WorldWideScience

Sample records for active stall wind

  1. Variable frequency operation of active stall wind farms using a dc connection to grid

    Iov, Florin; Blaabjerg, Frede; Sorensen, Poul;

    2005-01-01

    wind turbines/farms are clearly the variable speed operation and a grid connection through a power electronic interface, especially using doubly-fed induction generators. Using power electronics the control capabilities of these wind turbines/farms are extended and thus the grid requirements are...... active stall wind farms to the grid can provide these features and also maximize the produced power especially at low wind speeds by using variable voltage/frequency for the wind farm. The focus in this paper is in studying the variable speed operation for the active stall wind farms using a voltage...

  2. Modeling and Control of VSC Based DC Connection for Active Stall Wind Farms to Grid

    Iov, Florin; Sørensen, Poul; Hansen, Anca Daniela; Blaabjerg, Frede

    Currently, there is an increasing trend to connect large MW wind farms to the transmission system. Therefore the power system becomes more vulnerable and dependent on the wind energy production. At the same time requirements that focus on the influence of the farms on the grid stability and power quality, and on the control capabilities of wind farms have already been established. The main trends of modern wind turbines/farms are clearly the variable speed operation and a grid connection through a power electronic interface, especially using doubly-fed induction generators. Using power electronics the control capabilities of these wind turbines/farms are extended and thus the grid requirements are fulfilled. However, the traditional squirrel-cage generators based wind turbines/wind farms directly connected to the grid does not have such control capabilities. They produce maximum possible power in continuous operation and are becoming disconnected in the case of a grid fault. Moreover, these wind turbines/farms cannot regulate their production and contribute to power system stability. A DC transmission system for connection of the active stall wind farms to the grid can be a solution to these problems. Such a system has special regulating properties e.g. decoupled control of active and reactive power, continuous AC voltage regulation, variable frequency control, black-start capability, etc. This paper focuses on the modeling of such systems and proposes a control method of a voltage source converter based DC transmission system for connecting active stall wind farms to the grid.

  3. Modelling and Control of VSC based DC Connection for Active Stall Wind Farms to Grid

    Iov, Florin; Sørensen, Poul; Hansen, Anca Daniela;

    2006-01-01

    Currently, there is an increasing trend to connect large MW wind farms to the transmission system. Therefore the power system becomes more vulnerable and dependent on the wind energy production. At the same time requirements that focus on the influence of the farms on the grid stability and power...... quality, and on the control capabilities of wind farms have already been established. The main trends of modern wind turbines/farms are clearly the variable speed operation and a grid connection through a power electronic interface, especially using doubly-fed induction generators. Using power electronics...... in continuous operation and are becoming disconnected in the case of a grid fault. Moreover, these wind turbines/farms cannot regulate their production and contribute to power system stability. A DC transmission system for connection of the active stall wind farms to the grid can be a solution to...

  4. Modeling and Control of VSC based DC Connection for Active Stall Wind Farms to Grid

    Iov, Florin; Sorensen, Poul; Hansen, Anca-Daniela;

    2005-01-01

    Currently, there is an increasing trend to connect large MW wind farms to the transmission system. Therefore the power system becomes more vulnerable and dependent on the wind energy production. At the same time requirements that focus on the influence of the farms on the grid stability and power...... quality, and on the control capabilities of wind farms have already been established. The main trends of modem wind turbines/farms are clearly the variable speed operation and a grid connection through a power electronic interface, especially using doubly-fed induction generators. Using power electronics...... in continuous operation and are becoming disconnected in the case of a grid fault. Moreover, these wind turbines/farms cannot regulate their production and contribute to power system stability. A DC transmission system for connection of the active stall wind farms to the grid can be a solution to...

  5. Active stall control for large offshore horizontal axis wind turbines: a conceptual study considering different actuation methods

    Pereira, R.; Van Bussel, G.J.W.; Timmer, W.A.

    2014-01-01

    The increasing size of Horizontal Axis Wind Turbines and the trend to install wind farms further offshore demand more robust design options. If the pitch system could be eliminated, the availability of Horizontal Axis Wind Turbines should increase. This research investigates the use of active stall

  6. Active stall control for large offshore horizontal axis wind turbines; a conceptual study considering different actuation methods

    The increasing size of Horizontal Axis Wind Turbines and the trend to install wind farms further offshore demand more robust design options. If the pitch system could be eliminated, the availability of Horizontal Axis Wind Turbines should increase. This research investigates the use of active stall control to regulate power production in replacement of the pitch system. A feasibility study is conducted using a blade element momentum code and taking the National Renewable Energy Laboratory 5 MW turbine as baseline case. Considering half of the blade span is equipped with actuators, the required change in the lift coefficient to regulate power was estimated in ΔCl = 0.7. Three actuation technologies are investigated, namely Boundary Layer Transpiration, Trailing Edge Jets and Dielectric Barrier Discharge actuators. Results indicate the authority of the actuators considered is not sufficient to regulate power, since the change in the lift coefficient is not large enough. Active stall control of Horizontal Axis Wind Turbines appears feasible only if the rotor is re-designed from the start to incorporate active-stall devices

  7. Load prediction of stall regulated wind turbines

    Bjoerck, A.; Dahlberg, J.Aa. [Aeronautical Research Inst. of Sweden, Bromma (Sweden); Carlen, I. [Chalmers Univ. of Technology, Goeteborg (Sweden). Div. of Marine Structural Engineering; Ganander, H. [Teknikgruppen AB, Sollentua (Sweden)

    1996-12-01

    Measurements of blade loads on a turbine situated in a small wind farm shows that the highest blade loads occur during operation close to the peak power i.e. when the turbine operates in the stall region. In this study the extensive experimental data base has been utilised to compare loads in selected campaigns with corresponding load predictions. The predictions are based on time domain simulations of the wind turbine structure, performed by the aeroelastic code VIDYN. In the calculations a model were adopted in order to include the effects of dynamic stall. This paper describes the work carried out so far within the project and key results. 5 refs, 10 figs

  8. Grid connection of active stall wind farms using a VSC based DC transmission system

    Iov, Florin; Sorensen, Paul; Hansen, Anca-Daniela;

    2005-01-01

    Currently, there is an increasing trend to connect large MW wind farms to the transmission system. Requirements that focus on the influence of the farms on the grid stability and power quality, and on the control capabilities of wind farms have already been established. The main trends of modern...... wind turbines/farms are clearly the variable speed operation and a grid connection through a power electronic interface, especially using doubly fed induction generators. Using power electronics the control capabilities of these wind turbines/farms are extended and thus the grid requirements are...... fulfilled. However, the traditional squirrel-cage generators based wind turbines/wind farms directly connected to the grid have less control capabilities. These wind turbines/farms cannot regulate their production and contribute to power system stability. A DC transmission system for connection of the...

  9. Control of dynamic stall phenomenon for vertical axis wind turbine

    Frunzulicǎ, Florin; Dumitrescu, Horia; Dumitrache, Alexandru; Suatean, Bogdan

    2013-10-01

    In the last years the wind turbine with vertical axis (VAWT) began to be more attractive due benefits in exploitation, the power range covering usually the domain 2 kW-20 kW. But, VAWTs suffer from many complicated aerodynamically problems, of which dynamic stall is an inherent phenomenon when they are operating at low values of tip speed ratio (TSR VAWTs. For this reason, in the present work we perform a computational investigation of a two-dimensional dynamic stall phenomenon around a NACA0012 airfoil in oscillating motion at relative low Reynolds number (˜105). The unsteady flow is investigated numerically using RANS approach with two turbulence models (k-ω SST and transition SST). The same analysis was performed to evaluate three flow control methods: two passive and one active.

  10. Numerical and experimental investigation of low Reynolds number wind turbine airfoils under stall and post-stall conditions

    Daniele, Elia

    2013-01-01

    This work concerns a numerical and experimental investigation of low Reynolds number wind turbine airfoils under stall and post-stall conditions. A verification of high angle of attack semi empirical models, namely Viterna-Corrigan and Aerodas from Spera, is needed to assess the input data reliability for Blade Element Momentum (BEM) based Vertical Axis Wind Turbine (VAWT) performance code and also the performance predictions for Horizontal Axis Wind Turbine (HAWT) where passive stall con...

  11. Dynamic stall of an experimental wind turbine blade

    Melius, Matthew; Cal, Raúl Bayoán; Mulleners, Karen

    2016-03-01

    To understand the complex flow phenomena over wind turbine blades during stall development, a scaled three-dimensional non-rotating blade model is designed to be dynamically similar to a rotating full-scale NREL 5 MW wind turbine blade. A time-resolved particle image velocimetry (PIV) investigation of flow behavior during the stall cycle examines the processes of stall development and flow reattachment. Proper orthogonal decomposition (POD) and vortex detection techniques are applied to the PIV fields to quantify relevant flow characteristics such as vortex size, separation angle, and separation point throughout a dynamic pitching cycle. The behavior of the POD coefficients provides time scales for the transitional stages which are quantified and compared, revealing that transition from attached flow to full stall is delayed to higher angles of attack and occurs at a higher rate than the transition from full stall to attached flow. The instantaneous flow fields are then reconstructed using the first four POD modes to demonstrate their prominent roles throughout the stall cycle and their ability to capture the general separation behavior over the blade surface.

  12. Effect of oscillation frequency on wind turbine airfoil dynamic stall

    At the same oscillation amplitude, Reynolds Number, mean angle of attack, the dynamic stall characteristics of the NREL S809 airfoil undergoing sinusoidal pitch oscillations of different oscillation frequencies were investigated with modified k-ω SST turbulence model of CFD solution for two-dimensional numerical simulation. The predicted lift, drag coefficients and moment coefficients were compared with the Ohio State University wind tunnel test results, which showed a good agreement. The birth, development and breaking off of eddies were analyzed through streamline distribution around airfoil and the influence of oscillation frequencies on dynamic stall characteristics was also described and analyzed in detail, which enrich the database of dynamic stall characteristics needed by the quantization of oscillation frequencies on dynamic characteristics and prove that sliding mesh method is reliable when dealing with dynamic stall problems

  13. Dynamic stall model for wind turbine airfoils

    Larsen, J.W.; Nielsen, S.R.K.; Krenk, Steen

    2007-01-01

    function of the angle of attack. The static lift is described by two parameters, the lift at fully attached flow and the degree of attachment. A relationship between these parameters and the static lift is available from a thin plate approximation. Assuming the parameters to be known during static...... first-order filter. The latter is likely to occur during active pitch control of vibrations. It is shown that all included effects can be important when considering wind turbine blades. The proposed model is validated against test data from two load cases, one at fully attached flow conditions and one...

  14. Preliminary analysis of dynamic stall effects on a 91-meter wind turbine rotor

    Wilson, Robert E.

    1995-01-01

    Analytical investigation of dynamic stall on HAWT (horizontal-axis wind turbines) rotor loads was conducted. Dynamic stall was modeled using the Gormont approach on the MOD-2 rotor, treating the blade as a rigid body teetering about a fixed axis. Blade flapwise bending moments at station 370 were determined with and without dynamic stall for spatial variations in local wind speed due to wind shear and yaw. The predicted mean flapwise bending moments were found to be in good agreement with test results. Results obtained with and without dynamic stall showed no significant difference for the mean flapwise bending moment. The cyclic bending moments calculated with and without dynamic stall effects were substantially the same. None of the calculated cyclic loads reached the level of the cyclic loads measured on the MOD-2 using the Boeing five-minute-average technique.

  15. Initial design of a stall-controlled wind turbine rotor

    Nygaard, T.A. [Inst. for Energiteknikk, Kjeller (Norway)

    1997-08-01

    A model intended for initial design of stall-controlled wind turbine rotors is described. The user specifies relative radial position of an arbitrary number of airfoil sections, referring to a data file containing lift-and drag curves. The data file is on the same format as used in the commercial blade-element code BLADES-/2/, where lift- and drag coefficients are interpolated from tables as function of Reynolds number, relative thickness and angle of attack. The user can set constraints on a selection of the following: Maximum power; Maximum thrust in operation; Maximum root bending moment in operation; Extreme root bending moment, parked rotor; Tip speed; Upper and lower bounds on optimisation variables. The optimisation variables can be selected from: Blade radius; Rotational speed; Chord and twist at an arbitrary number of radial positions. The user can chose linear chord distribution and a hyperbola-like twist distribution to ensure smooth planform and twist, or cubic spline interpolation for one or both. The aerodynamic model is based on classical strip theory with Prandtl tip loss correction, supplemented by empirical data for high induction factors. (EG)

  16. A numerical investigation of the stall-delay phenomenon for horizontal axis wind turbine

    Frunzulica, Florin; Mahu, Razvan; Dumitrescu, Horia

    2012-11-01

    The flow characteristics and stall delay phenomenon of a stall regulated wind turbine rotor due to blade rotation in steady state non-yawed conditions are investigated. An incompressible Reynolds-averaged Navier-Stokes solver is applied to carry out the separate flow cases at high wind speeds from 11 m/s to 25 m/s with an interval of 2 m/s. The objective of the present research effort is to validate a first-principles based approach for modeling horizontal axis wind turbines (HAWT) under stalled flow conditions using NREL/ Phase VI rotor data. The computational results are compared with the experimental data and predicted values derived by a new stall-delay model.

  17. Active Suppression of Rotating Stall Inception with Distributed Jet Actuation

    Huu Duc Vo

    2007-06-01

    Full Text Available An analytical and experimental investigation of the effectiveness of full-span distributed jet actuation for active suppression of long length-scale rotating stall inception is carried out. Detailed modeling and experimental verification highlight the important effects of mass addition, discrete injectors, and feedback dynamics, which may be overlooked in preliminary theoretical studies of active control with jet injection. A model of the compression system incorporating nonideal injection and feedback dynamics is verified with forced response measurements to predict the right trends in the movement of the critical pole associated with the stall precursor. Active control experiments with proportional feedback control show that the predicted stall precursors are suppressed to give a 5.5% range extension in compressor flow coefficient. In addition, results suggest that the proposed model could be used to design a more sophisticated controller to further improve performance while reducing actuator bandwidth requirements.

  18. Development and application of a dynamic stall model for rotating wind turbine blades

    In unsteady conditions of wind turbines, both the dynamic stall phenomenon and the three-dimensional (3D) rotational effect affect the rotor aerodynamics. The dynamic stall mechanism for rotating wind turbine blades is first investigated. Through the comparison of the aerodynamic data between the rotating blade and the two-dimensional (2D) airfoil, the normal force slope in the attached flow and the separation point expression in the separated flow are modified in the Beddoes-Leishman (B-L) dynamic stall model for rotating NREL wind turbine blades. The modified model is validated by the comparison between the calculation results and the experimental results of the lift and drag coefficients at different radial positions. Both the hysteresis loop shapes and the calculation values are closer to the experiment than the 2D dynamic stall model. The present dynamic stall model is then coupled to a free vortex wake model. The coupled model is used to calculate the unsteady blade aerodynamic loads and the low speed shaft torque of the NREL wind turbine in a yawed condition. The accuracy is greatly improved by the corrections presented in the paper

  19. Aeroservoelastic Pitch Control of Stall-Induced Flap/Lag Flutter of Wind Turbine Blade Section

    Tingrui Liu

    2015-01-01

    The aim of this paper is to analyze aeroelastic stability, especially flutter suppression for aeroelastic instability. Effects of aeroservoelastic pitch control for flutter suppression on wind turbine blade section subjected to combined flap and lag motions are rarely studied. The work is dedicated to solving destructive flapwise and edgewise instability of stall-induced flutter of wind turbine blade by aeroservoelastic pitch control. The aeroelastic governing equations combine a flap/lag str...

  20. Simulating Dynamic Stall Effects for Vertical Axis Wind Turbines Applying a Double Multiple Streamtube Model

    Eduard Dyachuk

    2015-02-01

    Full Text Available The complex unsteady aerodynamics of vertical axis wind turbines (VAWT poses significant challenges to the simulation tools. Dynamic stall is one of the phenomena associated with the unsteady conditions for VAWTs, and it is in the focus of the study. Two dynamic stall models are compared: the widely-used Gormont model and a Leishman–Beddoes-type model. The models are included in a double multiple streamtube model. The effects of flow curvature and flow expansion are also considered. The model results are assessed against the measured data on a Darrieus turbine with curved blades. To study the dynamic stall effects, the comparison of force coefficients between the simulations and experiments is done at low tip speed ratios. Simulations show that the Leishman–Beddoes model outperforms the Gormont model for all tested conditions.

  1. Validation of the Beddoes-Leishman Dynamic Stall Model for Horizontal Axis Wind Turbines using MEXICO data

    Pereira, R.; Schepers, G.; Pavel, M.D.

    2011-01-01

    The aim of this study is to assess the load predicting capability of a classical Beddoes-Leishman dynamic stall model in a horizontal axis wind turbine (HAWT) environment, in the presence of yaw-misalignment. The dynamic stall model was tailored to the HAWT environment, and validated against unstead

  2. Models of Lift and Drag Coefficients of Stalled and Unstalled Airfoils in Wind Turbines and Wind Tunnels

    Spera, David A.

    2008-01-01

    Equations are developed with which to calculate lift and drag coefficients along the spans of torsionally-stiff rotating airfoils of the type used in wind turbine rotors and wind tunnel fans, at angles of attack in both the unstalled and stalled aerodynamic regimes. Explicit adjustments are made for the effects of aspect ratio (length to chord width) and airfoil thickness ratio. Calculated lift and drag parameters are compared to measured parameters for 55 airfoil data sets including 585 test points. Mean deviation was found to be -0.4 percent and standard deviation was 4.8 percent. When the proposed equations were applied to the calculation of power from a stall-controlled wind turbine tested in a NASA wind tunnel, mean deviation from 54 data points was -1.3 percent and standard deviation was 4.0 percent. Pressure-rise calculations for a large wind tunnel fan deviated by 2.7 percent (mean) and 4.4 percent (standard). The assumption that a single set of lift and drag coefficient equations can represent the stalled aerodynamic behavior of a wide variety of airfoils was found to be satisfactory.

  3. Modeling dynamic stall on wind turbine blades under rotationally augmented flow fields

    Guntur, S. [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Schreck, S. [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Sorensen, N. N. [Technical Univ. of Denmark, Lyngby (Denmark); Bergami, L. [Technical Univ. of Denmark, Lyngby (Denmark)

    2015-04-22

    It is well known that airfoils under unsteady flow conditions with a periodically varying angle of attack exhibit aerodynamic characteristics different from those under steady flow conditions, a phenomenon commonly known as dynamic stall. It is also well known that the steady aerodynamic characteristics of airfoils in the inboard region of a rotating blade differ from those under steady two-dimensional (2D) flow conditions, a phenomenon commonly known as rotational augmentation. This paper presents an investigation of these two phenomena together in the inboard parts of wind turbine blades. This analysis is carried out using data from three sources: (1) the National Renewable Energy Laboratory’s Unsteady Aerodynamics Experiment Phase VI experimental data, including constant as well as continuously pitching blade conditions during axial operation, (2) data from unsteady Delayed Detached Eddy Simulations (DDES) carried out using the Technical University of Denmark’s in-house flow solver Ellipsys3D, and (3) data from a simplified model based on the blade element momentum method with a dynamic stall subroutine that uses rotationally augmented steady-state polars obtained from steady Phase VI experimental sequences, instead of the traditional 2D nonrotating data. The aim of this work is twofold. First, the blade loads estimated by the DDES simulations are compared to three select cases of the N sequence experimental data, which serves as a validation of the DDES method. Results show reasonable agreement between the two data in two out of three cases studied. Second, the dynamic time series of the lift and the moment polars obtained from the experiments are compared to those from the dynamic stall subroutine that uses the rotationally augmented steady polars. This allowed the differences between the stall phenomenon on the inboard parts of harmonically pitching blades on a rotating wind turbine and the classic dynamic stall representation in 2D flow to be

  4. Investigation of the wind climate in connection with double-stall on wind turbines in Tarifa[Spain]; Undersoegelse af vindklima i forbindelse med dobbelt-stall paa vindmoeller i Tarifa

    Christensen, T. [ELSAMPROJEKT A/S, Fredericia, (Denmark); Jensen, L.E. [LM Glasfiber A/S, Lunderskov (Denmark)

    2000-08-01

    This project has compiled data to allow the Danish manufacturers of wind turbines and blades to improve their knowledge of double stall. On the basis of the double stall difficulties different types of turbines using different makes of blades have encountered in the Tarifa area in Southern Spain, meteorological parameters and production data from two turbines have been measured for a local site. Part of the acquired data have been analysed to reach an understanding of why double stall occurs. The analysis strongly suggests that a change in power level due to double stall can be a result of several external factors: (1) Rain cleaning the blades. (2) A more or less random change in the wind speed components uv, or w, which in some cases can affect a - probably - fairly thick boundary layer. (3) A change in the high frequency turbulence where the vortex impact is too insignificant to affect an - almost - randomly - thick boundary layer. (au)

  5. Aeroservoelastic Pitch Control of Stall-Induced Flap/Lag Flutter of Wind Turbine Blade Section

    Tingrui Liu

    2015-01-01

    Full Text Available The aim of this paper is to analyze aeroelastic stability, especially flutter suppression for aeroelastic instability. Effects of aeroservoelastic pitch control for flutter suppression on wind turbine blade section subjected to combined flap and lag motions are rarely studied. The work is dedicated to solving destructive flapwise and edgewise instability of stall-induced flutter of wind turbine blade by aeroservoelastic pitch control. The aeroelastic governing equations combine a flap/lag structural model and an unsteady nonlinear aerodynamic model. The nonlinear resulting equations are linearized by small perturbation about the equilibrium point. The instability characteristics of stall-induced flap/lag flutter are investigated. Pitch actuator is described by a second-order model. The aeroservoelastic control is analyzed by three types of optimal PID controllers, two types of fuzzy PID controllers, and neural network PID controllers. The fuzzy controllers are developed based on Sugeno model and intuition method with good results achieved. A single neuron PID control strategy with improved Hebb learning algorithm and a radial basic function neural network PID algorithm are applied and performed well in the range of extreme wind speeds.

  6. Visualization by PIV of dynamic stall on a vertical axis wind turbine

    Simão Ferreira, Carlos; van Kuik, Gijs; van Bussel, Gerard; Scarano, Fulvio

    2009-01-01

    The aerodynamic behavior of a vertical axis wind turbine (VAWT) is analyzed by means of 2D particle image velocimetry (PIV), focusing on the development of dynamic stall at different tip speed ratios. The VAWT has an unsteady aerodynamic behavior due to the variation with the azimuth angle θ of the blade’s sections’ angle of attack, perceived velocity and Reynolds number. The phenomenon of dynamic stall is then an inherent effect of the operation of a VAWT at low tip speed ratios, impacting both loads and power. The present work is driven by the need to understand this phenomenon, by visualizing and quantifying it, and to create a database for model validation. The experimental method uses PIV to visualize the development of the flow over the suction side of the airfoil for two different reference Reynolds numbers and three tip speed ratios in the operational regime of a small urban wind turbine. The field-of-view of the experiment covers the entire rotation of the blade and almost the entire rotor area. The analysis describes the evolution of the flow around the airfoil and in the rotor area, with special focus on the leading edge separation vortex and trailing edge shed vorticity development. The method also allows the quantification of the flow, both the velocity field and the vorticity/circulation (only the results of the vorticity/circulation distribution are presented), in terms of the phase locked average and the random component.

