march 2009 luncheon - cfd case studies in marine and offshore engineering

CFD Case Studiesin Marine and Offshore Engineering

Milovan Perić

CD-adapco, Nürnberg Office

www.cd-adapco.comMilovan.Peric@de.cd-adapco.com

Introduction

CD-adapco software: a brief overview

Case studies (from or for our clients):

− Prediction of resistance and propulsion;− Prediction of sea-keeping (dynamic position, maneuver, roll-

damping, hydro-dynamic coefficients etc.);− Prediction of cavitation (onset, extent, erosion);− Prediction of wave loads on vessels and offshore structures,

wave-added resistance etc.;− Prediction of VIV on ships and offshore structures;− Prediction of dispersion processes;− Prediction of multi-phase flows (separators etc.);− Simulation of fluid-structure-interaction (lifeboats, ships, etc.).

CD-adapco Software, I

CD-adapco is pioneering the technology for Computational Continuum Mechanics (CCM)...

CD-adapco is integrating all tools for the CAE process in a single software package with a unique user interface:

− geometry modeler (based on parasolid kernel);

− automatic surface-wrapping and repairing tools;

− automatic surface and volume meshing;

− analysis of fluid flow, solid deformation, heat transfer and other multi-physics;

− monitoring, reporting, visualizing, animating...

Main product: STAR-CCM+

CD-adapco Software, II

Finite volume method for fluid flow and solid deformation/stress analysis...

Control volumes can be of an arbitrary polyhedral shape...

2nd-order approximations (surface, volume and time integrals, gradients, interpolation...)

Iterative solution (coupled or segregated), AMG-solvers

Coupled solution of fluid flow, heat transfer, motion of flying or floating bodies, and solid deformation (not all features released yet)

Overlapping grids and grid morphing for adaptation to body motion or deformation...

Automatic generation of 1st and 5th-order Stokes waves...

CD-adapco Software, III

CD-adapco has implemented state-of-the-art physics models into STAR-solvers:

− Turbulence models (including robust Reynolds-stress model, non-linear two-equation models, transition model, DES, LES);

− Phase-change models (cavitation, boiling, condensation, melting, solidification)

− Phase-interaction models (Lagrangian-Eulerian and Eulerian-Eulerian analysis of multi-component, multiphase flows)

− Free-surface model (interface-capturing, including surface tension and contact angle effects, compressibility etc.);

− Heat transfer (conduction, convection, radiation, heat sources);

− Material laws (non-Newtonian fluids, elastic, elasto-plastic and visco-elastic solids, mushy-zone, porous media etc.).

Automatic handling of Complex Geometry, I

Surface-wrapping of an oil rig

Automatic handling of Complex Geometry, II

Re-meshed surface of an oil rig

Prediction of Ship Resistance, I

Boundary layer growth

KVLCC half model,wind tunnel test...

Prediction of Ship Resistance, II

Comparison of computed and measured data...

Experiment

CFD

Prediction of Ship Resistance, III

Comparison of measured and predicted velocity profiles

y/L

0.00 0.02 0.04 0.06 0.08 0.10

u/U

, v/

U,

w/U

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2u/U (exp.)v/U (exp.)w/U (exp.)u/U (CFD)v/U (CFD)w/U (CFD)

Velocity cut in propeller plane at z/L=-0.05

Prediction of Ship Resistance, IV

Comparison of computed and measured resistance...

Resistance of a Floating Vessel

9 kn 11 kn 13 kn 15 kn

A very goodagreementis achieved,when dynamicsinkage andtrim are takeninto account!

Courtesy of Voith Turbo Schneider Propulsion GmbH & Co. KG

Optimization of Hull Form

Voith should deliver a propeller but found that small changes to the hull form could improve the efficiency by 30% - much more than optimization of the propeller! Experiment at SVA Potsdam verified CFD results (see diagram).

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

8 9 10 11 12 13 14 15 16 17V [kn]

PD - Variant B (optimized design)

PD - Variant A (initial design)

Original design

Optimized design

Courtesy of Voith Turbo Schneider Propulsion GmbH & Co. KG

Prediction of Free-Surface Deformation

High-resolution interface-capturing (HRIC) scheme: distribution of liquid volume fraction after 101 periods of roll-oscillation in an LNG-tank...

No mixing: even unresolved drops and bubbles can be tracked until they reach free surface...

Roll-motion ofa full-size tank...

Free-surfaceresolution withinone cell...

Voith Ship Simulator, I

Voith uses a ship simulator to train captains...

Hydrodynamic coefficients used to come from experiments – now they come from CFD analyses...

