Han YuABS

IACS Polar Class Requirements and Hull Structural Design Applications

September 9, 2008Houston, Texas

2

Overview• IACS Polar Class Rules Background

• Ice Load Model

• Structural Rules

• Remaining Issues of Polar Class Rules

• ABS Approach for Polar Class Rules Application beyond Scantlings Requirements

3

Polar Class Rules: Background• The 1970s and 1980s saw dramatic

increases in Polar shipping Alaska and Canadian Beaufort Sea

• Several administrations made proposals to IMO* to develop a harmonized system of ice class rules

• Consensus was reached in IMOIMO would develop the overall framework for the initiativeIACS* would produce detailed requirements for construction-related items

* IMO : International Maritime OrganizationIACS: International Association of Classification Societies

4

IMO Arctic Guidelines and IACS Polar Class Rules

• The IMO Working Group drew on expertise from stakeholders and experts, including representatives from Class

• Consensus was reached early in the process to set up parallel groups with overlapping membership and meetings

IMO would develop the overall framework for the initiative

MSC Circular 1056/MEPC Circular 399, “Guidelines for Ships Operating in Arctic Ice Covered Waters” -formally applicable only to Arctic waters.

IACS would produce detailed requirements for construction-related items

IACS Unified Requirements for Polar Class ships

Maximum extent of application.MSC/Circ. 1056/MECP/Circ. 399

5

Definition of Polar Classes by IMO/IACS• Set lower bound to capture “Baltic-like” classes with successful

polar operating experience

• Set upper bound to include realistic capability limits for economically-viable vessels

Polar Class Ice Description (based on WMO Sea Ice Nomenclature)

PC 1 Year-round operation in all Polar waters

PC 2 Year-round operation in moderate multi-year ice conditions

PC 3 Year-round operation in second-year ice which may include multi-year ice inclusions.

PC 4 Year-round operation in thick first-year ice which may include old ice inclusions

PC 5 Year-round operation in medium first-year ice which may include old ice inclusions

PC 6 Summer/autumn operation in medium first-year ice which may include old ice inclusions

PC 7 Summer/autumn operation in thin first-year ice which may include old ice inclusions

6

Polar Classes• Lowest Polar Classes (PC7 and PC6): should have general

levels of strengthening roughly comparable to Baltic Ice Classes.

• Highest Polar Class (PC 1): capable of independent operation without limitations.

• The Polar Rules give on general guidance. All Polar class vessels can find ice that will damage the structure.

• Class selection is a balance among ice conditions, operational requirements and cost.

7

Polar Class Concept of Ice Loads (1)

• Polar Rules are based on the concept that ice loads can be rationally linked to a design scenario.

• Development working group wanted to ensure that iceload models were explicit, physics-based, and validated

• The design scenario is a glancing collision with an ice edge (edge of a channel, edge of a floe). This scenario is valid for both independent and escorted operations.

8

Polar Class Concept of Ice Loads (2)

• The load equation is derived from the solution of a Ship - Ice collision model.

Normal Kinetic Energy = Ice Indentation EnergyFind indentation Find force, area, pressure.

• Ice thickness, ice strength (crushing pressures), hull form, ship size and ship speed are all taken into account.

icenormal IEKE =

9

• Structural design based on realistic plastic response

Analytical (energy) solutions, Verified by FE analysis (and lab tests)Plate folding for shell plateBending/shear considerations for framesBuckling-based slenderness limits

Polar Class Concept of Structural Rules

Source: Prof. Claude Daley, Memorial University of Newfoundland, August 2007

10

IACS Unified Requirements (UR) for Polar Class Ships• I1: Polar Class Descriptions and Application

General

• I2: Structural Requirements for Polar Class ShipsHull Structures

• I3: Machinery Requirements for Polar Class ShipsMachinery

• Download available from IACS web site www.IACS.org.uk

Adopted by all IACS members andbecame effective March 2008.

11

Polar Class Descriptions and Application - UR I1

• Polar Class Notation (PC 1 ... PC 7)Ships are to satisfy I2 and I3 of Polar Class URI2 and I3 are in addition to the open water requirements of each class rules.

12

Major Parts of IACS Polar Class - UR I2• Hull Areas, (I2.2)

• Design Ice Loads, (I2.3)

• Shell Plate Requirements, (I2.4)

• Frame Requirements, (I2.5 - I2.9)

Transversely-framed Longitudinally-framed

• Structural Stability - Buckling

• Corrosion/Abrasion Additions and Steel Renewal, (I2.11)

• Materials, (I2.12)

• Longitudinal strength, (I2.13)

13

Hull Areas - Longitudinal & Vertical Direction

BowBowIntermediateMidbodyStern

UIWL - Upper Ice WaterlineLIWL - Lower Ice Waterline

Icebelt

Lower

14

Hull Areas - Bottom

BowBowIntermediateMidbodyStern

Icebelt

Lower

Bottom

15

Design Ice Loads• A glancing impact on the bow is the design scenario.

