Ismail, Kamal, Samsul; Purnomo, Sarjiya
2016-06-01
This investigation was conducted to identify the influences of the two positions (non-staggered and staggered) of wind turbine arrays. Identification on down-scaled size wind turbine arrays was carried out in an open circuit, suction-type wind tunnel. Based on the results of the experiment, empirical relations for the centreline velocity deficit, tipline velocity deficit and wake radius are proposed. The non-staggered position results are larger power generated than that of the staggered position, this influenced by the trend deficit in velocity that makes wind turbine generated power difference between staggered position and non-stagger position. The area used non-staggered position larger than staggered position. Result staggered position has become one of the solutions to harness wind farms confined areas.
Turbulent flow and scalar flux through and over aligned and staggered wind farms
Markfort, C. D.; Zhang, W.; Porté-Agel, F.
2012-04-01
Wind farm-atmosphere interaction is complicated by the effect of turbine array configuration on momentum, scalar and kinetic energy fluxes. Wind turbine arrays are often arranged in rectilinear grids and, depending on the wind direction, may be perfectly aligned or perfectly staggered. The two extreme configurations make up the end members of a spectrum of infinite possible layouts. A wind farm of finite length may be modeled as an added roughness or as a canopy in large-scale weather and climate models. However, it is not clear which analogy is physically more appropriate. Also, surface scalar flux, including heat, evaporation and trace gas (e.g. CO2) fluxes affected by wind farms, need to be properly parameterized in large-scale models. Experiments involving model wind farms in aligned and staggered configurations, consisting of 13 rows with equivalent turbine density, were conducted in a thermally-controlled boundary-layer wind tunnel. Measurements of the turbulent flow were made using a custom x-wire/cold wire within and over the wind farms. Particular focus was placed on studying the effect of wind farm layout on flow adjustment, momentum and scalar fluxes, and turbulent kinetic energy distribution. Results show that the turbulence statistics of the flow exhibit similar turbulent transport properties to those of canopy flows, but retain some characteristic surface layer properties in a limited region above the wind farms as well. The initial wake growth over columns of turbines in the aligned wind farm is faster. However, the overall wake adjusts within and grows more rapidly over the staggered farm. The effective roughness of the staggered farm was found to be significantly larger than that of the aligned farm. The flow equilibrates faster, and the overall momentum absorption is higher for the staggered compared to the aligned farm, which is consistent with canopy scaling. Lower surface heat flux was found for the wind farms compared to the boundary
Quantifying array losses due to spacing and staggering in offshore wind farms (Invited)
Archer, C. L.; Mirzaeisefat, S.; Lee, S.; Xie, S.
2013-12-01
The layout of wind turbines can have an impact on the power production of a wind farm. Design variables that define the layout of wind turbines within a wind farm include: orientation of the rows with respect to the prevailing wind direction, size and shape of the wind farm, spacing between turbines, and alignment of the turbines (i.e., whether in-line or staggered with one another). There are no universal layout recommendations for offshore wind farms, partly because isolating the contribution of each individual design variable is impossible at existing offshore wind farms, where multiple effects overlap non-linearly on one another, and partly because analyzing the sensitivity to design variables requires sophisticated and computer-intensive numerical codes, such as large-eddy simulations (LES), that can simulate the small-scale turbulent features of turbine wakes. The National Renewable Energy Laboratory (NREL) developed the only publicly available and open-source LES code that is capable of resolving wind turbine blades as rotating actuator lines (not fixed disks), includes both neutral and unstable atmospheric conditions (stable case is currently under development), and does not rely on periodic boundary conditions. This code, named Simulator for Offshore/Onshore Wind Farm Applications (SOWFA), is based on OpenFOAM and has been used successfully in the past for turbulent wake simulations. Here we address the issue of quantifying two design variables: turbine spacing (both along and across the prevailing wind direction) and alignment (in-line or staggered for consecutive rows). SOWFA is used to simulate an existing offshore wind farm in Lillgrund (Sweden), consisting of 48 Siemens 2.3 MW turbines with spacing of 3.2D across and 4.3D along the prevailing wind direction and without staggering, where D is the turbine diameter (93 m). This spacing is exceptionally tight, to our knowledge the tightest of all modern wind farms. While keeping the area and the shape of
Compressibility enhancement in an almost staggered interacting Harper model
Friedman, Bat-el; Berkovits, Richard
2015-03-01
We discuss the compressibility in the almost staggered fermionic Harper model with repulsive interactions in the vicinity of half-filling. It has been shown by Kraus et al. [Phys. Rev. B 89, 161106(R) (2014)], 10.1103/PhysRevB.89.161106 that for spinless electrons and nearest neighbors electron-electron interactions the compressibility in the central band is enhanced by repulsive interactions. Here we would like to investigate the sensitivity of this conclusion to the spin degree of freedom and longer range interactions. We use the Hartree-Fock (HF) approximation, as well as the density matrix renormalization group (DMRG) calculation to evaluate the compressibility. In the almost staggered Harper model, the central energy band is essentially flat and separated from the other bands by a large gap and therefore, the HF approximation is rather accurate. In both cases the compressibility of the system is enhanced compared to the noninteracting case, although the enhancement is weaker due to the inclusion of Hubbard and longer ranged interactions. We also show that the entanglement entropy is suppressed when the compressibility of the system is enhanced.
Persistent current in an almost staggered Harper model
Vasserman, A.; Berkovits, R.
2015-08-01
In this paper we study the persistent current (PC) of a staggered Harper model, close to the half-filling. The Harper model is different than other one dimensional disordered systems which are always localized, since it is a quasi-periodic system with correlated disorder resulting in the fact that it can be in the metallic regime. Nevertheless, the PC for a wide range of parameters of the Harper model does not show typical metallic behavior, although the system is in the metallic regime. This is a result of the nature of the central band states, which are a hybridization of Gaussian states localized in superlattice points. When the superlattice is not commensurate with the system length, the PC behaves as an insulator. Thus even in the metallic regime a typical finite Harper model may exhibit a PC expected from an insulator.
Staggered Flux State in Two-Dimensional Hubbard Models
Yokoyama, Hisatoshi; Tamura, Shun; Ogata, Masao
2016-12-01
The stability and other properties of a staggered flux (SF) state or a correlated d-density wave state are studied for the Hubbard (t-t'-U) model on extended square lattices, as a low-lying state that competes with the dx2 - y2-wave superconductivity (d-SC) and possibly causes the pseudogap phenomena in underdoped high-Tc cuprates and organic κ-BEDT-TTF salts. In calculations, a variational Monte Carlo method is used. In the trial wave function, a configuration-dependent phase factor, which is vital to treat a current-carrying state for a large U/t, is introduced in addition to ordinary correlation factors. Varying U/t, t'/t, and the doping rate (δ) systematically, we show that the SF state becomes more stable than the normal state (projected Fermi sea) for a strongly correlated (U/t ≳ 5) and underdoped (δ ≲ 0.16) area. The decrease in energy is sizable, particularly in the area where Mott physics prevails and the circular current (order parameter) is strongly suppressed. These features are consistent with those for the t-J model. The effect of the frustration t'/t plays a crucial role in preserving charge homogeneity and appropriately describing the behavior of hole- and electron-doped cuprates and κ-BEDT-TTF salts. We argue that the SF state does not coexist with d-SC and is not a "normal state" from which d-SC arises. We also show that a spin current (flux or nematic) state is never stabilized in the same regime.
Study of △I=2 staggering by perturbed particle-rotor model
Institute of Scientific and Technical Information of China (English)
邢正; 王晓春; 陈星蕖
1996-01-01
AI=2 staggering in superdefonned nuclei has been investigated by a perturbed particle-rotor model, of which all observed features are reproduced in the calculations. It is pointed out that the C4symmetry in Hamiltonian is not the only cause of AI=2 staggering. This model can be used to make a fit to the experimental data in odd-A superdeformed nuclei.
Effects of staggered magnetic field on entanglement in the anisotropic XY model
Sun, Z; Li, Y Q; Sun, Zhe; Wang, XiaoGuang; Li, You-Quan
2004-01-01
We investigate effects of staggered magnetic field on thermal entanglement in the anisotropic XY model. The analytic results of entanglement for the two-site cases are obtained. For the general case of even sites, we show that when the anisotropic parameter is zero, the entanglement in the XY model with a staggered magnetic field is the same as that with a uniform magnetic field.
Quantum search on the two-dimensional lattice using the staggered model with Hamiltonians
Portugal, R.; Fernandes, T. D.
2017-04-01
Quantum search on the two-dimensional lattice with one marked vertex and cyclic boundary conditions is an important problem in the context of quantum algorithms with an interesting unfolding. It avails to test the ability of quantum walk models to provide efficient algorithms from the theoretical side and means to implement quantum walks in laboratories from the practical side. In this paper, we rigorously prove that the recent-proposed staggered quantum walk model provides an efficient quantum search on the two-dimensional lattice, if the reflection operators associated with the graph tessellations are used as Hamiltonians, which is an important theoretical result for validating the staggered model with Hamiltonians. Numerical results show that on the two-dimensional lattice staggered models without Hamiltonians are not as efficient as the one described in this paper and are, in fact, as slow as classical random-walk-based algorithms.
Two-dimensional quantum compass model in a staggered field: some rigorous results
Institute of Scientific and Technical Information of China (English)
He Pei-Song; You Wen-Long; Tian Guang-Shan
2011-01-01
We study the properties of the two-dimensional quantum compass model in a staggered field. Using the PerronFr(o)enius theorem and the reflection positivity method, we rigorously determine the low energy spectrum of this model and its global ground state Ψ0. Furthermore, we show that Ψ0 has a directional long-range order.
Implementation of Newton-Rapshon iterations for parallel staggered-grid geodynamic models
Popov, A. A.; Kaus, B. J. P.
2012-04-01
Staggered-grid finite differences discretization has a good potential for solving highly heterogeneous geodynamic models on parallel computers (e.g. Tackey, 2008; Gerya &Yuen, 2007). They are inherently stable, computationally inexpensive and relatively easy to implement. However, currently used staggered-grid geodynamic codes employ almost exclusively the sub-optimal Picard linearization scheme to deal with nonlinearities. It was shown that Newton-Rapshon linearization can lead to substantial improvements of the solution quality in geodynamic problems, simultaneously with reduction of computer time (e.g. Popov & Sobolev, 2008). This work is aimed at implementation of the Newton-Rapshon linearization in the parallel geodynamic code LaMEM together with staggered-grid discretization and viso-(elasto)-plastic rock rheologies. We present the expressions for the approximate Jacobian matrix, and give detailed comparisons with the currently employed Picard linearization scheme, in terms of solution quality and number of iterations.
The staggered six-vertex model: Conformal invariance and corrections to scaling
Energy Technology Data Exchange (ETDEWEB)
Frahm, Holger [Institut für Theoretische Physik, Leibniz Universität Hannover, Appelstraße 2, 30167 Hannover (Germany); Seel, Alexander [Lehrstuhl für Theoretische Elektrotechnik und Photonik, Universität Siegen, Hölderlinstraße 3, 57068 Siegen (Germany)
2014-02-15
We study the emergence of non-compact degrees of freedom in the low energy effective theory for a class of Z{sub 2}-staggered six-vertex models. In the finite size spectrum of the vertex model this shows up through the appearance of a continuum of critical exponents. To analyze this part of the spectrum we derive a set of coupled nonlinear integral equations from the Bethe ansatz solution of the vertex model which allow to compute the energies of the system for a range of anisotropies and of the staggering parameter. The critical theory is found to be independent of the staggering. Its spectrum and density of states coincide with the SL(2,R)/U(1) Euclidean black hole conformal field theory which has been identified previously in the continuum limit of the vertex model for a particular ‘self-dual’ choice of the staggering. We also study the asymptotic behavior of subleading corrections to the finite size scaling and discuss our findings in the context of the conformal field theory.
The staggered six-vertex model: Conformal invariance and corrections to scaling
Frahm, Holger; Seel, Alexander
2014-02-01
We study the emergence of non-compact degrees of freedom in the low energy effective theory for a class of Z2-staggered six-vertex models. In the finite size spectrum of the vertex model this shows up through the appearance of a continuum of critical exponents. To analyze this part of the spectrum we derive a set of coupled nonlinear integral equations from the Bethe ansatz solution of the vertex model which allow to compute the energies of the system for a range of anisotropies and of the staggering parameter. The critical theory is found to be independent of the staggering. Its spectrum and density of states coincide with the SL(2,R)/U(1) Euclidean black hole conformal field theory which has been identified previously in the continuum limit of the vertex model for a particular ‘self-dual' choice of the staggering. We also study the asymptotic behavior of subleading corrections to the finite size scaling and discuss our findings in the context of the conformal field theory.
Zhang, Pu; Heyne, Mary A.; To, Albert C.
2015-10-01
We investigate the damping enhancement in a class of biomimetic staggered composites via a combination of design, modeling, and experiment. In total, three kinds of staggered composites are designed by mimicking the structure of bone and nacre. These composite designs are realized by 3D printing a rigid plastic and a viscous elastomer simultaneously. Greatly-enhanced energy dissipation in the designed composites is observed from both the experimental results and theoretical prediction. The designed polymer composites have loss modulus up to ~500 MPa, higher than most of the existing polymers. In addition, their specific loss modulus (up to 0.43 km2/s2) is among the highest of damping materials. The damping enhancement is attributed to the large shear deformation of the viscous soft matrix and the large strengthening effect from the rigid inclusion phase.
Skew information in the XY model with staggered Dzyaloshinskii-Moriya interaction
Energy Technology Data Exchange (ETDEWEB)
Qiu, Liang, E-mail: lqiu@cumt.edu.cn [School of Physics, China University of Mining and Technology, Xuzhou, Jiangsu 221116 (China); Quan, Dongxiao [State Key Laboratory of Integrated Services Networks, Xidian University, Xi' an, Shaanxi 710071 (China); Pan, Fei; Liu, Zhi [School of Physics, China University of Mining and Technology, Xuzhou, Jiangsu 221116 (China)
2017-06-01
We study the performance of the lower bound of skew information in the vicinity of transition point for the anisotropic spin-1/2 XY chain with staggered Dzyaloshinskii-Moriya interaction by use of quantum renormalization-group method. For a fixed value of the Dzyaloshinskii-Moriya interaction, there are two saturated values for the lower bound of skew information corresponding to the spin-fluid and Néel phases, respectively. The scaling exponent of the lower bound of skew information closely relates to the correlation length of the model and the Dzyaloshinskii-Moriya interaction shifts the factorization point. Our results show that the lower bound of skew information can be a good candidate to detect the critical point of XY spin chain with staggered Dzyaloshinskii-Moriya interaction.
Computational dispersion properties of horizontal staggered grids for atmospheric and ocean models
Fox-Rabinovitz, Michael S.
1991-01-01
The computational dispersion properties of horizontally and time-horizontally staggered grids utilizing corresponding centered-difference techniques for approximation of the adjustment, or gravity wave equations, are examined in terms of their group velocity characteristics. Results are acquired for oceanic and atmospheric models, the former being characterized by a much smaller Rossby radius of deformation. For all grids considered additional filtering is required to control and even eliminate waves with poor computational dispersion characteristics. Computational dispersion properties along with other computational characteristics and requirements give some guidance for an optimal selection of an appropriate grid for an ocean or atmospheric model.
Staggered domain wall fermions
Hoelbling, Christian
2016-01-01
We construct domain wall fermions with a staggered kernel and investigate their spectral and chiral properties numerically in the Schwinger model. In some relevant cases we see an improvement of chirality by more than an order of magnitude as compared to usual domain wall fermions. Moreover, we present first results for four-dimensional quantum chromodynamics, where we also observe significant reductions of chiral symmetry violations for staggered domain wall fermions.
Parametric modeling and stagger angle optimization of an axial flow fan
Li, M. X.; Zhang, C. H.; Liu, Y.; Y Zheng, S.
2013-12-01
Axial flow fans are widely used in every field of social production. Improving their efficiency is a sustained and urgent demand of domestic industry. The optimization of stagger angle is an important method to improve fan performance. Parametric modeling and calculation process automation are realized in this paper to improve optimization efficiency. Geometric modeling and mesh division are parameterized based on GAMBIT. Parameter setting and flow field calculation are completed in the batch mode of FLUENT. A control program is developed in Visual C++ to dominate the data exchange of mentioned software. It also extracts calculation results for optimization algorithm module (provided by Matlab) to generate directive optimization control parameters, which as feedback are transferred upwards to modeling module. The center line of the blade airfoil, based on CLARK y profile, is constructed by non-constant circulation and triangle discharge method. Stagger angles of six airfoil sections are optimized, to reduce the influence of inlet shock loss as well as gas leak in blade tip clearance and hub resistance at blade root. Finally an optimal solution is obtained, which meets the total pressure requirement under given conditions and improves total pressure efficiency by about 6%.
XFEM Modelling of Multi-holes Plate with Single-row and Staggered Holes Configurations
Directory of Open Access Journals (Sweden)
Supar Khairi
2017-01-01
Full Text Available Joint efficiency is the key to composite structures assembly design, good structures response is dependent upon multi-holes behavior as subjected to remote loading. Current benchmarking work were following experimental testing series taken from literature on multi-holes problem. Eleven multi-hole configurations were investigated with various pitch and gage distance of staggered holes and non-staggered holes (single-row holes. Various failure modes were exhibited, most staggered holes demonstrates staggered crack path but non-staggered holes series displayed crack path along net-section plane. Stress distribution were carried out and good agreement were exhibited in experimental observation as reported in the respective literature. Consequently, strength prediction work were carried out under quasi-static loading, most showed discrepancy between 8% -31%, better prediction were exhibited in thicker and non-staggered holes plate combinations.
Liu, X M; Cheng, W W; Liu, J-M
2016-01-19
We investigate the quantum Fisher information and quantum phase transitions of an XY spin chain with staggered Dzyaloshinskii-Moriya interaction using the quantum renormalization-group method. The quantum Fisher information, its first-derivatives, and the finite-size scaling behaviors are rigorously calculated respectively. The singularity of the derivatives at the phase transition point as a function of lattice size is carefully discussed and it is revealed that the scaling exponent for quantum Fisher information at the critical point can be used to describe the correlation length of this model, addressing the substantial role of staggered Dzyaloshinskii-Moriya interaction in modulating quantum phase transitions.
Bose-Hubbard models with staggered flux: Quantum phases, collective excitation, and tricriticality
Yao, Juan; Zhang, Shizhong
2014-08-01
We study the quantum phases of a Bose-Hubbard model with staggered magnetic flux in two dimensions, as was realized recently [M. Aidelsburger, M. Atala, M. Lohse, J. T. Barreiro, B. Paredes, and I. Bloch, Phys. Rev. Lett. 107, 255301 (2011), 10.1103/PhysRevLett.107.255301]. Within mean-field theory, we show how the structure of the condensates evolves from the weak- to the strong-coupling limit, exhibiting a tricritical point at the Mott-superfluid transition. Nontrivial topological structures (Dirac points) in the quasiparticle (hole) excitations in the Mott state are found within random phase approximation and we discuss how interaction modifies their structures. The excitation gap in the Mott state closes at different k points when approaching the superfluid states, which is consistent with the findings of mean-field theory.
DEFF Research Database (Denmark)
Thorborg, Jesper
of the method has been focused on high temperature processes such as casting and welding and the interest of using nonlinear constitutive stress-strain relations has grown to extend the applicability of the method. The work of implementing classical plasticity into the control volume formulation has been based...... on the $J_2$ flow theory describing an isotropic hardening material with a temperature dependent yield stress. This work has successfully been verified by comparing results to analytical solutions. Due to the comprehensive implementation in the staggered grid an alternative constitutive stress......-strain relation has been suggested. The intention of this method is to provide fast numerical results with reasonable accuracy in relation to the first order effects of the presented classical plasticity model. Application of the $J_2$ flow theory and the alternative method have shown some agreement...
VizieR Online Data Catalog: STAGGER-grid of 3D stellar models. I. (Magic+, 2013)
Magic, Z.; Collet, R.; Asplund, M.; Trampedach, R.; Hayek, W.; Chiavassa, A.; Stein, R. F.; Nordlund, A.
2013-07-01
The 3D model atmospheres presented here were constructed with a custom version of the Stagger-code, a state-of-the-art, multipurpose, radiative-magnetohydrodynamics (R-MHD) code originally developed by Nordlund & Galsgaard (1995, http://www.astro.ku.dk/~kg/Papers/MHD_code.ps.gz), and continuously improved over the years by its user community. (1 data file).
Levy, R.; Mcginness, H.
1976-01-01
Investigations were performed to predict the power available from the wind at the Goldstone, California, antenna site complex. The background for power prediction was derived from a statistical evaluation of available wind speed data records at this location and at nearby locations similarly situated within the Mojave desert. In addition to a model for power prediction over relatively long periods of time, an interim simulation model that produces sample wind speeds is described. The interim model furnishes uncorrelated sample speeds at hourly intervals that reproduce the statistical wind distribution at Goldstone. A stochastic simulation model to provide speed samples representative of both the statistical speed distributions and correlations is also discussed.
Yong, Peng; Huang, Jianping; Li, Zhenchun; Liao, Wenyuan; Qu, Luping; Li, Qingyang; Liu, Peijun
2017-02-01
In finite-difference (FD) method, numerical dispersion is the dominant factor influencing the accuracy of seismic modelling. Various optimized FD schemes for scalar wave modelling have been proposed to reduce grid dispersion, while the optimized time-space domain FD schemes for elastic wave modelling have not been fully investigated yet. In this paper, an optimized FD scheme with Equivalent Staggered Grid (ESG) for elastic modelling has been developed. We start from the constant P- and S-wave speed elastic wave equations and then deduce analytical plane wave solutions in the wavenumber domain with eigenvalue decomposition method. Based on the elastic plane wave solutions, three new time-space domain dispersion relations of ESG elastic modelling are obtained, which are represented by three equations corresponding to P-, S- and converted-wave terms in the elastic equations, respectively. By using these new relations, we can study the dispersion errors of different spatial FD terms independently. The dispersion analysis showed that different spatial FD terms have different errors. It is therefore suggested that different FD coefficients to be used to approximate the three spatial derivative terms. In addition, the relative dispersion error in L2-norm is minimized through optimizing FD coefficients using Newton's method. Synthetic examples have demonstrated that this new optimal FD schemes have superior accuracy for elastic wave modelling compared to Taylor-series expansion and optimized space domain FD schemes.
Heat Transfer Modeling of Staggered Bundle with Round Tubes Screened by Mesh
Directory of Open Access Journals (Sweden)
Dymo B.V.
2016-04-01
Full Text Available The article presents the results of CFD modeling of heat transfer and aerodynamic drag for the first three rows of cross-flowed staggered bundle consisting of round tubes screened by wire mesh. Geometric model of this bundle was developed. Selection of optimal parameters of the bundle finite element model realizes on the base of transition shear stress transport model. Two separate geometric models for even and odd rows of bundle have been elaborated for the scope of computational resources optimization. The results of numerical modeling of heat transfer for the first three rows of the bundle were approximated with the criteria dependences. It has been established that heat transfer stabilization occurs from the second row of the bundle. Stabilized heat transfer is 15 % higher than that for the first row of the bundle and 1.2 … 1.7 times as large in comparison with equivalent bare-tube bundle in a range of Reynolds number from 5000 to 35000. Aerodynamic drag data for the first three rows of the bundle have been obtained.
Kendall, William L.; Hines, James E.; Nichols, James D.; Grant, Evan H. Campbell
2013-01-01
Occupancy statistical models that account for imperfect detection have proved very useful in several areas of ecology, including species distribution and spatial dynamics, disease ecology, and ecological responses to climate change. These models are based on the collection of multiple samples at each of a number of sites within a given season, during which it is assumed the species is either absent or present and available for detection while each sample is taken. However, for some species, individuals are only present or available for detection seasonally. We present a statistical model that relaxes the closure assumption within a season by permitting staggered entry and exit times for the species of interest at each site. Based on simulation, our open model eliminates bias in occupancy estimators and in some cases increases precision. The power to detect the violation of closure is high if detection probability is reasonably high. In addition to providing more robust estimation of occupancy, this model permits comparison of phenology across sites, species, or years, by modeling variation in arrival or departure probabilities. In a comparison of four species of amphibians in Maryland we found that two toad species arrived at breeding sites later in the season than a salamander and frog species, and departed from sites earlier.
Institute of Scientific and Technical Information of China (English)
Zheng Rui; Liu Bang-Gui
2012-01-01
In order to gain a deeper understanding of the quantum criticality in the explicitly staggered dimerized Heisenberg models,we study a generalized staggered dimer model named the J0 J1-J2 model,which corresponds to the staggered J J’ model on a square lattice and a honeycomb lattice when J1/J0 equals 1 and 0,respectively.Using the quantum Monte Carlo method,we investigate all the quantum critical points of these models with J1/J0 changing from 0 to 1as a function of coupling ratio α =J2/J0.We extract all the critical values of the coupling ratio αc for these models,and we also obtain the critical exponents v,β/v,and η using different finite-size scaling ans(a)tz,.All these exponents are not consistent with the three-dimensional Heisenberg universality class,indicating some unconventional quantum ciritcial points in these models.
Engwirda, Darren
2017-01-01
An algorithm for the generation of non-uniform, locally orthogonal staggered unstructured spheroidal grids is described. This technique is designed to generate very high-quality staggered VoronoiDelaunay meshes appropriate for general circulation modelling on the sphere, including applications to atmospheric simulation, ocean-modelling and numerical weather prediction. Using a recently developed Frontal-Delaunay refinement technique, a method for the construction of high-quality unstructured spheroidal Delaunay triangulations is introduced. A locally orthogonal polygonal grid, derived from the associated Voronoi diagram, is computed as the staggered dual. It is shown that use of the Frontal-Delaunay refinement technique allows for the generation of very high-quality unstructured triangulations, satisfying a priori bounds on element size and shape. Grid quality is further improved through the application of hill-climbing-type optimisation techniques. Overall, the algorithm is shown to produce grids with very high element quality and smooth grading characteristics, while imposing relatively low computational expense. A selection of uniform and non-uniform spheroidal grids appropriate for high-resolution, multi-scale general circulation modelling are presented. These grids are shown to satisfy the geometric constraints associated with contemporary unstructured C-grid-type finite-volume models, including the Model for Prediction Across Scales (MPAS-O). The use of user-defined mesh-spacing functions to generate smoothly graded, non-uniform grids for multi-resolution-type studies is discussed in detail.
DEFF Research Database (Denmark)
Hansen, Anca Daniela; Margaris, Ioannis D.
project to be incorporated in the wind power plant level. This document describes the Type 4 wind turbine simulation model, implemented in the EaseWind project. The implemented wind turbine model is one of the initial necessary steps toward integrating new control services in the wind power plant level....... In the project, this wind turbine model will be further incorporated in a wind power plant model together with the implementation in the wind power control level of the new control functionalities (inertial response, synchronising power and power system damping). For this purpose an aggregate wind power plant...... (WPP) will be considered. The aggregate WPP model, which will be based on the upscaling of the individual wind turbine model on the electrical part, will make use of an equivalent wind speed. The implemented model follows the basic structure of the generic standard Type 4 wind turbine model proposed...
DEFF Research Database (Denmark)
Thorborg, Jesper
The objective of this thesis has been to improve and further develop the existing staggered grid control volume formulation of the thermomechanical equations. During the last ten years the method has proven to be efficient and accurate even for calculation on large structures. The application of ...
Institute of Scientific and Technical Information of China (English)
王宏光; 孙建逵
2011-01-01
为提高市轴风力机的效率,对可变叶片安装角的立轴风力机进行了分析,根据机翼升力与阻力的理论,在固定来流风速和旋转速度下计算了叶片在每个方位角上产生力矩最大的最佳安装角的变化规律,为了更好的运行,对最佳安装角的变化规律进行了一定修改.计算比较了固定安装角度的叶片与可变安装角度的叶片旋转一周产生的力矩,结果表明叶片在最佳安装角下运行时,每一转的正力矩都有明显增大,平均力矩町提高14倍.多个叶片在最佳安装角下运行时的力矩变化较平稳.可变叶片安装角立轴风力机是一种有发展前途的动力设备.%In order to improve the efficiency of vertical axis wind turbine (VAWT), the VAWT with variable stagger angle blade was studies. Optimum blade stagger angle was calculated for wind turbine maximum torque at fixed inlet wind velocity and rotational speed by the theory of aerofoil blade' s lift and drag. And the optimum blade stagger angle was modified for better run. The torque of VAWT with fixed stagger angle blade was compared with that of VAWT with variable stagger angle blade. Results show that the positive torque in each cycle is increased evidently and the average torque is increased by 14 times at optimum blade stagger angle. VAWT with multi-blade at optimum stagger angle provides capacity of smooth power and torque performance. It may be concluded that VAWT with stagger variable blades is one kind of promising power equipment.
Wind Farms: Modeling and Control
DEFF Research Database (Denmark)
Soleimanzadeh, Maryam
2012-01-01
provides the state space form of the dynamic wind farm model. The model provides an approximation of the behavior of the flow in wind farms, and obtains the wind speed in the vicinity of each wind turbine. The control algorithms in this work are mostly on the basis of the developed wind farm model......The primary purpose of this work is to develop control algorithms for wind farms to optimize the power production and augment the lifetime of wind turbines in wind farms. In this regard, a dynamical model for wind farms was required to be the basis of the controller design. In the first stage......, a dynamical model has been developed for the wind flow in wind farms. The model is based on the spatial discretization of the linearized Navier-Stokes equation combined with the vortex cylinder theory. The spatial discretization of the model is performed using the Finite Difference Method (FDM), which...
The Stagger-grid: A Grid of 3D Stellar Atmosphere Models - I. Methods and General Properties
Magic, Z; Asplund, M; Trampedach, R; Hayek, W; Chiavassa, A; Stein, R F; Nordlund, Å
2013-01-01
We present the Stagger-grid, a comprehensive grid of time-dependent, 3D hydrodynamic model atmospheres for late-type stars with realistic treatment of radiative transfer, covering a wide range in stellar parameters. This grid of 3D models is intended for various applications like stellar spectroscopy, asteroseismology and the study of stellar convection. In this introductory paper, we describe the methods used for the computation of the grid and discuss the general properties of the 3D models as well as their temporal and spatial averages (). All our models were generated with the Stagger-code, using realistic input physics for the equation of state (EOS) and for continuous and line opacities. Our ~220 grid models range in Teff from 4000 to 7000K in steps of 500K, in log g from 1.5 to 5.0 in steps of 0.5 dex, and [Fe/H] from -4.0 to +0.5 in steps of 0.5 and 1.0 dex. We find a tight scaling relation between the vertical velocity and the surface entropy jump, which itself correlates with the constant entropy va...
Institute of Scientific and Technical Information of China (English)
PEI Zheng-lin; WANG Shang-xu
2005-01-01
The paper presents a staggered-grid any even-order accurate finite-difference scheme for two-dimensional (2D),three-component (3C), first-order stress-velocity elastic wave equation and its stability condition in the arbitrary tilt anisotropic media; and derives a perfectly matched absorbing layer (PML) boundary condition and its staggered-grid any even-order accurate difference scheme in the 2D arbitrary tilt anisotropic media. The results of numerical modeling indicate that the modeling precision is high, the calculation efficiency is satisfactory and the absorbing boundary condition is better. The wave-front shapes of elastic waves are complex in the anisotropic media, and the velocity of qP wave is not always faster than that of qS wave. The wave-front triplication of qS wave and its events in both reflected domain and propagated domain, which are not commonly hyperbola, is a common phenomenon. When the symmetry axis is tilted in the TI media, the phenomenon of S-wave splitting is clearly observed in the snaps of three components and synthetic seismograms, and the events of all kinds of waves are asymmetric.
Development of Non-staggered, semi-implicit ICE numerical scheme for a two-fluid, three-field model
Energy Technology Data Exchange (ETDEWEB)
Jeong, Jae Jun; Yoon, H. Y.; Bae, S. W
2007-11-15
A pilot code for one-dimensional, transient, two-fluid, three-field model has been developed. In this code, the semi-implicit ICE numerical scheme has been adapted to a 'non-staggered' grid. Using several conceptual problems, the numerical scheme has been verified. The results of the verifications are summarized below: - It was confirmed that the basic pilot code can simulate various flow conditions (such as single-phase liquid flow, two-phase mixture flow, and single-phase vapor flow) and transitions of the flow conditions. A mist flow was not simulated, but it seems that the basic pilot code can simulate mist flow conditions. - The mass and energy conservation was confirmed for single-phase liquid and single-phase vapor flows. - It was confirmed that the inlet pressure and velocity boundary conditions work properly. - It was confirmed that, for single- and two-phase flows, the velocity and temperature of non-existing phase are calculated as intended. The non-staggered, semi-implicit ICE numerical scheme, which has been developed in this study, will be a starting point of a new code development that adopts an unstructured finite volume method.
Energy Technology Data Exchange (ETDEWEB)
Hui, Ning-Ju [Department of Applied Physics, Xi' an University of Technology, Xi' an 710054 (China); Xu, Yang-Yang; Wang, Jicheng; Zhang, Yixin [Jiangsu Provincial Research Center of Light Industrial Optoelectronic Engineering and Technology, School of Science, Jiangnan University, Wuxi 214122 (China); Hu, Zheng-Da, E-mail: huyuanda1112@jiangnan.edu.cn [Jiangsu Provincial Research Center of Light Industrial Optoelectronic Engineering and Technology, School of Science, Jiangnan University, Wuxi 214122 (China)
2017-04-01
We investigate the properties of geometric quantum coherence in the XY spin-1/2 chain with staggered Dzyaloshinsky-Moriya interaction via the quantum renormalization-group approach. It is shown that the geometric quantum coherence and its coherence susceptibility are effective to detect the quantum phase transition. In the thermodynamic limit, the geometric quantum coherence exhibits a sudden jump. The coherence susceptibilities versus the anisotropy parameter and the Dzyaloshinsky-Moriya interaction are infinite and vanishing, respectively, illustrating the distinct roles of the anisotropy parameter and the Dzyaloshinsky-Moriya interaction in quantum phase transition. Moreover, we also explore the finite-size scaling behaviors of the coherence susceptibilities. For a finite-size chain, the coherence susceptibility versus the phase-transition parameter is always maximal at the critical point, indicating the dramatic quantum fluctuation. Besides, we show that the correlation length can be revealed by the scaling exponent for the coherence susceptibility versus the Dzyaloshinsky-Moriya interaction.
Hui, Ning-Ju; Xu, Yang-Yang; Wang, Jicheng; Zhang, Yixin; Hu, Zheng-Da
2017-04-01
We investigate the properties of geometric quantum coherence in the XY spin-1/2 chain with staggered Dzyaloshinsky-Moriya interaction via the quantum renormalization-group approach. It is shown that the geometric quantum coherence and its coherence susceptibility are effective to detect the quantum phase transition. In the thermodynamic limit, the geometric quantum coherence exhibits a sudden jump. The coherence susceptibilities versus the anisotropy parameter and the Dzyaloshinsky-Moriya interaction are infinite and vanishing, respectively, illustrating the distinct roles of the anisotropy parameter and the Dzyaloshinsky-Moriya interaction in quantum phase transition. Moreover, we also explore the finite-size scaling behaviors of the coherence susceptibilities. For a finite-size chain, the coherence susceptibility versus the phase-transition parameter is always maximal at the critical point, indicating the dramatic quantum fluctuation. Besides, we show that the correlation length can be revealed by the scaling exponent for the coherence susceptibility versus the Dzyaloshinsky-Moriya interaction.
Bossuyt, Juliaan; Howland, Michael F.; Meneveau, Charles; Meyers, Johan
2017-01-01
Unsteady loading and spatiotemporal characteristics of power output are measured in a wind tunnel experiment of a microscale wind farm model with 100 porous disk models. The model wind farm is placed in a scaled turbulent boundary layer, and six different layouts, varied from aligned to staggered, are considered. The measurements are done by making use of a specially designed small-scale porous disk model, instrumented with strain gages. The frequency response of the measurements goes up to the natural frequency of the model, which corresponds to a reduced frequency of 0.6 when normalized by the diameter and the mean hub height velocity. The equivalent range of timescales, scaled to field-scale values, is 15 s and longer. The accuracy and limitations of the acquisition technique are documented and verified with hot-wire measurements. The spatiotemporal measurement capabilities of the experimental setup are used to study the cross-correlation in the power output of various porous disk models of wind turbines. A significant correlation is confirmed between streamwise aligned models, while staggered models show an anti-correlation.
CSIR Research Space (South Africa)
Bogaers, Alfred EJ
2012-07-01
Full Text Available In this paper we outline the development of a 1D finite volume model to solve for blood flow through the arterial system. The model is based on a staggered spatial discretization which leads to a stable solution scheme. This scheme can accurately...
Magic, Zazralt
2014-01-01
In the surface layers of late-type stars, stellar convection is manifested with its typical granulation pattern due to the presence of convective motions. The resulting photospheric up- and downflows leave imprints in the observed spectral line profiles. We perform a careful statistical analysis of stellar granulation and its properties for different stellar parameters. We employ realistic 3D radiative hydrodynamic (RHD) simulations of surface convection from the Stagger-grid, a comprehensive grid of atmosphere models that covers a large parameter space in terms of Teff, logg, and [Fe/H]. Individual granules are detected from the (bolometric) intensity maps at disk center with an efficient granulation pattern recognition algorithm. From these we derive their respective properties: diameter, fractal dimension (area-perimeter relation), geometry, topology, variation of intensity, temperature, density and velocity with granule size. Also, the correlation of the physical properties at the optical surface are stud...
The Stagger-grid: A grid of 3D stellar atmosphere models. I. Methods and general properties
Magic, Z.; Collet, R.; Asplund, M.; Trampedach, R.; Hayek, W.; Chiavassa, A.; Stein, R. F.; Nordlund, Å.
2013-09-01
Aims: We present the Stagger-grid, a comprehensive grid of time-dependent, three-dimensional (3D), hydrodynamic model atmospheres for late-type stars with realistic treatment of radiative transfer, covering a wide range in stellar parameters. This grid of 3D models is intended for various applications besides studies of stellar convection and atmospheres per se, including stellar parameter determination, stellar spectroscopy and abundance analysis, asteroseismology, calibration of stellar evolution models, interferometry, and extrasolar planet search. In this introductory paper, we describe the methods we applied for the computation of the grid and discuss the general properties of the 3D models as well as of their temporal and spatial averages (here denoted ⟨3D⟩ models). Methods: All our models were generated with the Stagger-code, using realistic input physics for the equation of state (EOS) and for continuous and line opacities. Our ~ 220 grid models range in effective temperature, Teff, from 4000 to 7000 K in steps of 500 K, in surface gravity, log g, from 1.5 to 5.0 in steps of 0.5 dex, and metallicity, [Fe/H], from - 4.0 to + 0.5 in steps of 0.5 and 1.0 dex. Results: We find a tight scaling relation between the vertical velocity and the surface entropy jump, which itself correlates with the constant entropy value of the adiabatic convection zone. The range in intensity contrast is enhanced at lower metallicity. The granule size correlates closely with the pressure scale height sampled at the depth of maximum velocity. We compare the ⟨3D⟩ models with currently widely applied one-dimensional (1D) atmosphere models, as well as with theoretical 1D hydrostatic models generated with the same EOS and opacity tables as the 3D models, in order to isolate the effects of using self-consistent and hydrodynamic modeling of convection, rather than the classical mixing length theory approach. For the first time, we are able to quantify systematically over a broad
Wake interaction and power production of variable height model wind farms
DEFF Research Database (Denmark)
Vested, Malene Hovgaard; Hamilton, N.; Sørensen, Jens Nørkær;
2014-01-01
of comparison. It was found that downstream of the exit row wind turbine, the power was increased by 25% in the case of a staggered height configuration. This is partly due to the fact that the taller turbines reach into a flow area with a softened velocity gradient. Another aspect is that the wake downstream......Understanding wake dynamics is an ongoing research topic in wind energy, since wakes have considerable effects on the power production when wind turbines are placed in a wind farm. Wind tunnel experiments have been conducted to study the wake to wake interaction in a model wind farm in tandem...... with measurements of the extracted power. The aim is to investigate how alternating mast height influences the interaction of the wakes and the power production. Via the use of stereo-particle image velocimetry, the flow field was obtained in the first and last rows of the wind turbine array as a basis...
Investigation of deformation mechanisms of staggered nanocomposites using molecular dynamics
Mathiazhagan, S.; Anup, S.
2016-08-01
Biological materials with nanostructure of regularly or stair-wise staggered arrangements of hard platelets reinforced in a soft protein matrix have superior mechanical properties. Applications of these nanostructures to ceramic matrix composites could enhance their toughness. Using molecular dynamics simulations, mechanical behaviour of the bio-inspired nanocomposites is studied. Regularly staggered model shows better flow behaviour compared to stair-wise staggered model due to the symmetrical crack propagation along the interface. Though higher stiffness and strength are obtained for stair-wise staggered models, rapid crack propagation reduces the toughness. Arresting this crack propagation could lead to superior mechanical properties in stair-wise staggered models.
Bucciantini, N
2013-01-01
Pulsar Wind Nebulae (PWNe) are ideal astrophysical laboratories where high energy relativistic phenomena can be investigated. They are close, well resolved in our observations, and the knowledge derived in their study has a strong impact in many other fields, from AGNs to GRBs. Yet there are still unresolved issues, that prevent us from a full clear understanding of these objects. The lucky combination of high resolution X-ray imaging and numerical codes to handle the outflow and dynamical properties of relativistic MHD, has opened a new avenue of investigation that has lead to interesting progresses in the last years. Despite all of this, we do not understand yet how particles are accelerated, and the functioning of the pulsar wind and pulsar magnetosphere, that power PWNe. I will review what is now commonly known as the MHD paradigm, and in particular I will focus on various approaches that have been and are currently used to model these systems. For each I will highlight its advantages, limitations, and de...
Institute of Scientific and Technical Information of China (English)
QIAN Jin; WU Shiguo; CUI Ruofei
2013-01-01
Seismic wave modeling is a cornerstone of geophysical data acquisition,processing,and interpretation,for which finite-difference methods are often applied.In this paper,we extend the velocitypressure formulation of the acoustic wave equation to marine seismic modeling using the staggered-grid finite-difference method.The scheme is developed using a fourth-order spatial and a second-order temporal operator.Then,we define a stability coefficient (SC) and calculate its maximum value under the stability condition.Based on the dispersion relationship,we conduct a detailed dispersion analysis for submarine sediments in terms of the phase and group velocity over a range of angles,stability coefficients,and orders.We also compare the numerical solution with the exact solution for a P-wave line source in a homogeneous submarine model.Additionally,the numerical results determined by a Marmousi2 model with a rugged seafloor indicate that this method is sufficient for modeling complex submarine structures.
Investigation of deformation mechanisms of staggered nanocomposites using molecular dynamics
Energy Technology Data Exchange (ETDEWEB)
Mathiazhagan, S., E-mail: smathi.research@gmail.com; Anup, S., E-mail: anupiist@gmail.com
2016-08-19
Biological materials with nanostructure of regularly or stair-wise staggered arrangements of hard platelets reinforced in a soft protein matrix have superior mechanical properties. Applications of these nanostructures to ceramic matrix composites could enhance their toughness. Using molecular dynamics simulations, mechanical behaviour of the bio-inspired nanocomposites is studied. Regularly staggered model shows better flow behaviour compared to stair-wise staggered model due to the symmetrical crack propagation along the interface. Though higher stiffness and strength are obtained for stair-wise staggered models, rapid crack propagation reduces the toughness. Arresting this crack propagation could lead to superior mechanical properties in stair-wise staggered models. - Highlights: • The deformation behaviour of staggered nanocomposites is studied. • Stair-wise staggered model has high stiffness and strength, but low toughness. • Rapid crack growth in overlap region causes this low toughness. • Toughness could be enhanced by arresting interfacial crack in the overlap.
DEFF Research Database (Denmark)
Feng, Ju; Shen, Wen Zhong
2015-01-01
Reliable wind modelling is of crucial importance for wind farm development. The common practice of using sector-wise Weibull distributions has been found inappropriate for wind farm layout optimization. In this study, we propose a simple and easily implementable method to construct joint distribu......Reliable wind modelling is of crucial importance for wind farm development. The common practice of using sector-wise Weibull distributions has been found inappropriate for wind farm layout optimization. In this study, we propose a simple and easily implementable method to construct joint...... quite well in terms of the coefficient of determination R-2. Then, the best of these joint distributions is used in the layout optimization of the Horns Rev 1 wind farm and the choice of bin sizes for wind speed and wind direction is also investigated. It is found that the choice of bin size for wind...... direction is especially critical for layout optimization and the recommended choice of bin sizes for wind speed and wind direction is finally presented....
Reliability Modeling of Wind Turbines
DEFF Research Database (Denmark)
Kostandyan, Erik
Cost reductions for offshore wind turbines are a substantial requirement in order to make offshore wind energy more competitive compared to other energy supply methods. During the 20 – 25 years of wind turbines useful life, Operation & Maintenance costs are typically estimated to be a quarter...... the actions should be made and the type of actions requires knowledge on the accumulated damage or degradation state of the wind turbine components. For offshore wind turbines, the action times could be extended due to weather restrictions and result in damage or degradation increase of the remaining...... for Operation & Maintenance planning. Concentrating efforts on development of such models, this research is focused on reliability modeling of Wind Turbine critical subsystems (especially the power converter system). For reliability assessment of these components, structural reliability methods are applied...
Directory of Open Access Journals (Sweden)
Ju Feng
2015-04-01
Full Text Available Reliable wind modelling is of crucial importance for wind farm development. The common practice of using sector-wise Weibull distributions has been found inappropriate for wind farm layout optimization. In this study, we propose a simple and easily implementable method to construct joint distributions of wind speed and wind direction, which is based on the parameters of sector-wise Weibull distributions and interpolations between direction sectors. It is applied to the wind measurement data at Horns Rev and three different joint distributions are obtained, which all fit the measurement data quite well in terms of the coefficient of determination . Then, the best of these joint distributions is used in the layout optimization of the Horns Rev 1 wind farm and the choice of bin sizes for wind speed and wind direction is also investigated. It is found that the choice of bin size for wind direction is especially critical for layout optimization and the recommended choice of bin sizes for wind speed and wind direction is finally presented.
Li, Y.; Han, B.; Métivier, L.; Brossier, R.
2016-09-01
We investigate an optimal fourth-order staggered-grid finite-difference scheme for 3D frequency-domain viscoelastic wave modeling. An anti-lumped mass strategy is incorporated to minimize the numerical dispersion. The optimal finite-difference coefficients and the mass weighting coefficients are obtained by minimizing the misfit between the normalized phase velocities and the unity. An iterative damped least-squares method, the Levenberg-Marquardt algorithm, is utilized for the optimization. Dispersion analysis shows that the optimal fourth-order scheme presents less grid dispersion and anisotropy than the conventional fourth-order scheme with respect to different Poisson's ratios. Moreover, only 3.7 grid-points per minimum shear wavelength are required to keep the error of the group velocities below 1%. The memory cost is then greatly reduced due to a coarser sampling. A parallel iterative method named CARP-CG is used to solve the large ill-conditioned linear system for the frequency-domain modeling. Validations are conducted with respect to both the analytic viscoacoustic and viscoelastic solutions. Compared with the conventional fourth-order scheme, the optimal scheme generates wavefields having smaller error under the same discretization setups. Profiles of the wavefields are presented to confirm better agreement between the optimal results and the analytic solutions.
The Stagger-grid: A grid of 3D stellar atmosphere models - V. Fe line shapes, shifts and asymmetries
Magic, Zazralt; Asplund, Martin
2014-01-01
We present a theoretical study of the effects and signatures of realistic velocity field and atmospheric inhomogeneities associated with convective motions at the surface of cool late-type stars on the emergent profiles of iron spectral lines for a large range in stellar parameters. We compute 3D spectral line flux profiles under the assumption of local thermodynamic equilibrium (LTE) by employing state-of-the-art, time-dependent, 3D, radiative-hydrodynamical atmosphere models from the Stagger-grid. A set of 35 real unblended, optical FeI and FeII lines of varying excitation potential are considered. Additionally, fictitious Fe i and Fe ii lines (5000A and 0, 2, 4 eV) are used to construct general curves of growth and enable comparison of line profiles with the same line strength to illustrate systematical trends stemming from the intrinsic structural differences among 3D model atmospheres with different stellar parameters. Theoretical line shifts and bisectors are derived to analyze the shapes, shifts, and a...
Magic, Zazralt; Hayek, Wolfgang; Asplund, Martin
2013-01-01
We study the implications of averaging methods with different reference depth scales for 3D hydrodynamical model atmo- spheres computed with the Stagger-code. The temporally and spatially averaged (hereafter denoted as ) models are explored in the light of local thermodynamic equilibrium (LTE) spectral line formation by comparing spectrum calculations using full 3D atmosphere structures with those from averages. We explore methods for computing mean stratifications from the Stagger-grid time-dependent 3D radiative hydro- dynamical atmosphere models by considering four different reference depth scales (geometrical depth, column-mass density, and two optical depth scales). Furthermore, we investigate the influence of alternative averages (logarithmic or enforced hydrostatic equilibrium, flux-weighted temperatures). For the line formation we compute curves of growth for Fe i and Fe ii lines in LTE . The resulting stratifications for the four reference depth scales can be considerably different. We find typica...
Institute of Scientific and Technical Information of China (English)
Zou Guangui; Peng Suping; Yin Caiyun; Deng Xiaojuan; Chen Fengying; Xu Yanyong
2011-01-01
A staggered-grid finite difference method is used to model seismic wave records in a coal bearing,porous medium.The variables analyzed include the order of the difference calculations,the use of a perfect match layer to provide absorbing boundary conditions,the source location,the stability conditions,and dispersion in the medium.The results show that the location of the first derivative of the dynamic variable with respect to space is coincident with the location of the first derivative of the kinematic variable with respect to time.Outgoing waves are effectively absorbed and reflection at the boundary is very weak when more than 20 perfect match layer cells are used.Biot theory considers the liquid phase to be homogeneous so the ratio of liquid to solid exposure of the seismic source depends upon the medium porosity.Numerical dispersion and generation of false frequencies is reduced by increasing the accuracy of the difference calculations and by reducing the grid size and time step.Temporal second order accuracy,a tenth order spatial accuracy,and a wavelength over more than ten grid points gave acceptable numerical results.Larger grid step sizes in the lateral direction and smaller grid sizes in the vertical direction allow control of dispersion when the medium is a low speed body.This provides a useful way to simulate seismic waves in a porous coal bearing medium.
Chu, Chunlei
2009-01-01
We analyze the dispersion properties and stability conditions of the high‐order convolutional finite difference operators and compare them with the conventional finite difference schemes. We observe that the convolutional finite difference method has better dispersion properties and becomes more efficient than the conventional finite difference method with the increasing order of accuracy. This makes the high‐order convolutional operator a good choice for anisotropic elastic wave simulations on rotated staggered grids since its enhanced dispersion properties can help to suppress the numerical dispersion error that is inherent in the rotated staggered grid structure and its efficiency can help us tackle 3D problems cost‐effectively.
Wind speed dynamical model in a wind farm
DEFF Research Database (Denmark)
Soleimanzadeh, Maryam; Wisniewski, Rafal
2010-01-01
, the dynamic model for wind flow will be established. The state space variables are determined based on a fine mesh defined for the farm. The end goal of this method is to assist the development of a dynamical model of a wind farm that can be engaged for better wind farm control strategies....
Etemadsaeed, Leila; Moczo, Peter; Kristek, Jozef; Ansari, Anooshiravan; Kristekova, Miriam
2016-10-01
We investigate the problem of finite-difference approximations of the velocity-stress formulation of the equation of motion and constitutive law on the staggered grid (SG) and collocated grid (CG). For approximating the first spatial and temporal derivatives, we use three approaches: Taylor expansion (TE), dispersion-relation preserving (DRP), and combined TE-DRP. The TE and DRP approaches represent two fundamental extremes. We derive useful formulae for DRP and TE-DRP approximations. We compare accuracy of the numerical wavenumbers and numerical frequencies of the basic TE, DRP and TE-DRP approximations. Based on the developed approximations, we construct and numerically investigate 14 basic TE, DRP and TE-DRP finite-difference schemes on SG and CG. We find that (1) the TE second-order in time, TE fourth-order in space, 2-point in time, 4-point in space SG scheme (that is the standard (2,4) VS SG scheme, say TE-2-4-2-4-SG) is the best scheme (of the 14 investigated) for large fractions of the maximum possible time step, or, in other words, in a homogeneous medium; (2) the TE second-order in time, combined TE-DRP second-order in space, 2-point in time, 4-point in space SG scheme (say TE-DRP-2-2-2-4-SG) is the best scheme for small fractions of the maximum possible time step, or, in other words, in models with large velocity contrasts if uniform spatial grid spacing and time step are used. The practical conclusion is that in computer codes based on standard TE-2-4-2-4-SG, it is enough to redefine the values of the approximation coefficients by those of TE-DRP-2-2-2-4-SG for increasing accuracy of modelling in models with large velocity contrast between rock and sediments.
Directory of Open Access Journals (Sweden)
Antonio J. Torregrosa
2017-05-01
Full Text Available Duct junctions play a major role in the operation and design of most piping systems. The objective of this paper is to establish the potential of a staggered mesh finite volume model as a way to improve the description of the effect of simple duct junctions on an otherwise one-dimensional flow system, such as the intake or exhaust of an internal combustion engine. Specific experiments have been performed in which different junctions have been characterized as a multi-port, and that have provided precise and reliable results on the propagation of pressure pulses across junctions. The results obtained have been compared to simulations performed with a staggered mesh finite volume method with different flux limiters and different meshes and, as a reference, have also been compared with the results of a more conventional pressure loss-based model. The results indicate that the staggered mesh finite volume model provides a closer description of wave dynamics, even if further work is needed to establish the optimal calculation settings.
Constraints on galactic wind models
Meiksin, Avery
2016-09-01
Observational implications are derived for two standard models of supernovae-driven galactic winds: a freely expanding steady-state wind and a wind sourced by a self-similarly expanding superbubble including thermal heat conduction. It is shown that, for the steady-state wind, matching the measured correlation between the soft X-ray luminosity and star formation rate of starburst galaxies is equivalent to producing a scaled wind mass-loading factor relative to the star formation rate of 0.5-3, in agreement with the amount inferred from metal absorption line measurements. The match requires the asymptotic wind velocity v∞ to scale with the star formation rate dot{M}_{ast } (in M⊙ yr-1) approximately as v_∞ ≃ (700-1000) {{km s^{-1}}} {dot{M}_{ast }}^{1/6}. The implied mass injection rate is close to the amount naturally provided by thermal evaporation from the wall of a superbubble in a galactic disc, suggesting that thermal evaporation may be a major source of mass loading. The predicted mass-loading factors from thermal evaporation within the galactic disc alone, however, are somewhat smaller, 0.2-2, so that a further contribution from cloud ablation or evaporation within the wind may be required. Both models may account for the 1.4 GHz luminosity of unresolved radio sources within starburst galaxies for plausible parameters describing the distribution of relativistic electrons. Further observational tests to distinguish the models are suggested.