Simulator

Experiment Simulation

Voith Ship Simulator, II

PMM-test using CFD:

− Pure yaw maneuver

− Pure sway maneuver

Ship orientation in PMM-tests:

Pure yaw maneuver:

Pure sway maneuver:

Voith Radial Propeller, I

Voith Radial Propeller, II

An automatic calculation strategy is developed that includes the following tasks:

- parametrization of geometry - automatic generation of geometry - automatic mesh generation - automatic computation and post-processing of results - embedding the procedure in an optimization loop

automatic optimization loop

Azimuth-Thruster Optimisation

Voith Radial Propeller: Velocity

0° 4°

6° 8°

Voith Radial Propeller: Pressure and Velocity

0°

8°

Voith Radial Propeller: Effective Thrust

40%

50%

60%

70%

80%

90%

100%

0 1 2 3 4 5 6 7 8 9 10

tilt angle [°]

tota

l th

rust

rat

io τ

[%]

Effective thrust acting on the structure: at 0°, 45% is lost due tointeraction, at 8° only 5% is lost...

Voith Radial Propeller: Force on Pontoon 2

Force acting on pontoon 2: comparison of simulation for the fullscale and experiment in model scale...

0

20

40

60

80

100

120

0 2 4 6 8 10

Tilt Angle [°]

Rel

ativ

e F

orc

e [%

]

CFD Full scale Reynoldsnumber

Model scale measurments

Prediction of VIV

A mega-yacht with 4propellers suffered from vibrationsat a cruising speed of about 16 kn.German Lloyd and CD-adapco solvedthe problem with the help of 2 CFD-simulations(after all other attempts have failed...).

Old design

New design

Prediction of Cavitation, I

Cavitation in experiment: flow around NACA0015 foil at 10.3° angle of attack (chord length 0.2 m, water speed 6 m/s, channel 0.57 x 0.57 m, cavitation number 1.7, absolute pressure 32000 Pa); HSVA in 1999.

t0 t0 + 10,4 ms t0 + 20,7 ms

t0 + 31 ms t0 + 41,4 ms t0 + 51,7 ms

Prediction of Cavitation, II

Simulation of cavitation: flow around NACA0015 foil at 10.3° angle of attack (chord length 0.2 m, water speed 6 m/s, channel 0.57 x 0.57 m, cavitation number 1.7, absolute pressure 32000 Pa): CD-adapco, 2009

t0

010 ms

20 ms 30 ms

40 ms 50 ms

Voith Water Jet: Original Design

The original design led to substantial cavitation in the upper range of speeds...Experiments (performed after simulation) confirmed this...

Simulation Experiment

Voith Water Jet: Optimized Design

With the optimized design, cavitation starts at a much higher speed and is less intensive – a substantial increase of efficiency has been achieved...

Voith Water Jet: Virtual Propulsion Test

Prediction of Hull-Propeller-Rudder Interaction

Courtesy of Germanischer Lloyd AG

Project sponsored by the European Union: several partners, extensivemodel-scale measurements done, good agreement between computed and measured forces and moments (report not published yet)

Tanker Ship in Waves, I

● Ship length: 266 m● Ship width: 44 m● Draft: 11 m● Speed: 6 kn

● Wave length: 260 m● Wave amplitude: 7.5 m● Regular sine wave specified at inlet

Mesh in free surface and on shiphull (overlapping trimmed mesh)

Tanker Ship in Waves, II

● Ship motion is controlled by outside sea forces and forces due to sloshing in its two tanks (filled up to 20%).

● 2 DOF motion: heave and pitching...

Tanker Ship in Waves, III

● Tanker position and free surface shape at three times...

Prediction of Dispersion Phenomena, I

Simulation of air flow around an oil platform

Prediction of Dispersion Phenomena, II

Simulation of pollutant dispersion around a refinery plant

Multiphase Flows, I

Gas lift separator

Multiphase Flows, II

Simulation of two-phase flow in a slug-catcher

Simulation of Bow Flare Slamming, I

Simulation of bow flare slamming at German Lloyd (Prof. Dr. Bettar El Moctar)

180 (Head waves)

0.607.326

Wave direction [°]Wave frequency [1/s]Wave height [m]Ship velocity [kn]

Ship main data:LPP = 173.0 m

B = 26.0 m

T = 6.5 m

∆ = 16800 t

Courtesy of Germanischer Lloyd AG

Simulation of Bow Flare Slamming, II

Simulation of bow flare slamming at German Lloyd: pressure sensor locations

1

2

3

47

8

9 6

5

Courtesy of Germanischer Lloyd AG

Simulation of Bow Flare Slamming, III

Pressure histories at two sensors (comparison experiment­simulation)

Courtesy of Germanischer Lloyd AG

Simulation of flow around ship in waves (both motion and deformation of ship accounted for; courtesy of GL, Hamburg)

Simulation of Bow Flare Slamming, IV

Simulation of Ship Motion in Waves

Comparison of measured and computed ship motions (simulations by German Lloyd, experiments by HSVA)

Pitch motions Vertical accelerations

Courtesy of Germanischer Lloyd AG

Coupled Simulation of Flow, Vessel Motion and its Deformation

• Coupled simulation of flow and motion of a full­size ship in waves and structural deformation (using an interface between CFD and FEM code, developed by German Lloyd)

Exaggerated deformation of ship structureat an instant of time during its motion in waves.

