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ZEIT4005ZEIT4005

NAVALNAVAL

ZEIT4005 NA & MEDr Warren Smith

AND MARINE AND MARINEENGINEERINGENGINEERING



SHIP STRUCTURESSHIP STRUCTURES

A difficult problem A difficult problemperhaps the most complex structural engineering perhaps the most complex structural engineering problem there isproblem there is Tupper Tupper


Chapters 14 and 15Chapters 14 and 15

SHIP STRUCTURESSHIP STRUCTURESInfluence of the EnvironmentInfluence of the Environment(defines aspects of the loading)(defines aspects of the loading)

Temperature Temperature


Waves WavesMarine PollutionMarine Pollution

Influenced by Ship Motions, Ship Operation andInfluenced by Ship Motions, Ship Operation andMaintenanceMaintenance

SHIP MOTIONSSHIP MOTIONS


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STRUCTURAL FAILURESTRUCTURAL FAILURE

Failure occurs when the structure can no longer carry Failure occurs when the structure can no longer carry out its intended functionout its intended function Tupper Tupper

DistortionDistortionCracking Cracking


Instability Instability

Primary Failure ModesPrimary Failure Modes Yield YieldFatigueFatigueBuckling Buckling Brittle FractureBrittle Fracture

HULL STRESSESHULL STRESSES- - forces due to wavesforces due to waves


LOADSLOADSExcluding inertia forces due to the motion, the primary Excluding inertia forces due to the motion, the primary static longitudinal loading is fromstatic longitudinal loading is from

Weight force (gravity) Weight force (gravity) Water pressure (buoyancy) Water pressure (buoyancy)


For longitudinal strength, a ship is considered to be anFor longitudinal strength, a ship is considered to be anelastic structure bending as a whole unit like a girder onelastic structure bending as a whole unit like a girder onan elastic foundationan elastic foundation

Referred to as ship girder or hull girderReferred to as ship girder or hull girder

A ship must also support transverse loads and local loads A ship must also support transverse loads and local loadsnormally considered separately from the longitudinal loadsnormally considered separately from the longitudinal loads

STRUCTURESTRUCTUREUsually convenient to divide the structure andUsually convenient to divide the structure andassociated response into three componentsassociated response into three components

Primary Primary Secondary Secondary


Tertiary Tertiary

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STRUCTURESSTRUCTURES


RESPONSESRESPONSES

Primary Response Primary Response is the response of the entire hullis the response of the entire hullbending and twisting as a beam under the externalbending and twisting as a beam under the externallongitudinal distribution of vertical, lateral and twisting loads.longitudinal distribution of vertical, lateral and twisting loads.

Secondary response Secondary response comprises the stress and deflection of comprises the stress and deflection of


a single panel of stiffened plating a single panel of stiffened plating eg eg the panel of bottom structure contained between twothe panel of bottom structure contained between twoadjacent transverse bulkheads.adjacent transverse bulkheads.

Tertiary response Tertiary response describes the outdescribes the out--of of--plane deflectionplane deflectionand associated stress of an individual panel of plating and associated stress of an individual panel of plating

PRIMARY STRENGTHPRIMARY STRENGTH

The first step in the structural analysis of a ship The first step in the structural analysis of a shipderivation of the maximum bending moment and shear forcederivation of the maximum bending moment and shear forceexperienced by the ship girder when floating in waves and theexperienced by the ship girder when floating in waves and thesubsequent derivation of the resulting stress levelssubsequent derivation of the resulting stress levels


raditionally assumed that the ship floats on araditionally assumed that the ship floats on a trochoidaltrochoidal wave of length equal to the length of the designed (deep) wave of length equal to the length of the designed (deep) waterline and a height equal to LWL/20 or waterline and a height equal to LWL/20 or 0.6 0.6 LWLLWL metresmetres

Later more generally employedLater more generally employed

Probabilistic approaches have also been taken in theProbabilistic approaches have also been taken in thederivation of a suitable wave height ( derivation of a suitable wave height (eg eg 100 year wave)100 year wave)

maximum wave height likely to be encountered by the ship over amaximum wave height likely to be encountered by the ship over ataking into account its expected route and its operating profiletaking into account its expected route and its operating profile

Area 47

Use a universalocean atlas toselect arepresentativesignificant waveheight andaverage period


Typical Ocean Atlas DataSource: Rawson & Tupper 1994, p 333.



