen, Yih-wei Tzeng, Ya-lin Tsai, Shiang-fen Chou

Department of Systems Engineering and Naval Architecture, National Taiwan Ocean University, Keelung, China

Abstract :

In this paper, a propeller design method based on the adjoint method is presented. For the optimization problems, the gradient methods are usually suffering from the inefficient computations of the gradients, and the adjoint method can remedy this problem. In this paper, the adjoint equation of the boundary element method is first derived, and it is then applied to the propeller design problems. The Lagrange-multiplier method with the adjoint equations for solving the gradients is used in this method. Two design examples are demonstrated in the paper, and both examples show that the presented method can successfully achieve the design goals.

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E4-1 Nonlinear analysis on wave-plate interaction due to disturbed vertical elastic plate

Guang-hua He, Masashi Kashiwagi

Department of Naval Architecture and Ocean Engineering, Osaka University, Suita, Osaka 565-0871, Japan

Abstract :

Hydroelastic behavior of wave-plate interaction due to an initial deflection of a vertical elastic plate is simulated by using a Mixed Eulerian Lagrangian method for the fluid and a Finite Element Method for the plate. An implicit boundary-condition method is developed to solve the coupled motions of fluid and plate. A hybrid wave absorbing beach is installed to prevent the wave reflection from a vertical wall at the end of the wave tank. The 4th order Runge-Kutta scheme with uniform time step is used for time marching. First, numerical results of the elastic vibration of a vertical plate induced by deformation of itself at initial time are validated by comparing with corresponding analytical solution. Then, further comparison between the results from mode-expansion method and FEM is made. Finally, the influences of the edge condition at the top of plate and the plate stiffness on the wave-plate interaction are investigated systematically.

E4-2 Lagrangian modeling of tidal bores passing through bridge piers

Jing Li, Hua-xing Liu, Soon Keat Tan

DHI-NTU Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, Singapore

Abstract :

The process of tidal bore passing through bridge piers is numerically simulated in an open channel using a pure Lagrangian method, i.e. Smooth Particle Hydrodynamics (SPH). Due to its “gridless” feature, SPH is intrinsically well suited for the complex hydrodynamic simulation when the fluid encounters a structure. The behavior of bores propagation along the channel is illustrated herein and includes the bore’s free surface properties and flow field, and in particular, the intricate behavior of unsteady flow during the passage of tidal bore. The generation of shock waves between the structures can be clearly observed in the numerical experiment. Intense vortical structures behind the bore front are generated as the bore propagate through the constriction.

 

E4-3 A new surface modification approach for CFD-based hull form optimization

Hyunyul Kim, Chi Yang

Department of Computational and Data Sciences, George Mason University, Fairfax,Virginia, USA

Abstract :

The main focus of this study is on the development of an efficient and effective hull surface modification technique for the CFD-based hull form optimization. Two approaches are utilized. One is based on the radial basis function interpolation, and the other the sectional area curve of the hull. Both local and global modifications of hull forms can be achieved by combining these two approaches. The hull surface modification technique developed in this study is used to vary the hull forms during the optimization process, in which the objective functions associated with the resistance is evaluated by a practical design-oriented CFD tool (SSF), and a multi-objective genetic algorithm is adopted to allow for multi-design speeds. For the purpose of illustration, the KRISO container ship (KCS) is taken as an initial hull to be optimized for reduced drag at given design speeds. Numerical results obtained in this study have shown that the present hull surface modification technique can produce smooth hull forms with reduced drag effectively and efficiently in the CFD-based hull form optimization.

 

E4-4 Pressure distribution computed by wave-interaction theory for adjacent multiple bodies

Masashi Kashiwagi, Qi-qi Shi

Dept of Naval Arch & Ocean Eng, Osaka University, Osaka, Japan.

Abstract :

In spite of a mathematical limitation that each interacting body must be far enough apart from the other bodies, the wave interaction theory has been used successfully even for a case where the separation distance between the bodies is virtually zero. Numerical investigation is made in this paper on the practical applicability of the wave interaction theory by considering four identical box-shaped bodies as a simplified example and comparing computed results with correct ones obtained by the higher-order boundary element method. It is shown that the wave force in the horizontal direction can be obtained favorably by the interaction theory even if the separation distance between the bodies is very small. To make reasons of this somewhat peculiar phenomenon clear, not only the integrated hydrodynamic force but also the pressure distribution on the body surface is calculated and compared with the results by the higher-order boundary element method. Discussion is made on whether the pressure is correctly obtained on the regions very close to adjacent bodies and fortuitous cancellation in the integration of the pressure occurs between the two vertical planes in close proximity.

 

E4-5 Hydrodynamic Pressure Distribution on Ship Hull At Very High Encounter Frequencies

X.B. Chen and S. Malenica

Research Department, Bureau Veritas, 67/71, Blvd du Chateau, 92571 Neuilly-Sur-Seine, France.

Abstract :

New developments to improve the wave diffraction and radiation solution are presented in the present work. They consist of the implementation of the supplemented boundary integral equation method to remove irregular frequencies, and the analytical integration of the waves terms in the Green function over a flat panel to ensure the numerical precision at high wave encounter frequencies. The hydro-structural interface is realized by recomputing the hydrodynamic pressure at points of structural model and the hydrodynamic coefficients (added mass and radiation damping) and wave excitation loads are computed following each mode of structural model. This provides a perfect equilibrium between inertial and pressure loads on the structural model.

