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Author : Karsten Hochkirch
Results 1 - 5 of 13
Maneuver Simulation and Optimization for AC50 Class
The stability and the dynamic behaviour is an integral part of designing hydrofoil supported sailing vessels, such as the America’s Cup (AC) 50 class. The foil design and the control systems have an important influence on the performance and stability of the vessel. Both foil and control system design also drive the maneuverability of the vessel and determine maneuvering procedures. The AC50 class requirements lead to complex foil control systems and the maneuvering procedures become sophisticated and multifaceted. Sailing and maintaining AC50 class yachts is a complex, expensive and time-consuming task. A dynamic velocity prediction program (DVPP) for the AC50 is therefore developed to assess the dynamic stability of different foil configurations and to simulate and optimize maneuvers. The goal is to evaluate certain design ideas and maneuvering procedures with this simulator so that sailing time on the water can be saved. The paper describes the principal concepts of developing a AC50 model in the DVPP FS-Equilibrium. The force components acting on the yacht are defined based on physical principles, computational fluid dynamics (CFD) simulations and experimental investigations. The control systems for adjusting the aero- and hydrodynamic surfaces are modelled. Controllers are utilized to simulate the human behaviour of performing sailing tasks. Maneuvers are then defined as sequences of crew actions and crew behaviours. In the paper examples of utilising the DVPP in preparation for the 35th America’s Cup in Bermuda are described. The DVPP is for example used to investigate the effect of different boat set-ups on stability and handling during maneuvers. With the sailing team, maneuver procedures are developed and tested. Procedures such as dagger board and rudder elevator movement and crew position are investigated and evaluated to minimize the distance lost during tacking and gybing. The DVPP is also employed for trajectory optimization during maneuvers.
Numerical Simulations of a Surface Piercing A-Class Catamaran Hydrofoil and Comparison against Model Tests
Hydrofoil supported sailing vessels gained more and
more importance within the last years. Due to new
processes of manufacturing it is possible to build slender
section foils with low drag coefficients and heave stable
hydrofoil geometries are becoming possible to construct.
These surface piercing foils often tend to ventilate and
undergo cavitation at high speeds. The aim of this work is
to define a setup to calculate the hydrodynamic forces on
such foils with a RANS based CFD method and to
investigate whether the onset of ventilation and cavitation
can be predicted with sufficient accuracy...
Performance Assessment and Optimization of a C-Class Catamaran Hydrofoil Configuration
Recent breakthroughs in the America's Cup have put hydrofoil technology in the focus of high-performance sailing. This paper describes the performance assessment of two different centreboard hydrofoils designed for a C-class catamaran. Regarding the numerous design criteria resulting from sailing on hydrofoils, a reliable performance assessment tool helps to find the best compromise [1]. A Velocity Prediction Program (VPP) has been developed in order to facilitate the analysis of numerical simulation results obtained for appendages and the wing-sail in terms of speed potential of the C-Cat. The approach used to model the hydroand aerodynamic forces on the catamaran is described, along with the challenges peculiar to a VPP model for sailing on hydrofoils. Different optimization schemes for trimming the wing-sail and hydrofoil configurations are tested to obtain the theoretically most efficient trim settings and to evaluate the different hydrofoil designs. Using the developed VPP model, realistic velocity prediction can be carried out. The catamaran flying on hydrofoils sails at up to 2.8 times the true wind speed in many conditions. Records and observations made during the International C Class Cup (ICCC) of 2013 confirm the predicted performance of the modelled C-Cat. Some remaining challenges in velocity prediction of vessels equipped with hydrofoils are highlighted.
Conceptual ideas on a double surface sail inflated by dynamic pressure
This paper presents conceptual ideas on an unconventional sailing system. It is designed in principle and compared in terms of performance with two established sailing systems. The concept is a double surface sail, which is to be inflated by the dynamic pressure at the leading edge of the profile. The fundamental principle is the same as used by paragliders and kites, where openings at the leading edge of the wing allow the air to “fill” the profile to give it a beneficial aerodynamic shape. For the analysis of the
structural mechanics of the sail system qualitative model tests in a wind tunnel are conducted. A profile segment is exposed to different angles of attack and the trim mechanism of mast rotation is varied. The resulting profile shapes and the profiles of the comparative sail types are then analysed to determine their characteristics by conducting 2D flow simulations. Also the effects of mast rotation to change the profile characteristics of camber and thickness are reviewed. The double surface sail showed a good-natured behaviour at a wide range of angles of attack and a competitive performance potential compared to conventional sail sections and a wing sail section.
Analysis of Wave Making Resistance And Optimization of Canting Keel Bulbs
In upwind sailing conditions, bulbs of canting keel
sailboats operate close to the water surface and therefore
induce non-negligible changes in the wave system, thus
influencing the wave making resistance of a sailboat. The
bulb could produce relatively positive as well as negative
effects, and therefore its design is suitable for optimization.
A case study for a modern 100-foot canting keel
sailboat is presented. The design space was explored to
determine the bulb shape that would produce favorable
interference with the hull wave system, reducing the total
resistance of the sailboat for an upwind sailing condition,
using the Response Surface Optimization (RSO)
methodology developed by the authors. In the 1,000 bulb
variations that were performed using an advanced
parametric modeler, the volume and location of the center
of gravity of the bulb were fixed so that the stability of the
sailboat was not altered and, therefore, the computed total
resistance became a direct measure of merit of the bulb
design.
An outlook is given to a combined optimization of
hull and bulb in order to gain optimum improvement.