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Some Considerations About The Bound Long Waves Evaluation


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R Gentile, L Rebaudengo Landò & G Scarsi


Some considerations about the bound long waves evaluation R. Gentile, L Rebaudengo Lando & G. Scarsi Department of Environmental Engineering, Genoa University, Italy. Abstract Two non linear propagation models (indicated by the notations [R] and [A]) are adopted to evaluate the height and period of the significant bound long waves which contribute to the low frequency range of the non linear spectra. The comparison made with some results obtained by using a numerical simulation indicates that the saturation process, which is considered in the [A]model, gives rise to more realistic values, in agreement with experimental results of other authors. 1 Introduction The non linear wave propagation spectral models usually adopted to describe the evolution of sea states in decreasing depths give rise to local wave spectra which exhibit, in the low frequency range, a part related to the bound long waves and, in the high frequency range around twice the main peak frequency, a part related to the bound short waves. The first part is of considerable interest as regards the behaviour of the port water areas, as long waves excite oscillations of the free surface which may become particularly troublesome with respect to the suitability for use of quays, when the amplitudes of the previously-mentioned waves exceed an operating threshold. The present paper shows how the choice of propagation model may greatly influence the results obtained with reference to the characteristics of the bound long waves, analysed here in terms of significant waves. The paper illustrates the following steps. A non linear wave propagation spectral model which takes into account the refraction process, which automatically involves the shoaling process, is introduced, that model being formalised by adjusting a procedure suggested by Hassel-