Establishing the equivalence between Szegedy's and coined quantum walks using the staggered model
Portugal, Renato
2016-04-01
Coined quantum walks (QWs) are being used in many contexts with the goal of understanding quantum systems and building quantum algorithms for quantum computers. Alternative models such as Szegedy's and continuous-time QWs were proposed taking advantage of the fact that quantum theory seems to allow different quantized versions based on the same classical model, in this case the classical random walk. In this work, we show the conditions upon which coined QWs are equivalent to Szegedy's QWs. Those QW models have in common a large class of instances, in the sense that the evolution operators are equal when we convert the graph on which the coined QW takes place into a bipartite graph on which Szegedy's QW takes place, and vice versa. We also show that the abstract search algorithm using the coined QW model can be cast into Szegedy's searching framework using bipartite graphs with sinks.
Active control: Wind turbine model
Energy Technology Data Exchange (ETDEWEB)
Bindner, Henrik
1999-07-01
This report is a part of the reporting of the work done in the project `Active Control of Wind Turbines`. This project aim is to develop a simulation model for design of control systems for turbines with pitch control and to use that model to design controllers. This report describes the model developed for controller design and analysis. Emphasis has been put on establishment of simple models describing the dynamic behavior of the wind turbine in adequate details for controller design. This has been done with extensive use of measurements as the basis for selection of model complexity and model validation as well as parameter estimation. The model includes a simple model of the structure of the turbine including tower and flapwise blade bending, a detailed model of the gear box and induction generator, a linearized aerodynamic model including modelling of induction lag and actuator and sensor models. The models are all formulated as linear differential equations. The models are validated through comparisons with measurements performed on a Vestas WD 34 400 kW wind turbine. It is shown from a control point of view simple linear models can be used to describe the dynamic behavior of a pitch controlled wind turbine. The model and the measurements corresponds well in the relevant frequency range. The developed model is therefore applicable for controller design. (au) EFP-91. 18 ills., 22 refs.
3D change detection in staggered voxels model for robotic sensing and navigation
Liu, Ruixu; Hampshire, Brandon; Asari, Vijayan K.
2016-05-01
3D scene change detection is a challenging problem in robotic sensing and navigation. There are several unpredictable aspects in performing scene change detection. A change detection method which can support various applications in varying environmental conditions is proposed. Point cloud models are acquired from a RGB-D sensor, which provides the required color and depth information. Change detection is performed on robot view point cloud model. A bilateral filter smooths the surface and fills the holes as well as keeps the edge details on depth image. Registration of the point cloud model is implemented by using Random Sample Consensus (RANSAC) algorithm. It uses surface normal as the previous stage for the ground and wall estimate. After preprocessing the data, we create a point voxel model which defines voxel as surface or free space. Then we create a color model which defines each voxel that has a color by the mean of all points' color value in this voxel. The preliminary change detection is detected by XOR subtract on the point voxel model. Next, the eight neighbors for this center voxel are defined. If they are neither all `changed' voxels nor all `no changed' voxels, a histogram of location and hue channel color is estimated. The experimental evaluations performed to evaluate the capability of our algorithm show promising results for novel change detection that indicate all the changing objects with very limited false alarm rate.
Dynamic inversion method based on the time-staggered stereo-modeling scheme and its acceleration
Jing, Hao; Yang, Dinghui; Wu, Hao
2016-12-01
A set of second-order differential equations describing the space-time behaviour of derivatives of displacement with respect to model parameters (i.e. waveform sensitivities) is obtained via taking the derivative of the original wave equations. The dynamic inversion method obtains sensitivities of the seismic displacement field with respect to earth properties directly by solving differential equations for them instead of constructing sensitivities from the displacement field itself. In this study, we have taken a new perspective on the dynamic inversion method and used acceleration approaches to reduce the computational time and memory usage to improve its ability of performing high-resolution imaging. The dynamic inversion method, which can simultaneously use different waves and multicomponent observation data, is appropriate for directly inverting elastic parameters, medium density or wave velocities. Full wavefield information is utilized as much as possible at the expense of a larger amount of calculations. To mitigate the computational burden, two ways are proposed to accelerate the method from a computer-implementation point of view. One is source encoding which uses a linear combination of all shots, and the other is to reduce the amount of calculations on forward modeling. We applied a new finite-difference (FD) method to the dynamic inversion to improve the computational accuracy and speed up the performance. Numerical experiments indicated that the new FD method can effectively suppress the numerical dispersion caused by the discretization of wave equations, resulting in enhanced computational efficiency with less memory cost for seismic modeling and inversion based on the full wave equations. We present some inversion results to demonstrate the validity of this method through both checkerboard and Marmousi models. It shows that this method is also convergent even with big deviations for the initial model. Besides, parallel calculations can be easily
Active control: Wind turbine model
DEFF Research Database (Denmark)
Bindner, H.
1999-01-01
This report is a part of the reporting of the work done in the project 'Active Control of Wind Turbines'. This project aim is to develop a simulation model for design of control systems for turbines with pitch control and to use that model to designcontrollers. This report describes the model...... developed for controller design and analysis. Emphasis has been put on establishment of simple models describing the dynamic behavior of the wind turbine in adequate details for controller design. This hasbeen done with extensive use of measurements as the basis for selection of model complexity and model...... validation as well as parameter estimation. The model includes a simple model of the structure of the turbine including tower and flapwise blade bending,a detailed model of the gear box and induction generator, a linearized aerodynamic model including modelling of induction lag and actuator and sensor models...
Magic, Z.; Weiss, A.; Asplund, M.
2015-01-01
Aims: We investigate the relation between 1D atmosphere models that rely on the mixing length theory and models based on full 3D radiative hydrodynamic (RHD) calculations to describe convection in the envelopes of late-type stars. Methods: The adiabatic entropy value of the deep convection zone, sbot, and the entropy jump, Δs, determined from the 3D RHD models, were matched with the mixing length parameter, αMLT, from 1D hydrostatic atmosphere models with identical microphysics (opacities and equation-of-state). We also derived the mass mixing length parameter, αm, and the vertical correlation length of the vertical velocity, C[vz,vz], directly from the 3D hydrodynamical simulations of stellar subsurface convection. Results: The calibrated mixing length parameter for the Sun is α๏MLT (Sbot) = 1.98. . For different stellar parameters, αMLT varies systematically in the range of 1.7 - 2.4. In particular, αMLT decreases towards higher effective temperature, lower surface gravity and higher metallicity. We find equivalent results for α๏MLT (ΔS). In addition, we find a tight correlation between the mixing length parameter and the inverse entropy jump. We derive an analytical expression from the hydrodynamic mean-field equations that motivates the relation to the mass mixing length parameter, αm, and find that it qualitatively shows a similar variation with stellar parameter (between 1.6 and 2.4) with the solar value of α๏m = 1.83.. The vertical correlation length scaled with the pressure scale height yields 1.71 for the Sun, but only displays a small systematic variation with stellar parameters, the correlation length slightly increases with Teff. Conclusions: We derive mixing length parameters for various stellar parameters that can be used to replace a constant value. Within any convective envelope, αm and related quantities vary strongly. Our results will help to replace a constant αMLT. Appendices are available in electronic form at http
Stellar Winds on the Main-Sequence I: Wind Model
Johnstone, C P; Lüftinger, T; Toth, G; Brott, I
2015-01-01
Aims: We develop a method for estimating the properties of stellar winds for low-mass main-sequence stars between masses of 0.4 and 1.1 solar masses at a range of distances from the star. Methods: We use 1D thermal pressure driven hydrodynamic wind models run using the Versatile Advection Code. Using in situ measurements of the solar wind, we produce models for the slow and fast components of the solar wind. We consider two radically different methods for scaling the base temperature of the wind to other stars: in Model A, we assume that wind temperatures are fundamentally linked to coronal temperatures, and in Model B, we assume that the sound speed at the base of the wind is a fixed fraction of the escape velocity. In Paper II of this series, we use observationally constrained rotational evolution models to derive wind mass loss rates. Results: Our model for the solar wind provides an excellent description of the real solar wind far from the solar surface, but is unrealistic within the solar corona. We run ...
Modeling wind adjustment factor and midflame wind speed for Rothermel's surface fire spread model
Patricia L. Andrews
2012-01-01
Rothermel's surface fire spread model was developed to use a value for the wind speed that affects surface fire, called midflame wind speed. Models have been developed to adjust 20-ft wind speed to midflame wind speed for sheltered and unsheltered surface fuel. In this report, Wind Adjustment Factor (WAF) model equations are given, and the BehavePlus fire modeling...
Constraints on galactic wind models
Meiksin, Avery
2016-01-01
Observational implications are derived for two standard models of supernovae-driven galactic winds: a freely expanding steady-state wind and a wind sourced by a self-similarly expanding superbubble including thermal heat conduction. It is shown that, for the steady-state wind, matching the measured correlation between the soft x-ray luminosity and star formation rate of starburst galaxies is equivalent to producing a scaled wind mass-loading factor relative to the star-formation rate of 0.5 - 3, in agreement with the amount inferred from metal absorption line measurements. The match requires the asymptotic wind velocity v_inf to scale with the star formation rate SFR (in solar masses per year) approximately as v_inf ~ (700 - 1000) km/s SFR^{1/6}. The corresponding mass injection rate is close to the amount naturally provided by thermal evaporation from the wall of a superbubble in a galactic disc, suggesting thermal evaporation may be a major source of mass-loading. The predicted mass-loading factors from the...
Gust modelling for wind loading
Verheij, F.J.; Cleijne, J.W.; Leene, J.A.
1992-01-01
In this paper the TNO gust analysis method and the resulting TNO gust model are described. The method has been applied to a set of 700 hours of stationary wind speed time series measured at the meteorological mast at Cabauw, The Netherlands. The results are discussed in this paper. The TNO gust mode
Gust modelling for wind loading
Verheij, F.J.; Cleijne, J.W.; Leene, J.A.
1992-01-01
In this paper the TNO gust analysis method and the resulting TNO gust model are described. The method has been applied to a set of 700 hours of stationary wind speed time series measured at the meteorological mast at Cabauw, The Netherlands. The results are discussed in this paper. The TNO gust
Kou, Jisheng
2017-06-09
In this paper, a new three-field weak formulation for Stokes problems is developed, and from this, a dual-mixed finite element method is proposed on a rectangular mesh. In the proposed mixed methods, the components of stress tensor are approximated by piecewise constant functions or Q1 functions, while the velocity and pressure are discretized by the lowest-order Raviart-Thomas element and the piecewise constant functions, respectively. Using quadrature rules, we demonstrate that this scheme can be reduced into a finite volume method on staggered grid, which is extensively used in computational fluid mechanics and engineering.
Model county ordinance for wind projects
Energy Technology Data Exchange (ETDEWEB)
Bain, D.A. [Oregon Office of Energy, Portland, OR (United States)
1997-12-31
Permitting is a crucial step in the development cycle of a wind project and permits affect the timing, cost, location, feasibility, layout, and impacts of wind projects. Counties often have the lead responsibility for permitting yet few have appropriate siting regulations for wind projects. A model ordinance allows a county to quickly adopt appropriate permitting procedures. The model county wind ordinance developed for use by northwest states is generally applicable across the country and counties seeking to adopt siting or zoning regulations for wind will find it a good starting place. The model includes permitting procedures for wind measurement devices and two types of wind systems. Both discretionary and nondiscretionary standards apply to wind systems and a conditional use permit would be issued. The standards, criteria, conditions for approval, and process procedures are defined for each. Adaptation examples for the four northwest states are provided along with a model Wind Resource Overlay Zone.
Bohlen, Thomas; Wittkamp, Florian
2016-03-01
We analyse the performance of a higher order accurate staggered viscoelastic time-domain finite-difference method, in which the staggered Adams-Bashforth (ABS) third-order and fourth-order accurate time integrators are used for temporal discretization. ABS is a multistep method that uses previously calculated wavefields to increase the order of accuracy in time. The analysis shows that the numerical dispersion is much lower than that of the widely used second-order leapfrog method. Numerical dissipation is introduced by the ABS method which is significantly smaller for fourth-order than third-order accuracy. In 1-D and 3-D simulation experiments, we verify the convincing improvements of simulation accuracy of the fourth-order ABS method. In a realistic elastic 3-D scenario, the computing time reduces by a factor of approximately 2.4, whereas the memory requirements increase by approximately a factor of 2.2. The ABS method thus provides an alternative strategy to increase the simulation accuracy in time by investing computer memory instead of computing time.
Wind Farm Decentralized Dynamic Modeling With Parameters
DEFF Research Database (Denmark)
Soltani, Mohsen; Shakeri, Sayyed Mojtaba; Grunnet, Jacob Deleuran;
2010-01-01
Development of dynamic wind flow models for wind farms is part of the research in European research FP7 project AEOLUS. The objective of this report is to provide decentralized dynamic wind flow models with parameters. The report presents a structure for decentralized flow models with inputs from...
NLTE wind models of hot subdwarf stars
Krticka, Jiri; 10.1007/s10509-010-0385-z
2010-01-01
We calculate NLTE models of stellar winds of hot compact stars (central stars of planetary nebulae and subdwarf stars). The studied range of subdwarf parameters is selected to cover a large part of these stars. The models predict the wind hydrodynamical structure and provide mass-loss rates for different abundances. Our models show that CNO elements are important drivers of subdwarf winds, especially for low-luminosity stars. We study the effect of X-rays and instabilities on these winds. Due to the line-driven wind instability, a significant part of the wind could be very hot.
Staggered chiral random matrix theory
Osborn, James C
2010-01-01
We present a random matrix theory (RMT) for the staggered lattice QCD Dirac operator. The staggered RMT is equivalent to the zero-momentum limit of the staggered chiral Lagrangian and includes all taste breaking terms at their leading order. This is an extension of previous work which only included some of the taste breaking terms. We will also present some results for the taste breaking contributions to the partition function and the Dirac eigenvalues.
Directory of Open Access Journals (Sweden)
Khalaf A. M.
2012-10-01
Full Text Available By using a computer simulated search program, the experimental gamma transition en- ergies for superdeformed rotational bands (SDRB’s in A 150 region are fitted to proposed three-parameters model. The model parameters and the spin of the bandhead were obtained for the selected ten SDRB’s namely: 150 Gd (yrast and excited SD bands, 151 Tb (yrast and excited SD bands, 152 Dy (yrast SD bands, 148 Gd (SD-1,SD-6, 149 Gd (SD-1, 153 Dy (SD-1 and 148 Eu (SD-1. The Kinematic J (1 and dynamic J (2 moments of inertia are studied as a function of the rotational frequency ~ ω . From the calculated results, we notic that the excited SD bands have identical energies to their Z + 1 neigh- bours for the twinned SD bands in N = 86 nuclei. Also the analysis done allows us to confirm Δ I = 2 staggering in the yrast SD bands of 148 Gd, 149 Gd, 153 Dy, and 148 Eu and in the excited SD bands of 148 Gd, by performing a staggering parameter analysis. For each band, we calculated the deviation of the gamma ray energies from smooth ref- erence representing the finite di ff erence approximation to the fourth derivative of the gamma ray transition energies at a given spin.
Energy Technology Data Exchange (ETDEWEB)
Draxl, C.; Hodge, B. M.; Orwig, K.; Jones, W.; Searight, K.; Getman, D.; Harrold, S.; McCaa, J.; Cline, J.; Clark, C.
2013-10-01
Regional wind integration studies in the United States require detailed wind power output data at many locations to perform simulations of how the power system will operate under high-penetration scenarios. The wind data sets that serve as inputs into the study must realistically reflect the ramping characteristics, spatial and temporal correlations, and capacity factors of the simulated wind plants, as well as be time synchronized with available load profiles. The Wind Integration National Dataset (WIND) Toolkit described in this paper fulfills these requirements. A wind resource dataset, wind power production time series, and simulated forecasts from a numerical weather prediction model run on a nationwide 2-km grid at 5-min resolution will be made publicly available for more than 110,000 onshore and offshore wind power production sites.
Modeling of Wind Energy on Isolated Area
Directory of Open Access Journals (Sweden)
Hachemi Glaoui
2014-03-01
Full Text Available In this paper, a model of the wind turbine (WT with permanent magnet generator (PMSG and its associated controllers is presented, The increase of wind power penetration in power systems has meant that conventional power plants are gradually being replaced by wind farms. In fact, today wind farms are required to actively participate in power system operation in the same way as conventional power plants. In fact, power system operators have revised the grid connection requirements for wind turbines and wind farms, and now demand that these installations be able to carry out more or less the same control tasks as conventional power plants. For dynamic power system simulations, the PMSG wind turbine model includes an aerodynamic rotor model, a lumped mass representation of the drive train system and generator model. In this paper we propose a model with an implementation in MATLAB / Simulink, each of the system components off-grid small wind turbines.
Dynamic Models for Wind Turbines and Wind Power Plants
Energy Technology Data Exchange (ETDEWEB)
Singh, M.; Santoso, S.
2011-10-01
The primary objective of this report was to develop universal manufacturer-independent wind turbine and wind power plant models that can be shared, used, and improved without any restrictions by project developers, manufacturers, and engineers. Manufacturer-specific models of wind turbines are favored for use in wind power interconnection studies. While they are detailed and accurate, their usages are limited to the terms of the non-disclosure agreement, thus stifling model sharing. The primary objective of the work proposed is to develop universal manufacturer-independent wind power plant models that can be shared, used, and improved without any restrictions by project developers, manufacturers, and engineers. Each of these models includes representations of general turbine aerodynamics, the mechanical drive-train, and the electrical characteristics of the generator and converter, as well as the control systems typically used. To determine how realistic model performance is, the performance of one of the models (doubly-fed induction generator model) has been validated using real-world wind power plant data. This work also documents selected applications of these models.
Directory of Open Access Journals (Sweden)
Rajesh Karki
2013-02-01
Full Text Available Adverse environmental impacts of carbon emissions are causing increasing concerns to the general public throughout the world. Electric energy generation from conventional energy sources is considered to be a major contributor to these harmful emissions. High emphasis is therefore being given to green alternatives of energy, such as wind and solar. Wind energy is being perceived as a promising alternative. This source of energy technology and its applications have undergone significant research and development over the past decade. As a result, many modern power systems include a significant portion of power generation from wind energy sources. The impact of wind generation on the overall system performance increases substantially as wind penetration in power systems continues to increase to relatively high levels. It becomes increasingly important to accurately model the wind behavior, the interaction with other wind sources and conventional sources, and incorporate the characteristics of the energy demand in order to carry out a realistic evaluation of system reliability. Power systems with high wind penetrations are often connected to multiple wind farms at different geographic locations. Wind speed correlations between the different wind farms largely affect the total wind power generation characteristics of such systems, and therefore should be an important parameter in the wind modeling process. This paper evaluates the effect of the correlation between multiple wind farms on the adequacy indices of wind-integrated systems. The paper also proposes a simple and appropriate probabilistic analytical model that incorporates wind correlations, and can be used for adequacy evaluation of multiple wind-integrated systems.
Magic, Z.; Collet, R.; Hayek, W.; Asplund, M.
2013-12-01
Aims: We study the implications of averaging methods with different reference depth scales for 3D hydrodynamical model atmospheres computed with the Stagger-code. The temporally and spatially averaged (hereafter denoted as ⟨3D⟩) models are explored in the light of local thermodynamic equilibrium (LTE) spectral line formation by comparing spectrum calculations using full 3D atmosphere structures with those from ⟨3D⟩ averages. Methods: We explored methods for computing mean ⟨3D⟩ stratifications from the Stagger-grid time-dependent 3D radiative hydrodynamical atmosphere models by considering four different reference depth scales (geometrical depth, column-mass density, and two optical depth scales). Furthermore, we investigated the influence of alternative averages (logarithmic, enforced hydrostatic equilibrium, flux-weighted temperatures). For the line formation we computed curves of growth for Fe i and Fe ii lines in LTE. Results: The resulting ⟨3D⟩ stratifications for the four reference depth scales can be very different. We typically find that in the upper atmosphere and in the superadiabatic region just below the optical surface, where the temperature and density fluctuations are highest, the differences become considerable and increase for higher Teff, lower log g, and lower [Fe / H]. The differential comparison of spectral line formation shows distinctive differences depending on which ⟨3D⟩ model is applied. The averages over layers of constant column-mass density yield the best mean ⟨3D⟩ representation of the full 3D models for LTE line formation, while the averages on layers at constant geometrical height are the least appropriate. Unexpectedly, the usually preferred averages over layers of constant optical depth are prone to increasing interference by reversed granulation towards higher effective temperature, in particular at low metallicity. Appendix A is available in electronic form at http://www.aanda.orgMean ⟨3D⟩ models are
Staggered Multi-Field Inflation
Battefeld, Diana; Davis, Anne-Christine
2008-01-01
We investigate multi-field inflationary scenarios with fields that drop out of the model in a staggered fashion. This feature is natural in certain multi-field inflationary setups within string theory; for instance, it can manifest itself when fields are related to tachyons that condense, or inter-brane distances that become meaningless when branes annihilate. Considering a separable potential, and promoting the number of fields to a smooth time-dependent function, we derive the formalism to deal with these models at the background and perturbed level, providing general expressions for the scalar spectral index and the running. We recover known results of e.g. a dynamically relaxing cosmological constant in the appropriate limits. We further show that isocurvature perturbations are suppressed during inflation, so that perturbations are adiabatic and nearly Gaussian. The resulting setup might be interpreted as a novel type of warm inflation, readily implemented within string theory and without many of the shor...
Reliability Modeling of Wind Turbines
DEFF Research Database (Denmark)
Kostandyan, Erik
and uncertainties are quantified. Further, estimation of annual failure probability for structural components taking into account possible faults in electrical or mechanical systems is considered. For a representative structural failure mode, a probabilistic model is developed that incorporates grid loss failures...... components. Thus, models of reliability should be developed and applied in order to quantify the residual life of the components. Damage models based on physics of failure combined with stochastic models describing the uncertain parameters are imperative for development of cost-optimal decision tools...... for Operation & Maintenance planning. Concentrating efforts on development of such models, this research is focused on reliability modeling of Wind Turbine critical subsystems (especially the power converter system). For reliability assessment of these components, structural reliability methods are applied...
Estimation of Wind Turbulence Using Spectral Models
DEFF Research Database (Denmark)
Soltani, Mohsen; Knudsen, Torben; Bak, Thomas
2011-01-01
The production and loading of wind farms are significantly influenced by the turbulence of the flowing wind field. Estimation of turbulence allows us to optimize the performance of the wind farm. Turbulence estimation is; however, highly challenging due to the chaotic behavior of the wind....... In this paper, a method is presented for estimation of the turbulence. The spectral model of the wind is used in order to provide the estimations. The suggested estimation approach is applied to a case study in which the objective is to estimate wind turbulence at desired points using the measurements of wind...... speed outside the wind field. The results show that the method is able to provide estimations which explain more than 50% of the wind turbulence from the distance of about 300 meters....
Wind farm models and control strategies
Energy Technology Data Exchange (ETDEWEB)
Soerensen, Poul; Hansen, Anca D.; Iov, F.; Blaabjerg, F.; Donovan, M.H.
2005-08-01
This report describes models and control strategies for 3 different concepts of wind farms. Initially, the potential in improvement of grid integration, structural loads and energy production is investigated in a survey of opportunities. Then simulation models are described, including wind turbine models for a fixed speed wind turbine with active stall control and a variable speed wind turbine with doubly-fed induction generator. After that, the 3 wind farm concepts and control strategies are described. The 3 concepts are AC connected doubly fed turbines, AC connected active stall turbines and DC connected active stall turbines. Finally, some simulation examples and conclusions are presented. (au)
Wind tunnel measurements of a large wind farm model approaching the infinite wind farm regime
Bossuyt, Juliaan; Howland, Michael; Meneveau, Charles; Meyers, Johan
2016-11-01
A scaled wind farm, with 100 porous disk models of wind turbines, is used to study the effect of wind farm layout on the wind farm power output and its variability, in a wind tunnel study. The wind farm consists of 20 rows and 5 columns. The porous disk models have a diameter of 0 . 03 m and are instrumented with strain gages to measure the thrust force, as a surrogate for wind turbine power output. The frequency response of the measurements goes up to the natural frequency of the models and allows studying the spatio-temporal characteristics of the power output for different layouts. A variety of layouts are considered by shifting the individual rows in the spanwise direction. The reference layout has a regular streamwise spacing of Sx / D = 7 and a spanwise spacing of Sy / D = 5 . The parameter space is further expanded by considering layouts with an uneven streamwise spacing: Sx / D = 3 . 5 & 10 . 5 and Sx / D = 1 . 5 & 12 . 5 . We study how the mean row power changes as a function of wind farm layout and investigate the appearance of an asymptotic limiting behavior as previously described in the literature by application of the top-down model for the spatially averaged wind farm - boundary layer interaction. Work supported by ERC (Grant No. 306471, the ActiveWindFarms project) and by NSF (OISE-1243482, the WINDINSPIRE project).
Wind farm models and control strategies
DEFF Research Database (Denmark)
Sørensen, Poul Ejnar; Hansen, Anca Daniela; Iov, F.;
2005-01-01
models for a fixed speed wind turbine with active stall control and a variable speed wind turbine with doubly-fed induction generator. After that, the 3 wind farm concepts and control strategies are described.The 3 concepts are AC connected doubly fed turbines, AC connected active stall turbines and DC......This report describes models and control strategies for 3 different concepts of wind farms. Initially, the potential in improvement of grid integration, structural loads and energy production is investigated in a survey of opportunities. Then simulationmodels are described, including wind turbine...
Model Predictive Control of Wind Turbines
DEFF Research Database (Denmark)
Henriksen, Lars Christian
the need for maintenance of the wind turbine. Either way, better total-cost-of-ownership for wind turbine operators can be achieved by improved control of the wind turbines. Wind turbine control can be improved in two ways, by improving the model on which the controller bases its design or by improving......Wind turbines play a major role in the transformation from a fossil fuel based energy production to a more sustainable production of energy. Total-cost-of-ownership is an important parameter when investors decide in which energy technology they should place their capital. Modern wind turbines...... are controlled by pitching the blades and by controlling the electro-magnetic torque of the generator, thus slowing the rotation of the blades. Improved control of wind turbines, leading to reduced fatigue loads, can be exploited by using less materials in the construction of the wind turbine or by reducing...
Wind Shear Target Echo Modeling and Simulation
Directory of Open Access Journals (Sweden)
Xiaoyang Liu
2015-01-01
Full Text Available Wind shear is a dangerous atmospheric phenomenon in aviation. Wind shear is defined as a sudden change of speed or direction of the wind. In order to analyze the influence of wind shear on the efficiency of the airplane, this paper proposes a mathematical model of point target rain echo and weather target signal echo based on Doppler effect. The wind field model is developed in this paper, and the antenna model is also studied by using Bessel function. The spectrum distribution of symmetric and asymmetric wind fields is researched by using the mathematical model proposed in this paper. The simulation results are in accordance with radial velocity component, and the simulation results also confirm the correctness of the established model of antenna.
Wang, Y.; Vogt, B.
2001-05-01
Recent worldwide earthquakes have resulted in staggering losses. The Northridge, California; Kobe, Japan; Loma Prieta, California; Izmit, Turkey; Chi-Chi, Taiwan; and Bhuj, India earthquakes, which range from magnitudes 6.7 to 7.7, have all occurred near populated areas. These earthquakes have resulted in estimated losses between \\3 and \\300 billion, with tens to tens of thousands of fatalities. Subduction zones are capable of producing the largest earthquakes. The 1939 M7.8 Chilean, the 1960 M9.5 Chilean, the 1964 M9.2 Alaskan, the 1970 M7.8 Peruvian, the 1985 M7.9 Mexico City and the 2001 M7.7 Bhuj earthquakes are damaging subduction zone quakes. The Cascadia fault zone poses a tremendous hazard in the Pacific Northwest due to the ground shaking and tsunami inundation hazards combined with the population. To address the Cascadia subduction zone threat, the Oregon Department of Geology and Mineral Industries conducted a preliminary statewide loss study. The 1998 Oregon study incorporated a M8.5 quake, the influence of near surface soil effects and default building, social and economic data available in FEMA's HAZUS97 software. Direct financial losses are projected at over \\$12 billion. Casualties are estimated at about 13,000. Over 5,000 of the casualties are estimated to result in fatalities from hazards relating to tsunamis and unreinforced masonry buildings.
Aggregated wind power plant models consisting of IEC wind turbine models
DEFF Research Database (Denmark)
Altin, Müfit; Göksu, Ömer; Hansen, Anca Daniela
2015-01-01
turbines, parameters and models to represent each individual wind turbine in detail makes it necessary to develop aggregated wind power plant models considering the simulation time for power system stability studies. In this paper, aggregated wind power plant models consisting of the IEC 61400-27 variable...
Yan, Hongyong; Yang, Lei; Li, Xiang-Yang
2016-12-01
High-order staggered-grid finite-difference (SFD) schemes have been universally used to improve the accuracy of wave equation modeling. However, the high-order SFD coefficients on spatial derivatives are usually determined by the Taylor-series expansion (TE) method, which just leads to great accuracy at small wavenumbers for wave equation modeling. Some conventional optimization methods can achieve high accuracy at large wavenumbers, but they hardly guarantee the small numerical dispersion error at small wavenumbers. In this paper, we develop new optimal explicit SFD (ESFD) and implicit SFD (ISFD) schemes for wave equation modeling. We first derive the optimal ESFD and ISFD coefficients for the first-order spatial derivatives by applying the combination of the TE and the sampling approximation to the dispersion relation, and then analyze their numerical accuracy. Finally, we perform elastic wave modeling with the ESFD and ISFD schemes based on the TE method and the optimal method, respectively. When the appropriate number and interval for the sampling points are chosen, these optimal schemes have extremely high accuracy at small wavenumbers, and can also guarantee small numerical dispersion error at large wavenumbers. Numerical accuracy analyses and modeling results demonstrate the optimal ESFD and ISFD schemes can efficiently suppress the numerical dispersion and significantly improve the modeling accuracy compared to the TE-based ESFD and ISFD schemes.
The applicability of the wind compression model
Cariková, Zuzana
2014-01-01
Compression of the stellar winds from rapidly rotating hot stars is described by the wind compression model. However, it was also shown that rapid rotation leads to rotational distortion of the stellar surface, resulting in the appearance of non-radial forces acting against the wind compression. In this note we justify the wind compression model for moderately rotating white dwarfs and slowly rotating giants. The former could be conducive to understanding density/ionization structure of the mass outflow from symbiotic stars and novae, while the latter can represent an effective mass-transfer mode in the wide interacting binaries.
Taste breaking in staggered fermions from random matrix theory
Energy Technology Data Exchange (ETDEWEB)
Osborna, James C
2004-03-01
We discuss the construction of a chiral random matrix model for staggered fermions. This model includes O(a{sup 2}) corrections to the continuum limit of staggered fermions and is related to the zero momentum limit of the Lee-Sharpe Lagrangian for staggered fermions. The naive construction based on a specific expansion in lattice spacing (a) of the Dirac matrix produces the term which gives the dominant contribution to the observed taste splitting in the pion masses. A more careful analysis can include extra terms which are also consistent with the symmetries of staggered fermions. Lastly I will mention possible uses of the model including studies of topology and fractional powers of the fermion determinant.
A Comparison of Wind Flow Models for Wind Resource Assessment in Wind Energy Applications
Directory of Open Access Journals (Sweden)
Mathieu Landry
2012-10-01
Full Text Available The objective of this work was to assess the accuracy of various coupled mesoscale-microscale wind flow modeling methodologies for wind energy applications. This is achieved by examining and comparing mean wind speeds from several wind flow modeling methodologies with observational measurements from several 50 m met towers distributed across the study area. At the mesoscale level, with a 5 km resolution, two scenarios are examined based on the Mesoscale Compressible Community Model (MC2 model: the Canadian Wind Energy Atlas (CWEA scenario, which is based on standard input data, and the CWEA High Definition (CWEAHD scenario where high resolution land cover input data is used. A downscaling of the obtained mesoscale wind climate to the microscale level is then performed, where two linear microscale models, i.e., MsMicro and the Wind Atlas Analysis and Application Program (WAsP, are evaluated following three downscaling scenarios: CWEA-WAsP, CWEA-MsMicro and CWEAHD-MsMicro. Results show that, for the territory studied, with a modeling approach based on the MC2 and MsMicro models, also known as Wind Energy Simulation Toolkit (WEST, the use of high resolution land cover and topography data at the mesoscale level helps reduce modeling errors for both the mesoscale and microscale models, albeit only marginally. At the microscale level, results show that the MC2-WAsP modeling approach gave substantially better results than both MC2 and MsMicro modeling approaches due to tweaked meso-micro coupling.
Modeling Sensitivities to the 20% Wind Scenario Report with the WinDS Model
Energy Technology Data Exchange (ETDEWEB)
Blair, N.; Hand, M.; Short, W.; Sullivan, P.
2008-06-01
In May 2008, DOE published '20% Wind Energy by 2030', a report which describes the costs and benefits of producing 20% of the nation's projected electricity demand in 2030 from wind technology. The total electricity system cost resulting from this scenario was modestly higher than a scenario in which no additional wind was installed after 2006. NREL's Wind Deployment System (WinDS) model was used to support this analysis. With its 358 regions, explicit treatment of transmission expansion, onshore siting considerations, shallow- and deep-water wind resources, 2030 outlook, explicit financing assumptions, endogenous learning, and stochastic treatment of wind resource variability, WinDS is unique in the level of detail it can bring to this analysis. For the 20% Wind Energy by 2030 analysis, the group chose various model structures (such as the ability to wheel power within an interconnect), and the wind industry agreed on a variety of model inputs (such as the cost of transmission or new wind turbines). For this paper, the analysis examined the sensitivity of the results to variations in those input values and model structure choices. These included wind cost and performance improvements over time, seasonal/diurnal wind resource variations, transmission access and costs, siting costs, conventional fuel cost trajectories, and conventional capital costs.
Hodge, B.; Orwig, K.; McCaa, J. R.; Harrold, S.; Draxl, C.; Jones, W.; Searight, K.; Getman, D.
2013-12-01
Regional wind integration studies in the United States, such as the Western Wind and Solar Integration Study (WWSIS), Eastern Wind Integration and Transmission Study (EWITS), and Eastern Renewable Generation Integration Study (ERGIS), perform detailed simulations of the power system to determine the impact of high wind and solar energy penetrations on power systems operations. Some of the specific aspects examined include: infrastructure requirements, impacts on grid operations and conventional generators, ancillary service requirements, as well as the benefits of geographic diversity and forecasting. These studies require geographically broad and temporally consistent wind and solar power production input datasets that realistically reflect the ramping characteristics, spatial and temporal correlations, and capacity factors of wind and solar power plant production, and are time-synchronous with load profiles. The original western and eastern wind datasets were generated independently for 2004-2006 using numerical weather prediction (NWP) models run on a ~2 km grid with 10-minute resolution. Each utilized its own site selection process to augment existing wind plants with simulated sites of high development potential. The original dataset also included day-ahead simulated forecasts. These datasets were the first of their kind and many lessons were learned from their development. For example, the modeling approach used generated periodic false ramps that later had to be removed due to unrealistic impacts on ancillary service requirements. For several years, stakeholders have been requesting an updated dataset that: 1) covers more recent years; 2) spans four or more years to better evaluate interannual variability; 3) uses improved methods to minimize false ramps and spatial seams; 4) better incorporates solar power production inputs; and 5) is more easily accessible. To address these needs, the U.S. Department of Energy (DOE) Wind and Solar Programs have funded two
Modelling the wind climate of Ireland
DEFF Research Database (Denmark)
Frank, H.P.; Landberg, L.
1997-01-01
The wind climate of Ireland has been calculated using the Karlsruhe Atmospheric Mesoscale Model KAMM. The climatology is represented by 65 frequency classes of geostrophic wind that were selected as equiangular direction sectors and speed intervals with equal frequency in a sector. The results...
Yang, Lei; Yan, Hongyong; Liu, Hong
2017-03-01
Implicit staggered-grid finite-difference (ISFD) scheme is competitive for its great accuracy and stability, whereas its coefficients are conventionally determined by the Taylor-series expansion (TE) method, leading to a loss in numerical precision. In this paper, we modify the TE method using the minimax approximation (MA), and propose a new optimal ISFD scheme based on the modified TE (MTE) with MA method. The new ISFD scheme takes the advantage of the TE method that guarantees great accuracy at small wavenumbers, and keeps the property of the MA method that keeps the numerical errors within a limited bound at the same time. Thus, it leads to great accuracy for numerical solution of the wave equations. We derive the optimal ISFD coefficients by applying the new method to the construction of the objective function, and using a Remez algorithm to minimize its maximum. Numerical analysis is made in comparison with the conventional TE-based ISFD scheme, indicating that the MTE-based ISFD scheme with appropriate parameters can widen the wavenumber range with high accuracy, and achieve greater precision than the conventional ISFD scheme. The numerical modeling results also demonstrate that the MTE-based ISFD scheme performs well in elastic wave simulation, and is more efficient than the conventional ISFD scheme for elastic modeling.
Modelling and Measuring Flow and Wind Turbine Wakes in Large Wind Farms Offshore
DEFF Research Database (Denmark)
Barthelmie, Rebecca Jane; Hansen, Kurt Schaldemose; Frandsen, Sten Tronæs
2009-01-01
power losses due to wakes and loads. The research presented is part of the EC-funded UpWind project, which aims to radically improve wind turbine and wind farm models in order to continue to improve the costs of wind energy. Reducing wake losses, or even reduce uncertainties in predicting power losses...... of models from computational fluid dynamics (CFD) to wind form models in terms of how accurately they represent wake losses when compared with measurements from offshore wind forms. The ultimate objective is to improve modelling of flow for large wind forms in order to optimize wind form layouts to reduce...... from wakes, contributes to the overall goal of reduced costs. Here, we assess the state of the art in wake and flow modelling for offshore wind forms, the focus so for has been cases at the Horns Rev wind form, which indicate that wind form models require modification to reduce under-prediction of wake...
Modeling and robust control of wind turbine
Gilev, Bogdan
2016-12-01
In this paper a model of a wind turbine is evaluated, consisting of: wind speed model, mechanical and electrical model of generator and tower oscillation model. This model is linearized around of a nominal point. By using the linear model with uncertainties is synthesized a uncertain model. By using the uncertain model and robust control theory is developed a robust controller, which provide mode of stabilizing the rotor frequency and damping the tower oscillations. Finally is simulated work of nonlinear system and robust controller
Extreme gust wind estimation using mesoscale modeling
DEFF Research Database (Denmark)
Larsén, Xiaoli Guo; Kruger, Andries
2014-01-01
through turbulent eddies. This process is modeled using the mesoscale Weather Forecasting and Research (WRF) model. The gust at the surface is calculated as the largest winds over a layer where the averaged turbulence kinetic energy is greater than the averaged buoyancy force. The experiments have been......Currently, the existing estimation of the extreme gust wind, e.g. the 50-year winds of 3 s values, in the IEC standard, is based on a statistical model to convert the 1:50-year wind values from the 10 min resolution. This statistical model assumes a Gaussian process that satisfies the classical...... done for Denmark and two areas in South Africa. For South Africa, the extreme gust atlases from South Africa were created from the output of the mesoscale modelling using Climate Forecasting System Reanalysis (CFSR) forcing for the period 1998 – 2010. The extensive measurements including turbulence...
Modelling the failure behaviour of wind turbines
Faulstich, S.; Berkhout, V.; Mayer, J.; Siebenlist, D.
2016-09-01
Modelling the failure behaviour of wind turbines is an essential part of offshore wind farm simulation software as it leads to optimized decision making when specifying the necessary resources for the operation and maintenance of wind farms. In order to optimize O&M strategies, a thorough understanding of a wind turbine's failure behaviour is vital and is therefore being developed at Fraunhofer IWES. Within this article, first the failure models of existing offshore O&M tools are presented to show the state of the art and strengths and weaknesses of the respective models are briefly discussed. Then a conceptual framework for modelling different failure mechanisms of wind turbines is being presented. This framework takes into account the different wind turbine subsystems and structures as well as the failure modes of a component by applying several influencing factors representing wear and break failure mechanisms. A failure function is being set up for the rotor blade as exemplary component and simulation results have been compared to a constant failure rate and to empirical wind turbine fleet data as a reference. The comparison and the breakdown of specific failure categories demonstrate the overall plausibility of the model.
Jahandari, Hormoz; Ansari, SeyedMasoud; Farquharson, Colin G.
2017-03-01
This study compares two finite-element (FE) and three finite-volume (FV) schemes which use unstructured tetrahedral grids for the modelling of electromagnetic (EM) data. All these schemes belong to a group of differential methods where the electric field is defined along the edges of the elements. The FE and FV schemes are based on both the EM-field and the potential formulations of Maxwell's equations. The EM-field FE scheme uses edge-based (vector) basis functions while the potential FE scheme uses vector and scalar basis functions. All the FV schemes use staggered tetrahedral-Voronoï grids. Three examples are used for comparisons in terms of accuracy and in terms of the computation resources required by generic iterative and direct solvers for solving the problems. Two of these examples represent survey scenarios with electric and magnetic sources and the results are compared with those from the literature while the third example is a comparison against analytical solutions for an electric dipole source. Exactly the same mesh is used for all examples to allow for direct comparison of the various schemes. The results show that while the FE and FV schemes are comparable in terms of accuracy and computation resources, the FE schemes are slightly more accurate but also more expensive than the FV schemes.
Stellar wind models of subluminous hot stars
Krticka, J; Krtickova, I
2016-01-01
Mass-loss rate is one of the most important stellar parameters. We aim to provide mass-loss rates as a function of subdwarf parameters and to apply the formula for individual subdwarfs, to predict the wind terminal velocities, to estimate the influence of the magnetic field and X-ray ionization on the stellar wind, and to study the interaction of subdwarf wind with mass loss from Be and cool companions. We used our kinetic equilibrium (NLTE) wind models with the radiative force determined from the radiative transfer equation in the comoving frame (CMF) to predict the wind structure of subluminous hot stars. Our models solve stationary hydrodynamical equations, that is the equation of continuity, equation of motion, and energy equation and predict basic wind parameters. We predicted the wind mass-loss rate as a function of stellar parameters, namely the stellar luminosity, effective temperature, and metallicity. The derived wind parameters (mass-loss rates and terminal velocities) agree with the values derived...
Modeling of the dynamics of wind to power conversion including high wind speed behavior
DEFF Research Database (Denmark)
Litong-Palima, Marisciel; Bjerge, Martin Huus; Cutululis, Nicolaos Antonio
2016-01-01
of power system studies, but the idea of the proposed wind turbine model is to include the main dynamic effects in order to have a better representation of the fluctuations in the output power and of the fast power ramping especially because of high wind speed shutdowns of the wind turbine. The high wind......This paper proposes and validates an efficient, generic and computationally simple dynamic model for the conversion of the wind speed at hub height into the electrical power by a wind turbine. This proposed wind turbine model was developed as a first step to simulate wind power time series...... for power system studies. This paper focuses on describing and validating the single wind turbine model, and is therefore neither describing wind speed modeling nor aggregation of contributions from a whole wind farm or a power system area. The state-of-the-art is to use static power curves for the purpose...
Wave Modeling of the Solar Wind.
Ofman, Leon
The acceleration and heating of the solar wind have been studied for decades using satellite observations and models. However, the exact mechanism that leads to solar wind heating and acceleration is poorly understood. In order to improve the understanding of the physical mechanisms that are involved in these processes a combination of modeling and observational analysis is required. Recent models constrained by satellite observations show that wave heating in the low-frequency (MHD), and high-frequency (ion-cyclotron) range may provide the necessary momentum and heat input to coronal plasma and produce the solar wind. This review is focused on the results of several recent solar modeling studies that include waves explicitly in the MHD and the kinetic regime. The current status of the understanding of the solar wind acceleration and heating by waves is reviewed.
Modeling Innovations Advance Wind Energy Industry
2009-01-01
In 1981, Glenn Research Center scientist Dr. Larry Viterna developed a model that predicted certain elements of wind turbine performance with far greater accuracy than previous methods. The model was met with derision from others in the wind energy industry, but years later, Viterna discovered it had become the most widely used method of its kind, enabling significant wind energy technologies-like the fixed pitch turbines produced by manufacturers like Aerostar Inc. of Westport, Massachusetts-that are providing sustainable, climate friendly energy sources today.
Spectral coherence model for power fluctuations in a wind farm
DEFF Research Database (Denmark)
Vigueras-Rodriguez, A.; Sørensen, Poul Ejnar; Viedma, A.;
2012-01-01
This paper provides a model for the coherence between wind speeds located in a horizontal plane corresponding to hub height of wind turbines in a large wind farm. The model has been developed using wind speed and power measurements from the 72 Wind Turbines and two of the meteorological masts from...
Time Series Model of Wind Speed for Multi Wind Turbines based on Mixed Copula
Directory of Open Access Journals (Sweden)
Nie Dan
2016-01-01
Full Text Available Because wind power is intermittent, random and so on, large scale grid will directly affect the safe and stable operation of power grid. In order to make a quantitative study on the characteristics of the wind speed of wind turbine, the wind speed time series model of the multi wind turbine generator is constructed by using the mixed Copula-ARMA function in this paper, and a numerical example is also given. The research results show that the model can effectively predict the wind speed, ensure the efficient operation of the wind turbine, and provide theoretical basis for the stability of wind power grid connected operation.
On staggered indecomposable Virasoro modules
Energy Technology Data Exchange (ETDEWEB)
Kytoelae, Kalle [Geneve Univ. (Switzerland); Ridout, David [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
2009-06-15
In this article, certain indecomposable Virasoro modules are studied. Specifically, the Virasoro mode L0 is assumed to be non-diagonalisable, possessing Jordan blocks of rank two. Moreover, the module is further assumed to have a highest weight submodule, the ''left module'', and that the quotient by this submodule yields another highest weight module, the ''right module''. Such modules, which have been called staggered, have appeared repeatedly in the logarithmic conformal field theory literature, but their theory has not been explored in full generality. Here, such a theory is developed for the Virasoro algebra using rather elementary techniques. The focus centres on two different but related questions typically encountered in practical studies: How can one identify a given staggered module, and how can one demonstrate the existence of a proposed staggered module. Given just the values of the highest weights of the left and right modules, themselves subject to simple necessary conditions, invariants are defined which together with the knowledge of the left and right modules uniquely identify a staggered module. The possible values of these invariants form a vector space of dimension zero, one or two, and the structures of the left and right modules limit the isomorphism classes of the corresponding staggered modules to an affine subspace (possibly empty). The number of invariants and affine restrictions is purely determined by the structures of the left and right modules. Moreover, in order to facilitate applications, the expressions for the invariants and restrictions are given by formulae as explicit as possible (they generally rely on expressions for Virasoro singular vectors). Finally, the text is liberally peppered throughout with examples illustrating the general concepts. These have been carefully chosen for their physical relevance or for the novel features they exhibit. (orig.)
On staggered indecomposable Virasoro modules
Kytölä, Kalle; Ridout, David
2009-12-01
In this article, certain indecomposable Virasoro modules are studied. Specifically, the Virasoro mode L0 is assumed to be nondiagonalizable, possessing Jordan blocks of rank 2. Moreover, the module is further assumed to have a highest weight submodule, the "left module," and that the quotient by this submodule yields another highest weight module, the "right module." Such modules, which have been called staggered, have appeared repeatedly in the logarithmic conformal field theory literature, but their theory has not been explored in full generality. Here, such a theory is developed for the Virasoro algebra using rather elementary techniques. The focus centers on two different but related questions typically encountered in practical studies: How can one identify a given staggered module, and how can one demonstrate the existence of a proposed staggered module. Given just the values of the highest weights of the left and right modules, themselves subject to simple necessary conditions, invariants are defined which together with the knowledge of the left and right modules uniquely identify a staggered module. The possible values of these invariants form a vector space of dimension 0, 1, or 2, and the structures of the left and right modules limit the isomorphism classes of the corresponding staggered modules to an affine subspace (possibly empty). The number of invariants and affine restrictions is purely determined by the structures of the left and right modules. Moreover, in order to facilitate applications, the expressions for the invariants and restrictions are given by formulas as explicit as possible (they generally rely on expressions for Virasoro singular vectors). Finally, the text is liberally peppered throughout with examples illustrating the general concepts. These have been carefully chosen for their physical relevance or for the novel features they exhibit.
Physical model tests for floating wind turbines
DEFF Research Database (Denmark)
Bredmose, Henrik; Mikkelsen, Robert Flemming; Borg, Michael
Floating offshore wind turbines are relevant at sites where the depth is too large for the installation of a bottom fixed substructure. While 3200 bottom fixed offshore turbines has been installed in Europe (EWEA 2016), only a handful of floating wind turbines exist worldwide and it is still...... an open question which floater concept is the most economically feasible. The design of the floaters for the floating turbines relies heavily on numerical modelling. While several coupled models exist, data sets for their validation are scarce. Validation, however, is important since the turbine behaviour...... is complex due to the combined actions of aero- and hydrodynamic loads, mooring loads and blade pitch control. The present talk outlines two recent test campaigns with a floating wind turbine in waves and wind. Two floater were tested, a compact TLP floater designed at DTU (Bredmose et al 2015, Pegalajar...
Numerical simulations of stellar winds polytropic models
Keppens, R
1999-01-01
We discuss steady-state transonic outflows obtained by direct numerical solution of the hydrodynamic and magnetohydrodynamic equations. We make use of the Versatile Advection Code, a software package for solving systems of (hyperbolic) partial differential equations. We proceed stepwise from a spherically symmetric, isothermal, unmagnetized, non-rotating Parker wind to arrive at axisymmetric, polytropic, magnetized, rotating models. These represent 2D generalisations of the analytical 1D Weber-Davis wind solution, which we obtain in the process. Axisymmetric wind solutions containing both a `wind' and a `dead' zone are presented. Since we are solving for steady-state solutions, we efficiently exploit fully implicit time stepping. The method allows us to model thermally and/or magneto-centrifugally driven stellar outflows. We particularly emphasize the boundary conditions imposed at the stellar surface. For these axisymmetric, steady-state solutions, we can use the knowledge of the flux functions to verify the...
Magic, Zazralt; Asplund, Martin
2014-01-01
We investigate the relation between 1D atmosphere models that rely on the mixing length theory and models based on full 3D radiative hydrodynamic (RHD) calculations to describe convection in the envelopes of late-type stars. The adiabatic entropy value of the deep convection zone, s_bot, and the entropy jump, {\\Delta}s, determined from the 3D RHD models, are matched with the mixing length parameter, {\\alpha}_MLT, from 1D hydrostatic atmosphere models with identical microphysics (opacities and equation-of-state). We also derive the mass mixing length, {\\alpha}_m, and the vertical correlation length of the vertical velocity, C[v_z,v_z], directly from the 3D hydrodynamical simulations of stellar subsurface convection. The calibrated mixing length parameter for the Sun is {\\alpha}_MLT (s_bot) = 1.98. For different stellar parameters, {\\alpha}_MLT varies systematically in the range of 1.7 - 2.4. In particular, {\\alpha}_MLT decreases towards higher effective temperature, lower surface gravity and higher metallicity...
Spatial modelling of wind speed around windbreaks
Vigiak, O.; Sterk, G.; Warren, A.; Hagen, L.J.
2003-01-01
This paper presents a model to integrate windbreak shelter effects into a Geographic Information System (GIS). The GIS procedure incorporates the 1999 version windbreak sub-model of the Wind Erosion Prediction System (WEPS). Windbreak shelter is modeled in terms of friction velocity reduction, which
Measuring and modelling of the wind on the scale of tall wind turbines
DEFF Research Database (Denmark)
Floors, Rogier Ralph
and the negative wind speed bias at larger heights were not improved when a different synoptic forcing and a different vertical resolution were used in the model. The effect of baroclinity was explored for the two sites. The surface geostrophic wind, the gradient wind and the thermal wind were derived from...... simulations with a mesoscale model. In both locations the thermal wind up to 970 m was approximately Gaussianly distributed with a standard deviation of three m s−1 and the thermal wind vector varied seasonally due to temperature differences between sea and land. The wind veer was particularly sensitive...
Wind deficit model in a wind farm using finite volume method
DEFF Research Database (Denmark)
Soleimanzadeh, Maryam; Wisniewski, Rafal
2010-01-01
A wind deficit model for wind farms is developed in this work using finite volume method. The main question addressed here is to calculate approximately the wind speed in the vicinity of each wind turbine of a farm. The procedure followed is to solve the governing equations of flow for the whole ...
Wind and Diffusion Modeling for Complex Terrain.
Cox, Robert M.; Sontowski, John; Fry, Richard N., Jr.; Dougherty, Catherine M.; Smith, Thomas J.
1998-10-01
Atmospheric transport and dispersion over complex terrain were investigated. Meteorological and sulfur hexafluoride (SF6) concentration data were collected and used to evaluate the performance of a transport and diffusion model coupled with a mass consistency wind field model. Meteorological data were collected throughout April 1995. Both meteorological and plume location and concentration data were measured in December 1995. The meteorological data included measurements taken at 11-15 surface stations, one to three upper-air stations, and one mobile profiler. A range of conditions was encountered, including inversion and postinversion breakup, light to strong winds, and a broad distribution of wind directions.The models used were the MINERVE mass consistency wind model and the SCIPUFF (Second-Order Closure Integrated Puff) transport and diffusion model. These models were expected to provide and use high-resolution three-dimensional wind fields. An objective of the experiment was to determine if these models could provide emergency personnel with high-resolution hazardous plume information for quick response operations.Evaluation of the models focused primarily on their effectiveness as a short-term (1-4 h) predictive tool. These studies showed how they could be used to help direct emergency response following a hazardous material release. For purposes of the experiments, the models were used to direct the deployment of mobile sensors intended to intercept and measure tracer clouds.The April test was conducted to evaluate the performance of the MINERVE wind field generation model. It was evaluated during the early morning radiation inversion, inversion dissipation, and afternoon mixed atmosphere. The average deviations in wind speed and wind direction as compared to observations were within 0.4 m s1 and less than 10° for up to 2 h after data time. These deviations increased as time from data time increased. It was also found that deviations were greatest during
A VERSATILE FAMILY OF GALACTIC WIND MODELS
Energy Technology Data Exchange (ETDEWEB)
Bustard, Chad; Zweibel, Ellen G. [Physics Department, University of Wisconsin-Madison, 1150 University Avenue, Madison, WI 53706 (United States); D’Onghia, Elena, E-mail: bustard@wisc.edu [Department of Astronomy, University of Wisconsin-Madison, 2535 Sterling Hall, 475 N. Charter Street, Madison, WI 53706 (United States)
2016-03-01
We present a versatile family of model galactic outflows including non-uniform mass and energy source distributions, a gravitational potential from an extended mass source, and radiative losses. The model easily produces steady-state wind solutions for a range of mass-loading factors, energy-loading factors, galaxy mass, and galaxy radius. We find that, with radiative losses included, highly mass-loaded winds must be driven at high central temperatures, whereas low mass-loaded winds can be driven at low temperatures just above the peak of the cooling curve, meaning radiative losses can drastically affect the wind solution even for low mass-loading factors. By including radiative losses, we are able to show that subsonic flows can be ignored as a possible mechanism for expelling mass and energy from a galaxy compared to the more efficient transonic solutions. Specifically, the transonic solutions with low mass loading and high energy loading are the most efficient. Our model also produces low-temperature, high-velocity winds that could explain the prevalence of low-temperature material in observed outflows. Finally, we show that our model, unlike the well-known Chevalier and Clegg model, can reproduce the observed linear relationship between wind X-ray luminosity and star formation rate (SFR) over a large range of SFR from 1–1000 M{sub ⊙} yr{sup −1} assuming the wind mass-loading factor is higher for low-mass, and hence, low-SFR galaxies. We also constrain the allowed mass-loading factors that can fit the observed X-ray luminosity versus SFR trend, further suggesting an inverse relationship between mass loading and SFR as explored in advanced numerical simulations.
