OTC 13213 Presentation

7/27/2019 OTC 13213 Presentation

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Design Tool for Green Sea,

Wave Impact, and Structural Response

on Bow and Deck Structures

. Hellan, O.A. Hermundstad and C.T. Stansberg,

MARINTEK, Trondheim, Norway

OTC 2001 - Paper No. 13213


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Development of a new engineering design tool

Work sponsored through the Norwegian JIP:

Design Loads and Integrity Assessment for Wave Impact

on Bow and Deck Structures- duration 2000 - 2001 (2002)

(NPD, Norsk Hydro, Statoil, APL, NAVION,Rolls Royce Marine, PGS)


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Contents:

- Background

- Design tool overview & objective

- Water kinematics due to random waves

- Water propagation and local loads

- Bow slamming

- Structural integrity assessment

- Concluding remarks


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Background

- Incidents with green sea on Norwegian & UK FPSOs

- Run-up & negative air-gap on floating platforms

- Uncertainties in prediction - need for a practical design tool

- In particular: Significance of impact from steep nonlinear waves

- Model test experience & theoretical expertise at

MARINTEK / NTNU

Establish an engineering tool based on available

knowledge and systematic use of experimental data


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Design tool overviewPhase 1 Phase2

SEMI

W a v e r u n u p sa n d s l a m m i n g

B o w s l a m m i n g

.PSO

G r e e n w a t e r s l a m m i n g o n d e c k

E x t r e m e w a v e sa n dd e c k s l a m m i n g

G r e e n w a t e r s l a m m i n g o n d e c k


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Objective

Prediction of:

- Probability of water on deck or bow slamming for FPSOs

- Probability of run-up, negative air-gap and wave impact onfloating platforms

- Design loads for bow slam, water impact loads and green sea

loading on deck-mounted equipment

- Structural integrity


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Phase 1 of JIP: FPSO

. P S O B OW

WAVE KINEMATICS

I N C I D E N T W A V E . R E E B O A R D E X C E E D A N C E , DJB O W G E O M E T R Y E N T R Y V E L O C I T Y , LJ S H I P M O T I O N

D E C K -H O U S E

LOCAL LOADSV O L U M E O . W A T E R P R E S S U R E A S O .WATER VEL OC I TY .U N CTI ON O.S U R . A C E A N G L E T I M E A N D S P A C E

p ( t )

D E C K -H O U S E

STRUCTURAL INTEGRITYP R E S S U R E A S . U N C T I O N D E . O R M A T I O N SO . T I M E A N D S P A C E S T R E S S E S D AMAG ES

p ( t )@ (t)I (t)D A M A G E

D E C K -H O U S E

WATER PROPAGATION

. R E E B O A R D E X C E E D A N C E WATER . LO WE N T R Y V E L O C I T Y V O L U M E , V( X , Y ) V E L O C I T Y , V ( X , Y )

S U R . A C E A N G L E

v o V

1 2

3 4


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Examples from FPSO case study experiment in random waves:

1) High wave + negative bow motion


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2) Jet due to extreme & steep wave


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Relative wave kinematics:

Time domain simulationwith ship motion

- Second-order wave(elevation & kinematics)

- Linear 3D diffraction

- Linear ship motion- Empirical correction

-45deg < 0 < +45deg

Anywhere around the ship


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Second-order random waves + linear diffraction at bow


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Water propagation on deckShallow water formulation: A) 3D dam-breaking model

.


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.


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.


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.


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Water propagation on deckShallow water formulation: B) Influence from wave kinematics.

A) Dam-breaking model B) Time-varying boundary conditio


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Local loads on deck house

Prediction by similarity solution.

Input from shallow water model:- velocity V

- angle

Example from measurement(2.75mx2.75m panel)


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Bow slamming

- Second-order random wave

+ linear diffraction + linear ship motion

- Change rate in wetted bow area

- Load prediction from existing program Slam2D:

Zero-gravity potential theory - Wagner method

2D boundary value problem


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Bow slamming

+ Slam2D

(x,t)

u(x,t)

c(t)


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Structural integrity assessment

- Load interface to industry-standard 3D Finite-Element tools

- Integrity assessment of plate structures underwater impact loading (1-DOF analysis, Biggs method)

- Acceptance criteria; e.g. NORSOK

- Hydro-elastic assessment of loads and responses

(likely to be of minor significance for deck-house loads)


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Plastic deformation of plate

Beam collapse plate elastic

Beam collapse plate plastic

Girder collapse

beam elastic- plate elastic or plasticGirder and beam collapse

plate elastic (i) or plastic (ii)

(i)(ii)

Plate divided inseparate components

plating alone

stiffeners transverse girders

ISO-damage curves

for each components

Envelope governing

SDOF analysis


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typical deckhouse structure3 different impulse shapes

0

0.25

0.5

0.75

1

0 0.25 0.5 0.75

Intensity

Time

Impulse 1Impulse 2Impulse 3


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Effect of impulse shape on predicted pressure-impulse capacity

0

200

400

600

800

1000

0 5 10 15 20 25

Pressure[k

N/m2]

Impulse [(kN/m2)*seconds]

Impulse 1Impulse 2Impulse 3


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- JIP - Wave impact: New engineering design tool

- Random wave input + water propagation + load + response

- FPSO and floating platforms (Phase 1 & Phase 2 of JIP)

- Benchmarking FPSO case study including model tests

- Important nonlinear effects in steep waves taken into account

- Detailed nonlinear modelling of water propagation and loads

- Structural response: Load interface to industry FEM tools

- Empirical calibration against model test data

OTC 13213 Presentation

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