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FREE MOTION SIMULATION OF A SAILING YACHT IN UP-WIND

CONDITION WITH ROUGH SEA

1STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10

STAR European Conference 2010London, 22-23 March

G. Lombardi, M. Maganzi, A. Mariotti

Dept. of Aerospace Engineering of PisaItaly

America’s Cup

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THE OLDEST SPORT EVENT IN THE WORLD

IT REPRESENTS THE TOP LEVEL IN SAILING RACES

• SAILORS

• TEAM ORGANIZATION• TECHNOLOGIES

• DESIGN

RESEARCH and DEVELOPMENT“To fully develop and promote

a green revolution on theAmerica's Cup Competition.

Driven by Science and i-Technology”

High impact

Cooperation with•University of California, Los Angeles

•Politecnico Turin

• University of Pisa

Fluid Dynamics In Yacth Design

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GREEN COMM Challenge planned both experimental and numerical approaches, but the design will be driven

essentially by CFD

In Yacht Design Fluid Dynamics assumes a crucial role

For CFD analysis different levels are foreseen:

• Analysis on the sails in reference conditions• Analysis on the hull in reference conditions• Optimisation procedures for several geometrical elements

These aspects are well established from previous analyses on different problems (boats, airplanes, cars),

BUT:

THE PROBLEM

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These analysis are carried out on simplified configurations and

in reference conditions.

From the design point of view, itis particularly important the

evaluation of the performance in

off-design conditions.

Interest to set-up a CFD procedure for the performance evaluation of

• COMPLETE configurations

• in GENERIC sea conditions

STAR CCM+ has the capability to evaluate the motion of the complete boat with rough sea

SOFTWARE

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CAD GEOMETRY

Surface GRID

Volume GRID

and CFD

CATIA V5 R19

ANSA 13.0.2

STAR CCM+

v4.04.011

HARDWARE

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Linux cluster: 16 SUN Fire X4100.

Each server: 2 AMD Opteron 285 (Dual Core) processors and 4GB RAM each

(64 processes)

The GEOMETRY

STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10

America’s Cup v5 yacht (2007), in up-wind condition.

mainsail

bulb

helm

hull

jib

wing

mast

SURFACE GRID

8

Base size for hull and sails 0.15 m Base size for domain external surfaces 1.20 m Total surface elements ≈ 200000

Skewness<0.5.

STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10

COARSE GRID

9

Trimmed volume grid with prism layers around the sails

Grid refinement at the free surface in order to have a correctedrepresentation of the wave profile.

VOLUME GRID

22-03-10 STAR EUROPEAN CONFERENCE – G. Lombardi et Al.

Computational domain: Lenght 100 mWidth 100 m“air” height 70 m“water” height 20 m

Number of cells in the prism layer 5 Height of the prism layer 0.15 m Total volume elements ≈ 16 Mil.

Free Surface Refinement

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Refinement for pitchmotion

Refinement for rollmotion

PHYSICAL MODEL

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3D unsteady

k-ε standard turbulence model

Wave model (VOF Waves)

6 degrees of freedom rigid body motion (6 DOF Motion)

WAVE MODEL (VOF Waves)

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Volume of Fluid Waves Model, with two phases (Multiphase Mixture).

The sea wave dynamics is represented by the 5° order Stokes theory.

The following characteristics are assigned:

Wave height, H

Wave period, T

Sea depth, d

Direction and velociy of the sea tide, cE

H

dcE

VOF WAVES set-up

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The corresponding Wave Lenght results l=21.7 m

• Wave direction 35° from the hull simmetry plane

• Wave height 0.8 m

• Wave period 3.7 s

• Sea depth 100 m

• Sea Tide 0

6 DOF Motion set-up

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THE MOTION OF THE BODY IS EVALUATED AS A FUNCTION OF THE AERODYNAMICS FORCES ON THE SAILS AND THE HYDRODYNAMICS FORCES ON THE IMMERSED HULL, EVALUATED AT EACH TIME STEP, TAKING INTO ACCOUNT THE INERTIAL CHARACTERISTICS.

Total mass, C.G. position and Inertial Moments are assigned

5 D.O.F.:• x, y, z translations• Roll• Pitch

The yawn rotation is kept fixed to take into account the control carried out by the wheelsman

EVALUATION EXAMPLE

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• Wind speed 10 m/s

• Wind direction 35° from the hull simmetry plane

TRANSIENT PHASE:Time Step 0.025 sIterations per Step 15Total Time 5 s

ANALYSED PHASE:

Time Step 0.025 sIterations per Step 15Total Time 20 s

RESULTS - the BOAT MOTION

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COMPUTATIONAL TIME

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TOTAL TIME FOR THE PRESENTED SIMULATION:

1 Month !!

Despite the coarse grid, the computational time is very high

TO OBTAIN ACCURATE RESULTS IN REASONABLE TIME IT IS NECESSARY TO HAVE A VERY LARGE COMPUTING CLUSTER

RESULTS

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A large amount of data is obtained by the evaluation

Information are available on:

• Boat speed

• Boat motion

• Aerodynamics behaviour of the sails

• Hydrodinamics behaviour of any element of the hull

• Correlation between different data. Ex.:

• boat speed and roll angle

• boat speed and pitch angle

• pitch rate and lift on the sails

• ………EXAMPLES

Boat Speed

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Boat Heel

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Speed – Heel correlation

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Poor correlation appears

Hull Drag

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Speed – Hull Drag correlation

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More evident correlation appears (with phase angle)

SAILS THRUST

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The Thrust is mainly from the jib

There is a phase angle between mainsail and jib thrusts

SAIL FLOW REPRESENTATION

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SAIL FLOW REPRESENTATION

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FLOW DETAILS….

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Vorticity Field on the deck

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CONCLUSIONS

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• The motion of the boat is evaluated as a function of the aerodynamics forces on the sails and the hydrodynamics forces on the immersed hull, taking into account the inertial characteristics.

• Rough sea is considered

• The case setting in STAR CCM+ did not shown particularly problems

• The results appear congruent with the real behaviour of the yacht

• The accuracy could be increased with a larger computational domain and a refined grid

• Despite the coarse grid, the computational time is very high

• To obtain accurate results in reasonable time it appears necessaryto have a very large computing cluster

ACKNOWLEDGEMENTS

Thanks are due to A. Ciampa and E. Mazzoni (INFN of Pisa) to

render the computing system very efficient and easy to use,

resulting from their research activities on computing networks,

applied to our cluster.

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THANK YOU