• The design ice load is characterized by an average pressure (Pavg) uniformly distributed over a rectangular load patch of height (b) and width (w).

Design Ice Load

w

Pavgb

• Within Bow Area - Design Ice Load is functions of

the actual bow shape ice thickness and strengthship size and speed

• Non-Bow Area - Design Ice Load is independent of the hull shape.

16

α, β, γ: Hull form angles

Hull Form Angles for Shape Coefficient (fa)

17

Design Ice Load - Bow Area• The whole bow is to be designed with one design ice load patch.• To arrive at the design load, 4 sub-region (i) values are calculated• The largest of Fi, Qi and pi are used in the assembles bow design

load. Shape coefficient (fa), Total glancing impact force (F), Line load (Q), Pressure (P)

3

1234

1234

Pavg

18

Simplification - Class Factors (CFn)• The class factors represent

the simplification of design conditions for each ice class.

• In deriving these values, hull geometry,ice thickness, Ice strength and ship size and speed

are all taken into account.

There are other class factors for other aspects.

Crushing FailureClass Factor

Example – Crushing Failure

19

Class Factors (CFn)

20

Other Factors - Hull Area Factors (AF)for Hull Areas Other than the Bow

• The areas other than the bow are designed for a portion of the bow load.

• The hull areas are defined based on the shape and waterlines of the vessel.

21

Other Factors - Peak Pressure Factors (PPF)Pressure within the Design Load Patch• Areas of higher, concentrated pressure exist within the load patch. In

general, smaller areas have higher local pressures. • Accordingly, the peak pressure factors listed in Table 2 are used to

account for the pressure concentration on localized structural members.

Average Pressure

Peak Pressure Factors

22

Scantling requirements - Shell• Minimum req’d shell plate thickness (I2.4)

"Net scantling" is required with "corrosion and abrasion allowance"

t = tnet + tstnet = f (Pavg, δy, Peak Pressure Factor, Hull Area Factor, b, s) ts: corrosion and abrasion allowance (I2.11)

• Framing Orientation is considered.Transversely framedLongitudinally framedObliquely framed

23

Scantling Requirements - Framing• Framing members

Local frames - longitudinal or vertical stiffeners Load carrying stringersWeb frames

• Local frames - requirementsNet effective shear areaNet effective plastic section modulus

• Stringers and web frames - requirementsScantlings are per class rulesStructural stability (buckling) requirements

24

Local frames - requirements• Transversely-Framed Side Structures and Bottom

StructuresNet effective shear area of the frame, At

Net effective plastic section modulus, Zpt

• Side Longitudinals for Longitudinally-Framed Ships

25

Corrosion/Abrasion Additions and Steel Renewal

• Effective protection against corrosion and ice-induced abrasion is recommended for shell plating.

• Minimum corrosion/abrasion addition of ts = 1.0 mm for stiffener webs and flanges.

• Steel renewal is required when the gauged thickness is less thantnet + 0.5 mm.

26

Fracture Toughness

• Fracture toughness : Ability of a material containing a crack to resist fracture

• Fracture toughness is decreased forBrittle materialThick platesLow service temperature Fatigue Crack

growth

Fracture

27

Material Classes for Polar Ice Class Vessels

28

Material Grades for Polar Ice Class Vessels• As-built thickness is considered

29

Longitudinal strength • Scenario: head-on ramming

• Ice load is to be only combined with still water loads (wave load may be ignored.)

• Parameters to be consideredDesign vertical ice force at the bowDesign vertical shear forceDesign vertical ice bending moment

30

Some Remaining Issues in Polar Class RulesReferred to Classification Rules

• Scantlings of web frame and stringer

• Grillage analysis of hull structures

• Direct calculation

• IACS and ABS EffortsIACS members have formed a Task Group to work on these subjects.ABS to provide guidance with "ABS Guidance Notes on Ice Class" to address these issues.

