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

6/27/2015Smögen Workshop ( )2 Outline  Background and motivation  Fatigue model in terms of Hs  Application of the fatigue model  Conclusions

6/27/2015Smögen Workshop ( )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

6/27/2015Smögen Workshop ( )4 How to estimate vessel’s fatigue damage 1.1, Background Rain-flow counting method (“correct” fatigue estimation) Narrow bound approximation (NBA) Theoretical method based on NBA

6/27/2015Smögen Workshop ( )5 1.1, Background Vessel’s response process is correlated with its encountered sea states (5/30 min stationary?)

6/27/2015Smögen Workshop ( )6  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 1.1, Background Method/Voyagevoy080106voy080129voy080218voy RFC for voyage signal RFC for 5 min signal RFC for 30 min signal

6/27/2015Smögen Workshop ( )7 1.1, Background  Theoretical fatigue estimation Hydrodynamic RAO’s depends on heading angles and velocity  A i means stress caused by each applied load  H v – transfer function for vertical bending moment  H h – transfer function for horizontal bending moment  H t – transfer function for torsional bending moment

6/27/2015Smögen Workshop ( )8 1.1, Background Linear wave model Directional wave spectrum Encountered sea states: Vessel’s response under encountered sea states

6/27/2015Smögen Workshop ( )9  NBA for expected fatigue damage Response zero-crossing frequency Significant response height 1.1, Background

6/27/2015Smögen Workshop ( )10  Measurement signal process X(t) Process zero-crossing frequency 1.1, Background Method based on the measured signal can be taken as the right fatigue criteria

6/27/2015Smögen Workshop ( )11  Comparing among different methods 1.1, Background Method/Voyagevoy080106voy080129voy080218voy Rain-flow method NBA estimation Theoretical method Note: Rain-flow and NBA method based on measured signal, Standard method based on theoretical simulation.

6/27/2015Smögen Workshop ( )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

6/27/2015Smögen Workshop ( )13 2, Fatigue model in terms of Hs  Response hs is very correlated with wave Hs,  Significant response height: 1, Relation between response and wave fixed wave Tz Severe sea states cause heavy stress response!!!

6/27/2015Smögen Workshop ( )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:

6/27/2015Smögen Workshop ( )15 2, Fatigue model in terms of Hs Significant response height hs observed vs from model Voyage namevoy080106voy080129voy080218voy Constant C , 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

6/27/2015Smögen Workshop ( )16 2, Fatigue model in terms of Hs Assume zero-crossing wave period as: Hs Tz (model) Tz (measure) This model is ok for the large Hs, but not in the small Hs area 2, Response zero crossing frequency

6/27/2015Smögen Workshop ( )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

6/27/2015Smögen Workshop ( )18 Response zero up-crossing frequency observed vs simplified model with U0=9m/s, HDG=0 2, Fatigue model in terms of Hs

6/27/2015Smögen Workshop ( )19 3, Application of the fatigue model 5 voyages from Europe to Canada 2 voyages from Canada to Europe 4 special voyages (strange relation between encountered sea states and response) Voyages between Atlantic ocean travelling in different seasons

6/27/2015Smögen Workshop ( )20 Fatigue damage distribution along voy from different estimation approaches 3, Application of the fatigue model

6/27/2015Smögen Workshop ( )21 3, Application of the fatigue model Fatigue damage distribution of voyages from different estimation approaches

6/27/2015Smögen Workshop ( )22 Rain-flow based on signal is “real” fatigue damage 5 and 30 minutes’ periods both assumed stationary 3, Application of the fatigue model Rain-flowNBA on signalNBA on Hs NBA on Hs C=19 Theoretical method voy voy voy voy voy

6/27/2015Smögen Workshop ( )23 2 voyages from Canada to EU 3, Application of the fatigue model

6/27/2015Smögen Workshop ( )24 Constant C and Fatigue damage accumulation 3, Application of the fatigue model Voyage namevoy080613voy Constant C Rain-flow NBA on signal NBA on Hs Theoretic al method voy voy

6/27/2015Smögen Workshop ( )25 4 special voyages from Canada to EU 3, Application of the fatigue model

6/27/2015Smögen Workshop ( )26 Constant C and Fatigue damage accumulation 3, Application of the fatigue model Voyage namevoy071018voy071030voy071106voy Constant C Rain-flow NBA on signal NBA on Hs Theoretica l method voy voy voy voy

6/27/2015Smögen Workshop ( )27 4, Conclusions 1. Our fatigue estimation model works quite well, and its precision is much better than the theoretical method 2. For the fatigue estimation location of above vessel, the constant C keeps about There are a lot of uncertainties in the model (hs, fz)… 4. Comparing to the other parameters, wave Hs is the most important factor of fatigue damage …(further work) 5. Need to check wave spectrum measurement by satellite wave model… 6. Put this model in shipping routing application…