Adaptation of STAR-CCM+ Numerical Wave Tank to an Offshore Floater Design Tool

Jang Whan KimChief Technical Advisor, Offshore Technology Services

Agenda

Introduction

Design Spiral

Requirements on Design Tools

Technology Readiness / Gap

Euler Overlay Method

Applications

Technip Presentation3

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

Technip Slide Library4

Offshore Floaters

WindFPSO/FLNGSparSemi-submersibleUnideck®TPG 500 TLP

Supporting subsea systemOperations in harsh environmentSurvive and protect crew / equipments in extreme environmentsSmall Motion

Design Spiral of Offshore Floater Design

Global Performance

WAMIT / MLTSIMMotion Solver

Model Test6 month after project start

Hull Sizing Calibration

Base Design

Air gap / green water / Slamming / VIM / Topsides wind load

•Wind•Wave•Tow

Design Spiral of Offshore Floater Design with CFD

Global Performance

Validation Model Test

before project

Hull Sizing

CFD

Less uncertainties

Shorter design period

More design optimization

Expectations on Design Tools (Global Performance)

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

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

Technology Readiness

STAR-CCM+ Features

Free-surface capturing

Moving mesh technique

DFBI

Embedded DFBI X

Overset 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)

Stampede – TACC, Univ. of Texas at Austin

11

Intel Sandy Bridge CPU 

102,400 Cores in 182 Racks

2 Peta (1011) FLOPS

STAR Program

• $25,000 Annual Fee for Access 

to 10,240 Cores

$0.05 / Core‐Hr

Technology Gap / Solution

Wave Input

5th-Order Stokes Wave

Good for deep water

Not good for shallow water extreme waves

Random wave input does not meet industry best practice

Random seeding

Wheeler stretching

Many users were using customized user functions

Far-Field Closure

No wave-absorbing mechanism in up-wave side

Larger domain required

Numerical damping sometimes help

Mooring / Riser Modeling

Built-in catenary model

Good for tendon and taut mooring

Not good for SCRs and non-taut mooring

No dynamics

Euler-Overlay Method

In-house Catenary / Rod models

Fully-nonlinear wave models

In-house wave codes

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

13

Long-Crested Wave and a Vertical Column (OMAE2012)

2D Euler Wave Flume

Length: 105 m

CFD Domain

Length: 2 m

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

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

Hull Optimization for Dry-Tree Semisubmersible

Footer can be customized17

Case1 & Case5: Original TTR and MooringC009201 & C0093: Revised TTR and Mooring

Computational Cost

TLP

3.0 mil cells, dt = 0.025 s

5 min simulation Stampede Star‐CCM+

Number 

of CoresRun Time

Service 

UnitUnit Cost Cost

Service 

UnitUnit Cost Cost Total Cost

640 11 7331 0.05 367 11 15 172 $     538.36 320 18 5760 0.05 288 18 15 270 $     558.00 

Semi

1.5 mil cells, dt = 0.1 s

1 hr simulation

Stampede Star‐CCM+

Number 

of CoresRun Time

Service 

UnitUnit Cost Cost

Service 

UnitUnit Cost Cost Total Cost

640 16 10240 0.05 512 16 15 240$      752.00 

Towards Industry Acceptance

NWT Technology Readiness

STAR-CCM+

Euler Overlay Method

Cloud computing

On-Going Improvements

Wave models

Wave re-construction

Mooring / riser modeling

Recommended Practice for Numerical Wave Tank

DnV leads

Numerical Wave Basin JDP in 2013

JIP to be announced in 2014