31

ABS Approach to Implement Polar Class Rules• Framework of Risk Based Design Review

Stake holders - Owner / Operator / Class / Designer / Builder Acceptable operational profile

• HAZID of Proposed Vessel and Operations

• Scantlings based on IACS Polar Class UR

ABS Polar quick check Software

• Direct Calculation for Additional Ice-Ship Interaction Scenarios based on HAZID

• Appropriate WinterizationDesign Stage / Operational Stage

• Collect actual ice loads from full scale measurements

32

Why Risk Based Design Review? (1)

First year pack ice with old ice ‘inclusions’Baltic Sea Winter Operation

• Lack of experience operating vessels in Arctic regions Most experiences in Baltic Sea (1ASuper max ice thickness 1m)Polar Class PC-6 in Medium fist year ice 0.7 – 1.2m with “old ice inclusion”Ice loads are among the most uncertain of all loads applied to ships

SS Manhattan in Northwest PassageIce Ridge Field in Kara Sea

33

• Most of Higher Ice Class experiences are learned from smaller ships.High ice classes of Canada, Russia – maximum about 30,000t DWT

Why Risk Based Design Review? (2)

MV ArcticDWT 28,418 t

Umiak IDWT 31,992 t

Norilsk NickelDWT 14,928 t

• Latest completion of 70K DWT Varandey Arctic Shuttle Tanker (2008)

34

• Polar Class Rules do not comprehensively address:Unique operation scenariosInteraction between primary members - grillage

Why Risk Based Design Review? (3)

IACS PolarRule Scenario

35

• Current Ice Class Rules do not explicitly address: the effects of ice loads on LNG cargo containment systemsthe effects of dynamic ice loads on fatigue performanceaccidental loads, such as growler collision

Why Risk Based Design Review? (4)

accidental loads - growler collision

the effects on LNG cargo containment systems

fatigue due to dynamic ice loads

36

Ice Loads Model for Direct CalculationConsistent with IACS Ice Load Model

Crushing FailureClass Factor

• Ship-Ice Collision Model same as Polar Class Rules

• Actual design values of hull geometry,ice thickness, Ice strength and ship size and speed

can be used based on operational scenarios.

Example – Crushing Failure

37

Application of Direct Calculation ScenariosExample Application - for Arctic LNG Carrier

• Joint Development Project For Large Arctic LNG Carrier DesignABS - HHI - BMT Fleet TechnologyBMT FTC Ice Load Model (IACS Polar UR) was used.

• HAZID of Ship Ice Interaction was carried out.

• Results were published:RINA Conference on Vessels Operating In Low Temperature Environments - 2007Arctic Shipping Conference - 2008SNAME Conference IceTech - 2008 http://www.eagle.org/news/press/apr09-2008.html

38

Arctic LNG Carriers DevelopmentA Joint Development by ABS, HHI and BMT Fleet Technology

39

Structural Integrity Assessment of Cargo Containment Systemsin Arctic LNG Carriers under Ice Loads *

Source: Arctic Shipping Conference 2008, St. Petersburg, Russia

40

Structural Integrity Assessment of Cargo Containment Systemsin Arctic LNG Carriers under Ice Loads *

Source: Arctic Shipping Conference 2008, St. Petersburg, Russia

41

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 5 10 15 20 25 30

Maxim um Displacem ent, D (m m )

App

lied

Load

/ D

esig

n Lo

ad

9m m 10m m11m m 12m m13m m 14m m15m m 16m m17m m

Application of Non-linear Finite Element Analysis

• ABS 2004 and 2005 Guidance Notes on Ice Class For Baltic class vessels - longitudinally framed structure

Side longitudinal designSide shell design

• To be updated in 2008Side stringer designGrillage AnalysisDirect Calculation

42

IACS Polar Class UR Software

Available for ABS Clients

43

Example: ABS POLAR quick check

• Plate and Frame CheckOutput: pass or fail

44

• Two documents in oneGuide –requirementsGuidance Notes – As appendices with additional explanations

• TopicsMaterialHull designArrangementSystemsHuman exposure

ABS Guide forVessels Operating in Low Temperature Environments

45

• Varandey Arctic Shuttle Tanker for SovcomflotBuilt by Samsung Heavy Industries 2008ABS/RS Dual Class, Ice Class LU-6Features presented at Arctic Shiping Conference 2008

Best Examples of Tanker Winterization

46

Full Scale Ice Load Measurement• Instrumentation on Varandey Arctic Shuttle Tanker

• ConocoPhillips, SHI and ABS initiated full scale ice load measurement for large arctic shuttle tanker.

The largest ice breaking tanker will be instrumented with over 150 fiber optic strain gages.Measurement campaign will start 2009 - 2010.

47

Conclusions • Development of the new Polar

Class Unified Requirements represents a unique collaboration between IACS and IMO, drawing in additional expert stakeholders.

• The Polar Class Rules are the best available basis for the design of the next generation of ice-capable ships.

• The limitations of Polar Class Rules can be supplemented by Risk Bases Design Review processes, direct calculations using realistic ice loads, and adequate winterization.

48

Thank you – Questions?

Han YuManager, R&D - ShipsABS Corporate TechnologyTel 281.877.6473e-mail hyu@eagle.org