Structural DesignAssessment

Primary Structure of Type BSpherical Tank LNG Ships

Guidance on direct calculations

May 2004

ShipRightDesign and construction

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Lloyd's Register, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as the Lloyd's Register Group. The Lloyd's Register Group assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Lloyd's Register Group entity for the provision of this information or advice and in that case any responsibility. Lloyds Register Marine Business Stream is a part of Lloyds Register.

Lloyds Register,2004

Document History

Document Date: Notes:

November 2001 Intranet user review version

July 2002 General release (Primary Structure of Bulk Carriers removed).

Notice 1 October 2002

Revisions as identified in History of Development up to January 2004.

May 2004 Revisions as identified in Structural Design Assessment Primary Structure of Type B Spherical Tank LNG ships, Changes incorporated in May 2004 version.

LLOYDS REGISTER

Chapter Contents

Primary Structure of Type B Spherical Tank LNG Ships May 2004

1 Introduction

2 Analysis of Primary Structure of Type B Spherical Tank LNG Ships

AppendixA Procedure to Apply Transverse

Asymmetric Loads to a Half-Breadth FE Model

PROCEDURES MANUAL

LLOYDS REGISTER

Contents

Primary Structure of Type B Spherical Tank LNG Ships May 2004

CHAPTER 1 INTRODUCTION 1

Section 1 Application2 Symbols3 Direct calculation procedures report

CHAPTER 2 ANALYSIS OF PRIMARY STRUCTURE OF TYPE B SPHERICAL TANK LNG SHIPS 5

Section 1 Objectives2 Structural modelling3 Boundary conditions3.1 Introduction3.2 Symmetric boundary conditions for global loads3.3 Symmetric boundary conditions for local loads3.4 Asymmetric boundary conditions for transverse loads3.5 Asymmetric boundary conditions for torsional moments4 Loading conditions4.1 Introduction4.2 Subload cases4.3 Procedures to derive subload cases5 Permissible stresses6 Buckling acceptance criteria

APPENDIX A PROCEDURE TO APPLY TRANSVERSEASYMMETRIC LOADS TO A HALF-BREADTH FE MODEL 43

Section A1 Procedure to apply transverse asymmetric loadsto a half-breadth FE model

PROCEDURES MANUAL

Primary Structure of Type B Spherical Tank LNG Ships May 2004

LLOYDS REGISTER

1LLOYDS REGISTER 1

Introduction

Primary Structure of Type B Spherical Tank LNG Ships May 2004

Chapter 1SECTION 1

Section 1: ApplicationSection 2: Symbols

Section 3: Direct calculation procedures report

Section 1: Application

1.1 The ShipRight Structural Design Assessment (SDA)procedure is mandatory for all LNG ships fitted withIndependent Type B spherical cargo tanks, as defined byLloyd's Register's Rules for Ships for Liquefied Gases.

1.2 The Rules and Regulations for the Construction andClassification of Ships for the Carriage of Liquefied Gases inBulk incorporating the IMO International Code for theConstruction and Equipment of Ships Carrying LiquefiedGases in Bulk (IGC Code) is referred to in this document asLloyd's Register's Rules for Ships for Liquefied Gases.References to the IGC Code in this procedure areequivalent to references to the Rules for Ships for LiquefiedGases.

1.3 For compliance with the ShipRight SDA procedure,direct calculations are to be adopted for the determinationand verification of the stress level and buckling capabilityof ship primary structural members, including the structuresupporting the cargo tanks as specified in Lloyds RegistersRules for Ships for Liquefied Gases.

1.4 The minimum requirments specified in thisprocedure, in addition to the requirements in LloydsRegisters Rules and Regulations for the Classification ofShips (hereinafter referred to as the Rules for Ships) are tobe complied with.

1.5 The SDA procedure requires the following: A detailed analysis of the ship's structural response to

applied static and dynamic loadings using finite elementanalysis.

Other direct calculations as applicable.

1.6 This document details the SDA procedure for thefinite element analysis of the ship's hull structure includingtank covers and foundation deck. The primary structure ofthe ship in the central and bow regions is to be verifiedusing the procedure specified in Chapter 2.

1.7 In general, the direct calculation is to be based on athree-dimensional finite element analysis (3-D FEA) carriedout in accordance with these procedures. Wherealternative procedures are proposed, these are to be agreed with Lloyds Register before commencement.

