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Hydrodynamic application for standard DTMB 5415 bare hull

with OpenFOAM

A. Penza SCAI Department, CINECA

a.penza@cineca.it

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Contents A.  anteFoam: who I am – why I am here

B.  Validation of interFoam solver

1.  DTMB5415: a standard hull 2.  Material and Methods 3.  OpenFOAM VS Gold-Standard comparisons 4.  OF scalability test 5.  Conclusions

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“anteFoam”

Ø  Who I am: aerodynamic engineer graduated @ PoliMi in April 2012

Ø  12 months internship (begin: 01/07/12) at CINECA in collaboration with Luna Rossa Challenge to investigate the usability of OpenFOAM in marine CFD

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Picasso Ø  Where we started: my first crash case

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DTMB 5415: a standard hull in marine CFD Ø  Standard study to validate

marine CFD analysis. Ø  Bibliography references:

•  L. Larsson, F. Stern, M. Vissonneau, “CFD in ship Hydrodynamics”

•  Y. M. Ahmed, “Numerical simulation for the free surface flow around a complex ship hull form at different Froude numbers ”

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CFD model 1.  Solver:

Ø  Multiphase flow (water/air) Ø  Volume Of Fluid method employed Ø  0 D.O.F. (captive-case) Ø  Unsteady case

In OpenFOAM we got the interFoam solver 2.  BC settings:

Constant pressure patch

Slip wall Velocity inflow

patch

No slip wall on boat surface

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CFD comparisons 1.  Qualitative:

Ø  Iso-surface of computed mass-fraction Ø  Pressure on hull surface Information about wave shape, flow separation, stress distribution on hull

2.  Quantitative: Ø  Pressure drag Ø  Viscous drag

My comparison is: OF vs GS (numerical)

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DTMB 5415: computational mesh

Ø  Particular refinement in the free surface region is crucial

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CFD results Ø  Convergence reached in 10 s

Ø  OpenFOAM vs Gold-Standard Drag values :

•  FxP: -0.34 % •  FxV: -4.95 %

Ø  Quite good agreement of results

GS GS

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Froude sensitivity •  Froude number:

•  At differnt Froude: different behaviours

•  Froude range of interest for DTMB hull: 0.38 – 0.55

Ø  @ Fr = 0.38: convergence

reached in approximately 20000 iterations

Ø  @ Fr = 0.55: convergence reached in approximately 30000 iterations

GS GS

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Ø  Coerent drag trend in agreement with increasing Froude number, as expected

Froude sensitivity

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OpenFOAM vs Gold-standard results Ø  Mass fraction visualized on hull surface: wave shape detected

Ø  Excellent agreement with Gold-Standard results OF GS

OF

GS

OF

GS

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Velocity field

Ø  Symmetry well caught by the solver in the velocity field computations

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Pressure field on hull

a)  Zero pressure distribution well caught b)  Zero pressure transom well caught c)  Bulb pressure distribution to be further investigated

a) b)

c)

OF GS

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Free surface and pressure field

Free-surface: iso-surface mass fracion α= 0.5

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Ø  Wave height visualized on 3D air/water interface surface (mass fraction 0.5)

Ø  Cone of influence identified: physical angle detected, in agreement with theory

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Half-hull simulations

Ø  save 43.5% computational time

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•  Formule scalability:

-  Speed-up: -  Efficiency:

•  Super-linearity behaviour observed: cache effect

Scalability tests

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Machine details OpenFOAM v2.1.0 - v2.1.1 (latest release)

on cluster Lagrange @ CINECA – Segrate (MI)

• 336 nodes BL460c & BL2x220 • 3200 cores Intel X5472 & X5660 • 6400 GB RAM • 30 TB disk (EVA4400 + MSA1500) • Infiniband QDR/DDR Voltaire

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Conclusions

Ø OF works well for marine studies

Ø Time consumption makes feasible also for industrial design

Ø HPC capabilities can be exploited

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Aknoledments •  G. Provinciali Luna Rossa Challenge 2013 •  A. Vergombello Luna Rossa Challenge 2013

•  R. Biscontini Luna Rossa Challenge 2013 •  R. Ponzini CINECA – SCAI Department

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Thank you for your attention

Questions?