DNVGL-CG-0151 Strength analysis of general cargo and multi-purpose dry cargo ships · 2016. 2....

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DNV GL AS

CLASS GUIDELINE

DNVGL-CG-0151 Edition February 2016

Strength analysis of general cargo andmulti-purpose dry cargo ships

FOREWORD

DNV GL class guidelines contain methods, technical requirements, principles and acceptancecriteria related to classed objects as referred to from the rules.

© DNV GL AS February 2016

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Class guideline — DNVGL-CG-0151. Edition February 2016 Page 3Strength analysis of general cargo and multi-purpose dry cargo ships

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CONTENTS

Changes – current.................................................................................................. 3

Section 1 Introduction............................................................................................ 51 General................................................................................................ 52 Ship characteristics............................................................................. 53 Objectives............................................................................................ 64 Application and scope..........................................................................65 Mandatory scope of calculation/analysis, Level 1................................66 Scope for Level 2 global analysis........................................................ 7

Section 2 Level 2 Global analysis............................................................................81 Model idealisation................................................................................82 Load generation.................................................................................103 Structure deformations and stopper forces at deflection limiters.......22

Changes – historic................................................................................................33

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SECTION 1 INTRODUCTION

1 GeneralThis class guideline (CG) should be considered in connection with the DNV GL’s Rules for classification ofships, RU SHIP Pt.3, Hull, and RU SHIP Pt.5 Ch.1 Sec.5, General Cargo and Multi-Purpose Dry Cargo Ships.This class guideline describes the scope and methods required for structural analysis of general cargo shipsand multi-purpose dry cargo ships and the background for how such analyses should be carried out. Thedescription is based on relevant rules for classification of ships, guidance and software.The DNV GL Rules for classification of ships may require direct structural strength analyses in case of acomplex structural arrangement, or unusual vessel size.Structural analyses carried out in accordance with the procedure outlined here and in the DNVGL CG 0127,Finite element analysis, fulfills the requirements for calculation in the rules.Where the text refers to the rules for classification of ships, the references refer to the latest edition of therules for classification of ships.

2 Ship characteristicsGeneral cargo and multi-purpose dry cargo ships, in the following referred to as MPV's, are equipped withappropriate facilities to carry general cargo, heavy cargo, project cargo and containers. This class guideline isrelevant for ships having a center cargo hold with a length greater than 50% of the cargo hold area and maybe characterized by the following:

— long center cargo hold— large deck openings and narrow deck strakes— heavy lift cranes, generally situated at the ship sides— large uniform distributed loads on tank tops (block loads)— large uniform distributed loads and container stack loads on weather deck covers— close fitted weather deck covers with stoppers at one ship side and if needed, stoppers at the opposite

side to limit transverse deformations— transmission of high hatch cover stopper forces into the hatch coaming at port and starboard sides— arrangement of tween deck covers at different vertical positions— arrangement of a stability pontoon for heavy lift operations.

2.1 Torsion responseMPV’s with a long center cargo hold are subject to large torsion response compared to ships having moreclosed cross-sections. Only considering the vertical hull girder force components is therefore not sufficient toappropriately consider hull girder strength.The torsion (stillwater torsion induced by cargo and unsymmetrical tank arrangement etc., and wave torsioninduced by oblique wave encounter) and the horizontal wave bending moment should therefore also beincluded in the hull girder strength assessments.The criticality of the torsion response will heavily depend on the hatch opening ratio and the ship size. ThisCG describes two different levels for longitudinal hull girder strength assessments including torsion analysisas shown in Table 1.

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3 ObjectivesThe objective of this CG is:

— to give a guidance for design and assessment of the hull structures of MPV’s in accordance with the Rulesfor Classification of Ships

— to give a general description on how to carry out relevant calculations and analyses— to suggest alternative methods for torsion response calculation— to achieve a reliable design by adopting rational design and analysis procedures.

4 Application and scope

4.1 Overview of different analysis levelsIn order to achieve the objectives described in [3], two different analysis levels are defined. The two differentanalysis levels are applicable for the design of MPV’s according to the vessel characteristics as described inTable 1.Level 1 analysis must be carried out as part of the mandatory procedure for the structural verification forMPV’s.Findings from the more comprehensive Level 2 analysis may result in additional strengthening.

Table 1 Analysis levels versus calculation/analysis scope

Level 1 Level 2

Mandatory scope ofcalculation/analysis

— Hull girder strength calculation and local rule scantlings— Rule check of hull girder ultimate strength— Rule fatigue strength calculation for longitudinal end connections and selected details

of upper hull— Cargo hold analysis based on rule-defined load combinations.

Supplementary scope ofanalysis

Global FE analysis with EDW’s from directwave load analysis(ULS and FLS)

RemarksSuitable for ships with conventionaldesign for which experience from previousdesign(s) is available

Required for novel design and/or complexstructural arrangement

5 Mandatory scope of calculation/analysis, Level 1

5.1 Rule check of hull girder strength and local scantlingsLongitudinal strength of the vessel and local scantlings must be verified by the rule-defined calculationprocedure as described in RU SHIP Pt.3 Ch.5 under consideration of vertical & horizontal bending and torsionmoments and vertical & torsional shear forces. Hull section scantlings shall be utilized for a suitable numberof cross-sections along the length of the ship. Special attention should be given to sections where thearrangement of longitudinal material changes. Sections close to the aft and the forward quarter-length aswell as at the transition between the engine room and cargo hold area need to be specially considered.

