|dc.description.abstract||Wind turbines are mainly classified into horizontal axis wind turbines (HAWTs) and
vertical axis wind turbines (VAWTs) based on different orientation of their axis of
rotation. Ever-increasing demand for energy boosts the application of the wind
turbines in the deep water. The applications of HAWTs in deep water using different
floating support structures have led to an increasing and versatile research due to their
commercial success. However, the application of the VAWTs in the offshore wind
industry also has some potential due to its economical installation and maintenance.
More and more efforts have been invested in developing floating vertical axis wind
turbines (FVAWTs), but the research on the FVAWTs is still at an early stage.
Although different concepts of the FVAWTs were proposed based on a combination of
a rotor and a floater, an optimized design is still an open question. The rotor covers
straight-blade rotor, Darrieus curved-blade type rotor and helical-blade rotor while a
floater could be a spar, semi-submersible or tension leg platform (TLP). To evaluate a
FVAWT, a simulation tool is needed to perform time domain numerical simulations.
The simulation tool should have the capability to calculate aerodynamic loads on the
rotor, hydrodynamic loads on the floater and structural dynamics of the rotor, and
include a controller. Based on the calculated dynamic response, a response analysis is
carried out to better understand the response characteristics of a FVAWT as a basis for
design and safety criteria according to serviceability. The objective of this thesis has
been the development of a coupled method for integrated dynamic analysis of the
FVAWTs and application in a systematic study of a Darrieus rotor on a
semi-submersible floating support structure.
The aerodynamic analysis of a VAWT differs from that of a HAWT, especially when
the VAWT is mounted on a floater. Thus, the aerodynamics of a VAWT is first
addressed and a model improvement for evaluating the effect of tower tilting on the
aerodynamics of a VAWT is performed. This improved model is validated against
experimental data collected for an H-Darrieus wind turbine in skewed flow conditions.
Based on the assumption that the velocity component parallel to the rotor shaft is
small in the downstream part of the rotor, the effect of tower tilting is quantified with
respect to power, rotor torque, thrust force and the normal force and tangential force
coefficients on the blades.
Secondly, a novel 5 MW FVAWT concept, based on a Darrieus rotor on a
semi-submersible support structure, is proposed. An aero-hydro-servo-elastic tool
Simo-Riflex-DMS is developed for modeling the dynamics of the FVAWT and
validated. This integrated dynamic model takes into account the wind inflow,
aerodynamics, hydrodynamics, structural dynamics (wind turbine, floating platform
and the mooring lines) and a generator controller. Thirdly, the response characteristics of the 5 MW FVAWT are studied based on
statistical analysis and spectral analysis of the response. The response characteristics
of the FVAWT under steady wind condition and those under turbulent wind condition
are compared to investigate the effect of the turbulent wind. The advantage in
reducing the 2P effect on the FVAWT is identified by comparing with the equivalent
land-based wind turbine. Furthermore, by comparing the FVAWT with a rigid
FVAWT, the aspect of rigid versus flexible rotor is quantified, and thus the effect of
the modeling method of the rotor on the responses is observed. Besides the normal
operating condition, the global motions and structural responses of the FVAWT as a
function of azimuthal angle are studied for the parked condition. To identify the effect
of wind-wave misalignment on the platform motion, structural response and mooring
lines, the dynamic response analysis of the FVAWT in selected misaligned wind and
wave conditions are conducted.
Moreover, it is also of great interest to compare the performance of a FVAWT with a
FHAWT. A comparative study of the studied FVAWT and a FHAWT with the 5 MW
NREL reference wind turbine mounted on the same semi-submersible is carried out. A
set of time domain simulations with different conditions, i.e., the decay tests, wave
only conditions, wind only conditions and the combined wind and wave conditions,
are conducted. The dynamic responses of the FVAWT and the FHAWT, such as the
global motions of the floater in six DOFs, the bending moment of the bottom of the
tower and the tension at the fairleads of the mooring lines, are compared based on
statistical results and power spectra.
Lastly, a novel hydrodynamic brake installed in the FVAWT is proposed in this thesis.
The FVAWTs with fixed-pitch blades experience large aerodynamic loads in high
wind speed condition or in stormy weather. The blades may be deformed or broken,
and the tower can collapse in more severe cases. Thus, initiating an emergency
shutdown is one of the most important concerns for the FVAWTs. Therefore, a
dynamic response analysis of the FVAWT with this installed hydrodynamic brake is
studied for possible use in connection with emergency shutdown event. The effects of
the hydrodynamic brake on the platform motions and structural loads under normal
operating conditions and during the emergency shutdown events are evaluated. The
use of both the hydrodynamic brake and mechanical brake is also investigated.||nb_NO
|dc.relation.ispartofseries||Doctoral thesis at NTNU;2015:89||
Wang, Kai; Moan, Torgeir; Hansen, Martin Otto Laver.
A Method for Modeling of Floating Vertical Axis Wind Turbine. I: 32nd International Conference on Ocean, Offshore and Arctic Engineering Volume 8: Ocean Renewable Energy. ASME Press - Is not included due to copyright available at
<a href="http://dx.doi.org/10.1115/OMAE2013-10289" target="_blank"> http://dx.doi.org/10.1115/OMAE2013-10289</a>||
Wang, Kai; Hansen, Martin Otto Laver; Moan, Torgeir.
Model improvements for evaluating the effect of tower tilting on the aerodynamics of a vertical axis wind turbine. Wind Energy 2015 ;Volum 18.(1) s. 91-110 <a href="http://dx.doi.org/10.1002/we.1685" target="_blank"> http://dx.doi.org/10.1002/we.1685</a>
Copyright © 2013 John Wiley & Sons, Ltd.||
Wang, Kai; Hansen, Martin Otto Laver; Moan, Torgeir.
Dynamic analysis of a floating vertical axis wind turbine under emergency shutdown using hydrodynamic brake. Energy Procedia 2014 ;Volum 53. s. 56-69
<a href="http://dx.doi.org/10.1016/j.egypro.2014.07.215" target="_blank"> http://dx.doi.org/10.1016/j.egypro.2014.07.215</a>
© 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license||
Wang, Kai; Luan, Chenyu; Moan, Torgeir; Hansen, Martin Otto Laver.
Comparative study of a FVAWT and a FHAWT with a semi-submersible floater. I: Proceedings of the Twenty-fourth (2014) International Offshore and Polar Engineering Conference, Busan, Korea. : International Society of Offshore and Polar Engineers (ISOPE) 2014. s. 302-310
Copyright © 2014 by the International Society of Offshore and Polar Engineers (ISOPE)||
Kai Wang, Torgeir Moan and Martin O.L. Hansen.
Stochastic dynamic response analysis of a floating vertical
axis wind turbine with a semi-submersible floater||
|dc.title||Modelling and dynamic analysis of a semi-submersible floating vertical axis wind turbine||nb_NO
|dc.subject.nsi||VDP::Technology: 500::Marine technology: 580||nb_NO