Wave Tank to an Offshore Floater Design Tool 18 MARCH 2013

Transcription

1 Adaptation of STAR-CCM+ Numerical Wave Tank to an Offshore Floater Design Tool STAR Global Conference MARCH 2013

2 Agenda Introduction Design Spiral Requirements Technology Readiness / Gap Euler Overlay Method Success Stories

3 Three Generations of Spar Platforms CLASSIC TRUSS CELL TRUSS Technip has delivered 14 out of the 19 spars worldwide, in a water depth range of 590 2,382 meters using both dry and wet tree completions. Four more spars are under design/construction by Technip 3 Technip Presentation

4 Offshore Floaters TPG 500 Unideck TLP Semi-submersible Spar Supporting subsea system Operations in harsh environment Survive and protect crew / equipments in extreme environments Small Motion 4 Technip Slide Library FPSO/FLNG Wind

5 Design Spiral of Offshore Floater Design Hull Sizing Global Performance WAMIT / MLTSIM Motion Solver Air gap / green water / Slamming Calibration Model Test 6 month after project start

6 Design Spiral of Offshore Floater Design with CFD Global Performance Hull Sizing CFD Less uncertainties Shorter design period More design optimization Validation Model Test before project

7 Expectations on Design Tools Accuracy Tolerance < 10% Preferably conservative side Robustness No crash No surprise Predictable schedule Speed (Screening Tool) Less than 10 min for a short-term (3-hr) simulation Runtime (Final Evaluation Tool) One run < 12 hr for diagnostic runs One run < 24 hr for production runs

8 Existing Design Tools Nonlinear Time-Domain Motion (MLTSIM) Hydrodynamic coeff. From WAMIT Morison drag Nonlinear Froude-Krylov force Large amplitude formulation Mooring / SCR Modeling Quasi-Static Analysis (FMOOR) Catenary model 5-10 min for 3-hr simulation Screening Tool Model Test MLTSIM Calibration Run up / Air Gap / Green Water Ringing 8

9 Design Tools with Numerical Wave Tank Nonlinear Time-Domain Motion (MLTSIM) Hydrodynamic coeff. From WAMIT Morison drag Nonlinear Froude-Krylov force Large amplitude formulation Mooring / SCR Modeling Quasi-Static Analysis (FMOOR) Catenary model 5-10 min for 3-hr simulation Screening Tool Numerical Wave Tank MLTSIM Calibration Run up / Air Gap / Green Water Ringing 9

10 Technology Readiness STAR-CCM+ Features Free-surface capturing Moving mesh technique DFBI Embedded DFBI Overset X X Powerful built-in pre/post processors Hardware In-house cluster (144 cores) TACC Stampede ( > 10,000 cores) 1-hr simulation in one day (Semi-submersible)

11 Technology Gap / Solution Wave Input 5th-Order Stokes Wave Good for deep water Not good for shallow water extreme waves Fully-nonlinear wave models Random wave input does not meet industry best practice Random seeding Wheeler stretching Many users were using customized user functions In-house wave codes Far-Field Closure No wave-absorbing mechanism in up-wave side Larger domain required Numerical damping sometimes help Euler-Overlay Method Mooring / Riser Modeling Built-in catenary model Good for tendon and taut mooring Not good for SCRs and non-taut mooring No dynamics In-house Catenary / Rod models

12 Euler Overlay Method History Bai & Yeung (1974): Matching FE/BE solution with analytic solution Kim & Bai (1991): Nonlinear radiation problem (Matching) Kim, Kyoung, Ertekin & Bai (2003): Nonlinear diffraction (Overlaying) Kim, Rajeev & O Sullivan (2011): Nonlinear diffraction (CFD, Overlaying) Kim, Read & O Sullivan (2012): Nonlinear diffraction (STAR-CCM+, Overlaying) Far-Field Solution Euler solution Overlaying Boundary condition Momentum and volume fraction source / sink term in blending zone 12

13 Long-Crested Wave and a Vertical Column 2D Euler Wave Flume Length: 105 m CFD Domain Length: 2 m 13

14 Ringing Analysis of a GBS (Short-Crested Irregular Wave) Dynamic amplification of structural load due to resonant response of structure to higher-harmonic load

15 Ringing Response of TLP Tendons Animation of simulated TLP motion and wave elevation (left). Time history (lower left) and power spectrum (lower right) of tendon tension. Blue curve is from model test and red curve is from CFD simulation. Leeside tendon tension is mostly from wave frequency response (wave modal frequency = Hz). Weather-side tendon tension shows strong ringing response at around heave and pitch natural frequency of the TLP (0.22 Hz and 0.23 Hz). Leeside tendon tension Weather-side tendon tension

16 Semi-Submersible Motion Simulation Mooring and Riser Model Look-up table for SCR and Mooring Force Heave RAO from White-Noise Wave Test 1-hr simulation 16 hours with 640 cores WAMIT

17 Conclusions / Path Forward NWT Technology Readiness STAR-CCM+ Euler Overlay Method Success Stories Air Gap / Green Water Analysis for Spar Ringing Analysis for GBS and TLP Motion Analysis for Semi-Submersible Improvements Wave models Mooring / riser modeling Building the Future Validation and Improvements through JIP Recommended Practice