  7. Visualization by PIV of dynamic stall on a vertical axis wind turbine

    Simao Ferreira, Carlos; Kuik, Gijs van; Bussel, Gerard van [Delft University of Technology, DUWIND, Wind Energy Section, HS Delft (Netherlands); Scarano, Fulvio [Delft University of Technology, Faculty of Aerospace, Aerodynamics, HS Delft (Netherlands)

    2009-01-15

    The aerodynamic behavior of a vertical axis wind turbine (VAWT) is analyzed by means of 2D particle image velocimetry (PIV), focusing on the development of dynamic stall at different tip speed ratios. The VAWT has an unsteady aerodynamic behavior due to the variation with the azimuth angle {theta} of the blade's sections' angle of attack, perceived velocity and Reynolds number. The phenomenon of dynamic stall is then an inherent effect of the operation of a VAWT at low tip speed ratios, impacting both loads and power. The present work is driven by the need to understand this phenomenon, by visualizing and quantifying it, and to create a database for model validation. The experimental method uses PIV to visualize the development of the flow over the suction side of the airfoil for two different reference Reynolds numbers and three tip speed ratios in the operational regime of a small urban wind turbine. The field-of-view of the experiment covers the entire rotation of the blade and almost the entire rotor area. The analysis describes the evolution of the flow around the airfoil and in the rotor area, with special focus on the leading edge separation vortex and trailing edge shed vorticity development. The method also allows the quantification of the flow, both the velocity field and the vorticity/circulation (only the results of the vorticity/circulation distribution are presented), in terms of the phase locked average and the random component. (orig.)

  8. Global surface pressure measurements of static and dynamic stall on a wind turbine airfoil at low Reynolds number

    Disotell, Kevin J.; Nikoueeyan, Pourya; Naughton, Jonathan W.; Gregory, James W.

    2016-05-01

    Recognizing the need for global surface measurement techniques to characterize the time-varying, three-dimensional loading encountered on rotating wind turbine blades, fast-responding pressure-sensitive paint (PSP) has been evaluated for resolving unsteady aerodynamic effects in incompressible flow. Results of a study aimed at demonstrating the laser-based, single-shot PSP technique on a low Reynolds number wind turbine airfoil in static and dynamic stall are reported. PSP was applied to the suction side of a Delft DU97-W-300 airfoil (maximum thickness-to-chord ratio of 30 %) at a chord Reynolds number of 225,000 in the University of Wyoming open-return wind tunnel. Static and dynamic stall behaviors are presented using instantaneous and phase-averaged global pressure maps. In particular, a three-dimensional pressure topology driven by a stall cell pattern is detected near the maximum lift condition on the steady airfoil. Trends in the PSP-measured pressure topology on the steady airfoil were confirmed using surface oil visualization. The dynamic stall case was characterized by a sinusoidal pitching motion with mean angle of 15.7°, amplitude of 11.2°, and reduced frequency of 0.106 based on semichord. PSP images were acquired at selected phase positions, capturing the breakdown of nominally two-dimensional flow near lift stall, development of post-stall suction near the trailing edge, and a highly three-dimensional topology as the flow reattaches. Structural patterns in the surface pressure topologies are considered from the analysis of the individual PSP snapshots, enabled by a laser-based excitation system that achieves sufficient signal-to-noise ratio in the single-shot images. The PSP results are found to be in general agreement with observations about the steady and unsteady stall characteristics expected for the airfoil.

  9. RANS study of unsteady flow around a profile blade : application to stall of horizontal axis wind turbine

    Belkheir, N. [Khemis Miliana Univ., Ain Defla (Algeria); Dizene, R. [Univ. des Sciences et de la Technologie Houari Boumediene, Algiers (Algeria). Laboratoire de Mecanique Avancee; Khelladi, S.; Massouh, F.; Dobrev, I. [Arts et Metiers Paris Tech., Paris (France)

    2010-07-01

    The shape of an airfoil is designed to achieve the best aerodynamic performance. An aerofoil section undergoes dynamic stall when subjected to any form of unsteady angle of pitch. The study of a horizontal-axis wind turbine (HAWT) under wind operating conditions is complex because it is subject to instantaneous speed and wind direction variation. When turbine blades are driven into a dynamic stall, the lift coefficient drops suddenly resulting in a degradation in aerodynamic performance. This study presented steady and unsteady wind load predictions over an oscillating S809 airfoil tested in a subsonic wind tunnel. A model of sinusoidal pitch oscillations was used. The values for the angles of attack in steady state ranged from -20 to +40 degrees. The model considered 3 frequencies and 2 amplitudes. The two-dimensional numerical model simulated the instantaneous change of wind direction with respect to the turbine blade. Results were compared with data measurements of S809 aerofoil. Reasonable deviations were obtained between the predicted and experimental results for pitch oscillations. The URANS approach was used to predict the stall while the software FLUENT was used for the numerical solution. It was concluded that the behaviour of the unsteady flow in the wind farm must be considered in order to obtain an accurate estimate of the wind turbine aerodynamic load. 12 refs., 5 figs.

  10. Coriolis effect on dynamic stall in a vertical axis wind turbine

    Tsai, Hsieh-Chen; Colonius, Tim

    2013-11-01

    The immersed boundary method is used to simulate the flow around a two-dimensional rotating NACA 0018 airfoil at moderate (sub-scale) Reynolds number in order to investigate separated flow occurring on a vertical-axis wind turbine (VAWT). The influence of dynamic stall on the forces is characterized as a function of tip-speed ratio. The influence of the Coriolis effect is also investigated by comparing the rotating airfoil to one undergoing a surging and pitching motion that produces an equivalent speed and angle-of-attack variation over the cycle. While the Coriolis force produces only small differences in the averaged forces, it plays an important role during dynamic stall. Due to the fact that the Coriolis force deflects the fluid and propagates the vortices differently, the wake-capturing phenomenon of the trailing edge vortex is observed in the flow around the rotating airfoil during a certain range of azimuthal angle. This wake-capturing of the trailing edge vortex leads to a large decrease in lift. However, because of the phase difference between each wake-capturing, there are only small differences in the average forces. The simulations are also compared to results from companion water-tunnel experiments at Caltech. This project is supported by the Gordon and Betty Moore Foundation.

  11. Investigating dynamic stall, 3-D and rotational effects on wind turbine blades by means of an unsteady quasi-3D Navier-Stokes solver

    Chaviaropoulos, P.K. [CRES-Center for Renewable Energy Sources, Pikermi Attiki (Greece)

    1997-08-01

    The blade element codes provide surprisingly accurate predictions of the aerodynamic loads provided that they are `fed` with proper lift and drag - incidence curves for the profiles mounted on the rotor blades. The evident question is how one can obtain such data. It is common experience that the use of the mostly available steady two-dimensional profile data may lead to serious discrepancies between measured and simulated loads. Although several correction techniques have been proposed as a remedy during the last years, from simplified dynamic stall models suitably tuned for wind turbines to 3-D correction schemes for profile data, the problem is by no means over-passed. Especially for the three-dimensional effects it seems that part of the difficulty is due to our limited understanding of the physical mechanism which is responsible for the extra loading of the inner part of the blades. Recognizing the importance of the above aspects two relevant Joule projects have been launched, the concluded `Dynamic Stall and 3-D Effects` JOU2-CT93-0345 and the ongoing `VISCWIND` JOR3-CT95-0007 project. Part of the activities in the first and all the activities in the second project are devoted to the identification and quantification of the dynamic stall and three-dimensional effects experienced by the wind turbine blades using Navier-Stokes computations. The contribution of CRES in these two projects is briefly presented in this paper. (EG)

  12. Dynamic Stall Patterns

    Davidson, Phillip; Babbitt, Ashli; Magstadt, Andrew; Nikoueeyan, Pourya; Naughton, Jonathan; Jonathan Naughton Team

    2014-11-01

    The performance of helicopter and wind turbine blades is affected by dynamic stall. Dynamic stall has received considerable attention, but it is still difficult to simulate and not fully understood. Over the past seven years, many airfoils for helicopter and wind turbine use ranging from 9.5 to 30% thick have been experimentally tested and simulated while dynamically pitching to further characterize dynamic stall. Tests have been run at chord Reynolds number between 225,000-440,000 for various reduced frequencies, mean angles of attack, and oscillation amplitudes. Characterization of stall has been accomplished using data from previous studies as well as the unsteady pressure and flow-field data available from our own work. Where available, combined surface and flow-field data allow for clear identification of the types of stall observed and the flow structure associated with them. The results indicate that thin airfoil stall, leading edge stall, and trailing edge stall are observed in the oscillating airfoil experiments and simulations. These three main stall types are further divided into subcategories. By improving our understanding of the features of dynamic stall, it is expected that physics-based simulations can be improved. Work supported by DOE and a gift from BP.

  13. Stall Inception Process and Prospects for Active Hub-Flap Control in Three-Stage Axial Flow Compressor

    Tomoya OKADA; Atsushi KAWAJIRI; Yutaka OHTA; Eisuke OUTA

    2008-01-01

    The possibility to apply the active hub-flap control method, which is a proven rotating stall control method for a single-stage compressor, to a 3-stage axial compressor is experimentally discussed, where complex rotating stall inception processes ate observed. The research compressor is a 3-stage one and could change the stagger angle settings for rotor blades and stator vanes. Sixteen rotor blade/stator vane configuration patterns were tested by changing stagger angle for the stator vanes. By measurement of surface-pressure fluctuation, stall inception proc-esses are investigated and the measured pressure fluctuation data is used as a predictive signal for rotating stall. The experimental results show that the stall detection system applied to active hub-flap control in a single-stage compressor could be usefully applied to that in a 3-stage compressor with a more complex stall inception process.

  14. Modeling dynamic stall on wind turbine blades under rotationally augmented flow fields

    Guntur, Srinivas; Sørensen, Niels N.; Schreck, Scott;

    2016-01-01

    reduced order dynamic stall model that uses rotationally augmented steady-state polars obtained from steady Phase VI experimental sequences, instead of the traditional two-dimensional, non-rotating data. The aim of this work is twofold. First, the blade loads estimated by the DDES simulations are compared...... qualitative agreement between the model and the experimental data in many cases, which suggests that the current two-dimensional dynamic stall model as used in blade element momentum-based aeroelastic codes may provide a reasonably accurate representation of three-dimensional rotor aerodynamics when used in...

  15. Multiple Rad5 activities mediate sister chromatid recombination to bypass DNA damage at stalled replication forks.

    Minca, Eugen C; Kowalski, David

    2010-06-11

    DNA damage that blocks replication is bypassed in order to complete chromosome duplication and preserve cell viability and genome stability. Rad5, a PCNA polyubiquitin ligase and DNA-dependent ATPase in yeast, is orthologous to putative tumor suppressors and controls error-free damage bypass by an unknown mechanism. To identify the mechanism in vivo, we investigated the roles of Rad5 and analyzed the DNA structures that form during damage bypass at site-specific stalled forks present at replication origins. Rad5 mediated the formation of recombination-dependent, X-shaped DNA structures containing Holliday junctions between sister chromatids. Mutants lacking these damage-induced chromatid junctions were defective in resolving stalled forks, restarting replication, and completing chromosome duplication. Rad5 polyubiquitin ligase and ATPase domains both contributed to replication fork recombination. Our results indicate that multiple activities of Rad5 function coordinately with homologous recombination factors to enable replication template switch events that join sister chromatids at stalled forks and bypass DNA damage. PMID:20541998

  16. Modeling Dynamic Stall for a Free Vortex Wake Model of Floating Offshore Wind Turbines

    Gaertner, Evan

    2015-01-01

    Floating offshore wind turbines in deep waters offer significant advantages to onshore and near-shore wind turbines. However, due to the motion of floating platforms in response to wind and wave loading, the aerodynamics are substantially more complex. Traditional aerodynamic models and design codes do not adequately account for the floating platform dynamics. Turbines must therefore be over designed due to loading uncertainty and are not fully optimized for their operating conditions. Previo...

  17. Study of the stall delay phenomenon and of wind turbine blade dynamics using numerical approaches and NREL's wind tunnel tests

    Breton, Simon-Philippe

    2008-06-15

    The production of electricity from wind has experienced an enormous growth worldwide in the last 20 years. It is now widely seen as a serious alternative to more conventional energy production methods. Improvements are however still possible to make it more cost-effective. This can be done through a better understanding of the fundamental phenomena involved in the interaction of the wind with the wind turbine rotor. This growth in the production of energy from wind is expected to continue at a similar rate in the years to come, helped by the installation of wind turbines at sea, that is becoming a hot topic in the wind energy field today. The phenomenon of stall delay affecting rotating wind turbine blades is an example of an aerodynamic phenomenon that is not yet fully understood. Several models exist to correct for this effect. Five such models were first tested within a vortex wake simulation code based on the modelling of a prescribed wake behind the rotor of the turbine. Comparison was made with wind tunnel test data acquired in head-on flow on a two-bladed 10.1 diameter wind turbine at the National Renewable Energy Laboratories (NREL) in 2000. It revealed a general overprediction of the stall delay effects, at the same time as great disparity was obtained between the different models. Conclusions from this work served as a starting point for a much more thorough investigation on this subject, where several models were tested in terms of different quantities using the same simulation code, and where the application of some of the models was improved. Overprediction of the loads was once again obtained when comparison was made to the NREL results in head-on flow, and none of the models was found to correctly represent the flow physics involved. The premises on which each of the models relies were discussed as a means of better understanding and modelling this phenomenon. The important issue of tip loss was also covered, and guidelines were suggested to improve

  18. Creating a benchmark of vertical axis wind turbines in dynamic stall for validating numerical models

    Castelein, D.; Ragni, D.; Tescione, G.; Ferreira, C. J. Simão; Gaunaa, Mac

    2015-01-01

    An experimental campaign using Particle Image Velocimetry (2C-PIV) technique has been conducted on a H-type Vertical Axis Wind Turbine (VAWT) to create a benchmark for validating and comparing numerical models. The turbine is operated at tip speed ratios (TSR) of 4.5 and 2, at an average chord...... phenomenon is numerically very hard to model, so a solid benchmark for a VAWT in DS is of great interest. The aim of the paper is to present the experimental flow fields, and the validated loads on the blades for both TSR....

  19. Numerical Investigations of Dynamic Stall Control

    Florin FRUNZULICA

    2014-04-01

    Full Text Available In this paper we investigated numerically the dynamic stall phenomenon and the possibilities to control it, with application to vertical axis wind turbines (for urban users. The Phenomenon appear at low tip speed ratio (TSR<4 and it has a great impact on structural integrity of the wind turbine and power performances. For this reason we performed a computational study of dynamic stall around NACA 0012 airfoil in pitching motion at relative low Reynolds number (105. Also, we performed the same analysis for four flow control methods: two passive (Gurney flap and slot and two active (blowing jet on the rounded trailing edge and synthetic jet periodically activated. The Results are compared to those of an existing experimental case test.

  20. HAWT performance with dynamic stall

    Hibbs, B. D.

    1986-02-01

    The effects of flow nonuniformities (wing shear, tower wake, yaw, and large-scale turbulence) on the performance of a horizontal axis wind turbine are calculated, accounting for dynamic stall. The PROP program was modified to incorporate and compare these effects with the uniform flow case. The MIT model, which predicts dynamic lift coefficients substantially higher than the static maximum values and includes a crude model of the vortex roll-off phenomenon, represented dynamic stall. As associated model for drag was also used. The dynamic stall model was tested against experimental data for three typical reduced frequencies. Good instantaneous correlation was obtained. The effects of nonuniformities with and without the dynamic stall were calculated using the Westinghouse Mod O and Enertech 44/25 turbines. Modeling the dynamic stall has little effect on performance. Furthermore, the performance with nonuniform flow differed only slightly from the uniform flow case. Thus the new PROP model provides a powerful general capability to handle nonuniform flows.

  1. Wind farm models and control strategies

    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)

  2. Multiple Rad5 activities mediate sister chromatid recombination to bypass DNA damage at stalled replication forks

    Minca, Eugen C; Kowalski, David

    2010-01-01

    DNA damage that blocks replication is bypassed in order to complete chromosome duplication and preserve cell viability and genome stability. Rad5, a PCNA polyubiquitin ligase and DNA-dependent ATPase in yeast, is orthologous to putative tumor suppressors and controls error-free damage bypass by an unknown mechanism. To identify the mechanism in vivo, we investigated the roles of Rad5 and analyzed the DNA structures that form during damage bypass at site-specific stalled forks present at repli...

  3. Stall Flutter Control of a Smart Blade Section Undergoing Asymmetric Limit Oscillations

    Nailu Li

    2016-01-01

    Full Text Available Stall flutter is an aeroelastic phenomenon resulting in unwanted oscillatory loads on the blade, such as wind turbine blade, helicopter rotor blade, and other flexible wing blades. Although the stall flutter and related aeroelastic control have been studied theoretically and experimentally, microtab control of asymmetric limit cycle oscillations (LCOs in stall flutter cases has not been generally investigated. This paper presents an aeroservoelastic model to study the microtab control of the blade section undergoing moderate stall flutter and deep stall flutter separately. The effects of different dynamic stall conditions and the consequent asymmetric LCOs for both stall cases are simulated and analyzed. Then, for the design of the stall flutter controller, the potential sensor signal for the stall flutter, the microtab control capability of the stall flutter, and the control algorithm for the stall flutter are studied. The improvement and the superiority of the proposed adaptive stall flutter controller are shown by comparison with a simple stall flutter controller.

  4. Dynamic stall on a pitching and surging airfoil

    Dunne, Reeve; McKeon, Beverley J.

    2015-08-01

    Vertical axis wind turbine blades undergo dynamic stall due to the large angle of attack variation they experience during a turbine rotation. The flow over a single blade was modeled using a sinusoidally pitching and surging airfoil in a non-rotating frame with a constant freestream flow at a mean chord Reynolds number of . Two-dimensional, time-resolved velocity fields were acquired using particle image velocimetry. Vorticity contours were used to visualize shear layer and vortex activity. A low-order model of dynamic stall was developed using dynamic mode decomposition, from which primary and secondary dynamic separation modes were identified. The interaction between these two modes was able to capture the physics of dynamic stall and as such can be extended to other turbine configurations and problems in unsteady aerodynamics. Results from the linear pitch/surge frame are extrapolated to the rotating VAWT frame to investigate the behavior of identified flow structures.

  5. Analysis of the Response of a 600 kW Stall Controlled Wind Turbine in Complex Terrain

    Cuerva, A.; Bercebal, D.; De la Cruz, S.; Lopez-Diez, S.; Lopez-Roque, V.; Vazquez-Aguado, A.; Marti, I.; Marchante, M.; Navarro, J. [CIEMAT. Madrid (Spain)

    1998-12-31

    This work presents a detailed analysis of the operating characteristics of a 600 kW rated power wind turbine installed in complex terrain. The description of the experimental set up and analysis system is included. The relationships between parameters that describe the wind turbine response and the environmental conditions are established via high level statistical analysis, fatigue analysis and analysis is the frequency domain. Dimensionless factors are calculated to explain the intrinsic response of the structure before stochastic and deterministic wind conditions, independently from its size and wind intensity. Finally, conclusions are presented regarding the parameters that affect the loading state and power production of the machine. (Author) 12 refs.

  6. Analysis of the Response of a 600 kW Stall Controlled Wind Turbine in Complex Terrain

    This work presents a detailed analysis of the operating characteristics of a 600 kW rated power wind turbine installed in complex terrain. The description of the experimental set up and analysis system is included. The relationships between parameters that describe the wind turbine response and the environmental conditions are established via high level statistical analysis, fatigue analysis and analysis in the frequency domain. Dimension less factors are calculated to explain the intrinsic response of the structure before stochastic and deterministic wind conditions, independently from its size and wind intensity. Finally, conclusions are presented regarding the parameters that affect the loading state and power production of the machine. (Author) 12 refs

  7. HAWT performance with dynamic stall

    Hibbs, B.D.

    1986-02-01

    In this report we calculated the effects of flow nonuniformities (wing shear, tower wake, yaw, and large-scale turbulence) on the performance of a horizontal axis wind turbine, accounting for dynamic stall. We modified the PROP program to incorporate and compare these effects with the uniform flow case. The MIT model, which predicts dynamic lift coefficients substantially higher than the static maximum values and includes a crude model of the vortex roll-off phenomenon, represented dynamic stall. As associated model for drag was also used. The dynamic stall model was tested against experimental data for three typical reduced frequencies. Good instantaneous correlation was obtained. The effects of nonuniformities with and without the dynamic stall were calculated using the Westinghouse Mod O and Enertech 44/25 turbines. Modeling the dynamic stall has little effect on performance. Furthermore, the performance with nonuniform flow differed only slightly from the uniform flow case. Thus the now PROP model provides a powerful general capability to handle nonuniform flows.

  8. Damage-induced DNA replication stalling relies on MAPK-activated protein kinase 2 activity

    Kopper, F.; Bierwirth, C.; Schon, M.;

    2013-01-01

    DNA damage can obstruct replication forks, resulting in replicative stress. By siRNA screening, we identified kinases involved in the accumulation of phosphohistone 2AX (gamma H2AX) upon UV irradiation-induced replication stress. Surprisingly, the strongest reduction of phosphohistone 2AX followed...... replication impaired by gemcitabine or by Chk1 inhibition. This rescue strictly depended on transiesion DNA polymerases. In conclusion, instead of being an unavoidable consequence of DNA damage, alterations of replication speed and origin firing depend on MK2-mediated signaling....... knockdown of the MAP kinase-activated protein kinase 2 (MK2), a kinase currently implicated in p38 stress signaling and G2 arrest. Depletion or inhibition of MK2 also protected cells from DNA damage-induced cell death, and mice deficient for MK2 displayed decreased apoptosis in the skin upon UV irradiation...

  9. Prediction of induced vibrations in stall

    Thirstrup Petersen, J.; Thomsen, K.; Aagaard Madsen, H. [Risoe National Lab., Wind Energy and Atmospheric Physics Dept., Roskilde (Denmark)

    1999-03-01

    The main results from recent research in stall induced vibrations are presented. The focus is on the edgewise blade vibrations, which during the last decade have turned out to be a potential threat against the stable operation of stall regulated wind turbines and a fact, which must be dealt with by the designer. The basic physical explanation for the phenomenon and examples of design precaution, which can be taken, are presented. (au)

  10. Three-dimensional flow separation and dynamic stall effects on wind turbine aerodynamics; Nagare no sanjigenteki hakuri to doteki shissoku ga furyoku tabin no kuryoku tokusei ni oyobosu eikyo

    Robinson, M.C.; Simms, D.A.; Hand, M.M.; Schreck, S.J. [National Renewable Energy Laboratory, CO (United States)

    2000-04-01

    Pressure measurement result of the wind turbine blade surface got from unsteady aerodynamic experiment which the national renewable energy laboratory carried out was analyzed, and the effect which dynamic stall phenomenon which arises in the down wind type horizontal axis wind turbine and peeling of the other three-dimensional flow bring about was evaluated. The vaned shape based on the measurement result the turbine that S809 and plain form had it and that it respectively has two kinds of wings of the rectangle and was obtained. Pressure mosquito data for either wing also evaluated the features according to largest negative pressure in leading edge, azimuth direction position of the wing, wind velocity of the inflow wind and yaw direction offset angle. In all positions except for the wing root vicinity (range of the 0-30% span), dynamic stall phenomenon local field inflow wind velocity generation limit yaw offset angle two-dimensional quantitatively. And, it was possible to investigate hydrodynamic force measured from the wing root in the position of the 30% span and discrepancy of estimated result by the two-dimensional theory by the result of three-dimensional unsteadiness distribution and visualization by Taft stuck on the surface area of the surface area pressure with attempting the elucidation of the three-dimensional developmental process of the unsteady peeling. As the result, it was proven that to perfectly estimate the complicated and three-dimensional flow observed actually in quasi-steady peeling model and dynamic stall model based on the two-dimensional flow was not possible. (translated by NEDO)

  11. Active control: Wind turbine model

    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....... The models are all formulated as linear differential equations. The models are validated throughcomparisons 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...

