In this paper, a new method to obtain a geometrically nonlinear structural dynamics model based on the full linear finite element model of slender structures is presented. For this purpose, a finite element model is divided into multiple segments along its span. For each segment, a modal analysis is carried out. Boundary grid points are defined on each segment and loaded by fictitious masses. The modal analysis produces a set of elastic modes and six rigid-body modes that have significant deformations near the boundary. These deformations facilitate high-accuracy integration of the segments into a coupled model, in which the fictitious masses are removed. The elastic modes are used as master modes that describe the deformation, whereas the rigid-body modes are used as slave modes to establish displacement compatibility between the segments. The modal analysis is carried out with the local segment attached to its own reference frame, yielding a local linear solution that is part of a global nonlinear analysis. Large rotations and displacements are provided by the rigid-body modes in a corotational framework.

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A novel configuration of an energy harvester for local actuation and sensing devices using limit cycle oscillations has been modeled, designed and tested. A wing section has been designed with two trailing-edge free-floating flaps. A free-floating flap is a flap that can freely rotate around a hinge axis and is driven by trailing edge tabs. In the rotational axis of each flap a generator is mounted that converts the vibrational energy into electricity. It has been demonstrated numerically how a simple electronic system can be used to keep such a system at stable limit cycle oscillations by varying the resistance in the electric circuit. Additionally, it was shown that the stability of the system is coupled to the charge level of the battery, with increasing charge level leading to a less stable system. The system has been manufactured and tested in the Open Jet Wind Tunnel Facility of the Technical University Delft. The numerical results could be validated successfully and voltage generation could be demonstrated at cost of a decrease in lift of 2%.@en

In this paper the reductions of fatigue and extreme loads of wind turbine components are analysed. An individual flap controller was designed to reduce cyclic loads. The load reduction potential was computed for power production and start-up load cases with normal and extreme turbulence, extreme gust events, and direction changes according to the certification specifications. Additional to the highly investigated reduction of the blade root fatigue damage equivalent load, also significant reductions could be shown for both shaft and tower loads. When applying smart rotors, most components experience a fatigue load reduction of 5–15%, with the exception of the flapwise blade root moment, which is decreased by 23.8% and the blade root torsional moment which increases 14%. For the simulated ultimate loads, the flapwise root bending moment is reduced by 8%, while tip deflections get reduced by 6%. The most significant extreme load reduction can be found for loads in the tower that relate to asymmetry of the inflow, namely tower torsion and the fore-aft moment at the tower top. The blade root torsional moment is increased significantly. The changes in the ultimate load of all other components remain below 2%@en

Trailing edge aps located outboard on wind turbine blades have recently shown considerable potential in the alleviation of turbine lifetime dynamic loads. The concept of the free-oating ap is speci_cally interesting for wind turbines, on account of its modularity and enhanced control authority. Such a ap is free to rotate about its axis; camberline control of the free-oating ap allows for aeroelastic control of blade loads. This paper describes the design of a scaled wind turbine blade instrumented with free-oating aps, intended for use in wind tunnel experiments. The nature of the ap introduces a coupled form of utter due to the aeroelastic coupling of ap rigid-body and blade out-of-plane modes; for maximal control authority it is desired to operate close to the utter limit. Analytical and numerical methods are used to perform a utter analysis of the turbine blade. It is shown that the potential ow aeroelastic model can be recast as a continuous-time Linear-Parameter-Varying (LPV) state space model of a low order, for which formal controller design methodologies are readily available. @en

Wind turbine load alleviation has traditionally been addressed in the literature using either full-span pitch control, which has limited bandwidth, or trailing-edge flap control, which typically shows low control authority due to actuation constraints. This paper combines both methods and demonstrates the feasibility and advantages of such a combined control strategy on a scaled prototype in a series of wind tunnel tests. The pitchable blades of the test turbine are instrumented with free-floating flaps close to the tip, designed such that they aerodynamically magnify the low stroke of high-bandwidth actuators. The additional degree of freedom leads to aeroelastic coupling with the blade flexible modes. The inertia of the flaps was tuned such that instability occurs just beyond the operational envelope of the wind turbine; the system can however be stabilised using collocated closed-loop control. A feedforward controller is shown to be capable of significant reduction of the deterministic loads of the turbine. Iterative feedforward tuning, in combination with a stabilising feedback controller, is used to optimise the controller online in an automated manner, to maximise load reduction. Since the system is non-linear, the controller gains vary with wind speed; this paper also shows that iterative feedforward tuning is capable of generating the optimal gain schedule online.@en

This paper presents an experimental aeroservoelastic investigation of a novel load al-leviation concept using trailing edge aps. These aps are autonomous units, which are self-powered and self-actuated, using trailing edge tabs, thereby demonstrating advantages in comparison with conventional ap systems in terms of wiring and structural integration. The aps are free-oating and mass underbalanced, such that they may utter at operation velocities unless suppressed by their own control system. This makes the system very re-sponsive for turbulence and control action. In the wind tunnel campaign presented in this paper, the limit cycle behavior of autonomous, free-oating aps was investigated. It has been shown that limit cycle oscillation can be reached either through structural limiters or by control actions of the trailing edge tabs. In the latter case, the amplitude of the limit cycle oscillation is adjustable to the required energy output. An energy balance of har-vested power and power consumption for actuators and sensing system was made showing that the vibration energy of limit cycle oscillations can be used to keep the amplitude of the limit cycle constant, while the electric batteries that power the load alleviation system are being charged.@en

In this paper a new method to obtain a geometrically non-linear wind turbine structural model based on the full linear finite element model is presented. For this purpose, the wind turbine model is divided into multiple segments, i.e. tower, drive train and blades. For each segment a modal analysis is carried out. Boundary grid points are defined on each segment and loaded by ficticious masses. The modal analysis produces a set of 6 rigid-body modes and elastic modes close to fixed-fixed analysis. For the aeroelastic turbine simulation, the ficticious masses are removed. The elastic modes are used as master modes that describe the deformation, while the rigid-body modes are used as slaves to establish compatibility between the segments. A modal analysis is carried out in the local segment attached reference frame, yielding a local linear solution that is part of a global non-linear analysis. Large rotations and displacements are provided by rigid-body modes in a co-rotational framework.

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