Three-Dimensional Imaging of the High Sea-State Wave Field Encompassing Ship Slamming Events

Understanding and modeling ship wave slamming necessitates characterizing the surface wave field that results in slamming events. Shipboard measurements of the incoming wave field were made during sea trials of the twin-hull Sea Fighter (FSF-1), using a three-dimensional (3D), stereo-optic imaging system. The data obtained were processed using an image matching algorithm resulting in 3D video sequences of the incoming wave field at forward speeds of 16–40 kt in head seas at sea state 4. Six wave slamming events were captured, characterized, and compared to the average wave field properties. It was found that the salient properties of the individual waves that resulted in ship slamming occurred in groups of two or more, were approximately 30% larger than the significant wave heights during the ∼2-min period encompassing the slamming events, and had wave slopes at least 2 times that of the preceding wave slope. Additionally, wave slamming corresponded to large ship pitching motions resulting from the incident waveforms.

Application of a Two-Fluid Finite Volume Method to Ship Slamming

A newly developed finite volume method was applied to ship slamming. The computational method accounts for arbitrary free surface deformations and uses unstructured grids for the discretization of the domain. A linear panel method was used to predict motions of a modern 2400 TEU container ship. Resulting relative velocities at the ship’s Keel were used to estimate the maximum vertical re-entry velocities at the bow in North Atlantic wave conditions. Water entry of three bow in North Atlantic wave conditions. Water entry of three bow sections was numerically simulated to determine pressures at the bow flare. Prescribed vertical velocity histories significantly affected the determination of realistic pressure levels.

The Effect of Air Compressibility in a First Approximation to the Ship Slamming Problem

It has been suggested that the high pressures exerted on the bottom of a ship's hull during slamming are developed in the air trapped between the hull and the water's surface. To test this hypothesis, the two-dimensional, unsteady problem of the flow of air, where compressibility is accounted for, between a rigid, flat-bottomed block falling towards a rigid plane, is solved using a numerical method. The computed pressures exceeded those found experimentally by Maclean [8],2 and it is concluded that the deformation of the water's free surface must be accounted for in order to obtain agreement with the experiment. To the author's knowledge, the numerical method, a modified version of Sauer's method of Near Characteristics, is applied here for the first time, and a maximum allowable time step, for this problem, is found by digital computer experimentation.

Hydrodynamic Theories of Ship Slamming Review and Extension

A critical review and evaluation of existing hydrodynamic theories of body-water impact is presented. It is shown, partly by comparison with available experimental data, that fitting methods are adequate only for bodies of reasonably large deadrise angle during later stages of the impact process. The ellipse-fitting technique is extended to a much broader class of body forms and more accurate formulations of the general problem are proposed that avoid linearization of the free-surface boundary condition and can account for compressibility effects during the initial stage of impact, although numerical procedures must be employed.

The Analysis of Ship Structures Subjected to Slamming Loads

This paper describes the results of a fundamental study of various phases of the ship structural design problem, as affected by slamming-type loads. By a slamming load, we mean a suddenly applied impact-type load such as is introduced for example, by: (a) The pitching and heaving motions induced by waves, which in turn cause the ship's bow to emerge and then reenter the seaway at a relatively high velocity. Upon reentering the sea, suddenly applied impact-type loads may be applied to the ship hull. These cause a sudden change in acceleration, generally felt as a shudder (or series of shudders or vibrations) which introduces the slam loading. (b) Berthing or docking of ships. If, for any reason the berthing introduces heavy impact loads due to sudden contact between the ship hull and the fender-dock system then we have a response very similar to that described in (a). The study[1]2 was concerned with several different facets of the over-all slam problem. Among the topics considered (and reported upon herein) are 1) time effect in ship-slamming problems; 2) damping of slam oscillations; 3) model scaling requirements for slam phenomena; 4) an approximate method of analysis for ship hulls (in the elastic range) subjected to slam loads; 5) comparisons between the method 4) and other methods; 6) extension of 4) to the elastoplastic range.