Bing Feng Ng

Model-based Aeroservoelastic Design and Load Alleviation of Large Wind Turbines

This paper presents an aeroservoelastic modeling approach for dynamic load alleviation in large wind turbines with trailing-edge aerodynamic surfaces. The tower, potentially on a moving base, and the rotating blades are modeled using geometrically non-linear composite beams, which are linearized around reference conditions with arbitrarily-large structural displacements. Time-domain aerodynamics are given by a linearized 3-D unsteady vortexlattice method and the resulting dynamic aeroelastic model is written in a state-space formulation suitable for model reductions and control synthesis. A linear model of a single blade is used to design a Linear-Quadratic-Gaussian regulator on its root-bending moments, which is finally shown to provide load reductions of about 20% in closed-loop on the full wind turbine non-linear aeroelastic model.

Optimal control for load alleviation in wind turbines

Nowadays, trailing edge flaps on wind turbine blades are considered to reduce loading stresses in wind turbine components. In this paper, an optimal control synthesis methodology for the design of gust load controllers for large wind turbine blades is proposed. We discuss a control synthesis approach that minimises the power expenditure of the actuated trailing edge flap, while at the same time guaranteeing that certain blade load measures remain bounded in a probabilistic sense. To illustrate our proposed control design methodology, a standard NREL 5-MW reference turbine was considered. The obtained numerical results indicate that through the use of optimal feedback considerable reductions in loading stresses could be achieved for moderate actuation power.

Efficient aeroservoelastic modeling and control using trailing-edge flaps of wind turbines

This paper presents a computationally efficient aeroservoelastic modeling approach for dynamic load alleviation in large wind turbines with trailing-edge aerodynamic control surfaces. The aeroelastic model is expressed directly in a state-space formulation and trailing-edge flaps are modeled directly in the unsteady aerodynamics. The linear model of a single rotating blade is used to design a Linear-Quadratic-Gaussian regulator for minimizing the root-bending moments, which is shown to provide load reductions of about 20% in closed-loop on the full wind turbine non-linear aeroelastic model.

Model-based aeroelastic analysis and blade load alleviation of offshore wind turbines

ABSTRACT Offshore wind turbines take advantage of the vast energy resource in open waters but face structural integrity challenges specific to their operating environment that require cost-effective load alleviation solutions. This paper introduces a computational methodology for model-based two- and three-dimensional design of load alleviation systems on offshore wind turbines. The aero-hydro-servoelastic model is formulated in a convenient state-space representation, coupling a multi-body composite beam description of the main structural elements with unsteady vortex-lattice aerodynamics and Morisons description of the hydrodynamics. The aerodynamics does not require empirical corrections and focuses on a control-oriented approach to the modelling. Numerical results show that through trailing-edge flaps actuated by a robust controller, more than 60% reduction in dynamic loading due to atmospheric turbulence can be achieved for the sectional model and close to 13% reduction in blade loads is obtained for the complete three-dimensional floating turbine.

Effects of Leading-Edge Tubercles on Wing Flutter Speeds

The dynamic aeroelastic effects on wings modified with bio-inspired leading-edge (LE) tubercles are examined in this study. We adopt a state-space aeroelastic model via the coupling of unsteady vortex-lattice method and a composite beam to evaluate stability margins as a result of LE tubercles on a generic wing. The unsteady aerodynamics and spanwise mass variations due to LE tubercles have counteracting effects on stability margins with the former having dominant influence. When coupled, flutter speed is observed to be 5% higher, and this is accompanied by close to 6% decrease in reduced frequencies as an indication of lower structural stiffness requirements for wings with LE tubercles. Both tubercle amplitude and wavelength have similar influences over the change in flutter speeds, and such modifications to the LE would have minimal effect on stability margins when concentrated inboard of the wing. Lastly, when used in sweptback wings, LE tubercles are observed to have smaller impacts on stability margins as the sweep angle is increased.