Trans RINA, Vol 153, Part B2, Intl J Small Craft Tech, 2011 Jul-Dec


C++ Server. It is fully parallelized using a domain decomposition approach and the SPMD (Single Program Multiple Data) approach to run


on a network of


individual machines. MPI (Message Passing Interface) is used as the underlying messaging and synchronization mechanism.


At YRU-Kiel Star-CCM+ runs on a 98-node Linux cluster. However, for a typical run only 48 processors have


been available for this study. For the study


presented here, a typical computational grid consists of approx. 2 million hexahedral grid cells. A typical run time for an individual run (one optimal boat speed for a specific TWA and TWS combination) on 48 processors is approx. 8 h to achieve an imbalance of body forces of less than 10 N.


Ideal turnaround times for a complete investigation would be around 24 hours. However, to the authors’ knowledge no RANSE based viscous CFD code is currently able to deliver such a through put. Typical times for appended hull testing in the context of big sailing sport


campaigns like Volvo Ocean Race or


America’s Cup are about 1 week per geometry either in numerical or experimental towing tank.


Taking into account 24/7 capabilities of a compute cluster, running a test matrix for both upwind and downwind


polar lines for 5 TWS would require


approximately 230 cluster nodes to get the results within a week. If only max VMG upwind and downwind is of interest, and one is willing to judge the results by comparing only 3 TWS, the results can be available in about 40 hours using the same numbers of computational nodes.


5. BENCHMARK DESIGN


For the following investigation a generic benchmark design has been created. Choice fell on a GP26 level class racer because this design is based on a box rule which makes the choices of principal dimensions; sail plan etc. much easier. Another reason for this choice is that


this boat type can be regarded as modern but


conventional, meaning that it has no canting keel, wing mast or something alike. This makes it easier to compare the results with VPP data gained by using hydrodynamic data from a regression of systematic hull variations.


The lines plan of the GP26 design is shown in Figure 4. The authors are not claiming to have come up with a particular good design, the design being just a basis for testing of the method.


Calculation of centre of gravity and mass moment of inertia have been carried out using estimations of the weight of keel, bulb, rig, accommodation and panel weight of the canoe body along with specifications of the class rule. The resulting principal dimensions and boat characteristics are shown in Table 1. Here the weight of


the boat reflects not the measurement weight but the sailing weight including crew and spare sails.


Figure 4: Lines plan of the GP26 design


Table 1: Principal dimensions and boat characteristics


Table 2 shows the characteristics of the sail plan for upwind and downwind sail set. The rig has an adjustable backstay, but no checkstay, the main sail has full battens and the asymmetric spinnaker is tacked on centreline. These rig characteristics are reflected in the aerodynamic coefficients of the sails.


6. SETUP


Starting point of the setup is the yacht in its initial sailing trim including crew and effects according to Table 1. This corresponds to a displacement of 1485.2kg and a CG of (3.609m, 0.0m,-0.181m) measured from aft and at height of DWL.


The geometry is blocked with a hexahedral volume grid. The grid consists of a body fitted O-Grid around yacht and appendages which then eradiates in the far field.


B-88 ©2011: The Royal Institution of Naval Architect


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