Browsing by Author "Matha, Denis"

Now showing 1 - 6 of 6

Open Access
Integrated optimization of floating wind turbine systems
(2014) Sandner, Frank; Schlipf, David; Matha, Denis; Cheng, Po Wen
An exemplary methodology is shown for the integrated conceptioning of a floating wind turbine system with focus on the spar-type hull and the wind turbine blade-pitch-to-feather controller. It is a special interest to use a standard controller, which is easily implementable, even at early design stages. The optimization of the system is done with adapted static and dynamic models through a stepwise narrowing of the design space according to the requirements of floating wind turbines. After selecting three spar-type hull geometries with variable draft a simplified nonlinear simulation model with four degrees of freedom is set up and then linearized including the aerodynamics with the blade pitch controller in the closed-loop. The linear system allows conventional procedures for SISO controller design giving a theoretically suitable range of controller gains. Subsequently, the nonlinear model is used to find the optimal controller gains for each platform. Finally, a nonlinear coupled model with nine degrees of freedom gives the optimal solution under realistic wind and wave loads.
Open Access
Nonlinear model predictive control of floating wind turbines
(2013) Schlipf, David; Sandner, Frank; Raach, Steffen; Matha, Denis; Cheng, Po Wen
In this work a nonlinear model predictive control method for a floating wind turbine is presented. A reduced nonlinear model including disturbance preview of wind and waves is derived and implemented to compute optimal input trajectories for collective pitch and the generator torque. A cost functional is introduced which fulfills all desired constraints and controller goals for above rated wind conditions. The controller is tested for extreme and fatigue load cases and a significant reduction of the power and rotor speed deviations is obtained. Furthermore, ultimate tower loads and damage equivalent loads on shaft and blades are decreased. Although more detailed testing is necessary, this preliminary results show the advantages of nonlinear model predictive control for floating wind turbines.
Open Access
Nonlinear model predictive control of floating wind turbines with individual pitch control
(2014) Raach, Steffen; Schlipf, David; Sandner, Frank; Matha, Denis; Cheng, Po Wen
In this work a nonlinear model predictive controller with individual pitch control for a floating offshore wind turbine is presented. An aerodynamic model of the collective pitch control approach is extended by describing pitching and yawing moments based on rotor disk theory. This extension is implemented in a reduced nonlinear model of the floating wind turbine including disturbance preview of wind speed, linear vertical and horizontal wind shear, and wave height to compute optimal input trajectories for the individual pitch control inputs and the generator torque. An extended cost functional for individual pitch control is proposed based on the collective pitch control approach. The controller is evaluated in aero-servo-hydro-elastic simulations of a 5MW reference wind turbine disturbed by a three-dimensional stochastic turbulent wind field. Results show a significant blade fatigue load reduction compared to a baseline controller through minimizing yawing and pitching moments on the rotor hub while maintaining the advantages of the model predictive control approach with collective pitch control.
Open Access
Reduced nonlinear model of a spar-mounted floating wind turbine
(2012) Sandner, Frank; Schlipf, David; Matha, Denis; Seifried, Robert; Cheng, Po Wen
Floating offshore wind turbines (FOWTs) are complex dynamic systems requiring a thorough design for optimal operating performance and stability. Advanced control strategies, like model predictive control, are part of the integrated development of new concepts. This paper presents a simplified and computationally efficient model of the spar-mounted OC3-Hywind FOWT. Applications are, e.g., the real-time integration within the controller or an assessment during conceptual design, possibly within an optimization algorithm. Symbolic equations of motion of a multibody system are available as a set of ordinary differential equations. Aerodynamic forces are computed based on a rotor effective wind speed at hub height using data tables for thrust and torque coefficients. Hydrodynamic impacts on the floating body are modeled in a way that only the wave height serves as the disturbance signal. This estimation is based on potential flow theory and Morison’s formula for slender cylinders. The reduced model code is fully compiled and has a real-time factor of approximately 100. Various simulations of common load cases with a comparison to the certified FAST code have shown to be promising.
Open Access
Simulation of rotor-foundation-interaction on tidal current turbines with computational fluid dynamics
(2013) Arnold, Matthias; Biskup, Frank; Matha, Denis; Cheng, Po Wen
In this research the interaction of the rotor hydrodynamics with the foundation of a Tidal Energy Converter (TEC) are investigated. A detailed model of the turbine is built up and simulated with Computational Fluid Dynamics (CFD). The results of these simulations are used to compare the 4 load states of up- and downstream, below and above rated operation with respect to the rotor performance coefficients. The paper concludes with a comparison to results of simplified models and shows that the interaction can be simulated by an empirical approach.
Open Access
Validation of INNWIND.EU scaled model tests of a semisubmersible floating wind turbine
(2016) Koch, Christian; Lemmer, Frank; Borisade, Friedemann; Matha, Denis; Cheng, Po Wen
The subject of this study is the verification and the validation of existing numerical codes for floating offshore wind turbine structures using wave tank model tests as part of the INNWIND.EU project. A model of the OC4-DeepCwind semisubmersible platform, together with a Froude scaled rotor model with low-Reynolds airfoils is tested in a combined wind-and-wave basin. The simulation environment comprises the multibody software SIMPACK with the HydroDyn module for the hydrodynamic loads, MAP++ for the mooring line forces and AeroDyn for the aerodynamic loads. The focus of this paper is the validation of the hydrodynamics of a modified model hull shape, which compensates for the excess mass of the nacelle. Furthermore also first steady wind simulations without wave excitation have been carried out. The results show that the model is validated and gives the basis for further research based on the conducted experiments.