1、 Guidance Notes on Strength Assessment of Membrane-Type LNG Containment Systems Under Sloshing Loads GUIDANCE NOTES ON STRENGTH ASSESSMENT OF MEMBRANE-TYPE LNG CONTAINMENT SYSTEMS UNDER SLOSHING LOADS APRIL 2006 (Updated February 2014 see next page) American Bureau of Shipping Incorporated by Act of
2、 Legislature of the State of New York 1862 Copyright 2006 American Bureau of Shipping ABS Plaza 16855 Northchase Drive Houston, TX 77060 USA Updates February 2014 consolidation includes: July 2009 version plus Corrigenda/Editorials July 2009 consolidation includes: April 2006 version plus Corrigenda
3、/Editorials ABSGUIDANCE NOTES ON STRENGTH ASSESSMENT OF MEMBRANE-TYPE LNG CONTAINMENT SYSTEMS UNDER SLOSHING LOADS .2006 iii Foreword Foreword As a supplement to the hull structural strength requirements of LNG carriers, these Guidance Notes provide procedures for determination of the sloshing load
4、on LNG cargo tanks and subsequent strength assessment of membrane type containment system. The technical approach adopted in these procedures is based on direct calculation method of applying sloshing load to the containment system using finite element analysis. Determination of sloshing load from n
5、umerical simulation and scaled model test is presented. The structural analysis of the containment system considers fluid-structure interaction between liquid cargo and the LNG containment system. The procedures also consider the effect of viscoelasticity when the containment system utilizes foam ma
6、terial. Acceptance criteria are provided for different part of the containment system considering the material properties and possible failure modes. Users are referred to Part 5C, Chapter 12 of the ABS Rules for Building and Classing Steel Vessels which provides guidance on the requirements for the
7、 strength of hull structure of the membrane type LNG carriers. ABS also provides guidance on strength assessment of pump tower inside of LNG tanks in the ABS Guidance Notes on Sloshing and Structural Analysis of LNG Pump Tower (2006). iv ABSGUIDANCE NOTES ON STRENGTH ASSESSMENT OF MEMBRANE-TYPE LNG
8、CONTAINMENT SYSTEMS UNDER SLOSHING LOADS .2006 Table of Contents GUIDANCE NOTES ON STRENGTH ASSESSMENT OF MEMBRANE-TYPE LNG CONTAINMENT SYSTEMS UNDER SLOSHING LOADS CONTENTS SECTION 1 Introduction 1 1 Background . 1 3 Overview of Sloshing Analysis and Strength Assessment Procedures 2 FIGURE 1 Flowch
9、art of Sloshing Analysis and Strength Assessment of LNG Containment System 3 SECTION 2 Design Sloshing Loads 4 1 Overview . 4 3 Environmental Conditions . 4 3.1 Basic Considerations . 4 3.3 Wave Scatter Diagram . 4 3.5 Wave Spectrum . 5 5 Loading Conditions . 6 5.1 Tank Location and Geometry 6 5.3 F
10、illing Levels 6 5.5 Loading Conditions for Seakeeping Analysis . 6 7 Analysis of Ship Motion and Extreme Value . 8 7.1 Overview 8 7.3 General Modeling Considerations 8 7.5 Diffraction-Radiation Methods . 8 7.7 Panel Model Development . 8 7.9 Vessel Motion and Tank Acceleration Response Amplitude Ope
11、rators . 9 7.11 Ship Speed 9 7.13 Roll Damping Model 10 7.15 Extreme Values for Ship Motion 10 9 Selection of Critical Wave Conditions for Design Sloshing Load . 10 9.1 Sea States for Sloshing Model Test . 10 9.3 Regular Wave Conditions for Sloshing Analysis 11 11 Determination of Design Sloshing Lo
