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Keyword : appendages
Results 1 - 5 of 19
Racing Yacht Appendages Optimisation Using Fluid-Structure Interactions
GSEA Design developed a fluid structure method (FSI) suitable for early design stage of appendage with complex shapes dedicated to the America’s Cup flying catamarans. The aerodynamic loading and the boat weight are counteracted by the appendages and mainly the dagger- board. Consequently, the appendage structural design is very critical. Based on a 3D lifting line and a modified beam element method, the GSEA Design FSI method takes less than one minute to compute. An illustrating example on a L-shape appendage shows that the FSI results compared to a non-FSI results can be particularly different at the elbow. Thanks to the short computational time of the method, multi-objective optimizations can be performed. For instance, a second illustrating example shows the optimization of the appendage weight and stiffness.
Exploratory Study on the Flutter Behavior of Modern Yacht Keels and Appendages
As a result of the tremendous increase in the speed of racing yachts over the last 2 decades, keel flutter has appeared as a
major technical issue for designers to address. Recently the IMOCA class rewrote its keel scantling rules, in part to address this issue.
Flutter occurs when different natural frequencies of a lifting surface (wing, keel, rudder, hydrofoil etc.) combine together causing a
coupling in the motion that draws energy from the surrounding fluid. The vibration or motion is self-excited and its amplitude grows
quickly, leading to dangerous and sometimes catastrophic outcomes.
In the field of aeroelasticity, flutter is a well-known instability phenomenon. Flutter is a synchronized vibration which takes place in a flexible structure moving through a fluid medium. It occurs when two regular, rhythmic motions coincide in such a way that one feeds the other, drawing additional energy from surrounding flow. A classic case of wing flutter might combine wing bending with either wing twisting. Flutter appeared for the first time on racing yacht keels with composite fins, so in water, in 2004, on both the IMOCA 60 POUJOULAT-ARMORLUX, which lost her keel, and SILL. Following these problems - particularly following the loss of the keel of Bernard STAMM sailboat, accident that could have dramatic consequences for the skipper - HDS company focused on the phenomenon. This paper will introduce the strategy of HDS faced to the problem and the analytical and numerical methods implemented to estimate the flutter critical speed. Our model is based on a truncated modal basis for the most energetic modes which are generally, for a bulb keel, the lateral bending predominant mode and the torsion predominant mode. One of our requirements was to make a simple model in order to integrate the calculation of the flutter critical speed in the first design loops of a composite or steel keel. Besides, an other requirement was to be able to calculate flutter critical speed on other type of appendages: hydrofoils, dagerfoils, daggerboards, rudders...This model has worked well for the two cases of flutter appeared on IMOCA sailboat keels. Besides, to verify the quality of the model and to complete our analysis of flutter phenomenon on racing yacht keels, a 3 dimensional multiphysic simulation has been developed using the software ADINA.
In this paper, a dynamic computation of the Groupama 3 foil is performed. Foils are thin profiles, placed under the hull of a ship, allowing it to provide a lifting force. This study is placed in the context of the 2013 America’s Cup, which will see the appearance of a new kind of high performance multihull. At high speeds, the foils are subject to intense hydrodynamic forces and to movement due to the sea state. The deformations are then sizable and there is a risk of ventilation, cavitation or vibration which could lead to a large modification of the hydrodynamic forces or to the destruction of the foil. The foil being light compared to the added mass effect, the interaction is a strongly coupled problem. In this paper, the problem is solved using a segregated approach. The main problems resulting of such a method are the numerical stability and remeshing. These problems are detailed and some results presented. As a first test case, the simulation of a vortex excited elastic plate proposed by Hubner is presented. This case is very demanding in terms of coupling stability and mesh deformation. Then, the foil of Groupama 3 is modeled in a simplified form without hull and free surface, and then in a more realistic conditions with free surface and waves.
The IMOCA 60 Class has a complicated set of appendages: with canted and tilted keels, cambered daggerboards that can be designed to be fitted to the hull in different orientations along with toed-in and twin rudders that can also be configured in different orientations. Curved dagger-boards and straight boards with positive lift inducing dihedral angles have been used in number of recent IMOCA 60 designs and in other classes, principally multi-hulls. These were considered an option by the client for their new Open 60 design and so a research and development programme was instigated by Owen Clarke Design to compare new curved designs with conventional straight daggerboards optimised for upwind conditions. It was felt that the modelling of the trim of the yacht was very important to the calculation and sharing of loads between all of the appendages, and so our group chose to use a combination of one third scale high speed towing tanks tests and computational fluid dynamics (CFD), rather than CFD alone to investigate the relative performance between these dagger-board types.