LNG sloshing for new designs, new operations and new trades

LNG sloshing for new designs, new operations and new trades

GastechBilbao, March 16th 2005

Wouter Pastoor, Tom Østvold, Eirik Byklum, Sverre Valsgård

Hydrodynamics & Structures

Det Norske Veritas

Sloshing structural response

Contents

Market developments → DNV Sloshing R&D

LNG sloshing loads

Market developments → DNV Sloshing R&D

LNG sloshing loads

Sloshing structural response

Sloshing guideline

Market developments & interests

Partially filled tanks

Rapid increasing fleetIncreasing carrier sizes

More trading in severe environmentsAlternative propulsion

and machinery

Alternative propulsion

and machinery

R&D focus at DNV

Partially filled tanks

Rapid increasing fleetIncreasing carrier sizes

More trading in severe environments

DNV R&D

SLOSHING

SLOSHING CLASS NOTES

VIBRATION /PROPULSION

SLOSHING /FATIGUE /

ICE OPERATION

Market developments – Focus on LNG sloshing

Offshore (off)loading

Increasing carrier sizes More trading in severe environments

Spot tradingMilk run Floating terminal

LNG Sloshing Challenges

Sloshing

What is the problem?

Sloshing causes fluid loads which needs to be assessed

Structural integrity issues (ultimate & fatigue loading):

• Containment system

• Pump tower and supports

• Hull structure

Sloshing is not new but …

• no stringerdecks!

• no webframes!

• no long. bulkheads!

Typical double-hull tanker LNG carrier

• LNG tank is large and smooth without sloshing “suppressors”

• Different structures, which means different ‘failure modes’

• Different consequences upon a penetration

• Different response dynamics

• Different repair possibilities

• Different repair price

Filling level restriction for unrestricted operation

10% of tank length

70% of tank height

Present filling restrictions for LNG carriers up to 150.000 m3 capacity

Market developments – Focus on LNG sloshing

Offshore (off)loading

Increasing carrier sizes More trading in severe environments

Spot tradingMilk run Floating terminal

Filling level restriction for unrestricted operation

10% of tank length

70% of tank height

Present filling restrictions for LNG carriers up to 150.000 m3 capacity

For partially filled operation a wave height restriction needs to be

determined

LNG Sloshing challenges from the market

Implications for a Class Society?

Update rules?

Issue new rules?

Develop a methodology!NEW COMPETENCE FIRST!

Membrane tanks - sloshing

Present qualification basis

• Structural tests + calculations of containment system, sub-assemblies and materials for ultimate and fatigue loading

• Large experience with membrane containment systems in ships over past decades

• Primary and secondary membrane (~hardware safety factor)

New competence?

Why a focus on new competence?

Rapid pace of new designs and new operations

Extend of the present qualification basis

Sloshing experimental and numerical R&D

LNG sloshing methodology

Assess these new designs and new operations.

LNG sloshing developments

Sloshing tests:• filling level & heading• sea severity• impact area• vessel speed• scaling• pump tower loading• fatigue loading

LNG sloshing technical studies at DNV 2003-…

CFD validity studies

SLOSHING LOADS

Structural tests

STRUCTURAL STRENGTH

Sloshing sensor qualification

Installation detailing

FULL-SCALE MEASUREMENTS

FE calibration & analyses

HAZID-Failure mode analysis

Verified LNG sloshing Class Note

LNG sloshing Class Note (2005)

Measuring campaign

Measurement analysesAcceptance criteria

Capacity determination

Sloshing load and structural strength assessment scheme

LOADS

STRENGTH

FULL-SCALE

MEASUREM.





