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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
2STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
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
3STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
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
4STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
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
5STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
CAD GEOMETRY
Surface GRID
Volume GRID
and CFD
CATIA V5 R19
ANSA 13.0.2
STAR CCM+
v4.04.011
HARDWARE
6STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
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
10STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
Refinement for pitchmotion
Refinement for rollmotion
PHYSICAL MODEL
11STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
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)
12STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
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
13STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
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
14STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
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
15STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
• 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
16STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
COMPUTATIONAL TIME
22-03-10 STAR EUROPEAN CONFERENCE – G. Lombardi et Al. 17
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
22-03-10 STAR EUROPEAN CONFERENCE – G. Lombardi et Al. 18
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
22-03-10 STAR EUROPEAN CONFERENCE – G. Lombardi et Al. 19
Boat Heel
22-03-10 STAR EUROPEAN CONFERENCE – G. Lombardi et Al. 20
Speed – Heel correlation
22-03-10 STAR EUROPEAN CONFERENCE – G. Lombardi et Al. 21
Poor correlation appears
Hull Drag
22-03-10 STAR EUROPEAN CONFERENCE – G. Lombardi et Al. 22
Speed – Hull Drag correlation
22-03-10 STAR EUROPEAN CONFERENCE – G. Lombardi et Al. 23
More evident correlation appears (with phase angle)
SAILS THRUST
22-03-10 STAR EUROPEAN CONFERENCE – G. Lombardi et Al. 24
The Thrust is mainly from the jib
There is a phase angle between mainsail and jib thrusts
SAIL FLOW REPRESENTATION
25STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
SAIL FLOW REPRESENTATION
26STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
FLOW DETAILS….
27STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
Vorticity Field on the deck
28STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
CONCLUSIONS
29STAR EUROPEAN CONFERENCE – G. Lombardi et Al.22-03-10
• 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.
22-03-10 STAR EUROPEAN CONFERENCE – G. Lombardi et Al. 31
THANK YOU