לוח שנה משולב

Our civilisation increasingly depends on shipping and ever expanding offshore activities. Rogue or freak waves are short wave groups of anomalously high and steep waves (compared to ordinary sea waves) which have propensity to come seemingly out of nowhere. Such waves represent real danger even to the largest ships and offshore structures.
There are two types of situations: "normal", where wind wave field is is characterized by broadbanded spectra and quasi-Gaussian statistics, and "abnorml", where the character of wave field differs qualitatively from normal". In this work only normal situations are considered. We will find the departure from Gaussianity from first principles.
The main idea is as follows. We consider evolution of random weakly nonlinear water waves in the space of transformed variables (the Zakharov variables) where quadratic nonlinearity is excluded by the transformation. Departure from Gaussianity is caused by two qualitatively different mechanisms. First, there is non-Gaussianity due to resonant interaction of normal modes in the Zakharov variables. These interactions are responsible for wave field evolution. Second, there is a contribution to non-Gaussianity due of observed wave statistics due to the nonlinearity of the transformation from the Zakharov's variables into original physical variables. That is Gaussian statistics in normal variables implies a non-Gaussian statistics in physical variables. We show that for the "normal" broadbanded wave fields the contribution from the transformation is dominant. This enables us to find wave statistics and its evolution.