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.

Scoring IMS Regattas - An Empirical Study of Alternative Methods

1995 ◽  
Author(s):  
John W. Cane
Keyword(s):  
Empirical Study ◽  
Measurement System ◽  
Alternative Methods ◽  
Prediction Program ◽  
Data Points ◽  
Velocity Prediction ◽  
International Measurement

The International Measurement System (IMS) uses a computerized velocity prediction program (VPP) to calculate the performance of a meas­ured hull and rig in winds from six to twenty knots, at any sailing angle. A regatta is scored by comparing a yacht's performance with pre­dictions of the VPP. The winner is the yacht whose performance, relative to its VPP predic­tions, is the best, compared to all other yachts in its class or division. This paper discusses different methods of malc­ing the comparison and accounting for various factors in the race such as wind shifts and cur­rent on the course. Decisions made by race man­agers and/or developers of scoring programs can significantly impact results. Illustrative examples show the effects that these decisions can have. In 1994 the number of data points available for use in scoring yachts in custom courses doubled. Alternative ways of using these data are illus­trated by application to a sample regatta.

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.

Aerodynamic Performance of Offwind Sails Attached to Sprits

2001 ◽  
Author(s):  
Robert Ranzenbach ◽  
Jim Teeters
Keyword(s):  
Aerodynamic Performance ◽  
Performance Potential ◽  
Prediction Program ◽  
Aerodynamic Modeling ◽  
Specific Goal ◽  
Velocity Prediction ◽  
Size Type ◽  
Improved Performance ◽  
Pole Configuration ◽  
International Measurement

The primary purpose of this offwind sail investigation was to better understand the relative performance of symmetric spinnakers flown from conventional poles and asymmetric spinnakers flown from conventional poles or sprits, i.e. poles restricted to the centerline. The specific goal was to improve the aerodynamic modeling of offwind sails used in the International Measurement System (IMS) handicapping formula to address perceived inequities in their performance potential, particularly when running at very deep angles. Running style offwind sails of varying size, type, and pole configuration were evaluated over appropriate ranges of angle of attack and trim settings. Improved performance coefficients were developed from this data for inclusion into the 2001 IMS velocity prediction program.

Videogrammetry of the Model’s Attitude in Wind Tunnel Testing

2012 ◽  
Vol 190-191 ◽  
pp. 1273-1277 ◽  
Author(s):  
Zheng Yu Zhang ◽  
Zhong Xiang Sun ◽  
Xu Hui Huang ◽  
Yan Sun
Keyword(s):  
Standard Deviation ◽  
Wind Tunnel ◽  
Drag Coefficient ◽  
Systematic Error ◽  
Measurement System ◽  
High Speed ◽  
Wind Tunnel Test ◽  
Wind Tunnel Testing ◽  
Supersonic Wind Tunnel ◽  
Tunnel Testing

The advanced precision of drag coefficient is 0.0001 for the high speed wind tunnel test of measuring forces, the model’s angle of attack precision is ≤0.01°following errors distribution. A videogrammetric method of model’s attitude is therefore proposed, its uncertainty is investigated, and a compensation method of its systematic error is also presented by this paper. The three engineering videogrammetric experiments of attack angle in 2 meter supersonic wind tunnel testing have demonstrated that measuring standard deviation of videogrammetric measurement system established by this paper is ≤0.0094°, in addition it neither destroys the model’s shape, nor changes the stiffness or strength, so it is useful and effective.

Analysis of Hull Shape Effects on Hydrodynamic Drag in Offshore Handicap Racing Rules

2003 ◽  
Author(s):  
Jim Teeters ◽  
Rob Pallard ◽  
Caroline Muselet
Keyword(s):  
Measurement System ◽  
Research Program ◽  
Hydrodynamic Drag ◽  
Joint Research ◽  
Fundamental Parameters ◽  
Calm Water ◽  
Shape Effects ◽  
Velocity Prediction ◽  
Joint Research Program ◽  
International Measurement

US Sailing and the Institute for Marine Dynamics (IMD) in St. John’s, Newfoundland, are collaborating in a joint research program to investigate the effects of hull shape variations on hydrodynamic drag. The results of this program are being used to support the development of rules that handicap racing yachts. A fleet of 9 models has been designed with systematic variations in the most fundamental parameters: displacement and beam for fixed length. Six of those models have been tested both appended and bare-hull, in calm water and head seas. Analysis of residuary resistance, both upright and heeled, has been used to improve the Velocity Prediction Programs (VPPs) employed by both the International Measurement System (IMS) and AMERICAP rules.

Test Technique Research for the Hinge Moment of a Grid Fin in High Speed Wind Tunnel

2014 ◽  
Vol 574 ◽  
pp. 480-484
Author(s):  
Jian Zhong Chen ◽  
Pei Qing Liu
Keyword(s):  
Control System ◽  
Wind Tunnel ◽  
Measurement System ◽  
High Speed ◽  
Wind Tunnel Test ◽  
Test Technique ◽  
Grid Fin ◽  
Fin Design ◽  
Development Center ◽  
Model Support

In order to study the test technique for the hinge moment of a grid fin in wind tunnel, a platform based on half model support technique was established in FL-23 and FL-31 wind tunnel in China Aerodynamics Research & Development Center (CARDC). The platform developed a wind tunnel test balance, rudder control system and the aerodynamics measurement system. This test technique was important to optimize aerodynamic configurations of a grid fin, design or evaluate the capability of the rudder control system. Nomenclature

Developments in the IMS VPP Formulations

1999 ◽  
Author(s):  
Andrew Claughton
Keyword(s):  
Aerodynamic Force ◽  
Wind Tunnel Test ◽  
Force Model ◽  
Added Resistance ◽  
Detailed Model ◽  
Prediction Program ◽  
Construction Methods ◽  
Force Modeling ◽  
Velocity Prediction ◽  
Lift And Drag

The paper describes the improvements made to the aerodynamic and hydrodynamic force models of the Offshore Racing Council (ORC) International Measurement System (IMS) sailing yacht velocity prediction program (VPP) since 1990. The paper explains the mechanisms of the force modeling used in the IMS VPP to provide a framework within which the modifications and revisions to the VPP are described. The major revisions fall into three categories. 1) The hydrodynamic model, where a revised formulation for residuary resistance and characteristic length has been introduced, which includes modifications to both the residuary and viscous resistance components. Revisions to the drag due to heel and induced drag formulations are described that more accurately reflect the behavior observed from towing tank tests. 2) The added resistance in waves module was introduced to assist with the equitable handicapping of diverse bull types and construction methods, which affect the behavior of sailing yachts in waves. The mechanism by which the sea state is charaterised and the added resistance calculated is described. 3) The aerodynamic force model, which derives complete rig lift and drag coefficients from standard sail types is described. The behavior of the VPP force model is compared with wind tunnel test results, and the recent additions of coefficient sets for a range of different sail types is described. Finally the components of a more detailed model of hull and rig windage are outlined.

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