  12. Wind farm models and control strategies

    Sørensen, Poul Ejnar; Hansen, Anca Daniela; Iov, F.; Blaabjerg, F.; Donovan, M.H.

    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...

  13. Wind Farm Active Power Dispatch for Output Power Maximizing Based on a Wind Turbine Control Strategy for Load Minimizing

    Zhang, Baohua; Hu, Weihao; Hou, Peng;

    2015-01-01

    Inclusion of the wake effect in the wind farm control design (WF) can increase the total captured power by wind turbines (WTs), which is usually implemented by derating upwind WTs. However, derating the WT without a proper control strategy will increase the structural loads, caused by operation in...... stall mode. Therefore, the WT control strategy for derating operation should be considered in the attempt at maximizing the total captured power while reducing structural loads. Moreover, electrical power loss on the transmission system inside a WF is also not negligible for maximizing the total output...... power of the WF. In this paper, an optimal active power dispatch strategy based on a WT derating strategy and considering the transmission loss is proposed for maximizing the total output power. The active power reference of each WT is chosen as the optimization variable. A partial swarm optimizing...

  14. Rotating Stall and Stall-Controlled Performance of a Single Stage Subsonic Axial Compressor

    Eisuke OUTA

    2006-01-01

    Activities by various authors on aerodynamics and control dynamics of rotating stall in axial compressor are first traced. Then, a process of stall cell evolution in a subsonic stage is discussed based on a 2-D CFD. A few numbers of vortices grow ahead of the rotor accumulating vorticity ejected from lightly stalled blades, and eventually organize a cell of circumferentially aligned huge vortices, which merge and recess repeatedly during the rotation. Such stall disturbance is intensified on trailing side of a circumferential inlet distortion and decays on the leading side. Considering these features, a new algorithm for stall warning is developed based on a correlation between pressure waveforms at each passing of a fixed blade. A remarkable change in the correlation level at near-stall provides a warning signal prior to the stall onset with sufficiently large time margin. This scheme is applied to achieve rotating stall prevention by actuating flaps installed on the hub. The last issue is on characteristics of forward swept blade which has much increased throttle margin with decreased tip loss. A 3-D computation shows that a secondary vortex generated in suction surface mid span interacts to reduce the tip leakage vortex that initiates the stall.

  15. Alternate Blade Stall and Rotating Stall in a Vaned Diffuser

    Sano, Takeshi; Nakamura, Yuki; Yoshida, Yoshiki; Tsujimoto, Yoshinobu

    Flow instability in a vaned diffuser with an even number of blades was examined experimentally and analytically. In the experiments, an alternate blade stall, an asymmetric stall, and two types of rotating stalls (backward/forward rotating stall) were observed depending on the impeller/diffuser clearance. For narrow clearance with strong impeller/diffuser interaction, the alternate blade stall and backward rotating stall mainly occurred. With increasing the clearance, the forward rotating stall also occurred, and the onset of rotating stall shifted toward the higher flow rate corresponding to the pressure performance in the vaned diffuser. Simple 2D stability analysis showed that the impeller/diffuser clearance affects the speed and direction of the stall propagation, and the slope of the diffuser pressure performance vs. flow rate curve affects fundamentally the onset of the flow instability within the diffuser.

  16. Science Activities in Energy: Wind Energy.

    Oak Ridge Associated Universities, TN.

    Included in this science activities energy package are 12 activities related to wind energy for elementary students. Each activity is outlined on a single card and is introduced by a question. Topics include: (1) At what time of day is there enough wind to make electricity where you live?; (2) Where is the windiest spot on your schoolground?; and…

  17. HAWT dynamic stall response asymmetries under yawed flow conditions

    Schreck, S.; Robinson, M.; Hand, M.; Simms, D.

    2000-10-01

    Horizontal axis wind turbines can experience significant time-varying aerodynamic loads, potentially causing adverse effects on structures, mechanical components and power production. As designers attempt lighter and more flexible wind energy machines, greater accuracy and robustness will become even more critical in future aerodynamics models. Aerodynamics modelling advances, in turn, will rely on more thorough comprehension of the three-dimensional, unsteady, vortical flows that dominate wind turbine blade aerodynamics under high-load conditions. To experimentally characterize these flows, turbine blade surface pressures were acquired at multiple span locations via the NREL Phase IV Unsteady Aerodynamics Experiment. Surface pressures and associated normal force histories were used to characterize dynamic stall vortex kinematics and normal force amplification. Dynamic stall vortices and normal force amplification were confirmed to occur in response to angle-of-attack excursions above the static stall threshold. Stall vortices occupied approximately one-half of the blade span and persisted for nearly one-fourth of the blade rotation cycle. Stall vortex convection varied along the blade, resulting in dramatic deformation of the vortex. Presence and deformation of the dynamic stall vortex produced corresponding amplification of normal forces. Analyses revealed consistent alterations to vortex kinematics in response to changes in reduced frequency, span location and yaw error. Finally, vortex structures and kinematics not previously documented for wind turbine blades were isolated. Published in 2000 by John Wiley & Sons, Ltd.

  18. Wind Powering America FY06 Activities Summary

    2007-02-01

    The Wind Powering America FY06 Activities Summary reflects the accomplishments of our state wind working groups, our programs at the National Renewable Energy Laboratory, and our partner organizations. The national WPA team remains a leading force for moving wind energy forward in the United States. WPA continues to work with its national, regional, and state partners to communicate the opportunities and benefits of wind energy to a diverse set of stakeholders. WPA now has 29 state wind working groups (welcoming New Jersey, Indiana, Illinois, and Missouri in 2006) that form strategic alliances to communicate wind's benefits to the state stakeholders. More than 120 members of national and state public and private sector organizations from 34 states attended the 5th Annual WPA All-States Summit in Pittsburgh in June.

  19. Active load control techniques for wind turbines.

    van Dam, C.P. (University of California, Davis, CA); Berg, Dale E.; Johnson, Scott J. (University of California, Davis, CA)

    2008-07-01

    This report provides an overview on the current state of wind turbine control and introduces a number of active techniques that could be potentially used for control of wind turbine blades. The focus is on research regarding active flow control (AFC) as it applies to wind turbine performance and loads. The techniques and concepts described here are often described as 'smart structures' or 'smart rotor control'. This field is rapidly growing and there are numerous concepts currently being investigated around the world; some concepts already are focused on the wind energy industry and others are intended for use in other fields, but have the potential for wind turbine control. An AFC system can be broken into three categories: controls and sensors, actuators and devices, and the flow phenomena. This report focuses on the research involved with the actuators and devices and the generated flow phenomena caused by each device.

  20. A CFD Database for Airfoils and Wings at Post-Stall Angles of Attack

    Petrilli, Justin; Paul, Ryan; Gopalarathnam, Ashok; Frink, Neal T.

    2013-01-01

    This paper presents selected results from an ongoing effort to develop an aerodynamic database from Reynolds-Averaged Navier-Stokes (RANS) computational analysis of airfoils and wings at stall and post-stall angles of attack. The data obtained from this effort will be used for validation and refinement of a low-order post-stall prediction method developed at NCSU, and to fill existing gaps in high angle of attack data in the literature. Such data could have potential applications in post-stall flight dynamics, helicopter aerodynamics and wind turbine aerodynamics. An overview of the NASA TetrUSS CFD package used for the RANS computational approach is presented. Detailed results for three airfoils are presented to compare their stall and post-stall behavior. The results for finite wings at stall and post-stall conditions focus on the effects of taper-ratio and sweep angle, with particular attention to whether the sectional flows can be approximated using two-dimensional flow over a stalled airfoil. While this approximation seems reasonable for unswept wings even at post-stall conditions, significant spanwise flow on stalled swept wings preclude the use of two-dimensional data to model sectional flows on swept wings. Thus, further effort is needed in low-order aerodynamic modeling of swept wings at stalled conditions.

  1. Stall Flutter Control of a Smart Blade Section Undergoing Asymmetric Limit Oscillations

    Nailu Li; Balas, Mark J.; Pourya Nikoueeyan; Hua Yang; Naughton, Jonathan W.

    2016-01-01

    Stall flutter is an aeroelastic phenomenon resulting in unwanted oscillatory loads on the blade, such as wind turbine blade, helicopter rotor blade, and other flexible wing blades. Although the stall flutter and related aeroelastic control have been studied theoretically and experimentally, microtab control of asymmetric limit cycle oscillations (LCOs) in stall flutter cases has not been generally investigated. This paper presents an aeroservoelastic model to study the microtab control of the...

  2. Wind Powering America FY07 Activities Summary

    2008-02-01

    The Wind Powering America FY07 Activities Summary reflects the accomplishments of our state wind working groups, our programs at the National Renewable Energy Laboratory, and our partner organizations. The national WPA team remains a leading force for moving wind energy forward in the United States. WPA continues to work with its national, regional, and state partners to communicate the opportunities and benefits of wind energy to a diverse set of stakeholders. WPA now has 30 state wind working groups (welcoming Georgia and Wisconsin in 2007) that form strategic alliances to communicate wind's benefits to the state stakeholders. More than 140 members of national and state public and private sector organizations from 39 U.S. states and Canada attended the 6th Annual WPA All-States Summit in Los Angeles in June. WPA's emphasis remains on the rural agricultural sector, which stands to reap the significant economic development benefits of wind energy development. Additionally, WPA continues its program of outreach, education, and technical assistance to Native American communities, public power entities, and regulatory and legislative bodies.

  3. FBH1 Catalyzes Regression of Stalled Replication Forks

    Fugger, Kasper; Mistrik, Martin; Neelsen, Kai J;

    2015-01-01

    DNA replication fork perturbation is a major challenge to the maintenance of genome integrity. It has been suggested that processing of stalled forks might involve fork regression, in which the fork reverses and the two nascent DNA strands anneal. Here, we show that FBH1 catalyzes regression of a...... model whereby FBH1 promotes early checkpoint signaling by remodeling of stalled DNA replication forks....... model replication fork in vitro and promotes fork regression in vivo in response to replication perturbation. Cells respond to fork stalling by activating checkpoint responses requiring signaling through stress-activated protein kinases. Importantly, we show that FBH1, through its helicase activity, is...

  4. Wind Turbine Rotors with Active Vibration Control

    Svendsen, Martin Nymann

    This thesis presents a framework for structural modeling, analysis and active vibration damping of rotating wind turbine blades and rotors. A structural rotor model is developed in terms of finite beam elements in a rotating frame of reference. The element comprises a representation of general...... that these are geometrically well separated. For active vibration control in three-bladed wind turbine rotors the present work presents a resonance-based method for groups of one collective and two whirling modes. The controller is based on the existing resonant format and introduces a dual system...... system. As in the method for non-rotating systems, an explicit procedure for optimal calibration of the controller gains is established. The control system is applied to an 86m wind turbine rotor by means of active strut actuator mechanisms. The prescribed additional damping ratios are reproduced almost...

  5. A review of UK wind energy activities

    Musgrove, P. J.

    1982-01-01

    Wind power activities in Great Britain are reviewed, including a brief summary of historical windmill usage and details of developmental efforts in large and small wind turbines. An annual average resource of 5 m/sec at 10 m has been extrapolated to predict an 8-10 m/sec resource at the hub heights of large wind turbines. Initial estimates indicate that at least half of Great Britain's annual electricity consumption can be produced from windpowered generators. The potential of offshore large WECS siting is being examined, although the wind-derived electricity from those regions are projected to cost three times that of land-based operation. Recorded wind patterns with 12-48 hr. duration have indicated that at least 20% penetration into the national grid is acceptable. A test 250 kW machine is being built as a model for a 3.7 MW machine, both intended for installation at Orkney, Scotland. Additionally, construction has begun on a 25-m diameter, vertical axis, variable geometry Musgrove wind turbine. The straight-bladed machine will produce a maximum of 130 kW, and is a prototype of multi-MW offshore units.

  6. Active system monitoring applied on wind turbines

    Niemann, Hans Henrik; Poulsen, Niels Kjølstad; Parbo, Henrik;

    2009-01-01

    A concept for active system monitoring (ASM) applied on wind turbines is presented in this paper. The concept is based on an injection of a small periodic auxiliary signal in the system. An investigation of the signature from the auxiliary input in residual (error) signals can then be applied for...

  7. Inviscid double wake model for stalled airfoils

    Marion, Lucas; Ramos García, Néstor; Sørensen, Jens Nørkær

    2014-01-01

    An inviscid double wake model based on a steady two-dimensional panel method has been developed to predict aerodynamic loads of wind turbine airfoils in the deep stall region. The separated flow is modelled using two constant vorticity sheets which are released at the trailing edge and at the...... separation point. A calibration of the code through comparison with experiments has been performed using one set of airfoils. A second set of airfoils has been used for the validation of the calibrated model. Predicted aerodynamic forces for a wide range of angles of attack (0 to 90 deg) are in overall good...

  8. Numerical investigation of airfoil dynamic stall in simultaneous harmonic oscillatory and translatory motion

    Ekaterinaris, J.A.; Sørensen, Niels N.; Rasmussen, F.

    1998-01-01

    Wind turbine blades are subject to complex flow conditions. For operation in yaw and turbulent inflow the blade sections appear to execute a motion more complex than a harmonic blade oscillation which causes dynamic stall. Predictions of dynamic stall caused by simple harmonic oscillation are...... crucial to efforts in understanding and improving wind turbine performance. investigation of dynamic stall development caused by a combined oscillatory and translatory motion contributes to better understand blade loading under complex flow conditions. In this paper, numerical predictions of light and...... deep stall caused by simple oscillatory motion are obtained first. The ability of the numerical solution to predict dynamic stall lends caused by a combined motion is further investigated The numerical solution is obtained with a factorized, upwind-biased numerical scheme. The turbulent flow region is...

  9. 小型失速型风力发电机实验测试及最大功率跟踪控制研究%Research on testing/experiment system and maximum power control for small stall regulation wind turbine

    张晓峰; 金鑫; 韩花丽

    2012-01-01

    以9台轴流式风机作为源动力,构建开放式风洞测试实验平台,用变频器调节风机转速以产生需要的模拟风速.通过测量风速值,以及1kW小型失速型风力发电机的输出电压和电流,经过数据采集卡,传送到工控机.为达到功率优化吸收,进行了系统硬件电路设计,通过控制计数器输出脉宽调制(PWM)脉冲来控制并优化小型失速型风力发电机的功率.开发的实验测试系统对小型失速型风力发电系统的研究具有重要意义.%A small wind tunnel test platform was built, in which 9 sets of axial fans as a source of power. The simulation speed was acquired by adjusting the fan speed with inverter. The measured wind speed values, small stall regulation wind turbine lkW output voltage,current,was sent to the industrial machine through the data acquisition card. In order to achieve optimal power absorption, the system hardware design,by controlling the PWM pulse counter output to control the optimization of small stall regulation wind turbine power. The test system developed for small stall regulation wind turbine systems research and development has engineering significance.

  10. Poly(ADP-ribose) binding to Chk1 at stalled replication forks is required for S-phase checkpoint activation

    Min, Wookee; Bruhn, Christopher; Grigaravicius, Paulius; Zhou, Zhong-Wei; Li, Fu; Krüger, Anja; Siddeek, Bénazir; Greulich, Karl-Otto; Popp, Oliver; Meisezahl, Chris; Calkhoven, Cornelis F.; Bürkle, Alexander; Xu, Xingzhi; Wang, Zhao-Qi

    2013-12-01

    Damaged replication forks activate poly(ADP-ribose) polymerase 1 (PARP1), which catalyses poly(ADP-ribose) (PAR) formation; however, how PARP1 or poly(ADP-ribosyl)ation is involved in the S-phase checkpoint is unknown. Here we show that PAR, supplied by PARP1, interacts with Chk1 via a novel PAR-binding regulatory (PbR) motif in Chk1, independent of ATR and its activity. iPOND studies reveal that Chk1 associates readily with the unperturbed replication fork and that PAR is required for efficient retention of Chk1 and phosphorylated Chk1 at the fork. A PbR mutation, which disrupts PAR binding, but not the interaction with its partners Claspin or BRCA1, impairs Chk1 and the S-phase checkpoint activation, and mirrors Chk1 knockdown-induced hypersensitivity to fork poisoning. We find that long chains, but not short chains, of PAR stimulate Chk1 kinase activity. Collectively, we disclose a previously unrecognized mechanism of the S-phase checkpoint by PAR metabolism that modulates Chk1 activity at the replication fork.

  11. Surge and stall in centrifugal compressors

    Vandenbraembussche, R.

    Surge and stall are defined, and experimental and theoretical investigations of surge in compressors, stall in vaned flow passages, and stall in vaneless flow passages are reviewed. Ways to delay surge and stall are outlined. Actions to influence the surge limit during design or to correct for an eventual misprediction often decrease efficiency when the range has to be increased. The main action to avoid surge and stall is a safe design of impeller and diffuser and a correct matching of both components.

  12. Field Test Results from a 10 kW Wind Turbine with Active Flow Control

    Rice, Thomas; Bychkova, Veronika; Taylor, Keith; Clingman, Dan; Amitay, Michael

    2015-11-01

    Active flow control devices including synthetic jets and dynamic vortex generators were tested on a 10 kW wind turbine at RPI. Previous work has shown that load oscillations caused by dynamic stall could be modified through the use of active flow control by injecting momentum into the flow field near the leading edge of a dynamically pitching model. In this study, this work has been extended to its logical conclusion, field-testing active flow control on a real wind turbine. The blades in the current study have a 0.28m chord and 3.05m span, no twist or taper, and were retrofitted with six synthetic jets on one blade and ten dynamic vortex generators on a second blade. The third blade of this turbine was not modified, in order to serve as a control. Strain gauges were installed on each blade to measure blades' deflection. A simple closed loop control was demonstrated and preliminary results indicate reduced vibrational amplitude. Future testing will be conducted on a larger scale, 600kW machine at NREL, incorporating information collected during this study.

  13. DEWEK '98: 4. German wind power conference; DEWEK '98: 4. Deutsche Windenergie-Konferenz. Tagungsband

    Gerdes, B. [ed.

    1999-07-01

    The conference report comprises 90 papers and posters on the following subjects: 1. Technological developments (e.g. use of adaptive structures systems, active stalle wind power systems, systems for early detection of errors); 2. Design and optimisation; 3. Wind forecasts; 4. Operation analyses (e.g. active and passive stall, collective loads, wind power systems in cold climates); 5. Wind power systems and the environment; 6. Offshore wind power generation; 7. Electric characteristics (e.g. modelling of flicker, energy conditioning in distribution systems with a high wind power share); 8. Economic efficiency (e.g. economic efficiency of offshore wind parks on the North Sea coast); 9. Network quality; 10. Rotor development (e.g. noise reduction); 11. Certification and methods of measurement. [German] Der Tagungsband enhaelt 90 Fach- und Posterbeitraege, die sich mit den folgenden Schwerpunkten befassen: 1. Technologische Entwicklungen (z.B. Einsatz von adaptiven Struktursystemen; Active-Stall-WKA; Fehlerfrueherkennungssystemen). 2. Auslegung und Optimierung. 3. Windprognosen. 4. Betriebsanalysen (z.B. Aktive Stall/Passive Stall im Vergleich; Lastkollektive von WKA; WKA in kaltem Klima). 5. Windenergieanlagen und Umwelt. 6. Offshore-Windenergienutzung. 7. Elektrische Eigenschaften (z.B. Modellierung des 'Flickerverhaltens' von WKA; Energiekonditionierung in Verteilnetzen mit hohem Windenergieanteil). 8. Wirtschaftlichkeit (z.B. Wirtschaftlichkeit von Offshore-Windparks der Norddeutschen Kuestenlinie). 9. Netzqualitaet. 10. Rotorentwicklung (z.B. Reduzierung der Schallabstrahlung von WKAs). 11. Zertifizierung von Messmethoden. (AKF)

  14. Investigating Stall Flutter using a DS model-An application for HAWTs

    As wind turbine blades become larger there is a tendency for the blade torsional stiffness to reduce, producing the possibility of dynamic instability at moderate windspeeds. While linearised methods can assess the envelope of allowable blade properties for avoiding classical flutter with attached flow aerodynamics, wind turbine aerofoils can experience stalled flow. Therefore, it is necessary to explore the possible effects of stall-flutter on blade stability. This paper aims to address methods for judging the stability of blade designs during both attached flow and stalled flow behaviour. This paper covers the following areas: i) Attached flow model A Beddoes-Leishman indicial model is presented and the choice of coefficients is explained in the context of Theodorsen's theory for flat-plate aerofoils and experimental results by Beddoes and Leishman. Special attention is given to the differing dynamic behaviour of the pitching moment due to flapping motion, pitching motion and dynamically varying inflow. (ii) Classical flutter analysis The time domain attached flow model is verified against a linear flutter analysis by comparing time domain results for a 3D model of a representative multi-megawatt turbine blade, varying the position of the centre of mass along the chord. The results show agreement to within 6% for a range of flutter onset speeds. (iii) Dynamic stall model On entering the stalled region, damping of torsional motion of an aerofoil section can become negative. A dynamic stall model which encompasses the effects of trailing edge separation and leading edge vortex detachment is presented and validated against published experimental data. (iv) Stall flutter The resulting time domain model is used in simulations validating the prediction of reduced flutter onset for stalled aerofoils. Representative stalled conditions for a multi-megawatt wind turbine blade are investigated to assess the possible reduction in flutter speed. A maximum reduction of 17

  15. NedWind: Cost reduction for 500 kW wind turbines; Application of flexible elements not likely. NedWind zoekt prijsverlaging 500 kW windturbine niet in flexibele elementen

    Voorter, P.H.C.

    1990-10-01

    The Dutch firms Newinco and Bouma, both active on the wind turbine market since 1976 and 1981, respectively, have decided to join forces in order to develop cost-efficient 250 kW and 500 kW wind turbines. Differences in wind turbine designs, for example stall regulated or pitch regulated wind turbines, will be phased out. The concept will be stall regulated wind turbines. Turbine blades will be polyester for the 250 kW, polyester or steel for the 500 kW wind turbine. Whether future developments include application of flexible elements (flexhat concepts) is uncertain. Cost calculations do not point in that direction at this moment. Reasons for this cooperation stem from plans of the joint Dutch electric utilities to realize 250 MW wind power in 1995. At the end of 1993 75 MW should be realized so the next two years three tenders for 25 MW each will be put out. 2 ills., 1 tab.

  16. 14 CFR 25.103 - Stall speed.

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Stall speed. 25.103 Section 25.103... STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Performance § 25.103 Stall speed. (a) The reference stall speed, VSR, is a calibrated airspeed defined by the applicant. VSR may not be less than a 1-g...

  17. Mitigation of Wind Power Fluctuation by Active Current Control of Variable Speed Wind Turbines

    Zhang, Yunqian; Chen, Zhe; Hu, Weihao; Cheng, Ming

    2013-01-01

    Wind shear and tower shadow are the sources of power fluctuation of grid connected wind turbines during continuous operation. This paper presents a simulation model of a MW-level doubly fed induction generator (DFIG) based variable speed wind turbine with a partial-scale back-to-back power...... converter in Simulink. A simple and effective method of wind power fluctuations mitigation by active current control of DFIG is proposed. It smoothes the generator output active power oscillations by adjusting the active current of the DFIG, such that the power oscillation is stored as the kinetic energy of...... the wind turbine. The simulations are performed on the NREL 1.5MW upwind reference wind turbine model. The simulation results are presented and discussed to demonstrate the validity of the proposed control method....

