CFD Case Studies in Marine and Offshore Engineering

Transcription

1 CFD Case Studies in Marine and Offshore Engineering Milovan Perić CD-adapco, Nürnberg Office

2 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, rolldamping, 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.).

3 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+

4 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...

5 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 EulerianEulerian 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.).

6 Automatic handling of Complex Geometry, I Surface-wrapping of an oil rig

7 Automatic handling of Complex Geometry, II Re-meshed surface of an oil rig

8 Prediction of Ship Resistance, I KVLCC half model, wind tunnel test... Boundary layer growth

9 Prediction of Ship Resistance, II Comparison of computed and measured data... Experiment CFD

10 Prediction of Ship Resistance, III Velocity cut in propeller plane at z/l= u/u (exp.) v/u (exp.) w/u (exp.) u/u (CFD) v/u (CFD) w/u (CFD) 1.0 u/u, v/u, w/u y/l Comparison of measured and predicted velocity profiles

11 Prediction of Ship Resistance, IV Comparison of computed and measured resistance...

12 Resistance of a Floating Vessel A very good agreement is achieved, when dynamic sinkage and trim are taken into account! Courtesy of Voith Turbo Schneider Propulsion GmbH & Co. KG 9 kn 11 kn 13 kn 15 kn

13 Optimization of Hull Form Original design 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). Courtesy of Voith Turbo Schneider Propulsion GmbH & Co. KG Optimized design PD - Variant B (optimized design) 7000 PD - Variant A (initial design) V [kn]

14 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 of a full-size tank... Free-surface resolution within one cell...

15 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

16 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:

17 Voith Radial Propeller, I

18 Voith Radial Propeller, II Azimuth-Thruster Optimisation 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

19 Voith Radial Propeller: Velocity

20 Voith Radial Propeller: Pressure and Velocity 0 8

21 Voith Radial Propeller: Effective Thrust 100% total thrust ratio τ [%] 90% 80% 70% 60% 50% 40% tilt angle [ ] Effective thrust acting on the structure: at 0, 45% is lost due to interaction, at 8 only 5% is lost...

22 Voith Radial Propeller: Force on Pontoon CFD Full scale Reynoldsnumber Relative Force [%] 100 Model scale measurments Tilt Angle [ ] Force acting on pontoon 2: comparison of simulation for the full scale and experiment in model scale...

23 Prediction of VIV Old design A mega-yacht with 4 propellers suffered from vibrations at a cruising speed of about 16 kn. German Lloyd and CD-adapco solved the problem with the help of 2 CFD-simulations (after all other attempts have failed...). New design

24 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 Pa); HSVA in t0 t ms t0 + 10,4 ms t0 + 20,7 ms t0 + 41,4 ms t0 + 51,7 ms

25 Prediction of Cavitation, II Simulation of cavitation: flow around NACA0015 foil at 10.3 angle of attack t0 (chord length 0.2 m, water speed 6 m/s, channel 0.57 x 0.57 m, cavitation number 1.7, absolute pressure Pa): CD-adapco, ms 40 ms 10 ms 30 ms 50 ms

26 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

27 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...

28 Voith Water Jet: Virtual Propulsion Test

29 Prediction of Hull-Propeller-Rudder Interaction Project sponsored by the European Union: several partners, extensive model-scale measurements done, good agreement between computed and measured forces and moments (report not published yet) Courtesy of Germanischer Lloyd AG

30 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 ship hull (overlapping trimmed mesh)

31 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...

32 Tanker Ship in Waves, III Tanker position and free surface shape at three times...

33 Prediction of Dispersion Phenomena, I Simulation of air flow around an oil platform

34 Prediction of Dispersion Phenomena, II Simulation of pollutant dispersion around a refinery plant

35 Multiphase Flows, I Gas lift separator

36 Multiphase Flows, II Simulation of two-phase flow in a slug-catcher

37 Simulation of Bow Flare Slamming, I Simulation of bow flare slamming at German Lloyd (Prof. Dr. Bettar El Moctar) Ship main data: LPP = m B = 26.0 m T = 6.5 m = t Ship velocity [kn] Wave height [m] Wave frequency [1/s] Wave direction [ ] Courtesy of Germanischer Lloyd AG 180 (Head waves)

38 Simulation of Bow Flare Slamming, II Simulation of bow flare slamming at German Lloyd: pressure sensor locations Courtesy of Germanischer Lloyd AG

39 Simulation of Bow Flare Slamming, III Pressure histories at two sensors (comparison experiment simulation) Courtesy of Germanischer Lloyd AG

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

41 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

42 Coupled Simulation of Flow, Vessel Motion and its Deformation Coupled simulation of flow and motion of a full size ship in waves and structural deformation (using an interface between CFD and FEM code, developed by German Lloyd) Exaggerated deformation of ship structure at an instant of time during its motion in waves. Courtesy of Germanischer Lloyd AG

43 Simulation of Life-Boat Launching, I Example: launching of a life-boat Courtesy of Prof. Hans Jørgen Mørch, CFD Marin, and Norsafe AS

44 Simulation of Life-Boat Launching, II Comparison of measured and predicted acceleration at front (left) and rear (right) seats in the lifeboat (launching hight 36 m, initial inclination 35, flat water surface, no wind, 3 DOF, less than cells, single polyhedral mesh)

45 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...

46 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 simulation to develop new rules...

47 Prediction of Hit Point Effects, I

48 Prediction of Hit Point Effects, II Pressure distribution on a lifeboat during water entry...

49 Lifeboat position and free-surface shape during water entry and re-surfacing for one hit point ms between frames 250 ms between frames

50 Prediction of Hit Point Effects, IV Predicted vertical acceleration at COG, following wave, 9 hit points 20 m apart...

51 Prediction of Hit Point Effects, V Predicted vertical acceleration at COG, head wave, 9 hit points 20 m apart...

52 Prediction of Hit Point Effects, VI Predicted angular acceleration at COG, following wave, 9 hit points 20 m apart...

53 Prediction of Hit Point Effects, VII Predicted angular acceleration at COG, head wave, 9 hit points 20 m apart...

54 Prediction of Hit Point Effects, VIII Predicted pressure at keel, following wave, 9 hit points 20 m apart...

55 Prediction of Hit Point Effects, IX Predicted pressure at keel, head wave, 9 hit points 20 m apart...

56 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 m Molded hull breadth 47.6 m Molded hull depth 5.5 m Elevated height above calm water level 8.35 m Leg diameter 3.66 m Overall leg length 64.0 m Unsupported leg length 48.3 m Gross tonnage 4033 t Net tonnage 3209 t

57 Wave-in-Deck Loads, II Parameters that were varied in the study: Wave height: 15.8 m, 19.9 m, 23.7 m Wavelength: m, m, 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

58 Wave-in-Deck Loads, III Platform geometry

59 Wave-in-Deck Loads, IV Free surface shape at two instants during impact, 1.0 s apart (19.9 m wave height)

60 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)

61 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)

62 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)

63 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)...

64 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...

65 Breaking Waves, IV Free surface deformation during impact of a breaking wave onto a simplified platform...

66 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, shortly after initialization Nearly-breaking wave, about one period later...

67 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...