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Modelling and Computer Animation of Damage Stability. K. Hasegawa, K. Ishibashi, Y. Yasuda. Presentation: Marcel van den Elst. Presentation Outline. Historical background damage stability issues Osaka University and Strathclyde University joint research on damage stability

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Modelling and Computer Animation of Damage Stability

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Modellingand Computer Animation of Damage Stability

K. Hasegawa, K. Ishibashi, Y. Yasuda

Presentation: Marcel van den Elst


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


    • 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


  • 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


  • 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


    Equations of Motion

    • General vector Equations of Motion for a damaged ship


    • 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


    • scalar expression for the sway force


    • scalar expression for the heave force


    • scalar expression for the roll moment


    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


    Residual Stability

    • static stability affected by flooding

    • important because it is used as a standard in stability regulations

    • calculated using an added mass method


    • 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


    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=1.5mGM=1.76mGM=2.0m


    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=1.5mGM=1.76mGM=2.0m


    Simulation of a Damaged Ship

    • ship model and capsizing scenario

    • simulation results

    • steady states

    • possible explanation


    • 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


    heel to lee-side

    Time(sec)


    Heel to weather-side

    Time(sec)


    capsize

    Time(sec)


    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


    • 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


    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


    • 3D animation software program structure

    Wave

    Generator

    Ship Motion

    Generator

    Ship

    Data

    3D Simulator


    • 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


    3D Animation video


    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


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