Time-domain simulation of large-amplitude ship motions including capsizing.

摘要

A Reynolds-Averaged Navier-Stokes (RANS) numerical method has been employed in conjunction with a chimera domain decomposition approach for time-domain simulation of large-amplitude ship motions including capsizing. The unsteady BANS equations are formulated in an earth-fixed reference frame and transformed into general curvilinear, moving coordinate systems. This generalized method can be used to evaluate two- and three-dimensional, laminar and turbulent, nonlinear free surface flows including relative motions among different components of a system.; Equations for ship motion are incorporated into the chimera BANS program to handle coupled ship motion and fluid flow problems. Forces and overturning moments due to current and waves are obtained by directly integrating hydrodynamic forces over all elements on the hull. Gravitational and hydrostatic forces are also accounted for in the motion equations. The grids for both the ship and ambient water are adjusted every time step to account for the ship and current/wave interactions.; In this method, a new domain decomposition technique is employed to handle the free surface problem involving large-amplitude ship roll motions. A grid generation module for free surface and ship roll motion is incorporated in the chimera BANS program. Special treatment is introduced for free surface/ship hull intersections. In this new approach, the ship grid blocks are allowed to move as rigid bodies in simple translational and rotational motions while the free surface grid blocks handle the instantaneous hull and free surface boundary conditions. This treatment allows the ship to undergo large-amplitude roll motions and capsizing without excessive grid distortions.; To demonstrate the feasibility of the method, it is employed to simulate the ship/fender interactions of a full-scale ship in berthing operation. Comparisons are made between the simulation results and the experimental data to provide a thorough validation of the present method. The method accurately predicts the flow induced by the berthing ship as well as the fender force resulted from the berthing operation. A parametric study is then performed for two full-scale naval vessels to evaluate the influence of ship geometry, approach speed, underkeel clearance, quay wall clearance distance, fender stiffness and other design parameters on the maximum fender deflection and impact loads.; In addition, the present study addresses some of the hydrodynamic issues relevant to the operation of a modular, submersible pontoon system (sea cache) in littoral water. Hydrodynamic forces on large pontoon structures while afloat or fully/partially submerged are investigated. Calculations are also performed for a fixed rectangular barge in beam sea conditions to provide a critical assessment on the capability of the present method for time-domain simulation of viscous, nonlinear free surface waves. The computed wave elevations, velocity vectors and vorticity contours are compared with the corresponding experimental data obtained from the Particle Image Velocimetry (PIV) measurements to illustrate the accuracy of the present simulation results. Finally, the method is generalized for time-domain simulation of the capsizing process of a two-dimensional barge in regular waves.