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The second formulation of Boccotti’s quasi-determinism theory is investigated. Deep water wave records collected in the Baltic Sea with AWAC (Nortek Acoustic Wave and Current profiler) are used in this study. The adequacy of Boccotti’s theory for Baltic Sea conditions is evaluated on the basis of some simulations of wave groups with a very large maximum wave height. The large waves are chosen using an abnormality index (ratio of maximum wave height to significant wave height) with a value greater than 2. Such values of this index are also used by different authors for the definition of freak waves. In order to obtain better results, JONSWAP formula is fitted to the measured spectra instead of using default JONSWAP parameters for the simulations. Verification of values of spectral parameters obtained from the autocovariance function against the same parameters calculated from smoothed and not smoothed spectra is presented. Much attention is given to spectral peak period value. The spectral width parameter, in QD theory known as narrow bandedness parameter, requires further investigation as the results obtained here did not allow the formulating of any functional relation with another – more often used – spectral width parameter. The low frequency of sampling of the data allowed only the most important aspects of the theory to be checked. A short Matlab function used in QD simulations is presented.
Content available remote Ale fenomenalne w żegludze morskiej
W pracy opisano proces planowania nawigacji w obszarach występowania fal fenomenalnych. Zdefiniowano fale fenomenalne, rejony i przyczyny ich powstawania. Przedstawiono kilka programów badawczych ukierunkowanych na propagację, występowanie i prognozowanie fal fenomenalnych. W zakończeniu wspomniano o konieczności wzmocnienia nowo budowanych kadłubów statków morskich z uwzględnieniem istnienia fal fenomenalnych.
In this paper the passage process have been described in the areas where freak waves occur. The freak wave’s definition has been given and the evidence distributes and generation of the freak waves in different sea areas has shown. Some research programs focused on freak waves propagation occurrence and forecast have been presented. Finally some notes on the new ship design to increase the ship structure in the light of freak wave existence in shipping have been mentioned.
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