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1、 GUIDANCE NOTES ON SLOSHING AND STRUCTURAL ANALYSIS OF LNG PUMP TOWER APRIL 2006 American Bureau of Shipping Incorporated by Act of Legislature of the State of New York 1862 Copyright 2006 American Bureau of Shipping ABS Plaza 16855 Northchase Drive Houston, TX 77060 USA Copyright American Bureau of
2、 Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 19:24:59 MDTNo reproduction or networking permitted without license from IHS -,-,- This Page Intentionally Left Blank Copyright American Bureau of Shipping Provided by IHS under license with ABS
3、 Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 19:24:59 MDTNo reproduction or networking permitted without license from IHS -,-,- ABS GUIDANCE NOTES ON SLOSHING AND STRUCTURAL ANALYSIS OF LNG PUMP TOWER . 2006 iii Foreword As the demand for Liquefied Natural Gas (LNG) grows worldwide, the
4、 size of LNG carriers increase and new tank designs emerge. The LNG industry wishes to apply more advanced and technically sound approaches for the structural assessment of the pump tower to ensure that the offered designs meet the requirements. This document provides guidance for applying direct ca
5、lculation procedures for the structural assessment of the pump tower structure. The procedures include ship motion calculation, determination of wave conditions for sloshing simulation, requirements for sloshing analysis, calculation of loads on pump tower structure, finite element analysis procedur
6、e and acceptance criteria for the strength assessment. This approach takes advantage of the principles and the experiences gained from the application of the ABS Dynamic Load Approach (DLA), advances in numerical simulation of the sloshing, and experiences from the structural analysis and evaluation
7、 of tubular structures. In addition to the strength assessment of pump tower structure, the methodology for fatigue and vibration analysis of pump tower structure is also addressed in this document. The requirements for the strength of hull structure of LNG carriers are addressed in the ABS Guide fo
8、r Building and Classing Membrane Tank LNG Vessels. ABS also provides Guidance Notes on Strength Assessment of Membrane-Type LNG Containment Systems under Sloshing Loads. Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2
9、008 19:24:59 MDTNo reproduction or networking permitted without license from IHS -,-,- This Page Intentionally Left Blank Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 19:24:59 MDTNo reproduction or networking pe
10、rmitted without license from IHS -,-,- ABS GUIDANCE NOTES ON SLOSHING AND STRUCTURAL ANALYSIS OF LNG PUMP TOWER . 2006 v GUIDANCE NOTES ON SLOSHING AND STRUCTURAL ANALYSIS OF LNG PUMP TOWER CONTENTS SECTION 1 Introduction1 1 Background1 3 The Concepts of Pump Tower Analysis Procedure.1 5 Overview of
11、 Sloshing Analysis and Structural Assessment of Pump Tower.2 5.1 Seakeeping Analysis of the Vessel.2 5.3 Selection of Critical Sloshing Wave Conditions.2 5.5 Sloshing Analysis2 5.7 Load Cases for Structural Analysis.3 5.9 FE Analysis of Pump Tower Structure 3 5.11 Acceptance Criteria.3 5.13 Fatigue
12、Analysis3 5.15 Vibration Analysis3 FIGURE 1 Typical Pump Tower Installed in LNG Tank 4 FIGURE 2 Flowchart for Sloshing Analysis and Structural Assessment of Pump Tower5 SECTION 2 Analysis of Ship Motions 7 1 Overview7 3 Environmental Condition7 3.1 Wave Scatter Diagram7 3.3 Wave Spectrum.7 5 Ship De
13、sign Considerations 8 5.1 Operational Condition .8 5.3 Filling Levels .8 5.5 Loading Conditions .9 5.7 Tank Location9 7 Spectral Analysis of Motion and Wave Load.10 7.1 General Modeling Considerations.10 7.3 Diffraction-Radiation Methods and Panel Model.11 7.5 Roll Damping Model11 7.7 Vessel Motion
14、and Tank Acceleration Response Amplitude Operators.11 9 Long-Term Response for Ship Motions.12 Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 19:24:59 MDTNo reproduction or networking permitted without license fro
15、m IHS -,-,- vi ABS GUIDANCE NOTES ON SLOSHING AND STRUCTURAL ANALYSIS OF LNG PUMP TOWER . 2006 TABLE 1 Standard Wave Data Recommended by IACS8 FIGURE 1 Definition Sketch of Membrane-Type LNG Tank.9 FIGURE 2 LNG Cargo Holds and No. 2 Tank Location10 SECTION 3 Wave Conditions for Sloshing Analysis13 1
16、 General 13 3 Resonance Sloshing Period 13 5 Sloshing Motion Parameters14 7 Critical Sloshing Wave Condition (CSWC)14 7.1 Equivalent Wave Amplitude.14 7.3 Critical Sloshing Wave Domain (CSWD).15 7.5 Motion Components 15 SECTION 4 Sloshing Analysis17 1 General 17 3 Sloshing Simulation .17 3.1 Require
17、ment for CFD Tool 17 3.3 Validation of CFD Tool 17 3.5 Modeling of LNG Tanks.17 3.7 Mesh Size and Time Stepping.17 3.9 Duration of Simulation.18 3.11 Numerical Results for Pump Tower Analysis.18 FIGURE 1 Modeling of LNG Tank for Two-Dimensional Sloshing Analysis.18 SECTION 5 Loads on Pump Tower 19 1
18、 General 19 3 Sloshing Load19 3.1 Morison Formula .19 3.3 Wave Impact Zone 21 3.5 Shielding Effect .22 5 Inertial loads.22 5.1 Inertial Loads in the FEM Structural Model22 7 Thermal Load and Pump Torque Load22 7.1 Thermal Load22 7.3 Pump Torque.22 9 Load Cases for Pump Tower Structural Analysis23 9.