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5.2 Rule check of hull girder ultimate strength (ULS)A global ULS hull girder criterion is given in RU SHIP Pt.3 Ch.5 Sec.4. This implies that the whole length ofthe ship is verified to have sufficient ultimate hull girder strength to resist an extreme vertical wave hoggingmoment without suffering hull girder collapse.

5.3 Rule fatigue strength calculation for longitudinal end connectionsIt is mandatory (see RU SHIP Pt.5 Ch.1 Sec.5 [9.2]), to assess the fatigue characteristics of longitudinalend connections using the prescriptive method as given in DNVGL CG 0129, Fatigue assessment of shipstructures.

5.4 Cargo hold analysis based on rule-defined load casesStrength of primary structural members shall be assessed through a cargo hold analysis for the midship areaas specified in RU SHIP Pt.5 Ch.1 Sec.5 [7.2] and in DNVGL CG 0127, Finite element analysis.

6 Scope for Level 2 global analysisLevel 2 analysis includes a global FE model covering the entire ship length. The objective is to obtain areliable description of the overall hull girder stiffness and to calculate and assess the global stresses anddeformations of all primary hull members for specified load cases resulting from realistic loading conditionsand equivalent design waves determined by direct wave load analysis. Particular the scantlings of memberswhich are influenced mainly by the torsional moment i.e. radii of the hatch corners shall be checked by aglobal analysis. Furthermore, effects of the integrated crane columns into the ship structure have to beinvestigated.Over the entire ship length the following global response evaluation shall be carried out:

— Yield check of nominal stresses in way of all structural members as required in RU SHIP Pt.5 Ch.1 Sec.5[7.1.7]

— Buckling check of two-axial nominal stresses in way of all structural members as required in RU SHIP Pt.5Ch.1 Sec.5 [7.1.8]

— Fatigue assessment of hatch corners and other welded details as required in RU SHIP Pt.5 Ch.1 Sec.5[7.1.5]

— Assessment of structure deformations and stopper forces at deflection limiters.

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SECTION 2 LEVEL 2 GLOBAL ANALYSIS

1 Model idealisationThe global FE-model shall include all primary structural components important for longitudinal and transversestrength and stiffness and shall be idealised as described in DNVGL CG 0127, Finite element analysis. AsMPV’s with their long holds and small deck strakes generally have a low global stiffness with respect totorsion and transverse loads, it is important to implement all structural reinforcements that increase thestiffness of the hull. Such reinforcements are, e.g., foundations of heavy lift cranes or heavy coaming staysand foundations for hatch cover stopper forces. Figure 1 shows a sample global finite element model of anMPV.Superstructures and aft and fore parts of the ship may generally be modelled coarsely. They are to representa realistic stiffness for load application only. Only in special cases, e.g., when vibration or slammingload cases shall be investigated, are more refined models necessary for the fore and aft ship or for thesuperstructure.To calculate locally increased stresses, mesh fineness shall be increased gradually in accordance with stressgradients. The mesh of the global model shall be suitable to develop refined detailed finite element modelsof, e.g., hatch corners for a fatigue analysis (sub model technique).The generation of loading conditions requires that loads are applied realistically, i.e., large loads shall betransferred at correct positions into the ship structure. To achieve this, in some cases auxiliary structuresonly used for load application are necessary.For crane load cases, simplified models of crane columns for load application have to be implemented intothe global model. These crane column models shall be able to transfer crane moments and forces from theirrotating assembly to the column foundation, requiring correct modelling of the stiffness of all major structuralcomponents of the crane column, see Figure 3. Suitable mesh fineness shall be chosen for the foundationbelow the upper deck and for the ship structure.

Figure 1 Sample global FE model of an MPV with stability pontoon

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Figure 2 Global model, inner structure

Figure 3 Model of crane column with coaming structure

The importance of the hatch cover stopper forces on local deformations of the hull, especially for the inward/outward deflections of the coaming, necessitates modelling the hatch covers or implementing an auxiliarysystem of hatch covers to correctly transfer hatch cover stopper forces at the top of the coaming into theship structure.

— Each cover shall be fitted with longitudinal and transverse stoppers according to the hatch cover forceplan. Typically, hatch covers are fixed in transverse direction on the side where ship cranes are arranged.

— Friction forces between hatch cover and coaming should be neglected for global strength checks. Thisenables the determination of maximum coaming deflections as well as maximum stopper forces atdeflection limiters.

— Furthermore, on each hatch cover it shall be possible to define loads acting at a prescribed position of thecargo’s centre of gravity.

