Modelling and Computer Animation of Damage Stability

1. Modellingand Computer Animation of Damage Stability K. Hasegawa, K. Ishibashi, Y. Yasuda Presentation: Marcel van den Elst

2. Presentation Outline • Historical background • damage stability issues • Osaka University and Strathclyde University joint research on damage stability • Mathematical Model • vectorial Equations of Motion for a damaged ship • scalar equations for sway, heave and roll • modelling the water ingress • residual stability and its calculation

3. Simulation of a damaged ship • selected ship model and capsizing scenario • simulation results • steady states • possible explanation • Computer animation of a damaged ship • animation software structure • animation software specifications • animation video • Conclusions

4. Historical Background • Damage stability issues • capsizing of Ro-Ro passenger ferries • prediction of (the effects of) water accumulation on bulkhead decks • both hydrostatic and hydrodynamic effects • need for simulations • Osaka University and Strathclyde University • Hasegawa’s stay at Strathclyde in 1996 resulted in joint research on damage stability • focus on model expansion, simulation and visualisation of simulation results

5. Mathematical Model • General vector Equations of Motion for a damaged ship • Scalar equations for sway, heave and roll • Modelling the water ingress • Residual Stability and its calculation

6. Equations of Motion • General vector Equations of Motion for a damaged ship

7. Damaged ship with progressive flooding • can be regarded as a single dynamic system • 3 dominant motions in beam seas are considered: sway, heave and roll • Radiation and Diffraction forces • calculated based on Ursell and Tasai method for sectional Lewis forms in still water • Froude-Krylov forces • calculated based on the Hamamoto method to account for variations of hull submersion in waves

8. scalar expression for the sway force

9. scalar expression for the heave force

10. scalar expression for the roll moment

11. Water Ingress • water ingress influenced by configuration of the opening area, position of the opening area, wave condition, etc. • CFD techniques not yet well enough developed to describe such a highly complex phenomenon • Vassalos e.a. proposed a simplified method based on interior and exterior water level difference, with complexities concentrated in flooding coefficient K

12. Residual Stability • static stability affected by flooding • important because it is used as a standard in stability regulations • calculated using an added mass method

13. center of each section of the ship hull calculated by the Hamamoto method • considers heave and pitch in balance so that • heave displacement and pitch angle calculated numerically using the Newton-Raphson method

14. GZ(m) GZ(m) GZ(m) Roll (deg) Roll (deg) Roll (deg) • resulting residual stability curves (Gzdamage) • wall sided Ro-Ro passenger ship • flooding into two compartments under bulkhead deck GM=1.5m GM=1.76m GM=2.0m

15. GZ(m) GZ(m) GZ(m) Roll (deg) Roll (deg) Roll (deg) • resulting residual stability curves (Gzdamage) • wall sided Ro-Ro passenger ship • flooding into the car deck GM=1.5m GM=1.76m GM=2.0m

16. Simulation of a Damaged Ship • ship model and capsizing scenario • simulation results • steady states • possible explanation

17. Ship model and capsizing scenario • a wall sided Ro-Ro passenger ship like the Estonia • a capsizing scenario conform IMO regulations for ship safety:flooding occurring simultaneously into watertight compartments under the bulkhead deck and onto a car deck above the bulkhead deck • different compartment layouts have been simulated to show general applicability of the method to ships other than Ro-Ro passenger ships

18. heel to lee-side Time(sec)

19. Heel to weather-side Time(sec)

20. capsize Time(sec)

21. H/ Wave period (sec) • simulation results show 3 steady states • heel to lee side • heel to weather side without capsize • heel to weather side with capsize

22. possible explanation for these states to occur heel to lee side • damage opening above water surface heel to weather side resulting in capsizing • roll moment of the waves larger than the restoring moment of the ship heel to weather side without capsizing • heel moment of accumulated water in phase with the moment of inclination of the ship • accumulated water level equals the wave surface

23. Computer Animation • important for qualitative understanding of the combined motions in case of flooding • two programs produce time-series data for respectively wave and ship motion • third program visualizes the scene • programmed in OpenInventor, a top layer on OpenGL

24. 3D animation software program structure Wave Generator Ship Motion Generator Ship Data 3D Simulator

25. 3D animation simulator specifications • simultaneously shows ship motions, waves, and accumulated water inside the flooded compartments • video output at 10 frames/second • viewpoint and zoom can be adjusted freely with a mouse during the animation to be able to view every part of the ship during the animation

26. 3D Animation video

27. Conclusions • A mathematical model that accounts for large rolling motions of damaged (passenger) ships in waves has been realised and simulated • Three steady state conditions of the damaged ship could be identified • A 3D animation software tool has been implemented to visualise the simulations