UPDATING FAILURE PROBABILITY

Transcription

1 UPDATING FAILURE PROBABILITY OF A WELDED JOINT IN OWT SUBSTRUCTURES Q. Mai 1 J.D. Sørensen 2 P. Rigo 1 1 Department of ArGEnCo University of Liege 2 Department of Civil Engineering Aalborg University OMAE Conference - Busan, 2016

2 Motivation Reduce O&M Costs 2 RBI Update Pf (insp.) Limit State Function

3 Message Objective 3 Fatigue Assessment Diagram can be used to update the failure probability of an existing OWT substructure when new information about either loading, structural responses or inspections is available.

4 Outline 4 Fatigue Assessment Diagram Updating Probability of Failure Results

5 Outline 5 Fatigue Assessment Diagram Updating Probability of Failure Results

6 Fatigue Assessment Diagram Kr Lr Figure: Level 2A Fatigue Assessment Diagram BS-7910, Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures. British Standard Institution (BSi).

7 Fatigue Assessment Diagram Kr L r,max = s Y + s U 2s Y Lr Figure: Level 2A Fatigue Assessment Diagram BS-7910, Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures. British Standard Institution (BSi).

8 Fatigue Assessment Diagram Kr L r = s ref s Y ; K r = K I K mat Lr Figure: Level 2A Fatigue Assessment Diagram BS-7910, Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures. British Standard Institution (BSi).

9 Fatigue Assessment Diagram Kr L r = s ref s Y ; K r = K I K mat 0.2 Safe Lr Figure: Level 2A Fatigue Assessment Diagram BS-7910, Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures. British Standard Institution (BSi).

10 Fatigue Assessment Diagram Unsafe Kr L r = s ref s Y ; K r = K I K mat Lr Figure: Level 2A Fatigue Assessment Diagram BS-7910, Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures. British Standard Institution (BSi).

11 Outline 7 Fatigue Assessment Diagram Updating Probability of Failure Results

12 Uncertainties 8 Variable Distr. Mean CoV Variable Value n No. of cycle/year t Steel thickness [mm] 65 R Outer radius [mm] 79.5 L Joint length [mm] 100 h s Bend. to memb. ratio 0.81 K tr Transition SIF range 196 m 1 Paris law, 1 st line 5.10 m 2 Paris law, 2 nd line 2.88 C a/c c C ratio for a and c 0.9 S Stress range [MPa] W k=0.8 N(µ,s) s Y Yield strength [MPa] LN s U Ultimate strength [MPa] LN K th SIF range threshold LN K mat Fracture toughness 3p W - - C 1 Paris law, 1 st line LN C 2 Paris law, 2 nd line LN a 0 Initial crack depth LN a 0/c 0 Initial aspect ratio LN B scf Uncertainty in SCF LN B sif Uncertainty in SIF LN

13 Updating method 9 Uncertainties

14 Updating method 9 a 0,c 0 SIF SCF s Y s U s K mat K th FM

15 Updating method 9 a 0,c 0 SIF SCF s Y s U s K mat K th FM Limit State Function Pf Yeter, B., Garbatov, Y., and Soares, C. G., Fatigue Reliability of an Offshore Wind Turbine Supporting Structure Accounting for Inspection and Repair. POD Decisions Updating Pf

16 Updating method 9 a 0,c 0 SIF SCF s Y s U s K mat K th FM Limit State Function Crack Growth Simulation POD Decisions

17 Updating method 9 a 0,c 0 SIF SCF s Y s U s K mat K th FM Limit State Function Crack Growth Simulation POD Decisions Updated Pf

18 Crack Growth Simulation 10 Crack depth a and crack length 2c are coupled during the simulation. 8 >< da dn = C a ( K a ) m K a K th dc (1) >: dn = C c ( K c ) m K c K th K a = SY a p pa (2) K c = SY c p pa (3)

19 Crack Growth Simulation 11 Semi crack length C Life time Figure: Crack growth in combination with inspections

20 Crack Growth Simulation 11 Semi crack length C C d i Inspection i Life time Figure: Crack growth in combination with inspections

21 Crack Growth Simulation 11 Semi crack length C C d i Inspection i Life time Figure: Crack growth in combination with inspections

22 Outline 12 Fatigue Assessment Diagram Updating Probability of Failure Results

23 Results Crack Propagation Crack depth [mm] Year Figure: Crack propagation

24 Results No Crack Detected 14 # No crack detected No inspection Annual Failure Probability 3.5 Probability Year Figure: Annual POF

25 Results Crack Detected & Repaired 15 # Normal Repair Perfect Repair Annual Failure Probability 2.5 Probability Year Figure: Annual POF

26 Summary 16 Fatigue Assessment Diagram can be used to update the failure probability of an existing OWT substructure when new information about either loading, structural responses or inspections is available. I Outlook I I Reduction of uncertainty related to stress-ranges given new information about loading and structural response Improved modelling of crack growth after reaching the wall thickness.

27 Acknowledgement 17 This research is funded by the National Fund for Scientific Research in Belgium F.R.I.A - F.N.R.S. About me: Quang MAI University of Liège, Belgium aq.mai@ulg.ac.be