Test calculation runs shall ensure that hatch covers can move freely on top of the coaming without restraintfrom the hull stiffness. Only large deformations and large contact forces affect the deformation of the hullby keeping the defined clearances at their deflection limiters. Under such conditions, hatch covers transfer

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forces from one ship side to the other. This leads to a nonlinear problem, which can be solved using contactelements.An auxiliary system should be able to show deformation plots of hatch covers and to calculate relativedeformations between hatch covers and coaming and between hatch covers themselves.At bay ends, loads from containers in holds shall be transferred into the ship structure according to theappropriate stowage and lashing system. Vertical load components are to act at the ship’s bottom, whereashorizontal load components shall be transferred to the ship’s side structure. To achieve this, auxiliary systemsfor hold containers can be implemented. Test calculation runs shall be performed to check whether theauxiliary systems can move freely without restraints from the hull stiffness.

2 Load generationEquivalent design waves are determined by a wave load analysis as described in DNVGL CG 0131, Strengthanalysis of hull structure in container ships, to calculate hull girder forces and moments corresponding to therule requirements. The numerical simulation of wave and acceleration forces ensures a realistic superpositionof the different hull girder load components. For MPV’s the assumption of symmetry is generally notapplicable. Therefore, wave directions from both sides have to be considered.Relevant seagoing load combinations for FE analyses generally shall be selected by evaluating sectionalforces and moments along the ship’s length for all analysed wave situations. They shall be chosen in a wayto obtain maximum stress values as well as stress ranges for a fatigue analysis. For these load combinations,vertical and horizontal wave bending and the torsional moments have to match design values defined in therules RU SHIP Pt.3 Ch.4. For strength assessment (ULS) a coefficient of fp = 0.75 shall be taken for all loadcomponents to represent the required probability level of 10-6. For fatigue assessment (FLS) the probabilitylevel of 10-2shall be fulfilled by the appropriate coefficient fp for the different load components as defined inRU SHIP Pt.3 Ch.4 Sec.3 and RU SHIP Pt.3 Ch.4 Sec.4.

2.1 Load combinations for MPVsIn accordance with the scope of work, several load combinations resulting from defined loading patterns forMPV’s have to be generated, such as:

— Harbour loading patterns: calculate maximum inward and outward deflections of hatch coaming topsto determine clearances of deflection limiters. Their clearances shall be sufficient to allow hatch coveroperations under all harbour loading patterns.

— Crane load cases causing maximum crane moments for crane outreaches to port and starboard side foropen, closed and partly closed hatch covers.

— Loading patterns causing high loads on weather deck hatch covers to obtain seagoing load cases incombination with large roll angles leading to large deformations of hatch coaming tops and severetransverse strength conditions (racking). If coaming deformations are within limits of the deflectionlimiters, no contact forces occur. Otherwise, contact forces shall be calculated. These evaluations have toconsider the limited inward and outward movements.

— Conventional container loading pattern, to calculate seagoing load cases causing maximum and minimumvertical and horizontal bending moments and maximum and minimum torsional moments. The load casesshall be generated according to DNVGL CG 0131, Strength analysis of hull structure in container ships.

— Block loading pattern, to evaluate the strength of the ship’s bottom structure.— Loading patterns with vertically topped and horizontally stowed crane jib positions, investigated in sea

conditions with large roll angles and large transverse accelerations.— Loads on the ship’s bow and stern, causing high global stresses in the longitudinal structure of the

transition region between hold ends and the fore and aft ship. The load cases shall be generated accordingto DNVGL CG 0131, Strength analysis of hull structure in container ships.

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2.2 Harbour load combinationsHarbour load combinations are assigned as static load combinations. Target values are harbour stillwaterforces and moments. Buoyancy pressures under stillwater conditions and inertia forces caused bygravitational acceleration result in a state of equilibrium.

2.2.1 Harbour loading patternsHarbour loading patterns cause inward and outward deflections at the top of the coaming, mainly effected bybending deformation of the double bottom under lateral loads. Lateral loads result from cargo on tank tops,ballast water in the double bottom and buoyancy pressures at the shell. Predominant buoyancy pressureslead to outward hull deflections, whereas predominant cargo pressures lead to inward hull deflections. Thesedeflections are important input data for hatch cover designs. Hatch covers must have the ability to be openedand closed under extreme but realistic harbour conditions. Although the vertical bending moments and shearforces are of less importance for these load combinations, maximum hogging or sagging harbour still waterbending moment shall be fulfilled, see Table 1.Loading patterns causing large outward deflections of the hold generally do not consider cargos on tank topsin the midship area, and they do not contain ballast water in double bottom tanks. Such loading patternscorrespond to ballast conditions at maximum possible draught, where the buoyancy pressure predominates.Loads acting in adjacent holds, if these holds exist, and loads acting at the fore and aft end of the main cargohold should be accounted for to increase the draught, and in this way the outward deflection in the hold mustbe considered. Generally, for these patterns the maximum design draught is not exceeded.Loading patterns causing large inward deflections in the hold generally have cargo located on tank tops. Ifreasonable ballast water tanks in double bottom may be full and other tanks outside the hold area should beempty. To obtain maximum cargo pressure on tank top, the load is concentrated in the middle of the maincargo hold. Adjacent holds should be free of cargo. Generally, the maximum scantling draught is reached inthese cases. Block load cases are typical loading patterns causing extreme inward deflections.Generally, up to four harbour loading patterns are generated, see Table 1.