Modeling of Wind Turbine Gearbox Mounting
Directory of Open Access Journals (Sweden)
Morten K. Ebbesen
2011-10-01
Full Text Available In this paper three bushing models are evaluated to find a best practice in modeling the mounting of wind turbine gearboxes. Parameter identification on measurements has been used to determine the bushing parameters for dynamic simulation of a gearbox including main shaft. The stiffness of the main components of the gearbox has been calculated. The torsional stiffness of the main shaft, gearbox and the mounting of the gearbox are of same order of magnitude, and eigenfrequency analysis clearly reveals that the stiffness of the gearbox mounting is of importance when modeling full wind turbine drivetrains.
Filament winding cylinders. I - Process model
Lee, Soo-Yong; Springer, George S.
1990-01-01
A model was developed which describes the filament winding process of composite cylinders. The model relates the significant process variables such as winding speed, fiber tension, and applied temperature to the thermal, chemical and mechanical behavior of the composite cylinder and the mandrel. Based on the model, a user friendly code was written which can be used to calculate (1) the temperature in the cylinder and the mandrel, (2) the degree of cure and viscosity in the cylinder, (3) the fiber tensions and fiber positions, (4) the stresses and strains in the cylinder and in the mandrel, and (5) the void diameters in the cylinder.
Aeroelastic instability stoppers for wind tunnel models
Doggett, R. V., Jr.; Ricketts, R. H. (Inventor)
1981-01-01
A mechanism for constraining models or sections thereof, was wind tunnel tested, deployed at the onset of aeroelastic instability, to forestall destructive vibrations in the model is described. The mechanism includes a pair of arms pivoted to the tunnel wall and straddling the model. Rollers on the ends of the arms contact the model, and are pulled together against the model by a spring stretched between the arms. An actuator mechanism swings the arms into place and back as desired.
An evolving MHD vortex street model for quasi-periodic solar wind fluctuations
Siregar, Edouard; Roberts, D. A.; Goldstein, Melvyn L.
1992-01-01
Magnetohydrodynamic (MHD) simulation are used to provide a dynamical basis for the 'vortex street' model of the quasi-periodic meridional flow observed by Voyager 2 in the outer heliosphere. Various observations suggest the existence near the current sheet at solar minimum, of a vorticity distribution of two opposite shear layers with an antisymmetric staggered velocity pattern due to structured high-speed wind surrounding low-speed equatorial flow. It is shown that this flow pattern leads to the formation of a highly stable vortex street through the nonlinear interaction of the two shear layers. Spatial profiles of various simulated parameters (velocity, density, meridional flow angle and the location of magnetic sector boundaries) and their relative locations in the quasi-steady vortex street are generally in good agreement with the observations.
Wind models for the NSTS ascent trajectory biasing for wind load alleviation
Smith, O. E.; Adelfang, S. I.; Batts, G. W.
1990-01-01
New concepts are presented for aerospace vehicle ascent wind profile biasing. The purpose for wind biasing the ascent trajectory is to provide ascent wind loads relief and thus decrease the probability for launch delays due to wind loads exceeding critical limits. Wind biasing trajectories to the the profile of monthly mean winds have been widely used for this purpose. The wind profile models presented give additional alternatives for wind biased trajectories. They are derived from the properties of the bivariate normal probability function using the available wind statistical parameters for the launch site. The analytical expressions are presented to permit generalizations. Specific examples are given to illustrate the procedures. The wind profile models can be used to establish the ascent trajectory steering commands to guide the vehicle through the first stage. For the National Space Transportation System (NSTS) program these steering commands are called I-loads.
Some challenges of wind modelling for modern wind turbines: The Weibull distribution
DEFF Research Database (Denmark)
Gryning, Sven-Erik; Batchvarova, Ekatarina; Floors, Rogier;
2012-01-01
Wind power assessments, as well as forecast of wind energy production, are key issues in wind energy and grid related studies. However the hub height of today’s wind turbines is well above the surface layer. Wind profiles studies based on mast data show that the wind profile above the surface layer...... depends on the planetary boundary layer (PBL) structure and height, thus parameters that are not accounted for in today’s traditional applied flow simulation models and parameterizations. Here we report on one year of measurements of the wind profile performed by use of a long range wind lidar (WSL 70) up...... to a height of 600 meters with 50 meters resolution. The lidar is located at a flat coastal site. The applicability of the WRF model to predict some of the important parameters for wind energy has been investigated. In this presentation, some general results on the ability of WRF to predict the wind profile...
Statistical Modelling of Wind Proles - Data Analysis and Modelling
DEFF Research Database (Denmark)
Jónsson, Tryggvi; Pinson, Pierre
The aim of the analysis presented in this document is to investigate whether statistical models can be used to make very short-term predictions of wind profiles.......The aim of the analysis presented in this document is to investigate whether statistical models can be used to make very short-term predictions of wind profiles....
Wind and diffusion modeling for complex terrain
Energy Technology Data Exchange (ETDEWEB)
Cox, R.M.; Sontowski, J.; Fry, R.N. Jr. [and others
1996-12-31
Atmospheric transport and dispersion over complex terrain were investigated. Meteorological and sulfur hexafluoride (SF{sub 6}) concentration data were collected and used to evaluate the performance of a transport and diffusion model coupled with a mass consistency wind field model. Meteorological data were collected throughout April 1995. Both meteorological and concentration data were measured in December 1995. The data included 11 to 15 surface stations, 1 to 3 upper air stations, and 1 mobile profiler. A range of conditions was encountered, including inversion and post-inversion breakup, light to strong winds, and a broad distribution of wind directions. The models used included the SCIPUFF (Second-order Closure Integrated Puff) transport and diffusion model and the MINERVE mass consistency wind model. Evaluation of the models was focused primarily on their effectiveness as a short term (one to four hours) predictive tool. These studies showed how they can be used to help direct emergency response following a hazardous material release. For purposes of the experiments, the models were used to direct the deployment of mobile sensors intended to intercept and measure tracer clouds.
Wake effects and wind farm modelling
Energy Technology Data Exchange (ETDEWEB)
Crespo, A.; Gomez-Elvira, R. [Univ. Politecnica de Madrid, Dept. of Energy and Fluid Mechanic (Spain)
1999-07-01
A model has been developed to treat simultaneously the changes in wind characteristics due to the transition from land to sea, and the wake effects in offshore wind farms. There are beneficial effects both in an increase of power production and in a reduction of turbulence loads when the distance from the farm to the land coast is increased, however, particularly for the turbulence loads, this effect reaches a limit beyond a certain distance of the order of 1 to 2 km. A method has been proposed to estimate the performance of offshore wind farms, that has been applied to places of interest to the project. As it was observed in the project East Coast of the UK, wake effects are important and significant increases can be obtained in power production by increasing the distance between machines and a better disposition of them, i.e. alternating positions in contiguous rows normal to the prevailing wind direction. The most efficient wind farms from the point of view of wake interference are Gedser and Omo with an efficiency of 89% and 86% respectively. A large wind farm like Rodsand has lower efficiency because of the cumulative effect of the wakes of many turbines. The calculated value of the capacity factor of the three Danish wind farms is larger than 36%. The value of the added turbulence intensity, averaged over rows normal to the incident wind, increases suddenly in the first rows and then reaches an almost constant value in the downstream rows, that is of the order of 10%. A method to calculate the performance of very large wind farms, such that they can change the planetary boundary layer is presented. This method has been applied to the wind farms of interest in the project, and small reductions of the order of 5% or less in power production may occur. However, for very large wind farms (with a of the order of 100 km), that may perturb the whole planetary boundary layer, much more drastic reductions, of the order of 50%, may appear, particularly in the
Model of wind shear conditional on turbulence and its impact on wind turbine loads
DEFF Research Database (Denmark)
Dimitrov, Nikolay Krasimirov; Natarajan, Anand; Kelly, Mark C.
2015-01-01
We analyse high-frequency wind velocity measurements from two test stations over a period of several years and at heights ranging from 60 to 200 m, with the objective to validate wind shear predictions as used in load simulations for wind turbine design. A validated wind shear model is thereby...... is most pronounced on the blade flap loads. It is further shown that under moderate wind turbulence, the wind shear exponents may be over-specified in the design standards, and a reduction of wind shear exponent based on the present measurements can contribute to reduced fatigue damage equivalent loads...
Simulation analysis of a wind farm with different aggregated models
DEFF Research Database (Denmark)
Li, H.; Wang, H.; Zhao, B.
2011-01-01
Based on a wind farm including wind turbines with squirrel cage induction generators (SCIGs), different aggregated models of a wind farm, such as a single weighted average model, a reduced-order re-scaled model, a parameter transformed model and a single weighted arithmetic model were presented......, as well as the detailed SCIG wind turbine model. Regarding for the two cases of a wind farm including SCIGs with identical parameters and different parameters, the dynamic characteristics and transient performances of the presented wind farm using different aggregated models were studied and compared...
Multivariable Wind Modeling in State Space
DEFF Research Database (Denmark)
Sichani, Mahdi Teimouri; Pedersen, B. J.
2011-01-01
Turbulence of the incoming wind field is of paramount importance to the dynamic response of wind turbines. Hence reliable stochastic models of the turbulence should be available from which time series can be generated for dynamic response and structural safety analysis. In the paper an empirical...... cross-spectral density function for the along-wind turbulence component over the rotor plane is taken as the starting point. The spectrum is spatially discretized in terms of a Hermitian cross-spectral density matrix for the turbulence state vector which turns out not to be positive definite. Since...... the succeeding state space and ARMA modeling of the turbulence rely on the positive definiteness of the cross-spectral density matrix, the problem with the non-positive definiteness of such matrices is at first addressed and suitable treatments regarding it are proposed. From the adjusted positive definite cross...
Validation of the filament winding process model
Calius, Emilo P.; Springer, George S.; Wilson, Brian A.; Hanson, R. Scott
1987-01-01
Tests were performed toward validating the WIND model developed previously for simulating the filament winding of composite cylinders. In these tests two 24 in. long, 8 in. diam and 0.285 in. thick cylinders, made of IM-6G fibers and HBRF-55 resin, were wound at + or - 45 deg angle on steel mandrels. The temperatures on the inner and outer surfaces and inside the composite cylinders were recorded during oven cure. The temperatures inside the cylinders were also calculated by the WIND model. The measured and calculated temperatures were then compared. In addition, the degree of cure and resin viscosity distributions inside the cylinders were calculated for the conditions which existed in the tests.
IEA Wind Task 37: Systems Modeling Framework and Ontology for Wind Turbines and Plants
Energy Technology Data Exchange (ETDEWEB)
Dykes, Katherine L [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Zahle, Frederik [Technical University of Denmark; Merz, Karl [SINTEF Energy Research; McWilliam, Mike [Technical University of Denmark; Bortolotti, Pietro [Technical University Munich
2017-08-14
This presentation will provide an overview of progress to date in the development of a system modeling framework and ontology for wind turbines and plants as part of the larger IEA Wind Task 37 on wind energy systems engineering. The goals of the effort are to create a set of guidelines for a common conceptual architecture for wind turbines and plants so that practitioners can more easily share descriptions of wind turbines and plants across multiple parties and reduce the effort for translating descriptions between models; integrate different models together and collaborate on model development; and translate models among different levels of fidelity in the system.
Actuator disk model of wind farms based on the rotor average wind speed
DEFF Research Database (Denmark)
Han, Xing Xing; Xu, Chang; Liu, De You;
2016-01-01
Due to difficulty of estimating the reference wind speed for wake modeling in wind farm, this paper proposes a new method to calculate the momentum source based on the rotor average wind speed. The proposed model applies volume correction factor to reduce the influence of the mesh recognition...
Mathematical model for the analysis of wind-turbine wakes
Liu, M.-K.; Yocke, M. A.; Myers, T. C.
1983-02-01
The concept of wind farms with clustered wind turbines at a given site seems to offer an attractive means for extracting wind power on a large scale. Techniques for minimizing the effect of upstream wind-turbine wakes on downstream wind turbines are needed to optimize overall performance of the wind-turbine array. A numerical model for prediction of the interaction of the wind turbine with the prevailing wind flow is described. The model is based on a numerical solution of the three-dimensional Navier-Stokes equations for the planetary boundary layer with the hydrostatic approximation. Three different hypothetical wind-turbine configurations are analyzed to demonstrate the utility of this model. Model predictions from the present study compare favorably with the basic characteristics of measured wind-turbine wakes.
A Versatile Family of Galactic Wind Models
Bustard, Chad; D'Onghia, Elena
2015-01-01
We present a versatile family of model galactic outflows including non-uniform mass and energy source distributions, a gravitational potential from an extended mass source, and radiative losses. The model easily produces steady-state wind solutions for a range of mass-loading factors, energy-loading factors, galaxy mass and galaxy radius. We find that, with radiative losses included, highly mass-loaded winds must be driven at high central temperatures, whereas low mass-loaded winds can be driven at low temperatures just above the peak of the cooling curve, meaning radiative losses can drastically affect the wind solution even for low mass-loading factors. By including radiative losses, we are able to show that subsonic flows can be ignored as a possible mechanism for expelling mass and energy from a galaxy compared to the more efficient transonic solutions. Specifically, the transonic solutions with low mass-loading and high energy-loading are the most efficient. Our model also produces low-temperature, high-...
Truncated Perfect Actions for Staggered Fermions
Bietenholz, W
1998-01-01
We discuss the behavior of free perfect staggered fermions and truncated versions thereof. The study includes flavor non-degenerate masses. We suggest a new blocking scheme, which provides excellent locality of the perfect lattice action. A truncation procedure adequate for the structure of staggered fermions is applied. We consider spectral and thermodynamic properties and compare truncated perfect actions, Symanzik improved and standard staggered fermions in two and four dimensions.
Perfect Lattice Actions for Staggered Fermions
Bietenholz, W; Chandrasekharan, S; Wiese, U J
1996-01-01
We construct a perfect lattice action for staggered fermions by blocking from the continuum. The locality, spectrum and pressure of such perfect staggered fermions are discussed. We also derive a consistent fixed point action for free gauge fields and discuss its locality as well as the resulting static quark-antiquark potential. This provides a basis for the construction of (classically) perfect lattice actions for QCD using staggered fermions.
Comparing satellite SAR and wind farm wake models
DEFF Research Database (Denmark)
Hasager, Charlotte Bay; Vincent, P.; Husson, R.
2015-01-01
The aim of the paper is to present offshore wind farm wake observed from satellite Synthetic Aperture Radar (SAR) wind fields from RADARSAT-1/-2 and Envisat and to compare these wakes qualitatively to wind farm wake model results. From some satellite SAR wind maps very long wakes are observed. Th...
Unsteady aerodynamic modelling of wind turbines
Energy Technology Data Exchange (ETDEWEB)
Coton, F.N.; Galbraith, R.A. [Univ. og Glasgow, Dept. of Aerospace Engineering, Glasgow (United Kingdom)
1997-08-01
The following current and future work is discussed: Collaborative wind tunnel based PIV project to study wind turbine wake structures in head-on and yawed flow. Prescribed wake model has been embedded in a source panel representation of the wind tunnel walls to allow comparison with experiment; Modelling of tower shadow using high resolution but efficient vortex model in tower shadow domain; Extension of model to yawing flow; Upgrading and tuning of unsteady aerodynamic model for low speed, thick airfoil flows. Glasgow has a considerable collection of low speed dynamic stall data. Currently, the Leishman - Beddoes model is not ideally suited to such flows. For example: Range of stall onset criteria used for dynamic stall prediction including Beddoes. Wide variation of stall onset prediction. Beddoes representation was developed primarily with reference to compressible flows. Analyses of low speed data from Glasgow indicate deficiencies in the current model; Predicted versus measured response during ramp down motion. Modification of the Beddoes representation is required to obtain a fit with the measured data. (EG)
Staggered and short-period solutions of the saturable discrete nonlinear Schrodinger equation
DEFF Research Database (Denmark)
Khare, A.; Rasmussen, K.O.; Samuelsen, Mogens Rugholm
2009-01-01
We point out that the nonlinear Schrodinger lattice with a saturable nonlinearity also admits staggered periodic aswell as localized pulse-like solutions. Further, the same model also admits solutions with a short period. We examine the stability of these solutions and find that the staggered...
Wind farm electrical power production model for load flow analysis
Energy Technology Data Exchange (ETDEWEB)
Segura-Heras, Isidoro; Escriva-Escriva, Guillermo; Alcazar-Ortega, Manuel [Institute for Energy Engineering, Universidad Politecnica de Valencia, Camino de Vera, s/n, edificio 8E, escalera F, 2a planta, 46022 Valencia (Spain)
2011-03-15
The importance of renewable energy increases in activities relating to new forms of managing and operating electrical power: especially wind power. Wind generation is increasing its share in the electricity generation portfolios of many countries. Wind power production in Spain has doubled over the past four years and has reached 20 GW. One of the greatest problems facing wind farms is that the electrical power generated depends on the variable characteristics of the wind. To become competitive in a liberalized market, the reliability of wind energy must be guaranteed. Good local wind forecasts are therefore essential for the accurate prediction of generation levels for each moment of the day. This paper proposes an electrical power production model for wind farms based on a new method that produces correlated wind speeds for various wind farms. This method enables a reliable evaluation of the impact of new wind farms on the high-voltage distribution grid. (author)
Some challenges of wind modelling for modern wind turbines: The Weibull distribution
Gryning, Sven-Erik; Batchvarova, Ekatarina; Floors, Rogier; Pena Diaz, Alfredo
2012-01-01
Wind power assessments, as well as forecast of wind energy production, are key issues in wind energy and grid related studies. However the hub height of today’s wind turbines is well above the surface layer. Wind profiles studies based on mast data show that the wind profile above the surface layer depends on the planetary boundary layer (PBL) structure and height, thus parameters that are not accounted for in today’s traditional applied flow simulation models and parameterizations. Here we r...
Directory of Open Access Journals (Sweden)
Shuting Wan
2015-06-01
Full Text Available Natural wind is stochastic, being characterized by its speed and direction which change randomly and frequently. Because of the certain lag in control systems and the yaw body itself, wind turbines cannot be accurately aligned toward the wind direction when the wind speed and wind direction change frequently. Thus, wind turbines often suffer from a series of engineering issues during operation, including frequent yaw, vibration overruns and downtime. This paper aims to study the effects of yaw error on wind turbine running characteristics at different wind speeds and control stages by establishing a wind turbine model, yaw error model and the equivalent wind speed model that includes the wind shear and tower shadow effects. Formulas for the relevant effect coefficients Tc, Sc and Pc were derived. The simulation results indicate that the effects of the aerodynamic torque, rotor speed and power output due to yaw error at different running stages are different and that the effect rules for each coefficient are not identical when the yaw error varies. These results may provide theoretical support for optimizing the yaw control strategies for each stage to increase the running stability of wind turbines and the utilization rate of wind energy.
Contribution to a dynamic wind turbine model validation from a wind farm islanding experiment
DEFF Research Database (Denmark)
Pedersen, Jørgen Kaas; Pedersen, Knud Ole Helgesen; Poulsen, Niels Kjølstad;
2003-01-01
and possible discrepancies are explained. The work with the wind turbine model validation relates to the dynamic stability investigations on incorporation of large amount of wind power in the Danish power grid, where the dynamic wind turbine model is applied.......Measurements from an islanding experiment on the Rejsby Hede wind farm, Denmark, are used for the validation of the dynamic model of grid-connected, stall-controlled wind turbines equipped with induction generators. The simulated results are found to be in good agreement with the measurements...
Wind flow conditions in offshore wind farms. Validation and application of a CFD wake model
Energy Technology Data Exchange (ETDEWEB)
Westerhellweg, Annette; Canadillas, Beatriz; Kinder, Friederike; Neumann, Thomas [Deutsches Windenergie-Institut GmbH (DEWI), Wilhelmshaven (Germany)
2013-04-01
Since August 2009, the first German offshore wind farm 'alpha ventus' is operating close to the wind measurement platform FINO1. Within the research project RAVE-OWEA the wind flow conditions in 'alpha ventus' were assessed in detail, simulated with a CFD wake model and compared with the measurements. Wind data measured at FINO1 have been evaluated for wind speed reduction and turbulence increase in the wake. Additionally operational data were evaluated for the farm efficiency. The atmospheric stability has been evaluated by temperature measurements of air and water and the impact of atmospheric stability on the wind conditions in the wake has been assessed. As an application of CFD models the generation of power matrices is introduced. Power matrices can be used for the continual monitoring of the single wind turbines in the wind farm. A power matrix based on CFD simulations has been created for 'alpha ventus' and tested against the measured data. (orig.)
A combinatorial wind field model
DEFF Research Database (Denmark)
Soleimanzadeh, Maryam; Wisniewski, Rafal; Sloth, Christoffer
2010-01-01
of ordinary dierential equations (ODE). Considering some assumptions on the ow model (e.g. steadiness), the sys- tem can be approximated by a linear n dimensional system. Partitioning the state space into cells is performed by dening Lyapunov function sets, such that each cell is the region between two...... neighboring level surfaces of Lyapunov functions. The resulting discrete system facilitates a supervisory approach to the control....
A combinatorial wind field model
DEFF Research Database (Denmark)
Soleimanzadeh, Maryam; Wisniewski, Rafal; Sloth, Christoffer
2010-01-01
of ordinary dierential equations (ODE). Considering some assumptions on the ow model (e.g. steadiness), the sys- tem can be approximated by a linear n dimensional system. Partitioning the state space into cells is performed by dening Lyapunov function sets, such that each cell is the region between two...... neighboring level surfaces of Lyapunov functions. The resulting discrete system facilitates a supervisory approach to the control....
The Wind Profile in the Coastal Boundary Layer: Wind Lidar Measurements and Numerical Modelling
DEFF Research Database (Denmark)
Floors, Rogier; Vincent, Claire Louise; Gryning, Sven-Erik;
2013-01-01
. By replacing the roughness value for the land-use category in the model with a more representative mesoscale roughness, the observed bias in friction velocity was reduced. A higher-order PBL scheme simulated the wind profile from the west with a lower wind-speed bias at the top of the PBL. For easterly winds...
An improved canopy wind model for predicting wind adjustment factors and wildland fire behavior
W. J. Massman; J. M. Forthofer; M. A. Finney
2017-01-01
The ability to rapidly estimate wind speed beneath a forest canopy or near the ground surface in any vegetation is critical to practical wildland fire behavior models. The common metric of this wind speed is the "mid-flame" wind speed, UMF. However, the existing approach for estimating UMF has some significant shortcomings. These include the assumptions that...
Interval forecasts of a novelty hybrid model for wind speeds
Shanshan Qin; Feng Liu; Jianzhou Wang; Yiliao Song
2015-01-01
The utilization of wind energy, as a booming technology in the field of renewable energies, has been highly regarded around the world. Quantification of uncertainties associated with accurate wind speed forecasts is essential for regulating wind power generation and integration. However, it remains difficult work primarily due to the stochastic and nonlinear characteristics of wind speed series. Traditional models for wind speed forecasting mostly focus on generating certain predictive values...
Dynamic stall model for wind turbine airfoils
DEFF Research Database (Denmark)
Larsen, J.W.; Nielsen, S.R.K.; Krenk, Steen
2007-01-01
A model is presented for aerodynamic lift of wind turbine profiles under dynamic stall. The model combines memory delay effects under attached flow with reduced lift due to flow separation under dynamic stall conditions. The model is based on a backbone curve in the form of the static lift...... conditions, nonstationary effects are included by three mechanisms: a delay of the lift coefficient of fully attached flow via a second-order filter, a delay of the development of separation represented via a first-order filter, and a lift contribution due to leading edge separation also represented via...... during dynamic stall conditions. The proposed model is compared with five other dynamic stall models including, among others, the Beddoes-Leishman model and the ONERA model. It is demonstrated that the proposed model performs equally well or even better than more complicated models and that the included...
Actuator Line Modeling of Wind Turbine Wakes
DEFF Research Database (Denmark)
Troldborg, Niels
2009-01-01
This thesis contains a comprehensive 3D Navier-Stokes computational study of the characteristics of wakes of wind turbines operating in various flow conditions including interacting wakes between a row of turbines. The computations were carried out using the actuator line technique combined...... and it is shown that the turbines are subject to rather severe yaw moments, even in situations where the mean wind is oriented along the row. This observation is indicative of large scale dynamics of the wakes....... with the 3D Navier Stokes solver EllipSys3D and a LES turbulence model. Simple models, based on applying body forces in the computational domain, are developed for imposing sheared and turbulent infow and their validity is discussed. A few computations on stand alone turbines are compared to measurements...
Fundamental time-domain wind turbine models for wind power studies
Energy Technology Data Exchange (ETDEWEB)
Santoso, Surya; Le, Ha Thu [Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78712 (United States)
2007-11-15
One critical task in any wind power interconnection study involves the modelling of wind turbines. This paper provides the most basic yet comprehensive time-domain wind turbine model upon which more sophisticated models along with their power and speed control mechanisms, can be developed. For this reason, this paper concentrates on the modelling of a fixed-speed wind turbine. The model includes turbine's aerodynamic, mechanical, and electrical components. Data for the rotor, drive-train, and electrical generator are given to allow replication of the model in its entirety. Each of the component-blocks of the wind turbine is modelled separately so that one can easily expand the model to simulate variable-speed wind turbines or customise the model to suit their needs. Then, an aggregate wind turbine model, or wind farm, is developed. This is followed by four case studies to demonstrate how the models can be used to study wind turbine operation and power grid integration issues. Results obtained from the case studies show that the models perform as expected. (author)
An improved market penetration model for wind energy technology forecasting
Energy Technology Data Exchange (ETDEWEB)
Lund, P.D. [Helsinki Univ. of Technology, Espoo (Finland). Advanced Energy Systems
1995-12-31
An improved market penetration model with application to wind energy forecasting is presented. In the model, a technology diffusion model and manufacturing learning curve are combined. Based on a 85% progress ratio that was found for European wind manufactures and on wind market statistics, an additional wind power capacity of ca 4 GW is needed in Europe to reach a 30 % price reduction. A full breakthrough to low-cost utility bulk power markets could be achieved at a 24 GW level. (author)
A hybrid wind farm parameterization for mesoscale and climate models
Pan, Y.; Archer, C. L.
2016-12-01
To better understand the potential impacts of wind farms on weather and climate at the local to regional scale, a new hybrid wind farm parameterization is proposed here for mesoscale models, such as the Weather Research and Forecasting Model (WRF), or climate models, such as the Community Atmosphere Model (CAM). All previous wind farm parameterizations treat all the wind turbines in the same grid cell as identical (i.e., they all share the same upstream wind velocity) and ignore the effect of wind direction. By contrast, the new hybrid model considers each individual wind turbine, based on its position in the layout and on wind direction. The new parameterization is developed starting from large eddy simulations (LES) of existing wind farms, in which the local flow around each wind turbine is directly simulated at high spatial ( 3.5 m) and temporal ( 0.1 s) resolutions and the effects of subgrid-scale processes are modeled. Based on analytic and statistical relationships between the LES results and several geometric properties of the wind farm layout (such as blockage ratio and blocking distance), the new hybrid parameterization predicts the local upstream wind speed of each individual wind turbine in the same grid cell, and thus successfully account for the effects of layout and wind direction with little computational cost. With the newly predicted upstream velocity, the turbine-induced forces and added turbulence kinetic energy (TKE) in the atmosphere are derived analytically. The wind speed, wind speed deficit, and TKE profiles and power production obtained with the hybrid parameterization for the test case (the 48-turbine Lillgrund wind farm in Sweden) are in better agreement with the LES results than previous parameterizations. Future work includes the insertion of the hybrid parameterization into the WRF code to assess impacts on near-surface properties, such as temperature and heat and momentum fluxes, in the region surrounding the wind farm.
Forecasting wind power production from a wind farm using the RAMS model
DEFF Research Database (Denmark)
Tiriolo, L.; Torcasio, R. C.; Montesanti, S.;
2015-01-01
The importance of wind power forecast is commonly recognized because it represents a useful tool for grid integration and facilitates the energy trading. This work considers an example of power forecast for a wind farm in the Apennines in Central Italy. The orography around the site is complex...... and the horizontal resolution of the wind forecast has an important role. To explore this point we compared the performance of two 48 h wind power forecasts using the winds predicted by the Regional Atmospheric Modeling System (RAMS) for the year 2011. The two forecasts differ only for the horizontal resolution...... of the ECMWF Integrated Forecasting System (IFS), whose horizontal resolution over Central Italy is about 25 km at the time considered in this paper. Because wind observations were not available for the site, the power curve for the whole wind farm was derived from the ECMWF wind operational analyses available...
Howland, Michael; Bossuyt, Juliaan; Kang, Justin; Meyers, Johan; Meneveau, Charles
2016-11-01
Reducing wake losses in wind farms by deflecting the wakes through turbine yawing has been shown to be a feasible wind farm control approach. In this work, the deflection and morphology of wakes behind a wind turbine operating in yawed conditions are studied using wind tunnel experiments of a wind turbine modeled as a porous disk in a uniform inflow. First, by measuring velocity distributions at various downstream positions and comparing with prior studies, we confirm that the nonrotating wind turbine model in yaw generates realistic wake deflections. Second, we characterize the wake shape and make observations of what is termed a "curled wake," displaying significant spanwise asymmetry. Through the use of a 100 porous disk micro-wind farm, total wind farm power output is studied for a variety of yaw configurations. Strain gages on the tower of the porous disk models are used to measure the thrust force as a substitute for turbine power. The frequency response of these measurements goes up to the natural frequency of the model and allows studying the spatiotemporal characteristics of the power output under the effects of yawing. This work has been funded by the National Science Foundation (Grants CBET-113380 and IIA-1243482, the WINDINSPIRE project). JB and JM are supported by ERC (ActiveWindFarms, Grant No. 306471).
A model to predict the power output from wind farms
Energy Technology Data Exchange (ETDEWEB)
Landberg, L. [Riso National Lab., Roskilde (Denmark)
1997-12-31
This paper will describe a model that can predict the power output from wind farms. To give examples of input the model is applied to a wind farm in Texas. The predictions are generated from forecasts from the NGM model of NCEP. These predictions are made valid at individual sites (wind farms) by applying a matrix calculated by the sub-models of WASP (Wind Atlas Application and Analysis Program). The actual wind farm production is calculated using the Riso PARK model. Because of the preliminary nature of the results, they will not be given. However, similar results from Europe will be given.
Fatigue Reliability and Effective Turbulence Models in Wind Farms
DEFF Research Database (Denmark)
Sørensen, John Dalsgaard; Frandsen, S.; Tarp-Johansen, N.J.
2007-01-01
behind wind turbines can imply a significant reduction in the fatigue lifetime of wind turbines placed in wakes. In this paper the design code model in the wind turbine code IEC 61400-1 (2005) is evaluated from a probabilistic point of view, including the importance of modeling the SN-curve by linear...
Simulation analysis of a wind farm with different aggregated models
DEFF Research Database (Denmark)
Li, H.; Wang, H.; Zhao, B.
2011-01-01
, as well as the detailed SCIG wind turbine model. Regarding for the two cases of a wind farm including SCIGs with identical parameters and different parameters, the dynamic characteristics and transient performances of the presented wind farm using different aggregated models were studied and compared...
Lorenz Wind Disturbance Model Based on Grey Generated Components
Directory of Open Access Journals (Sweden)
Yagang Zhang
2014-11-01
Full Text Available In order to meet the needs of wind speed prediction in wind farms, we consider the influence of random atmospheric disturbances on wind variations. Considering a simplified fluid convection mode, a Lorenz system can be employed as an atmospheric disturbance model. Here Lorenz disturbance is defined as the European norm of the solutions of the Lorenz equation. Grey generating and accumulated generating models are employed to explore the relationship between wind speed and its related disturbance series. We conclude that a linear or quadric polynomial generating model are optimal through the verification of short-term wind speed prediction in the Sotavento wind farm. The new proposed model not only greatly improves the precision of short-term wind speed prediction, but also has great significance for the maintenance and stability of wind power system operation.
Electric solar wind sail mass budget model
Directory of Open Access Journals (Sweden)
P. Janhunen
2013-02-01
Full Text Available The electric solar wind sail (E-sail is a new type of propellantless propulsion system for Solar System transportation, which uses the natural solar wind to produce spacecraft propulsion. The E-sail consists of thin centrifugally stretched tethers that are kept charged by an onboard electron gun and, as such, experience Coulomb drag through the high-speed solar wind plasma stream. This paper discusses a mass breakdown and a performance model for an E-sail spacecraft that hosts a mission-specific payload of prescribed mass. In particular, the model is able to estimate the total spacecraft mass and its propulsive acceleration as a function of various design parameters such as the number of tethers and their length. A number of subsystem masses are calculated assuming existing or near-term E-sail technology. In light of the obtained performance estimates, an E-sail represents a promising propulsion system for a variety of transportation needs in the Solar System.
无灯控错位交叉口交通流模型研究%Traffic Flow Model for Staggered Intersection without Signal Lamp
Institute of Scientific and Technical Information of China (English)
刘小明; 郑淑晖
2012-01-01
错位交叉口交通特性研究对于制定合理有效的错位交叉口交通管控策略具有重要意义.针对无灯控错位交叉口交通流间的冲突过程分别建立了相应的元胞自动机行为规则,进而应用上述规则对不同参数设置下的交通流演化过程进行数值模拟,并分析和讨论了主路进口道交通流密度变化对不同路段交通流平均速度的影响.研究结果表明,错位交叉口主路上较小的车流密度也能导致主路进口道及两T型口中间路段发生交通堵塞,每个T型口主路进口道交通流量变化会对另一个T型口主路进口道交通流平均速度产生较大影响,此外,无灯控下的交通堵塞也会呈现周期性的排队-消散过程.上述方法及结果可为错位交叉口实施信号控制提供有意义的指导.%Traffic characteristics investigation of staggered intersection lays the foundation of scientific and reasonable traffic control strategies. This paper first proposes the cellular automaton rules on the basis of the traffic conflict process analysis. Then with these rules, the traffic flow evolution under different parameters is presented by numerical simulations. The relationship between the arterial road traffic flow density and the average speed is explored. It is revealed that low traffic density on the main road of staggered intersections may lead to traffic congestions on the approach of main road and the road between two T-type intersections, and the average speed of traffic flow on each T-type import of main road was affected by the traffic flow changes of the other T-type approaches. Moreover, the traffic congestion on intersection without signal lamp is presented as a periodically queuing-dissipates process. The above methods and results provide meaningful guidance for traffic management and control implementation of staggered intersections without signal lamp.
Lorenz Wind Disturbance Model Based on Grey Generated Components
Yagang Zhang; Jingyun Yang; Kangcheng Wang; Yinding Wang
2014-01-01
In order to meet the needs of wind speed prediction in wind farms, we consider the influence of random atmospheric disturbances on wind variations. Considering a simplified fluid convection mode, a Lorenz system can be employed as an atmospheric disturbance model. Here Lorenz disturbance is defined as the European norm of the solutions of the Lorenz equation. Grey generating and accumulated generating models are employed to explore the relationship between wind speed and its related disturban...
Wind resource modelling for micro-siting - Validation at a 60-MW wind farm site
Energy Technology Data Exchange (ETDEWEB)
Hansen, J.C.; Gylling Mortensen, N. [Risoe National Lab., Wind Energy and Atmospheric Physics Dept., Roskilde (Denmark); Said, U.S. [New and Renewable Energy Authority, Cairo (Egypt)
1999-03-01
This paper investigates and validates the applicability of the WAsP-model for layout optimization and micro-siting of wind turbines at a given site for a 60-MW wind farm at Zafarana at the Gulf of Suez in Egypt. Previous investigations show large gradients in the wind climate within the area. For the design and optimization of the wind farm it was found necessary to verify the WAsP extrapolation of wind atlas results from 2 existing meteorological masts located 5 and 10 km, respectively, from the wind farm site. On-site measurements at the 3.5 x 3.5 km{sup 2} wind farm site in combination with 7 years of near-site wind atlas measurements offer significant amounts of data for verification of wind conditions for micro-siting. Wind speeds, wind directions, turbulence intensities and guests in 47.5 m a.g.l. have been measured at 9 locations across the site. Additionally, one of the site masts is equipped as a reference mast, measuring both vertical profiles of wind speed and temperature as well as air pressure and temperature. The exercise is further facilitated by the fact that winds are highly uni-directional; the north direction accounting for 80-90% of the wind resource. The paper presents comparisons of 5 months of on-site measurements and modeled predictions from 2 existing meteorological masts located at distances of 5 and 10 km, respectively, from the wind farm site. Predictions based on terrain descriptions of the Wind Atlas for the Gulf of Suez 1991-95 showed over-predictions of wind speeds of 4-10%. With calibrated terrain descriptions, made based on measured data and a re-visit to critical parts of the terrain, the average prediction error of wind speeds was reduced to about 1%. These deviations are smaller than generally expected for such wind resource modeling, clearly documenting the validity of using WAsP modeling for micro-siting and layout optimization of the wind farm. (au)
Fluctuations of offshore wind generation: Statistical modelling
DEFF Research Database (Denmark)
Pinson, Pierre; Christensen, Lasse E.A.; Madsen, Henrik
2007-01-01
The magnitude of power fluctuations at large offshore wind farms has a significant impact on the control and management strategies of their power output. If focusing on the minute scale, one observes successive periods with smaller and larger power fluctuations. It seems that different regimes...... production averaged at a 1, 5, and 10-minute rate. The exercise consists in one-step ahead forecasting of these time-series with the various regime-switching models. It is shown that the MSAR model, for which the succession of regimes is represented by a hidden Markov chain, significantly outperforms...
Estimation of Wind Turbulence Using Spectral Models
DEFF Research Database (Denmark)
Soltani, Mohsen; Knudsen, Torben; Bak, Thomas
2011-01-01
The production and loading of wind farms are significantly influenced by the turbulence of the flowing wind field. Estimation of turbulence allows us to optimize the performance of the wind farm. Turbulence estimation is; however, highly challenging due to the chaotic behavior of the wind. In thi...
Verification of high-speed solar wind stream forecasts using operational solar wind models
Reiss, Martin A.; Temmer, Manuela; Veronig, Astrid M.; Nikolic, Ljubomir; Vennerstrom, Susanne; Schoengassner, Florian; Hofmeister, Stefan J.
2016-01-01
High-speed solar wind streams emanating from coronal holes are frequently impinging on the Earth's magnetosphere causing recurrent, medium-level geomagnetic storm activity. Modeling high-speed solar wind streams is thus an essential element of successful space weather forecasting. Here we evaluate high-speed stream forecasts made by the empirical solar wind forecast (ESWF) and the semiempirical Wang-Sheeley-Arge (WSA) model based on the in situ plasma measurements from the ACE spacecraft for ...
Uncovering wind turbine properties through two-dimensional stochastic modeling of wind dynamics.
Raischel, Frank; Scholz, Teresa; Lopes, Vitor V; Lind, Pedro G
2013-10-01
Using a method for stochastic data analysis borrowed from statistical physics, we analyze synthetic data from a Markov chain model that reproduces measurements of wind speed and power production in a wind park in Portugal. We show that our analysis retrieves indeed the power performance curve, which yields the relationship between wind speed and power production, and we discuss how this procedure can be extended for extracting unknown functional relationships between pairs of physical variables in general. We also show how specific features, such as the rated speed of the wind turbine or the descriptive wind speed statistics, can be related to the equations describing the evolution of power production and wind speed at single wind turbines.
Mesoscale to microscale wind farm flow modeling and evaluation
DEFF Research Database (Denmark)
Sanz Rodrigo, Javier; Chávez Arroyo, Roberto Aurelio; Moriarty, Patrick
2017-01-01
of meteorological and wind engineering flow models and the definition of a formal model evaluation methodology, is a strong area of research for the next generation of wind conditions assessment and wind farm and wind turbine design tools. Some fundamental challenges are identified in order to guide future research...... design tools and meteorological models. The challenge is how to build the bridge between atmospheric and wind engineering model communities and how to establish a comprehensive evaluation process that identifies relevant physical phenomena for wind energy applications with modeling and experimental...... requirements. A framework for model verification, validation, and uncertainty quantification is established to guide this process by a systematic evaluation of the modeling system at increasing levels of complexity. In terms of atmospheric physics, 'building the bridge' means developing models for the so...
Verification of high-speed solar wind stream forecasts using operational solar wind models
Reiss, Martin A.; Temmer, Manuela; Veronig, Astrid M.; Nikolic, Ljubomir; Vennerstrom, Susanne; Schöngassner, Florian; Hofmeister, Stefan J.
2016-07-01
High-speed solar wind streams emanating from coronal holes are frequently impinging on the Earth's magnetosphere causing recurrent, medium-level geomagnetic storm activity. Modeling high-speed solar wind streams is thus an essential element of successful space weather forecasting. Here we evaluate high-speed stream forecasts made by the empirical solar wind forecast (ESWF) and the semiempirical Wang-Sheeley-Arge (WSA) model based on the in situ plasma measurements from the Advanced Composition Explorer (ACE) spacecraft for the years 2011 to 2014. While the ESWF makes use of an empirical relation between the coronal hole area observed in Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images and solar wind properties at the near-Earth environment, the WSA model establishes a link between properties of the open magnetic field lines extending from the photosphere to the corona and the background solar wind conditions. We found that both solar wind models are capable of predicting the large-scale features of the observed solar wind speed (root-mean-square error, RMSE ≈100 km/s) but tend to either overestimate (ESWF) or underestimate (WSA) the number of high-speed solar wind streams (threat score, TS ≈ 0.37). The predicted high-speed streams show typical uncertainties in the arrival time of about 1 day and uncertainties in the speed of about 100 km/s. General advantages and disadvantages of the investigated solar wind models are diagnosed and outlined.
Modeling and identification of harmonic instability problems in wind farms
DEFF Research Database (Denmark)
Ebrahimzadeh, Esmaeil; Blaabjerg, Frede; Wang, Xiongfei;
2016-01-01
to identify harmonic instability problems in wind farms, where many wind turbines, cables, transformers, capacitor banks, shunt reactors, etc, typically are located. This methodology introduces the wind farm as a Multi-Input Multi-Outpur (MIMO) control system, where the linearized models of fast inner control...
Review of Wind Energy Forecasting Methods for Modeling Ramping Events
Energy Technology Data Exchange (ETDEWEB)
Wharton, S; Lundquist, J K; Marjanovic, N; Williams, J L; Rhodes, M; Chow, T K; Maxwell, R
2011-03-28
Tall onshore wind turbines, with hub heights between 80 m and 100 m, can extract large amounts of energy from the atmosphere since they generally encounter higher wind speeds, but they face challenges given the complexity of boundary layer flows. This complexity of the lowest layers of the atmosphere, where wind turbines reside, has made conventional modeling efforts less than ideal. To meet the nation's goal of increasing wind power into the U.S. electrical grid, the accuracy of wind power forecasts must be improved. In this report, the Lawrence Livermore National Laboratory, in collaboration with the University of Colorado at Boulder, University of California at Berkeley, and Colorado School of Mines, evaluates innovative approaches to forecasting sudden changes in wind speed or 'ramping events' at an onshore, multimegawatt wind farm. The forecast simulations are compared to observations of wind speed and direction from tall meteorological towers and a remote-sensing Sound Detection and Ranging (SODAR) instrument. Ramping events, i.e., sudden increases or decreases in wind speed and hence, power generated by a turbine, are especially problematic for wind farm operators. Sudden changes in wind speed or direction can lead to large power generation differences across a wind farm and are very difficult to predict with current forecasting tools. Here, we quantify the ability of three models, mesoscale WRF, WRF-LES, and PF.WRF, which vary in sophistication and required user expertise, to predict three ramping events at a North American wind farm.
Pitchcontrol of wind turbines using model free adaptivecontrol based on wind turbine code
DEFF Research Database (Denmark)
Zhang, Yunqian; Chen, Zhe; Cheng, Ming;
2011-01-01
As the wind turbine is a nonlinear high-order system, to achieve good pitch control performance, model free adaptive control (MFAC) approach which doesn't need the mathematical model of the wind turbine is adopted in the pitch control system in this paper. A pseudo gradient vector whose estimation...
Offshore Wind Energy Cost Modeling Installation and Decommissioning
Kaiser, Mark J
2012-01-01
Offshore wind energy is one of the most promising and fastest growing alternative energy sources in the world. Offshore Wind Energy Cost Modeling provides a methodological framework to assess installation and decommissioning costs, and using examples from the European experience, provides a broad review of existing processes and systems used in the offshore wind industry. Offshore Wind Energy Cost Modeling provides a step-by-step guide to modeling costs over four sections. These sections cover: ·Background and introductory material, ·Installation processes and vessel requirements, ·Installation cost estimation, and ·Decommissioning methods and cost estimation. This self-contained and detailed treatment of the key principles in offshore wind development is supported throughout by visual aids and data tables. Offshore Wind Energy Cost Modeling is a key resource for anyone interested in the offshore wind industry, particularly those interested in the technical and economic aspects of installation and decom...
A transport-rate model of wind-blown sand
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Sand transport by wind plays an important role in environmental problems.Formulating the sand-transport rate model has been of continuing significance,because the majority of the existing models relate sand-transport rate to the wind-shear velocity.However,the wind-shear velocity readapted to blown sand is difficult to determine from the measured wind profiles when sand movement occurs,especially at high wind velocity.Detailed wind tunnel tests were carried out to reformulate the sand-transport rate model,followed by attempts to relate sand-transport rate to parameters of wind velocity,threshold shear-velocity,and grain size.Finally,we validated the model based on the data from field observations.
ΔI = 2 Nuclear Staggering in Superdeformed Rotational Bands
Okasha M. D.
2014-01-01
A four parameters model including collective rotational en ergies to fourth order is ap- plied to reproduce the ∆ I = 2 staggering in transition energies in four selected super deformed rotational bands, namely, 148 Gd (SD6), 194 Hg (SD1, SD2, SD3). The model parameters and the spin of the bandhead have been extracted a ssuming various val- ues to the lowest spin of the bandhead at nearest integer, in o rder to obtain a minim...
Modeling of wind turbines with doubly fed generator system
Fortmann, Jens
2014-01-01
Jens Fortmann describes the deduction of models for the grid integration of variable speed wind turbines and the reactive power control design of wind plants. The modeling part is intended as background to understand the theory, capabilities and limitations of the generic doubly fed generator and full converter wind turbine models described in the IEC 61400-27-1 and as 2nd generation WECC models that are used as standard library models of wind turbines for grid simulation software. Focus of the reactive power control part is a deduction of the origin and theory behind the reactive current requ
Effective turbulence models and fatigue reliability in wind farms
DEFF Research Database (Denmark)
Sørensen, John Dalsgaard; Frandsen, Sten Tronæs; Tarp-Johansen, N.J.
2008-01-01
intensity in wakes behind wind turbines can imply a significant reduction in the fatigue lifetime of wind turbines placed in wakes. Ill this paper the design code model ill the wind turbine code [IEC 61400-1, Wind turbine generator systems - Part 1: Safety requirements. 2005] is evaluated from...... a probabilistic point of view, including the importance of modeling the SN-curve by a bi-linear model. Fatigue models relevant for welded, cast steel and fiber reinforced details are considered. Further, the influence on the fatigue reliability is investigated from modeling the fatigue response by a stochastic...
Frequency weighted model predictive control of wind turbine
DEFF Research Database (Denmark)
Klauco, Martin; Poulsen, Niels Kjølstad; Mirzaei, Mahmood;
2013-01-01
This work is focused on applying frequency weighted model predictive control (FMPC) on three blade horizontal axis wind turbine (HAWT). A wind turbine is a very complex, non-linear system influenced by a stochastic wind speed variation. The reduced dynamics considered in this work...... are the rotational degree of freedom of the rotor and the tower for-aft movement. The MPC design is based on a receding horizon policy and a linearised model of the wind turbine. Due to the change of dynamics according to wind speed, several linearisation points must be considered and the control design adjusted...... accordingly. In practice is very hard to measure the effective wind speed, this quantity will be estimated using measurements from the turbine itself. For this purpose stationary predictive Kalman filter has been used. Stochastic simulations of the wind turbine behaviour with applied frequency weighted model...
Global empirical wind model for the upper mesosphere/lower thermosphere. I. Prevailing wind
Directory of Open Access Journals (Sweden)
Y. I. Portnyagin
Full Text Available An updated empirical climatic zonally averaged prevailing wind model for the upper mesosphere/lower thermosphere (70-110 km, extending from 80°N to 80°S is presented. The model is constructed from the fitting of monthly mean winds from meteor radar and MF radar measurements at more than 40 stations, well distributed over the globe. The height-latitude contour plots of monthly mean zonal and meridional winds for all months of the year, and of annual mean wind, amplitudes and phases of annual and semiannual harmonics of wind variations are analyzed to reveal the main features of the seasonal variation of the global wind structures in the Northern and Southern Hemispheres. Some results of comparison between the ground-based wind models and the space-based models are presented. It is shown that, with the exception of annual mean systematic bias between the zonal winds provided by the ground-based and space-based models, a good agreement between the models is observed. The possible origin of this bias is discussed.
Key words: Meteorology and Atmospheric dynamics (general circulation; middle atmosphere dynamics; thermospheric dynamics
Chiral random matrix theory for staggered fermions
Osborn, James C
2012-01-01
We present a completed random matrix theory for staggered fermions which incorporates all taste symmetry breaking terms at their leading order from the staggered chiral Lagrangian. This is an extension of previous work which only included some of the taste breaking terms. We will also discuss the effects of taste symmetry breaking on the eigenvalues in the weak and strong taste breaking limits, and compare with some results from lattice simulations.
交错桁架结构分析中楼板模型的比选%Slab model in the construction analysis of staggered-truss system
Institute of Scientific and Technical Information of China (English)
周诗强; 许红胜
2011-01-01
Combined with the domestic common structure design software ETABS,SAP2000 and PKPM,an example is analyzed based on the assumption of rigid slab and flexible slab,which can be used to analyse the influence of entire structure.It is demonstrated that the assumption of three-dimensional rigid slab can satisfy the accuracy of global analysis in staggered-truss system.%针对刚性楼板假定和柔性楼板假定,结合国内常用的结构设计软件ETABS、SAP2000和PKPM,通过算例对比分析,得出不同楼板假定对交错桁架整体分析结果的影响情况.研究结果表明,基于空间三维分析的刚性楼板假定能够满足交错桁架结构整体分析的精度要求.
DEFF Research Database (Denmark)
Draxl, Caroline; Hahmann, Andrea N.; Pena Diaz, Alfredo
2014-01-01
The existence of vertical wind shear in the atmosphere close to the ground requires that wind resource assessment and prediction with numerical weather prediction (NWP) models use wind forecasts at levels within the full rotor span of modern large wind turbines. The performance of NWP models...... regarding wind energy at these levels partly depends on the formulation and implementation of planetary boundary layer (PBL) parameterizations in these models. This study evaluates wind speeds and vertical wind shears simulated by theWeather Research and Forecasting model using seven sets of simulations...
Models for wind turbines - a collection
Energy Technology Data Exchange (ETDEWEB)
Larsen, G.C.; Hansen, M.H. (eds.); Baumgart, A.
2002-02-01
This report is a collection of notes which were intended to be short communications. Main target of the work presented is to supply new approaches to stability investigations of wind turbines. The authors opinion is that an efficient, systematic stability analysis can not be performed for large systems of differential equations (i.e. the order of the differential equations > 100), because numerical 'effects' in the solution of the equations of motion as initial value problem, eigenvalue problem or whatsoever become predominant. It is therefore necessary to find models which are reduced to the elementary coordinates but which can still describe the physical processes under consideration with sufficiently good accuracy. Such models are presented. (au)
A phenomenological model for the dynamic response of wind turbines to turbulent wind
Energy Technology Data Exchange (ETDEWEB)
Rauh, Alexander; Peinke, Joachim [Institut fur Physik, Universitat Oldenburg, D-26111 Oldenburg (Germany)
2004-02-01
To predict the average power output of a wind turbine, a response model is proposed which takes into account: (1) the delayed response to the longitudinal wind speed fluctuations; (2) a response function of the turbine with arbitrary frequency dependence; and (3) wind fields of arbitrary turbulence intensity. In the limit of low turbulence intensity, the dynamical ansatz as proposed in 1992 by Rosen and Sheinman is reproduced. It is shown, how the response function of the turbine can be obtained from simulation experiments of a specific wind turbine. For two idealized situations the dynamic effect of fluctuating wind is estimated at turbulence intensities 0{<=}I{sub u}{<=}0.5. At the special mean wind speed V=8m/s, the turbine response function is determined from simulation data published by Sheinman and Rosen in 1992 and 1994.
Wind Turbine and Wind Power Plant Modelling Aspects for Power System Stability Studies
DEFF Research Database (Denmark)
Altin, Müfit; Hansen, Anca Daniela; Göksu, Ömer;
2014-01-01
turbine model which is developed for the short-term voltage stability studies can be inaccurate and sufficient for the frequency stability studies. Accordingly, a complete and detailed wind power plant model for every kind of study is not feasible in terms of the computational time and also...... is not reasonable regarding the focus of the study. Therefore the power system operators should be aware of the modelling aspects of the wind power considering the related stability study and implement the required model in the appropriate power system toolbox. In this paper, the modelling aspects of wind turbines...... and wind power plants are reviewed for power system stability studies. Important remarks of the models are presented by means of simulations to emphasize the impact of these modelling details on the power system....
Condition Parameter Modeling for Anomaly Detection in Wind Turbines
Directory of Open Access Journals (Sweden)
Yonglong Yan
2014-05-01
Full Text Available Data collected from the supervisory control and data acquisition (SCADA system, used widely in wind farms to obtain operational and condition information about wind turbines (WTs, is of important significance for anomaly detection in wind turbines. The paper presents a novel model for wind turbine anomaly detection mainly based on SCADA data and a back-propagation neural network (BPNN for automatic selection of the condition parameters. The SCADA data sets are determined through analysis of the cumulative probability distribution of wind speed and the relationship between output power and wind speed. The automatic BPNN-based parameter selection is for reduction of redundant parameters for anomaly detection in wind turbines. Through investigation of cases of WT faults, the validity of the automatic parameter selection-based model for WT anomaly detection is verified.
Modelling studies of wind field on urban environment
Directory of Open Access Journals (Sweden)
K. Radics
2002-11-01
Full Text Available Increasing load of air pollution in urban environment emphasises the need for detailed evaluation of wind characteristics that significantly affect the air quality of urban areas, especially, in large agglomerations. This paper includes analysis of urban wind climatology and estimation of wind profiles based on measurements of the new urban climate station located at the Eötvös University, observations of the meteorological station network of the Budapest agglomeration area, and multi-level wind measurements near Hegyhátsál. Furthermore, wind field modelling (using the WAsP linear spectral wind flow model is presented over selected representative complex areas that demonstrates strong dependence between wind, height, topography, and roughness.
Directory of Open Access Journals (Sweden)
F. C. Odo, G. U. Akubue, S. U. Offiah, P. E. Ugwuoke
2013-01-01
Full Text Available In this paper, we use the correlation between the average wind speed and ambient temperature to develop models for predicting wind potentials for two Nigerian locations. Assuming that the troposphere is a typical heterogeneous mixture of ideal gases, we find that for the studied locations, wind speed clearly correlates with ambient temperature in a simple polynomial of 3rd degree. The coefficient of determination and root-mean-square error of the models are 0.81; 0.0024 and 0.56; 0.0041, respectively, for Enugu (6.40N; 7.50E and Owerri (5.50N; 7.00E. These results suggest that the temperature-based model can be used, with acceptable accuracy, in predicting wind potentials needed for preliminary design assessment of wind energy conversion devices for the locations and others with similar meteorological conditions.
