A new equivalent exponential storm model for long-term statistics of ocean waves

Abstract

The paper proposes a new solution, in the context of equivalent storm models, for long-term statistics of ocean storms. These models are essentially based on the concept of equivalent sea which consists of substituting the actual storms at a given location with a sequence of equivalent storms, achieved from a statistical perspective.Firstly the Equivalent Triangular Storm (ETS) was proposed in which triangular storms were considered. The model was then generalized assuming a power law for a more realistic description of the storm history in time domain. The two models were developed following the same logic and assuming the equivalent storm symmetric with respect to its peak. In both cases the solution for the calculation of return period of a sea storm whose maximum significant wave height is greater than a given threshold is achieved, but only for ETSs it has a closed form and for all the others shapes it requires a numerical calculation.The main focus of the present work is to combine in a unique model the main advantages of the two previous ones, that is to obtain an optimized shape (as for EPS) and closed from solutions for the long-term statistics (as for ETS). An exponential law is introduced, taking into account asymmetry in storm profile. The long-term statistics of ocean storms is then investigated via this new Equivalent Exponential Storm (EES) model, by analyzing the effects of asymmetry between the growth and decay phases of each storm. Data from National Data buoy Center (NDBC) are processed for the new EES model validation and comparison with previous ETS and EPS. The results show that the assumption of asymmetric storm profile does not lead to significant changes of the long-term statistics, but could be very useful in other kinds of application as it enables a more realistic representation of storm history. Finally, in comparison with ETS and EPS, it has been seen that EES provides a better representation of actual storm duration.