Enhanced Wind Tunnel and Full-Scale Sail Force Comparison

2007 ◽  
Author(s):  
Heikki Hansen ◽  
Peter J. Richards ◽  
Peter S. Jackson
Keyword(s):  
Wind Tunnel ◽  
Quantitative Agreement ◽  
Full Scale ◽  
Force Balance ◽  
Testing Procedures ◽  
Prediction Program ◽  
Surface Pressure Distribution ◽  
Velocity Prediction ◽  
The University ◽  
Scale Data

This paper presents a comparison between wind tunnel and full-scale aerodynamic sail force measurements using enhanced wind tunnel testing techniques to model the full-scale sailing conditions more accurately. The first comparison was conducted by Hansen et al., 2003a, in the Twisted Flow Wind Tunnel (TFWT) at The University of Auckland and followed standard testing procedures. Since then enhancements have been made and two aspects not considered in the original comparison are highlighted here. The interaction of the hull and sail forces is now considered and trim changes of the sails due to wind strength are included. For the enhanced comparison the interaction between the hull/deck and the sails is investigated by installing a secondary force balance inside the model to measure the hull/deck forces and by pressure tapping the hull/deck to determine the surface pressure distribution. It is found that the presence of the sails significantly affects the forces on hull/deck when sailing upwind, which should be accounted for consistently in comparisons of full-scale, wind tunnel, and computational fluid dynamics (CFD) data. In the original comparison the sails were trimmed in the wind tunnel to the aerodynamically optimal shape by maximizing the drive force. Trim variations due to wind strength were however noted in full-scale data so that depowering is considered in the enhanced comparison. The sails in the wind tunnel were trimmed based on the fullscale wind strength and the yacht performance by employing a Real-Time Velocity Prediction Program (VPP) to achieve realistically depowered sail shapes. Utilising the enhanced wind tunnel techniques a generally good qualitative and quantitative agreement with the full-scale data was achieved, but a conclusive judgment of the accuracy of the comparison cannot be made.

An Improved Upwind Sail Model For VPP's

2001 ◽  
Author(s):  
Peter Jackson
Keyword(s):  
Wind Tunnel ◽  
Full Scale ◽  
Original Solution ◽  
Wide Range ◽  
Velocity Prediction ◽  
Improved Model ◽  
Heeling Moment

In velocity prediction programs for yachts the problem of modelling sail forces is greatly complicated by the fact that the sail shapes are not fixed. For a given sail plan, alterations in sail trim produce a wide range of combinations of lift, drag and heeling moment. While the original solution to this problem using the well-known parameters flat and reef has been very successful, it has some obvious defects. In particular, it does not correctly model the practice of twisting a sail to reduce heeling moment. This paper therefore sets out an improved model which satisfies the essential requirements for upwind sails; namely that the model is based upon fundamental aerodynamic principles, allows all the unknowns to be determined from tests (full scale or wind tunnel) and permits the best sail trim to be selected for optimization of performance. The essential new step is to introduce a new trim parameter twist which correctly accounts for the practice of allowing the head of a sail to twist off in order to reduce heeling moment.

PCSAIL, A Velocity Prediction Program for a Home Computer

2001 ◽  
Author(s):  
David E. Martin ◽  
Robert F. Beck
Keyword(s):  
Design Stage ◽  
Rapid Evaluation ◽  
University Of Michigan ◽  
Prediction Program ◽  
Other Information ◽  
Velocity Prediction ◽  
Turn Around Time ◽  
Excel Solver ◽  
The University ◽  
Boat Speed

An Excel Velocity Prediction Program has been developed to allow for rapid evaluation of yacht performance at the initial design stage. The required input consists of only the basic hull and sail dimensions. Empirical equations, based on these basic dimensions, are used for initial estimates of required hull parameters. As the design progresses the user can easily replace these default values with refined estimates or actual values. Because of its simplicity, and short turn around time, the program has been used as a teaching aid at the University of Michigan. Reconstruction of the program, PCSAIL, may be made with equations and other information provided in the Appendix. The Excel "Solver" has been found to be a reliable means of finding the equilibrium boat speed and heel angle. It seeks the maximum boat speed by adjusting the sail flattening factor, F, and reef, R, and the lateral location of the "movable crew." In the case of a hinged centerboard, or dagger- board, it will also adjust the draft for maximum boat speed. For sloop rigs the program will also take in the jib and set the spinnaker, at the appropriate wind angle, in order to gain maximum boat speed. The program plots the speed "polar," and velocity made-good, and determines the tacking angles.