Modelling of offshore wind turbine wakes with the wind farm program FLaP
DEFF Research Database (Denmark)
Lange, B.; Waldl, H.P.; Guerrero, A.G.
2003-01-01
The wind farm layout program FLaP estimates the wind speed at any point in a wind farm and the power output of the turbines. The ambient flow conditions and the properties of the turbines and the farm are used as input. The core of the program is an axisymmetric wake model describing the wake...... been extended to improve the description of wake development in offshore conditions, especially the low ambient turbulence and the effect of atmospheric stability. Model results are compared with measurements from the Danish offshore wind farm Vindeby. Vertical wake profiles and mean turbulence...... intensities in the wake are compared for single-, double- and quintuple-wake cases with different mean wind speed, turbulence intensity and atmospheric stability. It is found that within the measurement uncertainties the results of the wake model compare well with the measurements for the most important...
Energy Technology Data Exchange (ETDEWEB)
Odo, F.C. [National Centre for Energy Research and Development, University of Nigeria, Nsukka (Nigeria); Department of Physics and Astronomy, University of Nigeria, Nsukka (Nigeria); Akubue, G.U.; Offiah, S.U.; Ugwuoke, P.E. [National Centre for Energy Research and Development, University of Nigeria, Nsukka (Nigeria)
2013-07-01
In this paper, we use the correlation between the average wind speed and ambient temperature to develop models for predicting wind potentials for two Nigerian locations. Assuming that the troposphere is a typical heterogeneous mixture of ideal gases, we find that for the studied locations, wind speed clearly correlates with ambient temperature in a simple polynomial of 3rd degree. The coefficient of determination and root-mean-square error of the models are 0.81; 0.0024 and 0.56; 0.0041, respectively, for Enugu (6.40N; 7.50E) and Owerri (5.50N; 7.00E). These results suggest that the temperature-based model can be used, with acceptable accuracy, in predicting wind potentials needed for preliminary design assessment of wind energy conversion devices for the locations and others with similar meteorological conditions.
Glide back booster wind tunnel model testing
Pricop, M. V.; Cojocaru, M. G.; Stoica, C. I.; Niculescu, M. L.; Neculaescu, A. M.; Persinaru, A. G.; Boscoianu, M.
2017-07-01
Affordable space access requires partial or ideally full launch vehicle reuse, which is in line with clean environment requirement. Although the idea is old, the practical use is difficult, requiring very large technology investment for qualification. Rocket gliders like Space Shuttle have been successfullyoperated but the price and correspondingly the energy footprint were found not sustainable. For medium launchers, finally there is a very promising platform as Falcon 9. For very small launchers the situation is more complex, because the performance index (payload to start mass) is already small, versus medium and heavy launchers. For partial reusable micro launchers this index is even smaller. However the challenge has to be taken because it is likely that in a multiyear effort, technology is going to enable the performance recovery to make such a system economically and environmentally feasible. The current paper is devoted to a small unitary glide back booster which is foreseen to be assembled in a number of possible configurations. Although the level of analysis is not deep, the solution is analyzed from the aerodynamic point of view. A wind tunnel model is designed, with an active canard, to enablea more efficient wind tunnel campaign, as a national level premiere.
Probabilistic Modeling of Wind Turbine Drivetrain Components
DEFF Research Database (Denmark)
Rafsanjani, Hesam Mirzaei
Wind energy is one of several energy sources in the world and a rapidly growing industry in the energy sector. When placed in offshore or onshore locations, wind turbines are exposed to wave excitations, highly dynamic wind loads and/or the wakes from other wind turbines. Therefore, most components....../nodules on fatigue life of cast iron samples. The cast iron samples scanned by 3D tomography equipment at the DTU Wind Energy (Risø campus), and the distribution of nodules are used to estimate the fatigue life....
An integrated dynamic model of a flexible wind turbine
Bongers, Peter M. M.; Bierbooms, Wim A. A.; Dijkstra, Sjoerd; Vanholten, Theo
1990-06-01
A model to study the dynamic behavior of flexible wind turbines was developed. The different subsystems of the wind turbine are individually modeled with about the same degree of accuracy. The aerodynamic part describes wind shear, gravity effects, unsteady effects, and dynamic inflow. The rotor blades are provided with degrees of freedom in lag and flap directions. The tower construction is modeled including the first bending mode. The first torsional mode of the transmission is included in the model. The model of synchronous generator with dc link consists of a nonlinear fourth order model, including saturation effects. The different models of the subsystems are coupled into one integrated dynamic model which is implemented as simulation code in the DUWECS (Delf University Wind Energy Converter Simulation Package) program. The DUWECS program is developed in such a manner that it is an easy to handle tool for the study of the dynamic features of wind turbine systems.
Institute of Scientific and Technical Information of China (English)
Zhuo-dong ZHANG; Ralf WIELAND; Matthias REICHE; Roger FUNK; Carsten HOFFMANN; Yong LI; Michael SOMMER
2012-01-01
To provide physically based wind modelling for wind erosion research at regional scale,a 3D computational fluid dynamics (CFD) wind model was developed.The model was programmed in C language based on the Navier-Stokes equations,and it is freely available as open source.Integrated with the spatial analysis and modelling tool (SAMT),the wind model has convenient input preparation and powerful output visualization.To validate the wind model,a series of experiments was conducted in a wind tunnel.A blocking inflow experiment was designed to test the performance of the model on simulation of basic fluid processes.A round obstacle experiment was designed to check if the model could simulate the influences of the obstacle on wind field.Results show that measured and simulated wind fields have high correlations,and the wind model can simulate both the basic processes of the wind and the influences of the obstacle on the wind field.These results show the high reliability of the wind model.A digital elevation model (DEM) of an area (3800 m long and 1700 m wide) in the Xilingele grassland in Inner Mongolia (autonomous region,China) was applied to the model,and a 3D wind field has been successfully generated.The clear implementation of the model and the adequate validation by wind tunnel experiments laid a solid foundation for the prediction and assessment of wind erosion at regional scale.
3-D Radiative Transfer Modeling of Structured Winds in Massive Hot Stars with Wind3D
Lobel, A; Blomme, R
2010-01-01
We develop 3-D models of the structured winds of massive hot stars with the Wind3D radiative transfer (RT) code. We investigate the physical properties of large-scale structures observed in the wind of the B-type supergiant HD 64760 with detailed line profile fits to Discrete Absorption Components (DACs) and rotational modulations observed with IUE in Si IV {\\lambda}1395. We develop parameterized input models Wind3D with large-scale equatorial wind density- and velocity-structures, or so-called `Co-rotating Interaction Regions' (CIRs) and `Rotational Modulation Regions' (RMRs). The parameterized models offer important advantages for high-performance RT calculations over ab-initio hydrodynamic input models. The acceleration of the input model calculations permits us to simulate and investigate a wide variety of physical conditions in the extended winds of massive hot stars. The new modeling method is very flexible for constraining the dynamic and geometric wind properties of RMRs in HD 64760. We compute that t...
SimWIND: A Geospatial Infrastructure Model for Wind Energy Production and Transmission
Middleton, R. S.; Phillips, B. R.; Bielicki, J. M.
2009-12-01
Wind is a clean, enduring energy resource with a capacity to satisfy 20% or more of the electricity needs in the United States. A chief obstacle to realizing this potential is the general paucity of electrical transmission lines between promising wind resources and primary load centers. Successful exploitation of this resource will therefore require carefully planned enhancements to the electric grid. To this end, we present the model SimWIND for self-consistent optimization of the geospatial arrangement and cost of wind energy production and transmission infrastructure. Given a set of wind farm sites that satisfy meteorological viability and stakeholder interest, our model simultaneously determines where and how much electricity to produce, where to build new transmission infrastructure and with what capacity, and where to use existing infrastructure in order to minimize the cost for delivering a given amount of electricity to key markets. Costs and routing of transmission line construction take into account geographic and social factors, as well as connection and delivery expenses (transformers, substations, etc.). We apply our model to Texas and consider how findings complement the 2008 Electric Reliability Council of Texas (ERCOT) Competitive Renewable Energy Zones (CREZ) Transmission Optimization Study. Results suggest that integrated optimization of wind energy infrastructure and cost using SimWIND could play a critical role in wind energy planning efforts.
Dynamic wind turbine models in power system simulation tool
DEFF Research Database (Denmark)
Hansen, Anca D.; Iov, Florin; Sørensen, Poul
This report presents a collection of models and control strategies developed and implemented in the power system simulation tool PowerFactory DIgSILENT for different wind turbine concepts. It is the second edition of Risø-R-1400(EN) and it gathers and describes a whole wind turbine model database...... strategies have different goals e.g. fast response over disturbances, optimum power efficiency over a wider range of wind speeds, voltage ride-through capability including grid support. A dynamic model of a DC connection for active stall wind farms to the grid including the control is also implemented...
Wall Correction Model for Wind Tunnels with Open Test Section
DEFF Research Database (Denmark)
Sørensen, Jens Nørkær; Shen, Wen Zhong; Mikkelsen, Robert Flemming
2004-01-01
In th paper we present a correction model for wall interference on rotors of wind turbines or propellers in wind tunnels. The model, that is based on a onedimensional momentum approach, is validated against results from CFD computations using a generalized actuator disc principle. Generally......, the corrections from the model are in very good agreement with the CFD computaions, demonstrating that one-dimensional momentum theory is a reliable way of predicting corrections for wall interference in wind tunnels with closed as well as open cross sections. Keywords: Wind tunnel correction, momentum theory...
Stochastic wind turbine modeling for individual pitch control
DEFF Research Database (Denmark)
Thomsen, Sven Creutz; Niemann, Hans Henrik; Poulsen, Niels Kjølstad
2009-01-01
By pitching the blades of a wind turbine individually it is possible to attenuate the asymmetric loads caused by a non-uniform wind field - this is denoted individual pitch control. In this work we investigate how to set up a simplified stochastic and deterministic description of the wind...... and a simplified description of the aerodynamics with sufficient detail to design model-based individual pitch controllers. Combined with a simplified model of the wind turbine, we exemplify how to use the model elements to systematically design an individual pitch controller. The design is investigated...
Accurate wind farm development and operation. Advanced wake modelling
Energy Technology Data Exchange (ETDEWEB)
Brand, A.; Bot, E.; Ozdemir, H. [ECN Unit Wind Energy, P.O. Box 1, NL 1755 ZG Petten (Netherlands); Steinfeld, G.; Drueke, S.; Schmidt, M. [ForWind, Center for Wind Energy Research, Carl von Ossietzky Universitaet Oldenburg, D-26129 Oldenburg (Germany); Mittelmeier, N. REpower Systems SE, D-22297 Hamburg (Germany))
2013-11-15
The ability is demonstrated to calculate wind farm wakes on the basis of ambient conditions that were calculated with an atmospheric model. Specifically, comparisons are described between predicted and observed ambient conditions, and between power predictions from three wind farm wake models and power measurements, for a single and a double wake situation. The comparisons are based on performance indicators and test criteria, with the objective to determine the percentage of predictions that fall within a given range about the observed value. The Alpha Ventus site is considered, which consists of a wind farm with the same name and the met mast FINO1. Data from the 6 REpower wind turbines and the FINO1 met mast were employed. The atmospheric model WRF predicted the ambient conditions at the location and the measurement heights of the FINO1 mast. May the predictability of the wind speed and the wind direction be reasonable if sufficiently sized tolerances are employed, it is fairly impossible to predict the ambient turbulence intensity and vertical shear. Three wind farm wake models predicted the individual turbine powers: FLaP-Jensen and FLaP-Ainslie from ForWind Oldenburg, and FarmFlow from ECN. The reliabilities of the FLaP-Ainslie and the FarmFlow wind farm wake models are of equal order, and higher than FLaP-Jensen. Any difference between the predictions from these models is most clear in the double wake situation. Here FarmFlow slightly outperforms FLaP-Ainslie.
A Reliability Based Model for Wind Turbine Selection
Directory of Open Access Journals (Sweden)
A.K. Rajeevan
2013-06-01
Full Text Available A wind turbine generator output at a specific site depends on many factors, particularly cut- in, rated and cut-out wind speed parameters. Hence power output varies from turbine to turbine. The objective of this paper is to develop a mathematical relationship between reliability and wind power generation. The analytical computation of monthly wind power is obtained from weibull statistical model using cubic mean cube root of wind speed. Reliability calculation is based on failure probability analysis. There are many different types of wind turbinescommercially available in the market. From reliability point of view, to get optimum reliability in power generation, it is desirable to select a wind turbine generator which is best suited for a site. The mathematical relationship developed in this paper can be used for site-matching turbine selection in reliability point of view.
A Method for Modeling of Floating Vertical Axis Wind Turbine
DEFF Research Database (Denmark)
Wang, Kai; Hansen, Martin Otto Laver; Moan, Torgeir
2013-01-01
. In order to assess the technical and economic feasibility of this novel concept, a comprehensive simulation tool for modeling of the floating vertical axis wind turbine is needed. This work presents the development of a coupled method for modeling of the dynamics of a floating vertical axis wind turbine......It is of interest to investigate the potential advantages of floating vertical axis wind turbine (FVAWT) due to its economical installation and maintenance. A novel 5MW vertical axis wind turbine concept with a Darrieus rotor mounted on a semi-submersible support structure is proposed in this paper....... This integrated dynamic model takes into account the wind inflow, aerodynamics, hydrodynamics, structural dynamics (wind turbine, floating platform and the mooring lines) and a generator control. This approach calculates dynamic equilibrium at each time step and takes account of the interaction between the rotor...
Model Predictive Control of Wind Turbines using Uncertain LIDAR Measurements
DEFF Research Database (Denmark)
Mirzaei, Mahmood; Soltani, Mohsen; Poulsen, Niels Kjølstad
2013-01-01
The problem of Model predictive control (MPC) of wind turbines using uncertain LIDAR (LIght Detection And Ranging) measurements is considered. A nonlinear dynamical model of the wind turbine is obtained. We linearize the obtained nonlinear model for different operating points, which are determined...... by the effective wind speed on the rotor disc. We take the wind speed as a scheduling variable. The wind speed is measurable ahead of the turbine using LIDARs, therefore, the scheduling variable is known for the entire prediction horizon. By taking the advantage of having future values of the scheduling variable...... on wind speed estimation and measurements from the LIDAR is devised to find an estimate of the delay and compensate for it before it is used in the controller. Comparisons between the MPC with error compensation, the MPC without error compensation and an MPC with re-linearization at each sample point...
Wind farm density and harvested power in very large wind farms: A low-order model
Cortina, G.; Sharma, V.; Calaf, M.
2017-07-01
In this work we create new understanding of wind turbine wakes recovery process as a function of wind farm density using large-eddy simulations of an atmospheric boundary layer diurnal cycle. Simulations are forced with a constant geostrophic wind and a time varying surface temperature extracted from a selected period of the Cooperative Atmospheric Surface Exchange Study field experiment. Wind turbines are represented using the actuator disk model with rotation and yaw alignment. A control volume analysis around each turbine has been used to evaluate wind turbine wake recovery and corresponding harvested power. Results confirm the existence of two dominant recovery mechanisms, advection and flux of mean kinetic energy, which are modulated by the background thermal stratification. For the low-density arrangements advection dominates, while for the highly loaded wind farms the mean kinetic energy recovers through fluxes of mean kinetic energy. For those cases in between, a smooth balance of both mechanisms exists. From the results, a low-order model for the wind farms' harvested power as a function of thermal stratification and wind farm density has been developed, which has the potential to be used as an order-of-magnitude assessment tool.
Modeling and Parameter Estimation of a Small Wind Generation System
Directory of Open Access Journals (Sweden)
Carlos A. Ramírez Gómez
2013-11-01
Full Text Available The modeling and parameter estimation of a small wind generation system is presented in this paper. The system consists of a wind turbine, a permanent magnet synchronous generator, a three phase rectifier, and a direct current load. In order to estimate the parameters wind speed data are registered in a weather station located in the Fraternidad Campus at ITM. Wind speed data were applied to a reference model programed with PSIM software. From that simulation, variables were registered to estimate the parameters. The wind generation system model together with the estimated parameters is an excellent representation of the detailed model, but the estimated model offers a higher flexibility than the programed model in PSIM software.
Staggered and short period solutions of the Saturable Discrete Nonlinear Schr\\"odinger Equation
Khare, Avinash; Samuelsen, Mogens R; Saxena, Avadh; 10.1088/1751-8113/42/8/085002
2010-01-01
We point out that the nonlinear Schr{\\"o}dinger lattice with a saturable nonlinearity also admits staggered periodic as well as localized pulse-like solutions. Further, the same model also admits solutions with a short period. We examine the stability of these solutions and find that the staggered as well as the short period solutions are stable in most cases. We also show that the effective Peierls-Nabarro barrier for the pulse-like soliton solutions is zero.
Modelling and measurements of wakes in large wind farms
DEFF Research Database (Denmark)
Barthelmie, Rebecca Jane; Rathmann, Ole; Frandsen, Sten Tronæs;
2007-01-01
The paper presents research conducted in the Flow workpackage of the EU funded UPWIND project which focuses on improving models of flow within and downwind of large wind farms in complex terrain and offshore. The main activity is modelling the behaviour of wind turbine wakes in order to improve...
Modelling and measurements of wakes in large wind farms
DEFF Research Database (Denmark)
Barthelmie, Rebecca Jane; Rathmann, Ole; Frandsen, Sten Tronæs
2007-01-01
The paper presents research conducted in the Flow workpackage of the EU funded UPWIND project which focuses on improving models of flow within and downwind of large wind farms in complex terrain and offshore. The main activity is modelling the behaviour of wind turbine wakes in order to improve p...
A Reduced Wind Power Grid Model for Research and Education
DEFF Research Database (Denmark)
Akhmatov, Vladislav; Lund, Torsten; Hansen, Anca Daniela;
2007-01-01
A reduced grid model of a transmission system with a number of central power plants, consumption centers, local wind turbines and a large offshore wind farm is developed and implemented in the simulation tool PowerFactory (DIgSILENT). The reduced grid model is given by Energinet.dk, Transmission ...
Rajesh Karki; Dinesh Dhungana; Roy Billinton
2013-01-01
Adverse environmental impacts of carbon emissions are causing increasing concerns to the general public throughout the world. Electric energy generation from conventional energy sources is considered to be a major contributor to these harmful emissions. High emphasis is therefore being given to green alternatives of energy, such as wind and solar. Wind energy is being perceived as a promising alternative. This source of energy technology and its applications have undergone significant researc...
A Wind Accretion Model for HLX-1
Miller, M Coleman; Maccarone, Thomas J
2014-01-01
The brightest ultraluminous X-ray source currently known, HLX-1, has been observed to undergo five outburst cycles. The periodicity of these outbursts, and their high inferred maximum accretion rates of $\\sim{\\rm few}\\times 10^{-4} M_\\odot {\\rm yr}^{-1}$, naturally suggest Roche lobe overflow at the pericenter of an eccentric orbit. It is, however, difficult for the Roche lobe overflow model to explain the apparent trend of decreasing decay times over the different outbursts while the integrated luminosity also drops. Thus if the trend is real rather than simply being a reflection of the complex physics of accretion disks, a different scenario may be necessary. We present a speculative model in which, within the last decade, a high-mass giant star had most of its envelope tidally stripped by the $\\sim 10^{4-5} M_\\odot$ black hole in HLX-1, and the remaining core plus low-mass hydrogen envelope now feeds the hole with a strong wind. This model can explain the short decay time of the disk, and could explain the...
Experimental studies on power transformer model winding provided with MOVs
Directory of Open Access Journals (Sweden)
G.H. Kusumadevi
2017-05-01
Full Text Available Surge voltage distribution across a HV transformer winding due to appearance of very fast rise time (rise time of order 1 μs transient voltages is highly non-uniform along the length of the winding for initial time instant of occurrence of surge. In order to achieve nearly uniform initial time instant voltage distribution along the length of the HV winding, investigations have been carried out on transformer model winding. By connecting similar type of metal oxide varistors across sections of HV transformer model winding, it is possible to improve initial time instant surge voltage distribution across length of the HV transformer winding. Transformer windings with α values 5.3, 9.5 and 19 have been analyzed. The experimental studies have been carried out using high speed oscilloscope of good accuracy. The initial time instant voltage distribution across sections of winding with MOV remains nearly uniform along length of the winding. Also results of fault diagnostics carried out with and without connection of MOVs across sections of winding are reported.
Meridional Winds derived from ionosonde measurements: comparison of different models
Katamzi, Zama; Bosco Habarulema, John; Aruliah, Anasuya
2016-07-01
Thermospheric meridional winds are derived from ionospheric F2 region peak parameters (i.e. F2 maximum density, NmF2, and F2 peak height, hmF2) obtained using South African ionosonde for solar maximum (2001 and 2014) and solar minimum (2009). The study uses several different techniques and models to investigate the climatology behaviour of the winds in order to understand wind variability over South Africa. Detailed solar cycle, seasonal and diurnal trends will help establish how the winds influence ionospheric behaviour at this latitude. Comparisons of ionosonde derived neutral winds with empirical and numerical models such as the Coupled Middle Atmosphere Thermosphere Model (CMAT2) and Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) are important to understand the validity of theoretical and empirical models.
Limited Area Forecasting and Statistical Modelling for Wind Energy Scheduling
DEFF Research Database (Denmark)
Rosgaard, Martin Haubjerg
forecast accuracy for operational wind power scheduling. Numerical weather prediction history and scales of atmospheric motion are summarised, followed by a literature review of limited area wind speed forecasting. Hereafter, the original contribution to research on the topic is outlined. The quality...... control of wind farm data used as forecast reference is described in detail, and a preliminary limited area forecasting study illustrates the aggravation of issues related to numerical orography representation and accurate reference coordinates at ne weather model resolutions. For the o shore and coastal...... sites studied limited area forecasting is found to deteriorate wind speed prediction accuracy, while inland results exhibit a steady forecast performance increase with weather model resolution. Temporal smoothing of wind speed forecasts is shown to improve wind power forecast performance by up to almost...
Turbulent flow and scalar transport in a large wind farm
Porte-Agel, F.; Markfort, C. D.; Zhang, W.
2012-12-01
Wind energy is one of the fastest growing sources of renewable energy world-wide, and it is expected that many more large-scale wind farms will be built and cover a significant portion of land and ocean surfaces. By extracting kinetic energy from the atmospheric boundary layer and converting it to electricity, wind farms may affect the transport of momentum, heat, moisture and trace gases (e.g. CO_2) between the atmosphere and the land surface locally and globally. Understanding wind farm-atmosphere interaction is complicated by the effects of turbine array configuration, wind farm size, land-surface characteristics, and atmospheric thermal stability. A wind farm of finite length may be modeled as an added roughness or as a canopy in large-scale weather and climate models. However, it is not clear which analogy is physically more appropriate. Also, surface scalar flux is affected by wind farms and needs to be properly parameterized in meso-scale and/or high-resolution numerical models. Experiments involving model wind farms, with perfectly aligned and staggered configurations, having the same turbine distribution density, were conducted in a thermally-controlled boundary-layer wind tunnel. A neutrally stratified turbulent boundary layer was developed with a surface heat source. Measurements of the turbulent flow and fluxes over and through the wind farm were made using a custom x-wire/cold-wire anemometer; and surface scalar flux was measured with an array of surface-mounted heat flux sensors far within the quasi-developed region of the wind-farm. The turbulence statistics exhibit similar properties to those of canopy-type flows, but retain some characteristics of surface-layer flows in a limited region above the wind farms as well. The flow equilibrates faster and the overall momentum absorption is higher for the staggered compared to the aligned farm, which is consistent with canopy scaling and leads to a larger effective roughness. Although the overall surface
Scaling forecast models for wind turbulence and wind turbine power intermittency
Duran Medina, Olmo; Schmitt, Francois G.; Calif, Rudy
2017-04-01
The intermittency of the wind turbine power remains an important issue for the massive development of this renewable energy. The energy peaks injected in the electric grid produce difficulties in the energy distribution management. Hence, a correct forecast of the wind power in the short and middle term is needed due to the high unpredictability of the intermittency phenomenon. We consider a statistical approach through the analysis and characterization of stochastic fluctuations. The theoretical framework is the multifractal modelisation of wind velocity fluctuations. Here, we consider three wind turbine data where two possess a direct drive technology. Those turbines are producing energy in real exploitation conditions and allow to test our forecast models of power production at a different time horizons. Two forecast models were developed based on two physical principles observed in the wind and the power time series: the scaling properties on the one hand and the intermittency in the wind power increments on the other. The first tool is related to the intermittency through a multifractal lognormal fit of the power fluctuations. The second tool is based on an analogy of the power scaling properties with a fractional brownian motion. Indeed, an inner long-term memory is found in both time series. Both models show encouraging results since a correct tendency of the signal is respected over different time scales. Those tools are first steps to a search of efficient forecasting approaches for grid adaptation facing the wind energy fluctuations.
Reference Manual for the System Advisor Model's Wind Power Performance Model
Energy Technology Data Exchange (ETDEWEB)
Freeman, J.; Jorgenson, J.; Gilman, P.; Ferguson, T.
2014-08-01
This manual describes the National Renewable Energy Laboratory's System Advisor Model (SAM) wind power performance model. The model calculates the hourly electrical output of a single wind turbine or of a wind farm. The wind power performance model requires information about the wind resource, wind turbine specifications, wind farm layout (if applicable), and costs. In SAM, the performance model can be coupled to one of the financial models to calculate economic metrics for residential, commercial, or utility-scale wind projects. This manual describes the algorithms used by the wind power performance model, which is available in the SAM user interface and as part of the SAM Simulation Core (SSC) library, and is intended to supplement the user documentation that comes with the software.
Modelling of the urban wind profile
DEFF Research Database (Denmark)
Gryning, Sven-Erik; Batchvarova, Ekaterina
2008-01-01
Analysis of meteorological measurements from tall masts in rural and urban areas show that the height of the boundary layer influences the wind profile even in the lowest hundreds of meters. A parameterization of the wind profile for the entire boundary layer is formulated with emphasis on the lo...
Modelling of a PMSG Wind Turbine with Autonomous Control
Chia-Nan Wang; Wen-Chang Lin; Xuan-Khoa Le
2014-01-01
The aim of this research is to model an autonomous control wind turbine driven permanent magnetic synchronous generator (PMSG) which feeds alternating current (AC) power to the utility grid. Furthermore, this research also demonstrates the effects and the efficiency of PMSG wind turbine which is integrated by autonomous controllers. In order for well autonomous control, two voltage source inverters are used to control wind turbine connecting with the grid. The generator-side inverter is used ...
Offshore Wind Balance-of-System Cost Modeling
Energy Technology Data Exchange (ETDEWEB)
Maness, Michael; Stehly, Tyler; Maples, Ben; Mone, Christopher
2015-09-29
Offshore wind balance-of-system (BOS) costs contribute up to 70% of installed capital costs. Thus, it is imperative to understand the impact of these costs on project economics as well as potential cost trends for new offshore wind technology developments. As a result, the National Renewable Energy Laboratory (NREL) developed and recently updated a BOS techno-economic model using project cost estimates created from wind energy industry sources.
Verification of high-speed solar wind stream forecasts using operational solar wind models
DEFF Research Database (Denmark)
Reiss, Martin A.; Temmer, Manuela; Veronig, Astrid M.
2016-01-01
High-speed solar wind streams emanating from coronal holes are frequently impinging on the Earth's magnetosphere causing recurrent, medium-level geomagnetic storm activity. Modeling high-speed solar wind streams is thus an essential element of successful space weather forecasting. Here we evaluate...... high-speed stream forecasts made by the empirical solar wind forecast (ESWF) and the semiempirical Wang-Sheeley-Arge (WSA) model based on the in situ plasma measurements from the Advanced Composition Explorer (ACE) spacecraft for the years 2011 to 2014. While the ESWF makes use of an empirical relation...... between the coronal hole area observed in Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images and solar wind properties at the near-Earth environment, the WSA model establishes a link between properties of the open magnetic field lines extending from the photosphere to the corona...
Wind modeling of Chihuahuan Desert dust outbreaks
Rivera Rivera, Nancy I.; Gill, Thomas E.; Gebhart, Kristi A.; Hand, Jennifer L.; Bleiweiss, Max P.; Fitzgerald, Rosa M.
The Chihuahuan Desert region of North America is a significant source of mineral aerosols in the Western Hemisphere, and Chihuahuan Desert dust storms frequently impact the Paso del Norte (El Paso, USA/Ciudad Juarez, Mexico) metropolitan area. A statistical analysis of HYSPLIT back trajectory residence times evaluated airflow into El Paso on all days and on days with synoptic (non-convective) dust events in 2001-2005. The incremental probability—a measure of the areas most likely to have been traversed by air masses arriving at El Paso during dusty days—was only strongly positively associated with the region west-southwest of the city, a zone of known dust source areas. Focused case studies were made of major dust events on 15 April and 15 December 2003. Trajectories approached the surface and MM5 (NCAR/Penn State Mesoscale Model) wind speeds increased at locations consistent with dust sources observed in satellite imagery on those dates. Back trajectory and model analyses suggested that surface cyclones adjacent to the Chihuahuan Desert were associated with the extreme dust events, consistent with previous studies of dust storms in the Southern High Plains to the northeast. The recognition of these meteorological patterns serves as a forecast aid for prediction of dust events likely to impact the Paso del Norte.
Wind Tunnel Experiments with Active Control of Bridge Section Model
DEFF Research Database (Denmark)
Hansen, Henriette I.; Thoft-Christensen, Palle
the flutter wind velocity for future ultra-long span suspension bridges. The purpose of the wind tunnel experiments is to investigate the principle to use this active flap control system. The bridge section model used in the experiments is therefore not a model of a specific bridge but it is realistic......This paper describes results of wind tunnel experiments with a bridge section model where movable flaps are integrated in the bridge girder so each flap is the streamlined part of the edge of the girder. This active control flap system is patented by COWIconsult and may be used to increase...... compared with a real bridge. Five flap configurations are investigated during the wind tunnel experiments and depending on the actual flap configuration it is possible to decrease or increase the flutter wind velocity for the model....
Optimization of the Single Staggered Wire and Tube Heat Exchanger
Directory of Open Access Journals (Sweden)
Arsana I Made
2016-01-01
Full Text Available Wire and tube heat exchanger consists of a coiled tube, and wire is welded on the two sides of it in normal direction of the tube. Generally,wire and tube heat exchanger uses inline wire arrangement between the two sides, whereas in this study, it used staggered wire arrangement that reduces the restriction of convection heat transfer. This study performed the optimization of single staggered wire and tube heat exchanger to increase the capacity and reduce the mass of the heat exchanger. Optimization was conducted with the Hooke-Jeeves method, which aims to optimize the geometry of the heat exchanger, especially on the diameter (dw and the distance between wires (pw. The model developed to present heat transfer correlations on single staggered wire and tube heat exchanger was valid. The maximum optimization factor obtained when the diameter wire was 0.9 mm and the distance between wires (pw was 11 mm with the fref value = 1.5837. It means that the optimized design only using mass of 59,10 % and could transfer heat about 98,5 % from the basis design.
Wind Speed Estimation and Wake model Re-calibration for Downregulated Offshore Wind Farms
Göçmen Bozkurt, Tuhfe; Giebel, Gregor; Kjølstad Poulsen, Niels; Réthoré, Pierre-Elouan; Mirzaei, Mahmood
2014-05-01
In recent years, the wind farm sizes have increased tremendously and with increasing installed capacity, the wind farms are requested to downregulate from their maximum possible power more frequently, especially in the offshore environment. Determination of the possible (or available) power is crucial not only because the reserve power has considerable market value but also for wind farm developers to be properly compensated for the loss during downregulation. While the available power calculation is straightforward for a single turbine, it gets rather complicated for the whole wind farm due to the change in the wake characteristics. In fact, the wake losses generated by the upstream turbine(s) decrease during downregulation and the downstream turbines therefore see more wind compared to the normal operation case. Currently, the Transmission System Operators (TSOs) have no real way to determine exactly the available power of a whole wind farm which is downregulated. Therefore, the PossPOW project aims to develop a verified and internationally accepted way to determine the possible power of a down-regulated offshore wind farm. The first phase of the project is to estimate the rotor effective wind speed. Since the nacelle anemometers are not readily available and are known to have reliability issues, the proposed method is to use power, pitch angle and rotational speed as inputs and combine it with a generic Cp model to estimate the wind speed. The performance of the model has been evaluated for both normal operation and downregulation periods using two different case studies: Horns Rev-I wind farm and NREL 5MW single turbine. During downregulation, the wake losses are not as severe and the velocity deficits at the downstream turbines are smaller as if also the wake is "downregulated". On the other hand, in order to calculate the available power, the wakes that would have been produced normally (if the turbines were not curtailed) are of importance, not the
A Multidirectional Wind Erosion Model for Western Saxony
Schmidt, Simon; Meusburger, Katrin; de Figueiredo, Tomás; Alewell, Christine
2016-04-01
Wind erosion can trigger a non-visible loss of fine soil up to 40 t ha-1 per single event and is as such a major soil threat and environmental concern in areas susceptible to wind erosion. Western Saxony was assessed to be among the most susceptible landscapes not only within Germany but even within Europe (Borelli et al., 2015; Borelli et al., 2014). Moreover, wind erosion events in eastern Germany cause very severe off-site effects with impacts on road traffic. So far the wind erosion model that is normally applied in Germany is based on the norm DIN standard 19706. The DIN standard 19706 was revised by new controlling factors and fuzzy logic to consider the multi-directionality of wind and make it more realistic to wind erosion processes. The new factors are based on different datasets like (i) wind and temperature data (1hr resolution) for 9 gauging stations and interpolated long-term wind speed (1981-2000, 200m resolution) provided by the German Weather Service, (ii) soil erodibility extracted from the digital soil map 1:50,000, (iii) landscape components from different data sources (ATKIS, OpenStreetMap and others), and (iv) a DEM (20m resolution) for local orographic modeling. For a risky sub-region, local wind speeds and directions were modelled based on the Wind Atlas Analysis and Application Programs (WAsP) orography-model to assess road bodies for priority actions. Major improvements of the proposed model are the consideration of changing wind directions and the implementation of factors on soil cover and field length. An estimation of the long-term spatiotemporal variability under changing climate is possible with the model conception. The revised model assesses 3.6% of western Saxonies agricultural fields under very high risk to wind erosion. Larger fields (greater than 116 ha) are connected to a higher frequency (51.7%) of very high risk. Only a small proportion (5.2%) of the high risk class was found in small fields (smaller than 21 ha). Fields under
Dynamic wind turbine models in power system simulation tool
DEFF Research Database (Denmark)
Hansen, A.; Jauch, Clemens; Soerensen, P.
The present report describes the dynamic wind turbine models implemented in the power system simulation tool DIgSILENT. The developed models are a part of the results of a national research project, whose overall objective is to create a model database in different simulation tools. The report...... provides a description of the wind turbine modelling, both at a component level and at a system level....
Modelling colliding wind binaries with RAMSES, extension to special relativity
Lamberts, Astrid; Dubus, Guillaume; Lesur, Geoffroy
2012-01-01
We present high resolution simulations with RAMSES of supersonic colliding stellar winds. The collision results in a double shock structure which is subject to different instabilities. The Kelvin-Helmholtz instability (KHI) introduces some mixing and variability. For isothermal winds, the Non-linear Thin Shell Instability violently affects the interaction region. Properly modelling these instabilities requires a high enough resolution and an adapted numerical method, especially when one of the winds strongly dominates the other one. At large scale, orbital motion is expected to turn the shocked zone into a spiral but we find that in some configurations the KHI may disrupt the spiral. A colliding wind structure is also expected in gamma-ray binaries composed of a massive star and a young pulsar which emits a highly relativistic wind. Numerical simulations are necessary to understand the geometry of such systems and should take into account the relativistic nature of the pulsar wind. We implemented a second ord...
Verification of high-speed solar wind stream forecasts using operational solar wind models
Reiss, Martin A; Veronig, Astrid M; Nikolic, Ljubomir; Vennerstrom, Susanne; Schoengassner, Florian; Hofmeister, Stefan J
2016-01-01
High-speed solar wind streams emanating from coronal holes are frequently impinging on the Earth's magnetosphere causing recurrent, medium-level geomagnetic storm activity. Modeling high-speed solar wind streams is thus an essential element of successful space weather forecasting. Here we evaluate high-speed stream forecasts made by the empirical solar wind forecast (ESWF) and the semiempirical Wang-Sheeley-Arge (WSA) model based on the in situ plasma measurements from the ACE spacecraft for the years 2011 to 2014. While the ESWF makes use of an empirical relation between the coronal hole area observed in Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images and solar wind properties at the near-Earth environment, the WSA model establishes a link between properties of the open magnetic field lines extending from the photosphere to the corona and the background solar wind conditions. We found that both solar wind models are capable of predicting the large-scale features of the observed sol...
Stochastic model for aerodynamic force dynamics on wind turbine blades in unsteady wind inflow
Luhur, Muhammad Ramzan; Kühn, Martin; Wächter, Matthias
2015-01-01
The paper presents a stochastic approach to estimate the aerodynamic forces with local dynamics on wind turbine blades in unsteady wind inflow. This is done by integrating a stochastic model of lift and drag dynamics for an airfoil into the aerodynamic simulation software AeroDyn. The model is added as an alternative to the static table lookup approach in blade element momentum (BEM) wake model used by AeroDyn. The stochastic forces are obtained for a rotor blade element using full field turbulence simulated wind data input and compared with the classical BEM and dynamic stall models for identical conditions. The comparison shows that the stochastic model generates additional extended dynamic response in terms of local force fluctuations. Further, the comparison of statistics between the classical BEM, dynamic stall and stochastic models' results in terms of their increment probability density functions gives consistent results.
A model of rotationally-sampled wind turbulence for predicting fatigue loads in wind turbines
Spera, David A.
1995-01-01
Empirical equations are presented with which to model rotationally-sampled (R-S) turbulence for input to structural-dynamic computer codes and the calculation of wind turbine fatigue loads. These equations are derived from R-S turbulence data which were measured at the vertical-plane array in Clayton, New Mexico. For validation, the equations are applied to the calculation of cyclic flapwise blade loads for the NASA/DOE Mod-2 2.5-MW experimental HAWT's (horizontal-axis wind turbines), and the results compared to measured cyclic loads. Good correlation is achieved, indicating that the R-S turbulence model developed in this study contains the characteristics of the wind which produce many of the fatigue loads sustained by wind turbines. Empirical factors are included which permit the prediction of load levels at specified percentiles of occurrence, which is required for the generation of fatigue load spectra and the prediction of the fatigue lifetime of structures.
Statistical Modeling for Wind-Temperature Meteorological Elements in Troposphere
Virtser, A; Golbraikh, E
2010-01-01
A comprehensive statistical model for vertical profiles of the horizontal wind and temperature throughout the troposphere is presented. The model is based on radiosonde measurements of wind and temperature during several years. The profiles measured under quite different atmospheric conditions exhibit qualitative similarity, and a proper choice of the reference scales for the wind, temperature and altitude levels allows to consider the measurement data as realizations of a random process with universal characteristics: means, the basic functions and parameters of standard distributions for transform coefficients of the Principal Component Analysis. The features of the atmospheric conditions are described by statistical characteristics of the wind-temperature ensemble of dimensional reference scales. The high effectiveness of the proposed approach is provided by a similarity of wind - temperature vertical profiles, which allow to carry out the statistical modeling in the low-dimension space of the dimensional ...
Importance of Dynamic Inflow Model Predictive Control of Wind Turbines
DEFF Research Database (Denmark)
Odgaard, Peter Fogh; Knudsen, Torben; Overgaard, Anders;
2015-01-01
The efficiency of including dynamic inflow in the model based design of wind turbine controller has been discussed for many years in the wind energy community with out getting to a safe conclusion. This paper delivers a good argument in favor of including dynamic inflow. The main contributions...
Modelling of a chaotic load of wind turbines drivetrain
Bielecki, Andrzej; Barszcz, Tomasz; Wójcik, Mateusz
2015-03-01
The purpose of this paper is to present a model of the load of the wind turbine gears for simulation of real, varying operational conditions for modelling of wind turbine vibration. The characteristics of the wind, which generates chaotically varying loads on the drivetrain components generating load in teeth and bearings of gears during torque transfer, are discussed. A generator of variable load of wind turbines drivetrain is proposed. Firstly, the module for generation of wind speed is designed. It is based on the approach in which the wind speed was considered as a time series approximated by the Weierstrass function. Secondly, the rotational speed of the main shaft is proposed as a function of the wind speed value. The function depends on a few parameters that are fitted by using a genetic algorithm. Finally, the model of torque of the main shaft is introduced. This model has been created by using a multi-layer artificial neural network. The results show that the proposed approach yields a very good fit for the experimental data. The fit brings about the proper reproducing of all the aspects of the load that are crucial for causing fatigue and, as a consequence, damaging of gears of the wind turbines.
Wind climate from the regional climate model REMO
DEFF Research Database (Denmark)
Larsén, Xiaoli Guo; Mann, Jakob; Berg, Jacob
2010-01-01
Selected outputs from simulations with the regional climate model REMO from the Max Planck Institute, Hamburg, Germany were studied in connection with wind energy resource assessment. It was found that the mean wind characteristics based on observations from six mid-latitude stations are well...
Wind Power Curve Modeling in Simple and Complex Terrain
Energy Technology Data Exchange (ETDEWEB)
Bulaevskaya, V. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Wharton, S. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Irons, Z. [Enel Green Power North America, Andover, MA (United States); Qualley, G. [Pentalum, Colleyville, TX (United States)
2015-02-09
Our previous work on wind power curve modeling using statistical models focused on a location with a moderately complex terrain in the Altamont Pass region in northern California (CA). The work described here is the follow-up to that work, but at a location with a simple terrain in northern Oklahoma (OK). The goal of the present analysis was to determine the gain in predictive ability afforded by adding information beyond the hub-height wind speed, such as wind speeds at other heights, as well as other atmospheric variables, to the power prediction model at this new location and compare the results to those obtained at the CA site in the previous study. While we reach some of the same conclusions at both sites, many results reported for the CA site do not hold at the OK site. In particular, using the entire vertical profile of wind speeds improves the accuracy of wind power prediction relative to using the hub-height wind speed alone at both sites. However, in contrast to the CA site, the rotor equivalent wind speed (REWS) performs almost as well as the entire profile at the OK site. Another difference is that at the CA site, adding wind veer as a predictor significantly improved the power prediction accuracy. The same was true for that site when air density was added to the model separately instead of using the standard air density adjustment. At the OK site, these additional variables result in no significant benefit for the prediction accuracy.
Model based active power control of a wind turbine
DEFF Research Database (Denmark)
Mirzaei, Mahmood; Soltani, Mohsen; Poulsen, Niels Kjølstad;
2014-01-01
in the electricity market that selling the reserve power is more profitable than producing with the full capacity. Therefore wind turbines can be down-regulated and sell the differential capacity as the reserve power. In this paper we suggest a model based approach to control wind turbines for active power reference...
Simple Model for Describing and Estimating Wind Turbine Dynamic Inflow
DEFF Research Database (Denmark)
Knudsen, Torben; Bak, Thomas
2013-01-01
Wind turbines operate with sudden change in pitch angle, rotor or wind speed. In such cases the wake behind the turbine, achieve steady state conditions only after a certain delay. This phenomenon is commonly called dynamic inflow. There are many models for dynamic inflow. The most accurate use a...
Selection of References in Wind Turbine Model Predictive Control Design
DEFF Research Database (Denmark)
Odgaard, Peter Fogh; Hovgaard, Tobias
2015-01-01
Lowering the cost of energy is one of the major focus areas in the wind turbine industry. Recent research has indicated that wind turbine controllers based on model predictive control methods can be useful in obtaining this objective. A number of design considerations have to be made when designi...
Interval forecasts of a novelty hybrid model for wind speeds
Directory of Open Access Journals (Sweden)
Shanshan Qin
2015-11-01
Full Text Available The utilization of wind energy, as a booming technology in the field of renewable energies, has been highly regarded around the world. Quantification of uncertainties associated with accurate wind speed forecasts is essential for regulating wind power generation and integration. However, it remains difficult work primarily due to the stochastic and nonlinear characteristics of wind speed series. Traditional models for wind speed forecasting mostly focus on generating certain predictive values, which cannot properly handle uncertainties. For quantifying potential uncertainties, a hybrid model constructed by the Cuckoo Search Optimization (CSO-based Back Propagation Neural Network (BPNN is proposed to establish wind speed interval forecasts (IFs by estimating the lower and upper bounds. The quality of IFs is assessed quantitatively using IFs coverage probability (IFCP and IFs normalized average width (IFNAW. Moreover, to assess the overall quality of IFs comprehensively, a tradeoff between informativeness (IFNAW and validity (IFCP of IFs is examined by coverage width-based criteria (CWC. As an applicative study, wind speeds from the Xinjiang Region in China are used to validate the proposed hybrid model. The results demonstrate that the proposed model can construct higher quality IFs for short-term wind speed forecasts.
A new ensemble model for short term wind power prediction
DEFF Research Database (Denmark)
Madsen, Henrik; Albu, Razvan-Daniel; Felea, Ioan
2012-01-01
As the objective of this study, a non-linear ensemble system is used to develop a new model for predicting wind speed in short-term time scale. Short-term wind power prediction becomes an extremely important field of research for the energy sector. Regardless of the recent advancements in the re-search...
Magnetosonic Waveguide Model of Solar Wind Flow Tubes
Indian Academy of Sciences (India)
A. K. Srivastava; B. N. Dwivedi
2006-06-01
We consider solar wind flow tubes as a magnetosonic wave-guide. Assuming a symmetric expansion in edges of slab-modelled wave-guide, we study the propagation characteristics of magnetosonic wave in the solar wind flow tubes. We present the preliminary results and discuss their implications.
Wind mass transfer in S-type symbiotic binaries I. Focusing by the wind compression model
Skopal, Augustin
2014-01-01
Context: Luminosities of hot components in symbiotic binaries require accretion rates that are higher than those that can be achieved via a standard Bondi-Hoyle accretion. This implies that the wind mass transfer in symbiotic binaries has to be more efficient. Aims: We suggest that the accretion rate onto the white dwarfs (WDs) in S-type symbiotic binaries can be enhanced sufficiently by focusing the wind from their slowly rotating normal giants towards the binary orbital plane. Methods: We applied the wind compression model to the stellar wind of slowly rotating red giants in S-type symbiotic binaries. Results: Our analysis reveals that for typical terminal velocities of the giant wind, 20 to 50 km/s, and measured rotational velocities between 6 and 10 km/s, the densities of the compressed wind at a typical distance of the accretor from its donor correspond to the mass-loss rate, which can be a factor of $\\sim$10 higher than for the spherically symmetric wind. This allows the WD to accrete at rates of $10^{-...
Robust Model Predictive Control of a Wind Turbine
DEFF Research Database (Denmark)
Mirzaei, Mahmood; Poulsen, Niels Kjølstad; Niemann, Hans Henrik
2012-01-01
In this work the problem of robust model predictive control (robust MPC) of a wind turbine in the full load region is considered. A minimax robust MPC approach is used to tackle the problem. Nonlinear dynamics of the wind turbine are derived by combining blade element momentum (BEM) theory...... and first principle modeling of the turbine flexible structure. Thereafter the nonlinear model is linearized using Taylor series expansion around system operating points. Operating points are determined by effective wind speed and an extended Kalman filter (EKF) is employed to estimate this. In addition...... of the uncertain system is employed and a norm-bounded uncertainty model is used to formulate a minimax model predictive control. The resulting optimization problem is simplified by semidefinite relaxation and the controller obtained is applied on a full complexity, high fidelity wind turbine model. Finally...
Staggered Multiple-PRF Ultrafast Color Doppler.
Posada, Daniel; Poree, Jonathan; Pellissier, Arnaud; Chayer, Boris; Tournoux, Francois; Cloutier, Guy; Garcia, Damien
2016-06-01
Color Doppler imaging is an established pulsed ultrasound technique to visualize blood flow non-invasively. High-frame-rate (ultrafast) color Doppler, by emissions of plane or circular wavefronts, allows severalfold increase in frame rates. Conventional and ultrafast color Doppler are both limited by the range-velocity dilemma, which may result in velocity folding (aliasing) for large depths and/or large velocities. We investigated multiple pulse-repetition-frequency (PRF) emissions arranged in a series of staggered intervals to remove aliasing in ultrafast color Doppler. Staggered PRF is an emission process where time delays between successive pulse transmissions change in an alternating way. We tested staggered dual- and triple-PRF ultrafast color Doppler, 1) in vitro in a spinning disc and a free jet flow, and 2) in vivo in a human left ventricle. The in vitro results showed that the Nyquist velocity could be extended to up to 6 times the conventional limit. We found coefficients of determination r(2) ≥ 0.98 between the de-aliased and ground-truth velocities. Consistent de-aliased Doppler images were also obtained in the human left heart. Our results demonstrate that staggered multiple-PRF ultrafast color Doppler is efficient for high-velocity high-frame-rate blood flow imaging. This is particularly relevant for new developments in ultrasound imaging relying on accurate velocity measurements.
A high wind geophysical model fuction for QuikSCAT wind retrievals and application to Typhoon IOKE
Institute of Scientific and Technical Information of China (English)
ZOU Juhong; ZENG Tao; CUI Songxue
2015-01-01
The geophysical model function (GMF) describes the relationship between a backscattering and a sea surface wind, and enables a wind vector retrieval from backscattering measurements. It is clear that the GMF plays an important role in an ocean wind vector retrieval. The performance of the existing Ku-band model function QSCAT-1 is considered to be effective at low and moderate wind speed ranges. However, in the conditions of higher wind speeds, the existing algorithms diverge alarmingly. owing to the lack ofin situ data required for developing the GMF for the high wind conditions, the QSCAT-1 appears to overestimate thes0, which results in underestimating the wind speeds. Several match-up QuikSCAT and special sensor microwave/imager (SSM/I) wind speed measurements of the typhoons occurring in the west Pacific Ocean are analyzed. The results show that the SSM/I wind exhibits better agreement with the “best track” analysis wind speed than the QuikSCAT wind retrieved using QSCAT-1. On the basis of this evaluation, a correction of the QSCAT-1 model function for wind speed above 16 m/s is proposed, which uses the collocated SSM/I and QuikSCAT measurements as a training set, and a neural network approach as a multiple nonlinear regression technologytechnology.In order to validate the revised GMF for high winds, the modified GMF was applied to the QuikSCAT observations of Hurricane IOKE. The wind estimated by the QuikSCAT for Typhoon IOKE in 2006 was improved with the maximum wind speed reaching 55 m/s. An error analysis was performed using the wind fields from the Holland model as the surface truth. The results show an improved agreement with the Holland model wind when compared with the wind estimated using the QSCAT-1. However, large bias still existed, indicating that the effects of rain must be considered for further improvement.
Calculation of extreme wind atlases using mesoscale modeling. Final report
DEFF Research Database (Denmark)
Larsén, Xiaoli Guo; Badger, Jake
This is the final report of the project PSO-10240 "Calculation of extreme wind atlases using mesoscale modeling". The overall objective is to improve the estimation of extreme winds by developing and applying new methodologies to confront the many weaknesses in the current methodologies...... as explained in Section 2. The focus has been put on developing a number of new methodologies through numerical modeling and statistical modeling....
A noise generation and propagation model for large wind farms
DEFF Research Database (Denmark)
Bertagnolio, Franck
2016-01-01
A wind turbine noise calculation model is combined with a ray tracing method in order to estimate wind farm noise in its surrounding assuming an arbitrary topography. The wind turbine noise model is used to generate noise spectra for which each turbine is approximated as a point source. However......, the detailed three-dimensional directivity features are taken into account for the further calculation of noise propagation over the surrounding terrain. An arbitrary number of turbines constituting a wind farm can be spatially distributed. The noise from each individual turbine is propagated into the far......-field using the ray tracing method. These results are added up assuming the noise from each turbine is uncorrelated. The methodology permits to estimate a wind farm noise map over the surrounding terrain in a reasonable amount of computational time on a personal computer....
Fourier Simulation of a Non-Isotropic Wind Field Model
DEFF Research Database (Denmark)
Mann, J.; Krenk, S.
Realistic modelling of three dimensional wind fields has become important in calculation of dynamic loads on same spatially extended structures, such as large bridges, towers and wind turbines. For some structures the along wind component of the of the turbulent flow is important while for others...... the vertical velocity fluctuations give rise to loads. There may even be structures where combinations of velocity fluctuations in different direction are of importance. Most methods that have been developed to simulate the turbulent wind field are based on one-point (cross-)spectra and two-point cross......-spectra. In this paper a method is described which builds on a recently developed model of a spectral tensor for atmospheric surface layer turbulence at high wind speeds. Although the tensor does not in principle contain more information than the cross-spectra, it leads to a more natural and direct representation...
DEFF Research Database (Denmark)
Moriarty, Patrick; Rodrigo, Javier Sanz; Gancarski, Pawel;
2014-01-01
.windbench.net). This paper provides an overview of the building-block validation approach applied to wind farm wake models, including best practices for the benchmarking and data processing procedures for validation datasets from wind farm SCADA and meteorological databases. A hierarchy of test cases has been proposed...
DEFF Research Database (Denmark)
Badger, Jake; Frank, Helmut; Hahmann, Andrea N.
2014-01-01
This paper demonstrates that a statistical dynamical method can be used to accurately estimate the wind climate at a wind farm site. In particular, postprocessing of mesoscale model output allows an efficient calculation of the local wind climate required for wind resource estimation at a wind...... turbine site. The method is divided into two parts: 1) preprocessing, in which the configurations for the mesoscale model simulations are determined, and 2) postprocessing, in which the data from the mesoscale simulations are prepared for wind energy application. Results from idealized mesoscale modeling...... experiments for a challenging wind farm site in northern Spain are presented to support the preprocessing method. Comparisons of modeling results with measurements from the same wind farm site are presented to support the postprocessing method. The crucial element in postprocessing is the bridging...
Wall correction model for wind tunnels with open test section
DEFF Research Database (Denmark)
Sørensen, Jens Nørkær; Shen, Wen Zhong; Mikkelsen, Robert Flemming
2006-01-01
In the paper we present a correction model for wall interference on rotors of wind turbines or propellers in wind tunnels. The model, which is based on a one-dimensional momentum approach, is validated against results from CFD computations using a generalized actuator disc principle. In the model...... the exchange of axial momentum between the tunnel and the ambient room is represented by a simple formula, derived from actuator disc computations. The correction model is validated against Navier-Stokes computations of the flow about a wind turbine rotor. Generally, the corrections from the model are in very...... good agreement with the CFD computations, demonstrating that one-dimensional momentum theory is a reliable way of predicting corrections for wall interference in wind tunnels with closed as well as open cross sections....
