J. Craig Mudge ee380 Stanford University 2/19/2003 1 Computer technology in America’s Cup Yacht Racing Dr. J. Craig Mudge Pacific Challenge ee380 Colloquium.
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1J. Craig Mudge ee380 Stanford University 2/19/2003
Computer technology in America’s Cup
Yacht Racing
Dr. J. Craig Mudge
Pacific Challenge
ee380 Colloquium
Computer Systems Laboratory
Stanford University
Feb 19, 2003www.pacific-challenge.com
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6 legs in America’s Cup course
Time
Min:sec
Delta in
seconds
Start 0
1 26:11 12
2 24:14 -34
3 26:37 -26
4 22:43 -14
5 27:33 -26
finish 25:43 7
Alinghi Race 2:-
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How a sailboat moves ahead
• Downwind– Push on sails
• Upwind – Lift from sails– Lift from keel
• Context – Changes in wind strength and direction– Changes in wave shape, direction, and frequency
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Defender vs Challenger
Video clips of last couple of days racing - what to watch for
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Elementary theory
Leeway angle
Aerodynamic forces from sails
hydrodynamic
Lift dragLift drag (or resistance)
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Tacking up wind
The boat that sails at an angle “closer to the wind”gets upwind faster
Wind directionZig-zagging up wind towards our destination
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Polar representations of boat speed
20
5
10
Radial representation of Boat speed at different true wind angles for one windspeed
(Adapted from 12 metre designed by S Killing)
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A list of computer usesArea Type
Design of hull Hydrodynamic modeling (to reduce drag)
Hull appendages Hydrodynamic modeling (lift and drag)
Design of sails Aerodynamic modeling; photogrammatic
Computational Fluid Dynamics (CFD)
Modeling, analysis, and visualization – sails, hulls, appendages
Two boat testing Data collection and data management
Navigation/tactics/ strategy
Performance parameters; predictions for next leg
Campaign Project/financial management, travel, web site
Weather Forecast wind patterns for each race
Sports media Visualization of race course from telemetry
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AcknowledgementsJim Antrim, naval architect
Richard Burton, sailor and computer scientist
Margot Gerritsen, Computational Fluid Dynamics (CFD) specialist, Stanford Yacht Research
Stan Honey, record-breaking navigator
Olivier Le Diouris, sailor and software engineer
Eric Steinberg, electronics on America True Brian Tramontana, PARC multimedia
* ESPN for video clips* americascup.yahoo.com for photos* Virtual Spectator for screenshots of race course
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Outline
Hull design- both canoe body and appendages
Sail design
Materials - hull and sails
Two-boat tuning
Winning races
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Adding heeling/righting moments to two forces
Leeway angle
Aerodynamic forces from sails
hydrodynamic
Heeling Righting Lift DragLift Drag (or resistance)
AerodynamicHeelingmoment
Hydro-mechanicalRightingmoment
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Lateral stability
Heeling moment from sails
Lead ballast is placed in the lower portion of the keel.
Extreme ballast from bulb (20 tons of a 24 ton IACC boat)
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Alternative to lead bulb for righting moment
Sydney Harbour 18 ft skiffs
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More 18 ft skiffs from Sydney
A very influential design - on modern racing yachts - on latest Olympic class (49er)
Yendys 1924
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Newer IACC boats are much narrower
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Resistance components - upwindup
right Wave
(pushing the water)
Viscous(friction from wetted surface)
heel
ed Added wavesInduced (from leeway)
Heel(extra viscous+wave)
(Fig 5.4, Larsson, 2000)
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Appendages: side force and resistance
Side force (also called Lift)From both keel and rudder
Lift/drag tradeoffAspect ratio
Bulb shape
Turbulence
Tip vortices if depth is limited
End wall not practical, so Winglets used
Winglets also provide lift when boat heeled
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Surface pressure and Streamlines around bulb
From M Sawley (2002) at Switzerland’s EPFL, in Lausanne, an advisor to Alinghi
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An overview of numerical modeling in yacht design
• Fundamental tool is a predictor of performance to compare different designs – Called a VPP (Velocity Prediction Program) -- since early 70s – Given a wind speed and wind angle, a VPP predicts boat
speed, heel, and leeway
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(Milgram, 1998)
Modeling boat speed - VPP
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An overview of numerical modeling in yacht design
• Fundamental tool is a predictor of performance to compare different designs – Called a VPP (Velocity Prediction Program) -- since early
70s – Given a wind speed and wind angle, a VPP predicts boat
speed, heel, and leeway• The balance equations are solved
– Keel lift and side force– Sails lift and drag– Overturning moment
• Modeling these forces in the balance equations is (currently) approximate – Navier Stokes equations (set of differential equations governing the
motion of a fluid) are central part – Models are combination of empirically based and approx of N-S equations
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Overall Hull Design process
1. Decide range of wind strength, sea state
2. Coarse exploration of shapes by numerical modeling, incl CFD
3. Then tank testing
4. Then build one real thing
5. Refine with two-boat testing
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An overview of numerical modeling in yacht design …contd.
