reliability anal ysis of ships - cesos - ntnu shu.pdf · constructed or a specified design e o ......

Reliability Analysis of Ships

Zhi ShuInocean EngineeringInocean Engineering

Outline

•Background

•Ship Structural Reliability

•Case StudyCase S udy

•Conclusions

Zhi Shu August 24, 2010

Background

•Importance of Ship’s Safety on Sea

•IMO Goal-based standard

•IACS CSR

•Bulk carrier casualty at sea


Backgrounds

•Importance of tankers and bulk carriers“Ships are to be designed and

t t d f ifi d d i lif t


constructed for a specified design life tobe safe and environmentally friendly,when properly operated and maintainedunder specified operating and •IACS CSR


under specified operating andenvironmental conditions, in intact andspecified damage conditions”


Backgrounds

•Importance of tankers and bulk carriers

Ultimate limit based design has beenimplemented in CSR


implemented in CSR

•Ultimate strength in sagging for tankers

•Ultimate strength in sagging and hogging •IACS CSR


for bulk carriers


Backgrounda


Main contributors for the losses of bulk carriers

•Goal-based standard•Aged bulk carrier with age larger than 10 years

•High density cargo loaded in alternate •IACS CSR


•High density cargo loaded in alternate hold loading (AHL) condition

•Heavy weather


Backgrounds


Bulk carrier casualty in sagging

•Goal-based standard

•IACS CSR

•Bulk carrier casualty at sea Eurobulker X (http://www.shipspotting.com)

Bulk carrier casualty in hogging

•The vessels sink very fast

•Total losses of ships and human lives onboard

•Even no time for taking a picture


Structural Reliability

•Limit state function

•Determination of Characteristic value and Uncertainty ModelingUncertainty Modeling

•Structural Reliability MethodStructural Reliability Method


Structural Reliability: Limit state function

( 0) ( )P P R S f r s drds

1) Basic formulation of reliability problem

0

( 0) ( , )f RSR S

P P R S f r s drds

0 ( )fP P g f d XX x x

0g X

1( )fP

2) Structural reliability analysis of ships in the ULS considering global hull failure

global hull failure induced by global loads only

global hull failure induced by combination of global andglobal hull failure induced by combination of global and local loads


Structural Reliability: Uncertainty Modeling

1) Still water load

2) Wave induced loadS i i l i• Statistical uncertainty

• Uncertainty in environmental conditionO ti l t i t• Operational uncertainty

• Model uncertainty• Model uncertainty due to

nonlinear effectnonlinear effect• Other uncertainty

3) Load combination3) Load combination

4) Hull girder ultimate strength


Structural Reliability: Method

•FORMSORM•SORM

•Response surface•Montel CarloMontel Carlo


Case Study: SRA of Ships Hull Girder in ULS

Target ships: Cape Size Bulk carrier

Load condition: Alternate hold loading

Main dimensionsMain dimensions


Case Study: Part I Ultimate hull girder strength

Combined Loads

global bending loads, internal cargo pressure, external sea pressure

Commercial FEM code: ABAQUS

Two Load cases:

heavy load AHL (CSR-LC-10) andhomogeneous load AHL (CSR LC 5)homogeneous load AHL (CSR-LC-5)

Various local load levels

Design modification factors


Structural model


Boundary conditions


Load Cases


Pure bending


Combined global and local loadsHeavy cargo AHL (CSR-LC-10)


Interaction relationship


Design modification


Case Study: Part II Structural Reliability Analysis

Limit state function

•Ultimate limit state under combine global and local loads

P

•Ultimate limit state considering all the uncertainties under combined global and local

( ) (1 )u tu

Pg X M MP

loads

, , , , , , , ,1 sp m s c wp oper wp envir wp m wp nl wp st w cP B B Pg M

,

, , , , , , , , ,

1u u cp u

swH m swH st swH c wvH oper wvH envir wvH m wvH nl wvH st wv wvH c

g MP

M B B M


Determination of Characteristic Value

Structural Capacity: Ultimate Hull Girder Strength Under Pure Bending

Nonlinear FEM Analysis

Characteristic Loads: Still Water and Wave Loads

(Global: Vertical Bending Moment; Local: Water Pressure)