2.3 Crane load combinations in harbourCrane load combinations are generally derived by superposition of a static and a dynamic part. The staticpart considers the mass distribution of the ship and crane without dynamic factors under stillwater floatingconditions. Under this floating condition, the permissible heeling angle for crane operations shall bemaintained. The dynamic part balances the dynamic crane forces and moments and the inertia forces of theship’s masses.Crane load combinations are generated to calculate stresses and deformations of the global ship structure,the foundations of the crane columns and the connection between columns and ship. It is outside the scopeof this investigation to check the strength of cranes and crane columns.Highest global stresses and deformations are expected when maximum permissible crane moments arereached and the cranes are working in transverse directions to port and starboard side simultaneously usinga cross beam. For heavy lift cranes large transverse deformations of the cross sections and the coaming topshall be expected.In special cases, it may be necessary and required by the Society to analyse diagonal jib directions to checkthe strength of the foundations at the fore and aft transverse sections of the columns.

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2.3.1 Application of crane forces and momentsIn general, a crane load is selected for the global strength analysis which gives the highest crane forces andmoments at the rotating assembly between crane house and crane column. Documented design crane forcesand moments have to be supplied by the vendor.Crane loads can be introduced in two different ways:

— Method 1, by directly specifying forces and moments at the rotating assembly, or— Method 2, by indirectly arranging crane masses according to crane position and outreach.

Method 1:The direct input of forces and moments does not require a mass distribution for the cranes. Forces andmoments are introduced during load case definitions.Method 2:Pertinent data, such as outreach, maximum permissible heeling angle and masses of working load, jib, ropesand crane house should be considered when generating masses. Design crane forces and moments includedynamic factors. These factors are generally not considered in the definition of mass distributions for craneload cases (method 2). Dynamic components of forces and moments are then introduced when generatingcrane load cases, as explained in [2.3.3].

2.3.2 Crane loading patterns in harbourMass distributions for crane loading patterns have to be defined with regard to the following aspects:

— Realistic cargo and ballast distributions corresponding to permissible heeling angles for crane operationsunder static stillwater conditions shall be defined.

— Maximum and minimum possible vertical bending moments shall be defined.— Maximum and minimum possible inward and outward deflections, mainly affected by lateral pressure and

bending deformations of the double bottom, shall be defined.— Loading patterns for the ballast condition, for a small draught and for the scantling draught shall be

defined.

A realistic cargo and ballast distribution, in case that a stability pontoon is arranged, requires modellingbased on the following aspects:

— Models of ship and pontoon shall be mounted relative to each other according to their particular draughtsbefore crane operations, e.g., the relative position depends on the draughts of ship and pontoon.

— Pontoon particulars, including ballast water mass and cantilever beam effects, have to be represented byan appropriate distribution of nodal masses.

Ballast or small draught loading conditions shall be generated for jib directions pointing outward andinward. An outboard directed jib causes a large outward coaming deflection; an inboard directed jib, a hightransverse load in the bilge area.Loading patterns at scantling draught have to be generated to induce maximum possible hogging andsagging moments. Mass distributions for hogging moments should be selected to cause maximum possibleoutward deflections. This can be obtained by placing marginal cargos on tank tops.Mass distributions for sagging moments should cause maximum possible inward deflections. This canbe obtained by placing heavy cargos on tank tops. Generally, maximum inward deflections are expectedfor transverse jib directions. Under such conditions, when deflection limiters are arranged, maximumcompression stopper forces are calculated. Outboard directed jib directions cause maximum transversebending stresses in the bilge area.

2.3.3 Dynamic conditions for crane load combinations in harbourIf crane forces and moments acting at the rotating assembly are used directly (method 1), design forcesand moments of cranes (including dynamic factors) and buoyancy forces for the Stillwater floating conditionare balanced by inertia forces of the ship’s masses. The buoyancy distribution shall fit the floating conditionunder static crane loads without considering dynamic effects.If the considered crane masses are located at their correct centers of gravity (method 2), a stillwater floatingcondition is initially determined, which accounts for the static part of the crane forces and moments. The

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remaining dynamic forces and moments are then applied at the rotating crane assembly and balanced byinertia forces of the ship’s masses.If a stability pontoon is used, it shall be considered for load combination generation. The advantage of astability pontoon is that it increases the moment of inertia of the water plane area and that it increases themetacentric height (GM), thus resulting in smaller heel and trim angles under crane load conditions.Figure 4 shows distributions of sectional forces and moments along the ship’s length for a crane loadcombination with an outboard jib outreach. Here, high torsional moments and steep gradients at thepositions of the cranes can be observed. The corresponding crane load combination at the same draught witha CL jib outreach shows similar graphs for bending moments and shear forces, but with considerably smallertorsional moments (Figure 5). This obviously will lead to smaller stresses in the hull due to reduced torsionalloads.Crane load combinations are summarized in Table 2.

