Challenges in Hydrodynamics of Ships and Ocean Structures

Violent fluid motions, high speed marine vehicles and Computational Fluid Dynamics (CFD) are selected as main topics. Violent fluid motions deal with green water on deck, sloshing and slamming. Slamming involves many physical effects. When analyzing slamming, one must always have the structural reaction in mind. This necessitates that hydroelastic effects are considered. Many hydrodynamic phenomena matter for the three main categories of highspeed vessels, i.e., vessels supported by the hull, foils and air cushions. Dynamic instabilities, cavitation and ventilation are limiting factors for their performance. The coupling with automatic control is discussed. A brief overview of the many different CFD methods is given and advantages and disadvantages are discussed

Challenges in Hydrodynamics of Ships and Ocean Structures

Violent fluid motions, high speed marine vehicles and Computational Fluid Dynamics (CFD) are selected as main topics. Violent fluid motions deal with green water on deck, sloshing and slamming. Slamming involves many physical effects. When analyzing slamming, one must always have the structural reaction in mind. This necessitates that hydroelastic effects are considered. Many hydrodynamic phenomena matter for the three main categories of highspeed vessels, i.e., vessels supported by the hull, foils and air cushions. Dynamic instabilities, cavitation and ventilation are limiting factors for their performance. The coupling with automatic control is discussed. A brief overview of the many different CFD methods is given and advantages and disadvantages are discussed

OMAE2005-67311 WATER ENTRY AND EXIT OF A HORIZONTAL CIRCULAR CYLINDER

ABSTRACT This paper describes the fully nonlinear free-surface deformations of initially calm water caused by water-entry and water-exit of a horizontal circular cylinder with both forced and free vertical motions. This has relevance for marine operations as well as for the ability to predict large amplitude motions of floating sea structures. A new numerical method called the CIP (Constrained Interpolation Profile) method is used to solve the problem. In this paper, the circular cylinder and free surface interaction is treated as a multiphase problem, which has liquid (water), gas (air) and solid (circular cylinder) phases. The flow is represented by one set of governing equations, which are solved numerically on a non-uniform, staggered Cartesian grid by a finite difference method. The free surface as well as the body boundary is immersed in the computational domain. The numerical results of the water entry and exit force, the free surface deformation and the vertical motion of the cylinder are compared with experimental results, and favorable agreement is obtained

Longitudinal stability augmentation of seaplanes in planing

The towing tank experiments conducted at Yokohama National University from November 30 to December 9 in 2005 suggested a new way of suppressing a dangerous coupled motion between heave and pitch called porpoising. The research in this paper was developed on the observations made in the experiments and conducted numerical simulations to further investigate the parametric design space. Two linear-time-invariant models were developed: rigid-body planing craft (conventional float planes or flying boats), and flexibly supported planing craft. The latter could simulate the new method found in the experiments for suppressing porpoising. In this study, the stability of the oscillatory motions was analyzed to see the effect of design variables on the inception of porpoising. The parametric study of flexibly supported float planes in the context of porpoising was a new contribution in the conceptual design of seaplanes

Slow Drift-Oscillations of a Ship in Irregular Waves

A procedure to calculate horizontal slow drift excitation forces on an infinitely long horizontal cylinder in irregular beam sea waves is presented. The hydrodynamic boundary-value problem is solved correctly to second order in wave amplitude. Results in the form of second order transfer functions are presented for different, two-dimensional shapes. It is concluded that Newman's approximative method is a practical way to calculate slow drift excitation forces on a ship in beam sea and it is suggested that it may be used in a more general case. Applications of the results for moored ships are discussed