Computer technology in America’s Cup Yacht Racing

1J. Craig Mudge ee380 Stanford University 2/19/2003

Computer technology in America’s Cup

Yacht Racing

Dr. J. Craig MudgePacific Challenge

ee380 Colloquium Computer Systems Laboratory

Stanford University Feb 19, 2003

www.pacific-challenge.com

6 legs in America’s Cup course

TimeMin: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:-

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

Defender vs Challenger Video clips of last couple of days racing - what to watch for

Elementary theory

Leeway angle

Aerodynamic forces from sails

hydrodynamic

Lift dragLift drag (or resistance)

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

Polar representations of boat speed

Radial representation of Boat speed at different true wind angles for one windspeed

(Adapted from 12 metre designed by S Killing)

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; photogrammaticComputational Fluid Dynamics (CFD)

Modeling, analysis, and visualization – sails, hulls, appendages

Two boat testing Data collection and data managementNavigation/tactics/ strategy

Performance parameters; predictions for next leg

Campaign Project/financial management, travel, web site

Weather Forecast wind patterns for each raceSports media Visualization of race course from telemetry

AcknowledgementsJim Antrim, naval architectRichard Burton, sailor and computer scientistMargot Gerritsen, Computational Fluid Dynamics (CFD) specialist, Stanford Yacht ResearchStan Honey, record-breaking navigatorOlivier Le Diouris, sailor and software engineerEric 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

Outline

Hull design- both canoe body and appendages

Sail designMaterials - hull and sailsTwo-boat tuningWinning races

Adding heeling/righting moments to two forces

Leeway angle

Aerodynamic forces from sails

hydrodynamic

Heeling Righting Lift DragLift Drag (or resistance)

AerodynamicHeelingmoment

Hydro-mechanicalRightingmoment

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)

Alternative to lead bulb for righting moment

Sydney Harbour 18 ft skiffs

More 18 ft skiffs from Sydney

A very influential design - on modern racing yachts - on latest Olympic class (49er)

Yendys 1924

Newer IACC boats are much narrower

Resistance components - upwindup

right Wave

(pushing the water)

Viscous(friction from wetted surface)

ed Added wavesInduced (from leeway)

Heel(extra viscous+wave)

(Fig 5.4, Larsson, 2000)

Appendages: side force and resistance

Side force (also called Lift)From both keel and rudder

Lift/drag tradeoffAspect ratioBulb shapeTurbulence

Tip vortices if depth is limited End wall not practical, so Winglets used

Winglets also provide lift when boat heeled

Surface pressure and Streamlines around bulb

From M Sawley (2002) at Switzerland’s EPFL, in Lausanne, an advisor to Alinghi

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

(Milgram, 1998)

Modeling boat speed - VPP

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

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 testing4. Then build one real thing5. Refine with two-boat testing

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.

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

Unveiling January 7, 2003 Alinghi

Oracle

Different winglet configurations and bulb shapes

Oracle

Alinghi

Team NZ

(based on photos at the unveiling 1/7/03)

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

Outline

Hull design

Sail designMaterialsTwo-boat tuningWinning races

Positioning and shapingCrew 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

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

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)

Apparent wind is the wind we feel on the boat, as opposed to the true wind.

Design of downwind sails

Wind tunnels in sail design University of Auckland Twisted Flow Wind Tunnel

Courtesy U Auckland,Seahorse magazine

Outline

Hull designSail design

Materials - hull, sails, and rigTwo-boat tuningWinning races

Ocean racers have to be stronger

Courtesy Richard Bennett

Forces on rig and hull

Prominent logo of sponsor

OneAustralia 1995

Older sail material

Courtesy: Mariners’ Museum

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)

Improved sail shape with modern materials

Novel designs

Lexcen keelOracle kiteCanting keel

Ben Lexcen’s winged keel 1983C

Oracle kite

Canting keel and canard

(Reichel-Puch, Dynayacht, 2002)

Wild Oats and Schock 40

Outline

Hull designSail designMaterials

Two-boat tuningWinning races

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;

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

A leg of a race selected for further analysis

Log of Wind Oscillations during a race

221º 299º

Two-boat tuning – Team NZ

Outline

Hull designSail designMaterialsTwo-boat tuning

Computer use in America’s Cup races

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

Currents Hauraki Gulf, NZ Feb 19

Time: 1400

Courtesy

David Brayshaw, GoFlow

Currents Hauraki Gulf, NZ Feb 19

Time: 1139Maximum ebb

Courtesy David Brayshaw, GoFlow

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)

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,

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

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

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.

■ Design shape flying shape

■ Square-rigged

■ Twist onset flow small

■ Extensive experimental data

280 ft

Maltese Falcon ideal test case

■ Prototype testing appealing

Stanford Yacht Research

(Gerritsen, Doyle, Perkins)

Kiwi clip on or hula

Contrast with panelled sails

Review: computer useArea Type

Design of hull Hydrodynamic modeling (to reduce drag)Hull appendages Hydrodynamic modeling (lift and drag)Design of sails Aerodynamic modeling; photogrammaticComputational Fluid Dynamics (CFD)

Modeling, analysis, and visualization – sails, hulls, appendages

Two boat testing Data collection and data managementNavigation/tactics/ strategy

Performance parameters; predictions for next leg

Campaign Project/financial management, travel, web site

Weather Forecast wind patterns for each raceSports media Visualization of race course from telemetry

Computer technology in America’s Cup Yacht Racing

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