Model predictive control of wind energy conversion systems
Yaramasu, Venkata Narasimha R
2017-01-01
The authors provide a comprehensive analysis on the model predictive control of power converters employed in a wide variety of variable-speed wind energy conversion systems (WECS). The contents of this book includes an overview of wind energy system configurations, power converters for variable-speed WECS, digital control techniques, MPC, modeling of power converters and wind generators for MPC design. Other topics include the mapping of continuous-time models to discrete-time models by various exact, approximate, and quasi-exact discretization methods, modeling and control of wind turbine grid-side two-level and multilevel voltage source converters. The authors also focus on the MPC of several power converter configurations for full variable-speed permanent magnet synchronous generator based WECS, squirrel-cage induction generator based WECS, and semi-variable-speed doubly fed induction generator based WECS.
Developments of the offshore wind turbine wake model Fuga
DEFF Research Database (Denmark)
Ott, Søren; Nielsen, Morten
's Offshore Wind Accelerator Stage 1 project called Linearized CFD Wake models. The earlier project resulted in the development, implementation and validation of the Fuga model. Fuga is a linearized CFD model that can predict wake effects for offshore wind farms. The main purpose of Stage 2 is to add more...... with the modified equations. - Meandering. Meandering has been included in the form of a post processing of the model results that bend and twist the wake centreline. The meandering centrelines are calculated using a Gaussian process developed on the basis of measured spectra. An analysis of meteorological data......This is the final report of the project entitled Risø DTU Modelling Services carried out by DTU Wind Energy (formerly known as Risø National Laboratory) as part of the Carbon Trust's Offshore Wind Accelerator Stage 2 under a contract with Carbon Trust. The project is a follow-up to a Carbon Trust...
Comparative Study of MHD Modeling of the Background Solar Wind
Gressl, C; Temmer, M; Odstrcil, D; Linker, J A; Mikic, Z; Riley, P
2013-01-01
Knowledge about the background solar wind plays a crucial role in the framework of space weather forecasting. In-situ measurements of the background solar wind are only available for a few points in the heliosphere where spacecraft are located, therefore we have to rely on heliospheric models to derive the distribution of solar wind parameters in interplanetary space. We test the performance of different solar wind models, namely Magnetohydrodynamic Algorithm outside a Sphere/ENLIL (MAS/ENLIL), Wang-Sheeley-Arge/ENLIL (WSA/ENLIL), and MAS/MAS, by comparing model results with in-situ measurements from spacecraft located at 1 AU distance to the Sun (ACE, Wind). To exclude the influence of interplanetary coronal mass ejections (ICMEs), we chose the year 2007 as a time period with low solar activity for our comparison. We found that the general structure of the background solar wind is well reproduced by all models. The best model results were obtained for the parameter solar wind speed. However, the predicted ar...
Modelling seabird collision risk with off-shore wind farms
Energy Technology Data Exchange (ETDEWEB)
Mateos, Maria; Arroyo, Gonzalo Munoz; Rosario, Jose Juan Alonso del
2011-07-01
Full text: Recent concern about the adverse effects of collision mortality of avian migrants at wind farms has highlighted the need to understand bird-wind turbine interactions. Here, a stochastic collision model, based on data of seabird behaviour collected on- site, is presented, as a flexible and easy to take tool to assess the collisions probabilities of off-shore wind farms in a pre-construction phase. The collision prediction model considering the wind farm area as a risk window has been constructed as a stochastic model for avian migrants, based on Monte Carlo simulation. The model calculates the probable number of birds collided per time unit. Migration volume, wind farm dimensions, vertical and horizontal distribution of the migratory passage, flight direction and avoidance rates, between other variables, are taken into account in different steps of the model as the input variables. In order to assess the weighted importance of these factors on collision probability predictions, collision probabilities obtained from the set of scenarios resulting from the different combinations of the input variables were modelled by using Generalised Additive Models. The application of this model to a hypothetical project for erecting a wind farm at the Strait of Gibraltar showed that collision probability, and consequently mortality rates, strongly depend on the values of the avoidance rates taken into account, and the distribution of birds into the different altitude layers. These parameters should be considered as priorities to be addressed in post-construction studies. (Author)
Stochastic modeling and performance monitoring of wind farm power production
Milan, Patrick; Peinke, Joachim
2015-01-01
We present a new stochastic approach to describe and remodel the conversion process of a wind farm at a sampling frequency of 1Hz. When conditioning on various wind direction sectors, the dynamics of the conversion process appear as a fluctuating trajectory around an average IEC-like power curve, see section II. Our approach is to consider the wind farm as a dynamical system that can be described as a stochastic drift/diffusion model, where a drift coefficient describes the attraction towards the power curve and a diffusion coefficient quantifies additional turbulent fluctuations. These stochastic coefficients are inserted into a Langevin equation that, once properly adapted to our particular system, models a synthetic signal of power output for any given wind speed/direction signals, see section III. When combined with a pre-model for turbulent wind fluctuations, the stochastic approach models the power output of the wind farm at a sampling frequency of 1Hz using only ten-minute average values of wind speed ...
Wind farms model aggregation using probabilistic clustering
Fernandes, Paula Odete; Ferreira, Ángela Paula
2013-10-01
The main objective of this research is the identification of homogeneous groups within wind farms of a major operator playing in the energy sector in Portugal, based on two multivariate analyses: Hierarchical Cluster Analysis and Discriminant Analysis, by using two independent variables: annual liquid hours and net production. From the produced outputs there were identified three homogenous groups of wind farms: (1) medium Installed Capacity and Induction Generator based Technology, (2) high Installed Capacity and Synchronous Generator based Technology and (3) medium Installed Capacity and Synchronous Generator based Technology, which includes the wind farms with the higher annual liquid hours. It has been found that the results obtained by cluster analysis are well classified, with a total percentage of correct classification of 97,1%, which can be considered excellent.
Kalnay, E.; Atlas, R.
1986-01-01
Instantaneous and 15-day time-averaged fields of surface wind, wind stress, curl of the wind stress, and wind divergence are presented. These fields are derived from the Goddard Laboratory for Atmospheres four-dimensional analysis/forecast cycle, for the period September 6-30, 1978, using conventional data, satellite temperature soundings, cloud-track winds, and subjectively dealiased Seasat scatterometer winds.
DEFF Research Database (Denmark)
Fortmann, Jens; Miller, Nicholas; Kazachkov, Yuri
This paper describes the latest developments in the standardization of wind plant and wind plant controller models. As a first step IEC TC88 WG 27 and WECC jointly developed generic wind turbine models which have been published by WECC in 2014 and IEC in 2015 as IEC 61400-27-1, which also included...... a draft plant controller model in an informative annex. In a second step, parallel activities have been going on in WECC and IEC TC88 WG 27 to create plant models that can include a number of wind turbines, a plant controller and optional equipment. The WECC models are intended to be finalized in 2015......, the IEC models are expected to be published in 2017....
A comprehensive numerical model of wind-blown sand
Kok, Jasper F
2009-01-01
Wind-blown sand, or "saltation", ejects dust aerosols into the atmosphere, creates sand dunes, and erodes geological features. We present a comprehensive numerical model of steady-state saltation that, in contrast to most previous studies, can simulate saltation over mixed soils. Our model simulates the motion of saltating particles due to gravity, fluid drag, particle spin, fluid shear, and turbulence. Moreover, the model explicitly accounts for the retardation of the wind due to drag from saltating particles. We also developed a physically-based parameterization of the ejection of surface particles by impacting saltating particles which matches experimental results. Our numerical model is the first to reproduce measurements of the wind shear velocity at the impact threshold (i.e., the lowest shear velocity for which saltation is possible) and of the aerodynamic roughness length in saltation. It also correctly predicts a wide range of other saltation processes, including profiles of the wind speed and partic...
Review of the dWind Model Conceptual Results
Energy Technology Data Exchange (ETDEWEB)
Baring-Gould, Ian; Gleason, Michael; Preus, Robert; Sigrin, Ben
2015-09-16
This presentation provides an overview of the dWind model, including its purpose, background, and current status. Baring-Gould presented this material as part of the September 2015 WINDExchange webinar.
Wind power electric systems modeling, simulation and control
Rekioua, Djamila
2014-01-01
The book helps readers understand key concepts in standalone and grid connected wind energy systems and features analysis into the modeling and optimization of commonly used configurations through the implementation of different control strategies.Utilizing several electrical machinery control approaches, such as vector control and direct torque control 'Wind Power Electric Systems' equips readers with the means to understand, assess and develop their own wind energy systems and to evaluate the performance of such systems.Mathematical models are provided for each system and a corresponding MAT
A Numerical Model for a Floating TLP Wind Turbine
DEFF Research Database (Denmark)
Kumari Ramachandran, Gireesh Kumar Vasanta
A numerical model is developed for a TLP configuration of a floating offshore wind turbine. The platform dynamics and hydrodynamic forces are derived and implemented in an advanced aero-elastic code, Flex5, to compute the hydro-aero-servo-elastic loads and responses on the floater and the wind...... irregular waves. In addition, the effect of wind-wave misalignment is investigated. Further, in the third step, the 3D platform dynamics and wave loading are implemented into Flex5, resulting in a fully coupled hydro-aero-servo-elastic code. The implementation is tested to make the model reliable and robust...
WRF Model Methodology for Offshore Wind Energy Applications
Directory of Open Access Journals (Sweden)
Evangelia-Maria Giannakopoulou
2014-01-01
Full Text Available Among the parameters that must be considered for an offshore wind farm development, the stability conditions of the marine atmospheric boundary layer (MABL are of significant importance. Atmospheric stability is a vital parameter in wind resource assessment (WRA due to its direct relation to wind and turbulence profiles. A better understanding of the stability conditions occurring offshore and of the interaction between MABL and wind turbines is needed. Accurate simulations of the offshore wind and stability conditions using mesoscale modelling techniques can lead to a more precise WRA. However, the use of any mesoscale model for wind energy applications requires a proper validation process to understand the accuracy and limitations of the model. For this validation process, the weather research and forecasting (WRF model has been applied over the North Sea during March 2005. The sensitivity of the WRF model performance to the use of different horizontal resolutions, input datasets, PBL parameterisations, and nesting options was examined. Comparison of the model results with other modelling studies and with high quality observations recorded at the offshore measurement platform FINO1 showed that the ERA-Interim reanalysis data in combination with the 2.5-level MYNN PBL scheme satisfactorily simulate the MABL over the North Sea.
Model simplification and optimization of a passive wind turbine generator
Sareni, Bruno; Abdelli, Abdenour; Roboam, Xavier; Tran, Duc-Hoan
2009-01-01
International audience; In this paper, the design of a "low cost full passive structure" of wind turbine system without active electronic part (power and control) is investigated. The efficiency of such device can be obtained only if the design parameters are mutually adapted through an optimization design approach. For this purpose, sizing and simulating models are developed to characterize the behavior and the efficiency of the wind turbine system. A model simplification approach is present...
Modeling and Identification of Harmonic Instability Problems In Wind Farms
DEFF Research Database (Denmark)
Ebrahimzadeh, Esmaeil; Blaabjerg, Frede; Wang, Xiongfei
2016-01-01
to identify harmonic instability problems in wind farms, where many wind turbines, cables, transformers, capacitor banks, shunt reactors, etc, typically are located. This methodology introduces the wind farm as a Multi-Input Multi-Outpur (MIMO) control system, where the linearized models of fast inner control......In power electronics based power systems like wind farms, the interactions between the inner control systems of the power converters and the passive components may lead to high frequency oscillations, which can be called harmonic instability. In this paper, a simple methodology is presented...... loops of the grid-side converters are considered. Therefore, instability problems of the whole wind farm are predicted based on the poles of the introduced MIMO system. In order to confirm the effectiveness of the proposed analytical approach, time-domain simulations are performed in the PSCAD...
Simulation platform to model, optimize and design wind turbines
Energy Technology Data Exchange (ETDEWEB)
Iov, F.; Hansen, A.D.; Soerensen, P.; Blaabjerg, F.
2004-03-01
This report is a general overview of the results obtained in the project 'Electrical Design and Control. Simulation Platform to Model, Optimize and Design Wind Turbines'. The motivation for this research project is the ever-increasing wind energy penetration into the power network. Therefore, the project has the main goal to create a model database in different simulation tools for a system optimization of the wind turbine systems. Using this model database a simultaneous optimization of the aerodynamic, mechanical, electrical and control systems over the whole range of wind speeds and grid characteristics can be achieved. The report is structured in six chapters. First, the background of this project and the main goals as well as the structure of the simulation platform is given. The main topologies for wind turbines, which have been taken into account during the project, are briefly presented. Then, the considered simulation tools namely: HAWC, DIgSILENT, Saber and Matlab/Simulink have been used in this simulation platform are described. The focus here is on the modelling and simulation time scale aspects. The abilities of these tools are complementary and they can together cover all the modelling aspects of the wind turbines e.g. mechanical loads, power quality, switching, control and grid faults. However, other simulation packages e.g PSCAD/EMTDC can easily be added in the simulation platform. New models and new control algorithms for wind turbine systems have been developed and tested in these tools. All these models are collected in dedicated libraries in Matlab/Simulink as well as in Saber. Some simulation results from the considered tools are presented for MW wind turbines. These simulation results focuses on fixed-speed and variable speed/pitch wind turbines. A good agreement with the real behaviour of these systems is obtained for each simulation tool. These models can easily be extended to model different kinds of wind turbines or large wind
Three-model ensemble wind prediction in southern Italy
Torcasio, Rosa Claudia; Federico, Stefano; Calidonna, Claudia Roberta; Avolio, Elenio; Drofa, Oxana; Landi, Tony Christian; Malguzzi, Piero; Buzzi, Andrea; Bonasoni, Paolo
2016-03-01
Quality of wind prediction is of great importance since a good wind forecast allows the prediction of available wind power, improving the penetration of renewable energies into the energy market. Here, a 1-year (1 December 2012 to 30 November 2013) three-model ensemble (TME) experiment for wind prediction is considered. The models employed, run operationally at National Research Council - Institute of Atmospheric Sciences and Climate (CNR-ISAC), are RAMS (Regional Atmospheric Modelling System), BOLAM (BOlogna Limited Area Model), and MOLOCH (MOdello LOCale in H coordinates). The area considered for the study is southern Italy and the measurements used for the forecast verification are those of the GTS (Global Telecommunication System). Comparison with observations is made every 3 h up to 48 h of forecast lead time. Results show that the three-model ensemble outperforms the forecast of each individual model. The RMSE improvement compared to the best model is between 22 and 30 %, depending on the season. It is also shown that the three-model ensemble outperforms the IFS (Integrated Forecasting System) of the ECMWF (European Centre for Medium-Range Weather Forecast) for the surface wind forecasts. Notably, the three-model ensemble forecast performs better than each unbiased model, showing the added value of the ensemble technique. Finally, the sensitivity of the three-model ensemble RMSE to the length of the training period is analysed.
Demonstration of the Ability of RCAS to Model Wind Turbines
Energy Technology Data Exchange (ETDEWEB)
Jonkman, J.; Cotrell, J.
2003-08-01
In recent years, the wind industry has sponsored the development, verification, and validation of comprehensive aeroelastic simulators, which are used for wind turbine design, certification, and research. Unfortunately, as wind turbines continue to grow in size and sometimes exhibit unconventional design characteristics, the existing codes do not always support the additional analysis features required for proper design. The development history, functionality, and advanced nature of RCAS (Rotorcraft Comprehensive Analysis System) make this code a sensible option. RCAS is an aeroelastic simulator developed over a 4-year cooperative effort amongst the U.S. Army's Aeroflightdynamics Directorate, Advanced Rotorcraft Technology (ART), Inc., and the helicopter industry. As its name suggests, RCAS was created for the rotorcraft industry but developed as a general purpose code for modeling the aerodynamic and structural response of any system with rotating and nonrotating subsystems (such as wind turbines). To demonstrate that RCAS can analyze wind turbines, models of a conventional, 1.5-MW, 3-bladed, upwind, horizontal axis wind turbine (HAWT) are created in RCAS and wind turbine analysis codes FAST (Fatigue, Aerodynamics, Structures, and Turbulence) and ADAMS (Automatic Dynamic Analysis of Mechanical Systems). Using these models, a side-by-side comparison of structural response predictions is performed under several test scenarios.
Empirical wind retrieval model based on SAR spectrum measurements
Panfilova, Maria; Karaev, Vladimir; Balandina, Galina; Kanevsky, Mikhail; Portabella, Marcos; Stoffelen, Ad
The present paper considers polarimetric SAR wind vector applications. Remote-sensing measurements of the near-surface wind over the ocean are of great importance for the understanding of atmosphere-ocean interaction. In recent years investigations for wind vector retrieval using Synthetic Aperture Radar (SAR) data have been performed. In contrast with scatterometers, a SAR has a finer spatial resolution that makes it a more suitable microwave instrument to explore wind conditions in the marginal ice zones, coastal regions and lakes. The wind speed retrieval procedure from scatterometer data matches the measured radar backscattering signal with the geophysical model function (GMF). The GMF determines the radar cross section dependence on the wind speed and direction with respect to the azimuthal angle of the radar beam. Scatterometers provide information on wind speed and direction simultaneously due to the fact that each wind vector cell (WVC) is observed at several azimuth angles. However, SAR is not designed to be used as a high resolution scatterometer. In this case, each WVC is observed at only one single azimuth angle. That is why for wind vector determination additional information such as wind streak orientation over the sea surface is required. It is shown that the wind vector can be obtained using polarimetric SAR without additional information. The main idea is to analyze the spectrum of a homogeneous SAR image area instead of the backscattering normalized radar cross section. Preliminary numerical simulations revealed that SAR image spectral maxima positions depend on the wind vector. Thus the following method for wind speed retrieval is proposed. In the first stage of the algorithm, the SAR spectrum maxima are determined. This procedure is carried out to estimate the wind speed and direction with ambiguities separated by 180 degrees due to the SAR spectrum symmetry. The second stage of the algorithm allows us to select the correct wind direction
Velocity measurement of model vertical axis wind turbines
Energy Technology Data Exchange (ETDEWEB)
Johnson, D.A.; McWilliam, M. [Waterloo Univ., ON (Canada). Dept. of Mechanical Engineering
2006-07-01
An increasingly popular solution to future energy demand is wind energy. Wind turbine designs can be grouped according to their axis of rotation, either horizontal or vertical. Horizontal axis wind turbines have higher power output in a good wind regime than vertical axis turbines and are used in most commercial class designs. Vertical axis Savonius-based wind turbine designs are still widely used in some applications because of their simplistic design and low wind speed performance. There are many design variables that must be considered in order to optimize the power output in a given wind regime in a typical wind turbine design. Using particle image velocimetry, a study of the air flow around five different model vertical axis wind turbines was conducted in a closed loop wind tunnel. A standard Savonius design with two semi-circular blades overlapping, and two variations of this design, a deep blade and a shallow blade design were among the turbine models included in this study. It also evaluated alternate designs that attempt to increase the performance of the standard design by allowing compound blade curvature. Measurements were collected at a constant phase angle and also at random rotor orientations. It was found that evaluation of the flow patterns and measured velocities revealed consistent and stable flow patterns at any given phase angle. Large scale flow structures are evident in all designs such as vortices shed from blade surfaces. An important performance parameter was considered to be the ability of the flow to remain attached to the forward blade and redirect and reorient the flow to the following blade. 6 refs., 18 figs.
Wind Turbine Control: Robust Model Based Approach
DEFF Research Database (Denmark)
Mirzaei, Mahmood
In the 1970s the oil price crisis encouraged investigation of non-petroleum energy sources of which wind energy was the most promising one. Lately global warming concerns have even intensified the demand for green and sustainable energy resources and opened up several lines of research in this area...
Models for wind turbines - a collection
DEFF Research Database (Denmark)
2002-01-01
This report is a collection of notes which were intended to be short communications. Main target of the work presented is to supply new approaches to stability investigations of wind turbines. The author's opinion is that an efficient, systematicstability analysis can not be performed for large...
Elements of extreme wind modeling for hurricanes
DEFF Research Database (Denmark)
Larsen, Søren Ejling; Ejsing Jørgensen, Hans; Kelly, Mark C.;
The report summarizes characteristics of the winds associated with Tropical Cyclones (Hurricanes, Typhoons). It has been conducted by the authors across several years, from 2012-2015, to identify the processes and aspects that one should consider when building at useful computer support system...
DEFF Research Database (Denmark)
Koukoura, Christina; Natarajan, Anand; Krogh, Thomas
2013-01-01
The variation in simulated monopile substructure loads is quantified by validating an aero-hydro-servo-elastic design tool with offshore foundation load measurements. A three bladed 3.6MW pitch controlled variable speed wind turbine for offshore monopile foundations is modeled in the HAWC2...... simulation code. A flexible soil model is included in the analysis. Fatigue loads analysis is performed for both the dynamic simulations and on-site foundation strain measurements. The wind farm wake effects on the monopile fatigue loads is also examined and compared with load measurements. Potential...
Wind climate estimation using WRF model output: method and model sensitivities over the sea
DEFF Research Database (Denmark)
Hahmann, Andrea N.; Vincent, Claire Louise; Peña, Alfredo
2015-01-01
setup parameters. The results of the year-long sensitivity simulations show that the long-term mean wind speed simulated by the WRF model offshore in the region studied is quite insensitive to the global reanalysis, the number of vertical levels, and the horizontal resolution of the sea surface......High-quality tall mast and wind lidar measurements over the North and Baltic Seas are used to validate the wind climatology produced from winds simulated by the Weather, Research and Forecasting (WRF) model in analysis mode. Biases in annual mean wind speed between model and observations at heights...... around 100m are smaller than 3.2% at offshore sites, except for those that are affected by the wake of a wind farm or the coastline. These biases are smaller than those obtained by using winds directly from the reanalysis. We study the sensitivity of the WRF-simulated wind climatology to various model...
Modelling and transient stability of large wind farms
DEFF Research Database (Denmark)
Akhmatov, Vladislav; Knudsen, Hans; Nielsen, Arne Hejde
2003-01-01
The paper is dealing-with modelling and short-term Voltage stability considerations of large wind farms. A physical model of a large offshore wind farm consisting of a large number of windmills is implemented in the dynamic simulation tool PSS/E. Each windmill in the wind farm is represented...... by a physical model of grid-connected windmills. The windmill generators ate conventional induction generators and the wind farm is ac-connected to the power system. Improvements-of short-term voltage stability in case of failure events in the external power system are treated with use of conventional generator...... of dynamic reactive compensation demands. In case of blade angle control applied at failure events, dynamic reactive compensation is not necessary for maintaining the voltage stability....
Wind Turbine Noise and Natural Sounds: Masking, Propagation and Modeling
Energy Technology Data Exchange (ETDEWEB)
Bolin, Karl
2009-05-15
Wind turbines are an environmentally friendly and sustainable power source. Unfortunately, the noise impact can cause deteriorated living conditions for nearby residents. The audibility of wind turbine sound is influenced by ambient sound. This thesis deals with some aspects of noise from wind turbines. Ambient sounds influence the audibility of wind turbine noise. Models for assessing two commonly occurring natural ambient sounds namely vegetation sound and sound from breaking waves are presented in paper A and B. A sound propagation algorithm has been compared to long range measurements of sound propagation in paper C. Psycho-acoustic tests evaluating the threshold and partial loudness of wind turbine noise when mixed with natural ambient sounds have been performed. These are accounted for in paper D. The main scientific contributions are the following.Paper A: A semi-empiric prediction model for vegetation sound is proposed. This model uses up-to-date simulations of wind profiles and turbulent wind fields to estimate sound from vegetation. The fluctuations due to turbulence are satisfactory estimated by the model. Predictions of vegetation sound also show good agreement to measured spectra. Paper B: A set of measurements of air-borne sound from breaking waves are reported. From these measurements a prediction method of sound from breaking waves is proposed. Third octave spectra from breaking waves are shown to depend on breaker type. Satisfactory agreement between predictions and measurements has been achieved. Paper C: Long range sound propagation over a sea surface was investigated. Measurements of sound transmission were coordinated with local meteorological measurements. A sound propagation algorithm has been compared to the measured sound transmission. Satisfactory agreement between measurements and predictions were achieved when turbulence were taken into consideration in the computations. Paper D: The paper investigates the interaction between wind
Measurements on and modelling of offshore wind farms
Energy Technology Data Exchange (ETDEWEB)
Frandsen, S. [ed.
1996-11-01
The primary project component was measurement on the Vindeby Offshore Wind Farm. Also included are analyses of fatigue loading on the turbines, sea climate, performance of the wind farm and modelling of flow characteristics inside the wind farm. These individual analyses were made to meet the overall objective, which was to devise an adequate design tool to take into account the increased dynamic loading in wind farms. Measurements have been conducted for several years on the wind farm at Vindeby 2-3 km off the coast of the island of Lolland in the South Baltic Sea. The Vindeby Wind Farm consists of 11 Bonus machines with installed capacities of 450 kW, hub height 38 m and rotor diameter 35 m. The separations of the machines in the rows are 300 m (8.6D), and the distance between the rows is equally 300 m. Two machines, 4W and 5E are instrumented for structural measurements; tower base bending, yaw and tilt and edge and flapwise blade root bending moments are measured and statistics for 1/2 hourly consecutive time periods are stored. The statistics include minimum, maximum, mean, standard deviation and the so-called equivalent load widths. The equivalent load width is popularly speaking the amplitude of a sinusoidal load with frequency equal - in this case - to rotational frequency of the wind turbine rotor that would consume the same fatigue life as the actual load sequence. Modelling of fatigue loading in offshore wind farms and the offshore wind climate was carried out with good results. Also, computational flow modelling was performed. (au) 40 tabs., 130 ills., 114 refs.
Towards an understanding of staggering effects in dissipative binary collisions
Energy Technology Data Exchange (ETDEWEB)
D' Agostino, M., E-mail: dagostino@bo.infn.it [Dipartimento di Fisica dell' Universita, Bologna (Italy); INFN, Bologna (Italy); Bruno, M. [Dipartimento di Fisica dell' Universita, Bologna (Italy); INFN, Bologna (Italy); Gulminelli, F. [CNRS, UMR6534, LPC, F-14050 Caen cedex and ENSICAEN, UMR6534, LPC, F-14050 Caen cedex (France); Morelli, L. [Dipartimento di Fisica dell' Universita, Bologna (Italy); INFN, Bologna (Italy); Baiocco, G. [Dipartimento di Fisica dell' Universita, Bologna (Italy); INFN, Bologna (Italy); CNRS, UMR6534, LPC, F-14050 Caen cedex and ENSICAEN, UMR6534, LPC, F-14050 Caen cedex (France); Bardelli, L. [INFN, Firenze (Italy); INFN, Catania (Italy); Barlini, S. [INFN, Firenze (Italy); Cannata, F. [INFN, Bologna (Italy); Casini, G. [INFN, Firenze (Italy); Geraci, E. [Dipartimento di Fisica dell' Universita, Catania (Italy); INFN, Catania (Italy); Gramegna, F.; Kravchuk, V.L. [INFN, Laboratori Nazionali di Legnaro (Italy); Marchi, T. [INFN, Laboratori Nazionali di Legnaro (Italy); Dipartimento di Fisica dell' Universita, Padova,Italy (Italy); Moroni, A. [INFN, Milano (Italy); Ordine, A. [INFN, Napoli (Italy); Raduta, Ad.R. [NIPNE, Bucharest-Magurele, POB-MG6 (Romania)
2012-02-01
The reactions {sup 32}S+{sup 58,64}Ni are studied at 14.5 A MeV. Evidence is found for important odd-even effects in isotopic observables of selected peripheral collisions corresponding to the decay of a projectile-like source. The influence of secondary decays on the staggering is studied with a correlation function technique. It is shown that this method is a powerful tool to get experimental information on the evaporation chain, in order to constrain model calculations. Specifically, we show that odd-even effects are due to interplay between pairing effects in the nuclear masses and in the level densities.
Towards an understanding of staggering effects in dissipative binary collisions
D'Agostino, M.; Bruno, M.; Gulminelli, F.; Morelli, L.; Baiocco, G.; Bardelli, L.; Barlini, S.; Cannata, F.; Casini, G.; Geraci, E.; Gramegna, F.; Kravchuk, V. L.; Marchi, T.; Moroni, A.; Ordine, A.; Raduta, Ad. R.
2012-02-01
The reactions S32+58Ni are studied at 14.5 A MeV. Evidence is found for important odd-even effects in isotopic observables of selected peripheral collisions corresponding to the decay of a projectile-like source. The influence of secondary decays on the staggering is studied with a correlation function technique. It is shown that this method is a powerful tool to get experimental information on the evaporation chain, in order to constrain model calculations. Specifically, we show that odd-even effects are due to interplay between pairing effects in the nuclear masses and in the level densities.
Bossuyt, Juliaan; Howland, Michael; Meneveau, Charles; Meyers, Johan
2015-11-01
To optimize wind farm layouts for a maximum power output and wind turbine lifetime, mean power output measurements in wind tunnel studies are not sufficient. Instead, detailed temporal information about the power output and unsteady loading from every single wind turbine in the wind farm is needed. A very small porous disc model with a realistic thrust coefficient of 0.75 - 0.85, was designed. The model is instrumented with a strain gage, allowing measurements of the thrust force, incoming velocity and power output with a frequency response up to the natural frequency of the model. This is shown by reproducing the -5/3 spectrum from the incoming flow. Thanks to its small size and compact instrumentation, the model allows wind tunnel studies of large wind turbine arrays with detailed temporal information from every wind turbine. Translating to field conditions with a length-scale ratio of 1:3,000 the frequencies studied from the data reach from 10-4 Hz up to about 6 .10-2 Hz. The model's capabilities are demonstrated with a large wind farm measurement consisting of close to 100 instrumented models. A high correlation is found between the power outputs of stream wise aligned wind turbines, which is in good agreement with results from prior LES simulations. Work supported by ERC (ActiveWindFarms, grant no. 306471) and by NSF (grants CBET-113380 and IIA-1243482, the WINDINSPIRE project).
Optimization of horizontal well staggered patterns
Institute of Scientific and Technical Information of China (English)
Zhao Chunsen; Li Peijing; Guan Dan; Liu Qingjuan
2008-01-01
Staggered line-drive patterns are widely used in oilfields. In this paper, to optimize a staggered pattern of horizontal wells, a 3D problem was divided into two 2D (x-y plane and y-z plane) problems with the pseudo-3D method, conformal transformation and superposition principle. A productivity equation for a horizontal well was deduced, which can be used to optimize the well pattern. A relationship between the length of horizontal wells and the shape factor of well patterns was established. The result shows that optimized well patterns can improve oil production from horizontal wells. This provides a theoretical basis for horizontal well applications to the development of oilfieids, especially for overall development of oilfields by horizontal wells.
DEFF Research Database (Denmark)
Collet, Remo; Magic, Zazralt; Asplund, Martin
2011-01-01
In this contribution, we present the STAGGERGRID, a collaborative project for the construction of a comprehensive grid of time-dependent, three-dimensional (3-D), hydrodynamic model atmospheres of solar- and late-type stars with different effective temperatures, surface gravities, and chemical co...... of their possible applications to elemental abundance analysis of stellar spectra in the context of large observational surveys.......In this contribution, we present the STAGGERGRID, a collaborative project for the construction of a comprehensive grid of time-dependent, three-dimensional (3-D), hydrodynamic model atmospheres of solar- and late-type stars with different effective temperatures, surface gravities, and chemical...
A new barotropic model of the wind-driven circulation
Institute of Scientific and Technical Information of China (English)
张庆华; 曲媛媛; 李坚克
1999-01-01
Rationalized by the observational circulation pattern in the upper ocean of the North Pacific, meridional friction term is first incorporated in a barotropic theoretical model of the wind-driven circulation. The governing potential vortieity equation thence has β term and wind stress curl term (the two of the Sverdrup balance), zonal friction term and meridional friction term. The analytical solution satisfactorily captures many important features of the wind-driven circulation in the North Pacific: Kuroshio, Oyashio, Kuroshio extension, North Equatorial Current, and especially the eastern boundary currents in the North Pacific, i.e. California current and Alaska current.
Multicriteria GIS modeling of wind and solar farms in Colorado
Energy Technology Data Exchange (ETDEWEB)
Janke, Jason R. [Metropolitan State College of Denver, Department of Earth and Atmospheric Sciences, CB 22 P.O. Box 173362-22, Denver, CO 80217-3362 (United States)
2010-10-15
The majority of electricity and heat in Colorado comes from coal and natural gas; however, renewable energy sources will play an integral role in the state's energy future. Colorado is the 11th windiest state and has more than 250 sunny days per year. The objectives of this research are to: 1) determine which landcover classes are affiliated with high wind and solar potential; and 2) identify areas that are suitable for wind and solar farms using multicriteria GIS modelling techniques. Renewable potential (NREL wind speed measurements at 50 m above the ground and NREL annual insolation data), landcover, population density, federal lands, and distance to roads, transmission lines, and cities were reclassified according to their suitability. Each was assigned weights based on their relative importance to one another. Superb wind classes are located in high alpine areas. Unfortunately, these areas are not suitable for large-scale wind farm development due to their inaccessibility and location within a sensitive ecosystem. Federal lands have low wind potential. According to the GIS model, ideal areas for wind farm development are located in northeastern Colorado. About 41 850 km{sup 2} of the state has model scores that are in the 90-100% range. Although annual solar radiation varies slightly, inter-mountain areas receive the most insolation. As far as federal lands, Indian reservations have the greatest solar input. The GIS model indicates that ideal areas for solar development are located in northwestern Colorado and east of Denver. Only 191 km{sup 2} of the state had model scores that were in the 90-100% range. These results suggest that the variables used in this analysis have more of an effect at eliminating non-suitable areas for large-scale solar farms; a greater area exists for suitable wind farms. However, given the statewide high insolation values with minimal variance, solar projects may be better suited for small-scale residential or commercial
Moriarty, Patrick; Sanz Rodrigo, Javier; Gancarski, Pawel; Chuchfield, Matthew; Naughton, Jonathan W.; Hansen, Kurt S.; Machefaux, Ewan; Maguire, Eoghan; Castellani, Francesco; Terzi, Ludovico; Breton, Simon-Philippe; Ueda, Yuko
2014-06-01
Researchers within the International Energy Agency (IEA) Task 31: Wakebench have created a framework for the evaluation of wind farm flow models operating at the microscale level. The framework consists of a model evaluation protocol integrated with a web-based portal for model benchmarking (www.windbench.net). This paper provides an overview of the building-block validation approach applied to wind farm wake models, including best practices for the benchmarking and data processing procedures for validation datasets from wind farm SCADA and meteorological databases. A hierarchy of test cases has been proposed for wake model evaluation, from similarity theory of the axisymmetric wake and idealized infinite wind farm, to single-wake wind tunnel (UMN-EPFL) and field experiments (Sexbierum), to wind farm arrays in offshore (Horns Rev, Lillgrund) and complex terrain conditions (San Gregorio). A summary of results from the axisymmetric wake, Sexbierum, Horns Rev and Lillgrund benchmarks are used to discuss the state-of-the-art of wake model validation and highlight the most relevant issues for future development.
Numerical properties of staggered overlap fermions
de Forcrand, Philippe; Panero, Marco
2010-01-01
We report the results of a numerical study of staggered overlap fermions, following the construction of Adams which reduces the number of tastes from 4 to 2 without fine-tuning. We study the sensitivity of the operator to the topology of the gauge field, its locality and its robustness to fluctuations of the gauge field. We make a first estimate of the computing cost of a quark propagator calculation, and compare with Neuberger's overlap.
Model predictive control for wind power gradients
DEFF Research Database (Denmark)
Hovgaard, Tobias Gybel; Boyd, Stephen; Jørgensen, John Bagterp
2015-01-01
ranges. The system dynamics are quite non-linear, and the constraints and objectives are not convex functions of the control inputs, so the resulting optimal control problem is difficult to solve globally. In this paper, we show that by a novel change of variables, which focuses on power flows, we can......We consider the operation of a wind turbine and a connected local battery or other electrical storage device, taking into account varying wind speed, with the goal of maximizing the total energy generated while respecting limits on the time derivative (gradient) of power delivered to the grid. We...... transform the problem to one with linear dynamics and convex constraints. Thus, the problem can be globally solved, using robust, fast solvers tailored for embedded control applications. We implement the optimal control problem in a receding horizon manner and provide extensive closed-loop tests with real...
Impacts of Wake Effect and Time Delay on the Dynamic Analysis of Wind Farms Models
El-Fouly, Tarek H. M.; El-Saadany, Ehab F.; Salama, Magdy M. A.
2008-01-01
This article investigates the impacts of proper modeling of the wake effects and wind speed delays, between different wind turbines' rows, on the dynamic performance accuracy of the wind farms models. Three different modeling scenarios were compared to highlight the impacts of wake effects and wind speed time-delay models. In the first scenario,…
Preliminary modelling study of ice accretion on wind turbines
DEFF Research Database (Denmark)
Pedersen, Marie Cecilie; Yin, Chungen
2014-01-01
One of the main challenges associated with cold-climate wind energy is icing on wind turbines and a series of icing-induced problems such as production loss, blade fatigue and safety issues. Because of the difficulties with on-site measurements, simulations are often used to understand and predict...... icing events. In this paper, a new methodology for prediction of icing-induced production loss is proposed, from which the fundamentals of ice accretion on wind turbines can be better understood and the operational production losses can be more reliably predicted. Computational fluid dynamics (CFD......) modelling of ice accretion on wind turbines is also performed for different ice events, resulting in a reliable framework for CFD-based ice accretion modelling which is one of the key elements in the new methodology....
Optimization model for rotor blades of horizontal axis wind turbines
Institute of Scientific and Technical Information of China (English)
LIU Xiong; CHEN Yan; YE Zhiquan
2007-01-01
This paper presents an optimization model for rotor blades of horizontal axis wind turbines. The model refers to the wind speed distribution function on the specific wind site, with an objective to satisfy the maximum annual energy output. To speed up the search process and guarantee a global optimal result, the extended compact genetic algorithm (ECGA) is used to carry out the search process.Compared with the simple genetic algorithm, ECGA runs much faster and can get more accurate results with a much smaller population size and fewer function evaluations. Using the developed optimization program, blades of a 1.3 MW stall-regulated wind turbine are designed. Compared with the existing blades, the designed blades have obviously better aerodynamic performance.
A high resolution WRF model for wind energy forecasting
Vincent, Claire Louise; Liu, Yubao
2010-05-01
The increasing penetration of wind energy into national electricity markets has increased the demand for accurate surface layer wind forecasts. There has recently been a focus on forecasting the wind at wind farm sites using both statistical models and numerical weather prediction (NWP) models. Recent advances in computing capacity and non-hydrostatic NWP models means that it is possible to nest mesoscale models down to Large Eddy Simulation (LES) scales over the spatial area of a typical wind farm. For example, the WRF model (Skamarock 2008) has been run at a resolution of 123 m over a wind farm site in complex terrain in Colorado (Liu et al. 2009). Although these modelling attempts indicate a great hope for applying such models for detailed wind forecasts over wind farms, one of the obvious challenges of running the model at this resolution is that while some boundary layer structures are expected to be modelled explicitly, boundary layer eddies into the inertial sub-range can only be partly captured. Therefore, the amount and nature of sub-grid-scale mixing that is required is uncertain. Analysis of Liu et al. (2009) modelling results in comparison to wind farm observations indicates that unrealistic wind speed fluctuations with a period of around 1 hour occasionally occurred during the two day modelling period. The problem was addressed by re-running the same modelling system with a) a modified diffusion constant and b) two-way nesting between the high resolution model and its parent domain. The model, which was run with horizontal grid spacing of 370 m, had dimensions of 505 grid points in the east-west direction and 490 points in the north-south direction. It received boundary conditions from a mesoscale model of resolution 1111 m. Both models had 37 levels in the vertical. The mesoscale model was run with a non-local-mixing planetary boundary layer scheme, while the 370 m model was run with no planetary boundary layer scheme. It was found that increasing the
Modeling an autonomous wind turbine electric pump system
Directory of Open Access Journals (Sweden)
Andreea Forcos
2009-10-01
Full Text Available Being one of the variable renewable energy sources, wind energy integration can be made using storage methods. All of these have been developed during time, but one might be more accessible than others because is using a free natural resource, water. This is pump storage. The purpose of this paper is modeling an autonomous wind turbine connected to an electric pump, in the aim of storage, and finally the determination of the efficiency.
Experimental investigation into the degradation of model superconducting windings
Energy Technology Data Exchange (ETDEWEB)
Trusov, N.B.; Broitman, I.M.; Pleshchunov, N.N.; Samoilov, S.F.
1984-01-01
Results are reported for an investigation into degradation of critical current in model compound-treated windings fabricated from type KETV-2NT superconducting conductors with nonsteady stabilization. It is shown that the way in which the critical current depends on the heat-removal conditions and the rate of entry of current is determined by a mechanism of steady-state heat release occationed by plastic strain of the winding materials under the action of ponderomotive forces.
Directory of Open Access Journals (Sweden)
Naresh Kumari
2016-04-01
Full Text Available The power generation with non-renewable energy sources has very harmful effects on the environment as well as these sources are depleting. On the other side the renewable energy sources are quite unpredictable source of power. The best trade-off is to use the combination of both kind of sources to make a hybrid system so that their individual power generation constraints can be overcome. The hybrid system taken for analysis in this work comprises of wind and diesel power generation systems. The complete modelling of the system has been done in MATLAB/SIMULINK environment. Doubly fed induction generator (DFIG is used for power generation in wind power system. The modelling has been done considering the changing wind speed and varying load conditions. The mathematical models of DFIG and diesel power generator have been used to develop the simulink model which can be used for analysis of various performances of the system like frequency response and power sharing between different sources with load variation .The generating margin of DFIG is also simulated for the frequency support during varying load conditions .The generating margin is created by the control of active power output from DFIG. Also as the power demand rises the generating margin of DFIG keeps the balance between the power generation and load. Proportional Integral controller has been used for diesel generator plant for frequency control. The controller gains have been optimized with Particle Swarm Optimization technique. The proper selection of controller gains and wind power reserve help to achieve the enhanced frequency response of the hybrid system.
2012-03-05
2003) and Schwadron et al. (2005) as constraints. The new relationship was tested by using it to drive the ENLIL 3‐D MHD solar wind model and obtain...it to drive the ENLIL 3‐D MHD solar wind model and obtain solar wind parameters at Earth (1.0 AU) and Ulysses (1.4 AU). The improvements in speed...propagated out into the heliosphere using the ENLIL solar wind model . ENLIL is a 3‐D Magne- tohydrodynamic ( MHD ) model of the heliosphere [Odstrcil, 2003
Evaluation of RCAS Inflow Models for Wind Turbine Analysis
Energy Technology Data Exchange (ETDEWEB)
Tangler, J.; Bir, G.
2004-02-01
The finite element structural modeling in the Rotorcraft Comprehensive Analysis System (RCAS) provides a state-of-the-art approach to aeroelastic analysis. This, coupled with its ability to model all turbine components, results in a methodology that can simulate complex system interactions characteristic of large wind. In addition, RCAS is uniquely capable of modeling advanced control algorithms and the resulting dynamic responses.
Nonlinear Eddy Viscosity Models applied to Wind Turbine Wakes
DEFF Research Database (Denmark)
Laan, van der, Paul Maarten; Sørensen, Niels N.; Réthoré, Pierre-Elouan;
2013-01-01
The linear k−ε eddy viscosity model and modified versions of two existing nonlinear eddy viscosity models are applied to single wind turbine wake simulations using a Reynolds Averaged Navier-Stokes code. Results are compared with field wake measurements. The nonlinear models give better results...
An aerodynamic noise propagation model for wind turbines
DEFF Research Database (Denmark)
Zhu, Wei Jun; Sørensen, Jens Nørkær; Shen, Wen Zhong
2005-01-01
A model based on 2-D sound ray theory for aerodynamic noise propagation from wind turbine rotating blades is introduced. The model includes attenuation factors from geometric spreading, sound directivity of source, air absorption, ground deflection and reflection, as well as effects from temperat......A model based on 2-D sound ray theory for aerodynamic noise propagation from wind turbine rotating blades is introduced. The model includes attenuation factors from geometric spreading, sound directivity of source, air absorption, ground deflection and reflection, as well as effects from...
Wind adaptive modeling of transmission lines using minimum description length
Jaw, Yoonseok; Sohn, Gunho
2017-03-01
The transmission lines are moving objects, which positions are dynamically affected by wind-induced conductor motion while they are acquired by airborne laser scanners. This wind effect results in a noisy distribution of laser points, which often hinders accurate representation of transmission lines and thus, leads to various types of modeling errors. This paper presents a new method for complete 3D transmission line model reconstruction in the framework of inner and across span analysis. The highlighted fact is that the proposed method is capable of indirectly estimating noise scales, which corrupts the quality of laser observations affected by different wind speeds through a linear regression analysis. In the inner span analysis, individual transmission line models of each span are evaluated based on the Minimum Description Length theory and erroneous transmission line segments are subsequently replaced by precise transmission line models with wind-adaptive noise scale estimated. In the subsequent step of across span analysis, detecting the precise start and end positions of the transmission line models, known as the Point of Attachment, is the key issue for correcting partial modeling errors, as well as refining transmission line models. Finally, the geometric and topological completion of transmission line models are achieved over the entire network. A performance evaluation was conducted over 138.5 km long corridor data. In a modest wind condition, the results demonstrates that the proposed method can improve the accuracy of non-wind-adaptive initial models on an average of 48% success rate to produce complete transmission line models in the range between 85% and 99.5% with the positional accuracy of 9.55 cm transmission line models and 28 cm Point of Attachment in the root-mean-square error.
Investigation on the integral output power model of a large-scale wind farm
Institute of Scientific and Technical Information of China (English)
BAO Nengsheng; MA Xiuqian; NI Weidou
2007-01-01
The integral output power model of a large-scale wind farm is needed when estimating the wind farm's output over a period of time in the future.The actual wind speed power model and calculation method of a wind farm made up of many wind turbine units are discussed.After analyzing the incoming wind flow characteristics and their energy distributions,and after considering the multi-effects among the wind turbine units and certain assumptions,the incoming wind flow model of multi-units is built.The calculation algorithms and steps of the integral output power model of a large-scale wind farm are provided.Finally,an actual power output of the wind farm is calculated and analyzed by using the practical measurement wind speed data.The characteristics of a large-scale wind farm are also discussed.
Wave modelling for the North Indian Ocean using MSMR analysed winds
Digital Repository Service at National Institute of Oceanography (India)
Vethamony, P.; Sudheesh, K.; Rupali, S.P.; Babu, M.T.; Jayakumar, S.; Saran, A.K.; Basu, S.K.; Kumar, R.; Sarkar, A.
NCMRWF (National Centre for Medium Range Weather Forecast) winds assimilated with MSMR (Multi-channel Scanning Microwave Radiometer) winds are used as input to MIKE21 Offshore Spectral Wave model (OSW) which takes into account wind induced wave...
Modeling of uncertainties for wind turbine blade design
DEFF Research Database (Denmark)
Sørensen, John Dalsgaard; Toft, Henrik Stensgaard
2014-01-01
Wind turbine blades are designed by a combination of tests and numerical calculations using finite element models of the blade. The blades are typically composite structures with laminates of glass-fiber and/or carbon-fibers glued together by a matrix material. This paper presents a framework...... for stochastic modelling of the load bearing capacity of wind turbine blades incorporating physical, model, measurement and statistical uncertainties at the different scales and also discusses the possibility to define numerical tests that can be included in the statistical basis. The stochastic modelling takes...... basis in the JCSS framework for modelling material properties, Bayesian statistical methods allowing prior / expert knowledge to be accounted for and the Maximum Likelihood Method. The stochastic framework is illustrated using simulated tests which represent examples relevant for wind turbine blades....
Wind waves in tropical cyclones: satellite altimeter observations and modeling
Golubkin, Pavel; Kudryavtsev, Vladimir; Chapron, Bertrand
2016-04-01
Results of investigation of wind-wave generation by tropical cyclones using satellite altimeter data are presented. Tropical cyclones are generally relatively small rapidly moving low pressure systems that are capable of generating severe wave conditions. Translation of a tropical cyclone leads to a prolonged period of time surface waves in the right sector remain under high wind forcing conditions. This effect has been termed extended fetch, trapped fetch or group velocity quasi-resonance. A tropical cyclone wave field is thus likely more asymmetrical than the corresponding wind field: wind waves in the tropical cyclone right sector are more developed with larger heights than waves in the left one. A dataset of satellite altimeter intersections of the Western Pacific tropical cyclones was created for 2010-2013. Data from four missions were considered, i.e., Jason-1, Jason-2, CryoSat-2, SARAL/AltiKa. Measurements in the rear-left and front-right sectors of tropical cyclones were examined for the presence of significant wave asymmetry. An analytical model is then derived to efficiently describe the wave energy distribution in a moving tropical cyclone. The model essentially builds on a generalization of the self-similar wave growth model and the assumption of a strongly dominant single spectral mode in a given quadrant of the storm. The model provides a criterion to anticipate wave enhancement with the generation of trapped abnormal waves. If forced during a sufficient timescale interval, also defined from this generalized self-similar wave growth model, waves can be trapped and large amplification of the wave energy will occur in the front-right storm quadrant. Remarkably, the group velocity and corresponding wavelength of outrunning wave systems will become wind speed independent and solely relate to the translating velocity. The resulting significant wave height also only weakly depends on wind speed, and more strongly on the translation velocity. Satellite
Effects of subgrid-scale modeling on wind turbines flows
Ciri, Umberto; Salvetti, Maria Vittoria; Leonardi, Stefano
2015-11-01
The increased demand for wind energy had led to a continuous increase in the size of wind turbines and, consequently, of wind farms. A potential drawback of such large clusters lies in the decrease in the efficiency due to the wake interference. Large-Eddy Simulations (LES) coupled with blade models have shown the capability of resolving the unsteady nature of wind turbine wakes. In LES, subgrid-scale (SGS) models are needed to introduce the effect of the turbulence small scales not resolved by the computational grid. Many LES of wind farms employ the classic Smagorinsky model, despite it suffers from some major drawbacks, e.g. (i) the presence of an input tuning parameter and (ii) the wrong behaviour near solid walls. In the present work an analysis of the effects of various SGS models is carried out for LES in which the turbine tower and nacelle are directly simulated with the Immersed Boundaries method. Particular attention is dedicated to the region of separated flow behind the tower where the impact of the SGS models is expected to be important. We focus herein on non-dynamic eddy-viscosity models, which have proven to have a correct behaviour near solid walls. A priori and a posteriori tests are performed for a configuration reproducing an experiment conducted at NTNU. The work is partially supported by the NSF PIRE Award IIA 1243482. TACC is acknowledged for providing computational time.
Using albedo to reform wind erosion modelling, mapping and monitoring
Chappell, Adrian; Webb, Nicholas P.
2016-12-01
Wind erosion and dust emission models are used to assess the impacts of dust on radiative forcing in the atmosphere, cloud formation, nutrient fertilisation and human health. The models are underpinned by a two-dimensional geometric property (lateral cover; L) used to characterise the three-dimensional aerodynamic roughness (sheltered area or wakes) of the Earth's surface and calibrate the momentum it extracts from the wind. We reveal a fundamental weakness in L and demonstrate that values are an order of magnitude too small and significant aerodynamic interactions between roughness elements and their sheltered areas have been omitted, particularly under sparse surface roughness. We describe a solution which develops published work to establish a relation between sheltered area and the proportion of shadow over a given area; the inverse of direct beam directional hemispherical reflectance (black sky albedo; BSA). We show direct relations between shadow and wind tunnel measurements and thereby provide direct calibrations of key aerodynamic properties. Estimation of the aerodynamic parameters from albedo enables wind erosion assessments over areas, across platforms from the field to airborne and readily available satellite data. Our new approach demonstrated redundancy in existing wind erosion models and thereby reduced model complexity and improved fidelity. We found that the use of albedo enabled an adequate description of aerodynamic sheltering to characterise fluid dynamics and predict sediment transport without the use of a drag partition scheme (Rt) or threshold friction velocity (u∗t). We applied the calibrations to produce global maps of aerodynamic properties which showed very similar spatial patterns to each other and confirmed the redundancy in the traditional parameters of wind erosion modelling. We evaluated temporal patterns of predicted horizontal mass flux at locations across Australia which revealed variation between land cover types that would not
Wind Tunnel Management and Resource Optimization: A Systems Modeling Approach
Jacobs, Derya, A.; Aasen, Curtis A.
2000-01-01
Time, money, and, personnel are becoming increasingly scarce resources within government agencies due to a reduction in funding and the desire to demonstrate responsible economic efficiency. The ability of an organization to plan and schedule resources effectively can provide the necessary leverage to improve productivity, provide continuous support to all projects, and insure flexibility in a rapidly changing environment. Without adequate internal controls the organization is forced to rely on external support, waste precious resources, and risk an inefficient response to change. Management systems must be developed and applied that strive to maximize the utility of existing resources in order to achieve the goal of "faster, cheaper, better". An area of concern within NASA Langley Research Center was the scheduling, planning, and resource management of the Wind Tunnel Enterprise operations. Nine wind tunnels make up the Enterprise. Prior to this research, these wind tunnel groups did not employ a rigorous or standardized management planning system. In addition, each wind tunnel unit operated from a position of autonomy, with little coordination of clients, resources, or project control. For operating and planning purposes, each wind tunnel operating unit must balance inputs from a variety of sources. Although each unit is managed by individual Facility Operations groups, other stakeholders influence wind tunnel operations. These groups include, for example, the various researchers and clients who use the facility, the Facility System Engineering Division (FSED) tasked with wind tunnel repair and upgrade, the Langley Research Center (LaRC) Fabrication (FAB) group which fabricates repair parts and provides test model upkeep, the NASA and LARC Strategic Plans, and unscheduled use of the facilities by important clients. Expanding these influences horizontally through nine wind tunnel operations and vertically along the NASA management structure greatly increases the
Overload prevention in model supports for wind tunnel model testing
Directory of Open Access Journals (Sweden)
Anton IVANOVICI
2015-09-01
Full Text Available Preventing overloads in wind tunnel model supports is crucial to the integrity of the tested system. Results can only be interpreted as valid if the model support, conventionally called a sting remains sufficiently rigid during testing. Modeling and preliminary calculation can only give an estimate of the sting’s behavior under known forces and moments but sometimes unpredictable, aerodynamically caused model behavior can cause large transient overloads that cannot be taken into account at the sting design phase. To ensure model integrity and data validity an analog fast protection circuit was designed and tested. A post-factum analysis was carried out to optimize the overload detection and a short discussion on aeroelastic phenomena is included to show why such a detector has to be very fast. The last refinement of the concept consists in a fast detector coupled with a slightly slower one to differentiate between transient overloads that decay in time and those that are the result of aeroelastic unwanted phenomena. The decision to stop or continue the test is therefore conservatively taken preserving data and model integrity while allowing normal startup loads and transients to manifest.
DEFF Research Database (Denmark)
Peña, Alfredo; Réthoré, Pierre-Elouan; Rathmann, Ole
2013-01-01
Here, we evaluate a modified version of the Park wake model against power data from a west-east row in the middle of the Horns Rev I offshore wind farm. The evaluation is performed on data classified in four different atmospheric stability conditions, for a narrow wind speed range, and a wide ran....... The simulations do not approach the limits of the infinite wind farm under any stability condition as winds are not parallel to the row....
Model 0A wind turbine generator FMEA
Klein, William E.; Lalli, Vincent R.
1989-01-01
The results of Failure Modes and Effects Analysis (FMEA) conducted for the Wind Turbine Generators are presented. The FMEA was performed for the functional modes of each system, subsystem, or component. The single-point failures were eliminated for most of the systems. The blade system was the only exception. The qualitative probability of a blade separating was estimated at level D-remote. Many changes were made to the hardware as a result of this analysis. The most significant change was the addition of the safety system. Operational experience and need to improve machine availability have resulted in subsequent changes to the various systems which are also reflected in this FMEA.
