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Nonlinear dynamics of ship capsize in extreme seas


Research objectives and content
Ship stability and capsize are examined from a dynamical systems perspective. The objectives are, (1) to develop a designmethodology for maximising resistance to capsize due to beam-sea resonance with full account of system nonlinearity; (2) to enhance understanding of astern-sea capsize at fundamental level. In respect to (1), the potential of two different capsizepredictors will be investigated based on (la) transient motions and the sudden erosion of the safe basin following the heteroclinic tangency of manifolds, predicted through Melnikov's theory, and, (lb) steady-state capsize due to a heteroclinic chain. The critical wave slope for either type of capsize will be derived, parameterized in respect to the system's restoring and damping coefficients. A multi-variable optimisation problem with equality and inequality constraints will be solved to find the combination of system parameter values that maximise survivability for the considered criteria. In respect to (2), the effect of yaw motion for the so-called broaching instability and the onset of capsize in astern seas will be investigated. In particular, we shall examine to what extent a simple, pendulum-like system, forced directly and/or parametrically, can reproduce the main features of broaching. Comparisons will be made with our predictions based on a multi-degree numerical model of surge, sway, yaw and roll motions and with earlier physical-model experimental results.
Training content (objective, benefit and expected impact)
Training objective: To acquire new skills in advanced optimisation methodologies so that to be able to integrate the analysis of nonlinearsystems with ship design. Also, to impart knowledge of
nonlinear dynamics acquired during the current fellowship at UCL,UK, to the members of the Host Research Group SDL-NTUA, Greece. Benefit: Development of expertise and specialisation in an important field of maritime transportation.
Impact: In addition to the furthering of knowledge of ship capsize, we shall be able to play a special role in pro- moting collaborations between the fields of nonlinear dynamics and design.
Links with industry / industrial relevance (22)
The Host Laboratory (SDL-NTUA) is task coordinator in the SAFER/EURORO project, a thematic network of major industrial and academic partners focusing on the improvement of safety of ferries, supported by The European Commission (DG XII). This provides great potential for effective dissemination of the results of this study to the industry and quick transfer into practical application. Also, SDL-NTUA maintains active links with a number of Greek Shipping and Consultancy companies and has been involved in the design of several prototype vessels especially for the high-speed market sector.


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