  18. Global Aerodynamic Modeling for Stall/Upset Recovery Training Using Efficient Piloted Flight Test Techniques

    Morelli, Eugene A.; Cunningham, Kevin; Hill, Melissa A.

    2013-01-01

    Flight test and modeling techniques were developed for efficiently identifying global aerodynamic models that can be used to accurately simulate stall, upset, and recovery on large transport airplanes. The techniques were developed and validated in a high-fidelity fixed-base flight simulator using a wind-tunnel aerodynamic database, realistic sensor characteristics, and a realistic flight deck representative of a large transport aircraft. Results demonstrated that aerodynamic models for stall, upset, and recovery can be identified rapidly and accurately using relatively simple piloted flight test maneuvers. Stall maneuver predictions and comparisons of identified aerodynamic models with data from the underlying simulation aerodynamic database were used to validate the techniques.

  19. Self-induced vibrations of a DU96-W-180 airfoil in stall

    Skrzypinski, Witold Robert; Gaunaa, Mac; Sørensen, Niels N.;

    2014-01-01

    degrees of freedom. The computations aimed at investigating the mechanisms of both vortex-induced and stall-induced vibrations related to a wind turbine blade at standstill conditions. In this work, a DU96-W-180 airfoil was used in the angle-of-attack region potentially corresponding to stallinduced...... likely to occur at modern wind turbine blades at standstill. In contrast, the predicted cut-in wind speed necessary for the onset of stall-induced vibrations appeared high enough for such vibrations to be unlikely. Copyright © 2013 John Wiley & Sons, Ltd....

  20. The onset of dynamic stall revisited

    Mulleners, Karen; Raffel, Markus [German Aerospace Center (DLR), Goettingen (Germany)

    2012-03-15

    Dynamic stall on a helicopter rotor blade comprises a series of complex aerodynamic phenomena in response to the unsteady change of the blade's angle of attack. It is accompanied by a lift overshoot and delayed massive flow separation with respect to static stall. The classical hallmark of the dynamic stall phenomenon is the dynamic stall vortex. The flow over an oscillating OA209 airfoil under dynamic stall conditions was investigated by means of unsteady surface pressure measurements and time-resolved particle image velocimetry. The characteristic features of the unsteady flow field were identified and analysed utilising different coherent structure identification methods. An Eulerian and a Lagrangian procedure were adopted to locate the axes of vortices and the edges of Lagrangian coherent structures, respectively; a proper orthogonal decomposition of the velocity field revealed the energetically dominant coherent flow patterns and their temporal evolution. Based on the complementary information obtained by these methods the dynamics and interaction of vortical structures were analysed within a single dynamic stall life cycle leading to a classification of the unsteady flow development into five successive stages: the attached flow stage; the stall development stage; stall onset; the stalled stage; and flow reattachment. The onset of dynamic stall was specified here based on a characteristic mode of the proper orthogonal decomposition of the velocity field. Variations in the flow field topology that accompany the stall onset were verified by the Lagrangian coherent structure analysis. The instantaneous effective unsteadiness was defined as a single representative parameter to describe the influence of the motion parameters. Dynamic stall onset was found to be promoted by increasing unsteadiness. The mechanism that results in the detachment of the dynamic stall vortex from the airfoil was identified as vortex-induced separation caused by strong viscous

  1. Model based active power control of a wind turbine

    Mirzaei, Mahmood; Soltani, Mohsen; Poulsen, Niels Kjølstad;

    2014-01-01

    In recent decades there has been increasing interest in green energies, of which wind energy is one of the most important. Wind turbines are the most common wind energy conversion systems and are hoped to be able to compete with traditional power plants in near future. This demands better...... technology to increase competitiveness of the wind power plants. One way to increase competitiveness of wind power plants is to offer grid services (also called ancillary services) that are normally offered by traditional power plants. One of the ancillary services is called reserve power. There are instants...... 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...

  2. Unsteady Double Wake Model for the Simulation of Stalled Airfoils

    Ramos García, Néstor; Cayron, Antoine; Sørensen, Jens Nørkær

    2015-01-01

    In the present work, the recent developed Unsteady Double Wake Model, USDWM, is used to simulate separated flows past a wind turbine airfoil at high angles of attack. The solver is basically an unsteady two-dimensional panel method which uses the unsteady double wake technique to model flow...... separation and its dynamics. In this paper, the calculated integral forces have been successfully validated against wind tunnel measurements for the FFA-W3-211 airfoil. Furthermore, the computed highly unsteady flow field is analyzed in detail for a set of angles of attack ranging from light to deep stall...

  3. Rotating Pip Detection and Stall Warning in High-Speed Compressors Using Structure Function

    Bright, Michelle M.; Qammar, Helen; Vhora, Hanif; Schaffer, Michael

    1999-01-01

    A statistic for both rotating pip and incipient stall detection, called Structure Function is introduced for use in high speed research compressor environments. Experimental studies on stall inception processes have long observed two types of pre-stall compressor activity. Presently there exist methods for indicating modal stall precursive events in the compressor. This is a first application of a new method to detect rotating pip activity prior to stall in research compressors. The algorithm requires a very short sample of data to distinguish pip activity prior to stall, and thus may be used in a real time application. Additionally, this Structure Function algorithm is also used as a single sensor stall warning method under a variety of operating conditions, including clean inlet conditions, radially and circumferentially distorted inlet conditions, and in examples of steady air injection along the casing, and controlled air injection conditions. Structure Function provides a potential advantage over linear spectral techniques and wavelet algorithms for stall detection due to the simplicity of the algorithm and because it does not rely on a priori knowledge of frequency content.

  4. The FFA dynamic stall model. The Beddoes-Leishman dynamic stall model modified for lead-lag oscillations

    Bjoerck, A. [FFA, The Aeronautical Research Institute of Sweden, Bromma (Sweden)

    1997-08-01

    For calculations of the dynamics of wind turbines the inclusion of a dynamic stall model is necessary in order to obtain reliable results at high winds. For blade vibrations in the lead-lag motion the velocity relative to the blade will vary in time. In the present paper modifications to the Beddoes-Leishman model is presented in order to improve the model for calculations of cases with a varying relative velocity. Comparisons with measurement are also shown and the influence on the calculated aerodynamic damping by the modifications are investigated. (au)

  5. Quasi static and dynamic stall computations applying a Navier-Stokes solver with {Kappa} -{epsilon} Baldwin-Lomax turbulence modelling

    Christensen, H.F.

    1995-08-01

    This report presents results on 2 D Quasi Static and Dynamic Stall on airfoils. The results are obtained by applying the Navier - Stokes code ElipsSys2D with both a {Kappa} - {epsilon} and a Baldwin - Lomax turbulence model. The results concerns computations made on the NACA 0012 and NACA 62{sub 1}218 airfoils. The work addresses the following questions related to Quasi Static and Dynamic Stall: (1) What is the difference between an oscillating inflow and a oscillating airfoil? (2) Which direction do the loops takes before Stall, in light and deep Dynamic Stall for different Reynolds numbers, amplitude in angle of attack and in reduced frequencies? (3) How well does the results from the Dynamic Stall models base on 2 D Navier - Stokes equations compare to measurements taken at the mid blade segment of a Horizontal Axis Wind Turbine operating in natural conditions? (4) What is the contribution to Dynamic Stall from respectively the time variation in relative velocity and angle of attack in the incoming flow? (5) What is the contribution to Dynamic Stall when the relative velocity and angle of attack in the incoming flow is in phase and counter phase. (6) Is it important to apply the unsteady Navier - Stokes equations instead of the steady equations when predicting Quasi Static Stall? (7) How does the choice of turbulence model influence the accuracy of the results, when modelling Quasi Static light and deep Stall? (au) 28 ills., 22 refs.

  6. Operation and control of large wind turbines and wind farms

    Soerensen, Poul; Hansen, Anca D.; Thomsen, Kenneth (and others)

    2005-09-01

    This report is the final report of a Danish research project 'Operation and control of large wind turbines and wind farms'. The objective of the project has been to analyse and assess operational strategies and possibilities for control of different types of wind turbines and different wind farm concepts. The potentials of optimising the lifetime/energy production ratio by means of using revised operational strategies for the individual wind turbines are investigated. Different strategies have been simulated, where the power production is decreased to an optimum when taking loads and actual price of produced electricity into account. Dynamic models and control strategies for the wind farms have also been developed, with the aim to optimise the operation of the wind farms considering participation in power system control of power (frequency) and reactive power (voltage), maximise power production, keep good power quality and limit mechanical loads and life time consumption. The project developed models for 3 different concepts for wind farms. Two of the concepts use active stall controlled wind turbines, one with AC connection and one with modern HVDC/VSC connection of the wind farm. The third concept is based on pitch controlled wind turbines using doubly fed induction generators. The models were applied to simulate the behaviour of the wind farm control when they were connected to a strong grid, and some initial simulations were performed to study the behaviour of the wind farms when it was isolated from the main grid on a local grid. Also the possibility to use the available information from the wind turbine controllers to predict the wind speed has been investigated. The main idea has been to predict the wind speed at a wind turbine using up-wind measurements of the wind speed in another wind turbine. (au)

  7. Flow separation on wind turbines blades

    Corten, G. P.

    2001-01-01

    In the year 2000, 15GW of wind power was installed throughout the world, producing 100PJ of energy annually. This contributes to the total electricity demand by only 0.2%. Both the installed power and the generated energy are increasing by 30% per year world-wide. If the airflow over wind turbine blades could be controlled fully, the generation efficiency and thus the energy production would increase by 9%. Power Control To avoid damage to wind turbines, they are cut out above 10 Beaufort (25 m/s) on the wind speed scale. A turbine could be designed in such a way that it converts as much power as possible in all wind speeds, but then it would have to be to heavy. The high costs of such a design would not be compensated by the extra production in high winds, since such winds are rare. Therefore turbines usually reach maximum power at a much lower wind speed: the rated wind speed, which occurs at about 6 Beaufort (12.5 m/s). Above this rated speed, the power intake is kept constant by a control mechanism. Two different mechanisms are commonly used. Active pitch control, where the blades pitch to vane if the turbine maximum is exceeded or, passive stall control, where the power control is an implicit property of the rotor. Stall Control The flow over airfoils is called "attached" when it flows over the surface from the leading edge to the trailing edge. However, when the angle of attack of the flow exceeds a certain critical angle, the flow does not reach the trailing edge, but leaves the surface at the separation line. Beyond this line the flow direction is reversed, i.e. it flows from the trailing edge backward to the separation line. A blade section extracts much less energy from the flow when it separates. This property is used for stall control. Stall controlled rotors always operate at a constant rotation speed. The angle of attack of the flow incident to the blades is determined by the blade speed and the wind speed. Since the latter is variable, it determines

  8. Simulator study of stall/post-stall characteristics of a fighter airplane with relaxed longitudinal static stability. [F-16

    Nguyen, L. T.; Ogburn, M. E.; Gilbert, W. P.; Kibler, K. S.; Brown, P. W.; Deal, P. L.

    1979-01-01

    A real-time piloted simulation was conducted to evaluate the high-angle-of-attack characteristics of a fighter configuration based on wind-tunnel testing of the F-16, with particular emphasis on the effects of various levels of relaxed longitudinal static stability. The aerodynamic data used in the simulation was conducted on the Langley differential maneuvering simulator, and the evaluation involved representative low-speed combat maneuvering. Results of the investigation show that the airplane with the basic control system was resistant to the classical yaw departure; however, it was susceptible to pitch departures induced by inertia coupling during rapid, large-amplitude rolls at low airspeed. The airplane also exhibited a deep-stall trim which could be flown into and from which it was difficult to recover. Control-system modifications were developed which greatly decreased the airplane susceptibility to the inertia-coupling departure and which provided a reliable means for recovering from the deep stall.

  9. Introduction to the Abrupt Wing Stall (AWS) Program

    Hall, Robert M.; Woodson, Shawn H.

    2003-01-01

    The Abrupt Wing Stall (AWS) Program has addressed the problem of uncommanded, transonic lateral motions, such as wing drop, with experimental, computational, and simulation tools. Background to the establishment of the AWS program is given as well as program objectives. In order to understand the fundamental flow mechanisms that caused the undesirable motions for a pre-production version of the F/A-18E, steady and unsteady flow field details were gathered from dedicated transonic wind-tunnel testing and computational studies. The AWS program has also adapted a free-to- roll (FTR) wind-tunnel testing technique traditionally used for low-speed studies of lateral dynamic stability to the transonic flow regime. This FTR capability was demonstrated first in a proof-of-concept study and then applied to an assessment of four different aircraft configurations. Figures of merit for static testing and for FTR testing have been evaluated for two configurations that demonstrated wing drop susceptibility during full-scale flight conditions (the pre-production F/A-l8E and the AV-8B at the extremes of its flight envelope) and two configurations that do not exhibit wing drop (the F/A-l8C and the F-l6C). Design insights have been obtained from aerodynamic computational studies of the four aircraft configurations and from computations quantifying the impact of the various geometric wing differences between the F/A-18C and the F/A-l8E wings. Finally, the AWS program provides guidance for assessing, in the simulator, the impact of experimentally determined lateral activity on flight characteristics before going to flight.

  10. Wind Tunnel Experiments with Active Control of Bridge Section Model

    Hansen, Henriette I.; Thoft-Christensen, Palle

    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 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...... 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....

  11. Computational studies of the effects of active and passive circulation enhancement concepts on wind turbine performance

    Tongchitpakdee, Chanin

    With the advantage of modern high speed computers, there has been an increased interest in the use of first-principles based computational approaches for the aerodynamic modeling of horizontal axis wind turbine (HAWT). Since these approaches are based on the laws of conservation (mass, momentum, and energy), they can capture much of the physics in great detail. The ability to accurately predict the airloads and power output can greatly aid the designers in tailoring the aerodynamic and aeroelastic features of the configuration. First-principles based analyses are also valuable for developing active means (e.g., circulation control), and passive means (e.g., Gurney flaps) of reducing unsteady blade loads, mitigating stall, and for efficient capture of wind energy leading to more electrical power generation. In this present study, the aerodynamic performance of a wind turbine rotor equipped with circulation enhancement technology (trailing edge blowing or Gurney flaps) is investigated using a three-dimensional unsteady viscous flow analysis. The National Renewable Energy Laboratory (NREL) Phase VI horizontal axis wind turbine is chosen as the baseline configuration. Prior to its use in exploring these concepts, the flow solver is validated with the experimental data for the baseline case under yawed flow conditions. Results presented include radial distribution of normal and tangential forces, shaft torque, root flap moment, surface pressure distributions at selected radial locations, and power output. Results show that good agreement has been for a range of wind speeds and yaw angles, where the flow is attached. At high wind speeds, however, where the flow is fully separated, it was found that the fundamental assumptions behind this present methodology breaks down for the baseline turbulence model (Spalart-Allmaras model), giving less accurate results. With the implementation of advanced turbulence model, Spalart-Allmaras Detached Eddy Simulation (SA-DES), the

  12. Evaluating Maximum Wind Energy Exploitation in Active Distribution Networks

    Siano, Pierluigi; Chen, Peiyuan; Chen, Zhe;

    2010-01-01

    The increased spreading of distributed and renewable generation requires moving towards active management of distribution networks. In this paper, in order to evaluate maximum wind energy exploitation in active distribution networks, a method based on a multi-period optimal power flow (OPF......) analysis is proposed. Active network management schemes such as coordinated voltage control, energy curtailment and power factor control are integrated in the method in order to investigate their impacts on the maximization of wind energy exploitation. Some case studies, using real data from a Danish...... distribution system, confirmed the effectiveness of the proposed method in evaluating the optimal applications of active management schemes to increase wind energy harvesting without costly network reinforcement for the connection of wind generation....

  13. Solar wind turbulence as a driver of geomagnetic activity

    Ikechukwu Ugwu, Ernest Benjamin; Nneka Okeke, Francisca; Ugonabo, Obiageli Josephine

    2016-07-01

    We carried out simultaneous analyses of interplanetary and geomagnetic datasets for the period of (solar Maunder) least (2009) and maximum (2002) solar activity to determine the nature of solar wind turbulence on geomagnetic activity using AE, ASY-D, and ASY-H indices. We determined the role played by Alfvénic fluctuations in the solar wind so as to find out the nature of the turbulence. Our analyses showed that solar wind turbulence play a role in geomagnetic processes at high latitudes during periods of low and high solaractivity but does not have any effect at mid-low latitudes.

  14. Design of a wind turbine pitch angle controller for power system stabilisation

    Jauch, Clemens; Islam, S.M.; Sørensen, Poul Ejnar;

    2007-01-01

    The design of a PID pitch angle controller for a fixed speed active-stall wind turbine, using the root locus method is described in this paper. The purpose of this controller is to enable an active-stall wind turbine to perform power system stabilisation. For the purpose of controller design, the...... transfer function of the wind turbine is derived from the wind turbine's step response. The performance of this controller is tested by simulation, where the wind turbine model with its pitch angle controller is connected to a power system model. The power system model employed here is a realistic model of...... controller can effectively contribute to power system stabilisation. (c) 2007 Elsevier Ltd. All rights reserved....

  15. Simple Activity Demonstrates Wind Energy Principles

    Roman, Harry T.

    2012-01-01

    Wind energy is an exciting and clean energy option often described as the fastest-growing energy system on the planet. With some simple materials, teachers can easily demonstrate its key principles in their classroom. (Contains 1 figure and 2 tables.)

  16. Active Power Controls from Wind Power: Bridging the Gaps

    Ela, E.; Gevorgian, V.; Fleming, P.; Zhang, Y. C.; Singh, M.; Muljadi, E.; Scholbrook, A.; Aho, J.; Buckspan, A.; Pao, L.; Singhvi, V.; Tuohy, A.; Pourbeik, P.; Brooks, D.; Bhatt, N.

    2014-01-01

    This paper details a comprehensive study undertaken by the National Renewable Energy Laboratory, Electric Power Research Institute, and the University of Colorado to understand how the contribution of wind power providing active power control (APC) can benefit the total power system economics, increase revenue streams, improve the reliability and security of the power system, and provide superior and efficient response while reducing any structural and loading impacts that may reduce the life of the wind turbine or its components. The study includes power system simulations, control simulations, and actual field tests using turbines at NREL's National Wind Technology Center (NWTC). The study focuses on synthetic inertial control, primary frequency control, and automatic generation control, and analyzes timeframes ranging from milliseconds to minutes to the lifetime of wind turbines, locational scope ranging from components of turbines to large wind plants to entire synchronous interconnections, and additional topics ranging from economics to power system engineering to control design.

  17. Unsteady aerodynamics of reverse flow dynamic stall on an oscillating blade section

    Lind, Andrew H.; Jones, Anya R.

    2016-07-01

    Wind tunnel experiments were performed on a sinusoidally oscillating NACA 0012 blade section in reverse flow. Time-resolved particle image velocimetry and unsteady surface pressure measurements were used to characterize the evolution of reverse flow dynamic stall and its sensitivity to pitch and flow parameters. The effects of a sharp aerodynamic leading edge on the fundamental flow physics of reverse flow dynamic stall are explored in depth. Reynolds number was varied up to Re = 5 × 105, reduced frequency was varied up to k = 0.511, mean pitch angle was varied up to 15∘, and two pitch amplitudes of 5∘ and 10∘ were studied. It was found that reverse flow dynamic stall of the NACA 0012 airfoil is weakly sensitive to the Reynolds numbers tested due to flow separation at the sharp aerodynamic leading edge. Reduced frequency strongly affects the onset and persistence of dynamic stall vortices. The type of dynamic stall observed (i.e., number of vortex structures) increases with a decrease in reduced frequency and increase in maximum pitch angle. The characterization and parameter sensitivity of reverse flow dynamic stall given in the present work will enable the development of a physics-based analytical model of this unsteady aerodynamic phenomenon.

  18. Control of wind turbines with 'Smart' rotors: proof of concept & LPV subspace identification

    Van Wingerden, J.W.

    2008-01-01

    Active control is becoming more and more important for the wind energy community. If we compare the 'old' stall regulated turbines with today's individual pitch controlled turbines we see that the loads can be considerably reduced, leading to lighter or larger turbines. However, limited actuator ba

  19. Electric Control Substituting Pitch Control for Large Wind Turbines

    Jon Kjellin

    2013-01-01

    turbine has fixed pitch and is only controlled electrically accommodated by passive stall of the blades. By electrically controlling the generator rotational speed with the inverter, passive stall regulation is enabled. The first results on experimental verification of stall regulation in gusty wind speeds are presented. The experiments show that the control system can keep the turbine rotational speed constant even at very gusty winds. It is concluded that electrical control accommodated by passive stall is sufficient as control of the wind turbine even at high wind speeds and can substitute mechanical control such as blade pitch.

  20. 14 CFR 23.201 - Wings level stall.

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Wings level stall. 23.201 Section 23.201... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Flight Stalls § 23.201 Wings level... airplane stalls. (b) The wings level stall characteristics must be demonstrated in flight as...

  1. Risk management of offshore wind activities in North America

    Smith, K.J. [Det Norske Veritas, Katy, TX (United States)

    2010-07-01

    Offshore wind energy projects present inherently different risks than onshore wind developments. However, many offshore industries are mature and have evolved risk management techniques and tools. This PowerPoint presentation discussed the techniques and tools that are being applied to European offshore wind projects in order to help the North American offshore wind industry incorporate the techniques into the development process. The Government of the Netherlands is currently using spatial analysis tools to determine the potential impact of wind power plants on shipping, fishing, and other competing activities. The tools are being used to identify areas with favourable conditions. Quantitative and qualitative risk evaluations are being used to determine complex issues related to harbour access and navigational safety, as the coastline of the Netherlands is among the busiest shipping lanes in the world. Navigation risk assessments are used to demonstrate the impacts of procedural changes on resulting structural and security risks. Datasets are compiled with geographic information system (GIS) maps. Marine accident risk calculation software (MARCS) is used to determine risks related to collisions as well as to quantify mitigation measures. Software tools have been developed to combine task and schedule elements with cost, performance, probability, and potential consequences. A project certification process was outlined, and conceptual design plans were presented. Details of the offshore wind safety joint industry project (JIP) were also provided. tabs., figs.

  2. Modelling of inboard stall delay due to rotation

    Dumitrescu, Horia; Cardos, Vladimir; Dumitrache, Alexandru [Institute of Statistics and Applied Mathematics, Bucharest (Romania)

    2007-07-15

    This paper investigates the boundary-layer characteristics on a wind turbine blade of small chord length. The three-dimensional form of momentum integral equations is derived and used to predict the boundary-layer growth and limiting streamline angles on the blade surface for both attached and separating flow. The chordwise skin friction coefficient is used to identify boundary layer separation and shear layer reattachment locations. The nature of flow near the axis of rotation is discussed and the physical mechanism associated with 3-D and rotational effects is identified. A semiempirical correction law for the lift coefficient based on 2-D airfoil data is established. Comparing calculated and measured lift curves of a stall controlled wind turbine, it is shown that the proposed correction law may improve significantly the accuracy of the predictions.

  3. Modelling of inboard stall delay due to rotation

    Dumitrescu, Horia; Cardoş, Vladimir; Dumitrache, Alexandru

    2007-07-01

    This paper investigates the boundary-layer characteristics on a wind turbine blade of small chord length. The three-dimensional form of momentum integral equations is derived and used to predict the boundary-layer growth and limiting streamline angles on the blade surface for both attached and separating flow. The chordwise skin friction coefficient is used to identify boundary layer separation and shear layer reattachment locations. The nature of flow near the axis of rotation is discussed and the physical mechanism associated with 3-D and rotational effects is identified. A semiempirical correction law for the lift coefficient based on 2-D airfoil data is established. Comparing calculated and measured lift curves of a stall controlled wind turbine, it is shown that the proposed correction law may improve significantly the accuracy of the predictions.