12、ad . 12 11.1 Overview 12 11.3 Sloshing Model Test 12 11.5 Panel Pressure 14 ABSGUIDANCE NOTES ON STRENGTH ASSESSMENT OF MEMBRANE-TYPE LNG CONTAINMENT SYSTEMS UNDER SLOSHING LOADS .2006 v 11.7 Idealization of Impact Load 15 11.9 Damage Index . 18 11.11 Statistical Analysis . 21 11.13 Design Sloshing
13、Load for Level 1 Assessment . 21 11.15 Design Sloshing Load by Level 2 Assessment 22 11.17 Design Sloshing Load for Level 3 Assessment . 22 11.19 Fluid-Structure Interaction . 23 TABLE 1 IACS Wave Scatter Diagrams for the North Atlantic . 5 TABLE 2 40-year and 1-year Waves for Sloshing Model Test Co
14、nditions . 11 FIGURE 1 LNG Cargo Holds and No. 2 Tank Location . 7 FIGURE 2 Definition Sketch of Membrane-Type LNG Tank 7 FIGURE 3 Flowchart for Evaluation of Design Sloshing Loads from the Model Test 13 FIGURE 4 Model Tank and Pressure Sensor Setup 13 FIGURE 5 Clustered Sensors at Tank Corner . 14
15、FIGURE 6 Time History of Local Impact Pressure at Sensors AP and Panel Pressure 15 FIGURE 7 Triangular Impulse for Uniform Pressure 16 FIGURE 8 Idealization Pressure Impulse by a Triangular Impulse 16 FIGURE 9 Sloshing Impact Pressure Time History 17 FIGURE 10 Sloshing Impact Patterns from a Model T
16、est 18 FIGURE 11 Critical Locations for Level 2 Strength Assessment for a Layered Foam Type Containment System . 20 FIGURE 12 Stress Response at Critical Locations for Different Impact Durations . 20 FIGURE 13 Failure Load, Pfailure, from the Failure Model at the Critical Locations . 20 FIGURE 14 Tw
17、o Different Scenarios for the Level 2 Strength Assessment . 22 FIGURE 15 Selection of the Response-based Design Sloshing Load for Level 3 Assessment for the Scenario Shown in Figure 14(b) . 23 SECTION 3 Strength Assessment Overview of LNG Containment System 24 1 Containment System Configuration 24 1
18、.1 Layered Foam Type Containment System 24 1.3 Box Type Containment System . 25 3 Static and Dynamic Material Properties 25 3.1 Isotropic Elasticity 26 3.3 Orthotropic Elasticity . 26 3.5 Viscoelasticity 27 3.7 Acoustic Medium . 28 3.9 Material Properties of Mastic, Plywood, Polyurethane Foam and LN
19、G 28 5 Overview of Strength Assessment of LNG Containment System. 29 vi ABSGUIDANCE NOTES ON STRENGTH ASSESSMENT OF MEMBRANE-TYPE LNG CONTAINMENT SYSTEMS UNDER SLOSHING LOADS .2006 TABLE 1 Material Properties of Mastic, Plywood, Polyurethane Foam and LNG 29 FIGURE 1 Schematic Drawing of GTT Mark III
20、 Containment System . 24 FIGURE 2 Schematic Drawing of GTT NO 96 Containment System . 25 FIGURE 3 Schematic Showing Coordinate System and Sample Labels for Plywood (PW) 26 FIGURE 4 Schematic Representation of Relaxation Modulus as a Function of Time in SLS 27 FIGURE 5 Three Levels of Strength Assess
21、ment for LNG Containment Systems 30 SECTION 4 Finite Element Analysis of Containment System (Level 1) . 31 1 General . 31 3 Geometry and Material Properties of Individual Components 31 5 Finite Element Mesh and Coordinate System 33 7 Loading and Boundary Conditions 35 9 Solution Procedures 36 9.1 Pr