Courtesy of Germanischer Lloyd AG

Simulation of Life-Boat Launching, I

Example: launching of a life-boat

Courtesy of Prof. Hans Jørgen Mørch, CFD Marin,and Norsafe AS

Simulation of Life-Boat Launching, II

Comparison of measured and predicted acceleration at front (left) andrear (right) seats in the lifeboat (launching hight 36 m, initial inclination35°, flat water surface, no wind, 3 DOF, less than 300000 cells, singlepolyhedral mesh)

Prediction of Effects of Geometry Change, I

Three shapes of a lifeboat were analysed:

− base model

− modified aft

− modified bow and aft

Launching under the same conditions

Effects of shape on acceleration studied...

Prediction of Effects of Geometry Change, II

The effects of shape on acceleration were correctly predicted...

… both qualitatively and quantitatively.

Rear part was more affected...

DNV and GL using simulationto develop new rules...

Prediction of Hit Point Effects, I

Prediction of Hit Point Effects, II

Pressure distribution on a lifeboat during water entry...

50 ms betweenframes

250 msbetween frames

Lifeboat position andfree-surface shapeduring water entry andre-surfacing for onehit point...

Prediction of Hit Point Effects, IV

Predicted vertical acceleration at COG, following wave, 9 hit points 20 m apart...

Prediction of Hit Point Effects, V

Predicted vertical acceleration at COG, head wave, 9 hit points 20 m apart...

Prediction of Hit Point Effects, VI

Predicted angular acceleration at COG, following wave, 9 hit points 20 m apart...

Prediction of Hit Point Effects, VII

Predicted angular acceleration at COG, head wave, 9 hit points 20 m apart...

Prediction of Hit Point Effects, VIII

Predicted pressure at keel, following wave, 9 hit points 20 m apart...

Prediction of Hit Point Effects, IX

Predicted pressure at keel, head wave, 9 hit points 20 m apart...

Wave-in-Deck Loads, I

Wave-in-deck loads on a platform can be efficiently simulated by initializing Stokes 5th-order wave a short distance upstream of the platform...

A detailed study was carried out for a jack-up platform in North Sea together with GL (Paper for OMAE2009).

Molded hull length 46.0 mMolded hull breadth 47.6 mMolded hull depth 5.5 mElevated height above calm water level 8.35 mLeg diameter 3.66 mOverall leg length 64.0 mUnsupported leg length 48.3 mGross tonnage 4033 tNet tonnage 3209 t

Wave-in-Deck Loads, II

Parameters that were varied in the study:

− Wave height: 15.8 m, 19.9 m, 23.7 m

− Wavelength: 220.7 m, 229.1 m, 236.7 m

− Wave period: 13 s in all cases

− Water depth: 33.5 m in all cases

− Wind speed: 0 m/s and 50 m/s

− Angle of attack: 0°, 60°, 90°, 180°

− Initial position of wave crest relative to platform

Wave-in-Deck Loads, III

Platform geometry

Wave-in-Deck Loads, IV

Free surface shape at two instants during impact, 1.0 s apart (19.9 m wave height)

Wave-in-Deck Loads, V

Pressure distribution at two instants during impact, 1.0 s apart (19.9 m wave height – correspond to the same times as in the previous slide)

Wave-in-Deck Loads, VI

Horizontal (left) and vertical (right) force onto platform for 15.8 m wave height (top), 19.9 m wave height (middle) and 23.7 m wave height (bottom).

Largest loads results for 180° wave incidence (following wave)

Breaking Waves, I

Waves are usually not as smooth as a Stokes 5th-order wave...

The Stokes 5th-order wave with19.9 m wave height in 33.5 m water depth breaks after about 1 period...

Shortly after initialization (top), after one period (middle)and after 1.5 periods (bottom)

Breaking Waves, II

Water velocity in the crest region increases with time as the wave tends to break: from 9.9 m/s after initialization to about 22.9 m/s during overturning (wave propagation: 17.6 m/s)...

Breaking Waves, III

Effects of varying the initial wave position by 10 m on forces on a simple platform.

Within 20 m range (10% of wave length), the effect is not large...

The load from wave impact can be more than 4 times larger when a breaking waves impacts a rigid wall than what is obtained from an impact of a regular Stokes wave...

Breaking Waves, IV

Free surface deformation during impact of a breaking wave onto a simplified platform...

Breaking Waves, V

Free surface deformation during impact of a regular Stokes wave (upper) and a breaking wave (lower) onto an oil platform...

Stokes wave, shortlyafter initialization

Nearly-breaking wave,about one period later...

Conclusions

CFD-simulations can help in design and optimization process by providing insight into the physics before any prototype is built...

Simulation should be used to design experiments (what to measure and where), when experimental validation is needed.

Even if the results of simulations are not quantitatively accurate (e.g. when the grid is coarse), they can help in correct ranking of prototypes...

Simulations are of great help when solving problems – they provide much more information than an experiment.

CFD is spreading within marine and offshore industries, with great success...