  4. Optimal parameters for the FFA-Beddoes dynamic stall model

    Bjoerck, A.; Mert, M. [FFA, The Aeronautical Research Institute of Sweden, Bromma (Sweden); Madsen, H.A. [Risoe National Lab., Roskilde (Denmark)

    1999-03-01

    Unsteady aerodynamic effects, like dynamic stall, must be considered in calculation of dynamic forces for wind turbines. Models incorporated in aero-elastic programs are of semi-empirical nature. Resulting aerodynamic forces therefore depend on values used for the semi-empiricial parameters. In this paper a study of finding appropriate parameters to use with the Beddoes-Leishman model is discussed. Minimisation of the `tracking error` between results from 2D wind tunnel tests and simulation with the model is used to find optimum values for the parameters. The resulting optimum parameters show a large variation from case to case. Using these different sets of optimum parameters in the calculation of blade vibrations, give rise to quite different predictions of aerodynamic damping which is discussed. (au)

  5. A Semi-active Control System for Wind Turbines

    Caterino, N.; Georgakis, Christos T.; Trinchillo, F.; Occhiuzzi, A.

    A semi-active (SA) control system based on the use of smart magnetorheological (MR) dampers to control the structural response of a wind turbine is proposed herein. The innovative approach is based on the implementation and use of a variable-properties base restraint. This is able to modify in re...

  6. Multi-pole permanent magnet synchronous generator wind turbines' grid support capability in uninterrupted operation during grid faults

    Hansen, Anca Daniela; Michalke, G.

    2009-01-01

    Emphasis in this paper is on the fault ride-through and grid support capabilities of multi-pole permanent magnet synchronous generator (PMSG) wind turbines with a full-scale frequency converter. These wind turbines are announced to be very attractive, especially for large offshore wind farms. A...... discussed by means of simulations with the use of a transmission power system generic model developed and delivered by the Danish Transmission System Operator Energinet.dk. The simulation results show how a PMSG wind farm equipped with an additional voltage control can help a nearby active stall wind farm...

  7. Modeling and control of surge and rotating stall in compressors

    Gravdahl, Jan Tommy

    1998-12-31

    Compressors are used in power generation and a variety of other applications. This thesis contains new results in the field of modeling and control of rotating stall and surge in compressors. A close coupled valve is included in the Moore-Greitzer compression system model and controllers for both surge and rotating stall is derived using backstepping. Disturbances, constant and time varying, are then taken into account, and non-linear controllers are derived. Stability results are given. Then, passivity is used to derive a simple surge control law for the closed coupled valve. This propositional control law is shown to stabilize the system even in the presence of time varying disturbances in mass flow and pressure. A novel model for an axial compression system with non-constant compressor speed is derived by extending the Moore-Greitzer model. Rotating stall and surge is studied in connection with acceleration of the compressor. Finally, a model for a centrifugal compression system with time varying compressor speed is derived. The variable speed compressor characteristic is derived based on energy losses in the compressor components. Active control of surge in connection with varying speed is studied. Semi-global exponential stability of the compression system with both surge and speed control is proven. 103 refs., 38 figs., 5 tabs.

  8. Dynamic stall and 3D effects

    Bjoerck, A.; Thor, S.E. [Aeronautical Research Inst. of Sweden, Bromma (Sweden)

    1996-12-01

    The JOULE II project `Dynamic stall and 3D effects` started in January 1994 and was completed in September 1995. The objective of the project has been to increase the understanding of the three-dimensional and unsteady aerodynamics of stall controlled HAWT`s. The objectives have also been to develop `engineering models` suitable for inclusion into aero-elastic codes. The project included the participation of 13 parties within Europe. This paper describes an overview of the work carried out within the project and key results. 3 refs, 4 figs

  9. The influence of solar wind turbulence on geomagnetic activity

    Jankovičová, Dana; Vörös, Zoltán; Šimkanin, Ján

    2008-01-01

    Roč. 15, č. 1 (2008), s. 53-59. ISSN 1023-5809 R&D Projects: GA AV ČR KJB300420509 Grant ostatní: INTAS Foundation(CH) 06-1000017-8943 Institutional research plan: CEZ:AV0Z30420517; CEZ:AV0Z30120515 Keywords : Solar wind * Turbulence * Geomagnetic activity Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 1.022, year: 2008 http://www.nonlin-processes-geophys.net/15/53/2008/

  10. Education stalls and subsequent stalls in African fertility: A descriptive overview

    Anne Goujon

    2015-12-01

    Full Text Available Background: Recent stalls in fertility decline have been observed in a few countries in sub-Saharan Africa, and so far no plausible common reason has been identified in the literature. This paper develops the hypothesis that these fertility stalls could be associated with stalls in the progress of education among the women of the relevant cohorts, possibly resulting partly from the Structural Adjustment Programs (SAPs of the 1980s. Methods: We descriptively link the change in the education composition of successive cohorts of young women in sub-Saharan Africa and the recent fertility stalls. We use reconstructed data on population by age, gender, and level of education from www.wittgenstein centre.org/dataexplorer, and fertility rates from the United Nations. Results: In most sub-Saharan African countries, we observe that the same countries that had fertility stalls had a stall in the progress of education, particularly for young women who were of primary school age during the 1980s, when most of the countries were under structural adjustment. Conversely, stalls in fertility are less common in countries that did not have an education stall, possibly in relation to SAPs. Conclusions: The results point to the possibility of a link between the recent fertility stalls and discontinuities in the improvement of the education of the relevant cohorts, which in turn could be related to the SAPs in the 1980s. This descriptive finding now needs to be corroborated through more detailed cohort-specific fertility analysis. If the education-fertility link can be further established, it will have important implications for the projections of population growth in affected countries.

  11. Assembling Markets for Wind Power

    Pallesen, Trine

    This project studies the making of a market for wind power in France. Markets for wind power are often referred to as ‘political markets: On the one hand, wind power has the potential to reduce CO2-emissions and thus stall the effects of electricity generation on climate change; and on the other ...

  12. Genome-wide localization of Rrm3 and Pif1 DNA helicases at stalled active and inactive DNA replication forks of Saccharomyces cerevisiae.

    Rossi, Silvia Emma; Carotenuto, Walter; Giannattasio, Michele

    2016-03-01

    The genome of the budding yeast Saccharomyces cerevisiae is sequenced and the location and dynamic of activation of DNA replication origins are known. G1 synchronized yeast cells can be released into S-phase in the presence of hydroxyurea (HU) (1), which slows down DNA replication and retains replication forks in proximity of DNA replication origins. In this condition, the Chromatin Immuno-Precipitation on chip (ChIP on chip) (2-4) of replisome components allows the precise localization of all active DNA replication forks. This analysis can be coupled with the ssDNA-BromodeoxyUridine (ssDNA-BrdU) Immuno-Precipitation on chip (ssDNA-BrdU IP on chip) technique (5-7), which detects the location of newly synthesized DNA. Comparison of binding and BrdU incorporation profiles allows to locate a factor of interest at DNA replication forks genome wide. We present datasets deposited in the gene expression omnibus (GEO) database under accession number GSE68214, which show how the DNA helicases Rrm3 and Pif1 (8) associate to active and inactive DNA replication forks. PMID:26981397

  13. Genome-wide localization of Rrm3 and Pif1 DNA helicases at stalled active and inactive DNA replication forks of Saccharomyces cerevisiae

    Silvia Emma Rossi

    2016-03-01

    Full Text Available The genome of the budding yeast Saccharomyces cerevisiae is sequenced and the location and dynamic of activation of DNA replication origins are known. G1 synchronized yeast cells can be released into S-phase in the presence of hydroxyurea (HU (1, which slows down DNA replication and retains replication forks in proximity of DNA replication origins. In this condition, the Chromatin Immuno-Precipitation on chip (ChIP on chip (2–4 of replisome components allows the precise localization of all active DNA replication forks. This analysis can be coupled with the ssDNA-BromodeoxyUridine (ssDNA-BrdU Immuno-Precipitation on chip (ssDNA-BrdU IP on chip technique (5–7, which detects the location of newly synthesized DNA. Comparison of binding and BrdU incorporation profiles allows to locate a factor of interest at DNA replication forks genome wide. We present datasets deposited in the gene expression omnibus (GEO database under accession number GSE68214, which show how the DNA helicases Rrm3 and Pif1 (8 associate to active and inactive DNA replication forks.

  14. Genome-wide localization of Rrm3 and Pif1 DNA helicases at stalled active and inactive DNA replication forks of Saccharomyces cerevisiae

    Silvia Emma Rossi; Walter Carotenuto; Michele Giannattasio

    2016-01-01

    The genome of the budding yeast Saccharomyces cerevisiae is sequenced and the location and dynamic of activation of DNA replication origins are known. G1 synchronized yeast cells can be released into S-phase in the presence of hydroxyurea (HU) (1), which slows down DNA replication and retains replication forks in proximity of DNA replication origins. In this condition, the Chromatin Immuno-Precipitation on chip (ChIP on chip) (2–4) of replisome components allows the precise localization of al...

  15. Genome-wide localization of Rrm3 and Pif1 DNA helicases at stalled active and inactive DNA replication forks of Saccharomyces cerevisiae

    Rossi, Silvia Emma; Carotenuto, Walter; Giannattasio, Michele

    2015-01-01

    The genome of the budding yeast Saccharomyces cerevisiae is sequenced and the location and dynamic of activation of DNA replication origins are known. G1 synchronized yeast cells can be released into S-phase in the presence of hydroxyurea (HU) (1), which slows down DNA replication and retains replication forks in proximity of DNA replication origins. In this condition, the Chromatin Immuno-Precipitation on chip (ChIP on chip) (2–4) of replisome components allows the precise localization of al...

  16. Tuberculosis Decline in U.S. Has Stalled, CDC Reports

    ... nlm.nih.gov/medlineplus/news/fullstory_157951.html Tuberculosis Decline in U.S. Has Stalled, CDC Reports Agency ... HealthDay News) -- Two decades of progress toward eliminating tuberculosis in the United States has stalled, with incidence ...

  17. Potentials for site-specific design of MW sized wind turbines

    Thomsen, K.; Fuglsang, P.; Schepers, G.

    2001-01-01

    The potential for site specific design of MW sized wind turbines is quantified by comparing design loads for wind turbines installed at a range of different sites. The sites comprise on-shore normal flat terrain stand-alone conditions and wind farm conditions together with offshore and mountainous...... complex terrain wind farms. The design loads are established for a 1 MW active stall regulated wind turbine with the aeroelastic code HAWC. The load analysis is limited to fatigue loads. We do not consider ultimate loads in this paper. The results illustrate the differences in design wind conditions for...... different sites and the related differences in design loads for the 1 MW wind turbine. Based on the difference in the design loads, the potentials for site specific design of the wind turbine main components are identified. The results show that the variation in aerodynamically driven loads and energy...

  18. Distributed Model Predictive Control of A Wind Farm for Optimal Active Power Control

    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 of...... partial linearization of the wind turbine model at selected operating points, the nonlinearities of the wind turbine model are represented by a piece-wise static function based on the wind turbine system inputs and state variables. The nonlinearity identification is based on the clustering-based algorithm...... other advanced optimal control applications of a wind farm....

  19. Effect of control activity on blade fatigue damage rate for a small horizontal axis wind turbine

    Riddle, A.F.; Freris, L.L.; Graham, J.M.R. [Imperial College, London (United Kingdom)

    1996-09-01

    An experiment into the effect of control activity on blade fatigue damage rate for a 5 kW, two bladed, teetered HAWT has been performed. It has been shown that control activity influences the distribution of strain in the blade but that in a high rotor speed, high cycle fatigue regime this has little influence on damage rate. The experiment was conducted on a small test turbine by implementing variable speed stall, pitch and yaw control strategies and measuring blade flapwise strain response at root and midspan locations. A full description of the investigation is provided. (au)

  20. 14 CFR 23.691 - Artificial stall barrier system.

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Artificial stall barrier system. 23.691... Construction Control Systems § 23.691 Artificial stall barrier system. If the function of an artificial stall barrier, for example, stick pusher, is used to show compliance with § 23.201(c), the system must...

  1. 16 CFR 1505.50 - Stalled motor testing.

    2010-01-01

    ... 16 Commercial Practices 2 2010-01-01 2010-01-01 false Stalled motor testing. 1505.50 Section 1505... USE BY CHILDREN Policies and Interpretations § 1505.50 Stalled motor testing. (a) § 1505.6(e)(4)(ii) requires that a motor-operated toy be tested with the motor stalled if the construction of the toy is...

  2. Appropriate Dynamic-Stall Models for Performance Predictions of VAWTs with NLF Blades

    Christian Masson; Christophe Leclerc; Ion Paraschivoiu

    1998-01-01

    This paper illustrates the relative merits of using Natural Laminar Flow (NLF) airfoils in the design of Vertical Axis Wind Turbines (VAWT). This is achieved by the application of the double-multiple-streamtube model of Paraschivoiu to the performance predictions of VAWTs equipped with conventional and NLF blades. Furthermore, in order to clearly illustrate the potential benefit of reducing the drag, the individual contributions of lift and drag to power are presented. The dynamic-stall pheno...

  3. Geographic Information Systems in Support of Wind Energy Activities at NREL: Preprint

    The National Renewable Energy Laboratory (NREL) uses Geographic Information Systems (GIS) to further the development of wind energy resources in support of the U.S. Department of Energy (DOE) Wind Energy Program and its Wind Powering America Initiative. Some of the elements of NREL's GIS data used in wind energy activities include wind measurement sites, transmission lines, federal facility information, and modeled wind resources. More complex GIS analyses can define relationships among the mapped wind energy resources, potential energy load characterization, and utility integration problems. A GIS is an outstanding tool for wind energy activities because data can be readily updated and the results of the GIS analyses can be expressed as charts, tables, and maps. These outputs are in digital formats that allow the results of GIS analyses to be quickly and efficiently distributed to the wind energy industry

  4. Grid Connected Wind Energy Conversions System Performance is Improved by Switching of Shunt Active Filter

    B.Vaikundaselvan; Ranithottungal

    2014-01-01

    This study presents a Grid connected Wind Energy Conversions System (WECS) where performance is improved by switching of Shunt Active Filter. Shunt active filter for non linear loads is designed to minimize the harmonics present in the wind power system. Due to large penetration of power electronic controllers in the wind power applications, switching of these power electronic circuits induces harmonics in the source which causes undesirable effects on the wind energy conversion systems and t...

  5. Numerical analysis of stall propagation in linear cascade

    The performance of gas turbine engines is affected by instabilities, like as rotating stall and/or surge. Rotating stall is a transient intermediate stage between normal flow and complete flow breakdown leading to engine surge. Rotating stall is associated with large amplitude nonaxisymmetric flow variations rotating around the compressor annulus. This paper presents the evolutions of stall propagation in a compressor cascade by numerical analysis. The flow phenomena due to stall cells and propagation speed are examined using 2 dimensional Navier-Stokes equations

  6. Performance augmentation with vortex generators: Design and testing for stall-regulated AWT-26 turbine

    Griffin, D.A. [Advanced Wind Turbines Inc., Seattle, WA (United States)

    1996-12-31

    A study investigated the use of vortex generators (VGs) for performance augmentation of the stall-regulated AWT-26 wind turbine. Based on wind-tunnel results and analysis, a VG array was designed for and tested on the AWT-26 prototype, designated Pt. Performance and loads data were measured for P1, both with and without VGs installed. The turbine performance with VGs met most of the design requirements; power output was increased at moderate wind speeds with a minimal effect on peak power. However, VG drag penalties caused a loss in power output for low wind speeds, such that performance with VGs resulted in a net decrease in AEP for wind speed sites up to 8.5 m/s. 8 refs., 8 figs., 3 tabs.

  7. Distributed Model Predictive Control of A Wind Farm for Optimal Active Power Control

    Zhao, Haoran; Wu, Qiuwei; Guo, Qinglai; Sun, Hongbin; Xue, Yusheng

    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 of...

  8. 78 FR 33908 - Commercial Wind Lease Issuance and Site Assessment Activities on the Atlantic Outer Continental...

    2013-06-05

    ... identified Wind Energy Area (WEA) on the OCS offshore Rhode Island (RI) and Massachusetts (MA). The revised... Bureau of Ocean Energy Management Commercial Wind Lease Issuance and Site Assessment Activities on the.... BOEM may issue one or more commercial wind energy leases in the WEA. The competitive lease process...

  9. Evidence that aerodynamic effects, including dynamic stall, dictate HAWT structural loads and power generation in highly transient time frames

    Shipley, D. E.; Miller, M. S.; Robinson, M. C.; Luttges, M. W.; Simms, D. A.

    1994-08-01

    Aerodynamic data collected from the National Renewable Energy Laboratory's Combined Experiment have shown three distinct performance regimes when the turbine is operated under relatively steady flow conditions. Operating at blade angles of attack below static stall, excellent agreement is achieved with two-dimensional wind tunnel data. Around the static stall angle, the cycle average normal force produced is greater than the static test data. Span locations near the hub produce extremely large values of normal force coefficient, well in excess of the two-dimensional data results. These performance regimes have been shown to be a function of the three-dimensional flow structure and cycle averaged dynamic stall effects. Power generation and root bending moments have also been shown to be directly dependent on the inflow wind velocity. Aerodynamic data, including episodes of dynamic stall, have been correlated on a cycle by cycle basis with the structural and power generation characteristics of a horizontal axis wind turbine. Instantaneous unsteady forces and resultant power generation indicate that peak transient levels can significantly exceed cycle averaged values. Strong coupling between transient aerodynamic and resonant response of the turbine was also observed. These results provide some initial insight into the contribution of unsteady aerodynamics on undesirable turbine structural response and fatigue life.

  10. Computational Fluid Dynamics Simulation Study of Active Power Control in Wind Plants

    Fleming, Paul; Aho, Jake; Gebraad, Pieter; Pao, Lucy; Zhang, Yingchen

    2016-08-01

    This paper presents an analysis performed on a wind plant's ability to provide active power control services using a high-fidelity computational fluid dynamics-based wind plant simulator. This approach allows examination of the impact on wind turbine wake interactions within a wind plant on performance of the wind plant controller. The paper investigates several control methods for improving performance in waked conditions. One method uses wind plant wake controls, an active field of research in which wind turbine control systems are coordinated to account for their wakes, to improve the overall performance. Results demonstrate the challenge of providing active power control in waked conditions but also the potential methods for improving this performance.

  11. Basic Wind Tech Course - Lesson Plans and Activities

    Swapp, Andy

    2011-07-01

    The funds from this project were used to purchase tools and instrumentation to help replicate actual on-the-job wind energy scenarios which provided the students with the practical or applied components of wind energy jobs. This project enhanced the educational experiences provided for the students in terms of engineering and science components of wind energy by using electronics, control systems, and electro-mechanical instrumentation to help students learn standardized wind-specific craftsman skills. In addition the tools and instrumentation helped the students learn the safety necessary to work in the wind industry.

  12. Harmonic Analysis and Active Filtering in Offshore Wind Power Plants

    Chaudhary, Sanjay Kumar; Freijedo Fernandez, Francisco Daniel; Guerrero, Josep M.; Teodorescu, Remus; Bak, Claus Leth; Kocewiak, Ł. H.; Jensen, C. F.

    the point of common coupling (PCC). The resonance conditions should be avoided in all cases. This paper describes the harmonic analysis techniques applied on an OWPP network model. A method is proposed to estimate the harmonic current compensation from a shunt-connected active power filter to mitigate......Due to presence of long high voltage cable networks, and power transformers for the grid connection, the offshore wind power plants (OWPPs) are susceptible to harmonic distortion and resonances. The grid connection of OWPP should not cause the harmonic distortion beyond the permissible limits at...... the harmonic voltage distortion at the PCC. Finally the harmonic distortions in the compensated and the uncompensated systems are compared to demonstrate the efficacy of the compensation....

  13. DOE/NREL supported wind energy activities in Indonesia

    Drouilhet, S.

    1997-12-01

    This paper describes three wind energy related projects which are underway in Indonesia. The first is a USAID/Winrock Wind for Island and Nongovernmental Development (WIND) project. The objectives of this project are to train local nongovernmental organizations (NGOs) in the siting, installation, operation, and maintenance of small wind turbines. Then to install up to 20 wind systems to provide electric power for productive end uses while creating micro-enterprises which will generate enough revenue to sustain the wind energy systems. The second project is a joint Community Power Corporation/PLN (Indonesian National Electric Utility) case study of hybrid power systems in village settings. The objective is to evaluate the economic viability of various hybrid power options for several different situations involving wind/photovoltaics/batteries/diesel. The third project is a World Bank/PLN preliminary market assessment for wind/diesel hybrid systems. The objective is to estimate the size of the total potential market for wind/diesel hybrid power systems in Indonesia. The study will examine both wind retrofits to existing diesel mini-grids and new wind-diesel plants in currently unelectrified villages.

  14. DOE/NREL supported wind energy activities in Alaska

    Drouilhet, S.

    1997-12-01

    This paper describes three wind energy projects implemented in Alaska. The first, a sustainable technology energy partnerships (STEP) wind energy deployment project in Kotzebue will install 6 AOC 15/50 wind turbines and connect to the existing village diesel grid, consisting of approximately 1 MW average load. It seeks to develop solutions to the problems of arctic wind energy installations (transport, foundations, erection, operation, and maintenance), to establish a wind turbine test site, and to establish the Kotzebue Electric Association as a training and deployment center for wind/diesel technology in rural Alaska. The second project, a large village medium-penetration wind/diesel system, also in Kotzebue, will install a 1-2 MW windfarm, which will supplement the AOC turbines of the STEP project. The program will investigate the impact of medium penetration wind energy on power quality and system stability. The third project, the Alaska high-penetration wind/diesel village power pilot project in Wales will install a high penetration (80-100%) wind/diesel system in a remote Alaskan village. The system will include about 180 kW installed wind capacity, meeting an average village load of about 60 kW. This program will provide a model for high penetration wind retrofits to village diesel power systems and build the capability in Alaska to operate, maintain, and replicate wind/diesel technology. The program will also address problems of: effective use of excess wind energy; reliable diesel-off operation; and the role of energy storage.

  15. Wind-Tunnel Tests of a Bridge Model with Active Vibration Control

    Hansen, H. I.; Thoft-Christensen, Palle; Mendes, P. A.;

    The application of active control systems to reduce wind vibrations in bridges is a new area of research. This paper presents the results that were obtained on a set of wind tunnel tests of a bridge model equipped with active movable flaps. Based on the monitored position and motion of the deck......, the flaps are regulated by a control algorithm so that the wind forces exerted on them counteract the deck oscillations....

