Two-dimensional water waves in the presence of a freely floating body: conditions for the absence of trapped modes

TL;DR

This paper analyzes the conditions under which water waves in a two-dimensional setting with a floating body do not form trapped modes, establishing bounds on frequencies that depend on the body's properties.

Contribution

It provides a theoretical framework showing that trapped water wave modes cannot exist above certain frequencies related to the floating body's characteristics.

Findings

Finite total energy of water motion established

Equipartition of energy demonstrated for the coupled system

No trapped modes exist above a frequency bound depending on the body's properties

Abstract

The coupled motion is investigated for a mechanical system consisting of water and a body freely floating in it. Water occupies either a half-space or a layer of constant depth into which an infinitely long surface-piercing cylinder is immersed, thus allowing us to study two-dimensional modes. Under the assumption that the motion is of small amplitude near equilibrium, a linear setting is applicable and for the time-harmonic oscillations it reduces to a spectral problem with the frequency of oscillations as the spectral parameter. It is essential that one of the problem's relations is linear with respect to the parameter, whereas two others are quadratic with respect to it. Within this framework, it is shown that the total energy of the water motion is finite and the equipartition of energy holds for the whole system. On this basis, it is proved that no wave modes can be trapped provided their frequencies exceed a bound depending on cylinder's properties, whereas its geometry is subject to some restrictions and, in some cases, certain restrictions are imposed on the type of mode.