Americas Cup Building Structural Design

Going faster - Cat sailors seek perfection

The aim is to be able to fly a hull in six to eight knots true wind with the sailor on trapeze. As pressure builds up to 15 knots, the sail is progressively flattened. Then the aeroelastic characteristics of the rig automatically depower it in response to gusts. Officially races are called off if the sustained wind speed exceeds 22 knots, though in flat water the boats might race in up to 25. Traditionally the variables were section shape and volume distribution (prismatic coefficient, rocker profile, deadrise angle and LCG). With the advent of curved foils, new variables are dynamic hull lift and lift contributed by the foils. The aim is now to strike a balance between lift induced drag and hull drag. Key is quantifying the induced drag ‘price’ of dynamic lift and comparing it to the drag of a minimum resistance hull with zero lift. Since the boats sail with some heel there is also a vertical component (down) from the rig. In heavy airs this can be significant and resisting it through reserve buoyancy or dynamic lift allows the boat to be pushed harder. The answer appears to be semiplaning hulls. The new boats no longer seek minimal cross-sectional area but instead have significant flat area in the sections from amidships to the transom. Sterns have been growing wider with a trend to moving the centre of gravity aft, together with the mast and the main crossbeam. Following the trend for inward-angled boards where the entire foil gave a vertical component at the price of more surface interference, curved centreboards (constant curvature or ‘C’) are becoming the norm. The lower part of the foil now contributes lift with a significant vertical component. With ‘C’ foils, horizontal lift can only be had with the foil fully down. The DNA design from Holland is extremely popular and seems to be achieving great results in the hands of skippers of varying skill levels. It uses very ‘U’ shaped sections with the LCB aft, wide transoms and significant planing area combined with curved asymmetric section boards which can be adjusted on the beach for rake, using a locating plate screwed in place at the top of the case. The DNA’s full sections also seem to be more tolerant of a wider range of crew weights.

Italian Boat Designer ABstructures Extends Usage of HyperWorks

ABstructures has been using the HyperWorks suite since its foundation in 2008. The company initially employed OptiStruct, from the HyperWorks suite for topology optimization, along with HyperMesh, the HyperWorks meshing tool. In December 2010, the company extended its use of HyperWorks to RADIOSS, the product suite’s solver, to its development process for the analysis of the behavior of composite materials. Altair’s new agreement with ABstructures includes the rental of 20.000 Grid Works Units (GWUs) for 2011, providing the company with access to every product of the suite, including the use of HyperWorks Partner Alliance (HWPA) products at no additional costs. In the past, ABstructures applied the HyperWorks suite in the design of the winning Volvo Ocean Race yacht Ericsson 4 as well as the Ericsson 3 yacht. ABstructures is now using HyperWorks to design and optimize three yachts for the forthcoming Volvo Ocean Race and is structurally designing for Artemis Racing, which will participate in the next America’s Cup in 2013 in San Francisco. To design and optimize the carbon structures of the yachts, ABstructures is using HyperWorks together with other computer-aided engineering (CAE) tools to simulate composites and fluid-structure interactions. ABstructures has achieved fundamental structural improvements of all the yachts it has designed, compared to older-generation yachts. The combination of cutting-edge CAE technology and the extensive hands-on experience of ABstructures’ designers, as well as the close collaboration with Altair Engineering, have enabled the company to deliver the best design for lightweight structural projects. “I began using HyperWorks in 2003 and have never stopped using it since then,” said Dr. Fabio Bressan, ABstructures. “When I first started to use HyperWorks, I was especially fond of its open platform and the ability to use it with any other available CAE or computer-aided design software. We also like the software suite because it enables us to handle most of the development tasks in structural design within one user interface and because it helps us to easily and quickly understand the challenges of our designs.” “It immediately gives us the answers we need and therefore helps us drive new ideas and innovation,” adds Dr. Andrea Avaldi, ABstructures.

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