  16. Influence of playing wind instruments on activity of masticatory muscles.

    Gotouda, A; Yamaguchi, T; Okada, K; Matsuki, T; Gotouda, S; Inoue, N

    2007-09-01

    The aim of this study was to elucidate the influence of change in sound tone of playing wind instruments on activity of jaw-closing muscles and the effect of sustained playing for a long time on fatigue of jaw-closing muscles. Electromyograms (EMG) of 19 brass instrument players and 14 woodwind instrument players were measured while playing instruments in tuning tone and high tone and under other conditions. Nine brass instrument players and nine woodwind instrument players played instruments for 90 min. Before and after the exercise, power spectral analyses of EMG from masseter muscles at 50% of maximum voluntary clenching level were performed and mean power frequency (MPF) were calculated. Root mean square (RMS) of EMG in masseter and temporal muscles while playing were slightly larger than those at rest but extremely small in comparison with those during maximum clenching. Root mean square in orbicularis oris and digastric muscles were relatively large when playing instruments. In the brass instrument group, RMS in high tone was significantly higher than that in tuning tone in all muscles examined. In the woodwind instrument group, RMS in high tone was not significantly higher than that in tuning tone in those muscles. Mean power frequency was not decreased after sustained playing in both instrument groups. These findings indicate that contractive load to jaw-closing muscles when playing a wind instrument in both medium and high tone is very small and playing an instrument for a long time does not obviously induce fatigue of jaw-closing muscles. PMID:17716263

  17. Tutorial of Wind Turbine Control for Supporting Grid Frequency through Active Power Control: Preprint

    Aho, J.; Buckspan, A.; Laks, J.; Fleming, P.; Jeong, Y.; Dunne, F.; Churchfield, M.; Pao, L.; Johnson, K.

    2012-03-01

    As wind energy becomes a larger portion of the world's energy portfolio and wind turbines become larger and more expensive, wind turbine control systems play an ever more prominent role in the design and deployment of wind turbines. The goals of traditional wind turbine control systems are maximizing energy production while protecting the wind turbine components. As more wind generation is installed there is an increasing interest in wind turbines actively controlling their power output in order to meet power setpoints and to participate in frequency regulation for the utility grid. This capability will be beneficial for grid operators, as it seems possible that wind turbines can be more effective at providing some of these services than traditional power plants. Furthermore, establishing an ancillary market for such regulation can be beneficial for wind plant owner/operators and manufacturers that provide such services. In this tutorial paper we provide an overview of basic wind turbine control systems and highlight recent industry trends and research in wind turbine control systems for grid integration and frequency stability.

  18. Dynamic security issues in autonomous power systems with increasing wind power penetration

    Margaris, I.D.; Hansen, Anca Daniela; Sørensen, Poul Ejnar;

    2011-01-01

    Technical requirements set by the network operators nowadays include various aspects, such as fault ride-through capability of wind turbines during faults, voltage-reactive power control and overall control of the wind farms as conventional power plants. Detailed models for the power system as well...... as for the wind farms are therefore essential for power system studies related to these issues, especially when applied to non interconnected systems with high wind power penetration. Detailed generic models for three different wind turbine technologies – Active Stall Induction Generator (ASIG), Doubly Fed...... Asynchronous Generator (DFAG) and Permanent Magnet Synchronous Generator (PMSG) – are applied and issues regarding interaction with the power system are investigated. This paper provides conclusions about the dynamic security of non-interconnected power systems with high wind power penetration based...

  19. 77 FR 39508 - Commercial Wind Lease Issuance and Site Assessment Activities on the Atlantic Outer Continental...

    2012-07-03

    ... specific project proposals on those leases) in an identified Wind Energy Area (WEA) on the OCS offshore... Activities on the Atlantic OCS Offshore RI and MA'' to: Program Manager, Office of Renewable Energy Programs... Bureau of Ocean Energy Management Commercial Wind Lease Issuance and Site Assessment Activities on...

  20. Wind turbine

    Cheney, Jr., Marvin C.

    1982-01-01

    A wind turbine of the type having an airfoil blade (15) mounted on a flexible beam (20) and a pitch governor (55) which selectively, torsionally twists the flexible beam in response to wind turbine speed thereby setting blade pitch, is provided with a limiter (85) which restricts unwanted pitch change at operating speeds due to torsional creep of the flexible beam. The limiter allows twisting of the beam by the governor under excessive wind velocity conditions to orient the blades in stall pitch positions, thereby preventing overspeed operation of the turbine. In the preferred embodiment, the pitch governor comprises a pendulum (65,70) which responds to changing rotor speed by pivotal movement, the limiter comprising a resilient member (90) which engages an end of the pendulum to restrict further movement thereof, and in turn restrict beam creep and unwanted blade pitch misadjustment.

  1. Research Activities of the SEP (Dutch cooperation of electric utilities) in the field of wind energy

    The Dutch electric utilities are actively involved in the development of the wind energy technology. The Dutch Integral research Program Wind energy (IPW) is an important stimulator for the development and the market of cost-effective wind turbines. The successful introduction of wind turbines however depends also on the expectations of potential users on the possible benefits which can be realized by the implementation of wind turbines. The wind pattern of a specific site is of great interest in the decision making, as well as the electric power demand and the availability of alternatives. Next to reliable data on wind potentials good simulation methods and evaluation techniques play important parts. The SEP realized a wind measuring network to collect data on the availability of wind on relevant heights. In combination with calculation models to analyze wind energy, thorough studies in the field of wind energy applications have been carried out during the last few years. Some results of these studies are presented. 10 figs., 2 tabs

  2. Empirically modelled Pc3 activity based on solar wind parameters

    T. Raita

    2010-09-01

    Full Text Available It is known that under certain solar wind (SW/interplanetary magnetic field (IMF conditions (e.g. high SW speed, low cone angle the occurrence of ground-level Pc3–4 pulsations is more likely. In this paper we demonstrate that in the event of anomalously low SW particle density, Pc3 activity is extremely low regardless of otherwise favourable SW speed and cone angle. We re-investigate the SW control of Pc3 pulsation activity through a statistical analysis and two empirical models with emphasis on the influence of SW density on Pc3 activity. We utilise SW and IMF measurements from the OMNI project and ground-based magnetometer measurements from the MM100 array to relate SW and IMF measurements to the occurrence of Pc3 activity. Multiple linear regression and artificial neural network models are used in iterative processes in order to identify sets of SW-based input parameters, which optimally reproduce a set of Pc3 activity data. The inclusion of SW density in the parameter set significantly improves the models. Not only the density itself, but other density related parameters, such as the dynamic pressure of the SW, or the standoff distance of the magnetopause work equally well in the model. The disappearance of Pc3s during low-density events can have at least four reasons according to the existing upstream wave theory: 1. Pausing the ion-cyclotron resonance that generates the upstream ultra low frequency waves in the absence of protons, 2. Weakening of the bow shock that implies less efficient reflection, 3. The SW becomes sub-Alfvénic and hence it is not able to sweep back the waves propagating upstream with the Alfvén-speed, and 4. The increase of the standoff distance of the magnetopause (and of the bow shock. Although the models cannot account for the lack of Pc3s during intervals when the SW density is extremely low, the resulting sets of optimal model inputs support the generation of mid latitude Pc3 activity predominantly through

  3. Permanent Magnet Synchronous Generator Driven Wind Energy Conversion System Based on Parallel Active Power Filter

    FERDI Brahim; DIB Samira; BERBAOUI Brahim

    2014-01-01

    This paper proposes a novel application of the instantaneous P-Q theory in a wind energy conversion system (WECS). The proposed WECS is formed by permanent magnet synchronous generator (PMSG) wind turbine system connected to the grid through parallel active power filter (PAPF). PAPF uses the generated wind energy to feed loads connected at the point of common coupling (PPC), compensates current harmonics and injects the excess of this energy into the grid using P-Q theory as control method. T...

  4. Theoretical analysis of transcription process with polymerase stalling

    Li, Jingwei

    2015-01-01

    Experimental evidences show that in gene transcription, RNA polymerase has the possibility to be stalled at certain position of the transcription template. This may be due to the template damage, or protein barriers. Once stalled, polymerase may backtrack along the template to the previous nucleotide to wait for the repair of the damaged site, or simply bypass the barrier or damaged site and consequently synthesize an incorrect messenger RNA, or degrade and detach from the template. Thus, the {\\it effective} transcription rate (the rate to synthesize correct product mRNA) and the transcription {\\it effectiveness} (the ratio of the {\\it effective} transcription rate to the {\\it effective} transcription initiation rate) are both influenced by polymerase stalling events. This study shows that, Without backtracking, detachment of stalled polymerase can also help to increase the {\\it effective} transcription rate and transcription {\\it effectiveness}. Generally, the increase of bypass rate of the stalled polymeras...

  5. Nonlinear aeroelastic behavior of an oscillating airfoil during stall-induced vibration

    Sarkar, S.; Bijl, H.

    2008-08-01

    In this paper, nonlinear aeroelastic behavior of a two-dimensional symmetric rotor blade in the dynamic stall regime is investigated. Two different oscillation models have been considered here: pitching oscillation and flap edgewise oscillation. Stall aeroelastic instability in such systems can potentially lead to structural damage. Hence it is an important design concern, especially for wind turbines and helicopter rotors, where such modes of oscillation are likely to take place. Most previous analyses of such dynamical systems are not exhaustive. System parameters like structural nonlinearity or initial conditions have not been studied which could play a significant role on the overall dynamics. In the present paper, a parametric study on the aeroelastic instability and the nonlinear dynamical behavior of the system has been performed. Emphasis is given on the effect of structural nonlinearity and initial conditions. The aerodynamic loads in the dynamic stall regime have been computed using the Onera model. The qualitative influence of the system parameters is different in the two systems studied. The effect of structural nonlinearity on the bifurcation pattern of the system response is significant in the case of pitching oscillation. The initial condition plays an important role on the aeroelastic stability as well as on the bifurcation pattern in both the systems. In the forced response study, interesting dynamical behavior, like period-3 response, has been observed in the pitching oscillation case. On the other hand, for the flap edgewise oscillation case, super-harmonic and quasi-harmonic response have been found.

  6. Solar activity variations of nocturnal thermospheric meridional winds over Indian longitude sector

    Madhav Haridas, M. K.; Manju, G.; Arunamani, T.

    2016-09-01

    The night time F-layer base height information from ionosondes located at two equatorial stations Trivandrum (TRV 8.5°N, 77°E) and Sriharikota (SHAR 13.7°N, 80.2°E) spanning over two decades are used to derive the climatology of equatorial nocturnal Thermospheric Meridional Winds (TMWs) prevailing during High Solar Activity (HSA) and Low Solar Activity (LSA) epochs. The important inferences from the analysis are 1) Increase in mean equatorward winds observed during LSA compared to HSA during pre midnight hours; 25 m/s for VE (Vernal Equinox) and 20 m/s for SS (Summer Solstice), AE (autumnal Equinox) and WS (Winter Solstice). 2) Mean wind response to Solar Flux Unit (SFU) is established quantitatively for all seasons for pre-midnight hours; rate of increase is 0.25 m/s/SFU for VE, 0.2 m/s/SFU for SS and WS and 0.08 m/s/SFU for AE. 3) Theoretical estimates of winds for the two epochs are performed and indicate the role of ion drag forcing as a major factor influencing TMWs. 4) Observed magnitude of winds and rate of flux dependencies are compared to thermospheric wind models. 5) Equinoctial asymmetry in TMWs is observed for HSA at certain times, with more equatorward winds during AE. These observations lend a potential to parameterize the wind components and effectively model the winds, catering to solar activity variations.

  7. FLOW SEPARATION CONTROL ON WIND TURBINE BLADES USING AN ARRAY OF FLUIDIC OSCILLATORS

    Rasheed, Fayaz

    2012-01-01

    Wind turbines produce energy by using the kinetic energy of the wind. It is one ofthe renewable sources of energy and has gained momentum in the present energy hungryworld. Increasing efficiency of wind turbines and stalling of turbine blades beyond themaximum cut off speed is critical for any wind turbine operation. Different types of flowseparation control devices have been studied over the recent years for controlling flowseparation, as well as for the purpose of stalling the turbine blade...

  8. Online wind turbine measurement laboratory

    Hansen, K.S.; Helgesen Pedersen, K.O.; Schmidt Paulsen, U.

    2006-01-01

    As part of the International Master of Science Program in Wind Energy at DTU, a complete interactive wind turbine measurement laboratory has been developed. A 500 kW stall regulated wind turbine has been instrumented with sensors for recording 1) turbine operational parameters, 2) meteorological...... quantities. Measurements are acquired by a PC placed at the wind turbine site near Risø National Laboratory. The PC can be remotely controlled from DTU, which gives the students the opportunity to work on an operating wind turbine. Furthermore, measurements are published on WindData.com, which facilitates...

  9. Prediction of H.A.W.T. blade stall and performance

    Giannakidis, G.; Graham, J.M.R. [Imperial College, Dept. of Aeronautics, London (United Kingdom)

    1996-09-01

    A model is being developed for the prediction of Horizontal Axis Wind Turbine blade stall and performance coupled with a simple aeroelastic analysis model. For the aerodynamic calculation a two dimensional unsteady Navier-Stokes solver on a sectional basis on the blade is coupled with a three dimensional vortex lattice wake. Pressure coefficient distributions are calculated from the two dimensional viscous flow in each blade section. The aerodynamic computations are coupled with a vibrating beam model in order to incorporate flapwise deformations of the blade. (au) 17 refs.

  10. Robust post-stall perching with a simple fixed-wing glider using LQR-Trees

    Birds routinely execute post-stall maneuvers with a speed and precision far beyond the capabilities of our best aircraft control systems. One remarkable example is a bird exploiting post-stall pressure drag in order to rapidly decelerate to land on a perch. Stall is typically associated with a loss of control authority, and it is tempting to attribute this agility of birds to the intricate morphology of the wings and tail, to their precision sensing apparatus, or their ability to perform thrust vectoring. Here we ask whether an extremely simple fixed-wing glider (no propeller) with only a single actuator in the tail is capable of landing precisely on a perch from a large range of initial conditions. To answer this question, we focus on the design of the flight control system; building upon previous work which used linear feedback control design based on quadratic regulators (LQR), we develop nonlinear feedback control based on nonlinear model-predictive control and ‘LQR-Trees’. Through simulation using a flat-plate model of the glider, we find that both nonlinear methods are capable of achieving an accurate bird-like perching maneuver from a large range of initial conditions; the ‘LQR-Trees’ algorithm is particularly useful due to its low computational burden at runtime and its inherent performance guarantees. With this in mind, we then implement the ‘LQR-Trees’ algorithm on real hardware and demonstrate a 95 percent perching success rate over 147 flights for a wide range of initial speeds. These results suggest that, at least in the absence of significant disturbances like wind gusts, complex wing morphology and sensing are not strictly required to achieve accurate and robust perching even in the post-stall flow regime. (papers)

  11. Wind energy research activities of the Dutch Electricity Generating Board

    The varying degrees of penetration of wind energy conversion systems (WECs) into the Dutch electricity generating system has been examined. A simulation has been carried out using wind data recorded at 6 sites spread across the area of interest in the Netherlands. The recorded wind data has been used in conjunction with a production costing model normally used by Sep (the Dutch Electricity Generating Board) for planning purposes. This model was modified to give a correct assessment of the quantity and value of fuel savings made by WECs. System studies were carried out for the year 2000 for zero wind penetration and for three distinctive penetration degrees of WECs, namely 5%, 10% and 15%. After incorporation of the WECS capacity, adjustments were made to the basic plant mix to allow the capacity credit WECs. Separate production cost simulations were executed for each distinct WECS capacity factor. Economic assessments were carried out using standard procedures. Except for the unpredictable development of fuel prices, the capital costs of the WECs proved to be the determinant for the economic viability of wind power. Significant improvements in costs and performance, as may be achieved through additional technological advances, are needed to made wind power competitive in widespread utility applications. (Author)

  12. 77 FR 74218 - Commercial Wind Leasing and Site Assessment Activities on the Atlantic Outer Continental Shelf...

    2012-12-13

    ... published a Notice of Availability (NOA) in the Federal Register (72 FR 62,672) of the Programmatic EIS for... Federal Register (77 FR 5560) of the Final EA for Commercial Wind Lease Issuance and Site Assessment... Bureau of Ocean Energy Management Commercial Wind Leasing and Site Assessment Activities on the...

  13. 78 FR 8190 - Commercial Wind Leasing and Site Assessment Activities on the Atlantic Outer Continental Shelf...

    2013-02-05

    ... published the Notice in the Federal Register (77 FR 74218) inviting Federal, state, local government... Bureau of Ocean Energy Management Commercial Wind Leasing and Site Assessment Activities on the Atlantic... Notice of Intent to Prepare an Environmental Assessment (EA) for Commercial Wind Leasing and...

  14. 77 FR 5830 - Commercial Wind Leasing and Site Assessment Activities on the Atlantic Outer Continental Shelf...

    2012-02-06

    ... (NOA) in the Federal Register (72 FR 62,672) of the Programmatic EIS for Alternative Energy Development... FR 30,616) of the EA for Issuance of Leases for Wind Resource Data Collection on the Outer... Bureau of Ocean Energy Management Commercial Wind Leasing and Site Assessment Activities on the...

  15. Selective enrichment yields robust ethene-producing dechlorinating cultures from microcosms stalled at cis-dichloroethene.

    Anca G Delgado

    Full Text Available Dehalococcoides mccartyi strains are of particular importance for bioremediation due to their unique capability of transforming perchloroethene (PCE and trichloroethene (TCE to non-toxic ethene, through the intermediates cis-dichloroethene (cis-DCE and vinyl chloride (VC. Despite the widespread environmental distribution of Dehalococcoides, biostimulation sometimes fails to promote dechlorination beyond cis-DCE. In our study, microcosms established with garden soil and mangrove sediment also stalled at cis-DCE, albeit Dehalococcoides mccartyi containing the reductive dehalogenase genes tceA, vcrA and bvcA were detected in the soil/sediment inocula. Reductive dechlorination was not promoted beyond cis-DCE, even after multiple biostimulation events with fermentable substrates and a lengthy incubation. However, transfers from microcosms stalled at cis-DCE yielded dechlorination to ethene with subsequent enrichment cultures containing up to 10(9 Dehalococcoides mccartyi cells mL(-1. Proteobacterial classes which dominated the soil/sediment communities became undetectable in the enrichments, and methanogenic activity drastically decreased after the transfers. We hypothesized that biostimulation of Dehalococcoides in the cis-DCE-stalled microcosms was impeded by other microbes present at higher abundances than Dehalococcoides and utilizing terminal electron acceptors from the soil/sediment, hence, outcompeting Dehalococcoides for H2. In support of this hypothesis, we show that garden soil and mangrove sediment microcosms bioaugmented with their respective cultures containing Dehalococcoides in high abundance were able to compete for H2 for reductive dechlorination from one biostimulation event and produced ethene with no obvious stall. Overall, our results provide an alternate explanation to consolidate conflicting observations on the ubiquity of Dehalococcoides mccartyi and occasional stalling of dechlorination at cis-DCE; thus, bringing a new

  16. Coupling of the solar wind to measures of magnetic activity

    The technique of linear prediction filtering has been used to generate empirical response functions relating the solar wind electric field to the most frequently used magnetic indices, AL, AU, Dst and ASYM. Two datasets, one from 1967-1968 and one from 1973-1974, provided the information needed to calculate the empirical response functions. These functions have been convolved with solar wind observations obtained during the IMS to predict the indices. These predictions are compared with the observed indices during two, three-day intervals studied extensively by participants in the CDAW-6 workshop. Differences between the observed and predicted indices are discussed in terms of the linear assumption and in terms of physical processes other than direct solar wind-magnetosphere interaction

  17. Offshore wind turbines and bird activity at Blyth

    NONE

    2005-07-01

    In 1996, a study was implemented to ultimately determine the impact of two 2MW wind turbines situated 900 metres offshore of the north-east of England. The turbines, with a hub height of 66 metres, began operation in December 2000. Earlier, similar studies were carried out on a row of wind turbines mounted on the harbour wall of the nearby town of Blyth. The report gives details of (i) total mortality and mortality due to the turbines; (ii) number of bird strikes; (iii) habitat displacement; (iv) feeding grounds; (v) flight routes and (vi) impact on bird populations of a nearby Site of Special Scientific Interest. The study was conducted by AMEC Wind Limited under contract to the DTI.

  18. Offshore wind energy. An overview on the activities in Germany; Offshore-Windenergie. Ein Ueberblick ueber die Aktivitaeten in Deutschland

    Worm, Anja [media consulta Deutschland GmbH, Berlin (Germany)

    2013-02-15

    The brochure under consideration provides an overview of the activities of offshore wind energy in Germany. The first offshore wind farms are built and generate more electricity than expected. The offshore wind farms serve as a field of learning for new technologies. The power of offshore wind farms opened new prospects for the economy. The northern Federal States of Germany as well as the traditional locations for mechanical engineering and steel production benefit from offshore wind energy.

  19. SERI advanced wind turbine blades

    Tangler, J.; Smith, B.; Jager, D.

    1992-02-01

    The primary goal of the Solar Energy Research Institute's (SERI) advanced wind turbine blades is to convert the kinetic energy in the wind into mechanical energy in an inexpensive and efficient manner. To accomplish this goal, advanced wind turbine blades have been developed by SERI that utilize unique airfoil technology. Performance characteristics of the advanced blades were verified through atmospheric testing on fixed-pitch, stall-regulated horizontal-axis wind turbines (HAWTs). Of the various wind turbine configurations, the stall-regulated HAWT dominates the market because of its simplicity and low cost. Results of the atmospheric tests show that the SERI advanced blades produce 10 percent to 30 percent more energy than conventional blades.

  20. Aeroelastic Optimization of a 10 MW Wind Turbine Blade with Active Trailing Edge Flaps

    Barlas, Athanasios; Tibaldi, Carlo; Zahle, Frederik;

    2016-01-01

    This article presents the aeroelastic optimization of a 10MW wind turbine ‘smart blade’ equipped with active trailing edge flaps. The multi-disciplinary wind turbine analysis and optimization tool HawtOpt2 is utilized, which is based on the open-source framework Open-MDAO. The tool interfaces to...... several state-of-the art simulation codes, allowing for a wide variety of problem formulations and combinations of models. A simultaneous aerodynamic and structural optimization of a 10 MW wind turbine rotor is carried out with respect to material layups and outer shape. Active trailing edge flaps are...

  1. Shifting towards offshore wind energy—Recent activity and future development

    To date, most of the existing wind farms have been built on-land but during the last few years many countries have also invested in offshore applications. The shift towards offshore wind project developments has mainly been driven by European energy policies, especially in north-west countries. In offshore sites the winds are stronger and steadier than on-land, making wind farms more productive with higher capacity factors. On the other hand, although offshore wind energy is not in its infancy period, most of the costs associated with its development are still much higher from onshore counterparts; however some recent technological progress may have the potential to narrow this gap in the years to come. In the present work, an overview of the activity noted in the field of offshore wind energy is carried out, with emphasis being given on the current status and future trends of the technology employed, examining at the same time energy production and availability issues as well as economic considerations. - Highlights: ► An overview of the activity noted in the field of offshore wind energy is carried out. ► Emphasis is given on the current status and future trends of the technology. ► Wind energy production and availability issues are discussed. ► Economic issues such as investment and energy production costs are also analysed.

  2. Wind Tunnel Testing of Active Control System for Bridges

    Hansen, Henriette I.; Thoft-Christensen, Palle

    This paper describes preparation of wind tunnel testing of the principle of using flaps to control the motion of suspension bridges. The experiment will take place at the Instituto Superior Technico Lisbon, Portugal. The bridge section model is constructed of foam with an aluminium frame. The flaps...

  3. Flux-tube geometry and solar wind speed during an activity cycle

    Pinto, R. F.; Brun, A. S.; Rouillard, A. P.