1.8 A detailed report of the calculations is to besubmitted and must include the information detailed in3.1. The report must show compliance with the specifiedstructural design criteria given in Sections 5 and 6 ofChapter 2.

1.9 If the computer programs employed are not recognised by Lloyds Register, full particulars of theprograms will also be required to be submitted, see Pt 3, Ch1,3.1 of the Rules for Ships.

1.10 Lloyds Register may require the submission ofcomputer input and output to further verify the adequacyof the calculations carried out.

Introduction

Primary Structure of Type B Spherical Tank LNG Ships May 2004

Chapter 1SECTIONS 1 & 2

LLOYDS REGISTER2

1.11 Ships which have novel features or unusual hullstructural or tank configurations may need special consideration and additional load cases may be required.

1.12 It is recommended that the designer consults withLloyds Register on the SDA analysis requirements early onin the design cycle.

Section 2: Symbols

2.1 For the purpose of this procedure the followingdefinitions apply:

2.1.1 Hull structure supporting the cargo containmentsystem includes the following structural items: foundation deck in way of skirts; underskirt support structure and all local areas of hull

structure to which they are connected; cross tank structure; hopper tank inner structure in way of base of skirts; and side shell and inner hull between the hopper crown and

the foundation deck in the forward hold.

2.1.2 Hull structure not supporting the cargocontainment system includes all structural items not listedin 2.1.1.

2.1.3 Upper surface of the foundation deck refers to theboundary between the hull structure and cargocontainment system.

2.1.4 Figs. 2.2.2 and 2.2.3 in Chapter 2 give thedefinitions of other structural items referred to in thisdocument.

2.2 The symbols used in this procedure are defined asfollows:

L = Rule length, in metres, see Pt 3, Ch 1,6 of theRules for Ships

B = moulded breadth, in metres, see Pt 3, Ch 1,6of the Rules for Ships

D = depth of ship, in metres, see Pt 3, Ch 1,6 ofthe Rules for Ships

kL, k = higher tensile steel factor, see Pt 3, Ch 2,1.2of the Rules for Ships

SWBM = still water bending momentVWBM = design vertical wave bending moment

Mw = design vertical wave bending moment,including hog and sag factor, f2 , and shipservice factor, f1 , see Pt 3, Ch 4,5 of theRules for Ships

Mwo = vertical wave bending moment, excludinghog and sag factor and ship service factor,see Pt 3, Ch 4,5 of the Rules for Ships

f1 = the ship service factor, see Pt 3, Ch 4,5 of theRules for Ships

f2 = the hogging/sagging factor, see Pt 3, Ch 4,5of the Rules for Ships

Ms = Rule permissible still water bending moment,see Pt 3, Ch 4,5 of the Rules for Ships

Ms = design still water bending moment, see Pt 3,Ch 4,5 of the Rules for Ships

Introduction

LLOYDS REGISTER 3

Primary Structure of Type B Spherical Tank LNG Ships May 2004

Chapter 1SECTION 2

Msw = still water bending moment distributionenvelope to be applied to the FE models forstress and buckling assessments. The valuesof Msw are to be greater than Ms and lessthan or equal to Ms. These values are to beincorporated into the ships Loading Manualand loading instrument as the assignedpermissible still water bending momentvalues. Msw hereinafter referred to as thepermissible still water bending moment

Tsc = scantling draughtT = condition draught = roll angle

Cb = block coefficient, see Pt 3, Ch 1,6 of the Rulesfor Ships

x = longitudinal distance from amidships to thecentre of gravity of the tank, x is positiveforward of amidships

V = service speed (knots)g = gravity constant = density of sea-water (specific gravity to be

taken as 1,025)h = local head for pressure evaluation

c = density of cargo (specific gravity to be takenas 0,5)

Po = design vapour pressure, see Ch 4,2.6 of theRules for Ships for Liquefied Gases

Ax, Ay, Az = maximum dimensionless acceleration factors(i.e. relative to the Acceleration of gravity) inthe longitudinal, transverse and verticaldirections respectively

hx, hy, hz = local head for pressure evaluation measuredfrom the tank reference point in thelongitudinal, transverse and verticaldirections respectively

t = thickness of platingtc = thickness deduction for corrosion

c = elastic critical buckling stresso = specified minimum yield stress of material

(special consideration will be given to steelwhere o 355 N/mm2, see Pt 3, Ch 2,1 ofthe Rules for Ships)