Stochastic Optimization of Wind Turbine Power Factor Using Stochastic Model of Wind Power
DEFF Research Database (Denmark)
Chen, Peiyuan; Siano, Pierluigi; Bak-Jensen, Birgitte
2010-01-01
. The optimization algorithm utilizes the stochastic models of wind power generation (WPG) and load demand to take into account their stochastic variation. The stochastic model of WPG is developed on the basis of a limited autoregressive integrated moving average (LARIMA) model by introducing a crosscorrelation......This paper proposes a stochastic optimization algorithm that aims to minimize the expectation of the system power losses by controlling wind turbine (WT) power factors. This objective of the optimization is subject to the probability constraints of bus voltage and line current requirements...... structure to the LARIMA model. The proposed stochastic optimization is carried out on a 69-bus distribution system. Simulation results confirm that, under various combinations of WPG and load demand, the system power losses are considerably reduced with the optimal setting of WT power factor as compared...
Critical review of wind tunnel modeling of atmospheric heat dissipation
Energy Technology Data Exchange (ETDEWEB)
Orgill, M.M.
1977-05-01
There is increasing concern by scientists that future proposed energy or power parks may significantly affect the environment by releasing large quantities of heat and water vapor to the atmosphere. A critical review is presented of the potential application of physical modeling (wind tunnels) to assess possible atmospheric effects from heat dissipation systems such as cooling towers. A short inventory of low-speed wind tunnel facilities is included in the review. The useful roles of wind tunnels are assessed and the state-of-the-art of physical modeling is briefly reviewed. Similarity criteria are summarized and present limitations in satisfying these criteria are considered. Current physical models are defined and limitations are discussed. Three experimental problems are discussed in which physical modeling may be able to provide data. These are: defining the critical atmospheric heat load; topographic and local circulation effects on thermal plumes; and plume rise and downstream effects.
Wake models developed during the Wind Shadow project
Energy Technology Data Exchange (ETDEWEB)
Larsen, S.; Ott, S.; Pena, A.; Berg, J.; Nielsen, M.; Rathmann, O.; Joergensen, H.
2011-11-15
The Wind Shadow project has developed and validated improved models for determining the wakes losses, and thereby the array efficiency of very large, closely packed wind farms. The rationale behind the project has been that the existing software has been covering these types of wind farms poorly, both with respect to the densely packed turbines and the large fetches needed to describe the collective shadow effects of one farm to the next. Further the project has developed the necessary software for the use of the models. Guidelines with recommendations for the use of the models are included in the model deliverables. The project has been carried out as a collaborative project between Risoe DTU, DONG, Vattenfall, DNV and VESTAS, and it has been financed by energinet.dk grant no. 10086. (Author)
Modelling of a PMSG Wind Turbine with Autonomous Control
Directory of Open Access Journals (Sweden)
Chia-Nan Wang
2014-01-01
Full Text Available The aim of this research is to model an autonomous control wind turbine driven permanent magnetic synchronous generator (PMSG which feeds alternating current (AC power to the utility grid. Furthermore, this research also demonstrates the effects and the efficiency of PMSG wind turbine which is integrated by autonomous controllers. In order for well autonomous control, two voltage source inverters are used to control wind turbine connecting with the grid. The generator-side inverter is used to adjust the synchronous generator as well as separating the generator from the grid when necessary. The grid-side inverter controls the power flow between the direct current (DC bus and the AC side. Both of them are oriented control by space vector pulse width modulation (PWM with back-to-back frequency inverter. Moreover, the proportional-integral (PI controller is enhanced to control both of the inverters and the pitch angle of the wind turbine. Maximum power point tracking (MPPT is integrated in generator-side inverter to track the maximum power, when wind speed changes. The simulation results in Matlab Simulink 2012b showing the model have good dynamic and static performance. The maximum power can be tracked and the generator wind turbine can be operated with high efficiency.
Retrieval algorithm of sea surface wind vectors for WindSat based on a simple forward model
Institute of Scientific and Technical Information of China (English)
ZHAO Yili
2013-01-01
WindSat/Coriolis is the first satellite-borne polarimetric microwave radiometer,which aims to improve the potential of polarimetric microwave radiometry for measuring sea surface wind vectors from space.In this paper,a wind vector retrieval algorithm based on a novel and simple forward model was developed for WindSat.The retrieval algorithm of sea surface wind speed was developed using multiple linear regression based on the simulation dataset of the novel forward model.Sea surface wind directions that minimize the difference between simulated and measured values of the third and fourth Stokes parameters were found using maximum likelihood estimation,by which a group of ambiguous wind directions was obtained.A median filter was then used to remove ambiguity of wind direction.Evaluated with sea surface wind speed and direction data from the U.S.National Data Buoy Center (NDBC),root mean square errors are 1.2 m/s and 30° for retrieved wind speed and wind direction,respectively.The evaluation results suggest that the simple forward model and the retrieval algorithm are practicable for near-real time applications,without reducing accuracy.
Film condensation of R-113 on staggered bundles of horizontal finned tubes
Energy Technology Data Exchange (ETDEWEB)
Honda, H. (Kyushu Univ., Fukuoka (Japan)); Uchima, B. (Kagawa Technical Coll., Marugame (Japan)); Nozu, S.; Torigoe, E.; Imai, S. (Okayama Univ., Tsushima (Japan))
1992-05-01
Film condensation of R-113 on staggered bundles of horizontal finned tubes with vertical vapor downflow was experimentally investigated. Two tubes with flat-sided annular fins and four tubes with three-dimensional fins were tested. The condensate flow and heat transfer characteristics were compared with the previous results for in-line bundles of the same test tubes and a staggered bundle of smooth tubes. The decrease in heat transfer characteristics were compared with the previous results for in-line bundles of the same test tubes and a staggered bundle of smooth tubes. The decrease in heat transfer due to condensate inundation was most significant for the in-line bundles of the three-dimensional fin tubes, whereas the decrease was very slow for both the staggered and in-line bundles of the flat-sided fin tubes. The predictions of the previous theoretical model for a bundle of flat-sided fin tubes agreed fairly well with the measured data at a low vapor velocity. The highest heat transfer performance was provided by the staggered bundle of flat-sided fin tubes with fin dimensions close to the theoretically determined optimum values.
错层结构的几点分析%Analytical Study on Staggered Floor Structure
Institute of Scientific and Technical Information of China (English)
谢靖中; 李国强; 屠成松
2001-01-01
The stress distribution of the staggered floor shear-wall structure is analyzed and its mechanical characteristics are discussed at first in this paper. With two relative mechanical models, the variations of lateral stiffness of the staggered floor structure is analyzed, and its obvious that the stiffness enhancement of the staggered floor structure is determined by the location of the staggered floor, the stiffness ratio of column to beam and the style of acting loads. At last, the influence of the staggered floor structure on the structural is also discussed.%首先分析了错层剪力墙结构的应力分布并讨论其受力特点。采用两种结构力学模型分析了错层构件的刚度变化情况，认为错层结构刚度增大幅度与错层位置、构件刚度比、加载方式等多种因素有关；并且讨论了错层对结构整体性的影响。
ΔI = 2 Nuclear Staggering in Superdeformed Rotational Bands
Directory of Open Access Journals (Sweden)
Okasha M. D.
2014-01-01
Full Text Available A four parameters model including collective rotational en ergies to fourth order is ap- plied to reproduce the ∆ I = 2 staggering in transition energies in four selected super deformed rotational bands, namely, 148 Gd (SD6, 194 Hg (SD1, SD2, SD3. The model parameters and the spin of the bandhead have been extracted a ssuming various val- ues to the lowest spin of the bandhead at nearest integer, in o rder to obtain a minimum root mean square deviation between calculated and the exper imental transition energies. This allows us to suggest the spin values for the energy level s which are experimentally unknown. For each band a staggering parameter represent the deviation of the transition energies from a smooth reference has been determined by calc ulating the fourth order derivative of the transition energies at a given spin. The st aggering parameter contains five consecutive transition energies which is denoted here a s the five-point formula. In order to get information about the dynamical moment of ine rtia, the two point for- mula which contains only two consecutive transition energi es has been also considered. The dynamical moment of inertia decreasing with increasing rotational frequency for A ∼ 150, while increasing for A ∼ 190 mass regions.
A Model fot the Sources of the Slow Solar Wind
Antiochos, S. K.; Mikic, Z.; Titov, V. S.; Lionello, R.; Linker, J. A.
2011-01-01
Models for the origin of the slow solar wind must account for two seemingly contradictory observations: the slow wind has the composition of the closed-field corona, implying that it originates from the continuous opening and closing of flux at the boundary between open and closed field. On the other hand, the slow wind also has large angular width, up to approx.60deg, suggesting that its source extends far from the open-closed boundary. We propose a model that can explain both observations. The key idea is that the source of the slow wind at the Sun is a network of narrow (possibly singular) open-field corridors that map to a web of separatrices and quasi-separatrix layers in the heliosphere. We compute analytically the topology of an open-field corridor and show that it produces a quasi-separatrix layer in the heliosphere that extends to angles far from the heliospheric current sheet. We then use an MHD code and MDI/SOHO observations of the photospheric magnetic field to calculate numerically, with high spatial resolution, the quasi-steady solar wind, and magnetic field for a time period preceding the 2008 August 1 total solar eclipse. Our numerical results imply that, at least for this time period, a web of separatrices (which we term an S-web) forms with sufficient density and extent in the heliosphere to account for the observed properties of the slow wind. We discuss the implications of our S-web model for the structure and dynamics of the corona and heliosphere and propose further tests of the model. Key words: solar wind - Sun: corona - Sun: magnetic topology
A Broadband Emission Model of Magnetar Wind Nebulae
Tanaka, Shuta J.
2016-08-01
Angular momentum loss by the plasma wind is considered as a universal feature of isolated neutron stars including magnetars. The wind nebulae that are powered by magnetars allow us to compare the wind properties and the spin evolution of magnetars with those of rotation-powered pulsars (RPPs). In this paper, we construct a broadband emission model of magnetar wind nebulae (MWNe). This model is similar to past studies of young pulsar wind nebulae (PWNe) around RPPs, but is modified for the application to MWNe that have far less observational information than the young PWNe. We apply the model to the MWN around the youngest (˜1 kyr) magnetar, 1E 1547.0-5408, which has the largest spin-down power L spin among all the magnetars. However, the MWN is faint because of the low L spin of 1E 1547.0-5408 when compared to the young RPPs. Since most parameters are not well constrained by only an X-ray flux upper limit of the MWN, we adopt the model’s parameters from the young PWN Kes 75 around PSR J1846-0258, which is a peculiar RPP showing magnetar-like behaviors. The model predicts that γ-ray flux will be detected in a future TeV γ-ray observation by CTA (Cherenkov Telescope Array). The MWN spectrum does not allow us to test the hypothesis that 1E 1547.0-5408 had a period of milliseconds at its birth because the particles injected during the early phase of evolution suffered from severe adiabatic and synchrotron losses. Furthermore, both observational and theoretical studies of the wind nebulae around magnetars are required to constrain the wind and the spin-down properties of magnetars.
Hydrodynamic Models of Line-Driven Accretion Disk Winds II Adiabatic Winds from Nonisothermal Disks
Pereyra, N A; Blondin, J M; Pereyra, Nicolas Antonio; Kallman, Timothy R.; Blondin, John M.
2000-01-01
We present here numerical hydrodynamic simulations of line-driven accretion disk winds in cataclysmic variable systems. We calculate wind mass-loss rate, terminal velocities, and line profiles for CIV (1550 A) for various viewing angles. The models are 2.5-dimensional, include an energy balance condition, and calculate the radiation field as a function of position near an optically thick accretion disk. The model results show that centrifugal forces produce collisions of streamlines in the disk wind which in turn generate an enhanced density region, underlining the necessity of two dimensional calculations where these forces may be represented. For disk luminosity Ldisk = Lsun, white dwarf mass Mwd = 0.6 Msun, and white dwarf radii Rwd = 0.01 Rsun, we obtain a wind mass-loss rate of dMwind/dt = 8.0E-12 Msun/yr, and a terminal velocity of ~3000 km/s. The line profiles we obtain are consistent with observations in their general form, in particular in the maximum absorption at roughly half the terminal velocity ...
Tieleman, H. W.; Reinhold, T. A.; Marshall, R. D.
1976-01-01
The lower part of the atmospheric boundary layer (strong wind conditions) was simulated in low speed wind tunnel for the modeling of wind loads on low-rise structures. The turbulence characteristics of the turbulent boundary layer in the wind tunnel are compared with full scale measurements and with measurements made at NASA Wallops Flight Center. Wind pressures measured on roofs of a 1:70 scale model of a small single family dwelling were compared with results obtained from full scale measurements. The results indicate a favorable comparison between full scale and model pressure data as far as mean, r.m.s. and peak pressures are concerned. In addition, results also indicate that proper modeling of the turbulence is essential for proper simulation of the wind pressures.
A Model for the Sources of the Slow Solar Wind
Antiochos, Spiro K.; Mikic, Z.; Lionello, R.; Titov, V.; Linker, J.
2010-05-01
Models for the origin of the slow solar wind must account for two seemingly contradictory observations: The slow wind has the composition of the closed-field corona, implying that it originates at the open-closed field boundary layer, but it also has large angular width, up to 40 degrees. We propose a model that can explain both observations. The key idea is that the source of the slow wind at the Sun is a network of narrow (possibly singular) open-field corridors that map to a web of separatrices and quasi-separatrix layers in the heliosphere. We calculate with high numerical resolution, the quasi-steady solar wind and magnetic field for a Carrington rotation centered about the August 1, 2008 total solar eclipse. Our numerical results demonstrate that, at least for this time period, a web of separatrices (S-web) forms with sufficient density and extent in the heliosphere to account for the observed properties of the slow wind. We discuss the implications of our S-web model for the structure and dynamics of the corona and heliosphere, and propose further tests of the model. This work was supported, in part, by the NASA HTP, TR&T and SR&T programs.
A Broadband Emission Model of Magnetar Wind Nebulae
Tanaka, Shuta J
2016-01-01
Angular momentum loss by the plasma wind is considered as a universal feature of isolated neutron stars including magnetars. The wind nebulae powered by magnetars allow us to compare the wind properties and the spin-evolution of magnetars with those of rotation-powered pulsars (RPPs). In this paper, we construct a broadband emission model of magnetar wind nebulae (MWNe). The model is similar to past studies of young pulsar wind nebulae (PWNe) around RPPs, but is modified for the application to MWNe that have far less observational information than the young PWNe. We apply the model to the MWN around the youngest ($\\sim$ 1kyr) magnetar 1E 1547.0-5408 that has the largest spin-down power $L_{\\rm spin}$ among all the magnetars. However, the MWN is faint because of low $L_{\\rm spin}$ of 1E 1547.0-5408 compared with the young RPPs. Since most of parameters are not well constrained only by an X-ray flux upper limit of the MWN, we adopt the model parameters from young PWN Kes 75 around PSR J1846-0258 that is a pecul...
Models for simulation of transient events in a wind farm
DEFF Research Database (Denmark)
Sørensen, P.; Hansen, A. D.; Bindner, H.
2002-01-01
with different tools with each other and with measurements. This present paper limits to describe the models including our reflections on which effects we expect to be essential for obtaining useful simulation results. The models comprise the substation, where the wind farm is connected, the power collection...
Conceptual models of the wind-driven and thermohaline circulation
Drijfhout, S.S.; Marshall, D.P.; Dijkstra, H.A.
2013-01-01
Conceptual models are a vital tool for understanding the processes that maintain the global ocean circulation, both in nature and in complex numerical ocean models. In this chapter we provide a broad overview of our conceptual understanding of the wind-driven circulation, the thermohaline
Conceptual models of the wind-driven and thermohaline circulation
Drijfhout, S.S.; Marshall, D.P.; Dijkstra, H.A.
2013-01-01
Conceptual models are a vital tool for understanding the processes that maintain the global ocean circulation, both in nature and in complex numerical ocean models. In this chapter we provide a broad overview of our conceptual understanding of the wind-driven circulation, the thermohaline circulatio
Short-Circuit Modeling of a Wind Power Plant: Preprint
Energy Technology Data Exchange (ETDEWEB)
Muljadi, E.; Gevorgian, V.
2011-03-01
This paper investigates the short-circuit behavior of a WPP for different types of wind turbines. The short-circuit behavior will be presented. Both the simplified models and detailed models are used in the simulations and both symmetrical faults and unsymmetrical faults are discussed.
Conceptual models of the wind-driven and thermohaline circulation
Drijfhout, S.S.; Marshall, D.P.; Dijkstra, H.A.
2013-01-01
Conceptual models are a vital tool for understanding the processes that maintain the global ocean circulation, both in nature and in complex numerical ocean models. In this chapter we provide a broad overview of our conceptual understanding of the wind-driven circulation, the thermohaline circulatio
Comparison of aerodynamic models for Vertical Axis Wind Turbines
Simao Ferreira, C.J.; Aagaard Madsen, H.; Barone, M.; Roscher, B.; Deglaire, P.; Arduin, I.
2014-01-01
Multi-megawatt Vertical Axis Wind Turbines (VAWTs) are experiencing an increased interest for floating offshore applications. However, VAWT development is hindered by the lack of fast, accurate and validated simulation models. This work compares six different numerical models for VAWTS: a multiple s
Trailing edge noise model applied to wind turbine airfoils
DEFF Research Database (Denmark)
Bertagnolio, Franck
The aim of this work is firstly to provide a quick introduction to the theory of noise generation that are relevant to wind turbine technology with focus on trailing edge noise. Secondly, the socalled TNO trailing edge noise model developed by Parchen [1] is described in more details. The model...
Wind energy conversion system analysis model (WECSAM) computer program documentation
Energy Technology Data Exchange (ETDEWEB)
Downey, W T; Hendrick, P L
1982-07-01
Described is a computer-based wind energy conversion system analysis model (WECSAM) developed to predict the technical and economic performance of wind energy conversion systems (WECS). The model is written in CDC FORTRAN V. The version described accesses a data base containing wind resource data, application loads, WECS performance characteristics, utility rates, state taxes, and state subsidies for a six state region (Minnesota, Michigan, Wisconsin, Illinois, Ohio, and Indiana). The model is designed for analysis at the county level. The computer model includes a technical performance module and an economic evaluation module. The modules can be run separately or together. The model can be run for any single user-selected county within the region or looped automatically through all counties within the region. In addition, the model has a restart capability that allows the user to modify any data-base value written to a scratch file prior to the technical or economic evaluation. Thus, any user-supplied data for WECS performance, application load, utility rates, or wind resource may be entered into the scratch file to override the default data-base value. After the model and the inputs required from the user and derived from the data base are described, the model output and the various output options that can be exercised by the user are detailed. The general operation is set forth and suggestions are made for efficient modes of operation. Sample listings of various input, output, and data-base files are appended. (LEW)
Modeling of Exterior Rotor Permanent Magnet Machines with Concentrated Windings
Vu Xuan, H.
2012-01-01
In this thesis modeling, analysis, design and measurement of exterior rotor permanent magnet (PM) machines with concentrated windings are dealt with. Special attention is paid to slotting effect. The PM machine is integrated in flywheel and used for small-scale ship application. Analytical model and
Extratropical transitioning in the RMS Japan typhoon wind field model
Loridan, Thomas; Scherer, Emilie; Khare, Shree
2013-04-01
Given its meridional extent and location within the Pacific basin, Japan is regularly impacted by strong winds from cyclones at different stages of their lifecycle. To quantify the associated risk of damage to properties, catastrophe models such as the ones developed by RMS aim to simulate wind fields from thousands of stochastic storms that extrapolate historical events. In a recent study using 25 years of reanalysis data, Kitabatake (2011) estimated that 40 % of all Pacific tropical cyclones completed their transition as an extra tropical system. From a cat modelling point of view it is the increase in wind field asymmetry observed during these transitioning episodes that is critical, with examples like typhoon Tokage in 2004 showing the potential for damaging gusts on both sides of the storm track. In this context a compromise has to be found between the need for complex numerical models able to simulate wind field variability around the cyclone during its entire evolution, and obvious running time constrains. The RMS wind field model is based on an optimized version of the Willoughby parametric profile (Willoughby et al., 2006) which requires calibration against targets representative of cyclone wind fields throughout their lifecycle. We here present the different sources of data involved in the development of this model. This includes (1) satellite products to characterize wind fields from fully tropical storms, (2) high resolution simulations of key transitioning events using the WRF mesoscale model to complement the database at other stages (i.e. for transitioning and fully extra tropical wind fields), and (3) reanalysis data which can be used with Hart (2003)'s cyclone phase space methodology to provide an estimate of the mean duration of transitioning episodes in the Pacific. Kitabatake, N., 2011: Climatology of extratropical transition of tropical cyclones in the Western North Pacific defined by using cyclone phase space. J. Meteor. Soc. Japan, 89, 309
Introducing WISDEM:An Integrated System Modeling for Wind Turbines and Plant (Presentation)
Energy Technology Data Exchange (ETDEWEB)
Dykes, K.; Graf, P.; Scott, G.; Ning, A.; King, R.; Guo, Y.; Parsons, T.; Damiani, R.; Felker, F.; Veers, P.
2015-01-01
The National Wind Technology Center wind energy systems engineering initiative has developed an analysis platform to leverage its research capabilities toward integrating wind energy engineering and cost models across wind plants. This Wind-Plant Integrated System Design & Engineering Model (WISDEM) platform captures the important interactions between various subsystems to achieve a better National Wind Technology Center wind energy systems engineering initiative has developed an analysis platform to leverage its research capabilities toward integrating wind energy engineering and cost models across wind plants. This Wind-Plant Integrated System Design & Engineering Model (WISDEM) platform captures the important interactions between various subsystems to achieve a better understanding of how to improve system-level performance and achieve system-level cost reductions. This work illustrates a few case studies with WISDEM that focus on the design and analysis of wind turbines and plants at different system levels.
A simple disc wind model for broad absorption line quasars
Higginbottom, N.; Knigge, C.; Long, K. S.; Sim, S. A.; Matthews, J. H.
2013-12-01
Approximately 20 per cent of quasi-stellar objects (QSOs) exhibit broad, blue-shifted absorption lines in their ultraviolet spectra. Such features provide clear evidence for significant outflows from these systems, most likely in the form of accretion disc winds. These winds may represent the `quasar' mode of feedback that is often invoked in galaxy formation/evolution models, and they are also key to unification scenarios for active galactic nuclei (AGN) and QSOs. To test these ideas, we construct a simple benchmark model of an equatorial, biconical accretion disc wind in a QSO and use a Monte Carlo ionization/radiative transfer code to calculate the ultraviolet spectra as a function of viewing angle. We find that for plausible outflow parameters, sightlines looking directly into the wind cone do produce broad, blue-shifted absorption features in the transitions typically seen in broad absorption line (BAL) QSOs. However, our benchmark model is intrinsically X-ray weak in order to prevent overionization of the outflow, and the wind does not yet produce collisionally excited line emission at the level observed in non-BAL QSOs. As a first step towards addressing these shortcomings, we discuss the sensitivity of our results to changes in the assumed X-ray luminosity and mass-loss rate, Ṁwind. In the context of our adopted geometry, Ṁwind ˜ Ṁacc is required in order to produce significant BAL features. The kinetic luminosity and momentum carried by such outflows would be sufficient to provide significant feedback.
Detailed signal model of coherent wind measurement lidar
Ma, Yuechao; Li, Sining; Lu, Wei
2016-11-01
Lidar is short for light detection and ranging, which is a tool to help measuring some useful information of atmosphere. In the recent years, more and more attention was paid to the research of wind measurement by lidar. Because the accurate wind information can be used not only in weather report, but also the safety guarantee of the airplanes. In this paper, a more detailed signal model of wind measurement lidar is proposed. It includes the laser transmitting part which describes the broadening of the spectral, the laser attenuation in the atmosphere, the backscattering signal and the detected signal. A Voigt profile is used to describe the broadening of the transmitting laser spectral, which is the most common situation that is the convolution of different broadening line shapes. The laser attenuation includes scattering and absorption. We use a Rayleigh scattering model and partially-Correlated quadratic-Velocity-Dependent Hard-Collision (pCqSDHC) model to describe the molecule scattering and absorption. When calculate the particles scattering and absorption, the Gaussian particles model is used to describe the shape of particles. Because of the Doppler Effect occurred between the laser and atmosphere, the wind velocity can be calculated by the backscattering signal. Then, a two parameter Weibull distribution is used to describe the wind filed, so that we can use it to do the future work. After all the description, the signal model of coherent wind measurement lidar is decided. And some of the simulation is given by MATLAB. This signal model can describe the system more accurate and more detailed, so that the following work will be easier and more efficient.
A review on solar wind modeling: kinetic and fluid aspects
Echim, Marius; Lie-Svendsen, Oystein
2013-01-01
We review the main advantages and limitations of the kinetic exospheric and fluid models of the solar wind (SW). We discuss the hydrostatic model imagined by Chapman, the first supersonic hydrodynamic models published by Parker and the first generation subsonic kinetic model proposed by Chamberlain. It is shown that a correct estimation of the electric field as in the second generation kinetic exospheric models developed by Lemaire and Scherer, provides a supersonic expansion of the corona, reconciling the hydrodynamic and the kinetic approach. The third generation kinetic exospheric models considers kappa velocity distribution function (VDF) instead of a Maxwellian at the exobase and in addition they treat a non-monotonic variation of the electric potential with the radial distance; the fourth generation exospheric models include Coulomb collisions based on the Fokker--Planck collision term. Multi-fluid models of the solar wind provide a coarse grained description and reproduce with success the spatio-tempor...
Extreme winds over Europe in the ENSEMBLES regional climate models
Directory of Open Access Journals (Sweden)
S. D. Outten
2013-01-01
Full Text Available Extreme winds cause vast amounts of damage every year and represent a major concern for numerous industries including construction, afforestation, wind energy and many others. Under a changing climate, the intensity and frequency of extreme events are expected to change, and accurate predictions of these changes will be invaluable to decision makers and society as a whole. This work examines four regional climate model downscalings over Europe from the "ENSEMBLE-based Predictions of Climate Changes and their Impacts" project (ENSEMBLES, and investigates the predicted changes in the 50 yr return wind speeds and the associated uncertainties. This is accomplished by employing the peaks-over-threshold method with the use of the Generalised Pareto Distribution. The models show that for much of Europe the 50 yr return wind is projected to change by less than 2 m s^{−1}, while the uncertainties associated with the statistical estimates are larger than this. In keeping with previous works in this field, the largest source of uncertainty is found to be the inter-model spread, with some locations showing differences in the 50 yr return wind of over 20 m s^{−1} between two different downscalings.
Extreme winds over Europe in the ENSEMBLES regional climate models
Directory of Open Access Journals (Sweden)
S. D. Outten
2013-05-01
Full Text Available Extreme winds cause vast amounts of damage every year and represent a major concern for numerous industries including construction, afforestation, wind energy and many others. Under a changing climate, the intensity and frequency of extreme events are expected to change, and accurate projections of these changes will be invaluable to decision makers and society as a whole. This work examines four regional climate model downscalings over Europe following the SRES A1B scenario from the "ENSEMBLE-based Predictions of Climate Changes and their Impacts" project (ENSEMBLES. It investigates the projected changes in the 50 yr return wind speeds and the associated uncertainties. This is accomplished by employing the peaks-over-threshold method with the use of the generalised Pareto distribution. The models show that, for much of Europe, the 50 yr return wind is projected to change by less than 2 m s−1, while the uncertainties associated with the statistical estimates are larger than this. In keeping with previous works in this field, the largest source of uncertainty is found to be the inter-model spread, with some locations showing differences in the 50 yr return wind of over 20 m s−1 between two different downscalings.
Modeling and analysis of DFIG in wind energy conversion system
Directory of Open Access Journals (Sweden)
Omer Elfaki Elbashir, Wang Zezhong, Liu Qihui
2014-01-01
Full Text Available This paper deals with the modeling, analysis, and simulation of a doubly-fed induction generator (DFIG driven by a wind turbine. The grid connected wind energy conversion system (WECS is composed of DFIG and two back to back PWM voltage source converters (VSCs in the rotor circuit. A machine model is derived in an appropriate dq reference frame. The grid voltage oriented vector control is used for the grid side converter (GSC in order to maintain a constant DC bus voltage, while the stator voltage orientated vector control is adopted in the rotor side converter (RSC to control the active and reactive powers.
Development of CFD-based icing model for wind turbines
DEFF Research Database (Denmark)
Pedersen, Marie Cecilie; Martinez, Benjamin; Yin, Chungen
2015-01-01
Operation of wind turbines in cold climate areas is challenged by icing-induced problems, such as loss of production, safety issues and blade fatique. Production losses are especially a big issue in Sweden, and due to difficulties with on-site measurements, simulations are often used to get...... an understanding and to predict icing events. In this paper a case study of modeling icing using Computational Fluid Dynamics (CFD) is proposed. The case study aims to form the basic of a general CFD model for icing on wind turbine blade sections....
Modeling Jets in the Corona and Solar Wind
Torok, T; Titov, V S; Leake, J E; Mikic, Z; Linker, J A; Linton, M G
2015-01-01
Coronal jets are transient, collimated eruptions that occur in regions of predominantly open magnetic field in the solar corona. Our understanding of these events has greatly evolved in recent years but several open questions, such as the contribution of coronal jets to the solar wind, remain. Here we present an overview of the observations and numerical modeling of coronal jets, followed by a brief description of "next-generation" simulations that include an advanced description of the energy transfer in the corona ("thermodynamic MHD"), large spherical computational domains, and the solar wind. These new models will allow us to address some of the open questions.
Stochastic Models of Defects in Wind Turbine Drivetrain Components
DEFF Research Database (Denmark)
Rafsanjani, Hesam Mirzaei; Sørensen, John Dalsgaard
2013-01-01
of the drivetrain will lead to substantial economic losses such as cost of lost energy production, cost of repairs, cost of crew and cost of transportation. For offshore wind turbines, the marine environment affects the repair & maintenance process and in some case because of the rush environment, the maintenance...... team cannot operate properly and the wind turbine does not work for several days and consequently the cost of lost energy increases drastically. In this paper is presented stochastic models for fatigue failure based on test data and the accuracy of the models are compared....
Winding vacuum energies in a deformed O(4) sigma model
Bazhanov, Vladimir V; Lukyanov, Sergei L
2014-01-01
We consider the problem of calculating the Casimir energies in the winding sectors of Fateev's SS-model, which is an integrable two-parameter deformation of the O(4) non-linear sigma model in two dimensions. This problem lies beyond the scope of all traditional methods of integrable quantum field theory including the thermodynamic Bethe ansatz and non-linear integral equations. Here we propose a solution based on a remarkable correspondence between classical and quantum integrable systems and express the winding energies in terms of certain solutions of the classical sinh-Gordon equation.
Winding vacuum energies in a deformed O(4) sigma model
Energy Technology Data Exchange (ETDEWEB)
Bazhanov, Vladimir V. [Department of Theoretical Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200 (Australia); Mathematical Sciences Institute, Australian National University, Canberra, ACT 0200 (Australia); Kotousov, Gleb A. [Department of Theoretical Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200 (Australia); Lukyanov, Sergei L., E-mail: sergei@physics.rutgers.edu [NHETC, Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08855-0849 (United States); L.D. Landau Institute for Theoretical Physics, Chernogolovka 142432 (Russian Federation)
2014-12-15
We consider the problem of calculating the Casimir energies in the winding sectors of Fateev's SS-model, which is an integrable two-parameter deformation of the O(4) non-linear sigma model in two dimensions. This problem lies beyond the scope of all traditional methods of integrable quantum field theory including the thermodynamic Bethe ansatz and non-linear integral equations. Here we propose a solution based on a remarkable correspondence between classical and quantum integrable systems and express the winding energies in terms of certain solutions of the classical sinh-Gordon equation.
Modeling of uncertainties for wind turbine blade design
DEFF Research Database (Denmark)
Sørensen, John Dalsgaard; Toft, Henrik Stensgaard
2014-01-01
Wind turbine blades are designed by a combination of tests and numerical calculations using finite element models of the blade. The blades are typically composite structures with laminates of glass-fiber and/or carbon-fibers glued together by a matrix material. This paper presents a framework...... basis in the JCSS framework for modelling material properties, Bayesian statistical methods allowing prior / expert knowledge to be accounted for and the Maximum Likelihood Method. The stochastic framework is illustrated using simulated tests which represent examples relevant for wind turbine blades....
QCD simulations with staggered fermions on GPUs
Bonati, C; D'Elia, M; Incardona, P
2011-01-01
We report on our implementation of the RHMC algorithm for the simulation of lattice QCD with two staggered flavors on Graphics Processing Units, using the NVIDIA CUDA programming language. The main feature of our code is that the GPU is not used just as an accelerator, but instead the whole Molecular Dynamics trajectory is performed on it. After pointing out the main bottlenecks and how to circumvent them, we discuss the obtained performances. We present some preliminary results regarding OpenCL and multiGPU extensions of our code and discuss future perspectives.
MODELING WIND TURBINES IN THE GRIDLAB-D SOFTWARE ENVIRONMENT
Energy Technology Data Exchange (ETDEWEB)
Fuller, J.C.; Schneider, K.P.
2009-01-01
In recent years, the rapid expansion of wind power has resulted in a need to more accurately model the effects of wind penetration on the electricity infrastructure. GridLAB-D is a new simulation environment developed for the U.S. Department of Energy (DOE) by the Pacifi c Northwest National Laboratory (PNNL), in cooperation with academic and industrial partners. GridLAB-D was originally written and designed to help integrate end-use smart grid technologies, and it is currently being expanded to include a number of other technologies, including distributed energy resources (DER). The specifi c goal of this project is to create a preliminary wind turbine generator (WTG) model for integration into GridLAB-D. As wind power penetration increases, models are needed to accurately study the effects of increased penetration; this project is a beginning step at examining these effects within the GridLAB-D environment. Aerodynamic, mechanical and electrical power models were designed to simulate the process by which mechanical power is extracted by a wind turbine and converted into electrical energy. The process was modeled using historic atmospheric data, collected over a period of 30 years as the primary energy input. This input was then combined with preliminary models for synchronous and induction generators. Additionally, basic control methods were implemented, using either constant power factor or constant power modes. The model was then compiled into the GridLAB-D simulation environment, and the power outputs were compared against manufacturers’ data and then a variation of the IEEE 4 node test feeder was used to examine the model’s behavior. Results showed the designs were suffi cient for a prototype model and provided output power similar to the available manufacturers’ data. The prototype model is designed as a template for the creation of new modules, with turbine-specifi c parameters to be added by the user.
MODELING WIND TURBINES IN THE GRIDLAB-D SOFTWARE ENVIRONMENT
Energy Technology Data Exchange (ETDEWEB)
Fuller, J.C.; Schneider, K.P.
2009-01-01
In recent years, the rapid expansion of wind power has resulted in a need to more accurately model the effects of wind penetration on the electricity infrastructure. GridLAB-D is a new simulation environment developed for the U.S. Department of Energy (DOE) by the Pacifi c Northwest National Laboratory (PNNL), in cooperation with academic and industrial partners. GridLAB-D was originally written and designed to help integrate end-use smart grid technologies, and it is currently being expanded to include a number of other technologies, including distributed energy resources (DER). The specifi c goal of this project is to create a preliminary wind turbine generator (WTG) model for integration into GridLAB-D. As wind power penetration increases, models are needed to accurately study the effects of increased penetration; this project is a beginning step at examining these effects within the GridLAB-D environment. Aerodynamic, mechanical and electrical power models were designed to simulate the process by which mechanical power is extracted by a wind turbine and converted into electrical energy. The process was modeled using historic atmospheric data, collected over a period of 30 years as the primary energy input. This input was then combined with preliminary models for synchronous and induction generators. Additionally, basic control methods were implemented, using either constant power factor or constant power modes. The model was then compiled into the GridLAB-D simulation environment, and the power outputs were compared against manufacturers’ data and then a variation of the IEEE 4 node test feeder was used to examine the model’s behavior. Results showed the designs were suffi cient for a prototype model and provided output power similar to the available manufacturers’ data. The prototype model is designed as a template for the creation of new modules, with turbine-specifi c parameters to be added by the user.
Evaluation protocol for the WIND system atmospheric models
Energy Technology Data Exchange (ETDEWEB)
Fast, J.D.
1991-12-31
Atmospheric transport and diffusion models have been developed for real-time calculations of the location and concentration of toxic or radioactive materials during a accidental release at the Savannah River Site (SRS). These models are have been incorporated into an automated menu-driven computer based system called the WIND (Weather INformation and Display) system. In an effort to establish more formal quality assurance procedures for the WIND system atmospheric codes, a software evaluation protocol is being developed. An evaluation protocol is necessary to determine how well they may perform in emergency response (real-time) situations. The evaluation of high-impact software must be conducted in accordance with WSRC QA Manual, 1Q, QAP 20-1. This report will describe the method that will be used to evaluate the atmospheric models. The evaluation will determine the effectiveness of the atmospheric models in emergency response situations, which is not necessarily the same procedure used for research purposes. The format of the evaluation plan will provide guidance for the evaluation of atmospheric models that may be added to the WIND system in the future. The evaluation plan is designed to provide the user with information about the WIND system atmospheric models that is necessary for emergency response situations.
Evaluation protocol for the WIND system atmospheric models
Energy Technology Data Exchange (ETDEWEB)
Fast, J.D.
1991-01-01
Atmospheric transport and diffusion models have been developed for real-time calculations of the location and concentration of toxic or radioactive materials during a accidental release at the Savannah River Site (SRS). These models are have been incorporated into an automated menu-driven computer based system called the WIND (Weather INformation and Display) system. In an effort to establish more formal quality assurance procedures for the WIND system atmospheric codes, a software evaluation protocol is being developed. An evaluation protocol is necessary to determine how well they may perform in emergency response (real-time) situations. The evaluation of high-impact software must be conducted in accordance with WSRC QA Manual, 1Q, QAP 20-1. This report will describe the method that will be used to evaluate the atmospheric models. The evaluation will determine the effectiveness of the atmospheric models in emergency response situations, which is not necessarily the same procedure used for research purposes. The format of the evaluation plan will provide guidance for the evaluation of atmospheric models that may be added to the WIND system in the future. The evaluation plan is designed to provide the user with information about the WIND system atmospheric models that is necessary for emergency response situations.
Wind Turbine Noise Propagation Modelling: An Unsteady Approach
Barlas, E.; Zhu, W. J.; Shen, W. Z.; Andersen, S. J.
2016-09-01
Wind turbine sound generation and propagation phenomena are inherently time dependent, hence tools that incorporate the dynamic nature of these two issues are needed for accurate modelling. In this paper, we investigate the sound propagation from a wind turbine by considering the effects of unsteady flow around it and time dependent source characteristics. For the acoustics modelling we employ the Parabolic Equation (PE) method while Large Eddy Simulation (LES) as well as synthetically generated turbulence fields are used to generate the medium flow upon which sound propagates. Unsteady acoustic simulations are carried out for three incoming wind shear and various turbulence intensities, using a moving source approach to mimic the rotating turbine blades. The focus of the present paper is to study the near and far field amplitude modulation characteristics and time evolution of Sound Pressure Level (SPL).
Improved upper winds models for several astronomical observatories.
Roberts, Lewis C; Bradford, L William
2011-01-17
An understanding of wind speed and direction as a function of height are critical to the proper modeling of atmospheric turbulence. We have used radiosonde data from launch sites near significant astronomical observatories and created averaged profiles of wind speed and direction and have also computed Richardson number profiles. Using data from the last 30 years, we confirm a 1977 Greenwood wind profile, and extend it to include parameters that show seasonal variations and differences in location. The added information from our models is useful for the design of adaptive optics systems and other imaging systems. Our analysis of the Richardson number suggests that persistent turbulent layers may be inferred when low values are present in our long term averaged data. Knowledge of the presence of these layers may help with planning for adaptive optics and laser communications.
On Practical tuning of Model Uncertainty in Wind Turbine Model Predictive Control
DEFF Research Database (Denmark)
Odgaard, Peter Fogh; Hovgaard, Tobias
2015-01-01
Model predictive control (MPC) has in previous works been applied on wind turbines with promising results. These results apply linear MPC, i.e., linear models linearized at different operational points depending on the wind speed. The linearized models are derived from a nonlinear first principle...
Modeling and Simulation for Hybrid of PV-Wind system
Directory of Open Access Journals (Sweden)
Maged N. F. Nashed
2015-04-01
Full Text Available The rising consumption rate of fossil fuels causes a significant pollution impact on the atmosphere, unwanted greenhouse gases has drawn worldwide attention towards renewable energy sources. Moreover, in recent year’s generation of electricity using the different types of renewable sources are specifically evaluated in the economical performance of the overall equipment. This paper focuses on the modeling and analysis of a Standalone Photovoltaic (PV- wind energy hybrid generation system under different conditions using MATLAB. The proposed system consists of two renewable sources i.e. wind and solar energy. Modeling of PV array and wind turbine is explained. The wind subsystem is equipped of an induction generator. In photovoltaic system, the variable DC output voltage is controlled using buck-boost converter for the MPPT. These two systems are combined to operate in parallel and the common bus collects the total energy from the wind and PV systems are uses it to the load and with change the load
Sustainable business models for wind and solar energy in Romania
Directory of Open Access Journals (Sweden)
Nichifor Maria Alexandra
2015-06-01
Full Text Available Renewable energy has become a crucial element for the business environment as the need for new energy resources and the degree of climate change are increasing. As developed economies strive towards greater progress, sustainable business models are of the essence in order to maintain a balance between the triple bottom line: people, planet and profit. In recent years, European Union countries have installed important capacities of renewable energy, especially wind and solar energy to achieve this purpose. The objective of this article is to make a comparative study between the current sustainable business models implemented in companies that are active in the wind and solar energy sector in Romania. Both sectors underwent tremendous changes in the last two years due to changing support schemes which have had a significant influence on the mechanism of the renewable energy market, as well as on its development. Using the classical Delphi method, based on questionnaires and interviews with experts in the fields of wind and solar energy, this paper offers an overview of the sustainable business models of wind and solar energy companies, both sectors opting for the alternative of selling electricity to trading companies as a main source of revenue until 2013 and as the main future trend until 2020. Furthermore, the participating wind energy companies noted a pessimistic outlook of future investments due to legal instability that made them to reduce their projects in comparison to PV investments, which are expected to continue. The subject of the article is of interest to scientific literature because sustainable business models in wind and photovoltaic energy have been scarcely researched in previous articles and are essential in understanding the activity of the companies in these two fields of renewable energy.
A Model for the Sources of the Slow Solar Wind
Antiochos, Spiro K.; Mikic, Z.; Titov, V. S.; Lionello, R.; Linker, J. A.
2010-01-01
Models for the origin of the slow solar wind must account for two seemingly contradictory observations: The slow wind has the composition of the closed-field corona, implying that it originates from the continuous opening and closing of flux at the boundary between open and closed field. On the other hand, the slow wind has large angular width, up to approximately 60 degrees, suggesting that its source extends far from the open-closed boundary. We propose a model that can explain both observations. The key idea is that the source of the slow wind at the Sun is a network of narrow (possibly singular) open-field corridors that map to a web of separatrices and quasi-separatrix layers in the heliosphere. We compute analytically the topology of an open-field corridor and show that it produces a quasi-separatrix layer in the heliosphere that extends to angles far front the heliospheric current sheet. We then use an MHD code and MIDI/SOHO observations of the photospheric magnetic field to calculate numerically, with high spatial resolution, the quasi-steady solar wind and magnetic field for a time period preceding the August 1, 2008 total solar eclipse. Our numerical results imply that, at least for this time period, a web of separatrices (which we term an S-web) forms with sufficient density and extent in the heliosphere to account for the observed properties of the slow wind. We discuss the implications of our S-web model for the structure and dynamics of the corona and heliosphere, and propose further tests of the model.
Model-based control of a ballast-stabilized floating wind turbine exposed to wind and waves
Energy Technology Data Exchange (ETDEWEB)
Christiansen, Soeren
2013-01-15
The wind turbine is a commercial product which is competing against other sources of energy, such as coal and gas. This competition drives a constant development to reduce costs and improve efficiency in order to reduce the total cost of the energy. The latest offshore development is the floating wind turbine, for water depths beyond 50 meters where winds are stronger and less turbulent. A floating wind turbine is subject to not only aerodynamics and wind induced loads, but also to hydrodynamics and wave induced loads. In contrast to a bottom fixed wind turbine, the floating structure, the hydrodynamics and the loads change the dynamic behavior of a floating wind turbine. Consequently, conventional wind turbine control cause instabilities on floating wind turbines. This work addresses the control of a floating spar buoy wind turbine, and focuses on the impact of the additional platform dynamics. A time varying control model is presented based on the wind speed and wave frequency. Estimates of the wind speed and wave frequency are used as scheduling variables in a gain scheduled linear quadratic controller to improve the electrical power production while reducing fatigue. To address the problem of negative damped fore-aft tower motion, additional control loops are suggested which stabilize the response of the onshore controller and reduce the impact of the wave induced loads. This research is then extended to model predictive control, to further address wave disturbances. In the context of control engineering, the dynamics and disturbances of a floating wind turbine have been identified and modeled. The objectives of maximizing the production of electrical power and minimizing fatigue have been reached by using advanced methods of estimation and control. (Author)
Turbulence Impact on Wind Turbines: Experimental Investigations on a Wind Turbine Model
Al-Abadi, A.; Kim, Y. J.; Ertunç, Ö.; Delgado, A.
2016-09-01
Experimental investigations have been conducted by exposing an efficient wind turbine model to different turbulence levels in a wind tunnel. Nearly isotropic turbulence is generated by using two static squared grids: fine and coarse one. In addition, the distance between the wind-turbine and the grid is adjusted. Hence, as the turbulence decays in the flow direction, the wind-turbine is exposed to turbulence with various energy and length scale content. The developments of turbulence scales in the flow direction at various Reynolds numbers and the grid mesh size are measured. Those measurements are conducted with hot-wire anemometry in the absence of the wind-turbine. Detailed measurements and analysis of the upstream and downstream velocities, turbulence intensity and spectrum distributions are done. Performance measurements are conducted with and without turbulence grids and the results are compared. Performance measurements are conducted with an experimental setup that allow measuring of torque, rotational speed from the electrical parameters. The study shows the higher the turbulence level, the higher the power coefficient. This is due to many reasons. First, is the interaction of turbulence scales with the blade surface boundary layer, which in turn delay the stall. Thus, suppressing the boundary layer and preventing it from separation and hence enhancing the aerodynamics characteristics of the blade. In addition, higher turbulence helps in damping the tip vortices. Thus, reduces the tip losses. Adding winglets to the blade tip will reduce the tip vortex. Further investigations of the near and far wake-surrounding intersection are performed to understand the energy exchange and the free stream entrainment that help in retrieving the velocity.
DEFF Research Database (Denmark)
Guo, Yifei; Gao, Houlei; Wu, Qiuwei
2017-01-01
factors are calculated. Secondly, the meteorological data are classified into several states using an improved Fuzzy C-means (FCM) algorithm. Then the Markov chain is used to model the chronological characteristics of meteorological states and wind speed. The proposed model was proved to be more accurate......Accurate wind speed simulation is an essential prerequisite to analyze the power systems with wind power. A wind speed model considering meteorological conditions and seasonal variations is proposed in this paper. Firstly, using the path analysis method, the influence weights of meteorological...... in capturing the characteristics of probability distribution, auto-correlation and seasonal variations of wind speed compared with the traditional Markov chain Monte Carlo (MCMC) and autoregressive moving average (ARMA) model. Furthermore, the proposed model was applied to adequacy assessment of generation...
Directory of Open Access Journals (Sweden)
B. H. Fiedler
2014-01-01
Full Text Available A subgrid parameterization is offered for representing wind turbines in weather prediction models. The parameterization models the drag and mixing the turbines cause in the atmosphere, as well as the electrical power production the wind causes in the wind turbines. The documentation of the parameterization is complete; it does not require knowledge of proprietary data of wind turbine characteristics. The parameterization is applied to a study of wind resource limits in a hypothetical giant wind farm. The simulated production density was found not to exceed 1 W m−2, peaking at a deployed capacity density of 5 W m−2 and decreasing slightly as capacity density increased to 20 W m−2.
Directory of Open Access Journals (Sweden)
Yichao Liu
2017-01-01
Full Text Available Along with the commercialization of offshore wind energy in China, the South China Sea has been identified as ideal for constructing offshore wind farms, especially for farms consisting of floating wind turbines over deep waters. Since the wind profiles and wave spectra are somewhat primitive for the design of an offshore wind turbine, engineering models describing the wind and wave characteristics in the South China Sea area are necessary for the offshore wind energy exploitation given the meteorological, hydrological, and geographical differences between the South China Sea and the North/Norwegian Sea, where the commonly used wind profile and wave spectrum models were designated. In the present study; a series of numerical simulations were conducted to reveal the wave characteristics in the South China Sea under both typhoon and non-typhoon conditions. By analyzing the simulation results; the applicability of the Joint North Sea Wave Project (JONSWAP spectrum model; in terms of characterizing the wind-induced wave fields in the South China Sea; was discussed. In detail; the key parameters of the JONSWAP spectrum model; such as the Phillips constant; spectral width parameter; peak-enhancement factor, and high frequency tail decay; were investigated in the context of finding suitable values.
Safi, Kamran; Kranstauber, Bart; Weinzierl, Rolf P.; Griffin, Larry; Reese, Eileen C.; Cabot, David; Cruz, Sebastian; Proaño, Carolina; Takekawa, John Y.; Newman, Scott H.; Waldenström, Jonas; Bengtsson, Daniel; Kays, Roland; Wikelski, Martin; Bohrer, Gil
2013-01-01
Background: Understanding how environmental conditions, especially wind, influence birds' flight speeds is a prerequisite for understanding many important aspects of bird flight, including optimal migration strategies, navigation, and compensation for wind drift. Recent developments in tracking technology and the increased availability of data on large-scale weather patterns have made it possible to use path annotation to link the location of animals to environmental conditions such as wind speed and direction. However, there are various measures available for describing not only wind conditions but also the bird's flight direction and ground speed, and it is unclear which is best for determining the amount of wind support (the length of the wind vector in a bird’s flight direction) and the influence of cross-winds (the length of the wind vector perpendicular to a bird’s direction) throughout a bird's journey. Results: We compared relationships between cross-wind, wind support and bird movements, using path annotation derived from two different global weather reanalysis datasets and three different measures of direction and speed calculation for 288 individuals of nine bird species. Wind was a strong predictor of bird ground speed, explaining 10-66% of the variance, depending on species. Models using data from different weather sources gave qualitatively similar results; however, determining flight direction and speed from successive locations, even at short (15 min intervals), was inferior to using instantaneous GPS-based measures of speed and direction. Use of successive location data significantly underestimated the birds' ground and airspeed, and also resulted in mistaken associations between cross-winds, wind support, and their interactive effects, in relation to the birds' onward flight. Conclusions: Wind has strong effects on bird flight, and combining GPS technology with path annotation of weather variables allows us to quantify these effects for
Modelling of a CFD Microscale Model and Its Application in Wind Energy Resource Assessment
Directory of Open Access Journals (Sweden)
Yue Jie-shun
2016-01-01
Full Text Available The prediction of a wind farm near the wind turbines has a significant effect on the safety as well as economy of wind power generation. To assess the wind resource distribution within a complex terrain, a computational fluid dynamics (CFD based wind farm forecast microscale model is developed. The model uses the Reynolds Averaged Navier-Stokes (RANS model to characterize the turbulence. By using the results of Weather Research and Forecasting (WRF mesoscale weather forecast model as the input of the CFD model, a coupled model of CFD-WRF is established. A special method is used for the treatment of the information interchange on the lateral boundary between two models. This established coupled model is applied in predicting the wind farm near a wind turbine in Hong Gang-zi, Jilin, China. The results from this simulation are compared to real measured data. On this basis, the accuracy and efficiency of turbulence characterization schemes are discussed. It indicates that this coupling system is easy to implement and can make these two separate models work in parallel. The CFD model coupled with WRF has the advantage of high accuracy and fast speed, which makes it valid for the wind power generation.
Energy Technology Data Exchange (ETDEWEB)
Narayana, P.B. [Green Life Energy Solutions LLP, Secunderabad (India); Rao, S.S. [National Institute of Technology. Dept. of Mechanical Engineering, Warangal (India); Reddy, K.H. [JNT Univ.. Dept. of Mechanical Engineering, Anantapur (India)
2012-07-01
Economics of wind power projects largely depend on the availability of wind power density. Wind resource assessment is a study estimating wind speeds and wind power densities in the region under consideration. The accuracy and reliability of data sets comprising of wind speeds and wind power densities at different heights per topographic region characterized by elevation or mean sea level, is important for wind power projects. Indian Wind Resource Assessment program conducted in 80's consisted of wind data measured by monitoring stations at different topographies in order to measure wind power density values at 25 and 50 meters above the ground level. In this paper, an attempt has been made to assess wind resource at a given location using artificial neural networks. Existing wind resource data has been used to train the neural networks. Location topography (characterized by longitude, latitude and mean sea level), air density, mean annual wind speed (MAWS) are used as inputs to the neural network. Mean annual wind power density (MAWPD) in watt/m{sup 2} is predicted for a new topographic location. Simple back propagation based neural network has been found to be sufficient for predicting these values with suitable accuracy. This model is closely linked to the problem of wind energy forecasting considering the variations of specific atmospheric variables with time horizons. This model will help the wind farm developers to have an initial estimation of the wind energy potential at a particular topography. (Author)
PIV in a model wind turbine rotor wake
DEFF Research Database (Denmark)
Meyer, Knud Erik; Naumov, Igor; Karbadin, Ivan
2013-01-01
Stereoscopic particle image velocimetry (PIV) measurements of the flow in the wake of scale model of a horizontal axis wind turbine is presented Near the rotor, measurements are made in vertical planes intersecting the rotor axis These planes capture flow effect from the tip and root vortices...
Model output statistics applied to wind power prediction
Energy Technology Data Exchange (ETDEWEB)
Joensen, A.; Giebel, G.; Landberg, L. [Risoe National Lab., Roskilde (Denmark); Madsen, H.; Nielsen, H.A. [The Technical Univ. of Denmark, Dept. of Mathematical Modelling, Lyngby (Denmark)
1999-03-01
Being able to predict the output of a wind farm online for a day or two in advance has significant advantages for utilities, such as better possibility to schedule fossil fuelled power plants and a better position on electricity spot markets. In this paper prediction methods based on Numerical Weather Prediction (NWP) models are considered. The spatial resolution used in NWP models implies that these predictions are not valid locally at a specific wind farm. Furthermore, due to the non-stationary nature and complexity of the processes in the atmosphere, and occasional changes of NWP models, the deviation between the predicted and the measured wind will be time dependent. If observational data is available, and if the deviation between the predictions and the observations exhibits systematic behavior, this should be corrected for; if statistical methods are used, this approaches is usually referred to as MOS (Model Output Statistics). The influence of atmospheric turbulence intensity, topography, prediction horizon length and auto-correlation of wind speed and power is considered, and to take the time-variations into account, adaptive estimation methods are applied. Three estimation techniques are considered and compared, Extended Kalman Filtering, recursive least squares and a new modified recursive least squares algorithm. (au) EU-JOULE-3. 11 refs.
