Publications

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Sandia National Laboratories has concluded field testing of its wind turbine rotor equipped with trailing-edge flaps. The blade design, fabrication, and integration which have been described in previous papers are briefly reviewed and then a portion of the data is presented and analyzed. Time delays observed in the time-averaged response to stepwise flap motions are consistent with the expected time scales of the structural and aerodynamic phenomena involved. Control authority of the flaps is clearly seen in the blade strain data and in hub-mounted video of the blade tip movement. © 2013 by the American Institute of Aeronautics and Astronautics, Inc.

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This report aims to unify several approaches for building stable projection-based reduced order models (ROMs). Attention is focused on linear time-invariant (LTI) systems. The model reduction procedure consists of two steps: the computation of a reduced basis, and the projection of the governing partial differential equations (PDEs) onto this reduced basis. Two kinds of reduced bases are considered: the proper orthog onal decomposition (POD) basis and the balanced truncation basis. The projection step of the model reduction can be done in two ways: via continuous projection or via discrete projection. First, an approach for building energy-stable Galerkin ROMs for linear hyperbolic or incompletely parabolic systems of PDEs using continuous projec tion is proposed. The idea is to apply to the set of PDEs a transformation induced by the Lyapunov function for the system, and to build the ROM in the transformed variables. The resulting ROM will be energy-stable for any choice of reduced basis. It is shown that, for many PDE systems, the desired transformation is induced by a special weighted L² inner product, termed the “symmetry inner product”. Atten tion is then turned to building energy-stable ROMs via discrete projection. A discrete counterpart of the continuous symmetry inner product, a weighted L² inner product termed the “Lyapunov inner product”, is derived. The weighting matrix that defines the Lyapunov inner product can be computed in a black-box fashion for a stable LTI system arising from the discretization of a system of PDEs in space. It is shown that a ROM constructed via discrete projection using the Lyapunov inner product will be energy-stable for any choice of reduced basis. Connections between the Lyapunov inner product and the inner product induced by the balanced truncation algorithm are made. Comparisons are also made between the symmetry inner product and the Lyapunov inner product. The performance of ROMs constructed using these inner products is evaluated on several benchmark test cases.

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A research project has recently begun to explore the viability of vertical axis wind turbines (VAWT) for future U.S. offshore installations, especially in resource-rich, deep-water locations. VAWTs may offer reductions in cost across multiple categories, including operations and maintenance (O&M), support structure, installation, and electrical infrastructure costs. The cost of energy (COE) reduction opportunities follow from three fundamental characteristics of the VAWT: lower turbine center of gravity, reduced machine complexity, and the opportunity for scaling the machine to very large sizes (10-20 MW). This paper discusses why VAWTs should be considered for offshore installation, describes the project that has been created to explore this prospect, and gives some early results from the project. These results indicate a potential for COE reduction of over 20%.

A research project has recently begun to explore the viability of vertical axis wind turbines (VAWT) for future U.S. offshore installations, especially in resource-rich, deep-water locations. VAWTs may offer reductions in cost across multiple categories, including operations and maintenance (O&M), support structure, installation, and electrical infrastructure costs. The cost of energy (COE) reduction opportunities follow from three fundamental characteristics of the VAWT: lower turbine center of gravity, reduced machine complexity, and the opportunity for scaling the machine to very large sizes (10-20 MW). This paper discusses why VAWTs should be considered for offshore installation, describes the project that has been created to explore this prospect, and gives some early results from the project. These results indicate a potential for COE reduction of over 20%.

Marine hydrokinetic (MHK) devices are currently being considered for the generation of electrical power in marine tidal regions. Turbulence generated in the boundary layers of these channels interacts with a turbine to excite the blades into low-to mid-frequency vibration. Additionally, the self-generated turbulent boundary layer on the turbine blade excites its trailing edge into vibration. Both of these hydrodynamic sources generate radiated noise. Being installed in a marine ecosystem, the noise generated by these MHK devices may affect the fish and marine mammal well-being. Since this MHK technology is relatively new, much of the design practice follows that from conventional horizontal axis wind turbines. In contrast to other underwater turbomachines like conventional merchant ships that have solid blades, wind turbine blades are made of hollow fiberglass composites. This paper systematically investigates the contrast of this design detail on the blade vibration and radiated noise for a particular MHK turbine design. Copyright © 2012 by ASME.

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