19、1 Load Cases 1 and 2: Transverse Force on Pump Tower 23 9.3 Load Case 3: Longitudinal Force on Pump Tower 23 9.5 Load Case 4 and 5: Transverse Force on Pump Tower Base Support.24 9.7 Load Case 6: Longitudinal Force on Pump Tower Base Support24 Copyright American Bureau of Shipping Provided by IHS un
20、der license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 19:24:59 MDTNo reproduction or networking permitted without license from IHS -,-,- ABS GUIDANCE NOTES ON SLOSHING AND STRUCTURAL ANALYSIS OF LNG PUMP TOWER . 2006 vii FIGURE 1 Definition of Length Coordinate and Normal Vec
21、tor.20 FIGURE 2 Typical Fluid Motion in Tank at a Partial Filling Condition20 FIGURE 3 Typical Sectional Force Profiles at Partial Filling Conditions21 FIGURE 4 Simplified Temperature Distribution for Thermal Analysis at Partial Filling Conditions.23 SECTION 6 Structural Analysis of Pump Tower .25 1
22、 General 25 3 Structural Members25 5 3-D Finite element modeling25 5.1 Coordinate System25 5.3 Material Properties25 5.5 Element Types26 7 Boundary Conditions27 TABLE 1 Material Properties of Stainless Steel ASTM A312 Gr. 304L26 FIGURE 1 Cargo Tank Configuration28 FIGURE 2 Plan View of Pump Tower28
23、FIGURE 3 Complete Pump Tower Model .29 FIGURE 4 Stress-Strain Curve for Stainless Steel .30 FIGURE 5 Pump Tower FE Model-Main Section30 FIGURE 6 Pump Tower FE Model Liquid Dome Cover.31 FIGURE 7 Pump Tower FE Model Base Plate.31 FIGURE 8 Boundary Conditions32 FIGURE 9 Schematics of the Sliding Joint
24、s Mounted on the Top Braces.33 SECTION 7 Acceptance Criteria .35 1 General 35 3 Tubular Members.35 3.1 Summary of Criteria for Tubular Members35 3.3 Individual Stresses35 3.5 Members Subjected to Combined Loads38 3.7 Local Buckling.39 5 Tubular Joints 40 5.1 Joint Types40 5.3 Joint Capacity41 5.5 St
25、rength State Limit.43 7 Liquid Dome Cover and Base Plate.43 7.1 F.E. Model.43 7.3 Strength Criterion43 Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 19:24:59 MDTNo reproduction or networking permitted without lic
26、ense from IHS -,-,- viii ABS GUIDANCE NOTES ON SLOSHING AND STRUCTURAL ANALYSIS OF LNG PUMP TOWER . 2006 TABLE 1 Strength Factor, Qu.42 FIGURE 1 Examples of Critical Buckling Stress .37 FIGURE 2 Geometry of Tubular Joints40 FIGURE 3 Examples of Tubular Joint Categoriztion.41 APPENDIX 1 References45
27、APPENDIX 2 Benchmark Tests for Sloshing CFD Tools47 1 Purpose of Benchmark Tests 47 3 Tank Geometry47 5 Tank Motion .48 7 Simulation Results.48 7.1 Velocity and Acceleration Time History.48 7.3 Velocity and Acceleration Profile.48 APPENDIX 3 Fatigue Assessment49 1 General 49 1.1 Load 49 1.3 Stress R
28、ange.49 1.5 S-N curve 50 1.7 Fatigue Damage50 3 Simplified Fatigue Assessment Method.50 5 Spectral-based Fatigue Assessment Method52 7 Reference 52 APPENDIX 4 Vibration Analysis of Pump Tower.53 1 General 53 1.1 Sources of Excitation.53 1.3 Loading Conditions53 1.5 Tank Location and Filling Levels .