Computational Fluid Dynamics (CFD)
RANS (Reynolds-Averaged Navier-Stokes) is a more computationally tractable form of the N-S equations.
In RANS, the flow variables are split into one time-averaged (mean) part, and one turbulent part. The mean values are solved. And the turbulent part is expressed in terms of the mean part.
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An overview of numerical modeling in yacht design …contd.
SGI Origin 3800 128 MIPS R14000 Pc (500Mhz; 64 GB RAM)
Swiss T1 64 DEC Alpha ev6 Pc (500 Mhz; 32GB RAM)
Dell Precision 530 2 Pentium Xeon Pc (1.7 GHz, 2GB RAM)
Largest RANS simulations: 5 million mesh cells: 10 hours on 16 Pc
c.f. AC2000 campaign: 2 million mesh cells: 10 hours on 12 Pc Origin 2000
Typical computer resources are these at EPFL, Lausanne
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Unveiling January 7, 2003 Alinghi
Oracle
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Different winglet configurations and bulb shapes
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Different winglet configurations and bulb shapes
Oracle
Alinghi
Team NZ
(based on photos at the unveiling 1/7/03)
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Universities working in yacht design• University of Auckland• Technical University of Berlin• Chalmers University of Technology• Kiel University• EPFL, Lausanne, Switzerland• MIT• University of Maryland• University of Michigan• University of Southampton• Stanford Yacht Research• Center for Turbulence Research, Stanford
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Outline
Hull design
Sail designMaterials
Two-boat tuning
Winning races
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Positioning and shaping
Crew positions the sails according to required angle of attack
- from polars
Sailors shape the sail using control lines attached to the edge of a sail
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What is the right shape?• Sailmaker designs each sail for a range of
wind strength and wave type. (Sailor selects a sail from the suite, according to expected conditions.)
• Want nice laminar flow, without separation and turbulence
• Lift vs drag curve; polars again
• Both wind tunnels and CFD used
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Vertical characteristics of wind
As we go from deck to top of mast, the wind increases in strength and apparent direction
Has implications for both sail designers and sailors (sail trimming)
8
7
5
Apparent wind is the wind we feel on the boat, as opposed to the true wind.
