Finite-Volume simulation of flows about a ship in maneuvering motion
TAKUYA OHMORI
Ship and Marine Technology Department, Research Institute, Ishikawajima-Harima Heavy Industries Co., Ltd., 1 Shin-Nakahara-cho, Isogo-ku, Yokohama 235-8501, Japan
Abstract： A finite-volume method of computing the viscous flow field about a ship in maneuvering motion was developed. The time-dependent Navier-Stokes equation discretized in the generalized boundary-fitted curvilinear coordinate system is solved numerically. A third-order upwind differencing scheme, a marker and cell (MAC)-type explicit time marching solution algorithm and a simplified subgrid scale (SGS) turbulence model are adopted. The simulation method is formulated, including the movement of a computational grid fitted to the body boundary that allows computation of the flow field around a body under unsteady motion.
To estimate the maneuvering ability of a ship, the accurate prediction of the hydrodynamic forces and moments of the hull is important. Therefore, experimental methods of finding the hydrodynamic forces of a ship in maneuvering motion, such as the oblique towing test, the circular motion test (CMT) and planar motion mechanism (PMM) test, were established. Numerical simulation methods for those captive model experiments were developed introducing computational fluid dynamics (CFD).
First, numerical methods for steady oblique tow and steady turn simulation were developed and then extended to unsteady forced motion. Simulations were conducted about several realistic hulls, and the results were verified by comparisons with measured results obtained in model experiments. Hydrodynamic forces and the moment, the longitudinal distribution of the hydrodynamic lateral force, and the pressure distribution on the hull surface showed good agreement.
Key words： computational fluid dynamics, maneuvering motion, unsteady flow, hydrodynamic force
Address correspondence to： T. Ohmori
Received for publication on May 12, 1997; accepted on June 15, 1998
Introduction
In recent years, the importance of navigational safety has become much greater; accordingly the maneuver-ability of a ship should comply with accepted maneuver-ability standards. An accurate estimation of a ship's maneuvering ability at the design stage is essential to meet these requirements. Therefore, the establishment of a prediction method for hydrodynamic forces and moments relating to the maneuvering motion, particularly those acting on the main hull of a ship, is indispensable.
There exist several theoretical or numerical methods of estimating the hydrodynamic sway force and yawing moment acting on a maneuvering ship's hull, which are mainly based on the slender body assumption1 or the nonlinear lifting surface theory.2 However, another approach based on the surface panel method was proposed recently.3 These methods concentrated on simplicity in use and an approximate estimation of the size of the hydrodynamic force rather than on the detailed structure of the flow field. However, they also require many empirical parameters, such as the determination of the point of flow separation or the strength of the free vortex. Further, these methods can only express the complicated hull form of real ships in a simplified manner such as the Lewis-form approximation. Therefore, the only accurate way to obtain the hydrodynamic forces and moments acting on a hull has been time-consuming model experiments, and a tool that can resolve the details of the flow field is felt to be necessary for the further advancement of ship design techniques.
On the other hand, numerical simulation methods for viscous flow fields, by solving the Navier-Stokes equation, have developed rapidly in line with recent advances in computer hardware. Numerical methods have the advantage of requiring no linear approximations, so they can deal with nonlinear flow phenomena. Numeri