1. Sagging 2. Hogging



Hogging and Sagging wave induced

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STRENGTH CURVESSTRENGTH CURVES

Weight distribution(s) Weight distribution(s)Buoyancy curves for still water and in wavesBuoyancy curves for still water and in waves

Forces plotted per unit lengthForces plotted per unit length

Problem addressedas a sim le beam of len thProblem addressedas a sim le beam of len th LWLLWL


with a variable load applied with a variable load applied

Resulting shear force, bending moment and deflection curvesResulting shear force, bending moment and deflection curvescan be determined by simple beam theory can be determined by simple beam theory Knowing the section modulus of the ship girder along itsKnowing the section modulus of the ship girder along itslength, bending stresses and shear stresses can be determined.length, bending stresses and shear stresses can be determined.

The load curve can also be used to set boundary conditions The load curve can also be used to set boundary conditionsfor FEA of the entire ship structure.for FEA of the entire ship structure.

STRUCTURESSTRUCTURES


SECTION MODULUS, Z=I/zSECTION MODULUS, Z=I/z

Function of longitudinal positionFunction of longitudinal positionOnly continuous structure is assumed to contribute to theOnly continuous structure is assumed to contribute to theship girder strength,ship girder strength, ieie., keel, longitudinal stiffeners, shell., keel, longitudinal stiffeners, shellplating and decksplating and decks


he superstructure is usually not taken into accounthe superstructure is usually not taken into account

Classification societies such as Lloyd's Register of Shipping andClassification societies such as Lloyd's Register of Shipping and American Bureau of Shipping (ABS) have developed their own American Bureau of Shipping (ABS) have developed their ownempirical methods of determining maximum bending momentsempirical methods of determining maximum bending momentsand minimum section modulus for their ships and these areand minimum section modulus for their ships and these arecontained in their published rules.contained in their published rules.

Primary Structural Sections for a RAN FFGPrimary Structural Sections for a RAN FFGSource: Gibbs & Cox,Source: Gibbs & Cox, DwgDwg No AO10873No AO10873


Strength Curves for a RAN FFGStrength Curves for a RAN FFGSource: Gibbs & Cox,Source: Gibbs & Cox, DwgDwg No AO10873No AO10873


Strength Curves for a RAN FFGStrength Curves for a RAN FFGSource: Gibbs & Cox,Source: Gibbs & Cox, DwgDwg No AO10873No AO10873


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Stress and Inertia Calculation Data for a RAN FFGStress and Inertia Calculation Data for a RAN FFGSource: Gibbs & Cox,Source: Gibbs & Cox, DwgDwg No AO10873No AO10873


Stress and Inertia Calculation Data for a RAN FFGStress and Inertia Calculation Data for a RAN FFGSource: Gibbs & Cox,Source: Gibbs & Cox, DwgDwg No AO10873No AO10873


TRANSVERSE STRENGTH TRANSVERSE STRENGTH

The transverse structure of a ship normally has to resist The transverse structure of a ship normally has to resistthe following loads:the following loads:

hydrostatic pressure against the hullhydrostatic pressure against the hull water loads on exposed decks water loads on exposed decks


loadings on internal decks (both dead and live loads)loadings on internal decks (both dead and live loads) wind loads on the superstructure wind loads on the superstructurestowage loadsstowage loadsloadings on internal bulkheadsloadings on internal bulkheadsloadings on tanksloadings on tanks

INDEPENDENT LOADSINDEPENDENT LOADS

These loads are usually local in nature and are These loads are usually local in nature and areconsidered independently of primary strength andconsidered independently of primary strength andtransverse strength. Examples are:transverse strength. Examples are:

slamming slamming


nuclear blastnuclear blastgun and missile blastgun and missile blast

dry docking dry docking underwater shock underwater shock aircraft landing aircraft landing