SLOSHING LOADS

Structural tests

STRUCTURAL STRENGTH








Measuring campaign




LOADS

Sloshing Loads – 6 experimental sloshing phases

scale = 1:70scale = 1:20Instrumented “Pump tower”

1. Filling level & sea state severity

2. Variation of load footprint area

3. Effect of ship speed

4. Scaling study

5. Long-term load distribution

6. Pump tower tests

Experimental set-up

• scale = 1:20

• 138.000 m3 LNG carrier

• No. 2 tank

Example sloshing issue - scaling

Scaling of sloshing model experiments

scale = 1:70scale = 1:20

Scaling of sloshing impacts

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0.01 0.10 1.00Scaled gas-liquid density ratio

Fro

ud

e-s

ca

led

pre

ssu

re

Small tank (1:70)Vacuum

Near vacuum

Light gas

Air-1 atm

Heavy gas


Scaling of sloshing impacts


0.0

1.0

2.0

3.0

4.0

5.0

6.0

0.01 0.10 1.00Scaled gas-liquid density ratio

Fro

ud

e-s

ca

led

pre

ssu

re

Large tank (1:20)

Small tank (1:70)Vacuum

Near vacuum

Light gas

Air-1 atm

Heavy gas

Air-1 atm

Heavy gas

Numerical sloshing simulation?

CFD for sloshing:

• Impact pressures are very difficult to predict (or impossible?)

• Velocities to calculate pump tower loads is possible

• Global sloshing loads for sloshing-ship motion coupling is possible

CFD – Computational Fluid Dynamics?





SLOSHING LOADS

Structural tests

STRUCTURAL STRENGTH








Measuring campaign




STRENGTH

Structural strength studies

1. HAZID – failure mode identification

2. Failure mode evaluation

3. Lab tests of materials and sub-assemblies

4. Calibration of FE models

5. Capacity determination

6. Develop strength assessment procedure

Dynamic strength

A

p

Membrane Cargo Containment Systems

MARK III

Test examples – 1 of 3

Ultimate strength and fatigue tests of a MkIII sub-assembly

(failure investigation of the foam)

Membrane Cargo Containment Systems

GT NO96


Ultimate strength and fatigue tests of plywood plates on shear failure


Dynamic buckling (inertia effects)

Temperature strength effects

h=23cm, t=9mm,

-2.00E+01

-1.00E+01

0.00E+00

1.00E+01

2.00E+01

3.00E+01

4.00E+01

5.00E+01

0.00E+00 5.00E-03 1.00E-02 1.50E-02 2.00E-02 2.50E-02 3.00E-02

Time

Lo

ad

[M

Pa]

t=0.625ms

t=1.25ms

t=2.5ms

t=5ms

t=10ms

t=50ms

23cm, 12mm, t=2.5ms

-10

0

10

20

30

40

50

0.00E+00 1.00E-03 2.00E-03 3.00E-03 4.00E-03 5.00E-03 6.00E-03

Time

Lo

ad

[M

Pa]

temp variation

no temp variation

Buckling ofplywood plates (NO96)

FE Analyses

Buckling strength criteria

0

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1 1.5 2 2.5

Slenderness

σu/σ

f

FEM, uniform load

Test, uniform load

Test, part load

Johnson-Ostenfeld

Elastic-Plastic





SLOSHING LOADS

Structural tests

STRUCTURAL STRENGTH








Measuring campaign




LOADS

STRENGTH

DNV Class Note

ObjectiveGuidance to assess LNG sloshing:

• larger carrier designs

• partial filling on specified trading route

• partial filling while off-loading

• floating terminals

DNV Class Note

Sloshing?

ApplyClass Note

Approval request

Approvalyesno

Limit State Analysis & Specifications

Design & operationalconditions

Sloshing Analysis

Loads

MkIII, NO96, CS1

no

yes StrengthAssessment

Structural SafetyAssessment

Report

DNV Class Note – Application oriented

Sloshing?

ApplyClass Note

Approval request

Approvalyesno

Limit State Analysis & Specifications

Design & operationalconditions

Sloshing Analysis

Loads

MkIII, NO96, CS1

no

yes StrengthAssessment

Structural SafetyAssessment

Report

• offshore (off)loading

• large LNG carriers

• spot trading / milk run

• receiving terminal

LNG sloshing for new designs, new operations and new trades

GastechBilbao, March 16th 2005

Wouter Pastoor, Tom Østvold, Eirik Byklum, Sverre Valsgård

Hydrodynamics & Structures

Det Norske Veritas

LNG sloshing for new designs, new operations and new trades

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