29、53 3 Free Vibration Analysis54 3.1 Local FE Model and Boundary Conditions 54 3.3 Added Mass 54 3.5 Natural Frequency and Mode Shape.54 5 Forced Vibration.55 5.1 Global FE Model and Boundary Conditions.55 5.3 Excitations.55 5.5 Critical Areas.55 7 Acceptance Criteria55 9 References.56 FIGURE 1 First
30、Mode Shape in Longitudinal and Transverse Modes 54 Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 19:24:59 MDTNo reproduction or networking permitted without license from IHS -,-,- ABS GUIDANCE NOTES ON SLOSHING A
31、ND STRUCTURAL ANALYSIS OF LNG PUMP TOWER . 2006 1 S E C T I O N 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 applicable requirements of the ABS Rules for Building and Classing Steel Vessels (Steel V
32、essel Rules). The design criteria for an LNG carrier are located in the Steel Vessel Rules, Part 5, Chapter 8. Alternative hull strength requirements in compliance with the SafeHull-based criteria are provided in the ABS Guide for Building and Classing Membrane Tank LNG Vessels (Guide for SafeHull L
33、NGC). Inside the LNG tank, there are two major structural systems other than the hull: LNG containment system and pump tower structure. These Guidance Notes supplement the Steel Vessel Rules and the Guide for SafeHull LNGC by providing a sloshing and structural analysis procedure for the structural
34、assessment of the pump tower. The structural assessment of the LNG containment system is addressed in the ABS Guidance Notes on Strength Assessment of Membrane-Type Containment System under Sloshing Load for LNG Carriers. The pump tower system consists of pipes and pumps to load and discharge the li
35、quid cargo and tubular members to support the structure. The pump tower is located close to the aft bulkhead, hanging over the liquid dome and connected to base support at the tank bottom, as shown in Section 1, Figure 1. The structural integrity of these systems is critical for the safe operation o
36、f the LNG carrier. Approval of the structural design of the pump tower systems has typically been made based on the analysis and assessment provided by the manufacturers of the systems. This is a practical and well- founded practice for the review of similar designs when the previous designs have sh
37、own good service experience. As the LNG market grows, the size of LNG carriers is increasing and the operational condition is diversifying. New cargo tank designs are also emerging. The LNG industry demands a more advanced and technically sound approach for the structural assessment of the pump towe
38、r to ensure that the offered designs meet the requirements. This document provides guidance for applying a direct calculation procedure for the structural assessment of the pump tower structure. This approach takes advantage of the basic principles and the experiences gained from the application of
39、the ABS Dynamic Load Approach (DLA), advances in numerical simulation of the sloshing, and experiences from the structural analysis and evaluation of tubular structures. 3 The Concepts of Pump Tower Analysis Procedure The analysis procedure provided in these Guidance Notes is a first-principle-based
40、, direct calculation approach to identify the critical sloshing load on the pump tower during its design life and to evaluate the structural integrity of the pump tower under that load. The procedure adopts an advanced but most practical analysis method. In particular, linear seakeeping analysis, tw
41、o-dimensional sloshing simulation and FE modeling/analysis of the pump tower structure by beam and plate elements are utilized. Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 19:24:59 MDTNo reproduction or network
42、ing permitted without license from IHS -,-,- Section 1 Introduction 2 ABS GUIDANCE NOTES ON SLOSHING AND STRUCTURAL ANALYSIS OF LNG PUMP TOWER . 2006 The analysis procedure includes Determination of long-term extreme ship motions arising from design environmental condition Determination of wave cond
43、itions that may produce a large sloshing motion Time domain simulation of the sloshing motion of liquid cargo Calculation of sloshing and accompanying loads on the pump tower structure Structural analysis of the pump tower, using the finite element method Strength assessment of the pump tower struct
44、ures in accordance with acceptance criteria 5 Overview of Sloshing Analysis and Structural Assessment of Pump Tower 5.1 Seakeeping Analysis of the Vessel Section 1, Figure 2 shows the flowchart of the pump tower analysis procedure that is covered in these Guidance Notes. The procedure starts with th
45、e seakeeping analysis of the vessel, which is described in Section 2. The main objective of the seakeeping analysis is to calculate the motion of the vessel and LNG tank for a given operating and environmental condition, to be used as motion input for the sloshing analysis. Response amplitude operat
46、ors (RAOs) of ship and tank motions are calculated by linear frequency- domain ship motion analysis, from the hull form and loading conditions provided by the ship designer. Long-term extreme responses of ship and tank motion for the design environmental condition are obtained by spectral analysis.
47、5.3 Selection of Critical Sloshing Wave Conditions The objective of the procedure described in Section 3 is to determine a set of regular wave conditions (wave period, heading and amplitude), called the Critical Sloshing Wave condition (CSWC), that are likely to produce a large sloshing motion in th
48、e cargo tank. Firstly, the Critical Sloshing Wave Domain (CSWD), which is a set of wave conditions (wave period and heading) that may produce a large sloshing motion, is defined based on tank motion response calculated from the seakeeping analysis and proximity of tank motion period to the sloshing natural period. Among the tank motion parameters, the local values of longitudinal and transverse acceleration at the tank center are used to determine the wave conditions in