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Time domain analysis and CFD

Torgils Skaar 3 Dec 2009

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TIME DOMAIN ANALYSIS AND CFD

Main outline of presentation Why analyses?

Offshore lifts compared to onshore lifts

Acergys strategy

Computational Fluid Dynamics: ANSYS CFX

Time domain analyses: SIMO

Some examples

ANSYS CFX

Ordinary lifting operations

Special operations

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TIME DOMAIN ANALYSIS AND CFD

Why analyses?

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TIME DOMAIN ANALYSIS AND CFD

Why analyses?

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TIME DOMAIN ANALYSIS AND CFD

Why analyses? Motion of floating vessel

Environmental forces

Change of stability condition of vessel during the lift

Entering or exit water-air boundary

Density of air: 1.3 kg/m3 Density of water: 1025.0 kg/m3

Stability of the lifted object!

Hydrodynamic forces on the lifted object

Waves and current will excite the object

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TIME DOMAIN ANALYSIS AND CFD

Why analyses? The dynamic effects in an offshore environment is of the

same magnitude as the static weight and need to be

understood

DNVs guidelines for analyses:

DNV-RP-H103 Modelling and Analyses of Marine

Operations

Basically two ways for analyses of the lift through thesplash zone:

Simplified method

Time domain analyses

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TIME DOMAIN ANALYSIS AND CFD

Why analyses? Simplified analyses:

Covers only the wave zone crossing

Highly simplified model High level of conservatism

Time domain analyses

All phases in the operation may be analysed

A complex model representing the whole system

Less conservatism in the analyses

Crucial input for both kind of analyses:

Hydrodynamic properties for the lifted object

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TIME DOMAIN ANALYSIS AND CFD

ACERGY Solution

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TIME DOMAIN ANALYSIS AND CFD

ACERGY Solution SIMO and ANSYS CFX in combination

ANSYS CFX Hydrodynamic properties for the lifted object

Input to SIMO analyses

Input to simplified analyses

SIMO: Time domain analyses

Input needed

Hydrodynamic coefficients (ANSYS CFX)

Vessel motion characteristics (MOSES)Geometry

Mass / volume distribution

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TIME DOMAIN ANALYSIS AND CFD

ACERGY Solution CFD Hydrodynamic properties, traditional approach

Simplified empirical results

Scaled model tests

DNV-RP-H103:

CFD (Computational Fluid Dynamics) may be used toestablish hydrodynamic properties

ANSYS CFX has been used in Acergy since 2007

A few examples:

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TIME DOMAIN ANALYSIS AND CFD

ACERGY Solution CFD

I-beam vs rectangular beam

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ACERGY Solution CFD

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ACERGY Solution CFD

Quadratic Damping [-]

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

0 2 4 6 8 10

KC [-]

Cdd

[-]

I-Beam

Rect. Beam

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TIME DOMAIN ANALYSIS AND CFD

ACERGY Solution CFD

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TIME DOMAIN ANALYSIS AND CFD

ACERGY Solution - CFD

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TIME DOMAIN ANALYSIS AND CFD

ACERGY Solution SIMO SIMO (Simulations of Marine Operations)

Developed by MARINTEK

Distributed by DNV Software

All phases in an offshore lifting operation may be modelledand analysed

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TIME DOMAIN ANALYSIS AND CFD

ACERGY Solution SIMO Lift-off from deck

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TIME DOMAIN ANALYSIS AND CFD

ACERGY Solution SIMO Deployment of OLSFD using Acergy Eagle

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TIME DOMAIN ANALYSIS AND CFD

ACERGY Solution SIMO Landing OLSFD spool on template

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ACERGY Solution SIMO Deployment of Skandi Acergy ACV

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TIME DOMAIN ANALYSIS AND CFD

ACERGY Solution SIMO Load transfer Skandi Acergy -

> Mid Water Arch

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TIME DOMAIN ANALYSIS AND CFD

ACERGY Solution- Conclusion SIMO + ANSYS CFX

All phases in an offshore lift can be analysed

Complicated operations in general can be analysed

Design loads and effects more accurately estimated

Increased understanding of the operations

Increased weather window => reduced installation time

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TIME DOMAIN ANALYSIS AND CFD

Questions?