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A study on floW field around full ship forms In maneuveling motion*

 

TAKUYA OHMORI1, MASATAKA FUJINO2, and HIDEAKI MIYATA2

 

1Ship and Marine Technology Department, Research Institute, Ishikawajima-Harima Heavy Industries Co., Ltd., 1 Shin-Nakahara-cho, Isogo-ku, Yokohama 235-0031, Japan

2Department of Naval Architecture and Ocean Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan

 

Abstract: To estimate the maneuvering ability of a Ship, an accurate estimation of the hydrodynamic forces and moment acting on the ship's hull is indispensable. For the purpose of developing a numerical method of computing the viscous flow field around a hull and evaluating its validity, the hydrodynamic pressure on the hull and the velocity field were measured. Two full ship models with different hull forms in the aft part were used for the experiment. From the results of pressure measurements, the distribution of hydrodynamic lateral forces was obtained. The simulation method is a numerical solution of the Navier-Stokes equation based on a finite-volume method and applied to the maneuvering motion. The measured' and computed results agree qualitatively well, and the method is a valuable tool for estimating the maneuvering ability of a ship. The typical characteristics of the flow field in the steady turning condition are revealed by the numerical simulation, and the mechanism of the relations between hull form, flow field, and hydrodynamic forces are clarified.

 

Key words: computational fluid dynamics, ship maneuver-ability, viscous flow, hydrodynamic force

 

Address correspondence to: T. Ohmori

Received for publication on Oct. 1, 1997; accepted on Nov. 17, 1997

* Translation and combination of articles that appeared in the Journal of the Society of Naval Architects of Japan, vols. 176, 177, 179 (1994-1996): The original article won the SNAJ prize, which is awarded annually to the best papers selected from the SNAJ Journal, JMST, or other quality journals in the field of naval architecture and ocean engineering.

 

Introduction

 

At the design stage of a ship, one of most important requirements is to satisfy the maneuverability standards or criteria. The maneuverability of a ship depends essentially on hull form, propeller, and rudder. Of these, the hydrodynamic characteristics of the hull, and particularly the hull form of the aft part, are particularly important. Therefore, to estimate the maneuverability of a ship, the hydrodynamic forces and moment acting on the hull should be predicted accurately.

For design purposes, computational methods are preferable to model experiments. Several computational methods exist to estimate hydrodynamic sway force and yaw moment which are based on the slender body theory1,2 or the panel method. 3 These methods give a valid estimate of the lateral force, but are not accurate enough to estimate the difference in maneuverability caused by modifications of hull form. Furthermore, to understand the dependence of maneuverability on hull form in more detail, complete information about the flow field is required, including the distribution of hydrodynamic lateral forces. A viscous flow simulation utilizing the numerical solution of the Navier-Stokes equation is believed to be the most suitable technique for this purpose,4 as it can deal with the highly nonlinear viscous flow around a practical hull form. In addition, the form of a hull can be represented exactly by this method.

With these points in mind, a series of extensive measurements of the hydrodynamic pressure on the hull surface and the velocity field at the AP section in oblique towing and steady turning conditions were conducted, together with the development of a computational method based on computational fluid dynamics.5-7 From the results of pressure measurements, the hydrodynamic lateral forces acting on various transverse sections of the ship are obtained by integrating the measured pressures along the contour of each transverse section. The ship models used were two tanker models with full hull forms.

Based on the distributions of hydrodynamic pressure, lateral force, and flow velocity obtained, the differences in the hydrodynamic characteristics of the two models

 

 

 

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