Dynamic analysis of a jacket structure for a wind turbine under extreme loads

The final scope of the present study is to obtain at first instance a Jacket substructure system and subsequently perform dynamic analysis with a dedicated software. The first part will be covered from chapter II to chapter IV. From an evaluation of the environmental actions present at the chosen site, we will begin to dimension a Jacket structure and try to obtain semi final dimensions by the results obtained from a static analysis. Midas software has been chosen since is capable to evaluate the loading effects of waves and currents on structures. The wind load acting at the tip of the wind tower will be evaluated separately. Another crucial step in this first phase is the geotechnical dimensioning of the piles foundations obtained by mean of the well-known API method. The piles properties were then converted in a set of multiple point springs. To check this procedure, we went through a validations stage where we calibrate the features of the Soil Structure Interaction, SSI from now on. Checks were performed on a simpler model in order to verify the accuracy of the SSI in Midas with a dedicated geotechnical software, considered as reference. Once dimensions are chosen, we performed the modal Response Spectrum Analysis, in order to perform a check of the loading frequencies against the set of frequencies of our Multi Degree Of Freedom System. Once this first stage is concluded, we have the dimensions of the jacket structure for the second phase. Next we introduce ELS. The ELS model is more like the final Jacket structure, in particular for what concerns the connections between the tubular elements at the joints. Even in ELS model we had to apply the pile foundations. Last, as we did with the Midas model, we performed a validation and check of the spring model applied in ELS. By means of MATLAB analysis we were able to obtain time-varying load in time. Once time histories loads are applied, ELS analysis will be run, and the results will be commented.