A multi-purpose platform (MPP) is an offshore system designed to serve the purposes of more than one offshore industry. Indeed, over the past decades, a number of industries have expanded, or are expanding, from onshore to offshore locations (renewables, aquaculture, tourism, mineral extractions, etc.), and the research on these type of platform is increasing. In the present work, a MPP able to accommodate wind turbines, wave energy converters, and aquaculture systems are considered. This work presents the first part (Part A) of the analyses of the dynamics of the floating support structure for this MPP, focusing on the rigid body dynamic response, while its complementary hydroelastic analysis is presented in Part B (OMAE2019-96282). The aim here is to assess the dynamic response of the platform with respect to the preliminary requirements imposed by the wind turbine, the aquaculture system, and the other ancillary systems. After describing the platform analyzed, and explaining the aero-hydro coupled model of dynamics approach adopted, two independent analyses are conducted, one using the SESAM package by DNV-GL, and another using ANSYS AQWA, in order to verify the results, in absence of experimental data. Considering a severe, but still operational, load case, the preliminary results seem to demonstrate that the chosen platform can satisfy the dynamics constraints imposed by the payload systems.

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Experimental investigation of floating structures represents the most direct way for achieving their dynamic identification and it is particularly valuable for relatively new concepts, such as floating supports for offshore wind turbines, in order to fully understand their dynamic behaviour. Traditional experimental campaigns on floating structures are carried out at small scale, in indoor laboratories, equipped with wave and wind generation facilities. This article presents the results of a 1:30 open-sea experimental activity on a scale model of the OC3-Hywind spar, in parked rotor conditions, carried out at the Natural Ocean Engineering Laboratory (NOEL) of Reggio Calabria (Italy). The aim of the experiment is twofold. Firstly, it aims to assess the feasibility of low-cost, intermediate-scale, open-sea activities on offshore structures, which are proposed to substitute or complement the traditional indoor activities in ocean basins. Secondly, it provides useful experimental data on damping properties of spar support structures for offshore wind turbines, with respect to heave, roll and pitch degrees of freedom. It has been proven that the proposed approach may overcome some limitations of traditional small-scale activities, namely high costs and small scale, and allows to enhance the fidelity of the experimental data currently available in literature for spar floating supports for offshore wind turbines. Keywords 1. Offshore structures 2. Spar 3. Floating wind turbines 4. Physical model 5. Heave damping 6. Roll damping development of reliable dynamic models, able to represent the coupled behaviour of the floating wind turbines [2-3]. While such models are usually implemented by means of numerical codes [4-5], experimental activities play a crucial role for their validation, as well as for the system identification. The experimental activities on floating offshore wind turbines may be classified in two groups, namely small-scale and large-scale ones. Traditional small-scale activities (1:50-1:100) are carried out in controlled environment such as wave tanks and ocean basins, where the desired wind-wave conditions can be reproduced, to measure the dynamic response of the structure and to calibrate opportunely the numerical codes [6-8]. Although the controlled environment allows to achieve very precise and reliable results, these activities have some relevant disadvantages, namely high rental fees of the basins, limited duration of the experiments, and limitations in representing all the relevant physical phenomena at scale level, which may alter significantly the dynamic behaviour of the model with respect to the full-scale structure. On the opposite side, large-scale activities (1:1-1:10) are carried out in open-sea and allow to represent all the relevant features of the offshore wind turbines, including turbine-support interaction, mooring system and grid connection, in relevant operational conditions [9-11]. Clearly, such projects are very expensive and usually represent pilot activities, which are carried out...

This document describes design and realization of a small-scale field experiment on a 1:30 model of spar floating support structure for offshore wind turbines. The aim of the experiment is to investigate the dynamic behaviour of the floating wind turbine under extreme wave and parked rotor conditions. The experiment has been going on in the Natural Ocean Engineering Laboratory of Reggio Calabria (Italy). In this article, all the stages of the experimental activity are presented, and some results are shown in terms of motions and response amplitude operators. Finally, a comparison with corresponding results obtained using ANSYS AQWA software package is shown, and conclusions are drawn. The presented experimental setup seems promising to test offshore floating structures for marine renewable energy at a relatively large scale in the Natural Ocean Engineering Laboratory field site.