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Figure 4 Sectional forces and moments for a crane load case with an outboard jib outreach

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Figure 5 Torsional moment for a crane load case with a CL jib outreach

2.4 Seagoing load combinations with heavy loads on hatch covers (rackingload cases)Load combinations with heavy loads on hatch covers are generated to check the transverse strength anddeformation behaviour of the hull and the top of the coaming under sea conditions causing large roll anglesand high transverse accelerations. These extreme racking conditions are important for the structural designand scantlings of MPV’s. Besides, large torsional moments and horizontal bending moments are additionallyinduced into the ship structure.

2.4.1 Loading patterns with heavy loads on hatch coversThese loading patterns have to induce up to 80 percent maximum design loads on hatch covers. Thereforeloading patterns with a small metacentric height are relevant. The centre of gravity of loads on hatch coversshould be located at a low but realistic vertical position.To obtain large transverse deformations, loads on hatch covers should be concentrated in the mid area of thehold. Loads on hatch covers at the ends of a hold only marginally influence global transverse deformations.Loads at specified hatch covers have to be defined with regard to following aspects:

— Maximum and minimum possible vertical bending moments have to be defined.— Maximum and minimum possible inward and outward deflections affected by lateral pressure and bending

deformations of the double bottom have to be defined. Loading conditions shall be defined for thescantling draught only.

If the ship is designed for two design draughts, corresponding to closed and open weather deck hatch covers,additional loading conditions have to be generated for open top cases. Under these loading conditions, wherenot all hatch covers are equipped with deflection limiters, maximum stopper forces at deflection limiters ofthe remaining hatch covers shall be verified.

2.4.2 Dynamic conditions with heavy loads on hatch coversThe roll angle for racking load combinations shall be adjusted to approximate the transverse accelerationof 0.5 g for the inertia forces of hatch cover loads, as defined in to be added. In this way it is assured thatcalculated stopper forces are in line with design hatch cover forces according to the rules.Due to the asymmetry of many MPV’s, load cases with roll angles to port and starboard side have to bedefined separately.

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The selection of load combinations postulates statistical independence between wave amplitudes and rollangles. Therefore, the design roll angle shall be considered simultaneously combined with reduced designwave amplitude of 50 percent. The wave length shall comply with the design wave.Generally, racking load cases shall be set up for hogging and sagging waves from ahead (angle of encounter180 degrees) with respect to variation of the side shell pressure. Therefore, load combinations with differentwave crest and wave trough positions in the area of largest transverse deformations shall be generated. Thisensures that the full effect of hydrodynamic pressures on transverse hull strength, hull deformations andstopper forces is accounted for.For long cargo holds (≥ 40m), three wave crest and three wave trough positions shall be considered. Forprismatic hold geometry, wave crest and wave trough positions can be assumed located at one-quarter, one-half and three-quarter lengths of the cargo hold.The load case selection described above leads, for a long cargo hold and for one loading condition, to 12racking load cases. These cases arise from six wave phases (positions), one wave length of design wavelength, one wave amplitude of 50 percent design wave amplitude, one angle of encounter of 180 degrees anddesign roll angles to port and starboard side. Figure 6 shows sectional forces and moments of sample rackingload cases. It can be seen that high horizontal bending moments and torsional moments occur as well.

For short cargo holds (< 40m), only one position for wave crest and trough is recommended. The positionhas to be estimated at one-half length of the cargo hold. The reduced number of wave phases and roll anglesto port and starboard side lead to four racking load cases.Load combinations with heavy loads on hatch covers are summarized in Table 3.

2.5 Seagoing container load combinationsAs MPVs generally are equipped for the carriage of containers, they shall also be designed for such loadingpatterns. Racking cases generally turn out to be the dominant ones; therefore, the analysis of container loadcombinations is only required for large MPV’s with L ≥ 150m, on a case-by-case basis.The selection of the critical container load combinations is described in DNVGL CG 0131 Sec.3 [1.4]. Theseagoing container load combinations are summarized in Table 3.

2.5.1 Loading patterns for seagoing cases with container loadsIn general, at least one hogging loading pattern shall be generated. It has to be defined with regard to thefollowing aspects:

— Maximum displacement at scantling draught with maximum permissible vertical hogging still waterbending moment shall be generated.

— A homogeneous weight distribution in all bays with large stack loads on deck and hatch covers shall begenerated.

— A relatively small metacentric height (GM) shall be considered.

2.6 Seagoing block load combinationsHigh stresses in the bottom structure can be expected for block load cases. Therefore, load cases for thestillwater condition and the conditions causing maximum wave hogging and sagging moments shall begenerated. The seagoing block load combinations are summarized in Table 3.

2.6.1 Loading patterns for seagoing cases with block loadsLoading patterns with block loads defined in the loading manual have to be investigated if applicable. Forthese cases, high cargo pressures at tank tops are transferred into the bottom structure.

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Figure 6 Example of sectional forces and moments for racking load cases

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2.7 Seagoing load combinations for crane jibs in vertical and horizontalpositionLoad combinations with vertically topped and horizontally stowed crane jib positions were generated in seaconditions with large roll angles and large transverse accelerations.If the topped jib position is permissible for sea transport under conditions causing large roll angles, thecorrespondent loading pattern shall be considered to calculate stresses and stress ranges in foundations ofcrane columns and in connections between crane columns and ship structure.