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Design of downwind sails
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Wind tunnels in sail design University of Auckland Twisted Flow Wind Tunnel
Courtesy U Auckland,Seahorse magazine
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Outline
Hull design
Sail design
Materials - hull, sails, and rigTwo-boat tuning
Winning races
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Ocean racers have to be stronger
Courtesy Richard Bennett
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Forces on rig and hull
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Prominent logo of sponsor
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OneAustralia 1995
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Older sail material
Courtesy: Mariners’ Museum
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Materials and shapingFlax Cotton Japara silk various polyesters (with or without film) (Kevlar is the best known of the aramid fibers) Carbon
Desired 3D shape in CAD model
Panel shape Mold shape
Sew panels Apply layers (liquid/fiber)
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Improved sail shape with modern materials
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Novel designs
Lexcen keel
Oracle kite
Canting keel
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Ben Lexcen’s winged keel 1983C
ourt
esy:
R
osen
feld
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Oracle kite
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Canting keel and canard
(Reichel-Puch, Dynayacht, 2002)
Wild Oats and Schock 40
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Outline
Hull design
Sail design
Materials
Two-boat tuningWinning races
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Why two-boat tuning
• Shortcomings of numerical modeling and tank testing
• Sensors not accurate enough– A two boat lead at end of a 3 mile leg
requires boat speed 0.7% accuracy; – Accuracy on wind direction, strength also
difficult hard to get accuracy;
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Instruments and data logging on J/105 Kookaburra
Data from instruments:- Wind speed (true and apparent); Boat position; Heading; Boat speed (through water and over the ground); Etc etc
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A leg of a race selected for further analysis
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Log of Wind Oscillations during a race
221º 299º
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Two-boat tuning – Team NZ
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Outline
Hull design
Sail design
Materials
Two-boat tuning
Computer use in America’s Cup races
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Performance
• Performance is a function of– Preparation before the race– Start– Boatspeed
• Design of hull and appendages• Design of sails • Boat handling by crew• Strategy• Tactics• Helmsman’s skill
– Navigation
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Currents Hauraki Gulf, NZ Feb 19
Time: 1400
Courtesy
David Brayshaw, GoFlow
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Currents Hauraki Gulf, NZ Feb 19
Time: 1139Maximum ebb
Courtesy David Brayshaw, GoFlow
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The start
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The start
Display of computed parameterstime to starttime to line tack+acceleration+ travel time (for boat speed, index into polars)
This nice result is helped by accurately estimating time to the starting line (Alinghi Race 3)
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On each legDisplay
time to next marktime in each tack remainingtime to layline
target boat speedetc
Predict next leg- given assumptions on wind
and mark, use polars to display:-course, wind angles,
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Topics not covered
• Effect of mast on flow past mainsail
• Trim tabs on aft end of keel• Heads-up display in navigator’s sunglasses • Modeling interaction of hull and sails
• Modeling of currents
• Analysis of materials and structure of hulls
• Techniques in rig design and analysis
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BibliographyJoubert, P N. and Oosannen van, P. The Development of the Winged Keel for
Twelve Metre Yachts, Rev. 1986.Killing, Steve.Yacht Design Explained, Norton, New York, 1998.Larsson, L and Eliasson, R. Principles of Yacht Design, 2nd ed. International Marine,
Camden, 2000.Milgram, Jerome H. Fluid Mechanics for Sailing Vessel Design, Annual Review of
Fluid Mechanics, 1998 30:613-653.Marchaj, C A. Sail Performance. International Marine, London, 1996.Sawley, M L. Numerical Flow Simulation for the America’s Cup. EPFL
Newsletter,2002.Whidden, Tom. The art and science of sails, St. Martins Press, New York,1990.
• Email mudge@pacific-challenge.com for a copy of this bibliography
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High performance yachts in the future
1. Materials– Surfaces
• Low drag (MEMS?)• Vortex generators (a la Formula 1 cars) – also slots, porosity
2. Control of sail shape– Auto-adjust (but without stored energy)
3. Rig and masts4. Better numerical modeling
– Downwind sail design– Sail shape optimization, including design in unsteady
conditions (waves, …)– Coupling of accurate CFD to structural analysis– Hull-sail interaction
Some possibilities
Rules will have to change in some cases.
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■ Design shape flying shape
■ Square-rigged
■ Twist onset flow small
■ Extensive experimental data
280 ft
160ft
65ft
Maltese Falcon ideal test case
■ Prototype testing appealing
Stanford Yacht Research
(Gerritsen, Doyle, Perkins)
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Kiwi clip on or hula
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3DL
Contrast with panelled sails
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Review: computer useArea Type
Design of hull Hydrodynamic modeling (to reduce drag)
Hull appendages Hydrodynamic modeling (lift and drag)
Design of sails Aerodynamic modeling; photogrammatic
Computational Fluid Dynamics (CFD)
Modeling, analysis, and visualization – sails, hulls, appendages
Two boat testing Data collection and data management
Navigation/tactics/ strategy
Performance parameters; predictions for next leg
Campaign Project/financial management, travel, web site
Weather Forecast wind patterns for each race
Sports media Visualization of race course from telemetry
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