Transcript Reliability based Ultimate Strength Structural Design for

RPD 2004 University of Strathclyde Research Presentation Day
Ultimate strength of intact ship hulls with diurnal
temperature effects: a reliability based approach
considering corrosion and load combination
Ioannis Moatsos MEng (Hons), GMRINA, MSNAME, SMIStructE, SMIMarE
ASRANet Ship Group Champion
Supervisor: Prof. P.K. Das
Overview
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The temperature problem.
Thermal stresses in Marine Structures
Research aims.
FPSO Concept.
Ultimate Strength.
Thermal Stress Modelling.
Corrosion in FPSO structures.
Loading.
Reliability Analysis.
Results.
Past-Present-Future Work.
Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day
The Temperature Problem
• Global Warming and
Weather and Temperature
Anomalies.
Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day
Thermal Stresses in Marine Structures
• Unless the problem is temperature dependent (LNGs/Nuclear),
the effects of temperature on marine structures are often
ignored as non significant.
• ABS in the 50s recorded major hull fractures occurring on
moored vessels in still water while temperature was changing.
• SSC Reports in the 60s mention records of high midship stress
on five bulk carriers indicating surprisingly high thermal effects.
Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day
Research Aims
 Investigate the effects of diurnal temperature variation
and the subsequent effect of thermal stresses generated
on the ultimate strength and reliability of stiffened plate
structures.
 Incorporate the effects of thermal stresses and slamming
in existing stochastic load combination methods.
 Investigate the effect of corrosion on the ultimate strength
and reliability of stiffened plate structures.
 Propose a methodology for incorporating temperature,
corrosion and slamming in ultimate strength reliability
based design.
Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day
The FPSO Concept
Source: Douglas-Westwood 2000 report
Image and video sources:
BP, Bluewater, SHELL
Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day
Source: Douglas-Westwood 2000 report
Ultimate Strength Analysis
• Using Advanced Closed Form
Analytical Formulation. (Paik 2001)
• Taking into account all possible
collapse modes.
Sagging
HoggingUltimate
UltimateMoment
MomentCapacity
Capacity
g
H oSU
H oSL
, H  C1D  C12 D 2  2C2 D
, H  C1 D  C12 D 2  2C 2 D ,g 
 uSU   oSL
 uSL   oSU
C1 

   



Ayo uB  Ay1 uIBA
AA 
Azj j 
 yB AoSL
uDj 0 AzjuSU uSL
ym
 j 0 

ym
2 yiyo oSU
C1 
n
n
 uSL   oSU uSU
Azj
 j0AoSL
zj  
n
m 1
n


j 0


 m 1

m 1 y i 
 Ayi D
Ayi
 j 1 Ayi yi
j 2
, C 2 , C 2 
 nn  Azj
 Ajzj0
 j 0 

m 1
oDi 1
1
m 1
M Vus   Aym uD D  g    uSU   oSL  i 1 Ayi gyi  y i2  m 1
1

2 
M Vuh  Ayo uB D  g  HAy1 uIB D  y1  g    uSL   uSU  Ayi g D  yi   D  yi  
H
1
H
m 1
n
n
 i2



  oSL i 1 Ayi  y i  g  
A
D

H
D  H  2 g  uSU  Ayo oB g 
Azj


zj
j

0
j

0
2 D
6D

1  n
 m 1









A
D

y

g

A


A
D

H
D

H

2
g



oSU
yi
i
ym
oDg
zj
uSL
 2 H  3g  uSU  H  3 g  oSL 
2 D  j 0 
 i 2



Universities of Glasgow and Strathclyde




H  n
  Azj 2 H  3g  uSL  H  3g  uSU 
6 D  j 0 
RPD 2004 Research Presentation Day




Thermal Stress Modelling
• 1 preventing long. fibres
from thermal expansion.
• 2 making the total
longitudinal force on the
section zero and 2 must
vary in proportion with E to in
order to equalize strain in all
fibres.
 E   E  ETdA
E  Ey
E 2 Ez
E 2

 ETzdA
 , A   dA
k  ET
, 2I oz  ETydA
y
dA
,
I

z dA


2
oy

EdA
Ey dA
Ez dA   E
E
E
E






 
kyky
kzkz
ET k k
  ET    ETdA

ETydA

ETdA
ETydA
ETzdA

I oyIoy  ETzdA
I ozIoz 
1   AA
Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day
• A set of stresses 3 and 4
corresponding to pure
bending in the xy (long.) and
xz planes respectively is
added so that the net
bending in the section equals
zero.
•Incorporating transverse
restrain modeling effect of
bulkheads
Corrosion in FPSO Structures
• Casualties of merchant ships occurring while under
operation as a result of structural failure of aging ships
in rough seas and weather.
• The need exists to develop corrosion mathematical
models based on statistical analysis of actual
measurements and incorporate them in structural
design procedures.
Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day
Loading
•Sea Spectra:
ISSC version of the Pierson-Moskowitz spectrum given by Warnsick (1964)
5
4


