Modeling IACC Sail Forces by Combining Measurements with CFD

1993 ◽  
Author(s):  
Jerome H. Milgram ◽  
Donald B. Peters ◽  
D. Noah Eckhouse
Keyword(s):  
Scale Model ◽  
Force Model ◽  
Actual Performance ◽  
Force Coefficients ◽  
Prediction Program ◽  
Induced Drag ◽  
Load Cells ◽  
Velocity Prediction ◽  
America’S Cup ◽  
Parasitic Components

A sailing dynamometer with a 42% scale model of an International America's Cup Class rig is used to measure sail forces and moments in actual sailing conditions. The sailing dynamometer is a 35-foot boat containing an internal frame connected to the hull by six load cells configured to measure all the forces and moments between the frame and the hull. All sailing rig components are attached to the frame, so that the sail forces are measured. Sail shapes in use are determined by computer-interfaced video. Computational fluid dynamics performed on the measured shapes provides the induced drag. This allows the measured drag to be decomposed into induced and form-and-parasitic components, which is necessary for generating a mathematical sail force model for a velocity prediction program (VPP). It is shown that VPP results using these new sail force coefficients are in better agreement with actual performance than are VPP results based on traditional sail force coefficients.

Schooner Brilliant Sail Coefficients and Speed Polars

2001 ◽  
Author(s):  
Howard Grant ◽  
Walter Stubner ◽  
Walter Alwang ◽  
Charles Henry ◽  
John Baird ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Wind Pressure ◽  
Scale Model ◽  
Experimental Program ◽  
Side Force ◽  
Prediction Program ◽  
Wind Speeds ◽  
Velocity Prediction ◽  
Horizontal Side ◽  
Study Performance

The sail coefficients for a schooner rig, as a function of wind angle and heel angle, are presented, based on an experimental program, for historic vessel research, at Mystic Seaport, using the 61'6" schooner Brilliant. The coefficients were determined by full-scale sailing tests and 9- scale model tow-tank tests. Sail coefficients CR and Cttare defined as the drive force and horizontal side force , due to the sails, rigging, and hull above the waterline, per unit of sail area, per unit of wind pressure. These coefficients can be used to study performance of historic schooner­rigged vessels, predict performance of new designs, and compare performance of schooners and sloops. Sail coefficients for sloops have long been available. A velocity prediction program for the schooner was also developed. The predicted and actual ship speeds agree, with standard deviation of0.028 in the ratio. Upwind sail coefficients for the schooner are found to be lower than for historic sloops, and display the expected droop with heel. The schooner velocity made good upwind is largest with the sail plan of four lowers plus fisherman staysail. The schooner and sloop both point higher as wind increases. The sloop outpoints the schooner at all wind speeds, by about 10°. On a beam reach or broad reach, schooner speed is largest with the sail plan of big jib, golliwobbler, and mainsail. This sail plan also produces the largest downwind velocity made good. The polars suggest that the schooner has the advantage over the sloop on a beam reach.

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.

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.

The Application of VPPs to Practical Sailing Problems

1987 ◽  
Author(s):  
Kart L. Kirkman
Keyword(s):  
Prediction Program ◽  
Widespread Acceptance ◽  
Velocity Prediction ◽  
Do So

The velocity prediction program, VPP, appeared on the yachting scene about ten years ago and it now dominates design and sailing. Originally implemented as a handicapping tool under the Measurement Handicap System, now accepted internationally as IMS, it has seen widespread acceptance for many other uses, from design to tuning and racing. This capability means that it is productive, even necessary, for the typical sailor interested in good performance to understand how to apply a VPP to his activities. To do so requires an appreciation of how a VPP functions and how it is applied to practical sailing problems, such as sail selection or tactics. The paper presents a review of VPP fundamentals and then treats the following applications: - Sail selection and strategy for offshore yachts. - Tuning and optimization of all boats. It is the goal of the paper to impart a working understand­ing of the VPP to many sailors so that they can take advantage of the technology in their normal activities.

Added Resistance in Seaways and its Impact on Yacht Performance

2007 ◽  
Author(s):  
Kai Graf ◽  
Marcus Pelz ◽  
Volker Bertram ◽  
H. Söding
Keyword(s):  
Strong Impact ◽  
Wave Spectra ◽  
Linear Extensions ◽  
Added Resistance ◽  
Optimum Length ◽  
Prediction Program ◽  
Strip Theory ◽  
Velocity Prediction ◽  
Added Resistance In Waves ◽  
Response Amplitude Operators

A method for the prediction of seakeeping behaviour of sailing yachts has been developed. It is based on linear strip theory with some non-linear extensions. The method is capable to take into account heeling and yawing yacht hulls, yacht appendages and sails. The yacht's response amplitude operators (RAO) and added resistance in waves can be predicted for harmonic waves as well as for natural wave spectra. The method is used to study added resistance in seaways for ACC-V5 yachts of varying beam. Results are used for further VPP investigations. The AVPP velocity prediction program is used to study optimum length to beam ratio of the yachts depending on wind velocity and upwind to downwind weighting. This investigation is carried out for flat water conditions as well as for two typical wave spectra. The results show that taking into account added resistance in seaways has a strong impact on predicted performance of the yacht.