22、ocedures for Layered Foam Type Containment System 36 9.3 Procedures for Box Type Containment System . 36 FIGURE 1 Simplified Model for Mark III Containment System . 32 FIGURE 2 Simplified Model for NO 96 Containment System 33 FIGURE 3 FE Mesh for Simplified Model of Mark III Containment System 34 FI
23、GURE 4 FE Mesh for Simplified Model of NO 96 Containment System 34 FIGURE 5 Loading and Boundary Conditions for Simplified Model of Mark III Containment System 35 FIGURE 6 Loading and Boundary Conditions for Simplified Model of NO 96 Containment System . 35 SECTION 5 Finite Element Analysis of Conta
24、inment System (Level 2) . 37 1 General . 37 3 Geometry and Material Properties of Individual Components 38 5 Finite Element Mesh and Coordinate System 38 7 Loading and Boundary Conditions 39 9 Solution Procedures 39 9.1 Procedures for Layered Foam Type Containment System 39 9.3 Procedures for Box Ty
25、pe Containment System . 40 FIGURE 1 FE Mesh for Simplified Model of Mark III Containment System 38 FIGURE 2 FE Mesh for Simplified Model of NO 96 Containment System 39 ABSGUIDANCE NOTES ON STRENGTH ASSESSMENT OF MEMBRANE-TYPE LNG CONTAINMENT SYSTEMS UNDER SLOSHING LOADS .2006 vii SECTION 6 Finite El
26、ement Analysis of Containment System (Level 3) . 41 1 General . 41 3 Geometry and Material Properties of Individual Components 41 5 Finite Element Mesh and Coordinate System 44 7 Loading and Boundary Conditions 45 9 Fluid-Structure Interaction . 47 11 Solution Procedures 48 11.1 Procedures for Layer
27、ed Foam Type Containment System 48 11.3 Procedures for Box Type Containment System . 49 FIGURE 1 Coupled Model for Mark III Containment System . 42 FIGURE 2 Coupled Model for NO 96 Containment System . 43 FIGURE 3 FE Mesh of Mark III Containment System 44 FIGURE 4 FE Mesh of NO 96 Containment System
28、 45 FIGURE 5 Loading and Boundary Conditions for Coupled Model in Mark III Containment System 46 FIGURE 6 Loading and Boundary Conditions for Coupled Model in NO 96 Containment System . 47 SECTION 7 Acceptance Criteria 50 1 General . 50 3 Failure Modes . 50 3.1 Yield/Rupture Failure . 50 3.3 Bucklin
29、g Failure . 50 3.5 Serviceability Limit . 50 5 Yield/Rupture Criterion 51 7 Buckling Criterion 52 9 Serviceability Limit Criterion . 52 TABLE 1 Applicable Values of Strength Reduction Factor (SRF) . 52 APPENDIX 1 Sloshing Model Test 53 1 Overview . 53 3 Test Facility . 53 3.1 Tank Model 53 3.3 Ullag
30、e and Density Effect 53 3.5 Pressure Sensors 53 5 Tank Motion 54 5.1 Generation of Tank Motion 54 5.3 Verification of Tank Motion 54 7 Data Acquisition 55 7.1 Specification of Data Acquisition System 55 7.3 Data Filtering . 55 7.5 Data Format for Submission 55 viii ABSGUIDANCE NOTES ON STRENGTH ASSE
31、SSMENT OF MEMBRANE-TYPE LNG CONTAINMENT SYSTEMS UNDER SLOSHING LOADS .2006 9 Spatially-Averaged Panel Pressure 55 9.1 Basic Considerations . 55 9.3 Load Cell vs. Spatial Averaging . 55 11 Search of Critical Sea States 55 11.1 Selection of Headings 55 11.3 Selection of Filling Levels 56 11.5 Repeated
32、 Test for Critical Condition 56 APPENDIX 2 Sloshing Analysis. 57 1 General . 57 3 Wave Conditions for Sloshing Analysis 57 3.1 Critical Sloshing Wave Domain (CSWD) . 57 3.3 Critical Sloshing Wave Conditions . 58 5 Sloshing Simulation 58 5.1 Requirement for CFD Tool . 58 5.3 Validation of CFD Tool .
