SPLASH code in America’s
Cup Design Process
The AmericaOne design team relied heavily on computer simulation methodology throughout their International America’s Cup Class yacht design development process for America’s Cup XXX.
key ingredient in this effort was use of SPLASH, a free-surface potential flow panel code developed by Bruce Rosen, president of South Bay Simulations, Inc. of Babylon, NY. SPLASH code applications were performed by AmericaOne design team member Dr. Warren Davis, a computational fluids dynamics expert and associate of Rosen’s at Northrup Grumman in Bethpage, NY where they apply their knowledge of applied aerodynamics to the development of advanced military aircraft.
SPLASH calculation for candidate AmericaOne yacht design
SPLASH Code/South Bay Simulations, Inc.
SPLASH is a sophisticated flow simulation package capable of reliably computing pressure distributions and resultant forces around a variety of hull and appendage geometries, including keels, flaps, bulbs, winglets, and rudders. Automated modeling routines generate high fidelity panelizations of all the surfaces, including the free-surfaces waves. The code’s non-linear sinkage, trim and free-surface shape iteration routines are unique and essential elements of the package that contribute to the accuracy of the converged results. Lift, induced drag (drag due to lift) and wavemaking drag (drag associated with the energy in the free-surface waves created) forces are calculated for each specified speed, heel and yaw condition, along with roll and yaw moments plus final sinkage and trim of the hull. Being a potential flow SPLASH can not model the viscous (friction) drag directly, but its non-linear capabilities provide reliable wetted surface areas and pressure distributions which provide strong basis for enhanced accuracy in calculating the viscous drag components. SPLASH-generated hull with free surface waves geometries were utilized to perform full 3-d Navier-Stokes (includes viscous boundary layer effects) analyses to better study the subtler effects of hull shaping on total drag and performance.
SPLASH also has unsteady performance modeling capabilities which were used to predict and compare motions and added resistance in waves of various appended hull models. Complete six degree-of-freedom motions capabilities were utilized for arbitrary incident wave lengths and headings with specified speeds, heel, yaw, flap and rudder angles. Both steady and unsteady SPLASH simulations were used to evaluate and improve hull designs in the AmericaOne design effort.
The AmericaOne design team was able to establish electronic file transfer protocols to virtually automate the numerical model testing and performance analysis process. Designs moved directly from the designers’ 3-d surface modeling software to SPLASH for hydrodynamic analysis, with those results passed to a hydro surface fitting program for input into the final VPP (Velocity Prediction Program) where equilibrium with the sail aero forces is computed to complete the performance simulation process on the total configuration. In this manner, SPLASH was used as a numerical towing tank to provide hydrodynamic data for each design, thus supplementing the traditional tow tank testing of scale models (which is time-consuming and expensive) and focusing the fewer required number of tests towards only the most promising performers. Over the course of the campaign, numerous designs were quickly and efficiently analyzed using SPLASH and evaluated using the VPP for trends in performance and guidance in the development of final candidate designs. Dr. Davis was able to deliver complete SPLASH results, containing100-200 test points (where each test point is a distinct setting of forward speed and heel, yaw, flap and rudder angles - mimicking actual tow tank tests) within 24 hours of receipt of a new design geometry file – a small fraction of the time and cost required to perform a tank test. These results formed a cornerstone of the AmericaOne hull design development program and illustrate how computer simulations are currently being used in yacht design to accelerate and enhance the developmental process.