An extensive database of simulated loads representing almost 100 years of operation of a utility-scale wind turbine has been developed using high-performance computing resources. Such a large amount of data makes it possible to evaluate several proposals being considered in planned revisions of industry guidelines such as the International Electrotechnical Commission's 61400-1 wind turbine design standard. Current design provisions, especially those dependent on large amounts of data, can be critically examined and validated or alternative proposals can be made based on studies using this loads database. We discuss one design load case in particular that requires nominal 50-year loads, often difficult to establish with limited simulations followed by statistical extrapolation, to which a load factor (1.25) is applied. Alternatives that use other load statistics easier to establish from simulations are systematically evaluated. Such robust load statistics are associated with lower levels of uncertainty. Load factors to be applied to such alternative nominal loads are higher than those for the 50-year load. We discuss how the loads database developed enabled systematic study of a proposal that can serve as an alternative to use of a factored 50-year load. Calibration of this proposal accounts for the uncertainty in estimation of loads from simulation and the large database allows assessment against 50-year loads with quantifiable (and low) uncertainty.
This report documents the data post-processing and analysis performed to date on the field test data. Results include the control capability of the trailing edge flaps, the combined structural and aerodynamic damping observed through application of step actuation with ensemble averaging, direct observation of time delays associated with aerodynamic response, and techniques for characterizing an operating turbine with active rotor control.
Simulations of a rectangular cavity containing a model captive store are performed using a Hybrid Reynolds-averaged Navier-Stokes/Large Eddy Simulation (RANS/LES) model. The fluid flow simulations are coupled to a structural dynamics finite element model using a one-way pressure transfer procedure. Simulation results for pressure fluctuation spectra and store acceleration are compared to measurements made on the same configuration in a tri-sonic wind tunnel at Mach numbers of 0.60, 0.80, and 1.47. The simulation results are used to calculate unsteady integrated forces and moments acting on the store. Spectra of the forces and moments reveal that a complex relationship exists between the unsteady integrated forces and the measured resonant cavity modes as indicated in the cavity wall pressure measurements. Predictions of the store accelerations from the coupled model show some success in predicting both forced and natural modal responses of the store within the cavity environment, while also highlighting some challenges in obtaining statistically converged results for this class of problems.
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 orthogonal 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 projection 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 %E2%80%9Csymmetry inner product%E2%80%9D. Attention 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 %E2%80%9CLyapunov inner product%E2%80%9D, 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.
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%.