2.7.1 Loading patterns for seagoing cases with crane jibs in vertical and horizontal positionIt is common practice to stow crane jibs vertically topped when awkwardly shaped cargo makes it impossibleto stow the jib in its normal horizontal position.Over one-half of the ship’s lifetime, it is assumed that crane jibs are stowed either in the vertical orhorizontal position. Therefore, in principle two loading patterns shall be set up to cover the entire lifetimeand to be able to perform a fatigue analysis. The ship’s mass distribution may be the same although the jibpositions may differ.Corresponding loading patterns shall be defined with regard to following aspects:

— Maximum displacement at scantling draught with maximum permissible vertical hogging Stillwaterbending moment causing a homogeneous weight distribution in holds and on hatch covers shall bemaintained.

— As horizontal accelerations of jibs under seagoing conditions are of major importance, a high but realisticmetacentric height (GM) should be considered.

2.7.2 Dynamic conditions for seagoing cases with crane jibs in vertical and horizontal positionMost serious conditions for jibs are caused in extreme roll conditions with high transverse accelerationsdue to the ships inclination. However, horizontal and vertical accelerations contribute to the transverseacceleration as well. Selected roll angles for load cases shall be adjusted to obtain a reasonableapproximation of the design acceleration according to RU SHIP Pt.3 Ch.4 Sec.3 [3.2.2] at different jibpositions. The applied max roll angle θmax shall not exceed the design value as given in RU SHIP Pt.3 Ch.4Sec.3 [2.1.1].The selection of load combinations postulates statistical independence between wave amplitude and lateraldesign acceleration. Therefore, the design acceleration related to the maximum roll angle θmax shall beconsidered simultaneously with reduced design wave amplitude of 50 percent. The wave length has tocomply with the design wave.The following load combinations shall be generated:

— As both loading patterns differ only in the position of crane jibs, the vertical bending for both loadingconditions may be considered equal. Therefore, it is sufficient to generate the stillwater condition, themaximum vertical wave hogging condition and the (absolute) maximum vertical wave sagging conditionfor one loading condition only.

— Wave hogging and sagging conditions with lateral accelerations to port and starboard side shall be derivedfor both loading conditions.

This leads to seven load combinations with stowage of crane jibs in vertically topped position and to four loadcombinations with stowage of crane jibs in horizontal position.The seagoing load combinations for crane jibs in vertical and horizontal position are summarized in Table 3.

2.8 Loads on bow and stern structuresConsideration of slamming loads is crucial for ships with excessive bow flare and stern overhang. Sincedirect calculation of slamming loads is extensive and time consuming, a simplified method based on ruledefined impact pressures is recommended for global strength analysis. The concept used to obtain balancedslamming load cases is described in DNVGL CG 0131 Sec.2 [1.5].

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Table 1 Load combinations ‘harbour’ (refer to [2.2])D

escr

ipti

on

Dra

ug

ht

SW

BM

Load

ing

Hee

l an

gle

[deg

]

Wav

e am

plit

ud

e

Wav

e d

irec

tion

Wav

e cr

est

pos

itio

n[%

of

hol

d a

rea

len

gth

]

Wav

e th

rou

gh

pos

itio

n[%

of

hol

d a

rea

len

gth

]

Rem

ark

Coamingdeflectioninward

TSC Hogging

Predominantuniform cargopressure ondouble bottom

0 - - - - Mandatory

Coamingdeflectioninward

TSC SaggingBlock load atL/2 0 - - - - Mandatory

Coamingdeflectionoutward

Tballast HoggingHold's endsloaded 0 - - - - Mandatory

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Table 2 Load combinations ‘crane in harbour’ (refer to [2.3])D

escr

ipti

on

Dra

ug

ht

SW

BM

Load

ing

Hee

l an

gle

[deg

]

Wav

e am

plit

ud

e

Wav

e d

irec

tion

Wav

e cr

est

pos

itio

n[%

of

hol

d a

rea

len

gth

]

Wav

e th

rou

gh

pos

itio

n[%

of

hol

d a

rea

len

gth

]

Rem

ark

Coamingoutreachoutward

Tsmall HoggingMax. cranemoment

-3 to -5perm.Values

- - - - Mandatory

Coamingoutreachinward

Tsmall HoggingMax. cranemoment

+3 to +5perm.Values

- - - - Mandatory


TSC HoggingMax. cranemoment

-3 to -5perm.values

- - - - Mandatory


TSC HoggingMax. cranemoment

+3 to +5perm.Values

- - - - Mandatory


TSC SaggingMax. cranemoment

-3 to -5perm.values

- - - - Mandatory


TSC SaggingMax. cranemoment

+3 to +5perm.values

- - - - Mandatory

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Table 3 Load combinations ‘seagoing’D

escr

ipti

on

Dra

ug

ht

SW

BM

Load

ing

Hee

l/ro

ll an

gle

[deg

]

