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Spectral Analysis and non-linear high wave groups in wind generated sea states

The present thesis deals with the analysis of records of the free-surface displacement measured in the northen North Sea and on the investigation of the mechanics of surface waves. The characteristics both of the random sea states and of the sea wave groups with very large sea waves have been deeply analyzed. Results are of interest to simulate the wave motion interacting with ocean structures and to correctly predict loads given by extreme waves for the design of these structures. Data coming from North Alwyn platform located in North Sea has been analyzed. The first part of the thesis has been involved on the analysis of 282 sea states, which have been classified in three groups with respect to the shape of the spectrum. Then the attention has been focused on the 25 narrower unimodal spectra and on the statistical properties of these records; by applying the Quasi-Determinism theory, the deterministic profiles are obtained up to the second order, and a comparison has been carried out between those obtained from theoretical spectra and those obtained starting from data. Finally, the accuracy of the theory with respect to the spectral characteristics is verified by mean of a comparison between the mean wave profile of the first 10 higher waves recorded at the platform and the non-linear deterministic wave profile obtained from the QD theory.

Mostra/Nascondi contenuto.
4 Introduction Engineering works are varied and complex. Particularly, maritime and ocean structures can be of different types: breakwaters for ports and harbors, seawalls for shore protection, platform for exploitation of oil beneath the seabed are some examples. Earthquakes, currents, effects of wind, waves are just some of the actions generated in the natural environmental subjected to the listed structures must perform their functions. In order to ensure their designated performance, deep investigation must be carried out, to be able to correctly understand the environmental conditions. Moving in the specific, waves are the most important phenomenon to be considered among the environmental conditions affecting maritime structures; since they exercise the greatest influence the presence of waves makes the design procedure for maritime structures quite different from that of structures on land. In this view, description and assessment of wind generated ocean waves provide vital information for the design and operation of marine systems such as ships and ocean and coastal structures. However, it must be said that waves are one of the most complex and changeable phenomena in nature and it is not easy to achieve a full understanding of their fundamental character and behavior. Wind-generated seas continuously vary over a wide range of severity depending on geographical location, season, presence of tropical cyclones etc. Furthermore, the wave profile in a given sea state is extremely irregular in time and space and thus any sense of apparent regularity is totally absent. Having said this, the random wave behavior of sea waves can be interpreted by mean of stochastic prediction approach that allows to estimate the response of marine systems with reasonable accuracy. Such probabilistic approach has become an integrated part of modern design technology in naval, ocean and coastal engineering. In this view, the main objective of this work is to investigate the random behavior of the wave motion by means of stochastic approach in order to interpret the nature

Tesi di Laurea Magistrale

Facoltà: Ingegneria

Autore: Federica Maria Strati Contatta »

Composta da 178 pagine.

 

Questa tesi ha raggiunto 30 click dal 13/11/2013.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.