Constantine Michailides

Effect of Flap Type Wave Energy Converters on the Response of a Semi-Submersible Wind Turbine in Operational Conditions

In the present paper the effect of flap type wave energy converters on the response of a floating semi-submersible wind turbine is investigated and reported. Two different layouts with regard to the number of rotating flaps that are utilized are considered and compared with the case of a pure floating semi-submersible wind turbine. Comparisons of response in terms of stability, motions and internal loads are made for selected environmental conditions. The combined operation of the rotating flaps results in an increase of the produced power without affecting significantly selected critical response quantities of the semi-submersible platform.Copyright

Modeling and Analysis of a 5 MW Semi-Submersible Wind Turbine Combined With Three Flap-Type Wave Energy Converters

Semi-submersible floating structures might be an attractive system to support wind turbines and wave energy converters (WECs) in areas with abundant wind and wave energy resources. The combination of wind turbines and WECs may increase the total power production and reduce the cost of the power.A concept of a semi-submersible with a 5 MW horizontal axis wind turbine combined with three flap-type WECs is presented in this paper. The concept is named as Semi-submersible Flap Combination (SFC). The WECs of the SFC are inspired by an optimized bottom-fixed rotating flap-type wave energy absorber. Each WEC of SFC includes an elliptical cylinder, two supporting arms, a rotational axis and a power take off (PTO) system.A time domain numerical modeling method for the SFC is presented. The numerical model is using the state-of-the-art code Simo/Riflex/Aerodyn. Linear rotational damping is introduced to model the effects of the PTO system. The choice of a PTO damping coefficient and of the mass of the elliptical cylinders has a significant effect on the power generated by the WECs. Such effects have been addressed and discussed in the paper through a sensitivity study.Copyright

V-shaped semisubmersible offshore wind turbine subjected to misaligned wave and wind

The dynamic behavior of the V-shaped semisubmersible offshore wind turbine subjected to misaligned wave and wind loads in operational conditions is presented in this paper. During the life time of an offshore wind turbine,wave and wind can be misaligned which may affect the dynamic response and as a result the functionality of the floating wind turbine. Especially for asymmetric floating structures such as the V-shaped semisubmersible, the misalignment of the wave and wind may result in unexpected behavior. In the present study, integrated aero-hydro-servo-elastic analysis for coupled mooring-floater-turbine is carried out in order to investigate possible effects under misaligned wave and wind conditions. For misaligned wave and wind conditions, the wave-induced as well as the wave-wind-induced motions, tension of mooring lines, and functionality of the turbine such as power production, rotational speed, and controller actions like blade-pitch-angle are studied and presented. The results show that the V-shaped semisubmersible offshore wind turbine is not affected in an undesirable way by the misaligned wave and wind loads in operational conditions and can be considered as enough robust in such environmental conditions. Also, the functionality and power production of the current concept is not affected by the misalignment of the wave and wind. The wave-induced responses of the V-shaped floating wind turbine are relatively small compared to wave-wind-induced responses. The dynamic responses of the V-shaped semisubmersible offshore wind turbine in coupled wave-wind-induced analyses are mainly dominated by the wind loads effects.

Comparison of Experimental Data of a Moored Multibody Wave Energy Device With a Hybrid CFD and BIEM Numerical Analysis Framework

In the present paper, a hybrid Computational Fluid Dynamics (CFD) and Boundary Integral Element Method (BIEM) framework is developed in order to study the response of a moored Multibody wave Energy Device (MED) to a panchromatic sea state. The relevant results are the surge and heave responses of the MED. The Numerical Analysis Framework (NAF) includes two different models; the first model uses Navier-Stokes equations to describe the flow field and is solved with an in-house CFD code to quantify the viscous damping effect, while the second model uses boundary-integral equation method and is solved with the tool WAMIT\SIMO\RIFLEX. By studying the free decay tests with the Navier-Stokes based model, the uncoupled linear and quadratic damping coefficients of the MED in surge and heave directions are calculated. These coefficients are given as input to the WAMIT\SIMO\RIFLEX model and the responses of the MED to different wave conditions are determined. These responses are compared with the experimental data and very good agreement is obtained. The MED responses calculated by the presented NAF have been obtained in connection with a hydrodynamic modeling competition and selected as one of the numerical models, which well predict the blind experimental data that were unknown to the authors.Copyright

A comparative study of different methods for predicting the long-term extreme structural responses of the combined wind and wave energy concept semisubmersible wind energy and flap-type wave energy converter

The combined wind and wave concept semisubmersible wind energy and flap-type wave energy converter was developed in the EU FP7 project MARINA Platform. It consists of a four-column semisubmersible with a 5-MW wind turbine placed on top of the central column and three flap-type wave energy converters on top of three pontoons that connect the four columns. Numerical and experimental studies have been performed to demonstrate the functionality and the survivability of the combined concept. In extreme conditions, both wind turbine and wave energy converters are set in a protection mode which reduces the dynamic loads and responses. In this article, different methods for predicting long-term (50-year) extreme responses considering the wind and wave conditions at two given European offshore sites are carried out, and structural response quantities are calculated, compared and presented. The full long-term analysis was performed and regarded as the reference method, and the corresponding results are compared with the modified environmental contour method and the environmental contour method. The response quantities studied here are the axial forces and bending moments of the semisubmersible wind energy and flap-type wave energy converter, including those of the wind turbine (blade, shaft and tower), arms of the flap-type wave energy converters and mooring lines, as well as the platform motion in 6 degrees of freedom. The extreme responses that are dominated by the aerodynamic loadings are effectively calculated either by the full long-term analysis or the modified environmental contour method. Compared to the full long-term analysis, the environmental contour method gives an under-prediction of the long-term extreme responses of quantities related to the wind turbine (e.g. internal loads of blades and tower). For the extreme responses that are dominated by the hydrodynamic loadings, all the three methods provide similar results.