LNG sloshing for new designs, new operations and new trades

LNG sloshing for new designs, new operations and new trades Gastech Bilbao, March 16 th 2005 Wouter Pastoor, Tom Østvold, Eirik Byklum, Sverre Valsgård Hydrodynamics & Structures Det Norske Veritas

Contents Market developments DNV Sloshing R&D LNG sloshing loads Sloshing structural response Sloshing guideline

Partially filled tanks Market developments & interests Increasing carrier sizes Rapid increasing fleet More trading in severe environments Alternative propulsion and machinery

R&D focus at DNV Increasing carrier sizes SLOSHING Partially filled tanks SLOSHING Rapid increasing fleet CLASS NOTES DNV R&D More trading in severe environments SLOSHING / FATIGUE / ICE OPERATION Alternative propulsion VIBRATION / PROPULSION and machinery

Market developments Focus on LNG sloshing Increasing carrier sizes More trading in severe environments LNG Sloshing Challenges Offshore (off)loading Milk run Spot trading Floating terminal

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 Typical double-hull tanker LNG carrier no stringerdecks! no webframes! no long. bulkheads! 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 Present filling restrictions for LNG carriers up to 150.000 m3 capacity 70% of tank height 10% of tank length

Market developments Focus on LNG sloshing Increasing carrier sizes More trading in severe environments Offshore (off)loading Milk run Spot trading Floating terminal

Filling level restriction for unrestricted operation Present filling restrictions for LNG carriers up to 150.000 m3 capacity For partially filled operation a wave height restriction needs to be determined 70% of tank height 10% of tank length

LNG Sloshing challenges from the market Implications for a Class Society? Update rules? Issue new rules? NEW COMPETENCE FIRST! Develop a methodology!

Membrane tanks - sloshing Present qualification basis Structural tests + calculations of containment system, subassemblies 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 technical studies at DNV 2003- LNG sloshing developments SLOSHING LOADS STRUCTURAL STRENGTH FULL-SCALE MEASUREMENTS Sloshing tests: filling level & heading sea severity impact area vessel speed scaling pump tower loading fatigue loading LOADS CFD validity studies HAZID-Failure mode analysis Structural tests FE calibration & analyses STRENGTH Acceptance criteria Capacity determination Sloshing sensor qualification Installation detailing Measuring campaign FULL-SCALE MEASUREM. Measurement analyses Sloshing load and structural strength assessment scheme LNG sloshing Class Note (2005) Verified LNG sloshing Class Note

LNG sloshing technical studies at DNV 2003- LNG sloshing developments SLOSHING LOADS STRUCTURAL STRENGTH FULL-SCALE MEASUREMENTS Sloshing tests: filling level & heading sea severity impact area vessel speed scaling pump tower loading fatigue loading LOADS CFD validity studies HAZID-Failure mode analysis Structural tests FE calibration & analyses Acceptance criteria Capacity determination Sloshing sensor qualification Installation detailing Measuring campaign Measurement analyses Sloshing load and structural strength assessment scheme LNG sloshing Class Note (2005) Verified LNG sloshing Class Note

Sloshing Loads 6 experimental sloshing phases 1. 2. 3. 4. 5. 6. Filling level & sea state severity Variation of load footprint area Effect of ship speed Scaling study Long-term load distribution Pump tower tests scale = 1:20 scale = 1:70 Instrumented Pump tower

Experimental set-up scale = 1:20 138.000 m 3 LNG carrier No. 2 tank

Example sloshing issue - scaling Scaling of sloshing model experiments scale = 1:20 scale = 1:70

Scaling of sloshing impacts Scaling of sloshing model experiments 6.0 5.0 Vacuum Light gas Small tank (1:70) Froude-scaled pressure 4.0 3.0 2.0 Near vacuum Air-1 atm Heavy gas 1.0 0.0 0.01 0.10 1.00 Scaled gas-liquid density ratio