 




S  0.11H sTm  Tm
 exp  0.44 Tm
 
 2 
 2  

•RAOs:
All headings in increments of 10, 30, 45o
•Cumulative long-term distribution:

Q x  xi     px | mo  f R r dr where f R r dr  f H s , Tz , , v, c dH s dTz ddvdc
xi o
•Probability of exceeding amplitude:

Qx  xi    e

x2
2 m0
f R r dr
0
A Weibull distribution was fitted to the resulting distribution to determine
scale (k) and shape (b) parameters against Q(Mw>Mi) using:
  M w b 

QM w  M i   exp  
  k  


Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day
Load Combination
1
u w  k .lnn w b
Vertical Wave Bending
Type I Gumbel Distribution (Guedes Soares 1984)
1
Still Water Bending Moment
VBM s  u ns  
 ns
1


F t( VBM)
F es( VBM)
0.6
F ew( VBM)

a VBM t

0.4
0.2
0
0
0
50
0




 VBM t  z  u nw  

F t  VBM t   
exp exp 
 dnorm z  s   s d z




 nw







3
  1 10

RPD 2004 Research Presentation Day
150
200
250
300
350
340
VBM
Load Combination Factor
Total Vertical Bending Moment
VBM t
100
VBM
Ferry Borges-Castanheta Method (1971)
Universities of Glasgow and Strathclyde
Tc
Tz
0.8
Type I Gumbel Distribution (Guedes Soares 1984)


F es VBM s   exp exp 


b
k
nw 
FGumb M we   exp exp   M we  u 
1b
b
 w  .lnnw 
ns
w 
1
0.5
Ft 1 0.5  Fsw
Fw1 0.5
Reliability Analysis
• Using FORM (First Order Reliability Method).
• Results obtained improved using SORM (Second Order
Reliability Method).
– U-X Transformation using Rosenblatt, Nataf, Hermite.
• Computer Codes Used: CalRel, PROBAN, STRUREL.
– All codes converged to similar results.
– Results & levels of safety compared to existing published literature.
(DNV, Bureau Veritas, ABS, SSC, HSE).
Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day
Failure Function and Stochastic Model
g   u M u  M se      n M we
M u  UltimateBending MomentCapacity.
Variable
u  Uncertainty on Ultimate Strength.
Distribution
COV
Mean
Normal
0.10
1
LogNormal
0.10
Calc.
Gumbel Extreme
0.15
Calc.
Ultimate Strength Uncertainty
u
M se  Still WaterBending
Moment.
   LoadCombinatio
Factor. Ultimate Strength
Mn
u
  Uncertainty in WaveLoad prediction.
Mse
Most Probable Extreme Still Water
Bending Moment
 n  Non - linear effects.
f
Load Combination Factor
Constant
N/A
0.78

Uncertainty in Wave Load Prediction
Constant
N/A
0.1
n
Non-Linear Effects
Constant
N/A
1.2 S
0.8 H
Me
Extreme Vertical Wave Bending
Moment
Gumbel Extreme
0.15
Calc.