 

E5-1 Dynamic pressures on curved front seawall models under random waves

K. V. Anand, V. Sundar , S. A. Sannasiraj

Research Department, Bureau Veritas, 67/71, Blvd du Chateau, 92571 Neuilly-Sur-Seine, France

Abstract :

The shoreline erosion is a major problem that persist world wide and seawall still remain as one of the most widely adopted coastal protection structure. The design of an efficient seawall should be such that overtopping is minimized even during coastal flooding and extreme events by maintaining its crest elevation also was possible. This can be obtained with curved front face sea walls. Two such curved configurations have been chosen for the study. The experimental investigation on dynamic pressure variation along the surface of the seawall models placed over a bed slope of 1 in 30 and subjected to the action of random waves following the PM spectrum were conducted. The results on the variations of dynamic pressures on the seaward face of both the models along the relative depth are compared and discussed.

 

E5-2 Experimental and numerical investigations on fast catamarans interference effects

Stefano Zaghi, Riccardo Broglia, Andrea di Mascio

INSEAN - Italian Ship Model Basin, Rome, Italy.

Abstract :

Experimental and numerical analysis of the interference effect for a fast catamaran is carried out. This work presents the status of an ongoing NICOP project, the focus is on the effect of the separation distance between the demihull on the performances as well as on the interference. To this aim, experiments and numerical simulations are performed for five different separation lengths (and for the monohull configuration) and for a wide range of Froude number (from 0.2 to 0.8).

 

E5-3 The hydrodynamic model for simulating themotions of a ship moored near the quay in waves

Ming-chung Fang, Bou-chaun Hsu , Joe-ming Yang

Department of Systems and Naval Mechatronic Engineering, National Cheng Kung University, Tainan, China

Abstract :

In this study, a hydrodynamic mathematical model for simulating the motions of a ship moored near the quay in waves is presented. The related hydrodynamic coefficients such as the added mass, damping coefficient and wave exciting force are calculated by the two-dimensional source distribution method. The strip theory is then applied to integrate the whole ship hydrodynamic characteristics along the ship length and the ship motion behaviors in waves can be obtained through the equations of motions. The bank effects are treated by using the image method which is similar to the treatments of the twin hull ship except the differences on some coupled hydrodynamic forces. The time domain simulation technique is made to analyze the motions deeply by using the 4th order Runge-Kutta method. Different wave conditions are considered with respect to different clearances between the ship and bank and shallow water effect is neglected for simplicity. The present results will be helpful for the design on the ship mooring system arrangement near the quay or the wharf.

 

E5-4 Time-domain simulation of tank sloshing pressure and experimental validation

Shuo Huang, Wen-yang Duan, Xin Zhu

College of shipbuilding Engineering, Harbin Engineering University Harbin, China

Abstract :

In this paper, a time-domain Green function based BEM (boundary elements method) in presented to simulate tank sloshing problems. NURBS based higher-order panel method is developed to solve the boundary integral equation. To get physical real stable results, a modified tank wall boundary condition is presented. The model experiments were carried out using partially filled rectangular tank with forced sway motion. Sloshing-induced internal pressures and wave elevation have been obtained numerically and experimentally. It is observed that the present numerical methods provide a fair agreement with experimental results. Long-time simulations have also been carried out to demonstrate the stability of the method.

 

E5-5 RANS and PANEL method for unsteady flow propeller analysis

S. Gaggero, D. Villa, S. Brizzolara

University of Genoa, Department of Naval Architecture and Marine Engineering, Genoa, Italy.

Abstract :

A spatial non uniform inflow is the usual inflow to which a marine propeller is subjected to. Inside a ship wake, in inclined shaft condition, in tandem/contra rotating configurations, the spatial non uniformity of the incoming flow on the propeller plane leads to the unsteadiness responsible of thrust and torque fluctuations, induced pressures, cavitation and the associated noise. Any design method and, moreover, each analysis tool should be able to treat these phenomena, to carry out a more consistent ship oriented propeller design and to better understand the flow features and the performances of an already designed propeller. In the present work two different numerical approaches, a commercial RANS solver and a in house developed Panel Method, are addressed and applied for the analysis of marine propellers subjected to an oblique inflow, showing, through the comparison with the experimental measures, their capabilities and their limitations.

 

E5-6 Design and analysis of counter-rotating propellers-comparison of numerical and experimental results

Davide Grassi, Stefano Brizzolara, Michele Viviani, Luca Savio,Sara Caviglia

ZF Marine Arco s.p.a. Arco (Tn), Italy

Abstract :

In these last years a growing interest has been devoted to counter-rotating propellers especially for pod/stern drive applications for pleasure boats. In this context DINAV has been interested in the framework of an industrial R&D project to develop design/analysis computer codes for such kind of propulsors which is based on a modern liftingline/lifting surface design method [1-4]. The present work is devoted to the comparison between the foregoing numerical design/analysis tools and the results of the cavitation tunnel tests. The validation study has been performed on a set counter rotating propellers designed to be installed on a commercial pod drive system. Despite some uncertainty intrinsically connected to the nature of the test, results are very well in agreement with design points, allowing to validate the theoretical codes developed so far and to obtain semi-empirical correction factors for future application.