Sloshing VesselSloshing VesselCAE ExampleCAE ExampleSloshing VesselSloshing VesselCAE ExampleCAE Example

Martin WaltersMartin WaltersMartin WaltersMartin Walters

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Storage Vessel Design

Effects of FPSO Movement

• Liquid-gas interface unstable

• Need to reduce sloshing to maintain separation efficiency

• What stresses are seen by components?

– Can we still use standard baffle configurations?

– Bolts and welds

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– Bolts and welds

– Fatigue loading

• Not something that’s easy to do experimentally!

– Potentially dangerous

– Significant cost of rig & instrumentation

Objectives

• Design study for a 12m long storage tank on

board an FPSO

• Design considerations:

– Internal baffle arrangement to reduce sloshing

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– Operational load characteristics

• Sloshing loading

• Fatigue

• Welds and bolts

Vessel motion

• Inertial reference frame

– Ship moving at fixed speed

– No waves or swell

– No acceleration force

– No sloshing!x

y

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x’y’

z’

• Non-Inertial Frame

– Bow of the ship in a storm

– 3 Rotations• Roll, Pitch & Yaw

– 3 Linear Accelerations• Surge, Sway & Heave

– Sloshing expected!

z

Methodology

• Hydrodynamic analysis with a given sea state provides

motion profile for CFD and FEA

• Velocity motion profiles applied using Six Degree Of

Freedom model in CFD solver

– accelerations could be applied directly to momentum

equations

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equations

• Volume of Fluid model used to model gas-liquid interface in

CFD solver

• Transient one-way FSI, surface pressures mapped from

CFD analysis to FEA model

• Displacement profiles from Hydrodynamic solver applied to

FEA model to account for inertia of solid structure

Simulation Process

Step Solver Design Consideration Output Data

1 Hydrodynamic

Asses ship hydrodynamic

response to different sea

states

Motion Profiles:

Velocities for CFD

Displacements for FEA

2Computational

Fluid Dynamics

Analyse baffle design to

assess sloshing

Surface Pressure

Profiles

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2Fluid Dynamics assess sloshing Profiles

3Structural

Finite Element

Analyse stresses to look at

welds and bolt arrangements

and fatigue loading

Velocity

ProfilesPressures &

Displacements

Hydrodynamics CFD FEA

Workbench Project

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Hydrodynamic Analysis

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• Motion Profile Output for all six motions, used for CFD

and Structural FE models

• Displacements, Velocities and Accelerations

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Surface Pressure

Profile used for

Structural model

Computational Fluid

Dynamics Analysis

Structural FEA

• AQWA stuff to get data • Pressure Loading ONLY

• Fluid inertia considered

• Fixed constraints to feet

• Inertia of solid structure ignored

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Structural FEA

with CFD Free Surface

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Conclusions

• High fidelity loading conditions for structural

model with design information at each step

• Further work:

– Structural FEA sub model to look at specific

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problems

– Fatigue analysis

– Different sea state conditions

– Design Exploration and Optimisation Studies

within Workbench