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Fatigue damage estimation along vessel ’ s voyages

Fatigue damage estimation along vessel ’ s voyages. Chalmers University of Technology. Wengang Mao Igor Rychlik. Outline. Background and motivation Fatigue model in terms of Hs Application of the fatigue model Conclusions. 1.1, Background. Vessel construction period

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Fatigue damage estimation along vessel ’ s voyages

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  1. Fatigue damage estimation along vessel’s voyages Chalmers University of Technology Wengang Mao Igor Rychlik

  2. Outline • Background and motivation • Fatigue model in terms of Hs • Application of the fatigue model • Conclusions Smögen Workshop (2008-08)

  3. 1.1, Background • Vessel construction period • Loading period • Shipping period 1, Vessel’s fatigue location 2, Loading condition 3, Shipping condition 4, Encountered sea states Smögen Workshop (2008-08)

  4. 1.1, Background How to estimate vessel’s fatigue damage • Rain-flow counting method (“correct” fatigue estimation) • Narrow bound approximation (NBA) • Theoretical method based on NBA Smögen Workshop (2008-08)

  5. 1.1, Background • Vessel’s response process is correlated with its encountered sea states (5/30 min stationary?) Smögen Workshop (2008-08)

  6. 1.1, Background • 30 minutes’ stationary process check • Rain-flow based on the whole voyage signal • Rain-flow based on 5 minutes’ signal • Rain-flow based on 30 minutes’ signal Smögen Workshop (2008-08)

  7. 1.1, Background • Theoretical fatigue estimation • Hydrodynamic RAO’s depends on heading angles and velocity • Ai means stress caused by each applied load • Hv– transfer function for vertical bending moment • Hh– transfer function for horizontal bending moment • Ht– transfer function for torsional bending moment Smögen Workshop (2008-08)

  8. Linear wave model Directional wave spectrum 1.1, Background Encountered sea states: • Vessel’s response under encountered sea states Smögen Workshop (2008-08)

  9. 1.1, Background • NBA for expected fatigue damage Response zero-crossing frequency Significant response height Smögen Workshop (2008-08)

  10. 1.1, Background • Measurement signal process X(t) Process zero-crossing frequency Method based on the measured signal can be taken as the right fatigue criteria Smögen Workshop (2008-08)

  11. 1.1, Background • Comparing among different methods Note: Rain-flow and NBA method based on measured signal, Standard method based on theoretical simulation. Smögen Workshop (2008-08)

  12. 1.2, Motivation—fatigue model of Hs • Drawbacks of the two typical methods 1, Measured signal is seldom available 2, Theoretical RAO’s need more precision 3, RAO’s (FEM & Hydrodynamic software simulation) • Main motivation 1, Compare different influence factors 2, Simply fatigue model (precise) only in terms of Hs 3, Check model’s validity Smögen Workshop (2008-08)

  13. 2, Fatigue model in terms of Hs 1, Relation between response and wave • Response hs is very correlated with wave Hs, • Significant response height: Severe sea states cause heavy stress response!!! fixed wave Tz Smögen Workshop (2008-08)

  14. 2, Fatigue model in terms of Hs Fixed wave Hs, its associate Tz from 4s to 12s has distribution f(t) Weighted arithmetic average C: Mean C: Smögen Workshop (2008-08)

  15. 2, Fatigue model in terms of Hs Significant response height hs observed vs from model • 1, Constant C works quite well for the model in left figure. • 2, Constant C for these voyages around 19 • 3,C from measurement agrees well with theoretical value Smögen Workshop (2008-08)

  16. 2, Fatigue model in terms of Hs 2, Response zero crossing frequency Assume zero-crossing wave period as: This model is ok for the large Hs, but not in the small Hs area Smögen Workshop (2008-08)

  17. 2, Fatigue model in terms of Hs • Ship’s response frequency should be corresponding to its encountered wave frequency • Encountered wave frequency is also related with shipping velocity and heading angles Note: Here the frequency should be encountered wave frequency Smögen Workshop (2008-08)

  18. 2, Fatigue model in terms of Hs Response zero up-crossing frequency observed vs simplified model with U0=9m/s, HDG=0 Smögen Workshop (2008-08)

  19. 5 voyages from Europe to Canada 2 voyages from Canada to Europe 4 special voyages (strange relation between encountered sea states and response) 3, Application of the fatigue model Voyages between Atlantic ocean travelling in different seasons Smögen Workshop (2008-08)

  20. 3, Application of the fatigue model Fatigue damage distribution along voy080106 from different estimation approaches Smögen Workshop (2008-08)

  21. Fatigue damage distribution of voyages from different estimation approaches 3, Application of the fatigue model Smögen Workshop (2008-08)

  22. 3, Application of the fatigue model • Rain-flow based on signal is “real” fatigue damage • 5 and 30 minutes’ periods both assumed stationary Smögen Workshop (2008-08)

  23. 3, Application of the fatigue model 2 voyages from Canada to EU Smögen Workshop (2008-08)

  24. 3, Application of the fatigue model Constant C and Fatigue damage accumulation Smögen Workshop (2008-08)

  25. 3, Application of the fatigue model 4 special voyages from Canada to EU Smögen Workshop (2008-08)

  26. 3, Application of the fatigue model Constant C and Fatigue damage accumulation Smögen Workshop (2008-08)

  27. 4, Conclusions • Our fatigue estimation model works quite well, and its precision is much better than the theoretical method • For the fatigue estimation location of above vessel, the constant C keeps about 19 • There are a lot of uncertainties in the model (hs, fz)… • Comparing to the other parameters, wave Hs is the most important factor of fatigue damage …(further work) • Need to check wave spectrum measurement by satellite wave model… • Put this model in shipping routing application… Smögen Workshop (2008-08)

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