Hull - Appendage Interaction of a Sailing Yacht, Investigated with Wave Cut Techniques

1997 ◽  
Author(s):  
Jonathan R. Binns ◽  
Kim Klaka ◽  
Andrew Dovell
Keyword(s):  
Approximate Method ◽  
Wave Pattern ◽  
Wave Resistance ◽  
Full Scale ◽  
Research Centre ◽  
Cooperative Research ◽  
Prediction Program ◽  
Velocity Prediction ◽  
Sailing Yacht

The research explained in this paper was carried out to investigate the effects of hull-appendage interaction on the resistance of a sailing yacht, and the effects these changes have on the velocity prediction for a sailing yacht. To accomplish this aim a series of wave-cut experiments was carried out and analysed using a modified procedure. The processed results have then been incorporated into an existing velocity prediction program. For the purposes of this research two variables were investigated for the Australian Maritime Engineering Cooperative Research Centre (AMECRC) parent model 004, a model derived from the Delft IMS series of yachts. Wave-cut procedures inevitably raise questions about scaling procedures for full scale extrapolation as the inviscid wave-pattern resistance is calculated to be less than the residuary or wave resistance. These questions have been dealt with by an approximate method, briefly explained in this paper.

The Nippon Challenge America's Cup 1992 - Progress in Hull Development

1993 ◽  
Author(s):  
Yoshihiro Nagami
Keyword(s):  
Full Scale ◽  
Wind Tunnel Testing ◽  
Design Development ◽  
Prediction Program ◽  
New Class ◽  
Simulation Techniques ◽  
Final Design ◽  
Velocity Prediction ◽  
America’S Cup ◽  
Fine Tune

In 1992, the class rule for the America's Cup was changed to the IACC. The Nippon Challenge decided that in order to build a successful challenger to a new class rule, the design would have to rely heavily on the results of a systematic series of tank and wind tunnel testing. The results of these simulations would then be used to build full scale boats which would be tested. The results of the full scale trials would be used to adjust the simulation techniques to fine tune the final design. The data from the model tests were used to develop the input parameters for a Velocity Prediction Program (VPP). The VPP was used to determine the specifications for the design of the first two boats. After full scale testing, the VPP was compared to the results for about 6 months. After this verification and refinement of the VPP, a final boat was built. Finally the results of the race were evaluated and confirm that the basic design development process was correct.

Changes to Sail Aerodynamics in the IMS Rule

2003 ◽  
Author(s):  
Jim Teeters ◽  
Robert Ranzenbach ◽  
Martyn Prince
Keyword(s):  
Wind Tunnel ◽  
Reverse Engineering ◽  
Measurement System ◽  
Wind Tunnel Test ◽  
Prediction Program ◽  
Aerodynamic Model ◽  
Velocity Prediction ◽  
International Measurement

US Sailing, the Offshore Racing Council (ORC), the Glenn L. Martin Wind Tunnel (GLMWT), Quantum Sail Design Group (QSDG), the Wolfson Unit and North Sails have collaborated on a series of wind tunnel test programs to investigate the performance of both upwind and offwind sails. These programs were initiated in response to perceived inequities in the ratings of boats of various rig designs sailing under the International Measurement System (IMS). Observations of on-the-water performance have lead to the conclusion that there are biases within the rule with respect to rig planform design. Specifically, it has been concluded that large spinnakers are penalized so that a fractional rig, with its small spinnaker, is favored when sailing offwind, that there are un-rated benefits to a masthead rig upwind, and that there are errors in the relative handicapping of overlapping and non-overlapping jibs. The IMS Rule uses a Velocity Prediction Program (VPP) in which sail forces are represented by algorithms that are based on a combination of science and reverse engineering from the measured sailing performance of real boats. The results of investigations at both GLMWT and Wolfson have been used to modify this IMS aerodynamic model, thereby reducing the pre-existing biases.

A Velocity Prediction Program for a Planning Dinghy

2005 ◽  
Author(s):  
Todd Carrico
Keyword(s):  
Hydrodynamic Resistance ◽  
Side Force ◽  
Prediction Program ◽  
Fundamental Goal ◽  
Velocity Prediction ◽  
Sailing Yacht ◽  
Series Of Experiments ◽  
College Of Engineering ◽  
The University ◽  
Visual Basic 6.0

This paper summarizes the author’s graduate thesis in Naval Architecture accepted by the University of New Orleans, College of Engineering. The author sought to investigate the complicated interactions between the hydrodynamics and aerodynamics of a sailboat. The type of sailboat investigated was the Olympic dinghy class called the Laser. It was the author’s understanding that at that time, no work has been completed in the area of velocity prediction for this type of sailboat. Thus, the fundamental goal of this thesis was to develop a velocity prediction program specific to the Laser. In order to accomplish the goal of creating a velocity prediction program, multiple essential pieces of the data were needed. In particular, the hydrodynamic resistance data, aerodynamic drive and side force data, and hydrodynamic side forces were needed. To determine the dynamic trim of the dinghy, a series of experiments were conducted. In addition, a data acquisition system was developed in which full scale tow testing could be done. Next, a complete tow test series was conducted for the Laser. The aerodynamic sail coefficients were derived from Marchaj’s Aero-Hydrodynamics of Sailing. To determine the hydrodynamic side force, a two dimensional approach was employed. The coding of the velocity prediction program was done using Microsoft’s Visual Basic 6.0 and Excel 2000. The algorithms published in the 15th Chesapeake Sailing Yacht Symposium and Principles of Yacht Design pertaining to velocity prediction were used as a baseline. Finally, validation and verification was performed with the shareware program PCSAIL.

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