Overview
Improving the design of ship structures that are exposed to rough climate. This will help the European shipping industry to adapt to climate change.
The strategic objective of EXTREME SEAS is to enable European shipping industry to improve the design of ship structures that are exposed to rough climate, by providing technology and methodology that need to be a part of design for ship safety in extreme seas.
The project will relate and adapt to safety regulations including Classification Societies Rules. The design procedures provided will be formulated in terms of recipes supporting harmonised standards that give presumption of conformity to the safety requirements. The project results will help shipping industry to adapt to climate change. The project addresses assessment of extreme sea states, and ship behaviour in such sea states.
The project will study physical and statistical properties of extreme waves, and develop advanced numerical and physical simulation models for wave-structure interaction. A further objective is to develop warning criteria for marine structures against extreme sea states and extraordinarily large waves, and to implement them in a marine weather forecasting system operated by a meteorological office belonging to the Consortium. The developed warning criteria will be available for decision support systems for marine structures. The developed methodology and tools will be generally applicable to different ship types.
The case studies considered in EXTREME SEAS will be devoted to container vessels, to passenger ships, to LNG carriers and to product and chemical tankers. Critical responses will be investigated including green water impact on superstructures of the passenger ships. Weaknesses of the current design procedures for ship structures will be highlighted.
Funding
Results
Extreme wind and wave conditions that pose the greatest structural risk to ships. The project provides an overview on the problem of rogue wave (freak wave) formation in the ocean. A rogue wave is a sporadic occurrence of unexpectedly high waves on the sea surface, causing serious danger to ships and people. These waves are a specific kind of sea wave, not taken into account by conventional models for sea wind waves.
Combined experimental and numerical study of spatial evolution of unidirectional random water-waves has been performed. Numerous realisations of wave fields were generated by a wavemaker in long wave tank. The Cubic Schrödinger Equation ('CSE') and the Modified Nonlinear Schrödinger ('MNLS') set of equations have been used as the theoretical models. Detailed analysis of the wave field evolution along the wave tank was performed. Statistical wave parameters were calculated based on the whole ensemble of realisations. Comparison of the spatial variation of the computed statistical characteristics of the random wave field with laboratory measurements, indicated that they compare reasonably well with results derived from the MNLS model simulations. Results show that the probability of extremely large waves (the so-called rogue or freak waves) is highest when the local spectral width attains its maximum.
The project also considered the problem of rogue wave generation in the presence of wind forcing or dissipation. Wind/dissipation has an impact on the modulational instability. By applying a suitable transformation, the project has mapped the forced/damped Nonlinear Schrödinger (NLS) equation into the standard NLS with constant coefficients. Approximate rogue wave solutions of the equation have been presented and discussed.
Innovation aspects
The results deepen insight in the effects of wind and dissipation on the formation of rogue waves.
Strategy targets
Innovating for the future (technology and behaviour): A European Transport Research and Innovation Policy