Modelling the pultrusion process of off shore wind turbine blades
Baran, Ismet
2014-01-01
This thesis is devoted to the numerical modelling of the pultrusion process for industrial products such as wind turbine blades and structural profiles. The main focus is on the thermo-chemical and mechanical analyses of the process in which the process induced tresses and shape distortions together
Code Shift: Grid Specifications and Dynamic Wind Turbine Models
DEFF Research Database (Denmark)
Ackermann, Thomas; Ellis, Abraham; Fortmann, Jens
2013-01-01
Grid codes (GCs) and dynamic wind turbine (WT) models are key tools to allow increasing renewable energy penetration without challenging security of supply. In this article, the state of the art and the further development of both tools are discussed, focusing on the European and North American...
Scale Adaptive Simulation Model for the Darrieus Wind Turbine
DEFF Research Database (Denmark)
Rogowski, K.; Hansen, Martin Otto Laver; Maroński, R.
2016-01-01
Accurate prediction of aerodynamic loads for the Darrieus wind turbine using more or less complex aerodynamic models is still a challenge. One of the problems is the small amount of experimental data available to validate the numerical codes. The major objective of the present study is to examine...
Wind Farm parametrization in the mesoscale model WRF
DEFF Research Database (Denmark)
Volker, Patrick; Badger, Jake; Hahmann, Andrea N.
2012-01-01
The project’s objective is to investigate and develop methods for prediction of mesoscale climate, wake effects and atmospheric feedbacks, for scenarios where large portions of the sea are covered with wind farms. The atmospheric flow is simulated with the WRF mesoscale model, since it has signif...
An agent-based multi-scale wind generation model
Energy Technology Data Exchange (ETDEWEB)
Kremers, E.; Lewald, N. [Karlsruhe Univ., Karlsruhe (Germany). European Inst. for Energy Research; Barambones, O.; Gonzalez de Durana, J.M. [Univ. of the Basque Country, Vitoria (Spain). Dept. of Engineering
2009-07-01
The introduction of renewable energies, the liberalization of energy markets and the emergence of new, distributed producers that feed into the grid at almost every level of the system have all contributed to a paradigm shift in energy systems. This paper presented an agent-based model for simulating wind power systems on multiple time scales. The purpose of the study was to generate a flexible model that would permit simulating the output of a wind farm. The model was developed using multiparadigm modelling. It also combined a variety of approaches such as agent-based modelling, discrete events and dynamic systems. The paper explained the theoretical background concerning the basic models for wind speed generation and power turbines, as well as the fundamentals of agent-based modelling. The implementation of these models was illustrated. The paper also discussed several sample simulations and discussed the application of the model. It was concluded that the paradigm change encompassed new tools and methods that could deal with decentralized decision-making, planning and self-organisation. The large amount of new technologies in the energy production chain requires a shift from a top-down to a more bottom-up approach. 12 refs., 1 tab., 7 figs.
Stochastic Models for Strength of Wind Turbine Blades using Tests
DEFF Research Database (Denmark)
Toft, Henrik Stensgaard; Sørensen, John Dalsgaard
2008-01-01
The structural cost of wind turbine blades is dependent on the values of the partial safety factors which reflect the uncertainties in the design values, including statistical uncertainty from a limited number of tests. This paper presents a probabilistic model for ultimate and fatigue strength...... of wind turbine blades especially considering the influence of prior knowledge and test results and how partial safety factors can be updated when additional full-scale tests are performed. This updating is performed by adopting a probabilistic design basis based on Bayesian statistical methods....
Videogrammetric Model Deformation Measurement Technique for Wind Tunnel Applications
Barrows, Danny A.
2006-01-01
Videogrammetric measurement technique developments at NASA Langley were driven largely by the need to quantify model deformation at the National Transonic Facility (NTF). This paper summarizes recent wind tunnel applications and issues at the NTF and other NASA Langley facilities including the Transonic Dynamics Tunnel, 31-Inch Mach 10 Tunnel, 8-Ft high Temperature Tunnel, and the 20-Ft Vertical Spin Tunnel. In addition, several adaptations of wind tunnel techniques to non-wind tunnel applications are summarized. These applications include wing deformation measurements on vehicles in flight, determining aerodynamic loads based on optical elastic deformation measurements, measurements on ultra-lightweight and inflatable space structures, and the use of an object-to-image plane scaling technique to support NASA s Space Exploration program.
A latitude-dependent wind model for Mira's cometary head
Raga, A C; De Colle, F; Esquivel, A; Kajdic, P; Rodríguez-González, A; Velázquez, P F
2008-01-01
We present a 3D numerical simulation of the recently discovered cometary structure produced as Mira travels through the galactic ISM. In our simulation, we consider that Mira ejects a steady, latitude-dependent wind, which interacts with a homogeneous, streaming environment. The axisymmetry of the problem is broken by the lack of alignment between the direction of the relative motion of the environment and the polar axis of the latitude-dependent wind. With this model, we are able to produce a cometary head with a ``double bow shock'' which agrees well with the structure of the head of Mira's comet. We therefore conclude that a time-dependence in the ejected wind is not required for reproducing the observed double bow shock.
A wind-shell interaction model for multipolar planetary nebulae
Steffen, W; Esquivel, A; Garcia-Segura, G; Garcia-Diaz, Ma T; Lopez, J A; Magnor, M
2013-01-01
We explore the formation of multipolar structures in planetary and pre-planetary nebulae from the interaction of a fast post-AGB wind with a highly inhomogeneous and filamentary shell structure assumed to form during the final phase of the high density wind. The simulations were performed with a new hydrodynamics code integrated in the interactive framework of the astrophysical modeling package SHAPE. In contrast to conventional astrophysical hydrodynamics software, the new code does not require any programming intervention by the user for setting up or controlling the code. Visualization and analysis of the simulation data has been done in SHAPE without external software. The key conclusion from the simulations is that secondary lobes in planetary nebulae, such as Hubble 5 and K3-17, can be formed through the interaction of a fast low-density wind with a complex high density environment, such as a filamentary circumstellar shell. The more complicated alternative explanation of intermittent collimated outflow...
Partial dynamical symmetry and odd-even staggering in deformed nuclei
Leviatan, A
2015-01-01
Partial dynamical symmetry (PDS) is shown to be relevant for describing the odd-even staggering in the $\\gamma$-band of $^{156}$Gd while retaining solvability and good SU(3) symmetry for the ground and $\\beta$ bands. Several classes of interacting boson model Hamiltonians with SU(3) PDS are surveyed.
Partial dynamical symmetry and odd-even staggering in deformed nuclei
Directory of Open Access Journals (Sweden)
Leviatan A.
2015-01-01
Full Text Available Partial dynamical symmetry (PDS is shown to be relevant for describing the odd-even staggering in the γ-band of 156Gd while retaining solvability and good SU(3 symmetry for the ground and β bands. Several classes of interacting boson model Hamiltonians with SU(3 PDS are surveyed.
Understanding Dynamic Model Validation of a Wind Turbine Generator and a Wind Power Plant: Preprint
Energy Technology Data Exchange (ETDEWEB)
Muljadi, Eduard; Zhang, Ying Chen; Gevorgian, Vahan; Kosterev, Dmitry
2016-09-01
Regional reliability organizations require power plants to validate the dynamic models that represent them to ensure that power systems studies are performed to the best representation of the components installed. In the process of validating a wind power plant (WPP), one must be cognizant of the parameter settings of the wind turbine generators (WTGs) and the operational settings of the WPP. Validating the dynamic model of a WPP is required to be performed periodically. This is because the control parameters of the WTGs and the other supporting components within a WPP may be modified to comply with new grid codes or upgrades to the WTG controller with new capabilities developed by the turbine manufacturers or requested by the plant owners or operators. The diversity within a WPP affects the way we represent it in a model. Diversity within a WPP may be found in the way the WTGs are controlled, the wind resource, the layout of the WPP (electrical diversity), and the type of WTGs used. Each group of WTGs constitutes a significant portion of the output power of the WPP, and their unique and salient behaviors should be represented individually. The objective of this paper is to illustrate the process of dynamic model validations of WTGs and WPPs, the available data recorded that must be screened before it is used for the dynamic validations, and the assumptions made in the dynamic models of the WTG and WPP that must be understood. Without understanding the correct process, the validations may lead to the wrong representations of the WTG and WPP modeled.
Avian collision risk models for wind energy impact assessments
Energy Technology Data Exchange (ETDEWEB)
Masden, E.A., E-mail: elizabeth.masden@uhi.ac.uk [Environmental Research Institute, North Highland College-UHI, University of the Highlands and Islands, Ormlie Road, Thurso, Caithness KW14 7EE (United Kingdom); Cook, A.S.C.P. [British Trust for Ornithology, The Nunnery, Thetford IP24 2PU (United Kingdom)
2016-01-15
With the increasing global development of wind energy, collision risk models (CRMs) are routinely used to assess the potential impacts of wind turbines on birds. We reviewed and compared the avian collision risk models currently available in the scientific literature, exploring aspects such as the calculation of a collision probability, inclusion of stationary components e.g. the tower, angle of approach and uncertainty. 10 models were cited in the literature and of these, all included a probability of collision of a single bird colliding with a wind turbine during passage through the rotor swept area, and the majority included a measure of the number of birds at risk. 7 out of the 10 models calculated the probability of birds colliding, whilst the remainder used a constant. We identified four approaches to calculate the probability of collision and these were used by others. 6 of the 10 models were deterministic and included the most frequently used models in the UK, with only 4 including variation or uncertainty in some way, the most recent using Bayesian methods. Despite their appeal, CRMs have their limitations and can be ‘data hungry’ as well as assuming much about bird movement and behaviour. As data become available, these assumptions should be tested to ensure that CRMs are functioning to adequately answer the questions posed by the wind energy sector. - Highlights: • We highlighted ten models available to assess avian collision risk. • Only 4 of the models included variability or uncertainty. • Collision risk models have limitations and can be ‘data hungry’. • It is vital that the most appropriate model is used for a given task.
Calculation of BSM Kaon B-parameters using Staggered Quarks
Jang, Yong-Chull; Kim, Jangho; Kim, Seonghee; Lee, Weonjong; Leem, Jaehoon; Pak, Jeonghwan; Park, Sungwoo; Jung, Chulwoo; Kim, Hyung-Jin; Sharpe, Stephen R; Yoon, Boram
2014-01-01
We present updated results for kaon B-parameters for operators arising in models of new physics. We use HYP-smeared staggered quarks on the $N_f = 2+1$ MILC asqtad lattices. During the last year we have added new ensembles, which has necessitated chiral-continuum fitting with more elaborate fitting functions. We have also corrected an error in a two-loop anomalous dimension used to evolve results between different scales. Our results for the beyond-the-Standard-Model B-parameters have total errors of $5-10$\\%. We find that the discrepancy observed last year between our results and those of the RBC/UKQCD and ETM collaborations for some of the B-parameters has been reduced from $4\\!-\\!5\\,\\sigma$ to $2\\!-\\!3\\,\\sigma$.
Coupled wake boundary layer model of wind-farms
Stevens, Richard J A M; Meneveau, Charles
2014-01-01
We present and test a coupled wake boundary layer (CWBL) model that describes the distribution of the power output in a wind-farm. The model couples the traditional, industry-standard wake expansion/superposition approach with a top-down model for the overall wind-farm boundary layer structure. The wake expansion/superposition model captures the effect of turbine positioning, while the top-down portion adds the interaction between the wind-turbine wakes and the atmospheric boundary layer. Each portion of the model requires specification of a parameter that is not known a-priori. For the wake model the wake expansion coefficient is required, while the top-down model requires an effective span-wise turbine spacing within which the model's momentum balance is relevant. The wake expansion coefficient is obtained by matching the predicted mean velocity at the turbine from both approaches, while the effective span-wise turbine spacing depends on turbine positioning and thus can be determined from the wake expansion...
An Analytic Model of Galactic Winds and Mass Outflows
Institute of Scientific and Technical Information of China (English)
Cheng-Gang Shu; Hou-Jun Mo; Shu-De Mao
2005-01-01
Galactic winds and mass outflows are observed both in nearby starburst galaxies and in high-redshift star-forming galaxies. We develop a simple analytic model to understand the observed superwind phenomenon with a discussion of the model uncertainties. Our model is built upon the model of McKee & Ostriker for the interstellar medium. It allows one to predict how properties of a superwind,such as wind velocity and mass outflow rate, are related to properties of its star forming host galaxy, such as size, gas density and star formation rate. The model predicts a threshold of star formation rate density for the generation of observable galactic winds. Galaxies with more concentrated star formation activities produce superwinds with higher velocities. The predicted mass outflow rates are compara ble to (or slightly larger than) the corresponding star formation rates. We apply our model to both local starburst galaxies and high-redshift Lyman break galaxies, and find its predictions to be in good agreement with current observations. Our model is simple and so can be easily incorporated into numerical simulations and semi-analytical models of galaxy formation.
Modelling wave-boundary layer interaction for wind power applications
Jenkins, A. D.; Barstad, I.; Gupta, A.; Adakudlu, M.
2012-04-01
Marine wind power production facilities are subjected to direct and indirect effects of ocean waves. Direct effects include forces due to wave orbital motions and slamming of the water surface under breaking wave conditions, corrosion and icing due to sea spray, and the effects of wave-generated air bubbles. Indirect effects include include the influence of waves on the aerodynamic sea-surface roughness, air turbulence, the wind velocity profile, and air velocity oscillations, wave-induced currents and sediment transport. Field observations within the boundary layers from floating measurement may have to be corrected to account for biases induced as a result of wave-induced platform motions. To estimate the effect of waves on the atmospheric boundary layer we employ the WRF non-hydrostatic mesoscale atmosphere model, using the default YSU planetary boundary layer (PBL) scheme and the WAM spectral wave model, running simultaneously and coupled using the open-source coupler MCEL which can interpolate between different model grids and timesteps. The model is driven by the WRF wind velocity at 10 m above the surface. The WRF model receives from WAM updated air-sea stress fields computed from the wind input source term, and computes new fields for the Charnock parameter and marine surface aerodynamic roughness. Results from a North Atlantic and Nordic Seas simulation indicate that the two-way coupling scheme alters the 10 metre wind predicted by WRF by up to 10 per cent in comparison with a simulation using a constant Charnock parameter. The changes are greatest in developing situations with passages of fronts, moving depressions and squalls. This may be directly due to roughness length changes, or may be due to changes in the timing of front/depression/squall passages. Ongoing work includes investigating the effect of grid refinement/nesting, employing different PBL schemes, and allowing the wave field to change the direction of the total air-sea stress.
A Simple Disk Wind Model for Broad Absorption Line Quasars
Higginbottom, N; Long, K S; Sim, S A; Matthews, J H
2013-01-01
Approximately 20% of quasi-stellar objects (QSOs) exhibit broad, blue-shifted absorption lines in their ultraviolet spectra. Such features provide clear evidence for significant outflows from these systems, most likely in the form of accretion disk winds. These winds may represent the "quasar" mode of feedback that is often invoked in galaxy formation/evolution models, and they are also key to unification scenarios for active galactic nuclei (AGN) and QSOs. To test these ideas, we construct a simple benchmark model of an equatorial, biconical accretion disk wind in a QSO and use a Monte Carlo ionization/radiative transfer code to calculate the ultraviolet spectra as a function of viewing angle. We find that for plausible outflow parameters, sightlines looking directly into the wind cone do produce broad, blue-shifted absorption features in the transitions typically seen in broad absorption line QSOs. However, our benchmark model is intrinsically X-ray weak in order to prevent overionization of the outflow, an...
Distributed Model Predictive Control for Active Power Control of Wind Farm
DEFF Research Database (Denmark)
Zhao, Haoran; Wu, Qiuwei; Rasmussen, Claus Nygaard;
2014-01-01
This paper presents the active power control of a wind farm using the Distributed Model Predictive Controller (D- MPC) via dual decomposition. Different from the conventional centralized wind farm control, multiple objectives such as power reference tracking performance and wind turbine load can......-scale wind farm control....
Energy Technology Data Exchange (ETDEWEB)
TamizhMani, G.; Ji, L.; Tang, Y.; Petacci, L.; Osterwald, C.
2003-06-01
In order to predict the energy production of photovoltaic (PV) modules, it is necessary to predict the module temperature as a function of ambient temperature, wind speed, wind direction, total irradiance, and relative humidity. This paper presents a mathematical model to predict the module temperature based on the field monitored real data of module temperature, ambient temperature, wind speed, wind direction and relative humidity.
Zhang, Ning; Du, Yunsong; Miao, Shiguang; Fang, Xiaoyi
2016-08-01
The simulation performance over complex building clusters of a wind simulation model (Wind Information Field Fast Analysis model, WIFFA) in a micro-scale air pollutant dispersion model system (Urban Microscale Air Pollution dispersion Simulation model, UMAPS) is evaluated using various wind tunnel experimental data including the CEDVAL (Compilation of Experimental Data for Validation of Micro-Scale Dispersion Models) wind tunnel experiment data and the NJU-FZ experiment data (Nanjing University-Fang Zhuang neighborhood wind tunnel experiment data). The results show that the wind model can reproduce the vortexes triggered by urban buildings well, and the flow patterns in urban street canyons and building clusters can also be represented. Due to the complex shapes of buildings and their distributions, the simulation deviations/discrepancies from the measurements are usually caused by the simplification of the building shapes and the determination of the key zone sizes. The computational efficiencies of different cases are also discussed in this paper. The model has a high computational efficiency compared to traditional numerical models that solve the Navier-Stokes equations, and can produce very high-resolution (1-5 m) wind fields of a complex neighborhood scale urban building canopy (~ 1 km ×1 km) in less than 3 min when run on a personal computer.
Effect of wind turbine generator model and siting on wind power changes out of large WECS arrays
Schleuter, R. A.; Park, G. L.; Lotfalian, M.; Dorsey, J.; Shayanfar, H.
1981-01-01
Methods of reducing the WECS generation change through selection of the wind turbine model for each site, selection of an appropriate siting configuration, and wind array controls are discussed. An analysis of wind generation change from an echelon and a farm for passage of a thunderstorm is presented. Reduction of the wind generation change over ten minutes is shown to reduce the increase in spinning reserve, unloadable generation and load following requirements on unit commitment when significant WECS generation is present and the farm penetration constraint is satisfied. Controls on the blade pitch angle of all wind turbines in an array or a battery control are shown to reduce both the wind generation change out of an array and the effective farm penetration in anticipation of a storm so that the farm penetration constraint may be satisfied.
Summary Report: The Shadow effect of large wind farms: measurements, data analysis and modelling
DEFF Research Database (Denmark)
Frandsen, Sten Tronæs; Barthelmie, Rebecca Jane; Rathmann, Ole;
It was the goal of the project – by means of data from the demonstration wind farms Horns Rev and Nysted, analyses of these data and modelling – to facilitate prediction of the power losses from a wind farm should a new wind farm be built upwind relative to the prevailing wind direction. Or conve......It was the goal of the project – by means of data from the demonstration wind farms Horns Rev and Nysted, analyses of these data and modelling – to facilitate prediction of the power losses from a wind farm should a new wind farm be built upwind relative to the prevailing wind direction....... The databases – one for each site – include production and operational statistics for the wind turbines and statistics for the meteorological measurements carries out in the vicinity of the wind farms. Several different modelling activities were carried out, which intentionally to some extent are redundant...
DEFF Research Database (Denmark)
Gaumond, M.; Réthoré, Pierre-Elouan; Ott, Søren;
2014-01-01
of the power deficit in a single wake situation is improved. The robustness of the method is verified using the Jensen model, the Larsen model and Fuga, which are three different engineering wake models. The results indicate that the discrepancies between the traditional numerical simulations and power...... production data for narrow wind direction sectors are not caused by an inherent inaccuracy of the current wake models, but rather by the large wind direction uncertainty included in the dataset. The technique can potentially improve wind farm control algorithms and layout optimization because both...
2D Models for Dust-driven AGB Star Winds
Woitke, P
2006-01-01
New axisymmetric (2D) models for dust-driven winds of C-stars are presented which include hydrodynamics with radiation pressure on dust, equilibrium chemistry and time-dependent dust formation with coupled grey Monte Carlo radiative transfer. Considering the most simple case without stellar pulsation (hydrostatic inner boundary condition) these models reveal a more complex picture of the dust formation and wind acceleration as compared to earlier published spherically symmetric (1D) models. The so-called exterior $\\kappa$-mechanism causes radial oscillations with short phases of active dust formation between longer phases without appreciable dust formation, just like in the 1D models. However, in 2D geometry, the oscillations can be out-of-phase at different places above the stellar atmosphere which result in the formation of dust arcs or smaller caps that only occupy a certain fraction of the total solid angle. These dust structures are accelerated outward by radiation pressure, expanding radially and tangen...
A new ensemble model for short term wind power prediction
DEFF Research Database (Denmark)
Madsen, Henrik; Albu, Razvan-Daniel; Felea, Ioan;
2012-01-01
As the objective of this study, a non-linear ensemble system is used to develop a new model for predicting wind speed in short-term time scale. Short-term wind power prediction becomes an extremely important field of research for the energy sector. Regardless of the recent advancements in the re......-search of prediction models, it was observed that different models have different capabilities and also no single model is suitable under all situations. The idea behind EPS (ensemble prediction systems) is to take advantage of the unique features of each subsystem to detain diverse patterns that exist in the dataset....... The conferred results show that the prediction errors can be decreased, while the computation time is reduced....
Krtička, J.; Kubát, J.
2017-10-01
We calculate global (unified) wind models of main-sequence, giant, and supergiant O stars from our Galaxy. The models are calculated by solving hydrodynamic, kinetic equilibrium (also known as NLTE) and comoving frame (CMF) radiative transfer equations from the (nearly) hydrostatic photosphere to the supersonic wind. For given stellar parameters, our models predict the photosphere and wind structure and in particular the wind mass-loss rates without any free parameters. Our predicted mass-loss rates are by a factor of 2-5 lower than the commonly used predictions. A possible cause of the difference is abandoning of the Sobolev approximation for the calculation of the radiative force, because our models agree with predictions of CMF NLTE radiative transfer codes. Our predicted mass-loss rates agree nicely with the mass-loss rates derived from observed near-infrared and X-ray line profiles and are slightly lower than mass-loss rates derived from combined UV and Hα diagnostics. The empirical mass-loss rate estimates corrected for clumping may therefore be reconciled with theoretical predictions in such a way that the average ratio between individual mass-loss rate estimates is not higher than about 1.6. On the other hand, our predictions are by factor of 4.7 lower than pure Hα mass-loss rate estimates and can be reconciled with these values only assuming a microclumping factor of at least eight.
Directory of Open Access Journals (Sweden)
Sujay Kulkarni
2014-01-01
Full Text Available The centennial trends in the surface wind speed over North America are deduced from global climate model simulations in the Climate Model Intercomparison Project—Phase 5 (CMIP5 archive. Using the 21st century simulations under the RCP 8.5 scenario of greenhouse gas emissions, 5–10 percent increases per century in the 10 m wind speed are found over Central and East-Central United States, the Californian Coast, and the South and East Coasts of the USA in winter. In summer, climate models projected decreases in the wind speed ranging from 5 to 10 percent per century over the same coastal regions. These projected changes in the surface wind speed are moderate and imply that the current estimate of wind power potential for North America based on present-day climatology will not be significantly changed by the greenhouse gas forcing in the coming decades.
Directory of Open Access Journals (Sweden)
Wagner Sousa de Oliveira
2012-01-01
Full Text Available This paper makes a review and systematize methods and techniques of economic evaluation applied to renewable energy projects, specific to wind energy projects. Both project and cost methodologies of economic evaluation are reviewed for a model optimization construction for a proposed optimization model with its objective function most appropriated. It is necessary to engage in different approaches, but complementary, microeconomic project evaluation methods and optimization methods applied to engineering solutions in wind energy converter systems. Optimization model for economic evaluation of wind farms can be as an efficient planning and resource management, which is the key to the success of an energy project. Wind energy is one of the most potent alternative energy resources; however the economics of wind energy is not yet universally favorable to place wind at a competitive platform with coal and natural gas (fossil fuels. Economic evaluation models of wind projects developed would allow investors to better plan their projects, as well as provide valuable insight into the areas that require further development to improve the overall economics of wind energy projects.
Institute of Scientific and Technical Information of China (English)
CHEN Hao; WANG Xiuming; ZHAO Haibo
2006-01-01
A rotated staggered grid finite-difference (FD) method with a perfectly matched layer (PML) method is proposed for numerically solving elastic wave equations in inhomogeneous elastic and poroe- lastic media. Compared with a standard staggered- grid FD, the former has the advantage over the latter in that its physical variables need only to be defined at two locations. In the rotated staggered grid, stress and strain components (or particle velocity and displacement components) are defined at elementary cell centers, and the velocity or displacement components (or the stress and strain components) are defined at vertexes. In this way, no elastic moduli need to be interpolated or averaged. Numerical results from the proposed method have been compared with the standard staggered FD method. The results are in good agreement with each other. Our numerical results show that the proposed algorithm can handle much stronger impedance contrast. This is especially true when simulating fractured medium filled with fluids such as water or gas without giving special treatment. On the other hand, the implemented PML absorbing boundary condition works well in efficiently reducing reflected waves from the artificial interfaces. It generates almost no reflection at artificial interfaces with a boundary of PML thickness of half a wavelength. Our theoretical analysis and numerical tests proved that the PML absorbing algorithm in the rotated staggered grid is almost identical to those in the standard staggered grid. In this paper, we also presented all of the formulations of the PML implementation and modeling examples in elastic, poroelastic, and anisotropic media.
Airship Model Tests in the Variable Density Wind Tunnel
Abbott, Ira H
1932-01-01
This report presents the results of wind tunnel tests conducted to determine the aerodynamic characteristics of airship models. Eight Goodyear-Zeppelin airship models were tested in the original closed-throat tunnel. After the tunnel was rebuilt with an open throat a new model was tested, and one of the Goodyear-Zeppelin models was retested. The results indicate that much may be done to determine the drag of airships from evaluations of the pressure and skin-frictional drags on models tested at large Reynolds number.
Estimation of rotor effective wind speeds using autoregressive models on Lidar data
Giyanani, A.; Bierbooms, W. A. A. M.; van Bussel, G. J. W.
2016-09-01
Lidars have become increasingly useful for providing accurate wind speed measurements in front of the wind turbine. The wind field measured at distant meteorological masts changes its structure or was too distorted before it reaches the turbine. Thus, one cannot simply apply Taylor's frozen turbulence for representing this distant flow field at the rotor. Wind turbine controllers can optimize the energy output and reduce the loads significantly, if the wind speed estimates were known in advance with high accuracy and low uncertainty. The current method to derive wind speed estimations from aerodynamic torque, pitch angle and tip speed ratio after the wind field flows past the turbine and have their limitations, e.g. in predicting gusts. Therefore, an estimation model coupled with the measuring capability of nacelle based Lidars was necessary for detecting extreme events and for estimating accurate wind speeds at the rotor disc. Nacelle-mounted Lidars measure the oncoming wind field from utpo 400m(5D) in front of the turbine and appropriate models could be used for deriving the rotor effective wind speed from these measurements. This article proposes an auto-regressive model combined with a method to include the blockage factor in order to estimate the wind speeds accurately using Lidar measurements. An Armax model was used to determine the transfer function that models the physical evolution of wind towards the wind turbine, incorporating the effect of surface roughness, wind shear and wind variability at the site. The model could incorporate local as well as global effects and was able to predict the rotor effective wind speeds with adequate accuracy for wind turbine control actions. A high correlation of 0.86 was achieved as the Armax modelled signal was compared to a reference signal. The model could also be extended to estimate the damage potential during high wind speeds, gusts or abrupt change in wind directions, allowing the controller to act appropriately
A Bayesian hierarchical model for wind gust prediction
Friederichs, Petra; Oesting, Marco; Schlather, Martin
2014-05-01
A postprocessing method for ensemble wind gust forecasts given by a mesoscale limited area numerical weather prediction (NWP) model is presented, which is based on extreme value theory. A process layer for the parameters of a generalized extreme value distribution (GEV) is introduced using a Bayesian hierarchical model (BHM). Incorporating the information of the COMSO-DE forecasts, the process parameters model the spatial response surfaces of the GEV parameters as Gaussian random fields. The spatial BHM provides area wide forecasts of wind gusts in terms of a conditional GEV. It models the marginal distribution of the spatial gust process and provides not only forecasts of the conditional GEV at locations without observations, but also uncertainty information about the estimates. A disadvantages of BHM model is that it assumes conditional independent observations. In order to incorporate the dependence between gusts at neighboring locations as well as the spatial random fields of observed and forecasted maximal wind gusts, we propose to model them jointly by a bivariate Brown-Resnick process.
A Model for the Sources of the Slow Solar Wind
Antiochos, S K; Titov, V S; Lionello, R; Linker, J A
2011-01-01
Models for the origin of the slow solar wind must account for two seemingly contradictory observations: The slow wind has the composition of the closed field corona, implying that it originates from the continuous opening and closing of flux at the boundary between open and closed field. On the other hand, the slow wind also has large angular width, up to ~ 60{\\circ}, suggesting that its source extends far from the open-closed boundary. We propose a model that can explain both observations. The key idea is that the source of the slow wind at the Sun is a network of narrow (possibly singular) open-field corridors that map to a web of separatrices and quasi-separatrix layers in the heliosphere. We compute analytically the topology of an open-field corridor and show that it produces a quasi-separatrix layer in the heliosphere that extends to angles far from the heliospheric current sheet. We then use an MHD code and MDI/SOHO observations of the photospheric magnetic field to calculate numerically, with high spat...
A multiple flux-tube solar wind model
Pinto, Rui F
2016-01-01
We present a new model, MULTI-VP, that computes the three-dimensional structure of the solar wind which includes the chromosphere, the transition region, and the corona and low heliosphere. MULTI- VP calculates a large ensemble of wind profiles flowing along open magnetic field-lines which sample the whole three-dimensional atmosphere or, alternatively, on a given region of interest. The radial domain starts from the photosphere and extends, typically, to about 30 $R_{sun}$ . The elementary uni-dimensional wind solutions are based on a mature numerical scheme which was adapted in order to accept any flux-tube geometry. We discuss here the first results obtained with this model. We use Potential Field Source-Surface (PFSS) extrapolations of magnetograms from the Wilcox Solar Observatory (WSO) to determine the structure of the background magnetic field. Our results support the hypothesis that the geometry of the magnetic flux-tubes in the lower corona controls the distribution of slow and fast wind flows. The i...
A perturbative improvement of the staggered fermions using fat links
Lee, W
2002-01-01
We study possibility of improving staggered fermions using various fat links in order to reduce perturbative corrections to the gauge-invariant staggered fermion operators. We prove five theorems on SU(3) projection, triviality in renormalization, multiple SU(3) projections, uniqueness and equivalence. As a result of these theorems, we show that, at one loop level, the renormalization of staggered fermion operators is identical between SU(3) projected Fat7 links and hypercubic links, as long as the action and operators are constructed by imposing the same perturbative improvement condition. In addition, we propose a new view of SU(3) projection as a tool of tadpole improvement for the staggered fermion doublers. As a conclusion, we present alternative choices of constructing fat links to improve the staggered fermion action and operators, which deserve further investigation.
Effective field theories for QCD with rooted staggered fermions
Bernard, Claude; Shamir, Yigal
2007-01-01
Even highly improved variants of lattice QCD with staggered fermions show significant violations of taste symmetry at currently accessible lattice spacings. In addition, the "rooting trick" is used in order to simulate with the correct number of light sea quarks, and this makes the lattice theory nonlocal, even though there is good reason to believe that the continuum limit is in the correct universality class. In order to understand scaling violations, it is thus necessary to extend the construction of the Symanzik effective theory to include rooted staggered fermions. We show how this can be done, starting from a generalization of the renormalization-group approach to rooted staggered fermions recently developed by one of us. We then explain how the chiral effective theory follows from the Symanzik action, and show that it leads to "rooted" staggered chiral perturbation theory as the correct chiral theory for QCD with rooted staggered fermions. We thus establish a direct link between the renormalization-gro...
Reductions in transformer losses achieved by staggering lamination layers
Albir, R. S.; Moses, A. J.
1989-05-01
The total loss of identical 3-phase, 3-limb, mitred and staggered cores assembled from 0.3 mm thick, conventional high permeability and laser scribed grain oriented silicon iron have been compared. The croes built from conventional material produced the best improvements when staggered and these were chosen to carry out further investigation to examine the effect of the stacking number and the T-joint design on the power loss of the cores. The power loss generally increased as the stagger length was increased, but an optimum stagger length range was determined at which the power loss was lowest. The percentage improvement in the power loss due to the introduction of the staggered technique is dependent upon the orientation of the material and the T-joint design. The best loss reduction compared to a mitred core of the same rating was around 5% using a core assembled from conventional material.
Pseudospin induced chirality with Staggered Optical Graphene
Liu, Jianlong; Zhang, Shuang
2016-01-01
Pseudospin plays a very important role in understanding various interesting physical phenomena associated with 2D materials such as graphene. It has been proposed that pseudospin is directly related to angular momentum, and it was recently experimentally demonstrated that orbit angular momentum is an intrinsic property of pseudospin in a photonic honeycomb lattice. However, in photonics, the interaction between spin and pseudospin for light has never been investigated. In this Letter, we propose that, in an optical analogue of staggered graphene, i.e. a photonic honeycomb lattice waveguide with in-plane inversion symmetry breaking, the pseudospin mode can strongly couple to the spin of an optical beam incident along certain directions. The spin-pseudospin coupling, caused by the spin-orbit conversion in the scattering process, induces a strong optical chiral effect for the transmitted optical beam. Spin-pseudospin coupling of light opens door to the design of pseudospin-mediated spin or valley selective photo...
Power module assemblies with staggered coolant channels
Herron, Nicholas Hayden; Mann, Brooks S; Korich, Mark D
2013-07-16
A manifold is provided for supporting a power module assembly with a plurality of power modules. The manifold includes a first manifold section. The first face of the first manifold section is configured to receive the first power module, and the second face of the first manifold section defines a first cavity with a first baseplate thermally coupled to the first power module. The first face of the second manifold section is configured to receive the second power module, and the second face of the second manifold section defines a second cavity with a second baseplate thermally coupled to the second power module. The second face of the first manifold section and the second face of the second manifold section are coupled together such that the first cavity and the second cavity form a coolant channel. The first cavity is at least partially staggered with respect to second cavity.
Lowrank seismic-wave extrapolation on a staggered grid
Fang, Gang
2014-05-01
© 2014 Society of Exploration Geophysicists. We evaluated a new spectral method and a new finite-difference (FD) method for seismic-wave extrapolation in time. Using staggered temporal and spatial grids, we derived a wave-extrapolation operator using a lowrank decomposition for a first-order system of wave equations and designed the corresponding FD scheme. The proposed methods extend previously proposed lowrank and lowrank FD wave extrapolation methods from the cases of constant density to those of variable density. Dispersion analysis demonstrated that the proposed methods have high accuracy for a wide wavenumber range and significantly reduce the numerical dispersion. The method of manufactured solutions coupled with mesh refinement was used to verify each method and to compare numerical errors. Tests on 2D synthetic examples demonstrated that the proposed method is highly accurate and stable. The proposed methods can be used for seismic modeling or reverse-time migration.
Advanced optical position sensors for magnetically suspended wind tunnel models
Lafleur, S.
1985-01-01
A major concern to aerodynamicists has been the corruption of wind tunnel test data by model support structures, such as stings or struts. A technique for magnetically suspending wind tunnel models was considered by Tournier and Laurenceau (1957) in order to overcome this problem. This technique is now implemented with the aid of a Large Magnetic Suspension and Balance System (LMSBS) and advanced position sensors for measuring model attitude and position within the test section. Two different optical position sensors are discussed, taking into account a device based on the use of linear CCD arrays, and a device utilizing area CID cameras. Current techniques in image processing have been employed to develop target tracking algorithms capable of subpixel resolution for the sensors. The algorithms are discussed in detail, and some preliminary test results are reported.
Parker's Model for Stellar Wind and Magnetohydrodynamic Extensions
Shivamoggi, B K
2016-01-01
In this paper, we first revisit Parker's hydrodynamic model for a stellar wind and make further analytic considerations. We show that the visualization of an effective de Laval type nozzle associated with Parker's model is valid only in a superficial sense and not on the dynamical level. We then make an analytic considerations on the Weber-Davis magnetohydrodynamic (MHD) extension of Parker's model with a view to provide a qualitative understanding of the coupling between the magnetic field and the plasma motion in the stellar wind. We find that, *the MHD azimuthal velocity profile actually resembles that for hydrodynamic Lamb-Oseen vortex; *Keplerian-orbit conditions prevail near a strong rotator even in a magnetized situation; *Parker's hydrodynamic scenario \\cite{Par} seems to reappear in the strong magnetization regime.\\end{itemize}
Modeling and investigation of Gulf El-Zayt wind farm for stability studying during extreme
Directory of Open Access Journals (Sweden)
Omar Noureldeen
2014-03-01
Full Text Available This paper investigates the impact of extreme gust wind as a case of wind speed variation on a wind farm interconnected electrical grid. The impact of extreme gust wind speed variation on active and reactive power of the wind farms is studied for variable speed wind farm equipped with Doubly Fed Induction Generators (DFIGs. A simulation model of the under implementation 120 MW wind farm at Gulf El-Zayt region, Red Sea, Egypt, is simulated as a case study. A detailed model of extreme gust wind speed variation is implemented and simulated, using MATLAB/Simulink toolbox, based on International Electrotechnical Commission IEC 61400-1 and climate characteristic of Gulf El-Zayt site. The simulation results show the influence of different extreme gust wind speed variations on the fluctuation of active power and reactive power at the Point of Common Coupling (PCC of the studied wind farm.
Validation of Model Forecasts of the Ambient Solar Wind
Macneice, P. J.; Hesse, M.; Kuznetsova, M. M.; Rastaetter, L.; Taktakishvili, A.
2009-01-01
Independent and automated validation is a vital step in the progression of models from the research community into operational forecasting use. In this paper we describe a program in development at the CCMC to provide just such a comprehensive validation for models of the ambient solar wind in the inner heliosphere. We have built upon previous efforts published in the community, sharpened their definitions, and completed a baseline study. We also provide first results from this program of the comparative performance of the MHD models available at the CCMC against that of the Wang-Sheeley-Arge (WSA) model. An important goal of this effort is to provide a consistent validation to all available models. Clearly exposing the relative strengths and weaknesses of the different models will enable forecasters to craft more reliable ensemble forecasting strategies. Models of the ambient solar wind are developing rapidly as a result of improvements in data supply, numerical techniques, and computing resources. It is anticipated that in the next five to ten years, the MHD based models will supplant semi-empirical potential based models such as the WSA model, as the best available forecast models. We anticipate that this validation effort will track this evolution and so assist policy makers in gauging the value of past and future investment in modeling support.
Developing a Local Neurofuzzy Model for Short-Term Wind Power Forecasting
Directory of Open Access Journals (Sweden)
E. Faghihnia
2014-01-01
Full Text Available Large scale integration of wind generation capacity into power systems introduces operational challenges due to wind power uncertainty and variability. Therefore, accurate wind power forecast is important for reliable and economic operation of the power systems. Complexities and nonlinearities exhibited by wind power time series necessitate use of elaborative and sophisticated approaches for wind power forecasting. In this paper, a local neurofuzzy (LNF approach, trained by the polynomial model tree (POLYMOT learning algorithm, is proposed for short-term wind power forecasting. The LNF approach is constructed based on the contribution of local polynomial models which can efficiently model wind power generation. Data from Sotavento wind farm in Spain was used to validate the proposed LNF approach. Comparison between performance of the proposed approach and several recently published approaches illustrates capability of the LNF model for accurate wind power forecasting.
A Predictive Model for Wind Farms Using Dynamic Mode Decomposition
Thomas, Vaughan; Meneveau, Charles; Gayme, Dennice
2016-11-01
In this work we extend traditional dynamic mode decomposition (DMD) to develop a linear predictive model for the time evolution of the velocity field for a multiple-turbine wind farm. Traditional DMD identifies a set of DMD modes which can be used to produce a linear system that approximates the dynamics of the original system. Typically, these DMD modes consist of those that both grow and decay, but in order to develop a predictive model we need a system that evolves along a manifold that neither grows nor decays. Here we modify the DMD calculation to build such a model. We then apply this method to three dimensional large eddy simulations (LES) of a multi-turbine wind farm. Our predictive wind farm model is initialized with a small time series of data independent of the original data used to create the system. When initialized in this manner our DMD based model can reproduce the subsequent time evolution of the velocity field over ten inter-turbine convective timescales with a gradual falloff in performance. This work is supported by the National Science Foundation (Grants ECCS-1230788 and OISE-1243482, the WINDINSPIRE project).
Mesoscale Wind Predictions for Wave Model Evaluation
2016-06-07
N0001400WX20041(B) http://www.nrlmry.navy.mil LONG TERM GOALS The long-term goal is to demonstrate the significance and importance of high...ocean waves by an appropriate wave model. OBJECTIVES The main objectives of this project are to: 1. Build the infrastructure to generate the...temperature for all COAMPS grids at the resolution of each of these grids. These analyses are important for the proper 2 specification of the lower
Comparison of aerodynamic models for Vertical Axis Wind Turbines
DEFF Research Database (Denmark)
Ferreira, C. Simão; Aagaard Madsen, Helge; Barone, M.
2014-01-01
Multi-megawatt Vertical Axis Wind Turbines (VAWTs) are experiencing an increased interest for floating offshore applications. However, VAWT development is hindered by the lack of fast, accurate and validated simulation models. This work compares six different numerical models for VAWTS: a multiple...... streamtube model, a double-multiple streamtube model, the actuator cylinder model, a 2D potential flow panel model, a 3D unsteady lifting line model, and a 2D conformal mapping unsteady vortex model. The comparison covers rotor configurations with two NACA0015 blades, for several tip speed ratios, rotor...... solidity and fixed pitch angle, included heavily loaded rotors, in inviscid flow. The results show that the streamtube models are inaccurate, and that correct predictions of rotor power and rotor thrust are an effect of error cancellation which only occurs at specific configurations. The other four models...
Transport of Solar Wind Fluctuations: A Two-Component Model
Oughton, S.; Matthaeus, W. H.; Smith, C. W.; Breech, B.; Isenberg, P. A.
2011-01-01
We present a new model for the transport of solar wind fluctuations which treats them as two interacting incompressible components: quasi-two-dimensional turbulence and a wave-like piece. Quantities solved for include the energy, cross helicity, and characteristic transverse length scale of each component, plus the proton temperature. The development of the model is outlined and numerical solutions are compared with spacecraft observations. Compared to previous single-component models, this new model incorporates a more physically realistic treatment of fluctuations induced by pickup ions and yields improved agreement with observed values of the correlation length, while maintaining good observational accord with the energy, cross helicity, and temperature.
3D Staggered-Grid Finite-Difference Simulation of Acoustic Waves in Turbulent Moving Media
Symons, N. P.; Aldridge, D. F.; Marlin, D.; Wilson, D. K.; Sullivan, P.; Ostashev, V.
2003-12-01
Acoustic wave propagation in a three-dimensional heterogeneous moving atmosphere is accurately simulated with a numerical algorithm recently developed under the DOD Common High Performance Computing Software Support Initiative (CHSSI). Sound waves within such a dynamic environment are mathematically described by a set of four, coupled, first-order partial differential equations governing small-amplitude fluctuations in pressure and particle velocity. The system is rigorously derived from fundamental principles of continuum mechanics, ideal-fluid constitutive relations, and reasonable assumptions that the ambient atmospheric motion is adiabatic and divergence-free. An explicit, time-domain, finite-difference (FD) numerical scheme is used to solve the system for both pressure and particle velocity wavefields. The atmosphere is characterized by 3D gridded models of sound speed, mass density, and the three components of the wind velocity vector. Dependent variables are stored on staggered spatial and temporal grids, and centered FD operators possess 2nd-order and 4th-order space/time accuracy. Accurate sound wave simulation is achieved provided grid intervals are chosen appropriately. The gridding must be fine enough to reduce numerical dispersion artifacts to an acceptable level and maintain stability. The algorithm is designed to execute on parallel computational platforms by utilizing a spatial domain-decomposition strategy. Currently, the algorithm has been validated on four different computational platforms, and parallel scalability of approximately 85% has been demonstrated. Comparisons with analytic solutions for uniform and vertically stratified wind models indicate that the FD algorithm generates accurate results with either a vanishing pressure or vanishing vertical-particle velocity boundary condition. Simulations are performed using a kinematic turbulence wind profile developed with the quasi-wavelet method. In addition, preliminary results are presented
Mack, Robert J.
2007-01-01
Low-boom model pressure signatures are often measured at two or more wind-tunnel facilities. Preliminary measurements are made at small separation distances in a wind tunnel close at hand, and a second set of pressure signatures is measured at larger separation distances in a wind-tunnel facility with a larger test section. In this report, a method for correcting and standardizing the wind-tunnel-measured pressure signatures obtained in different wind tunnel facilities is presented and discussed.
Wind farm production prediction - The Zephyr model
Energy Technology Data Exchange (ETDEWEB)
Landberg, L. [Risoe National Lab., Wind Energy Dept., Roskilde (Denmark); Giebel, G. [Risoe National Lab., Wind Energy Dept., Roskilde (Denmark); Madsen, H. [IMM (DTU), Kgs. Lyngby (Denmark); Nielsen, T.S. [IMM (DTU), Kgs. Lyngby (Denmark); Joergensen, J.U. [Danish Meteorologisk Inst., Copenhagen (Denmark); Lauersen, L. [Danish Meteorologisk Inst., Copenhagen (Denmark); Toefting, J. [Elsam, Fredericia (DK); Christensen, H.S. [Eltra, Fredericia (Denmark); Bjerge, C. [SEAS, Haslev (Denmark)
2002-06-01
This report describes a project - funded by the Danish Ministry of Energy and the Environment - which developed a next generation prediction system called Zephyr. The Zephyr system is a merging between two state-of-the-art prediction systems: Prediktor of Risoe National Laboratory and WPPT of IMM at the Danish Technical University. The numerical weather predictions were generated by DMI's HIRLAM model. Due to technical difficulties programming the system, only the computational core and a very simple version of the originally very complex system were developed. The project partners were: Risoe, DMU, DMI, Elsam, Eltra, Elkraft System, SEAS and E2. (au)
Improvement in torque and power transmission system of Savonius wind turbine
Energy Technology Data Exchange (ETDEWEB)
Ghosh, K.; Kumar, A.; Gupta, S. [Indian Inst. of Technology, Kanpur (India). Aerospace Engineering Dept.
2006-07-01
The Savonius vertical axis wind turbine has a simple geometry and is inexpensive to build due to its high power coefficient. However, because its torque coefficient varies widely with wind angles and even becomes negative twice in a revolution, it has not been widely commercialized. A Savonius rotor is conventionally built in 2 or 3 tiers, with 90-degree or 60-degree stagger between tiers for smoother torque. The torque coefficient versus wind angle data for multi-tier rotors can be generated by overlapping single-tier data with requisite stagger. This process ignores aerodynamic interference between tiers. The torque coefficient versus wind angle was measured in static mode and the power coefficient was measured in rotating mode of a 2-tier Savonius using a wind tunnel technique involving the brake-dynamometer principle and wind tunnel balance. A significant aerodynamic interference and lower power coefficient were observed. Static and dynamic testing procedures were described and smoke flow models and visualization were also presented. Subsequently, a discussion of the results of the testing were presented. It was concluded that there is significant aerodynamic interference between the tiers of a 2-tier model leading to reduced values of torque and power. Modification of the Savonius wind turbine by adding 20 per cent thick symmetrical airfoils results in improved torque, without significantly increasing average wake width. 3 refs., 1 tab., 13 refs.
Energy Technology Data Exchange (ETDEWEB)
Honrubia-Escribano, A.; Gomez Lazaro, E.; Jimenez-Buendia, F.; Muljadi, Eduard
2016-11-01
The International Electrotechnical Commission Standard 61400-27-1 was published in February 2015. This standard deals with the development of generic terms and parameters to specify the electrical characteristics of wind turbines. Generic models of very complex technological systems, such as wind turbines, are thus defined based on the four common configurations available in the market. Due to its recent publication, the comparison of the response of generic models with specific vendor models plays a key role in ensuring the widespread use of this standard. This paper compares the response of a specific Gamesa dynamic wind turbine model to the corresponding generic IEC Type III wind turbine model response when the wind turbine is subjected to a three-phase voltage dip. This Type III model represents the doubly-fed induction generator wind turbine, which is not only one of the most commonly sold and installed technologies in the current market but also a complex variable-speed operation implementation. In fact, active and reactive power transients are observed due to the voltage reduction. Special attention is given to the reactive power injection provided by the wind turbine models because it is a requirement of current grid codes. Further, the boundaries of the generic models associated with transient events that cannot be represented exactly are included in the paper.
CFD Wake Modelling with a BEM Wind Turbine Sub-Model
Directory of Open Access Journals (Sweden)
Anders Hallanger
2013-01-01
Full Text Available Modelling of wind farms using computational fluid dynamics (CFD resolving the flow field around each wind turbine's blades on a moving computational grid is still too costly and time consuming in terms of computational capacity and effort. One strategy is to use sub-models for the wind turbines, and sub-grid models for turbulence production and dissipation to model the turbulent viscosity accurately enough to handle interaction of wakes in wind farms. A wind turbine sub-model, based on the Blade Momentum Theory, see Hansen (2008, has been implemented in an in-house CFD code, see Hallanger et al. (2002. The tangential and normal reaction forces from the wind turbine blades are distributed on the control volumes (CVs at the wind turbine rotor location as sources in the conservation equations of momentum. The classical k-epsilon turbulence model of Launder and Spalding (1972 is implemented with sub-grid turbulence (SGT model, see Sha and Launder (1979 and Sand and Salvesen (1994. Steady state CFD simulations were compared with flow and turbulence measurements in the wake of a model scale wind turbine, see Krogstad and Eriksen (2011. The simulated results compared best with experiments when stalling (boundary layer separation on the wind turbine blades did not occur. The SGT model did improve turbulence level in the wake but seems to smear the wake flow structure. It should be noted that the simulations are carried out steady state not including flow oscillations caused by vortex shedding from tower and blades as they were in the experiments. Further improvement of the simulated velocity defect and turbulence level seems to rely on better parameter estimation to the SGT model, improvements to the SGT model, and possibly transient- instead of steady state simulations.
MHD Wind Models in X-Ray Binaries and AGN
Behar, Ehud; Fukumura, Keigo; Kazanas, Demosthenes; Shrader, Chris R.; Tombesi, Francesco; Contopoulos, Ioannis
2017-08-01
Self-similar magnetohydrodynamic (MHD) wind models that can explain both the kinematics and the ionization structure of outflows from accretion sources will be presented.The X-ray absorption-line properties of these outflows are diverse, their velocity ranging from 0.001c to 0.1c, and their ionization ranging from neutral to fully ionized.We will show how the velocity structure and density profile of the wind can be tightly constrained, by finding the scaling of the magnetic flux with the distance from the center that best matches observations, and with no other priors.It will be demonstrated that the same basic MHD wind structure that successfully accounts for the X-ray absorber properties of outflows from supermassive black holes, also reproduces the high-resolution X-ray spectrum of the accreting stellar-mass black hole GRO J1655-40 for a series of ions between ~1A and ~12A.These results support both the magnetic nature of these winds, as well as the universal nature of magnetic outflows across all black hole sizes.
Modelling Jets, Tori and Flares in Pulsar Wind Nebulae
Porth, Oliver; Buehler, Rolf; Olmi, Barbara; Komissarov, Serguei; Lamberts, Astrid; Amato, Elena; Yuan, Yajie; Rudy, Alexander
2017-03-01
In this contribution we review the recent progress in the modelling of Pulsar Wind Nebulae (PWN). We start with a brief overview of the relevant physical processes in the magnetosphere, the wind-zone and the inflated nebula bubble. Radiative signatures and particle transport processes obtained from 3D simulations of PWN are discussed in the context of optical and X-ray observations. We then proceed to consider particle acceleration in PWN and elaborate on what can be learned about the particle acceleration from the dynamical structures called GwispsG observed in the Crab nebula. We also discuss recent observational and theoretical results of gamma-ray flares and the inner knot of the Crab nebula, which had been proposed as the emission site of the flares. We extend the discussion to GeV flares from binary systems in which the pulsar wind interacts with the stellar wind from a companion star. The chapter concludes with a discussion of solved and unsolved problems posed by PWN.
Implications of solar wind measurements for solar models and composition
Serenelli, Aldo; Scott, Pat; Villante, Francesco L.; Vincent, Aaron C.; Asplund, Martin; Basu, Sarbani; Grevesse, Nicolas; Peña-Garay, Carlos
2016-11-01
We critically examine recent claims of a high solar metallicity by von Steiger & Zurbuchen (2016, vSZ16) based on in situ measurements of the solar wind, rather than the standard spectroscopically inferred abundances (Asplund et al. 2009, hereafter AGSS09). We test the claim by Vagnozzi et al. (2016) that a composition based on the solar wind enables one to construct a standard solar model in agreement with helioseismological observations and thus solve the decades-old solar modelling problem. We show that, although some helioseismological observables are improved compared to models computed with spectroscopic abundances, most are in fact worse. The high abundance of refractory elements leads to an overproduction of neutrinos, with a predicted 8B flux that is nearly twice its observed value, and 7Be and CNO fluxes that are experimentally ruled out at high confidence. A combined likelihood analysis shows that models using the vSZ16 abundances are worse than AGSS09 despite a higher metallicity. We also present astrophysical and spectroscopic arguments showing the vSZ16 composition to be an implausible representation of the solar interior, identifying the first ionization potential effect in the outer solar atmosphere and wind as the likely culprit.
DEFF Research Database (Denmark)
Pinson, Pierre; Madsen, Henrik
2012-01-01
optimized is based on penalized maximum likelihood, with exponential forgetting of past observations. MSAR models are then employed for one-step-ahead point forecasting of 10 min resolution time series of wind power at two large offshore wind farms. They are favourably compared against persistence...
DEFF Research Database (Denmark)
Pinson, Pierre; Madsen, Henrik
optimized is based on penalized maximum-likelihood, with exponential forgetting of past observations. MSAR models are then employed for 1-step-ahead point forecasting of 10-minute resolution time-series of wind power at two large offshore wind farms. They are favourably compared against persistence and Auto...
Energy Technology Data Exchange (ETDEWEB)
Porch, W.M.; Lange, R.
1982-11-01
Recent studies in The Geysers region of Northern California have concentrated on drainage wind effects on tracer transport and diffusion in complex terrain, as part of the Atmospheric Studies in Complex Terrain (ASCOT) project. These studies combined tracer measurements, conventional tower and remote sensing meteorological measurements, and numerical wind field transport and diffusion models. One part of the meteorological measurement support used eight optical cross-path wind sensors across the principle air drainage valleys. These sensors had varying optical path lengths within the drainage layer of approx. 300 m to 3 km. Results of this study indicate that the combination of spatially averaged cross-path optical wind sensor and conventional tower mounted cup-vane anemometer data into a numerical plume transport and diffusion model for complex terrain has provided useful results. The most important of these results is an independent measure of wind data on a spatial scale compatible with necessarily large grid scales in numerical wind field models with topography. This allows assessment of terrain associated exposure problems for tower anemometers in complex terrain. The optical cross wind data can be used to compare necessary averaging times, and spatial distribution of point sensors and provide verification data to improve the logistics of instrument placement in combination with numerical models.