Rule Formulations (CSR)

Direct Calculation

1 20

1.25 Without Heavy weather avoidanceRVERES=1.22

Long-term statistics analysisProcedure of long term prediction recommend by IACS 1.00

1.05

1.10

1.15

1.20 VERESRWASIM=1.01

AC

S)

and

rule

val

ue)

-Scatter diagram in the North Atlantic.-Pierson-Moskowitz spectrum-Short crested waves with 0.80

0.85

0.90

0.95

Bul

k C

arrie

r (IA

of d

irect

cal

cula

tion

With Heavy weather avoidance VERES Method1 WASIM Method1 VERES Method2WASIM Method2

spreading function cos2θ -Uniform distribution of heading-Only zero speed is to be consideredProper corrections for

8 9 10 11 12 13 140.65

0.70

0.75(R

atio

Hs

WASIM Method2 VERES Method3 WASIM Method3


-Proper corrections for nonlinear effects

Heavy Weather Avoidance

Avoidance of heavy weather based on forecast

• Rule formulation in CSR

without consideration of heavy weather

avoidanceO ti l l• Operational envelopes determined based criteria and the assumption that these criteria be fulfilled during

tioperation• Assessment of operations in

view of sea state forecasts.

• A bias factor of 0 85 isA bias factor of 0.85 is proposed if operational restriction is imposed to avoid heavy weather with Hs>10mHs>10m


Uncertainties


Effect of Correlation between global and local loads

, , , , , , , ,1 sp m s c wp oper wp envir wp m wp nl wp st w cP B B Pg M

,

, , , , , , , , ,

1u u cp u


g MP

M B B M


Probability of failure

, , , , , , , ,, 1 sp m s c wp oper wp envir wp m wp nl wp st w c

u u c

P B B Pg M

P

Zhi Shu August 24, 2010 , , , , , , , , ,

p u


P

M B B M

Importance factor

without heavy weather avoidance

Zhi Shu August 24, 2010DMF = 1.4

Parametric study


29

Conclusions

it is very important to consider the effect of how to deal with local loads and heavy weather avoidance for bulk carriers in hogging and alternate hold loading condition.

It is found that the failure probability is about 10% of that without consideration of local loads.

Account of heavy weather avoidance can reduce the failure probability to 10% of that without consideration of heavy weather avoidance.

A proper determination and evaluation of resistances and load effects and associated uncertainties of loads and structural capacity are the most important for structural reliability assessment in the ultimate limit state.


Thank you very much for Thank you very much for your attention !


References

Shu Z. and Moan T. Ultimate hull girder strength of a bulk carrier under combined global and local loads in the hogging and alternate hold loading condition using nonlinear finite element analysis. Journal of Marine Science and Technology, v.17, no.1, 2012 March, p.94(20)

Moan T., Shu Z. and Jia H. Reliability of Intact and Damaged Ships in the Ultimate Limit State: A Review. Centre for Marine Technology and Engineering (CENTEC) Anniversary Book. CRC Press, Lisbon, Portugal, 2012. ISBN 978-0-415-69808-5.

Shu Z. and Moan T. Reliability analysis of a bulk carrier in ultimate limit state under combined global and local loads in the hogging and alternate hold loading condition. Journal of Marine Structures, v.14, no.1, 2011, p.1-22.

Shu Z. Uncertainty Assessment of Wave Loads and Ultimate Strength of Tankers and Bulk Carriers in a Reliability Framework. Doctoral thesis, Norwegian Unniversity of Science and Technology, 2010.

Shu Z. and Moan T. Effects of Avoidance of Heavy Weather on the Wave-Induced Load on Ships. Journal of Offshore Mechanics and Arctic Engineering, v.130, no.2, 2008.


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