33、58 5.5 Modeling of LNG Tanks . 58 5.7 Mesh Size and Time Stepping . 58 5.9 Duration of Simulation . 59 5.11 Panel Pressure 59 5.13 Numerical Results for Impact Pressure . 59 7 Design Sloshing Loads . 59 7.1 Combination of Sloshing Load . 59 7.3 Comparative Evaluation of Design Sloshing Load . 60 FIG
34、URE 1 Modeling of LNG Tank for Two-Dimensional Sloshing Analysis . 60 FIGURE 2 Example of Segment Paneling: Segment 1 for Transverse Motion . 60 APPENDIX 3 Triangular Impulse Response Function . 61 1 Definition . 61 3 Synthesis of Structural Response . 61 FIGURE 1 Synthesis of a Triangular impulse b
35、y Shorter-Duration Pulses . 62 FIGURE 2 Synthesis of a Stress Response by a Triangular Impulse Response Function . 63 APPENDIX 4 Material Properties . 65 TABLE 1 Material Properties of Mastic 65 TABLE 2 Material Properties of Plywood . 65 TABLE 3 Material Properties of Polyurethane Foam . 65 TABLE 4
36、 Material Properties of LNG . 66 TABLE 5 Ultimate Strengths of Polyurethane Foam, Plywood, and Mastic 66 ABSGUIDANCE NOTES ON STRENGTH ASSESSMENT OF MEMBRANE-TYPE LNG CONTAINMENT SYSTEMS UNDER SLOSHING LOADS .2006 ix APPENDIX 5 Parametric Study of Material Properties and Loading Patterns . 67 FIGURE
37、 1 Effect of Material Properties on Stress Response at Interface from Hydro-elastic/Hydro-visco-elastic Analysis on Mark III Containment System 68 FIGURE 2 Hydro-elastic/Hydro-visco-elastic Load Factor for Different Skewness and Durations in Mark III Containment System . 69 This Page Intentionally L
38、eft Blank ABSGUIDANCE NOTES ON STRENGTH ASSESSMENT OF MEMBRANE-TYPE LNG CONTAINMENT SYSTEMS UNDER SLOSHING LOADS .2006 1 Section 1: Introduction SECTION 1 Introduction 1 Background The design and construction of the hull, superstructure and deckhouses of an ocean-going vessel are to be based on all
39、applicable requirements of the ABS Rules for Building and Classing Steel Vessels, (referred to as ABS Steel Vessel Rules). In particular, the LNG carrier specific requirements are provided in ABS Steel Vessel Rules, Part 5C, Chapter 8. ABS also provides alternative strength requirements of hull stru
40、cture based on dynamic loading approach, known as the ABS SafeHull approach, in Part 5C, Chapter 12 of the ABS Rules for Building and Classing Steel Vessels. Inside of the membrane-type LNG tank hull structure, there are two major structural systems LNG containment system and pump tower structure. T
41、hese Guidance Notes provide procedures for determination of the sloshing load inside of LNG cargo tanks and subsequent strength assessment of membrane-type containment systems. ABS also provides guidance on strength assessment of the pump tower inside LNG tanks in the ABS Guidance Notes on Sloshing
42、and Structural Analysis of LNG Pump Tower. The membrane-type LNG containment system consists of thin metal membranes to prevent cargo leakage, foam or powdery insulation material to maintain the low temperature to keep the LNG cargo in a liquid state and an associated structure to retain the membran
43、e and insulation material and to secure them to the hull structure. Sloshing of LNG cargo can cause high impact loads on the supporting and containing structures. This is particularly critical for membrane-type tanks since these will have flat surfaces and corner regions which can lead to increased
44、peak pressures for sloshing impacts. Sloshing loads are typically estimated using a scaled model test or numerical simulation using computational fluid dynamics (CFD) methods. In the scaled model test, a tank partially filled with water is subjected to oscillatory motions to simulate the ship motion
45、s. The resulting pressures on the tank wall are then measured. Sloshing in a real LNG tank involves many complicated physical phenomena such as wave breaking, phase transition between liquid and gas during the impact, gas entrapment, cushioning effect due to corrugation, etc. The membrane-type conta
46、inment system is much more flexible compared to the steel hull structure. As a result, fluid-structure interaction plays an important role in the structural analysis of the containment system under sloshing load. Furthermore the property of foam material is viscoelastic that the structural response
47、of containment system is dependent on the time rate of sloshing impact loading. These Guidance Notes are prepared in response to the need to offer a more advanced strength assessment of the containment system beyond the simpler comparative method. The technical approach adopted in these procedures i
48、s based on the direct calculation method of applying sloshing loads to the containment system using finite element analysis. Determination of sloshing loads from numerical simulation and scaled model test is presented. The structural analysis of the containment system considers fluid-structure inter
49、action between liquid cargo and the LNG containment system The procedures also consider the effect of viscoelasticity when the containment system is partly made of foam material. Acceptance criteria are provided for different members of the containment system, considering the material properties and possible failure modes. The safety is of paramount concern to ABS and all the parties involved in design, construction and operation of the LNG carriers. ABS considers the procedures in these Guidance Notes “best engineering practice” to determine the safety of the containment system,