Wav

e am

plit

ud

e [%

of

hog

g.

or s

agg

. d

esig

n w

ave]

Wav

e d

irec

tion

[d

eg]

Wav

e cr

est

pos

itio

n[%

of

hol

d a

rea

len

gth

]

Wav

e th

rou

gh

pos

itio

n[%

of

hol

d a

rea

len

gth

]

Rem

ark

0 - - - - Mandatory

0 100% hogg. 0 or 180 1) 1) Mandatory

+θmax 50% hogg. 180 25, 50, 75 Mandatory

-θmax 50% hogg. 180 25, 50, 75 Mandatory

0 100% sagg. 0 or 180 1) 1) Mandatory

+θmax 50% sagg. 180 25, 50, 75 Mandatory

Heavy loadson hatchcovers [2.4]

TSCMax.possiblehogging

Heavyloads onhatchcovers

-θmax 50% sagg. 180 25, 50, 75 Mandatory

0 - - - - Mandatory

0 100% hogg. 0 or 180 1) 1) Mandatory

+θmax 50% hogg. 180 25, 50, 75 Mandatory

-θmax 50% hogg. 180 25, 50, 75 Mandatory

0 100% sagg. 0 or 180 1) 1) Mandatory

+θmax 50% sagg. 180 25, 50, 75 Mandatory

Heavy loadson hatchcovers [2.4]

TSCMax.possiblesagging

Heavyloads onhatchcovers

-θmax 50% sagg. 180 25, 50, 75 Mandatory

Containerloads [2.5] TSC

Permissiblehogging

Uniformlydistributedloads

See DNVGL CG 0131 Sec.2 Table 1

0 - - - - If applicable

0 100% hogg. 0 or 180 1) 1) If applicable

Hoggingacc.loadingmanual

Blockloads foreand aft

0 100% sagg. 0 or 180 1) 1) If applicable



Block loads[2.6] TSC Sagging

acc.loadingmanual

Blockloads mid


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Des

crip

tion

Dra

ug

ht

SW

BM

Load

ing

Hee

l/ro

ll an

gle

[deg

]

Wav

e am

plit

ud

e [%

of

hog

g.

or s

agg

. d

esig

n w

ave]

Wav

e d

irec

tion

[d

eg]

Wav

e cr

est

pos

itio

n[%

of

hol

d a

rea

len

gth

]

Wav

e th

rou

gh

pos

itio

n[%

of

hol

d a

rea

len

gth

]

Rem

ark



+θmax 50% hogg. 0 or 180 1) 1) If applicable

-θmax 50% hogg. 0 or 180 1) 1) If applicable


+θmax 50% sagg. 0 or 180 1) 1) If applicable

Jibs inverticallytoppedposition[2.7]

TSCPermissiblehogging


-θmax 50% sagg. 0 or 180 1) 1) If applicable

+θmax 50% hogg. 0 or 180 1) 1) If applicable

-θmax 50% hogg. 0 or 180 1) 1) If applicable

+θmax 50% sagg. 0 or 180 1) 1) If applicable

Jibs inhorizontalposition[2.7]

TSCPermissiblehogging


-θmax 50% sagg. 0 or 180 1) 1) If applicable

1) In agreement with the corresponding design wave

3 Structure deformations and stopper forces at deflection limitersEssential characteristics of MPV’s, such as large deck openings, long cargo holds, etc., generally give riseto large deformations in harbour conditions as well as in sea conditions, primarily caused by torsional andtransverse loads. These deformations shall be limited to assure a safe working ship structure.In particular, severe racking load cases may cause large inward and outward deflections, which makeit impossible to design safe working hatch covers without resorting to modifications. An establishedmodification measure is the arrangement of deflection limiters to ensure that predetermined maximuminward and outward deflections are not exceeded.The clearance of these deflection limiters shall be large enough to allow hatch cover operations in all harbourconditions. During heavy lift operations, however, this requirement may be disregarded. In those cases,deformations may exceed stopper clearances and hatch covers then transfer the loads. Certainly, under suchconditions the hatch covers cannot be moved.The calculation shall be performed as follows:

— calculate maximum inward and outward coaming deflections under harbour conditions and determineclearances for deflection limiters

— calculate inward and outward deflections for crane load cases— calculate inward and outward deflections for seagoing load cases— evaluate coaming deflections and specify number and arrangement of deflection limiters

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— calculate stopper forces at deflection limiters by solving nonlinear contact problems and determinemaximum design stopper forces

— evaluate final deformations affected by deflection limiters, determine hatch cover movements on top ofcoaming and relative displacements between hatch covers and obtain maximum design movements anddisplacements.

3.1 Deformations for harbour load casesThe magnitude of harbour deformations is an important indicator for the appropriateness of the maincharacteristics of the design. Relevant geometric parameters, besides the length of cargo hold, are thefollowing:

— breadth of ship, width of cargo hold and size of double hull— double bottom height— draught— height of coaming stays.

