Surface-piercing Bodies Research Articles

The acoustic radiation from a semisubmerged elastic cylinder

A large number of techniques have been developed to predict the acoustic radiation of totally immersed elastic structures, but they have not been applied to surface piercing bodies. The case of an infinite elastic cylinder, governed by Donnell's equations, is first considered, its axis lying on the pressure release surface. An analytic theory is derived, and applied to give the radiated field due to a point force excitation. The position of the excitation point with respect to the free surface is discussed as well as the differences between the partially loaded and the totally immersed cylinder. Then a numerical method based on finite elements and integral equations is presented and applied to the case of the partially immersed finite cylinder.

Effects of Waves on the Boundary Layer of a Surface-Piercing Body

The boundary-value problem for the boundary layer of a surface-piercing body is formulated in a rigorous manner in which proper consideration is given to the viscous-fluid free-surface boundary conditions. Simplifications that are appropriate for small-amplitude waves are investigated. To this end, order-of-magnitude estimates are derived for the flow field in the neighborhood of the body-boundary-layer/free-surface juncture. It is shown that, for laminar flow, the parameter Ak/ϵ, where Ak is the wave steepness and ϵ is the nondimensional boundary-layer thickness, is important for characterizing the flow. In particular, for Ak/ϵ sufficiently large such that the free-surface boundary conditions have a significant influence a consistent formulation requires the solution of higher-order viscous-flow equations. For turbulent flow, these conclusions cannot be reached with the same degree of certainty. Numerical results are presented for the model problem of a combination Stokes-wave/flat plate. For this initial investigation, the usual thin-boundary-layer equations were solved using a three-dimensional implicit finite-difference method. The calculations are for laminar and turbulent flow and both demonstrate and quantify the influence of waves on boundary-layer development. Calculations were made using both the small-amplitude-wave and more approximate free-surface boundary conditions. Both the external-flow pressure gradients and the free-surface boundary conditions are shown to have a significant influence. The former influence penetrates to a depth of about half the wavelength and the latter is confined to a region very close to the free surface.

Free-surface effects on the hydrodynamic coefficients of a laterally oscillating slender body at forward speed

In order to predict the manoeuvring motion of a surface-piercing body in waves, one needs to know the hydrodynamic forces acting upon the body. The present paper describes a method to calculate these hydrodynamic forces on a laterally oscillating sle

Uniqueness in linearized two-dimensional water-wave problems

A geometrical condition sufficient for uniqueness in two-dimensional time-periodic linear water-wave problems is derived, and some examples are given. The technique can be seen as a generalization of work by John (1950), who established uniqueness for surface-piercing bodies that have the property that vertical lines down from the free surface do not intersect the body.The paper is in two parts. Part 1 provides a review of current knowledge on the topic of uniqueness, and gives a simple form of John's proof. Part 2 describes the recent progress, in which the ideas of John's proof are extended so that uniqueness can be demonstrated for surface-piercing bodies that do not satisfy John's geometrical criterion. In fact the new technique proves uniqueness for a large class of problems involving floating bodies, submerged bodies and multiple-body systems. However, the present work still does not constitute a general proof of uniqueness for all configurations.

On the hydrodynamical source singularities for surface ships with special refference to Line Integral

The equivalent source singularities distributed over the hull are analysed based upon the exact linear free surface condition. The role of “Line Integral” on the Neumann-Kelvin problem is primarily studied, which since Brard's suggestion calls intensive discussions.The present analysis shows two kinds of solutions for Wigley model. One is for the surface piercing body. The other is for the limiting case of the submerged body. Comparing the both results the prominent contribution of the line integral term is clarified.1) “Line Integral” has a serious contribution on the determination of the source of the main hull just beneath the free surface.2) It brings the better prediction of the wavemaking resistance.3) “Line Integral” should be taken into account for mathematical consistency of the boundary value problem.

On Sway and Roll Motion of some Surface-piercing Bodies

On the sway and roll motion of some surface-piercing bodies of Lewis form section in free surface, two dimensional appropriate boundary value problems are solved by using the method derived from Gauss' variational principle. The results of numerical calculation are compared with Tasai's and Tamura's results.The same method are applied on deriving the formula to estimate the effect of a pair of bilge keel in sway and roll motion in non-viscous water.