SHIP STRUCTURALLOADS

LOADS TO BECOMBINED

BASICLOADS

Standard live loads

Deadloads

SEAENVIRONMENT

Hullgirderloads

Sealoads

INDIVIDUAL LOADS

OPERATIONALENVIRONMENT

Slamming

Floodin

COMBATENVIRONMENT

Shock

Airblast


l s

Liquid/tank loads

Loads based onknown equipmentand

cargo (including parkedaircraft)

l s

Weatherloads

Ship motion loads

l i

Aircraftlanding

Tank overfill

Docking

GeneralOperations

i l s t

Fragments

Gun blast& accidentalignition

Load Application MatrixLoad Application Matrix


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FATIGUEFATIGUE

Because of the dynamic periodic rate of loading on theBecause of the dynamic periodic rate of loading on theship structure, structural fatigue considerations,ship structure, structural fatigue considerations,although very complex, are important whenalthough very complex, are important when analysing analysing the ships structure.the ships structure.


MATERIALSMATERIALS

Material used most frequently in ship structures is mildMaterial used most frequently in ship structures is mildsteel because of its low cost and relative ease of welding steel because of its low cost and relative ease of welding

Alternatives: Alternatives:High yield (HY80) steel is used in high strength areas such asHigh yield (HY80) steel is used in high strength areas such as


bilge and sheer strakes of the shell to arrest primary cracking bilge and sheer strakes of the shell to arrest primary cracking this steel needs to be preheated before welding and production is costly.this steel needs to be preheated before welding and production is costly.

High strength low alloy steelHigh strength low alloy steelhas a high yield strength, can be welded without preheat treatment andhas a high yield strength, can be welded without preheat treatment andalthough more costly than mild steel, it is not as expensive as HY80 steelalthough more costly than mild steel, it is not as expensive as HY80 steel

Aluminium Aluminium Alloys and Composites Alloys and CompositesSpecial applications (superstructures, masts and internal partitionSpecial applications (superstructures, masts and internal partitionbulkheads, specialist hull forms)bulkheads, specialist hull forms)

Definition of Definition of Panel StressesPanel Stresses


Panel Modes of Structural FailurePanel Modes of Structural FailurePanel Collapse (4)Panel Collapse (4)

stiffener flexurestiffener flexurecombined buckling combined buckling membrane yieldmembrane yieldstiffener buckling stiffener buckling

Panel Yield (4)Panel Yield (4)

Girder Collapse (3)Girder Collapse (3)tripping tripping compression, flange/platecompression, flange/plate

Girder Yield (4)Girder Yield (4)bending/tension, flange/platebending/tension, flange/plate

Frame Collapse (1)Frame Collapse (1)


tension/compression,tension/compression,flange/plateflange/plate

Panel Serviceability (2)Panel Serviceability (2)plate bending,plate bending,transverse/longitudinaltransverse/longitudinal

Panel Failure (1)Panel Failure (1)local buckling local buckling

plastic hingeplastic hinge

Frame Yield (4)Frame Yield (4)tension/compression,tension/compression,flange/plateflange/plate

(and then there (and then there are the load cases?) are the load cases?)

NEW SHIPNEW SHIPRemaining life = Design Life?Remaining life = Design Life?


Remaining life?Remaining life?


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SECOND HAND SHIPSECOND HAND SHIPRemaining life = ???Remaining life = ???


Current trendsCurrent trendsMore rigorous design analysisMore rigorous design analysis

more efficiently designed structuresmore efficiently designed structureslighterlighterlower safety factorslower safety factorslower marginslower marginshi her stresseshi her stresses


greater demand on quality of construction andgreater demand on quality of construction andmaintenancemaintenance

Reduced manning Reduced manning

CASE STUDIESCASE STUDIES

HMAS SuccessHMAS SuccessFFGsFFGs


Commercial ExamplesCommercial Examples

HMAS SuccessHMAS Success - - stiffener bracketstiffener bracket


Case Study ACase Study A -- HMAS SuccessHMAS SuccessBottom stiffener fatigue perceived as problemBottom stiffener fatigue perceived as problem1982 in1982 in--house hand calculationshouse hand calculations (3 years to crack)(3 years to crack)Lloyds Register of Shipping Lloyds Register of Shipping (Theoretically 14 years to crack but final(Theoretically 14 years to crack but finalestimate using historical data was 25 years)estimate using historical data was 25 years)