Data Mining Methods to Generate Severe Wind Gust Models
Directory of Open Access Journals (Sweden)
Subana Shanmuganathan
2014-01-01
Full Text Available Gaining knowledge on weather patterns, trends and the influence of their extremes on various crop production yields and quality continues to be a quest by scientists, agriculturists, and managers. Precise and timely information aids decision-making, which is widely accepted as intrinsically necessary for increased production and improved quality. Studies in this research domain, especially those related to data mining and interpretation are being carried out by the authors and their colleagues. Some of this work that relates to data definition, description, analysis, and modelling is described in this paper. This includes studies that have evaluated extreme dry/wet weather events against reported yield at different scales in general. They indicate the effects of weather extremes such as prolonged high temperatures, heavy rainfall, and severe wind gusts. Occurrences of these events are among the main weather extremes that impact on many crops worldwide. Wind gusts are difficult to anticipate due to their rapid manifestation and yet can have catastrophic effects on crops and buildings. This paper examines the use of data mining methods to reveal patterns in the weather conditions, such as time of the day, month of the year, wind direction, speed, and severity using a data set from a single location. Case study data is used to provide examples of how the methods used can elicit meaningful information and depict it in a fashion usable for management decision making. Historical weather data acquired between 2008 and 2012 has been used for this study from telemetry devices installed in a vineyard in the north of New Zealand. The results show that using data mining techniques and the local weather conditions, such as relative pressure, temperature, wind direction and speed recorded at irregular intervals, can produce new knowledge relating to wind gust patterns for vineyard management decision making.
Impact of wind power in autonomous power systems—power fluctuations—modelling and control issues
DEFF Research Database (Denmark)
Margaris, Ioannis D.; Hansen, Anca Daniela; Cutululis, Nicolaos Antonio;
2011-01-01
technologies, power system protection and load. Analytical models for wind farms with three different wind turbine technologies, namely Doubly Fed Induction Generator, Permanent Magnet Synchronous Generator and Active Stall Induction Generator-based wind turbines, are included. Likewise, analytical models...... for diesel and steam generation plants are applied. The power grid, including speed governors, automatic voltage regulators, protection system and loads is modelled in the same platform. Results for different load and wind profile cases are being presented for the case study of the island Rhodes, in Greece......This paper describes a detailed modelling approach to study the impact of wind power fluctuations on the frequency control in a non-interconnected system with large-scale wind power. The approach includes models for wind speed fluctuations, wind farm technologies, conventional generation...
SAR Observation and Modeling of Gap Winds in the Prince William Sound of Alaska
Directory of Open Access Journals (Sweden)
Karl Volz
2008-08-01
Full Text Available AlaskaÃ¢Â€Â™s Prince William Sound (PWS is a unique locale tending to have strong gap winds, especially in the winter season. To characterize and understand these strong surface winds, which have great impacts on the local marine and aviation activities, the surface wind retrieval from the Synthetic Aperture Radar data (SAR-wind is combined with a numerical mesoscale model. Helped with the SAR-wind observations, the mesoscale model is used to study cases of strong winds and relatively weak winds to depict the nature of these winds, including the area of extent and possible causes of the wind regimes. The gap winds from the Wells Passage and the Valdez Arm are the most dominant gap winds in PWS. Though the Valdez Arm is north-south trending and Wells Passage is east-west oriented, gap winds often develop simultaneously in these two places when a low pressure system is present in the Northern Gulf of Alaska. These two gap winds often converge at the center of PWS and extend further out of the Sound through the Hinchinbrook Entrance. The pressure gradients imposed over these areas are the main driving forces for these gap winds. Additionally, the drainage from the upper stream glaciers and the blocking effect of the banks of the Valdez Arm probably play an important role in enhancing the gap wind.
Distributed Model Predictive Control of A Wind Farm for Optimal Active Power Control
DEFF Research Database (Denmark)
Zhao, Haoran; Wu, Qiuwei; Guo, Qinglai;
2015-01-01
This paper presents a dynamic discrete-time Piece- Wise Affine (PWA) model of a wind turbine for the optimal active power control of a wind farm. The control objectives include both the power reference tracking from the system operator and the wind turbine mechanical load minimization. Instead......, which combines the clustering, linear identification and pattern recognition techniques. The developed model, consisting of 47 affine dynamics, is verified by the comparison with a widely-used nonlinear wind turbine model. It can be used as a predictive model for the Model Predictive Control (MPC......) or other advanced optimal control applications of a wind farm....
Energy Technology Data Exchange (ETDEWEB)
Palma, J.M.L.M. [CEsA, Research Centre for Wind Energy and Atmospheric Flows, FEUP, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto (Portugal); Castro, F.A. [CEsA, Research Centre for Wind Energy and Atmospheric Flows, ISEP, Instituto Superior de Engenharia do Porto, Rua Dr. Antonio Bernardino de Almeida 431, 4200-072 Porto (Portugal); Ribeiro, L.F. [CEsA, Research Centre for Wind Energy and Atmospheric Flows, IPB, Instituto Politecnico de Braganca, Campus de Santa Apolonia - Apartado 1038, 5301-854 Braganca (Portugal); Rodrigues, A.H.; Pinto, A.P. [CEsA, Research Centre for Wind Energy and Atmospheric Flows, INEGI, Instituto de Engenharia Mecanica e Gestao Industrial, Rua Dr. Roberto Frias s/n, 4200-465 Porto (Portugal)
2008-12-15
The current trend of increasing the electricity production from wind energy has led to the installation of wind farms in areas of greater orographic complexity, raising doubts on the use of simple, linear, mathematical models of the fluid flow equations, so common in the wind energy engineering. The present study shows how conventional techniques, linear models and cup anemometers, can be combined with flow simulation by computational fluid dynamics techniques (nonlinear models) and measurements by sonic anemometers, and discuss their relative merits in the characterisation of the wind over a coastal region - a cliff over the sea. The computational fluid dynamic techniques were particularly useful, providing a global view of the wind flow over the cliff and enabling the identification of separated flow regions, clearly unsuitable for installation of wind turbines. These locations display a pulsating flow, with periods between 1 and 7 min, in agreement with sonic anemometer measurements, and both a turbulence intensity and a gust factor well above the wind turbine design conditions. (author)
Intercomparison of state-of-the-art models for wind energy resources with mesoscale models:
Olsen, Bjarke Tobias; Hahmann, Andrea N.; Sempreviva, Anna Maria; Badger, Jake; Joergensen, Hans E.
2016-04-01
1. Introduction Mesoscale models are increasingly being used to estimate wind conditions to identify perspective areas and sites where to develop wind farm projects. Mesoscale models are functional for giving information over extensive areas with various terrain complexities where measurements are scarce and measurement campaigns costly. Several mesoscale models and families of models are being used, and each often contains thousands of setup options. Since long-term integrations are expensive and tedious to carry out, only limited comparisons exist. To remedy this problem and for evaluating the capabilities of mesoscale models to estimate site wind conditions, a tailored benchmarking study has been co-organized by the European Wind Energy Association (EWEA) and the European Energy Research Alliance Joint Programme Wind Energy (EERA JP WIND). EWEA hosted results and ensured that participants were anonymous. The blind evaluation was performed at the Wind Energy Department of the Technical University of Denmark (DTU) with the following objectives: (1) To highlight common issues on mesoscale modelling of wind conditions on sites with different characteristics, and (2) To identify gaps and strengths of models and understand the root conditions for further evaluating uncertainties. 2. Approach Three experimental sites were selected: FINO 3 (offshore, GE), Høvsore (coastal, DK), and Cabauw (land-based, NL), and three other sites without observations based on . The three mast sites were chosen because the availability of concurrent suitable time series of vertical profiles of winds speed and other surface parameters. The participants were asked to provide hourly time series of wind speed, wind direction, temperature, etc., at various vertical heights for a complete year. The methodology used to derive the time series was left to the choice of the participants, but they were asked for a brief description of their model and many other parameters (e.g., horizontal and
Prediction models for wind speed at turbine locations in a wind farm
DEFF Research Database (Denmark)
Knudsen, Torben; Bak, Thomas; Soltani, Mohsen
2011-01-01
on the result related to effective wind speed, it is possible to predict wind speeds at neighboring turbines, with a separation of over 700 m, up to 1 min ahead reducing the error by 30% compared with a persistence method. The methodological results are demonstrated on data from an off-shore wind farm...
Wind profile modelling using WAsP and "tall" wind measurements
DEFF Research Database (Denmark)
Floors, Rogier Ralph; Kelly, Mark C.; Troen, Ib
2015-01-01
A and B in the geostrophic drag law was taken into account by specifying a mean offset between the thermal and surface geostrophic wind vector and a mean magnitude of the thermal wind vector. Wind lidar and mast measurements from 11 different sites (that were not used in determining the empirical...
Institute of Scientific and Technical Information of China (English)
Zhao Hai-Bo; Wang Xiu-Ming; Chen Hao
2006-01-01
In modelling elastic wave propagation in a porous medium, when the ratio between the fluid viscosity and the medium permeability is comparatively large, the stiffness problem of Biot's poroelastic equations will be encountered. In the paper, a partition method is developed to solve the stiffness problem with a staggered high-order finite-difference. The method splits the Biot equations into two systems. One is stiff, and solved analytically, the other is nonstiff,and solved numerically by using a high-order staggered-grid finite-difference scheme. The time step is determined by the staggered finite-difference algorithm in solving the nonstiff equations, thus a coarse time step 05 be employed.Therefore, the computation efficiency and computational stability are improved greatly. Also a perfect by matched layer technology is used in the split method as absorbing boundary conditions. The numerical results are compared with the analytical results and those obtained from the conventional staggered-grid finite-difference method in a homogeneous model, respectively. They are in good agreement with each other. Finally, a slightly more complex model is investigated and compared with related equivalent model to illustrate the good performance of the staggered-grid finite-difference scheme in the partition method.
The Making of a Second-generation Wind Farm Efficiency Model Complex
DEFF Research Database (Denmark)
Frandsen, Sten Tronæs; Ejsing Jørgensen, Hans; Barthelmie, Rebecca Jane
2009-01-01
kilometres down to the size of the individual wind turbine. Flow within wind farms is difficult to predict. The analytical and modified WAsP/park models show promise; however, these require further development/evaluation. For the flow downwind of the wind farm, several intermediate-scale models fit...
DEFF Research Database (Denmark)
Xu, Chang; Han, Xingxing; Wang, Xin
2015-01-01
the underestimation issue of the wind speed deficit when applying the STD k-ε model. In addition, the model also introduced a radial distribution function to assess the non-uniform load on the actuator disk and a coefficient C4ε of the turbulent source. To validate the model, the wind turbines of Nibe `B' and Dawin...
Wind and Water Power Modeling and Simulation at the NWTC (Fact Sheet)
Energy Technology Data Exchange (ETDEWEB)
2015-02-01
Researchers and engineers at the National Wind Technology Center have developed a wide range of computer modeling and simulation tools to support the wind and water power industries with state-of-the-art design and analysis capabilities.
Power System Modeling of 20% Wind-Generated Electricity by 2030: Preprint
Energy Technology Data Exchange (ETDEWEB)
Hand, M.; Blair, N.; Bolinger, M.; Wiser, R.; O' Connell, R.; Hern, T.; Miller, B.
2008-06-01
This paper shows the results of the Wind Energy Deployment System model used to estimate the costs and benefits associated with producing 20% of the nation's electricity from wind technology by 2030.
Model Wind Turbines Tested at Full-Scale Similarity
Miller, M. A.; Kiefer, J.; Westergaard, C.; Hultmark, M.
2016-09-01
The enormous length scales associated with modern wind turbines complicate any efforts to predict their mechanical loads and performance. Both experiments and numerical simulations are constrained by the large Reynolds numbers governing the full- scale aerodynamics. The limited fundamental understanding of Reynolds number effects in combination with the lack of empirical data affects our ability to predict, model, and design improved turbines and wind farms. A new experimental approach is presented, which utilizes a highly pressurized wind tunnel (up to 220 bar). It allows exact matching of the Reynolds numbers (no matter how it is defined), tip speed ratios, and Mach numbers on a geometrically similar, small-scale model. The design of a measurement and instrumentation stack to control the turbine and measure the loads in the pressurized environment is discussed. Results are then presented in the form of power coefficients as a function of Reynolds number and Tip Speed Ratio. Due to gearbox power loss, a preliminary study has also been completed to find the gearbox efficiency and the resulting correction has been applied to the data set.
Radiative striped wind model for gamma-ray bursts
Bégué, D; Lyubarski, Y
2016-01-01
In this paper we revisit the striped wind model in which the wind is accelerated by magnetic reconnection. In our treatment, radiation is included as an independent component, and two scenarios are considered. In the first one, radiation cannot stream efficiently through the reconnection layer, while the second scenario assumes that radiation is homogeneous in the striped wind. We show how these two assumptions affect the dynamics. In particular, we find that the asymptotic radial evolution of the Lorentz factor is not strongly modified whether radiation can stream through the reconnection layer or not. On the other hand, we show that the width, density and temperature of the reconnection layer are strongly dependent on these assumptions. We then apply the model to the gamma-ray burst context and find that photons cannot diffuse efficiently through the reconnection layer below radius $r_{\\rm D}^{\\Delta} \\sim 10^{10.5}$ cm, which is about an order of magnitude below the photospheric radius. Above $r_{\\rm D}^{\\...
Radiative striped wind model for gamma-ray bursts
Bégué, D.; Pe'er, A.; Lyubarsky, Y.
2017-01-01
In this paper we revisit the striped wind model in which the wind is accelerated by magnetic reconnection. In our treatment, radiation is included as an independent component, and two scenarios are considered. In the first one, radiation cannot stream efficiently through the reconnection layer, while the second scenario assumes that radiation is homogeneous in the striped wind. We show how these two assumptions affect the dynamics. In particular, we find that the asymptotic radial evolution of the Lorentz factor is not strongly modified whether radiation can stream through the reconnection layer or not. On the other hand, we show that the width, density and temperature of the reconnection layer are strongly dependent on these assumptions. We then apply the model to the gamma-ray burst context and find that photons cannot diffuse efficiently through the reconnection layer below radius r_D^{Δ } ˜ 10^{10.5} cm, which is about an order of magnitude below the photospheric radius. Above r_D^{Δ }, the dynamics asymptotes to the solution of the scenario in which radiation can stream through the reconnection layer. As a result, the density of the current sheet increases sharply, providing efficient photon production by the Bremsstrahlung process which could have profound influence on the emerging spectrum. This effect might provide a solution to the soft photon problem in GRBs.
Newest insights from MHD numerical modeling of Pulsar Wind Nebulae
Olmi, B.; Del Zanna, L.; Amato, E.; Bucciantini, N.; Bandiera, R.
2016-06-01
Numerical MHD models are considered very successful in accounting for many of the observed properties of Pulsar Wind Nebulae (PWNe), especially those concerning the high energy emission morphology and the inner nebula dynamics. Although PWNe are known to be among the most powerful accelerators in nature, producing particles up to PeV energies, the mechanisms responsible of such an efficient acceleration are still a deep mystery. Indeed, these processes take place in one of the most hostile environment for particle acceleration: the relativistic and highly magnetized termination shock of the pulsar wind. The newest results from numerical simulations of the Crab Nebula, the PWN prototype, will be presented, with special attention to the problem of particle acceleration. In particular it will be shown how a multi-wavelengths analysis of the wisps properties can be used to constrain the particle acceleration mechanisms working at the Crab's termination shock, by identifying the particle acceleration site at the shock front.
Validation and comparison of aerodynamic modelling approaches for wind turbines
Blondel, F.; Boisard, R.; Milekovic, M.; Ferrer, G.; Lienard, C.; Teixeira, D.
2016-09-01
The development of large capacity Floating Offshore Wind Turbines (FOWT) is an interdisciplinary challenge for the design solvers, requiring accurate modelling of both hydrodynamics, elasticity, servodynamics and aerodynamics all together. Floating platforms will induce low-frequency unsteadiness, and for large capacity turbines, the blade induced vibrations will lead to high-frequency unsteadiness. While yawed inflow conditions are still a challenge for commonly used aerodynamic methods such as the Blade Element Momentum method (BEM), the new sources of unsteadiness involved by large turbine scales and floater motions have to be tackled accurately, keeping the computational cost small enough to be compatible with design and certification purposes. In the light of this, this paper will focus on the comparison of three aerodynamic solvers based on BEM and vortex methods, on standard, yawed and unsteady inflow conditions. We will focus here on up-to-date wind tunnel experiments, such as the Unsteady Aerodynamics Experiment (UAE) database and the MexNext international project.
Scale Adaptive Simulation Model for the Darrieus Wind Turbine
Rogowski, K.; Hansen, M. O. L.; Maroński, R.; Lichota, P.
2016-09-01
Accurate prediction of aerodynamic loads for the Darrieus wind turbine using more or less complex aerodynamic models is still a challenge. One of the problems is the small amount of experimental data available to validate the numerical codes. The major objective of the present study is to examine the scale adaptive simulation (SAS) approach for performance analysis of a one-bladed Darrieus wind turbine working at a tip speed ratio of 5 and at a blade Reynolds number of 40 000. The three-dimensional incompressible unsteady Navier-Stokes equations are used. Numerical results of aerodynamic loads and wake velocity profiles behind the rotor are compared with experimental data taken from literature. The level of agreement between CFD and experimental results is reasonable.
Atmospheric stability-dependent infinite wind-farm models and the wake-decay coefficient
DEFF Research Database (Denmark)
Peña, Alfredo; Rathmann, Ole
2014-01-01
We extend the infinite wind-farm boundary-layer (IWFBL) model of Frandsen to take into account atmospheric static stability effects. This extended model is compared with the IWFBL model of Emeis and to the Park wake model used inWind Atlas Analysis and Application Program (WAsP), which is computed...... for an infinite wind farm. The models show similar behavior for the wind-speed reduction when accounting for a number of surface roughness lengths, turbine to turbine separations and wind speeds under neutral conditions. For a wide range of atmospheric stability and surface roughness length values, the extended...... IWFBL model of Frandsen shows a much higher wind-speed reduction dependency on atmospheric stability than on roughness length (roughness has been generally thought to have a major effect on the wind-speed reduction). We further adjust the wake-decay coefficient of the Park wake model for an infinite...
The k-ε-fP model applied to wind farms
DEFF Research Database (Denmark)
Laan, van der, Paul Maarten; Sørensen, Niels N.; Réthoré, Pierre-Elouan;
2015-01-01
The recently developed k-ε-fP eddy-viscosity model is applied to one on-shore and two off-shore wind farms. The results are compared with power measurements and results of the standard k-ε eddy-viscosity model. In addition, the wind direction uncertainty of the measurements is used to correct...... by the turbulence models becomes smaller for wind turbines that are located further downstream. Moreover, the difference between the capability of the turbulence models to estimate the wind farm efficiency reduces with increasing wind farm size and wind turbine spacing. Copyright © 2014 John Wiley & Sons, Ltd....... the model results with a Gaussian filter. The standard k-ε eddy-viscosity model underpredicts the power deficit of the first downstream wind turbines, whereas the k-ε-fP eddy-viscosity model shows a good agreement with the measurements. However, the difference in the power deficit predicted...
Preview Scheduled Model Predictive Control For Horizontal Axis Wind Turbines
Laks, Jason H.
This research investigates the use of model predictive control (MPC) in application to wind turbine operation from start-up to cut-out. The studies conducted are focused on the design of an MPC controller for a 650˜KW, three-bladed horizontal axis turbine that is in operation at the National Renewable Energy Laboratory's National Wind Technology Center outside of Golden, Colorado. This turbine is at the small end of utility scale turbines, but it provides advanced instrumentation and control capabilities, and there is a good probability that the approach developed in simulation for this thesis, will be field tested on the actual turbine. A contribution of this thesis is a method to combine the use of preview measurements with MPC while also providing regulation of turbine speed and cyclic blade loading. A common MPC technique provides integral-like control to achieve offset-free operation. At the same time in wind turbine applications, multiple studies have developed "feed-forward" controls based on applying a gain to an estimate of the wind speed changes obtained from an observer incorporating a disturbance model. These approaches are based on a technique that can be referred to as disturbance accommodating control (DAC). In this thesis, it is shown that offset-free tracking MPC is equivalent to a DAC approach when the disturbance gain is computed to satisfy a regulator equation. Although the MPC literature has recognized that this approach provides "structurally stable" disturbance rejection and tracking, this step is not typically divorced from the MPC computations repeated each sample hit. The DAC formulation is conceptually simpler, and essentially uncouples regulation considerations from MPC related issues. This thesis provides a self contained proof that the DAC formulation (an observer-controller and appropriate disturbance gain) provides structurally stable regulation.
Stochastic Modeling of Turbulence-Driven Systems: Application to Wind Energy
Milan, P.; Waechter, M.; Peinke, J.
2010-11-01
The recent increase in the exploitation of the wind energy resource stresses the need for fundamental research in fluid dynamics. The complex wind inflows that drive wind turbines affect their availability in terms of electric power production, as well as in operation lifetime. Short-scale turbulent effects in the wind such as intermittency, as well as large-scale atmospheric non-stationarity lead to ever-changing power signals fed into the electric grid. This calls for a theoretical classification of wind energy phenomena into complex, turbulence-driven systems. Our raising dependence on wind energy requires a better understanding of these phenomena, as well as reliable models. A stochastic model is proposed as an alternative to standard wind energy models that often neglect turbulent effects or CFD models that cannot decribe large wind turbines yet. This model is based on the stochastic equation of Langevin that can simulate these complex systems after their proper characterization. This stochastic model can be applied separately on both atmospheric wind speed signals as well as wind turbine power production signals, after the wind turbine was characterized properly. The signals generated display the proper statistics and represent fast and flexible models for wind energy applications such as monitoring, availability prediction or grid integration. A future analysis of fatigue loads is also under development.
Lei Wang; Tao Shen; Chen Chen
2014-01-01
The safety and reliability of the wind turbines wholly depend on the completeness and reliability of the control system which is an important problem for the validity of the wind energy conversion systems (WECSs). A method based on multimodel modeling and predictive control is proposed for the optimal operation of direct-drive wind turbine with permanent magnet synchronous generator in this paper. In this strategy, wind turbine with direct-drive permanent magnet synchronous generator is model...
Lei Wang; Tao Shen; Chen Chen
2014-01-01
The safety and reliability of the wind turbines wholly depend on the completeness and reliability of the control system which is an important problem for the validity of the wind energy conversion systems (WECSs). A method based on multimodel modeling and predictive control is proposed for the optimal operation of direct-drive wind turbine with permanent magnet synchronous generator in this paper. In this strategy, wind turbine with direct-drive permanent magnet synchronous generator is model...
Recommendations on Model Fidelity for Wind Turbine Gearbox Simulations: Preprint
Energy Technology Data Exchange (ETDEWEB)
Guo, Y.; Keller, J.; La Cava, W.; Austin, J.; Nejad, A. R.; Halse, C.; Bastard, L.; Helsen, J.
2015-01-01
This work investigates the minimum level of fidelity required to accurately simulate wind turbine gearboxes using state-of-the-art design tools. Excessive model fidelity including drivetrain complexity, gearbox complexity, excitation sources, and imperfections, significantly increases computational time, but may not provide a commensurate increase in the value of the results. Essential design parameters are evaluated, including the planetary load-sharing factor, gear tooth load distribution, and sun orbit motion. Based on the sensitivity study results, recommendations for the minimum model fidelities are provided.
The Kinematics of Quasar Broad Emission Line Regions Using a Disk-Wind Model
Yong, Suk Yee; Webster, Rachel L.; King, Anthea L.; Bate, Nicholas F.; O'Dowd, Matthew J.; Labrie, Kathleen
2017-09-01
The structure and kinematics of the broad line region in quasars are still unknown. One popular model is the disk-wind model that offers a geometric unification of a quasar based on the viewing angle. We construct a simple kinematical disk-wind model with a narrow outflowing wind angle. The model is combined with radiative transfer in the Sobolev, or high velocity, limit. We examine how angle of viewing affects the observed characteristics of the emission line. The line profiles were found to exhibit distinct properties depending on the orientation, wind opening angle, and region of the wind where the emission arises.
Atmospheric Dispersion Model Validation in Low Wind Conditions
Energy Technology Data Exchange (ETDEWEB)
Sawyer, Patrick
2007-11-01
Atmospheric plume dispersion models are used for a variety of purposes including emergency planning and response to hazardous material releases, determining force protection actions in the event of a Weapons of Mass Destruction (WMD) attack and for locating sources of pollution. This study provides a review of previous studies that examine the accuracy of atmospheric plume dispersion models for chemical releases. It considers the principles used to derive air dispersion plume models and looks at three specific models currently in use: Aerial Location of Hazardous Atmospheres (ALOHA), Emergency Prediction Information Code (EPIcode) and Second Order Closure Integrated Puff (SCIPUFF). Results from this study indicate over-prediction bias by the EPIcode and SCIPUFF models and under-prediction bias by the ALOHA model. The experiment parameters were for near field dispersion (less than 100 meters) in low wind speed conditions (less than 2 meters per second).
Atmospheric Dispersion Model Validation in Low Wind Conditions
Energy Technology Data Exchange (ETDEWEB)
Sawyer, Patrick
2007-11-01
Atmospheric plume dispersion models are used for a variety of purposes including emergency planning and response to hazardous material releases, determining force protection actions in the event of a Weapons of Mass Destruction (WMD) attack and for locating sources of pollution. This study provides a review of previous studies that examine the accuracy of atmospheric plume dispersion models for chemical releases. It considers the principles used to derive air dispersion plume models and looks at three specific models currently in use: Aerial Location of Hazardous Atmospheres (ALOHA), Emergency Prediction Information Code (EPIcode) and Second Order Closure Integrated Puff (SCIPUFF). Results from this study indicate over-prediction bias by the EPIcode and SCIPUFF models and under-prediction bias by the ALOHA model. The experiment parameters were for near field dispersion (less than 100 meters) in low wind speed conditions (less than 2 meters per second).
Energy Technology Data Exchange (ETDEWEB)
Jonkman, J.; Larsen, T.; Hansen, A.; Nygaard, T.; Maus, K.; Karimirad, M.; Gao, Z.; Moan, T.; Fylling, I.
2010-04-01
Offshore wind turbines are designed and analyzed using comprehensive simulation codes that account for the coupled dynamics of the wind inflow, aerodynamics, elasticity, and controls of the turbine, along with the incident waves, sea current, hydrodynamics, and foundation dynamics of the support structure. This paper describes the latest findings of the code-to-code verification activities of the Offshore Code Comparison Collaboration, which operates under Subtask 2 of the International Energy Agency Wind Task 23. In the latest phase of the project, participants used an assortment of codes to model the coupled dynamic response of a 5-MW wind turbine installed on a floating spar buoy in 320 m of water. Code predictions were compared from load-case simulations selected to test different model features. The comparisons have resulted in a greater understanding of offshore floating wind turbine dynamics and modeling techniques, and better knowledge of the validity of various approximations. The lessons learned from this exercise have improved the participants' codes, thus improving the standard of offshore wind turbine modeling.
A Chance-Constrained Economic Dispatch Model in Wind-Thermal-Energy Storage System
Directory of Open Access Journals (Sweden)
Yanzhe Hu
2017-03-01
Full Text Available As a type of renewable energy, wind energy is integrated into the power system with more and more penetration levels. It is challenging for the power system operators (PSOs to cope with the uncertainty and variation of the wind power and its forecasts. A chance-constrained economic dispatch (ED model for the wind-thermal-energy storage system (WTESS is developed in this paper. An optimization model with the wind power and the energy storage system (ESS is first established with the consideration of both the economic benefits of the system and less wind curtailments. The original wind power generation is processed by the ESS to obtain the final wind power output generation (FWPG. A Gaussian mixture model (GMM distribution is adopted to characterize the probabilistic and cumulative distribution functions with an analytical expression. Then, a chance-constrained ED model integrated by the wind-energy storage system (W-ESS is developed by considering both the overestimation costs and the underestimation costs of the system and solved by the sequential linear programming method. Numerical simulation results using the wind power data in four wind farms are performed on the developed ED model with the IEEE 30-bus system. It is verified that the developed ED model is effective to integrate the uncertain and variable wind power. The GMM distribution could accurately fit the actual distribution of the final wind power output, and the ESS could help effectively decrease the operation costs.
An analytical canopy-type model for wind farm-atmosphere interaction
Markfort, C. D.; Zhang, W.; Porte-Agel, F.
2013-12-01
We present a new model for the interactions between large-scale wind farms and the atmospheric boundary layer (ABL) based on similarity to canopy flows. Wind farms capture momentum from the atmospheric boundary layer both at the leading edge and from above. Based on our recent findings that turbulent flow in and above wind farms is similar to canopy-type flows, we examine this further with an analytical model that can predict the development length of the wind farm flow as well as vertical momentum absorption. Within the region of flow development, momentum is advected into the wind farm and wake turbulence draws excess momentum in from between turbines. This is characterized by large dispersive fluxes of momentum. Once the flow within the farm is developed, the area-averaged velocity profile exhibits an inflection point, characteristic of canopy-type flows. The inflected velocity profile is associated with the presence of a dominant characteristic turbulence scale, which may be responsible for a significant portion of the vertical momentum flux. Prediction of this scale is useful for determining the amount of available power for harvesting. The new model is tested with results from wind tunnel experiments, which characterize the turbulent flow in and above model wind farms. The model is useful for representing wind farms in meteorological and wind resource assessment models, for optimizing wind turbine spacing and layout, and for assessing the impacts of wind farms on nearby wind resources and the environment.
On the strange quark mass with improved staggered quarks
Hein, J.; Davies, C.; Lepage, G. P.; Mason, Q.; Trottier, H.
2002-01-01
We present results on the sum of the masses of light and strange quark using improved staggered quarks. Our calculation uses 2+1 flavours of dynamical quarks. The effects of the dynamical quarks are clearly visible.
STEADY-STATE MODEL OF SOLAR WIND ELECTRONS REVISITED
Energy Technology Data Exchange (ETDEWEB)
Yoon, Peter H.; Kim, Sunjung; Choe, G. S., E-mail: yoonp@umd.edu [School of Space Research, Kyung Hee University, Yongin, Gyeonggi 446-701 (Korea, Republic of)
2015-10-20
In a recent paper, Kim et al. put forth a steady-state model for the solar wind electrons. The model assumed local equilibrium between the halo electrons, characterized by an intermediate energy range, and the whistler-range fluctuations. The basic wave–particle interaction is assumed to be the cyclotron resonance. Similarly, it was assumed that a dynamical steady state is established between the highly energetic superhalo electrons and high-frequency Langmuir fluctuations. Comparisons with the measured solar wind electron velocity distribution function (VDF) during quiet times were also made, and reasonable agreements were obtained. In such a model, however, only the steady-state solution for the Fokker–Planck type of electron particle kinetic equation was considered. The present paper complements the previous analysis by considering both the steady-state particle and wave kinetic equations. It is shown that the model halo and superhalo electron VDFs, as well as the assumed wave intensity spectra for the whistler and Langmuir fluctuations, approximately satisfy the quasi-linear wave kinetic equations in an approximate sense, thus further validating the local equilibrium model constructed in the paper by Kim et al.
Modelling wind turbine wakes using the turbulent entrainment hypothesis
Luzzatto-Fegiz, Paolo
2015-11-01
Simple models for turbine wakes have been used extensively in the wind energy community, both as independent tools, as well as to complement more refined and computationally-intensive techniques. Jensen (1983; see also Katić et al. 1986) developed a model assuming that the wake radius grows linearly with distance x, approximating the velocity deficit with a top-hat profile. While this model has been widely implemented in the wind energy community, recently Bastankhah & Porté-Agel (2014) showed that it does not conserve momentum. They proposed a momentum-conserving theory, which assumed a Gaussian velocity deficit and retained the linear-spreading assumption, significantly improving agreement with experiments and LES. While the linear spreading assumption facilitates conceptual modeling, it requires empirical estimates of the spreading rate, and does not readily enable generalizations to other turbine designs. Furthermore, field measurements show sub-linear wake growth with x in the far-wake, consistently with results from fundamental turbulence studies. We develop a model by relying on a simple and general turbulence parameterization, namely the entrainment hypothesis, which has been used extensively in other areas of geophysical fluid dynamics. Without assuming similarity, we derive an analytical solution for a circular turbine wake, which predicts a far-wake radius increasing with x 1 / 3, and is consistent with field measurements and fundamental turbulence studies. Finally, we discuss developments accounting for effects of stratification, as well as generalizations to other turbine designs.
Directory of Open Access Journals (Sweden)
Evans Samuel P.
2017-01-01
Full Text Available This paper investigates the applicability of the assumed wind fields in International Electrotechnical Commission (IEC standard 61400 Part 2, the design standard for small wind turbines, for a turbine operating in the built environment, and the effects these wind fields have on the predicted performance of a 5 kW Aerogenesis turbine using detailed aeroelastic models developed in Fatigue Aerodynamics Structures and Turbulence (FAST. Detailed wind measurements were acquired at two built environment sites: from the rooftop of a Bunnings Ltd. warehouse at Port Kennedy (PK (Perth, Australia and from the small wind turbine site at the University of Newcastle at Callaghan (Newcastle, Australia. For both sites, IEC 61400-2 underestimates the turbulence intensity for the majority of the measured wind speeds. A detailed aeroelastic model was built in FAST using the assumed wind field from IEC 61400-2 and the measured wind fields from PK and Callaghan as an input to predict key turbine performance parameters. The results of this analysis show a modest increase in the predicted mean power for the higher turbulence regimes of PK and Callaghan as well as higher variation in output power. Predicted mean rotor thrust and blade flapwise loading showed a minor increase due to higher turbulence, with mean predicted torque almost identical but with increased variations due to higher turbulence. Damage equivalent loading for the blade flapwise moment was predicted to be 58% and 11% higher for a turbine operating at Callaghan and PK respectively, when compared with IEC 61400-2 wind field. Time series plots for blade flapwise moments and power spectral density plots in the frequency domain show consistently higher blade flapwise bending moments for the Callaghan site with both the sites showing a once-per-revolution response.
Multivariate Modelling of Extreme Load Combinations for Wind Turbines
DEFF Research Database (Denmark)
Dimitrov, Nikolay Krasimirov
2015-01-01
We demonstrate a model for estimating the joint probability distribution of two load components acting on a wind turbine blade cross section. The model addresses the problem of modelling the probability distribution of load time histories with large periodic components by dividing the signal...... into a periodic part and a perturbation term, where each part has a known probability distribution. The proposed model shows good agreement with simulated data under stationary conditions, and a design load envelope based on this model is comparable to the load envelope estimated using the standard procedure...... for determining contemporaneous loads. By defining a joint probability distribution and full return-period contours for multiple load components, the suggested procedure gives the possibility for determining the most critical loading direction in a blade cross section, or for carrying out reliability analysis...
Filament winding cylinders. II - Validation of the process model
Calius, Emilio P.; Lee, Soo-Yong; Springer, George S.
1990-01-01
Analytical and experimental studies were performed to validate the model developed by Lee and Springer for simulating the manufacturing process of filament wound composite cylinders. First, results calculated by the Lee-Springer model were compared to results of the Calius-Springer thin cylinder model. Second, temperatures and strains calculated by the Lee-Springer model were compared to data. The data used in these comparisons were generated during the course of this investigation with cylinders made of Hercules IM-6G/HBRF-55 and Fiberite T-300/976 graphite-epoxy tows. Good agreement was found between the calculated and measured stresses and strains, indicating that the model is a useful representation of the winding and curing processes.
Visualization of Wind Data on Google Earth for the Three-dimensional Wind Field (3DWF) Model
2012-09-01
AND ADDRESS(ES) U.S. Army Research Laboratory ATTN: RDRL- CIE -D 2800 Powder Mill Road Adelphi, MD 20783-1197 8. PERFORMING ORGANIZATION...terrain, while the color contours in the lower right corner indicate strong wind speeds above a deep canyon...handled in a similar fashion. Finally, a color fill can be assigned to the polygon, which is related to the magnitude and/or direction of a modeled wind
Winds on the West Florida Shelf: Regional comparisons between observations and model estimates
Mayer, Dennis A.; Weisberg, Robert H.; Zheng, Lianyuan; Liu, Yonggang
2017-02-01
Wind fields on the West Florida Continental Shelf are investigated using observations from five University of South Florida Coastal Ocean Monitoring and Prediction System buoys and seven of NOAA's National Ocean Service and National Weather Service, National Data Buoy Center stations or buoys spanning the 10 year period, 2004-2013. These observations are compared with NOAA's National Center for Environmental Prediction (NCEP) reanalysis wind fields (NCEP winds). The analyses consist of vector correlations in both the time and frequency domains. The primary findings are that winds observed on and near the coastline underestimate those observed offshore and that NCEP winds derived from assimilating mostly land-based observations also underestimate winds observed offshore. With regard to wind stress, and depending upon location, wind stress derived from NCEP winds are 6%-49% lower than what is computed from observations over open water. A corollary is that wind forcing fields that are underestimated may result in coastal ocean model circulation fields that are also underestimated. These analyses stress the importance of having offshore wind observations, and suggest that adding more offshore wind observations will lead to improved coastal ocean wind fields and hence to improved model renditions of coastal ocean model circulation and related water property fields.
Dynamic wind turbine models in power system simulation tool DIgSILENT
DEFF Research Database (Denmark)
Hansen, A.D.; Jauch, C.; Sørensen, Poul Ejnar
2004-01-01
The present report describes the dynamic wind turbine models implemented in the power system simulation tool DIgSILENT (Version 12.0). The developed models are a part of the results of a national research project, whose overall objective is to create amodel database in different simulation tools....... The report contains both the description of DIgSILENT built-in models for the electrical components of a grid connected wind turbine (e.g. inductiongenerators, power converters, transformers) and the models developed by the user, in the dynamic simulation language DSL of DIgSILENT, for the non......-electrical components of the wind turbine (wind model, aerodynamic model, mechanical model). Theinitialisation issues on the wind turbine models into the power system simulation are also presented. However, the main attention in this report is drawn to the modelling at the system level of two wind turbine concepts: 1...
ARIMA-Based Time Series Model of Stochastic Wind Power Generation
DEFF Research Database (Denmark)
Chen, Peiyuan; Pedersen, Troels; Bak-Jensen, Birgitte
2010-01-01
This paper proposes a stochastic wind power model based on an autoregressive integrated moving average (ARIMA) process. The model takes into account the nonstationarity and physical limits of stochastic wind power generation. The model is constructed based on wind power measurement of one year from...... the Nysted offshore wind farm in Denmark. The proposed limited-ARIMA (LARIMA) model introduces a limiter and characterizes the stochastic wind power generation by mean level, temporal correlation and driving noise. The model is validated against the measurement in terms of temporal correlation...... and probability distribution. The LARIMA model outperforms a first-order transition matrix based discrete Markov model in terms of temporal correlation, probability distribution and model parameter number. The proposed LARIMA model is further extended to include the monthly variation of the stochastic wind power...
DEFF Research Database (Denmark)
Kocewiak, Lukasz Hubert; Hjerrild, Jesper; Bak, Claus Leth
2009-01-01
The offshore wind farm with installed back-to-back power converter in wind turbines is studied. As an example the Burbo Bank offshore wind farm with Siemens Wind Power wind turbines is taken into consideration. The wind farm is simulated in DIgSILENT Power Factory software in order to determine...... results are compared with measurement data from the Burbo Bank offshore wind farm. The delimitations of both power converter models with referent to harmonic analysis are shown in this paper....
Kocewiak, Lukasz Hubert; Hjerrild, Jesper; Bak, Claus Leth
2009-01-01
The offshore wind farm with installed back-to-back power converter in wind turbines is studied. As an example the Burbo Bank offshore wind farm with Siemens Wind Power wind turbines is taken into consideration. The wind farm is simulated in DIgSILENT Power Factory software in order to determine and assess harmonic emission in the point of common coupling. Different modelling methods of power electronic devices installed in wind turbines are presented. Harmonic load flow analysis and impedance...
DEFF Research Database (Denmark)
Christiansen, Søren; Tabatabaeipour, Seyed Mojtaba; Bak, Thomas;
2013-01-01
Floating wind turbines are considered as a new and promising solution for reaching higher wind resources beyond the water depth restriction of monopile wind turbines. But on a floating structure, the wave-induced loads significantly increase the oscillations of the structure. Furthermore, using...... a controller designed for an onshore wind turbine yields instability in the fore-aft rotation. In this paper, we propose a general framework, where a reference model models the desired closed-loop behavior of the system. Model predictive control combined with a state estimator finds the optimal rotor blade...... compared to a baseline floating wind turbine controller at the cost of more pitch action....
Implications of solar wind measurements for solar models and composition
Serenelli, Aldo; Villante, Francesco L; Vincent, Aaron C; Asplund, Martin; Basu, Sarbani; Grevesse, Nicolas; Pena-Garay, Carlos
2016-01-01
We critically examine recent claims of a high solar metallicity by von Steiger \\& Zurbuchen (2016; vSZ16) based on in situ measurements of the solar wind, rather than the standard spectroscopically-inferred abundances (Asplund et al. 2009). We test the claim by Vagnozzi et al. (2016) that a composition based on the solar wind enables one to construct a standard solar model in agreement with helioseismological observations and thus solve the decades-old solar modelling problem. We show that, although some helioseismological observables are improved compared to models computed with established abundances, most are in fact worse. The high abundance of refractory elements leads to an overproduction of neutrinos, with a predicted $^8$B flux that is nearly twice its observed value, and $^7$Be and CNO fluxes that are experimentally ruled out at high confidence. A combined likelihood analysis shows that models using the vSZ16 abundances fare much worse than AGSS09 despite a higher metallicity. We also present ast...
Investigation and Improvement of the Staggered Labyrinth Seal
Institute of Scientific and Technical Information of China (English)
LIN Zhirong; WANG Xudong; YUAN Xin; SHIBUKAWANaoki; NOGUCHI Taro
2015-01-01
Recent studies on staggered labyrinth seals have focused on the effects of different parameters, such as the pressure ratio and rotational speed on the leakage flow rate. However, few investigations pay sufficient attention to flow details and the sealing mechanism, which would be of practical importance in designing seals having higher performance. This paper establishes a theoretical model to study the seal mechanism, thus revealing that leakage is determined by the pressure ratio and geometric structure. Numerical simulation is implemented to illustrate details of the flow field within the seal structure. Viscous dissipation is used to quantitatively investigate the contribution that each location makes to the seal performance, revealing that orifices and stagnation points are the most important positions in the seal structure, generating the most dissipation. The orifice is carefully studied by using the theoretical model. Experiments for different pressure ratios are conducted and the results match well with those of the theoretical model and numerical simulation, verifying the theoretical model and analysis of the seal mechanism. Three new designs, based on a good understanding of the seal mechanism, are presented, with one reducing leakage by 24.5%.
Modelling and control of variable speed wind turbines for power system studies
DEFF Research Database (Denmark)
Michalke, Gabriele; Hansen, Anca Daniela
2010-01-01
Modern wind turbines are predominantly variable speed wind turbines with power electronic interface. Emphasis in this paper is therefore on the modelling and control issues of these wind turbine concepts and especially on their impact on the power system. The models and control are developed...... and implemented in the power system simulation tool DIgSILENT. Important issues like the fault ride-through and grid support capabilities of these wind turbine concepts are addressed. The paper reveals that advanced control of variable speed wind turbines can improve power system stability. Finally......, it will be shown in the paper that wind parks consisting of variable speed wind turbines can help nearby connected fixed speed wind turbines to ride-through grid faults. Copyright © 2009 John Wiley & Sons, Ltd....
Ensemble downscaling in coupled solar wind-magnetosphere modeling for space weather forecasting.
Owens, M J; Horbury, T S; Wicks, R T; McGregor, S L; Savani, N P; Xiong, M
2014-06-01
Advanced forecasting of space weather requires simulation of the whole Sun-to-Earth system, which necessitates driving magnetospheric models with the outputs from solar wind models. This presents a fundamental difficulty, as the magnetosphere is sensitive to both large-scale solar wind structures, which can be captured by solar wind models, and small-scale solar wind "noise," which is far below typical solar wind model resolution and results primarily from stochastic processes. Following similar approaches in terrestrial climate modeling, we propose statistical "downscaling" of solar wind model results prior to their use as input to a magnetospheric model. As magnetospheric response can be highly nonlinear, this is preferable to downscaling the results of magnetospheric modeling. To demonstrate the benefit of this approach, we first approximate solar wind model output by smoothing solar wind observations with an 8 h filter, then add small-scale structure back in through the addition of random noise with the observed spectral characteristics. Here we use a very simple parameterization of noise based upon the observed probability distribution functions of solar wind parameters, but more sophisticated methods will be developed in the future. An ensemble of results from the simple downscaling scheme are tested using a model-independent method and shown to add value to the magnetospheric forecast, both improving the best estimate and quantifying the uncertainty. We suggest a number of features desirable in an operational solar wind downscaling scheme.
Documentation, User Support, and Verification of Wind Turbine and Plant Models
Energy Technology Data Exchange (ETDEWEB)
Robert Zavadil; Vadim Zheglov; Yuriy Kazachkov; Bo Gong; Juan Sanchez; Jun Li
2012-09-18
As part of the Utility Wind Energy Integration Group (UWIG) and EnerNex's Wind Turbine Modeling Project, EnerNex has received ARRA (federal stimulus) funding through the Department of Energy (DOE) to further the progress of wind turbine and wind plant models. Despite the large existing and planned wind generation deployment, industry-standard models for wind generation have not been formally adopted. Models commonly provided for interconnection studies are not adequate for use in general transmission planning studies, where public, non-proprietary, documented and validated models are needed. NERC MOD (North American Electric Reliability Corporation) reliability standards require that power flow and dynamics models be provided, in accordance with regional requirements and procedures. The goal of this project is to accelerate the appropriate use of generic wind turbine models for transmission network analysis by: (1) Defining proposed enhancements to the generic wind turbine model structures that would allow representation of more advanced; (2) Comparative testing of the generic models against more detailed (and sometimes proprietary) versions developed by turbine vendors; (3) Developing recommended parameters for the generic models to best mimic the performance of specific commercial wind turbines; (4) Documenting results of the comparative simulations in an application guide for users; (5) Conducting technology transfer activities in regional workshops for dissemination of knowledge and information gained, and to engage electric power and wind industry personnel in the project while underway; (6) Designing of a "living" homepage to establish an online resource for transmission planners.
An Experimental Investigation of FNN Model for Wind Speed Forecasting Using EEMD and CS
Directory of Open Access Journals (Sweden)
Jianzhou Wang
2015-01-01
Full Text Available With depletion of traditional energy and increasing environmental problems, wind energy, as an alternative renewable energy, has drawn more and more attention internationally. Meanwhile, wind is plentiful, clean, and environmentally friendly; moreover, its speed is a very important piece of information needed in the operations and planning of the wind power system. Therefore, choosing an effective forecasting model with good performance plays a quite significant role in wind power system. A hybrid CS-EEMD-FNN model is firstly proposed in this paper for multistep ahead prediction of wind speed, in which EEMD is employed as a data-cleaning method that aims to remove the high frequency noise embedded in the wind speed series. CS optimization algorithm is used to select the best parameters in the FNN model. In order to evaluate the effectiveness and performance of the proposed hybrid model, three other short-term wind speed forecasting models, namely, FNN model, EEMD-FNN model, and CS-FNN model, are carried out to forecast wind speed using data measured at a typical site in Shandong wind farm, China, over three seasons in 2011. Experimental results demonstrate that the developed hybrid CS-EEMD-FNN model outperforms other models with more accuracy, which is suitable to wind speed forecasting in this area.
Dynamic Modeling of Wind Turbine Gearboxes and Experimental Validation
DEFF Research Database (Denmark)
Pedersen, Rune
is presented. The model takes into account the effects of load and applied grinding corrections. The results are verified by comparing to simulated and experimental results reported in the existing literature. Using gear data loosely based on a 1 MW wind turbine gearbox, the gear mesh stiffness is expanded...... analysis in relation to gear dynamics. A multibody model of two complete 2.3MWwind turbine gearboxes mounted back-to-back in a test rig is built. The mean values of the proposed gear mesh stiffnesses are included. The model is validated by comparing with calculated and measured eigenfrequencies and mode...... shapes. The measured eigenfrequencies have been identified in accelerometer signals obtained during run-up tests. Since the calculated eigenfrequencies do not match the measured eigenfrequencies with sufficient accuracy, a model updating technique is applied to ensure a better match by adjusting...
Comparing mixing-length models of the diabatic wind profile over homogeneous terrain
DEFF Research Database (Denmark)
Pena Diaz, Alfredo; Gryning, Sven-Erik; Hasager, Charlotte Bay
2010-01-01
Models of the diabatic wind profile over homogeneous terrain for the entire atmospheric boundary layer are developed using mixing-length theory and are compared to wind speed observations up to 300 m at the National Test Station for Wind Turbines at Høvsøre, Denmark. The measurements are performed...
Design and Study of a Low-Cost Laboratory Model Digital Wind Power Meter
Radhakrishnan, Rugmini; Karthika, S.
2010-01-01
A vane-type low-cost laboratory model anemometer cum power meter is designed and constructed for measuring low wind energy created from accelerating fluids. The constructed anemometer is a device which records the electrical power obtained by the conversion of wind power using a wind sensor coupled to a DC motor. It is designed for its…
Investigation of a Hybrid Winding Concept for Toroidal Inductors using 3D Finite Element Modeling
DEFF Research Database (Denmark)
Schneider, Henrik; Andersen, Thomas; Mønster, Jakob Døllner;
2013-01-01
This paper investigates a hybrid winding concept for a toroidal inductor by simulating the winding resistance as a function of frequency. The problem of predicting the resistance of a non-uniform and complex winding shape is solved using 3D Finite Element Modeling. A prototype is built and tested...
Review of dWindDS Model Initial Results; NREL (National Renewable Energy Laboratory)
Energy Technology Data Exchange (ETDEWEB)
Baring-Gould, Ian; Gleason, Michael; Preus, Robert; Sigrin, Ben
2015-06-17
The dWindDS model analyses the market diffusion of distributed wind generation for behind the meter applications. It is consumer decision based and uses a variety of data sets including a high resolution wind data set. It projects market development through 2050 based on input on specified by the user. This presentation covers some initial runs with draft base case assumptions.
Model Validation at the 204 MW New Mexico Wind Energy Center: Preprint
Energy Technology Data Exchange (ETDEWEB)
Muljadi, E.; Butterfield, C. P.; Ellis, A.; Mechenbier, J.; Hochheimer, J.; Young, R.; Miller, N.; Delmerico, R.; Zavadil, R.; Smith, J. C.
2006-06-01
In this paper, we describe methods to derive and validate equivalent models for a large wind farm. FPL Energy's 204-MW New Mexico Wind Energy Center, which is interconnected to the Public Service Company of New Mexico (PNM) transmission system, was used as a case study. The methods described are applicable to any large wind power plant.
Design and Study of a Low-Cost Laboratory Model Digital Wind Power Meter
Radhakrishnan, Rugmini; Karthika, S.
2010-01-01
A vane-type low-cost laboratory model anemometer cum power meter is designed and constructed for measuring low wind energy created from accelerating fluids. The constructed anemometer is a device which records the electrical power obtained by the conversion of wind power using a wind sensor coupled to a DC motor. It is designed for its…
Digital Control System For Wind-Tunnel Model
Hoadley, Sherwood T.; Mcgraw, Sandra
1995-01-01
Multiple functions performed by multiple coordinated processors for real-time control. Multiple input, multiple-output, multiple-function digital control system developed for wind-tunnel model of advanced fighter airplane with actively controlled flexible wings. Digital control system provides flexibility in selection of control laws, sensors, and actuators, plus some redundancy to accommodate failures in some of its subsystems. Implements feedback control scheme providing simultaneously for suppression of flutter, control of roll angle, roll-rate tracking during maximized roll maneuvers, and alleviation of loads during roll maneuvers.
A neural network based wake model for small wind turbine siting near obstacles
Brunskill, Andrew William
Many potential small wind turbine locations are near obstacles such as buildings and shelterbelts, which can have a significant, detrimental effect on the local wind climate. This thesis describes the creation of a new model which can predict the wind speed, turbulence intensity, and wind power density at any point in an obstacle's region of influence, relative to unsheltered conditions. Artificial neural networks were used to learn the relationship between an obstacle's characteristics and its effects on the local wind. The neural network was trained using measurements collected in the wakes of scale models exposed to a simulated atmospheric boundary layer in a wind tunnel. A field experiment was conducted to validate the wind tunnel measurements. Model predictions are most accurate in the far wake region. The estimated mean uncertainties associated with model predictions of velocity deficit, power density deficit, and turbulence intensity excess are 5.0%, 15%, and 12.8%, respectively.
Modular structure of wind turbine models in IEC 61400-27-1
DEFF Research Database (Denmark)
Sørensen, Poul Ejnar; Andresen, Bjørn; Fortmann, Jens;
2013-01-01
This paper presents the modular structure of wind turbine models to be published in a new standard IEC 61400-27 for “Electrical simulation models for wind power generation”. The purpose of this standardization work is to define generic simulation models for wind turbines (Part 1) and wind power...... plants (Part 2), which are intended for short-term power system stability analyses. Part 1 has passed the first committee draft stage, whereas Part 2 is in an early stage of development. Initially, the paper describes the interfaces between wind turbine, wind power plant and grid models, and then gives...... a more detailed description of the modular structure of the types of wind turbines that are included in Part 1....
A Statistical Model for the Prediction of Wind-Speed Probabilities in the Atmospheric Surface Layer
Efthimiou, G. C.; Hertwig, D.; Andronopoulos, S.; Bartzis, J. G.; Coceal, O.
2016-11-01
Wind fields in the atmospheric surface layer (ASL) are highly three-dimensional and characterized by strong spatial and temporal variability. For various applications such as wind-comfort assessments and structural design, an understanding of potentially hazardous wind extremes is important. Statistical models are designed to facilitate conclusions about the occurrence probability of wind speeds based on the knowledge of low-order flow statistics. Being particularly interested in the upper tail regions we show that the statistical behaviour of near-surface wind speeds is adequately represented by the Beta distribution. By using the properties of the Beta probability density function in combination with a model for estimating extreme values based on readily available turbulence statistics, it is demonstrated that this novel modelling approach reliably predicts the upper margins of encountered wind speeds. The model's basic parameter is derived from three substantially different calibrating datasets of flow in the ASL originating from boundary-layer wind-tunnel measurements and direct numerical simulation. Evaluating the model based on independent field observations of near-surface wind speeds shows a high level of agreement between the statistically modelled horizontal wind speeds and measurements. The results show that, based on knowledge of only a few simple flow statistics (mean wind speed, wind-speed fluctuations and integral time scales), the occurrence probability of velocity magnitudes at arbitrary flow locations in the ASL can be estimated with a high degree of confidence.
DEFF Research Database (Denmark)
Pena Diaz, Alfredo; Réthoré, Pierre-Elouan; Rathmann, Ole
2014-01-01
We evaluate a modified version of the Park wake model against power data from a west-east row in the middle of the Horns Rev I offshore wind farm. The evaluation is performed on data classified in four different atmospheric stability conditions, for a narrow wind speed range, and a wide range of ...... are different. The ensemble average of the simulations does not approach the limits of the infinite wind farm under any stability condition as such averages account for directions misaligned with the row....