    2016-07-01

    Context. The solar wind speed at 1 AU shows cyclic variations in latitude and in time which reflect the evolution of the global background magnetic field during the activity cycle. It is commonly accepted that the terminal (asymptotic) wind speed in a given magnetic flux-tube is generally anti-correlated with its total expansion ratio, which motivated the definition of widely used semi-empirical scaling laws relating one to the other. In practice, such scaling laws require ad hoc corrections (especially for the slow wind in the vicinities of streamer/coronal hole boundaries) and empirical fits to in situ spacecraft data. A predictive law based solely on physical principles is still missing. Aims: We test whether the flux-tube expansion is the controlling factor of the wind speed at all phases of the cycle and at all latitudes (close to and far from streamer boundaries) using a very large sample of wind-carrying open magnetic flux-tubes. We furthermore search for additional physical parameters based on the geometry of the coronal magnetic field which have an influence on the terminal wind flow speed. Methods: We use numerical magneto-hydrodynamical simulations of the corona and wind coupled to a dynamo model to determine the properties of the coronal magnetic field and of the wind velocity (as a function of time and latitude) during a whole 11-yr activity cycle. These simulations provide a large statistical ensemble of open flux-tubes which we analyse conjointly in order to identify relations of dependence between the wind speed and geometrical parameters of the flux-tubes which are valid globally (for all latitudes and moments of the cycle). Results: Our study confirms that the terminal (asymptotic) speed of the solar wind depends very strongly on the geometry of the open magnetic flux-tubes through which it flows. The total flux-tube expansion is more clearly anti-correlated with the wind speed for fast rather than for slow wind flows, and effectively controls the

  4. Natures of Rotating Stall Cell in a Diagonal Flow Fan

    N. SHIOMI; K. KANEKO; T. SETOGUCHI

    2005-01-01

    In order to clarify the natures of a rotating stall cell, the experimental investigation was carried out in a high specific-speed diagonal flow fan. The pressure field on the casing wall and the velocity fields at the rotor inlet and outlet were measured under rotating stall condition with a fast response pressure transducer and a single slant hot-wire probe, respectively. The data were processed using the "Double Phase-Locked Averaging (DPLA)"technique, which enabled to obtain the unsteady flow field with a rotating stall cell in the relative co-ordinate system fixed to the rotor. As a result, the structure and behavior of the rotating stall cell in a high specific-speed diagonal flow fan were shown.

  5. Flap motion of helicopter rotors with novel, dynamic stall model

    Han Wei

    2016-07-01

    Full Text Available In this paper, a nonlinear flapping equation for large inflow angles and flap angles is established by analyzing the aerodynamics of helicopter blade elements. In order to obtain a generalized flap equation, the Snel stall model was first applied to determine the lift coefficient of the helicopter rotor. A simulation experiment for specific airfoils was then conducted to verify the effectiveness of the Snel stall model as it applies to helicopters. Results show that the model requires no extraneous parameters compared to the traditional stall model and is highly accurate and practically applicable. Based on the model, the relationship between the flapping angle and the angle of attack was analyzed, as well as the advance ratio under the dynamic stall state.

  6. Review of Compressible Dynamic Stall and Its Control

    Chandrasekhara, M. S.

    1999-01-01

    A review of compressibility effects on dynamic stall of pitching airfoils and unsteady separation control by manipulation of unsteady vorticity using a deformable leading edge airfoil design is presented.

  7. Exploratory study of the effects of wing-leading-edge modifications on the stall/spin behavior of a light general aviation airplane

    1979-01-01

    Configurations with full-span and segmented leading-edge flaps and full-span and segmented leading-edge droop were tested. Studies were conducted with wind-tunnel models, with an outdoor radio-controlled model, and with a full-scale airplane. Results show that wing-leading-edge modifications can produce large effects on stall/spin characteristics, particularly on spin resistance. One outboard wing-leading-edge modification tested significantly improved lateral stability at stall, spin resistance, and developed spin characteristics.

  8. Signatures of Slow Solar Wind Streams from Active Regions in the Inner Corona

    Slemzin, V.; Harra, L.; Urnov, A.; Kuzin, S.; Goryaev, F.; Berghmans, D.

    2013-08-01

    The identification of solar-wind sources is an important question in solar physics. The existing solar-wind models ( e.g., the Wang-Sheeley-Arge model) provide the approximate locations of the solar wind sources based on magnetic field extrapolations. It has been suggested recently that plasma outflows observed at the edges of active regions may be a source of the slow solar wind. To explore this we analyze an isolated active region (AR) adjacent to small coronal hole (CH) in July/August 2009. On 1 August, Hinode/EUV Imaging Spectrometer observations showed two compact outflow regions in the corona. Coronal rays were observed above the active-region coronal hole (ARCH) region on the eastern limb on 31 July by STEREO-A/EUVI and at the western limb on 7 August by CORONAS- Photon/TESIS telescopes. In both cases the coronal rays were co-aligned with open magnetic-field lines given by the potential field source surface model, which expanded into the streamer. The solar-wind parameters measured by STEREO-B, ACE, Wind, and STEREO-A confirmed the identification of the ARCH as a source region of the slow solar wind. The results of the study support the suggestion that coronal rays can represent signatures of outflows from ARs propagating in the inner corona along open field lines into the heliosphere.

  9. Active Tuned Mass Dampers for Control of In-Plane Vibrations of Wind Turbine Blades

    Fitzgerald, B.; Basu, Biswajit; Nielsen, Søren R.K.

    2013-01-01

    This paper investigates the use of active tuned mass dampers (ATMDs) for the mitigation of in-plane vibrations in rotating wind turbine blades. The rotating wind turbine blades with tower interaction represent time-varying dynamical systems with periodically varying mass, stiffness, and damping...... matrices. The aim of this paper is to determine whether ATMDs could be used to reduce in-plane blade vibrations in wind turbines with better performance than compared with their passive counterparts. A Euler–Lagrangian wind turbine mathematical model based on energy formulation was developed for this...... purpose, which considers the structural dynamics of the system and the interaction between in-plane and out-of-plane vibrations. Also, the interaction between the blades and the tower including the tuned mass dampers is considered. The wind turbine with tuned mass dampers was subjected to gravity...

  10. Rotating Stall Region of Water-Jet Pump

    Li, Cheng; Weijun, Qi

    2014-01-01

    There is a rotating stall region, which is the so-called unstable head curve when water jet is operated. This region should be usually avoided because of the risk of instabilities during the pump starting and operation. Experimental and numerical research on the relation between the instability in the head curve and the magnitude of unsteady hydraulic forces are presented. It is found that the rotating stall region is strongly influenced by the clearance gap between the impeller blades and th...

  11. Active Circulation Control for Horizontal Axis Wind Turbine

    Dumitrache, Alexandru; Dumitrescu, Horia; Preotu, Octavian

    2011-09-01

    A based method for modeling the aerodynamics of horizontal axis wind turbine has been developed. Circulation control is implemented by tangentially blowing a small high-velocity jet over a highly curved surface, such as a rounded trailing edge. This causes the boundary layer and the jet sheet to remain attached along the curved surface due to the Coanda effect and causing the jet to turn without separation. This analysis has been validated for the experimental data of a rotor tested at NASA Ames Research Center. Comparisons have been done against measurements for surface pressure distribution, force coefficients normal and tangential to the chord line, torque and root bending moments. This approach for enhancing the circulation around the airfoil sections (and hence L/D and power production) has been examined and found to produce useful increases in power at low wind speeds.

  12. Dynamic wind turbine models in power system simulation tool DIgSILENT

    Hansen, A.D.; Iov, F.; Soerensen, Poul.; Cutululis, N.; Jauch, C.; Blaabjerg, F.

    2007-08-15

    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 Risoe-R-1400(EN) and it gathers and describes a whole wind turbine model database built-op and developed during several national research projects, carried out at Risoe DTU National Laboratory for Sustainable Energy and Aalborg University, in the period 2001-2007. The overall objective of these projects was to create a wind turbine model database able to support the analysis of the interaction between the mechanical structure of the wind turbine and the electrical grid during different operational modes. The report provides thus a description of the wind turbines modelling, both at a component level and at a system level. The report contains both the description of DIgSILENT built-in models for the electrical components of a grid connected wind turbine (e.g. induction generators, 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). The initialisation issues on the wind turbine models into the power system simulation are also presented. The main attention in the report is drawn to the modelling at the system level of the following wind turbine concepts: (1) Fixed speed active stall wind turbine concept (2) Variable speed doubly-fed induction generator wind turbine concept (3) Variable speed multi-pole permanent magnet synchronous generator wind turbine concept These wind turbine concept models can be used and even extended for the study of different aspects, e.g. the assessment of power quality, control strategies, connection of the wind turbine at different types of grid and storage systems. Different control strategies have been developed and implemented for these wind turbine

  13. The Effects of Applying Organic Matter in Wind Blown Soil on Microbial Biomass and Enzyme Activity

    2003-01-01

    Field experiment was conducted to study the effect of applying organic matter in wind blown soil on microbial biomass and enzyme activity.The results showed that microbial biomass and enzyme activity keep dynamic changes during wheat growing season in wind blown soil,and reached the peak level in wheat booting stage.Compared with chemical fertilizer,all the other treatments could increase the microbial biomass in different degree,the same as catalsae and alkaline phosphatase activity,But urease activity was slightly difference from them.

  14. DNA-PKcs and PARP1 Bind to Unresected Stalled DNA Replication Forks Where They Recruit XRCC1 to Mediate Repair.

    Ying, Songmin; Chen, Zhihui; Medhurst, Annette L; Neal, Jessica A; Bao, Zhengqiang; Mortusewicz, Oliver; McGouran, Joanna; Song, Xinming; Shen, Huahao; Hamdy, Freddie C; Kessler, Benedikt M; Meek, Katheryn; Helleday, Thomas

    2016-03-01

    A series of critical pathways are responsible for the detection, signaling, and restart of replication forks that encounter blocks during S-phase progression. Small base lesions may obstruct replication fork progression and processing, but the link between repair of small lesions and replication forks is unclear. In this study, we investigated a hypothesized role for DNA-PK, an important enzyme in DNA repair, in cellular responses to DNA replication stress. The enzyme catalytic subunit DNA-PKcs was phosphorylated on S2056 at sites of stalled replication forks in response to short hydroxyurea treatment. Using DNA fiber experiments, we found that catalytically active DNA-PK was required for efficient replication restart of stalled forks. Furthermore, enzymatically active DNA-PK was also required for PARP-dependent recruitment of XRCC1 to stalled replication forks. This activity was enhanced by preventing Mre11-dependent DNA end resection, suggesting that XRCC1 must be recruited early to an unresected stalled fork. We also found that XRCC1 was required for effective restart of a subset of stalled replication forks. Overall, our work suggested that DNA-PK and PARP-dependent recruitment of XRCC1 is necessary to effectively protect, repair, and restart stalled replication forks, providing new insight into how genomic stability is preserved. Cancer Res; 76(5); 1078-88. ©2015 AACR. PMID:26603896

  15. Final Report 02-ERD-056 Active Load Control& Mitigation Using Microtabs: A Wind Energy Application

    Nakafuji, D Y

    2003-02-24

    With public concern over the security and reliability of our existing electricity infrastructure and the resurgence of wind energy, the wind industry offers an immediate, first point of entry for the application and demonstration of an active load control technology. An innovative microtab approach is being investigated and demonstrated for active aerodynamic load control applications under the mid-year LDRD (June-Sept. 2002) effort. With many of these million dollar turbines failing at only half the design lifespans, conventional techniques for stiffening rotors, enlarging generators and gearboxes, and reinforcing towers are insufficient to accommodate the demands for bigger, taller and more powerful turbines. The DOE through the National Renewable Energy Laboratory (NREL) supports R&D efforts to develop lighter, more efficient and longer lasting wind turbines and advance turbine components. However, as wind turbine systems continue to increase in size and complexity, fundamental research and technology development has not kept pace with needs. New technologies to increase turbine life spans and to reduce costs are needed to realize wind electricity generation potentials. It is becoming quite evident that without a better understanding of static and dynamic response to normal and abnormal operating loads coupled with sophisticated flow analysis and control techniques, large turbine operating life and component life will be severely limited. Promising technologies include active load control and load alleviation systems to mitigate peak loads from damaging key components. This project addresses science and engineering challenges of developing enabling technologies for active load control for turbine applications using an innovative, translational microtab approach. Figure 1.1 illustrates the microtabs as applied on a wind turbine system. Extending wind turbine operating life is a crucial component for reducing the cost of wind-generated electricity, enabling wind

  16. On the Relationship Between Solar Wind Speed, Geomagnetic Activity, and the Solar Cycle Using Annual Values

    Wilson, Robert M.; Hathaway, David H.

    2008-01-01

    The aa index can be decomposed into two separate components: the leading sporadic component due to solar activity as measured by sunspot number and the residual or recurrent component due to interplanetary disturbances, such as coronal holes. For the interval 1964-2006, a highly statistically important correlation (r = 0.749) is found between annual averages of the aa index and the solar wind speed (especially between the residual component of aa and the solar wind speed, r = 0.865). Because cyclic averages of aa (and the residual component) have trended upward during cycles 11-23, cyclic averages of solar wind speed are inferred to have also trended upward.

  17. Determining the solar wind speed above active regions using remote radio-wave observations

    Fainberg, J.; Stone, R. G.; Bougeret, J.-L.

    1983-01-01

    A new technique has made it possible to measure the velocity of portions of the solar wind during its flow outward from the sun. This analysis utilizes spacecraft (ISEE-3) observations of radio emission generated in regions of the solar wind associated with solar active regions. By tracking the source of these radio waves over periods of days, it is possible to measure the motion of the emission regions. Evidence of solar wind acceleration during this outward flow, consistent with theoretical models, has also been obtained.

  18. Smart dynamic rotor control using active flaps on a small-scale wind turbine: aeroelastic modeling and comparison with wind tunnel measurements

    Barlas, Thanasis K.; van Wingerden, W.; Hulskamp, A.W.;

    2013-01-01

    using the aeroelastic tool, load predictions are compared with the wind tunnel measurements, and similar control concepts are compared and evaluated in the numerical environment. Conclusions regarding evaluation of the performance of smart rotor concepts for wind turbines are drawn from this threefold......In this paper, the proof of concept of a smart rotor is illustrated by aeroelastic simulations on a small-scale rotor and comparison with wind tunnel experiments. The application of advanced feedback controllers using actively deformed flaps in the wind tunnel measurements is shown to alleviate...

  19. Classical Flutter and Active Control of Wind Turbine Blade Based on Piezoelectric Actuation

    Tingrui Liu

    2015-01-01

    The aim of this article is to analyze classical flutter and active control of single-cell thin-walled composite wind turbine blade beam based on piezoelectric actuation. Effects of piezoelectric actuation for classical flutter suppression on wind turbine blade beam subjected to combined transverse shear deformation, warping restraint effect, and secondary warping are investigated. The extended Hamilton’s principle is used to set up the equations of motion, and the Galerkin method is applied t...

  20. Compensating active power imbalances in power system with large-scale wind power penetration

    Basit, Abdul; Anca Daniela HANSEN; Altin, Müfit; Sørensen, Poul Ejnar; Gamst, Mette

    2016-01-01

    Large-scale wind power penetration can affectthe supply continuity in the power system. This is a matterof high priority to investigate, as more regulating reservesand specified control strategies for generation control arerequired in the future power system with even more highwind power penetration. This paper evaluates the impact oflarge-scale wind power integration on future power systems.An active power balance control methodology is usedfor compensating the power imbalances between thede...

  1. Optimum Power Output Control of a Wind Turbine Rotor

    S. Wijewardana

    2016-01-01

    Full Text Available An active and optimum controller is applied to regulate the power output from a wind turbine rotor. The controller is synthesized in two steps. The first step defines the equilibrium operation point and ensures that the desired equilibrium point is stable. The stability of the equilibrium point is guaranteed by a control law that is synthesized by applying the methodology of model predictive control (MPC. The method of controlling the turbine involves pitching the turbine blades. In the second step the blade pitch angle demand is defined. This involves minimizing the mean square error between the actual and desired power coefficient. The actual power coefficient of the wind turbine rotor is evaluated assuming that the blade is capable of stalling, using blade element momentum theory. This ensures that the power output of the rotor can be reduced to any desired value which is generally not possible unless a nonlinear stall model is introduced to evaluate the blade profile coefficients of lift and drag. The relatively simple and systematic nonlinear modelling and MPC controller synthesis approach adopted in this paper clearly highlights the main features on the controller that is capable of regulating the power output of the wind turbine rotor.

  2. Active Power Control Simulation Platform Research of Wind Farm Based on Multi-Agent

    Liu Xingjie

    2015-01-01

    Full Text Available The realization of the automation, routinization and intelligentization of dispatch control in wind farms is the key to the integration of wind farms into power grid management system. Active power regulate and control system in wind farms has increasingly high demand on timeliness, but at present this system is mostly equipped with centralized unidirectional control with poor timeliness and low utilization ratio for wind energy resources. The characteristics of distribution and instantaneity owned by the active power regulate and control system in wind farms are highly consistent with Multi-Agent system. This paper discusses a kind of processing method that is used in real-time, distributed and parallel computation and processing for multiple simultaneously running wind turbines, which is based on Multi-Agent technology and adopting JADE development platform. This method converts massive centralized computation to distributed computation, which optimizes the effect of the power control. This method makes the effectiveness of active power regulate and control system better, wins time for timely allocating electricity generation assignments and dealing with problems, and avoids the heavy loss of resources.

  3. Grid Connected Wind Energy Conversions System Performance is Improved by Switching of Shunt Active Filter

    B.Vaikundaselvan

    2014-05-01

    Full Text Available This study presents a Grid connected Wind Energy Conversions System (WECS where performance is improved by switching of Shunt Active Filter. Shunt active filter for non linear loads is designed to minimize the harmonics present in the wind power system. Due to large penetration of power electronic controllers in the wind power applications, switching of these power electronic circuits induces harmonics in the source which causes undesirable effects on the wind energy conversion systems and the electrical components which is in the power system network. Shunt active filter is a harmonic mitigating device comprising of voltage source inverter fed through a DC capacitor. The control strategy is based on extraction of harmonics using synchronous reference frame theory. The major contributions of this study is to extract harmonics from the grid connected Wind Energy Conversion Systems (WECS by generating the PWM signals using the Space Vector Pulse Width Modulation (SVPWM to control the Voltage Source Inverter (VSI which has reduced the losses. The proposed method has been simulated and validated using MATLAB/SIMULINK. The end result of the proposed system shows that the Total Harmonic Distortion (THD of the grid connected wind generator has been reduced at the Point of Common Coupling (PCC.

  4. Classical Flutter and Active Control of Wind Turbine Blade Based on Piezoelectric Actuation

    Tingrui Liu

    2015-01-01

    Full Text Available The aim of this article is to analyze classical flutter and active control of single-cell thin-walled composite wind turbine blade beam based on piezoelectric actuation. Effects of piezoelectric actuation for classical flutter suppression on wind turbine blade beam subjected to combined transverse shear deformation, warping restraint effect, and secondary warping are investigated. The extended Hamilton’s principle is used to set up the equations of motion, and the Galerkin method is applied to reduce the aeroelastic coupled equations into a state-space form. Active control is developed to enhance the vibrational behavior and dynamic response to classical aerodynamic excitation and stabilize structures that might be damaged in the absence of control. Active optimal control scheme based on linear quadratic Gaussian (LQG controller is implemented. The research provides a way for rare study of classical flutter suppression and active control of wind turbine blade based on piezoelectric actuation.

  5. Stability and control of wind farms in power systems

    Jauch, C.

    2006-10-15

    The Ph.D. project 'Stability and Control of Wind Farms in Power Systems' deals with some selected problems related to wind power in power systems. With increasing wind power penetration, wind turbines substitute the power production of conventional power plants. Therefore, wind turbines also have to take over the power system stabilisation and control tasks, that were traditionally carried out by conventional power plants. Out of the many aspects related to this problem, this project focuses on transient fault ride-through and power system stabilisation. The selection of turbine types considered in this project is limited to active-stall turbines and variable speed, variable pitch turbines with gearboxes and full-scale converter-connected synchronous generators. As a basis for the project, a study into the state of the art is conducted at the beginning of the project. Grid connection requirements that were in force, or published as drafts, at the time, and scientific literature related to the topic, are studied. The project is based on simulations of wind turbines in a power system simulations tool. Some of the models used in this project were readily available prior to the project; the development of others is part of the project. The most extensive modelling work deals with the design of the electrical part of the variable speed turbine and its controls. To simulate realistic grid operation the wind turbine models are connected to an aggregated model of the Nordic power system. For that purpose the Nordic power system model, which was available prior to the project, is extended with a realistic feeder configuration. It is commonly demanded from modern wind turbines, that they must not disconnect in case of transient faults. Therefore, controllers are designed that enable the two turbine types to ride through transient faults. With these transient fault controllers the wind turbines can stay connected to the grid, such that their generation capacity is

  6. Schlieren Photographic Studies Of Dynamic Stall

    Carr, L.; Chandrasekhara, M.

    1992-01-01

    Report describes stroboscopic Schlieren photographic observations of flows around airfoil oscillating sinusoidally about fixed angle of attack. Conducted in wind tunnel on (NACA) 0012 airfoil oscillating with amplitude of 10 degrees about mean angle of attack of 10 degrees. Photographs taken along span of airfoil. Mach numbers and frequencies chosen to encompass conditions on retreating blades of helicopter rotors in forward flight.

  7. Aeroelastic instability problems for wind turbines

    Hansen, M. E. [Wind Energy Department, Riso National Laboratory, Technical University of Denmark, Frederiksborgvej 399, DK-4000 Roskilde, (Denmark)

    2007-09-05

    This paper deals with the aeroelastic instabilities that have occurred and may still occur for modern commercial wind turbines: stall-induced vibrations for stall-turbines, and classical flutter for pitch-regulated turbines. A review of previous works is combined with derivations of analytical stability limits for typical blade sections that show the fundamental mechanisms of these instabilities. The risk of stall-induced vibrations is mainly related to blade airfoil characteristics, effective direction of blade vibrations and structural damping; whereas the blade tip speed, torsional blade stiffness and chordwise position of the center of gravity along the blades are the main parameters for flutter. These instability characteristics are exemplified by aeroelastic stability analyses of different wind turbines. The review of each aeroelastic instability ends with a list of current research issues that represent unsolved aeroelastic instability problems for wind turbines. (Author).

  8. Wavelet Methods Developed to Detect and Control Compressor Stall

    Le, Dzu K.

    1997-01-01

    A "wavelet" is, by definition, an amplitude-varying, short waveform with a finite bandwidth (e.g., that shown in the first two graphs). Naturally, wavelets are more effective than the sinusoids of Fourier analysis for matching and reconstructing signal features. In wavelet transformation and inversion, all transient or periodic data features (as in compressor-inlet pressures) can be detected and reconstructed by stretching or contracting a single wavelet to generate the matching building blocks. Consequently, wavelet analysis provides many flexible and effective ways to reduce noise and extract signals which surpass classical techniques - making it very attractive for data analysis, modeling, and active control of stall and surge in high-speed turbojet compressors. Therefore, fast and practical wavelet methods are being developed in-house at the NASA Lewis Research Center to assist in these tasks. This includes establishing user-friendly links between some fundamental wavelet analysis ideas and the classical theories (or practices) of system identification, data analysis, and processing.

  9. Accretion disk winds in active galactic nuclei: X-ray observations, models, and feedback

    Tombesi, Francesco

    2016-01-01

    Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. A strong support of this "quasar mode" feedback came from the recent X-ray observation of a mildly relativistic accretion disk wind in a ultraluminous infrared galaxy (ULIRG) and its connection with a large-scale molecular outflow, providing a direct link between the SMBH and the gas out of which stars form. Spectroscopic observations, especially in the X-ray band, show that such accretion disk winds may be common in local AGN and quasars. However, their origin and characteristics are still not fully understood. Detailed theoretical models and simulations focused on radiation, magnetohydrodynamic (MHD) or a combination of these two processes to investigate the possible acceleration mechanisms and the dynamics of these winds. Some of these models have been dir...