Scaling of sloshing impacts Scaling of sloshing model experiments 6.0 5.0 Vacuum Air-1 atm Light gas Large tank (1:20) Small tank (1:70) Froude-scaled pressure 4.0 3.0 2.0 Near vacuum Air-1 atm Heavy gas Heavy gas 1.0 0.0 0.01 0.10 1.00 Scaled gas-liquid density ratio

Numerical sloshing simulation? CFD Computational Fluid Dynamics? 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

LNG sloshing technical studies at DNV 2003- LNG sloshing developments SLOSHING LOADS STRUCTURAL STRENGTH FULL-SCALE MEASUREMENTS Sloshing tests: filling level & heading sea severity impact area vessel speed scaling pump tower loading fatigue loading CFD validity studies HAZID-Failure mode analysis Structural tests FE calibration & analyses STRENGTH Acceptance criteria Capacity determination Sloshing sensor qualification Installation detailing Measuring campaign Measurement analyses Sloshing load and structural strength assessment scheme LNG sloshing Class Note (2005) Verified LNG sloshing Class Note

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 p Dynamic strength A

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

Test examples 2 of 3 Ultimate strength and fatigue tests of plywood plates on shear failure

Test examples 3 of 3 Buckling of plywood plates (NO96) FE Analyses Dynamic buckling (inertia effects) h=23cm, t=9mm, 5.00E+01 1.2 1 0.8 FEM, uniform load Test, uniform load Test, part load Johnson-Ostenfeld Elastic-Plastic Load [MPa] 4.00E+01 3.00E+01 2.00E+01 1.00E+01 t=0.625ms t=1.25ms t=2.5ms t=5ms t=10ms t=50ms σu/σf 0.6 0.00E+00-1.00E+01 0.00E+00 5.00E-03 1.00E-02 1.50E-02 2.00E-02 2.50E-02 3.00E-02 0.4-2.00E+01 Time 0.2 0 0 0.5 1 1.5 2 2.5 Slenderness Temperature strength effects 23cm, 12mm, t=2.5ms 50 40 30 Load [MPa] 20 temp variation no temp variation 10 Buckling strength criteria 0 0.00E+00 1.00E-03 2.00E-03 3.00E-03 4.00E-03 5.00E-03 6.00E-03-10 Time

LNG sloshing technical studies at DNV 2003- LNG sloshing developments SLOSHING LOADS STRUCTURAL STRENGTH FULL-SCALE MEASUREMENTS Sloshing tests: filling level & heading sea severity impact area vessel speed scaling pump tower loading fatigue loading LOADS CFD validity studies HAZID-Failure mode analysis Structural tests FE calibration & analyses STRENGTH Acceptance criteria Capacity determination Sloshing sensor qualification Installation detailing Measuring campaign Measurement analyses Sloshing load and structural strength assessment scheme LNG sloshing Class Note (2005) Verified LNG sloshing Class Note

DNV Class Note Objective Guidance to assess LNG sloshing: larger carrier designs partial filling on specified trading route partial filling while off-loading floating terminals

DNV Class Note Sloshing? Apply Class Note Limit State Analysis & Specifications Design & operational conditions Sloshing Analysis Loads no Approval request Approval yes MkIII, NO96, CS1 yes Structural Safety Assessment no Strength Assessment Report

DNV Class Note Application oriented Sloshing? Apply Class Note Limit State Analysis & Specifications Design & operational conditions Sloshing Analysis offshore (off)loading large LNG carriers spot trading / milk run receiving terminal Loads no Approval request Approval yes MkIII, NO96, CS1 yes Structural Safety Assessment no Strength Assessment Report

LNG sloshing for new designs, new operations and new trades Gastech Bilbao, March 16 th 2005 Wouter Pastoor, Tom Østvold, Eirik Byklum, Sverre Valsgård Hydrodynamics & Structures Det Norske Veritas