Abstract

This paper deals with a sensitivity study of wave and wind induced responses of the combined energy concept SFC in operational and survival conditions. The sensitivity study is conducted based on experimental data. The measured responses that are studied include motions of the semisubmersible, rotation of the flap-type WECs, tension of mooring lines, internal loads of the arms of the WECs, bending moment at the base of the wind turbine tower and produced power by WECs. The effect of both the change of the mean heeling angle of the SFC and the aerodynamic damping is studied. The effect of the wind loading in structural responses of different parts of WECs of SFC is small.

Introduction

The technology in offshore renewable energy sector which can be considered mature enough is the Offshore Wind Turbines (OWTs) technology. The Levelised Cost Of Energy (LCOE) of OWTs in 2013 is in the range of 130–330 USD/MWh (World Energy Council, 2013). The cost of OWTs is the main handicap for their further utilization. In order to reduce the cost of generated power, the development of large rated wind turbines in deep seas is considered as an efficient potential direction. For deep seas the use of Floating type OWTs (FOWTs) is considered as the most cost-efficient. Different floating support platform configurations are possible for use with FOWTs (Jonkman and Matha, 2011). A major type of support configuration is the semisubmersible platform consisting of columns that are connected with the use of braces (Robertson et al., 2014; Roddier et. al, 2010). Alternatively, the columns of the semisubmersible platform can be connected by pontoons with large dimensions without braces (Olav Olsen, 2015; Luan et al., 2015; Karimirad and Michailides, 2015).

Ocean waves are an extremely abundant and promising resource of alternative and clean energy. Many different types of Wave Energy Converters (WECs) have been proposed. The first patent of a WEC has been registered in 1799 in France by a father and a son named Girard (Michailides, 2015). Unfortunately the technology of WECs cannot be considered mature yet for large-scale commercial deployment. The LCOE of WECs in the 2013 is in the range of 280–1000 USD/MWh (World Energy Council, 2013).

It might be beneficial to combine offshore renewable energy systems of different technology into one floating platform. Possible advantages as a result of the use of offshore combined concepts are:

  • increase of the energy production per unit area of space,

  • decrease of the cost related with the support platform,

  • decrease of the cost related with the required electric grid infrastructure and (d) decrease of the cost related with operation (e.g. installation) and maintenance (e.g. inspection). Recently, EU research projects have been introduced to accelerate the development of offshore combined energy systems. These projects are the MARINA Platform (2015), ORECCA (2015), TROPOS (2015), H2Ocean (2015) and MERMAID (2015).

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