scholarly journals Rowing VPP(Velocity Prediction Program)

2003 ◽  
Vol 2003 (194) ◽  
pp. 67-73
Author(s):  
Hiroshi Kobayashi ◽  
Takeshi Kinoshita
Keyword(s):  
Prediction Program ◽  
Velocity Prediction

scholarly journals High Froude Number Experimental Investigation of the 2 DOF Behavior of a Multihull Float in Head Waves

2021 ◽  
Vol 6 (01) ◽  
pp. 1-20
Author(s):  
Paul Kerdraon ◽  
Boris Horel ◽  
Patrick Bot ◽  
Adrien Letourneur ◽  
David David Le Touzé
Keyword(s):  
High Performance ◽  
Good Representation ◽  
Prediction Program ◽  
Modeling Approach ◽  
Head Waves ◽  
Wide Range ◽  
Dynamic Velocity ◽  
Velocity Prediction ◽  
High Froude Number ◽  
Stability Issues

Dynamic Velocity Prediction Programs are taking an increasingly prominent role in high performance yacht design, as they allow to deal with seakeeping abilities and stability issues. Their validation is however often neglected for lack of time and data. This paper presents an experimental campaign carried out in the towing tank of the Ecole Centrale de Nantes, France, to validate the hull modeling in use in a previously presented Dynamic Velocity Prediction Program. Even though with foils, hulls are less frequently immersed, a reliable hull modeling is necessary to properly simulate the critical transient phases such as touchdowns and takeoffs. The model is a multihull float with a waterline length of 2.5 m. Measurements were made in head waves in both captive and semi-captive conditions (free to heave and pitch), with the model towed at constant yaw and speed. To get as close as possible to real sailing conditions, experiments were made at both zero and non-zero leeway angles, sweeping a wide range of speed values, with Froude numbers up to 1.2. Both linear and nonlinear wave conditions were studied in order to test the limits of the modeling approach, with wave steepness reaching up to 7% in captive conditions and 3.5% in semi-captive ones. The paper presents the design and methodology of the experiments, as well as comparisons of measured loads and motions with simulations. Loads are shown to be consistent, with a good representation of the sustained non-linearities. Pitch and heave motions depict an encouraging correlation which confirms that the modeling approach is valid.

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.

Relative Performance of Conventional Versus Movable-Ballast Racing Yachts

2005 ◽  
Author(s):  
Frank DeBord ◽  
Harry Dunning
Keyword(s):  
Physical Model ◽  
Morning Glory ◽  
Cfd Analysis ◽  
Design Issues ◽  
Design Features ◽  
Prediction Program ◽  
The Past ◽  
Trade Offs ◽  
Physical Model Tests ◽  
Velocity Prediction

Over the past few years several advanced concepts have gained wider acceptance from owners of large racing yachts and organizers of major international events. Two of these concepts, water ballast and canting keels, were evaluated during the design of the maxZ86 yachts Pyewacket and Morning Glory. This paper presents the key design features of these large movable ballast racing yachts and compares their performance to conventional racing yachts of similar size. Comparisons include results of physical model tests, CFD analysis using a panel code, velocity prediction program modeling, and sailing data from the existing boats. These results are accompanied by physical explanations of the differences, and the special testing and analysis requirements for the movable-ballast configurations are detailed. Finally, some of the design issues unique to the movable-ballast concepts and design trade-offs are discussed.

Upwind Sail Performance Prediction for a VPP including “Flying Shape” Analysis

2009 ◽  
Author(s):  
Brian Maskew ◽  
Frank DeBord
Keyword(s):  
Grid Point ◽  
Flow Simulation ◽  
Lattice Method ◽  
Prediction Program ◽  
Aerodynamic Pressure ◽  
Dynamic Velocity ◽  
Velocity Prediction ◽  
Coupled Structures ◽  
And Performance ◽  
Ultimate Objective

A coupled aerodynamic/structures approach is presented for predicting the flying shape and performance of yacht sails in upwind conditions. The method is incorporated in a flow simulation computer program, and is part of an ultimate objective for a simultaneous aeroelastic/hydro analysis in a Dynamic Velocity Prediction Program (DVPP), that will include a 6DOF motion solver, and at some point could include calculations in waves. The time-stepping aerodynamic module uses an advanced vortex lattice method for the sails and a panel method with special base separation treatment to represent the abovewater part of the hull and mast. A coupled inverse boundary layer analysis is applied on all surfaces including both sides of each sail membrane; this computes the skinfriction drag and the source displacement effects of the boundary layers and wakes, including bubble and leeside “trailing-edge” type separations. . At each step, the computed aerodynamic pressure and skin-friction loads are transferred to a coupled structures module that uses a network grid of tension “cords” in each sail membrane, each cord representing a collection of fiber “strings”. The solution of a structural equilibrium matrix provides the displacements needed to achieve balance between the aerodynamic and tension loads at each grid point as the shape iterations proceed. Details of the methodology used are presented and comparisons of predicted aerodynamic forces to wind tunnel results and an existing VPP sail model are provided. In addition, predictions are compared to some simple experiments to demonstrate the aerodynamic/structural coupling necessary to predict flying shape. Finally, an outline is given for incorporation of this methodology into the planned Dynamic Velocity Prediction Program.

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