Inward and outward deflections under harbour load combinations predominantly result from transversestrength, i.e., double bottom deformations in combination with the height of the coaming top.The influence of the vertical hull bending deformation is minor.Generally, it is recommended to limit the sum of inward and outward deflections to about 100 mm in total. Ifthe hatch cover manufacturer assures properly working hatch covers also for larger deflections, larger valuescan be approved.Figure 7 to Figure 9 show typical deformations of the coaming, main deck and cross sections for harbour loadcombinations. These figures show a torsional deformation which is mainly caused by the weights of heavy liftcranes at the port side.

Figure 7 Deformations for inward deflections

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Figure 8 Deformations for outward deflections

Figure 9 Deformations for inward/outward deflections

3.2 Deformations for crane load casesCrane load cases shall be evaluated for different operating conditions. Most unfavourable conditions withmaximum relative displacements between hatch covers and the top of the coaming appear if no hatchcover with a deflection limiter is in position. Displacements in general exceed values calculated for extremeharbour load cases and, therefore, shall be regarded for hatch cover designs. Furthermore, clearances of thedeflection limiters are exceeded.During heavy lift operations and completely closed hatch covers, high contact forces at the deflectionlimiters have to be expected. Forces are greatest when only one hatch cover limits the inward and outwarddeflections. This especially applies to hatch covers with stoppers at positions directly opposite the cranes.Crane load cases are often decisive to determine maximum design contact forces acting at deflection limiters.Figure 10 and Figure 11 show global deformations of the hull for crane load cases with jib outreaches to portside and with jib outreaches in transverse direction to CL, respectively. It is obvious that the deformation notonly affects the crane column area, but also the whole length of the cargo hold.

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Figure 10 Cranes are working to port side

Figure 11 Cranes are working to CL

Deformation plots of the main deck under crane operation are given in Figure 14 and Figure 15. It isassumed here that the deflection limiters are not active, i.e., the inward and outward movements are notlimited. A comparison of deformations for harbour load cases (Figure 7, Figure 8) and crane load cases(Figure 14, Figure 15) shows that deformations for crane load cases are considerably larger.Figure 16 and Figure 17 show deformations for completely closed hatch covers. In these figures the inwardand outward deflections at the coaming top are limited by the arrangement of four deflection limiters.

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Stopper forces at the deflection limiters shall be calculated by solving a nonlinear contact problem. Thisensures that the clearances of deflection limiters are maintained. Compared to Figure 14 and Figure 15,considerably smaller deformations are shown.Figure 18 and Figure 19 show deformations for the case where only one hatch cover is in position at the topof the coaming. Here, the inward and outward deflections are limited only by one deflection limiter. Generally,under such conditions the contact forces are maximal.

3.3 Deformations for seagoing load casesAll seagoing load cases shall be evaluated for deformations and stopper forces. Furthermore, maximumdesign forces and displacements shall be determined.Figure 12 and Figure 13 show global deformations under loading conditions with high hatch cover loads. Theoutward deformations for a roll angle to port side increase under wave trough conditions (Figure 12), whilethe inward deformations for a roll angle to starboard increase under wave crest conditions (Figure 13).

Figure 12 Racking load case, roll angle to port side, wave trough

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Figure 13 Racking load case, roll angle to starboard, wave crest

Figure 22 and Figure 23 show deformations for four active deflection limiters. Especially for a roll angle tostarboard, large stopper forces were determined, resulting in considerably smaller inward deflections than forthe theoretical case with inactive deflection limiters, see Figure 20 and Figure 21.

Note:For sea-going load cases, the hatch covers will always be closed, i.e. deflection limiters are active.

---e-n-d---o-f---n-o-t-e---

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Figure 14 Crane jib to port side, inactive deflection limiters

Figure 15 Crane jib to CL, inactive deflection limiters

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Figure 16 Crane jib to port side, completely closed weather deck hatch covers

Figure 17 Crane jib to CL, completely closed weather deck hatch covers

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Figure 18 Crane jib to port side, only one hatch cover in position at top of coaming

Figure 19 Crane jib to CL, only one hatch cover in position at top of coaming

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Figure 20 Racking load case, roll angle to port side, inactive deflection limiters

Figure 21 Racking load case, roll angle to starboard, inactive deflection limiters

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Figure 22 Racking load case, roll angle to port side, active deflection limiters

Figure 23 Racking load case, roll angle to starboard, active deflection limiters

Cha

nges

– h

isto

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CHANGES – HISTORICThere are currently no historical changes for this document.

DNV GLDriven by our purpose of safeguarding life, property and the environment, DNV GL enablesorganizations to advance the safety and sustainability of their business. We provide classification andtechnical assurance along with software and independent expert advisory services to the maritime,oil and gas, and energy industries. We also provide certification services to customers across a widerange of industries. Operating in more than 100 countries, our 16 000 professionals are dedicated tohelping our customers make the world safer, smarter and greener.

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CONTENTSChanges – currentSection 1 Introduction1 General2 Ship characteristics3 Objectives4 Application and scope5 Mandatory scope of calculation/analysis, Level 16 Scope for Level 2 global analysis

Section 2 Level 2 Global analysis1 Model idealisation2 Load generation3 Structure deformations and stopper forces at deflection limiters

Changes – historic

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