M we  ExtremeVertical
WaveBending Moment.
Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day
Analysis & Design
Temperature Effect on the Probability of Failure
Temperature Effect on the Reliability Index
6.75
1E-4
6.50
6.25
5.50
5.25
5.00
 Hogging
 Sagging
4.75
4.50
4.25
4.00
3.75
3.50
Probability of Failure Pf
5.75
Reliability Index 
Pf Hogging
Pf Sagging
1E-5
6.00
1E-6
1E-7
1E-8
1E-9
1E-10
1E-11
3.25
3.00
0
5
10
15
20
0
5
10
Representative
Alphas of Variables FLIM(1) [HOG.PTI]
20
15
o
o
Temperature Change C
Temperature Change C
fR   s M s   wM w
E xtS WM -0.21661
E xtWB M -0.20879
Xu
0.53660
Xw
-0.18984
UltS tr
0.76519
S um of a^2 1.00000
Temperature Effect on PSF in Sagging
Elasticities of Mean Values FLIM(1) [HOG.PTI]
Elasticity
1. 9716
2.0
Partial Safety Factor
1. 6917
1. 4117
1.5
1. 1317
1.0
0. 8517
0. 5718
Extr. Still Water BM
Extr. Wave BM
Ultimate Str. Uncertainty
Uncert. in Wave Load Prediction
Ultimate Strength
0.5
0.0
0. 2918
0. 0118
-0.2682
-0.5481
0
5
10
15
o
Temperature Change C
20
-0.8281
ExtSW M
ExtW BM
Xu
Basi c Ran d om Variab les
Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day
Xw
UltStr
Past-Present-Future Work
• Review and comparison of thermal modelling procedures recommended
by the Ship Structure Committee (SSC) and based on Thermal Stress
Theory (Jasper 1956, Corlett 1950). Procedures for analysis of ship
structures suggested.
• Review and comparison of ultimate strength modelling procedures
(analytical, progressive collapse & FE methods) and incorporation of the
effects of corrosion (Paik and Mansour 2001, Paik 2003, Smith 1977).
Methodology for analysis of ship structures has been suggested.
• Significant reduction of the hull girder ultimate strength (5-10%) when
thermal stresses where taken into account. Extreme diurnal temperature
variations during the summer months.
Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day
Past-Present-Future Work
• Review and comparison of existing load combination methods
and extended to incorporate the effects of temperature and
slamming (Ferry Borges-Castanheta 1971, Ferro and Mansour
1985, Friis Hansen 1994). Procedures for analysis of ship
structures were developed.
• Using a number of different reliability techniques (FORM,
SORM, Monte Carlo) the reliability of a number of FPSO
structures has been determined and partial safety factors have
been obtained for use in design.
• Future work in modelling the effects of temperature on stiffened
plate FE model and performing reliability analysis using Monte
Carlo simulation and calibrate partial safety factors for use in
design.
Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day
Publications
1. MOATSOS, I. and DAS, P.K. (2003), “Reliability based ultimate strength structural design for safety”, Proceedings
of the 8th International Marine Design Conference (IMDC 2003), Athens Greece, May 2003.
2. MOATSOS, I. and DAS, P.K. (2003), “Temperature dependent FPSO ultimate strength reliability”, Proceedings of
the 13th International Offshore and Polar Engineering Conference (ISOPE 2003, Honolulu Hawaii USA, May 2003.
3. MOATSOS, I. and DAS, P.K. (2003), “Temperature and corrosion effects on FPSO ultimate strength: a reliability
based approach”, Proceedings of the 22nd International Conference on Offshore Mechanics and Arctic Engineering
(OMAE 2003), Cancun Mexico, June 2003.
4. MOATSOS, I. and DAS, P.K. (2004), “Modelling the effect of extreme diurnal temperature changes on ship
structures for the assessment of structural reliability load combination techniques”, 2004-JSC-320, Abstract accepted
and paper to be published in the Proceedings of the 14 th International Offshore and Polar Engineering Conference
(ISOPE 2004), Toulon France, May 2004.
5. MOATSOS, I. and DAS, P.K. (2004), “Assessment of structural reliability of ships under combined loading
including extreme diurnal temperature effects”, OMAE2004-51316, Abstract accepted and paper to be published in the
Proceedings of the 23nd International Conference on Offshore Mechanics and Arctic Engineering (OMAE 2004),
Vancouver Canada, June 2004.
6. MOATSOS, I. and DAS, P.K. (2004), “Structural Reliability of Ship Structures with Advanced Hull Girder
Modelling”, Abstract accepted and paper to be published in the Proceedings of the 2 nd ASRANet International
Colloquium, Barcelona Spain, July 2004.
7. MOATSOS, I. and DAS, P.K. (2004), “Implementation of combined loading techniques modelling the effects of
diurnal thermal loads, slamming and corrosion to determine the reliability of Tanker/FPSO structures.” Journal Paper
to be submitted for publication in the Marine Structures Journal, Elsevier Applied Science Publishing.
Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day
Research Support
Sponsors and Supporters
• The UK Engineering and Physical Sciences Research Council.
• UK The Health and Safety Executive.
• The Alexander S. Onassis Public Benefit Foundation.
• Mr. Michel Huther & Bureau Veritas.
• The UN World Meteorological Organization.
• Prof. Douglas Faulkner.
• SHELL UK Exploration and Production.
Awards
• ISOPE Offshore Mechanics Award 2003.
• Royal Society of Edinburgh Lessels Award 2003.
• Selection for the 2003 Young Engineers Presentations
Reception in the House of Commons.
Universities of Glasgow and Strathclyde
RPD 2004 Research Presentation Day