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Keyword : planing
Results 1 - 5 of 10
Moderate-Cost Approaches for Hydrodynamic Testing of High Performance Sailing Vessels
This study examines the relative merits of physical testing techniques which may be used in early stage design for assessment of the resistance of high-performance sailing vessels. The hull chosen as a benchmark form is a high-speed hard-chine sailing dinghy. The hull proportions and shape are typical of modern trends in skiff design, but may also be considered to be broadly similar to some high performance yacht hulls. The 4.55m hull was tested at full scale in a moderate size towing tank, at 1:2.5 scale in the same tank, and at full-scale by towing on open water.
Modern racing yacht semi-planing hull forms provide a number of complex challenges for designers and other professionals involved in yacht rating. The SYRF Wide Light Project was initiated as a means of (1) providing data with which to assess a range of alternative computation methodologies to analyse sailing yacht hydrodynamic forces and moments, (2) making this data available to the entire sailing yacht research community and (3) demonstrating how this type of study can be used to inform the rating process. This paper presents a comprehensive set of tank test results in both canoe body only and appended configurations to be used as a benchmark for a defined geometry of a modern semi-planing hull. Five different CFD stakeholders carried out ‘blind’ CFD analysis on the same test matrix using a range of different computational codes and approaches. The results are presented here along with feedback detailing the software, methods and resources used to generate the results. This project offers a comprehensive set of public domain data which researchers may use to validate and develop their numerical tools as well as highlighting how successfully commercial CFD codes may be used to confidently predict the variation of the forces on a sailing yacht hull as speed, heel and leeway change. Finally, discussion will be made on how this first phase of the project may be used to inform handicap rule makers
The angle formed by ship wakes is usually found close to the value predicted by Kelvin, α=19.47°. However we recently showed that the angle of maximum wave amplitude can be significantly smaller at large Froude number. We show how the finite range of wavenumbers excited by the ship explains the observed decrease of the wake angle as 1/Fr for Fr>0.5, where Fr=U/(gL)^0.5 is the Froude number based on the hull length L. At such large Froude numbers, sailing boats are in the planing regime, and a decrease of the wave drag is observed. We discuss in this paper the possible connection between the decrease of the wake angle and the decrease of the wave drag at large Froude number.
The performance of racing yachts has increased significantly over the past 10-15 years without significant changes to the prediction methods used in the early stages of the design. Tank testing or CFD-simulation are not always an option and especially in the early stages of design a requirement for reliable numerical methods exists...
On the choice of CFD codes in the design process of planing sailing yachts
The discussion is based on results gathered during the first two years of a 3 years research program for the benefits of Groupe Finot-Conq, Naval Architects. The introduction presents the objectives of the program: Setting up a practical method using numerical and experimental available tools to design fast planing sailing yachts. The aim of this paper is to compare advantages and disadvantages of four different kinds of CFD codes which are linear and non-linear potential flow approach, RANSE solver using finite differences method and RANSE solver using volume of fluid method. The Fluid Mechanics Laboratory of the Ecole Centrale de Nantes (France) has developed those three approaches so those homemade codes will be used for this study. The first one is REVA, a potential flow code with a linearised free surface condition. ICARE is a RANSE solver using finite differences method with a non linear free surface condition. It is extensively used for industrial projects as for sailing yachts projects (ACC for example). ISIS-CFD is a RANSE solver using finite volume method to build the spatial discretization of the transport equations with unstructured mesh. The latter is able to compute sprays for fast planing ships but is also the slower in terms of CPU time. In addition, we had the opportunity to test FS-FLOW which is a potential flow code with a non linear free surface condition distributed by FRIENDSHIP CONSULTING. Numerical results for the four codes are compared with the other codes' results as with tank tests data. Those tank tests were made using captive model test technique on two Open60' models. Reasons of the choice of the captive model technique are explained and experimental procedures are briefly described. Comparisons between codes are mainly based on the easiness of use, the cost in CPU time and the confidence we can have in the results as a function of the boat speed. Flow visualizations, pressure maps, free surface deformation are shown and compared. Analysis of local quantities integrated or by zone is also presented. Results are analyzed focusing on the ability of each code to represent flow dynamics for every speed with a special attention to high speeds.The practical question raised is to know which kind of answers each code can bring in terms of tendencies evaluation or sensitivity to hull geometry modifications. The main goal is to be able to judge if those codes are able to make reliable and consistent comparisons of different designs. Conclusion is that none of the codes is perfect and gather all the advantages. It is still difficult to propose a definitive methodology to estimate hydrodynamic performances at every speed and at every stage of the design process. Knowing each code limitations, it appears more coherent to use each of them at different stages of the design process: the quickest and less reliable to understand the main tendencies and the longest and more precise to validate the final options.