1 r rvi i r i1 r rvi i r i

RAN StateRAN State--of of--PracticePractice


vi i ivi i ioriginal analysis in itself was insufficient due to the statisticaloriginal analysis in itself was insufficient due to the statisticalnature of fatigue analysis and the assumptions on loading nature of fatigue analysis and the assumptions on loading

FFG LifeFFG Lifeextensionextension


superstructuresuperstructurecrackingcracking

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FFG SuperstructureFFG Superstructure - - known fixesknown fixes


Case Study BCase Study B -- RAN FFGRAN FFG--7s7saim to extend life of shipaim to extend life of shipknown defect (superstructure cracking)known defect (superstructure cracking)fatigue analysisfatigue analysis

RAN StateRAN State--of of--PracticePractice


decision to extend even though cracking decision to extend even though cracking will continue will continue

FFG DetailFFG Detail - - Finite Element ModelFinite Element Model


Commercial ShipsCommercial Ships

examples of damage / failureexamples of damage / failure

MV Gi a 2MV Gi a 2


MT KirkiMT Kirki

MV Giga 2 alongsideMV Giga 2 alongside


MV Giga 2MV Giga 2

Malaysian Flag bulk carrierMalaysian Flag bulk carrierClassNK ClassNK (Japan)(Japan)Built 1981Built 1981On 5 November 1996 (age 15)On 5 November 1996 (age 15)


Trim problems during unloading led to Trim problems during unloading led toballasting of adjacent holdballasting of adjacent holdCargo hold bulkhead failureCargo hold bulkhead failure

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Typical structural configuration of cargo Typical structural configuration of cargohold for a single skin bulk carrierhold for a single skin bulk carrier


MV Giga 2MV Giga 2


failed upper stoolfailed upper stool

MV Giga 2MV Giga 2


failed bulkheadfailed bulkhead

MT Kirki under tow MT Kirki under tow


MT KirkiMT Kirki

Greek registered 97083Greek registered 97083 tonnetonne tanker built in 1969tanker built in 1969On 20 July 1991 (age 22)On 20 July 1991 (age 22)

Loss of bow section, fire and evacuation of crew, 55 milesLoss of bow section, fire and evacuation of crew, 55 milesoff WA coastoff WA coast


maintained in conformity with requirementsmaintained in conformity with requirements

MT KirkiMT Kirki

failed transversefailed transverse


sectionsection

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MT KirkiMT Kirki


sectionsection

MT KirkiMT Kirkicorroded platingcorroded plating


for small ships, local loading, not global longitudinalfor small ships, local loading, not global longitudinalstrength, determines scantlings and life extensions arestrength, determines scantlings and life extensions arepossible following possible following survey survey

Some GeneralSome General Heuristics forHeuristics forRemaining LifeRemaining Life


where overall longitudinal strength is a critical factor, where overall longitudinal strength is a critical factor,detailed information on the original design is requireddetailed information on the original design is requiredand examined in the light of current knowledge andand examined in the light of current knowledge andpracticepractice

StateState--of of--ResearchResearch

Mechanical properties of aged structureMechanical properties of aged structureHull Condition Monitoring Hull Condition Monitoring NonNon--prescriptive design methodsprescriptive design methods


Maintenance ManagementMaintenance Management

Failure modesFailure modesexcessive tensile or compressive yield, buckling due toexcessive tensile or compressive yield, buckling due tocompressive or shear instability, fatigue, brittle fracturecompressive or shear instability, fatigue, brittle fracture

Effects of age and service lifeEffects of age and service lifepreservation and repair, condition monitoring preservation and repair, condition monitoring

Structural Design IssuesStructural Design Issues


corrosion, deformation, fatigue, change in materialcorrosion, deformation, fatigue, change in materialpropertiesproperties


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