Evaluation of the dynamic behaviour of a typical wind energy recuperation offshore system for the Black Sea costal area (I)

Abstract

Based on some previous results related to the dynamics of various offshore structures, the present paper is focused on the evaluation of the dynamics of a typical offshore system, known as WindFloat Concept, taking into consideration the specific conditions on a location in the Black Sea. The capability to be used for wind energy recuperation is investigated using the seakeeping performances in terms of response amplitude operators (RAO’s) of motions, exciting forces and accelerations. To this purpose, two different 3D computer codes have been used. The intention wasn’t to evaluate comparatively the merits of the two applications, but to check the eventual differences which could appear and which are the parameters which could significantly influence the results. As a preliminary investigation, different theoretical approaches are available taking into account structure’s shape, water depth, appropriate wave theory on the location, etc. As a matter of fact, the complexity of such evaluations leads to very deep investigations related to the influence of different factors to be taken into account during the design stages, starting with preliminary ones when the main parameters have to be considered. From this point of view, some influences, like damping coefficient values, number of panels used for discretization, etc., are evaluated and important observations are made in order to be able to take the necessary precautions for practical applications. When floating structures are considered, a preliminary analysis of behaviour of the station keeping system (mooring, dynamic positioning, etc.) is mandatory to be carried out considering the “stiffness” of the system. Mention should be made that in the present paper only free floating condition is investigated. The results are finally compared with the source of excitation forces, using the Black Sea Spectrum for a range of wind speeds. The importance of these preliminary evaluations is to have a first consistent evaluation of the utilization of the concept, adapted to the specific of the location and to provide reliable input data for further analysis.