Hydroelastic behaviour of a sailing yacht in waves

Louarn, Frédéric (1999) Hydroelastic behaviour of a sailing yacht in waves. University of Southampton, Doctoral Thesis.

Abstract

The dynamic behaviour of a racing yacht (Whitbread 60) is investigated using three dimensional hydroelasticity theory. This is a new approach to the structural analysis of such craft as well as a new field of application for hydroelasticity theory.

Global structural responses (e.g. stresses) in waves are obtained corresponding to the upright as well as to the more realistic heeled sailing configurations, revealing the connection between the ballast keel and the hull as being a critical area of the structure.

For the 'dry hull' analysis, a global finite element model is developed, incorporating the hull and deck shell, the internal structure, the ballast keel and the rig together with rigging loads. The modular nature of the model is used in order to assess the relative influence of each of the aforementioned components upon the required characteristic dynamic properties (e.g. natural frequencies and principal mode shapes).

Regarding the 'wet hull' analysis, a three dimensional Green's function technique, using pulsating sources distributed over the wetted surface, provides a numerical solution to the case of the yacht sailing in regular waves, at arbitrary heading. Principal coordinates for the rigid body motions and flexible distortions of interest are evaluated and the latter are used to obtain the dynamic stresses in waves based on a modal summation.

The applicability and limitations of hydroelasticity theory regarding this type of structures are discussed in the light of the results obtained for the upright and heeled operational conditions, as well as from the point of view of design aspects such as "L" and "T" keel configurations.

Commonly used quasi-static structural design criteria provided by the American Bureau of Shipping (A.B.S) Guide are compared with the results obtained from the dynamic analysis.

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