  10. Permanent Magnet Synchronous Generator Driven Wind Energy Conversion System Based on Parallel Active Power Filter

    FERDI Brahim

    2014-05-01

    Full Text Available This paper proposes a novel application of the instantaneous P-Q theory in a wind energy conversion system (WECS. The proposed WECS is formed by permanent magnet synchronous generator (PMSG wind turbine system connected to the grid through parallel active power filter (PAPF. PAPF uses the generated wind energy to feed loads connected at the point of common coupling (PPC, compensates current harmonics and injects the excess of this energy into the grid using P-Q theory as control method. To demonstrate the feasibility and the performance of the proposed control scheme, simulation of this wind system has been realized using MATLAB/SIMULINK software. Simulation results show the accuracy and validity of the proposed control scheme for the PMSGPAPF system.

  11. Examining Dynamic Stall for an Oscillating NACA 4412 Hydrofoil

    McVay, Eric; Lang, Amy; Gamble, Lawren; Bradshaw, Michael

    2013-11-01

    Dynamic stall is unsteady separation that occurs when a hydrofoil pitches through the static stall angle while simultaneously experiencing a rapid change in angle of attack. The NACA 4412 hydrofoil was selected for this research because it has strong trailing edge turbulent boundary layer separation characteristics. General dynamic stall angle of attack for approximately symmetric airfoils has been recorded to occur at 24 degrees, with separation beginning at about 16 degrees. It is predicted that the boundary layer will stay attached at a higher angle of attack because of the cambered geometry of the hydrofoil. It is also hypothesized that the boundary layer separation occurs closer to the trailing edge and that the dynamic stall angle of attack occurs somewhere between 24 and 28 degrees for the oscillating NACA 4412 hydrofoil. This research was conducted in a water tunnel facility using Time Resolved Digital Particle Image Velocimetry (TR-DPIV). The hydrofoil was pitched up from 0 to 30 degrees at Reynolds numbers of 60,000, 80,000 and 100,000. Flow characteristics, dynamic stall angles of attack, and points of boundary layer separation were compared at each velocity with both tripped and un-tripped surfaces. Follow-on research will be conducted using flow control techniques from sharks and dolphins to examine the potential benefits of these natural designs for separation control. Support for this research by NSF REU Grant #1062611 and CBET Grant #0932352 is gratefully acknowledged.

  12. Stall Recovery Guidance Algorithms Based on Constrained Control Approaches

    Stepanyan, Vahram; Krishnakumar, Kalmanje; Kaneshige, John; Acosta, Diana

    2016-01-01

    Aircraft loss-of-control, in particular approach to stall or fully developed stall, is a major factor contributing to aircraft safety risks, which emphasizes the need to develop algorithms that are capable of assisting the pilots to identify the problem and providing guidance to recover the aircraft. In this paper we present several stall recovery guidance algorithms, which are implemented in the background without interfering with flight control system and altering the pilot's actions. They are using input and state constrained control methods to generate guidance signals, which are provided to the pilot in the form of visual cues. It is the pilot's decision to follow these signals. The algorithms are validated in the pilot-in-the loop medium fidelity simulation experiment.

  13. Fluid mechanics mechanisms in the stall process of helicopters

    Young, W. H., Jr.

    1981-01-01

    Recent experimental results from airfoils in the Mach number, Reynolds number, or reduced frequency ranges typical of helicopter rotor blades have identified the most influential flow mechanisms in the dynamic stall process. The importance of secondary shed vortices, downstream wake action, and the flow in the separated region is generally acknowledged but poorly understood. By means of surface pressure cross-correlations and flow field measurements in static stall, several new hypotheses have been generated. It is proposed that vortex shedding may be caused by acoustic disturbances propagating forward in the lower (pressure) surface boundary layer, that wake closure is a misnomer, and that the shed vortex leaves a trail of vorticity that forms a turbulent free shear layer. The known dynamic stall flow mechanisms are reviewed and the potential importance of recently proposed and hypothetical flow phenomena with respect to helicopter blade aeroelastic response are assessed.

  14. ATEFlap aerodynamic model, a dynamic stall model including the effects of trailing edge flap deflection

    Bergami, L.; Gaunaa, M.

    2012-02-15

    The report presents the ATEFlap aerodynamic model, which computes the unsteady lift, drag and moment on a 2D airfoil section equipped with Adaptive Trailing Edge Flap. The model captures the unsteady response related to the effects of the vorticity shed into the wake, and the dynamics of flow separation a thin-airfoil potential flow model is merged with a dynamic stall model of the Beddoes-Leishmann type. The inputs required by the model are steady data for lift, drag, and moment coefficients as function of angle of attack and flap deflection. Further steady data used by the Beddoes- Leishmann dynamic stall model are computed in an external preprocessor application, which gives the user the possibility to verify, and eventually correct, the steady data passed to the aerodynamic model. The ATEFlap aerodynamic model is integrated in the aeroelastic simulation tool HAWC2, thus al- lowing to simulate the response of a wind turbine with trailing edge flaps on the rotor. The algorithms used by the preprocessor, and by aerodynamic model are presented, and modifications to previous implementations of the aerodynamic model are briefly discussed. The performance and the validity of the model are verified by comparing the dynamic response computed by the ATEFlap with solutions from CFD simulations. (Author)

  15. Optimum Duty Cycle of Unsteady Plasma Aerodynamic Actuation for NACA0015 Airfoil Stall Separation Control

    Sun, Min; Yang, Bo; Peng, Tianxiang; Lei, Mingkai

    2016-06-01

    Unsteady dielectric barrier discharge (DBD) plasma aerodynamic actuation technology is employed to suppress airfoil stall separation and the technical parameters are explored with wind tunnel experiments on an NACA0015 airfoil by measuring the surface pressure distribution of the airfoil. The performance of the DBD aerodynamic actuation for airfoil stall separation suppression is evaluated under DBD voltages from 2000 V to 4000 V and the duty cycles varied in the range of 0.1 to 1.0. It is found that higher lift coefficients and lower threshold voltages are achieved under the unsteady DBD aerodynamic actuation with the duty cycles less than 0.5 as compared to that of the steady plasma actuation at the same free-stream speeds and attack angles, indicating a better flow control performance. By comparing the lift coefficients and the threshold voltages, an optimum duty cycle is determined as 0.25 by which the maximum lift coefficient and the minimum threshold voltage are obtained at the same free-stream speed and attack angle. The non-uniform DBD discharge with stronger discharge in the positive half cycle due to electrons deposition on the dielectric slabs and the suppression of opposite momentum transfer due to the intermittent discharge with cutoff of the negative half cycle are responsible for the observed optimum duty cycle. supported by National Natural Science Foundation of China (No. 21276036), Liaoning Provincial Natural Science Foundation of China (No. 2015020123) and the Fundamental Research Funds for the Central Universities of China (No. 3132015154)

  16. Dynamic Response of Flexible Wind Turbine Blade

    Yu-qiao Zheng; Rong-zhen ZHAO; Hong liu

    2013-01-01

    Aiming at the non-stationary and stall flutter problems of wind turbine blade caused by transient load fluctuations, the dynamic properties of wind turbine were studied, the blade was simplify to a cantilever beam in case of the action of shear deformation and cross section rotating effect were considered in this analysis, equations of the blade were established based on D'Alemberts' principle and the principle of virtual displacement. The dynamic response of the wind turbine was solved by us...

  17. Probabilistic Approach to Optimizing Active and Reactive Power Flow in Wind Farms Considering Wake Effects

    Yong-Cheol Kang

    2013-10-01

    Full Text Available This paper presents a novel probabilistic optimization algorithm for simultaneous active and reactive power dispatch in power systems with significant wind power integration. Two types of load and wind-speed uncertainties have been assumed that follow normal and Weibull distributions, respectively. A PV bus model for wind turbines and the wake effect for correlated wind speed are used to achieve accurate AC power flow analysis. The power dispatch algorithm for a wind-power integrated system is modeled as a probabilistic optimal power flow (P-OPF problem, which is operated through fixed power factor control to supply reactive power. The proposed P-OPF framework also considers emission information, which clearly reflects the impact of the energy source on the environment. The P-OPF was tested on a modified IEEE 118-bus system with two wind farms. The results show that the proposed technique provides better system operation performance evaluation, which is helpful in making decisions about power system optimal dispatch under conditions of uncertainty.

  18. Flux-tube geometry and wind speed during an activity cycle

    Pinto, R F; Rouillard, A P

    2016-01-01

    The solar wind speed at 1 AU shows variations in latitude and in time which reflect the evolution of the global background magnetic field during the activity cycle. It is commonly accepted that the terminal wind speed in a magnetic flux-tube is anti-correlated with its expansion ratio, which motivated the definition of widely-used semi-empirical scaling laws relating one to the other. In practice, such scaling laws require ad-hoc corrections. A predictive law based solely on physical principles is still missing. We test whether the flux-tube expansion is the controlling factor of the wind speed at all phases of the cycle and at all latitudes using a very large sample of wind-carrying open magnetic flux-tubes. We furthermore search for additional physical parameters based on the geometry of the coronal magnetic field which have an influence on the terminal wind flow speed. We use MHD simulations of the corona and wind coupled to a dynamo model to provide a large statistical ensemble of open flux-tubes which we...

  19. A dynamic stall model for airfoils with deformable trailing edges

    Andersen, Peter Bjørn; Gaunaa, Mac; Bak, Dan Christian; Hansen, Morten Hartvig

    2007-01-01

    airfoil section undergoing arbitrary motion in heave, lead-lag, pitch, Trailing Edge (TE) flapping. In the linear region, the model reduces to the inviscid model of Gaunaa [4], which includes the aerodynamic effect of a thin airfoil with a deformable camberline in inviscid flow. Therefore, the proposed......The present work contains an extension of the Beddoes-Leishman (B-L) type dynamic stall model, as described by Hansen et al. [7]. In this work a Deformable Trailing Edge Geometry (DTEG) has been added to the dynamic stall model. The model predicts the unsteady aerodynamic forces and moments on an...

  20. An examination of gas compressor stability and rotating stall

    Fozi, Aziz A.

    1987-01-01

    The principal sources of vibration related reliability problems in high pressure centrifugal gas compressors are the re-excitation of the first critical speed or Resonant Subsynchronous Vibration (RSSV), and the forced vibration due to rotating stall in the vaneless diffusers downstream of the impellers. An example of such field problems is given elsewhere. This paper describes the results of a test program at the author's company, initiated in 1983 and completed during 1985, which studied the RSSV threshold and the rotating stall phenomenon in a high pressure gas compressor.

  1. A dynamic stall model for airfoils with deformable trailing edges

    Andersen, Peter Bjørn; Gaunaa, Mac; Bak, Christian; Hansen, Morten Hartvig

    2009-01-01

    The present work contains an extension of the Beddoes-Leishman-type dynamic stall model. In this work, a deformable trailing-edge flap has been added to the dynamic stall model. The model predicts the unsteady aerodynamic forces and moments on an airfoil section undergoing arbitrary motion in heave......, lead-lag, pitch, trailing-edge flapping. In the linear region, the model reduces to the inviscid model, which includes the aerodynamic effect of a thin airfoil with a deformable camberline in inviscid flow. Therefore, the proposed model can be considered a crossover between the work of Gaunaa for the...

  2. Grid fault and design-basis for wind turbines. Final report

    Hansen, A.D.; Cutululis, N.A.; Markou, H.; Soerensen, Poul; Iov, F.

    2010-01-15

    This is the final report of a Danish research project 'Grid fault and design-basis for wind turbines'. The objective of this project has been to assess and analyze the consequences of the new grid connection requirements for the fatigue and ultimate structural loads of wind turbines. The fulfillment of the grid connection requirements poses challenges for the design of both the electrical system and the mechanical structure of wind turbines. The development of wind turbine models and novel control strategies to fulfill the TSO's requirements are of vital importance in this design. Dynamic models and different fault ride-through control strategies have been developed and assessed in this project for three different wind turbine concepts (active stall wind turbine, variable speed doublyfed induction generator wind turbine, variable speed multipole permanent magnet wind turbine). A computer approach for the quantification of the wind turbines structural loads caused by the fault ride-through grid requirement, has been proposed and exemplified for the case of an active stall wind turbine. This approach relies on the combination of knowledge from complimentary simulation tools, which have expertise in different specialized design areas for wind turbines. In order to quantify the impact of the grid faults and grid requirements fulfillment on wind turbines structural loads and thus on their lifetime, a rainflow and a statistical analysis for fatigue and ultimate structural loads, respectively, have been performed and compared for two cases, i.e. one when the turbine is immediately disconnected from the grid when a grid fault occurs and one when the turbine is equipped with a fault ride-through controller and therefore it is able to remain connected to the grid during the grid fault. Different storm control strategies, that enable variable speed wind turbines to produce power at wind speeds higher than 25m/s and up to 50m/s without substantially increasing

  3. Estimating Sea Surface Salinity and Wind Using Combined Passive and Active L-Band Microwave Observations

    Yueh, Simon H.; Chaubell, Mario J.

    2012-01-01

    Several L-band microwave radiometer and radar missions have been, or will be, operating in space for land and ocean observations. These include the NASA Aquarius mission and the Soil Moisture Active Passive (SMAP) mission, both of which use combined passive/ active L-band instruments. Aquarius s passive/active L-band microwave sensor has been designed to map the salinity field at the surface of the ocean from space. SMAP s primary objectives are for soil moisture and freeze/thaw detection, but it will operate continuously over the ocean, and hence will have significant potential for ocean surface research. In this innovation, an algorithm has been developed to retrieve simultaneously ocean surface salinity and wind from combined passive/active L-band microwave observations of sea surfaces. The algorithm takes advantage of the differing response of brightness temperatures and radar backscatter to salinity, wind speed, and direction, thus minimizing the least squares error (LSE) measure, which signifies the difference between measurements and model functions of brightness temperatures and radar backscatter. The algorithm uses the conjugate gradient method to search for the local minima of the LSE. Three LSE measures with different measurement combinations have been tested. The first LSE measure uses passive microwave data only with retrieval errors reaching 1 to 2 psu (practical salinity units) for salinity, and 1 to 2 m/s for wind speed. The second LSE measure uses both passive and active microwave data for vertical and horizontal polarizations. The addition of active microwave data significantly improves the retrieval accuracy by about a factor of five. To mitigate the impact of Faraday rotation on satellite observations, the third LSE measure uses measurement combinations invariant under the Faraday rotation. For Aquarius, the expected RMS SSS (sea surface salinity) error will be less than about 0.2 psu for low winds, and increases to 0.3 psu at 25 m/s wind speed

  4. Transcriptional stalling in B-lymphocytes: a mechanism for antibody diversification and maintenance of genomic integrity.

    Sun, Jianbo; Rothschild, Gerson; Pefanis, Evangelos; Basu, Uttiya

    2013-01-01

    B cells utilize three DNA alteration strategies-V(D)J recombination, somatic hypermutation (SHM) and class switch recombination (CSR)-to somatically mutate their genome, thereby expressing a plethora of antibodies tailor-made against the innumerable antigens they encounter while in circulation. Of these three events, the single-strand DNA cytidine deaminase, Activation Induced cytidine Deaminase (AID), is responsible for SHM and CSR. Recent advances, discussed in this review article, point toward various components of RNA polymerase II "stalling" machinery as regulators of AID activity during antibody diversification and maintenance of B cell genome integrity. PMID:23584095

  5. Dynamic Stall Flow Control Through the Use of a Novel Plasma Based Actuator Technology Project

    National Aeronautics and Space Administration — Lynntech proposes a novel flow control methodology for airfoils undergoing dynamic stall. Dynamic stall refers to an aerodynamic phenomenon that is experienced by...

  6. Design, manufacturing and characterization of aero-elastically scaled wind turbine blades for testing active and passive load alleviation techniques within a ABL wind tunnel

    In the research described in this paper, a scaled wind turbine model featuring individual pitch control (IPC) capabilities, and equipped with aero-elastically scaled blades featuring passive load reduction capabilities (bend-twist coupling, BTC), was constructed to investigate, by means of wind tunnel testing, the load alleviation potential of BTC and its synergy with active load reduction techniques. The paper mainly focus on the design of the aero-elastic blades and their dynamic and static structural characterization. The experimental results highlight that manufactured blades show desired bend-twist coupling behavior and are a first milestone toward their testing in the wind tunnel

  7. A High Step-Down Interleaved Buck Converter with Active-Clamp Circuits for Wind Turbines

    Chih-Lung Shen

    2012-12-01

    Full Text Available In this paper, a high step-down interleaved buck coupled-inductor converter (IBCC with active-clamp circuits for wind energy conversion has been studied. In high step-down voltage applications, an IBCC can extend duty ratio and reduce voltage stresses on active switches. In order to reduce switching losses of active switches to improve conversion efficiency, a IBCC with soft-switching techniques is usually required. Compared with passive-clamp circuits, the IBCC with active-clamp circuits have lower switching losses and minimum ringing voltage of the active switches. Thus, the proposed IBCC with active-clamp circuits for wind energy conversion can significantly increase conversion efficiency. Finally, a 240 W prototype of the proposed IBCC with active-clamp circuits was built and implemented. Experimental results have shown that efficiency can reach as high as 91%. The proposed IBCC with active-clamp circuits is presented in high step-down voltage applications to verify the performance and the feasibility for energy conversion of wind turbines.

  8. 76 FR 40925 - Commercial Wind Lease Issuance and Site Characterization Activities on the Atlantic Outer...

    2011-07-12

    ... renewable energy leases (which includes reasonably foreseeable site characterization activities--geophysical...-Atlantic WEAs (76 FR 7226), which requested public input with regard to the identification of the important... Bureau of Ocean Energy Management, Regulation and Enforcement Commercial Wind Lease Issuance and...

  9. Overview of PV Wind hybrid system activities in Germany

    Bopp, G.; Gabler, H.; Kiefer, K.; Preiser, K.; Wiemken, E. [Fraunhofer Institute for Solar Energy Systems ISE, Freiburg (Germany)

    1997-12-31

    Photovoltaic solar generators combined with diesel engines, in some cases additionally with wind energy converters, and battery energy storage are powering isolated mountain lodges, information centers in nature parks, isolated farms or dwellings all over Europe. A total of 300,000 buildings in Europe are estimated to be not connected to the public grid. This represents a major market potential for photovoltaic, as often photovoltaic power generation is less expensive than a connection to the electric utility. The Fraunhofer Institute for Solar Energy Systems ISE has planned, realized and monitored about 30 hybrid remote energy supply systems with PV generators typically around 5 kW for loads typically around 20 kWh per day. More than one hundred years of operational experience accumulated so far, are a sound foundation on which to draw an interim balance over problems solved and technical questions still under development. Room for further technical development is seen in the domain of system reliability and the reduction of operating costs as well as in the optimization of the utilization of the electric energy produced by the PV generator. [Espanol] Para la electrificacion en toda Europa de casas de campo en la montana, centros de informacion, parques naturales, granjas aisladas o conjuntos habitacionales, se estan usando generadores fotovoltaicos combinados con maquinas diesel, en algunos casos adicionalmente con convertidores de energia del viento y baterias para el almacenamiento de energia. Se estima que en Europa un total de 300,000 edificios no estan conectados a la red publica. Esto representa un gran mercado potencial para los sistemas fotovoltaicos, ya que a menudo la generacion fotovoltaica es menos costosa que una conexion a la empresa electrica. El Instituto Fraunhofer para Sistemas de Energia Solar ISE ha planeado, llevado a cabo y monitoreado alrededor de 30 sistemas hibridos remotos de suministro de energia con generadores fotovoltaicos

  10. URANS simulations of separated flow with stall cells over an NREL S826 airfoil

    Sarlak, H.; Nishino, T.; Sørensen, J. N.

    2016-06-01

    A series of wind tunnel measurements and oil flow visualization was recently carried out at the Technical University of Denmark in order to investigate flow characteristics over a 14% thick NREL S826 airfoil at low Reynolds numbers. This paper aims at presenting numerical simulations of the same airfoil using unsteady Reynolds-averaged Navier-Stokes (URANS) approach. Results of the simulations are demonstrated in terms of mean flow velocity, lift and drag, as well as pressure distribution, and validated against available experimental data. The simulations are carried out with a wide computational domain (with a span-to-chord ratio of 5) and it is illustrated that the URANS approach is capable of predicting 3D spanwise structures, known as stall cells.

  11. Recent NASA Research on Aerodynamic Modeling of Post-Stall and Spin Dynamics of Large Transport Airplanes

    Murch, Austin M.; Foster, John V.

    2007-01-01

    A simulation study was conducted to investigate aerodynamic modeling methods for prediction of post-stall flight dynamics of large transport airplanes. The research approach involved integrating dynamic wind tunnel data from rotary balance and forced oscillation testing with static wind tunnel data to predict aerodynamic forces and moments during highly dynamic departure and spin motions. Several state-of-the-art aerodynamic modeling methods were evaluated and predicted flight dynamics using these various approaches were compared. Results showed the different modeling methods had varying effects on the predicted flight dynamics and the differences were most significant during uncoordinated maneuvers. Preliminary wind tunnel validation data indicated the potential of the various methods for predicting steady spin motions.

  12. Investigating power control in autonomous power systems with increasing wind power penetration

    Margaris, Ioannis D. [National Technical Univ. of Athens (Greece). Electric Energy Systems Lab.; Hansen, Anca D.; Sorensen, Poul [Risoe National Laboratory, Roskilde (Denmark). Wind Energy Dept.; Hatziargyriou, Nikos D. [National Technical Univ. of Athens (Greece). Electric Energy Systems Lab.; Public Power Corporation S.A., Athens (Greece)

    2009-07-01

    Increasing levels of wind penetration in autonomous power systems has set intensively high standards with respect to wind turbine technology during the last years. Special features of non-interconnected power systems make security issues rather critical, as the operation of large wind farms like conventional power plants is becoming a necessity. This paper includes the study case of Rhodos island, in Greece, where rapidly increasing wind penetration has started to impose serious security issues for the immediate future. The scenarios studied here correspond to reference year of study 2012 and include wind farms with three different wind turbine technologies - namely Doubly Fed Induction Generator (DFIG), Permanent Magnet Synchronous Generator (PMSG) and Active Stall Induction Generator (ASIG) based wind turbines. Aggregated models of the wind farms are being used and results for different load cases are being analyzed and discussed. The ability of wind farms to assist in some of the power system control services traditionally carried out by conventional synchronous generation is being investigated and discussed. The power grid of the island, including speed governors and automatic voltage regulators, is simulated in the dedicated power system simulation program Power Factory from DIgSILENT. (orig.)

  13. An Axisymmetric, Hydrodynamical Model for the Torus Wind in Active Galactic Nuclei

    Dorodnitsyn, A.; Kallman, T.; Proga, D.

    2008-01-01

    We report on time-dependent axisymmetric simulations of an X-ray-excited flow from a parsec-scale, rotating, cold torus around an active galactic nucleus. Our simulations account for radiative heating and cooling and radiation pressure force. The simulations follow the development of a broad biconical outflow induced mainly by X-ray heating. We compute synthetic spectra predicted by our simulations. The wind characteristics and the spectra support the hypothesis that a rotationally supported torus can serve as the source of a wind which is responsible for the warm absorber gas observed in the X-ray spectra of many Seyfert galaxies.

  14. Flux-tube geometry and wind speed during an activity cycle

    Pinto, R. F.; Brun, A. S.; Rouillard, A. P.

    2016-01-01

    The solar wind speed at 1 AU shows variations in latitude and in time which reflect the evolution of the global background magnetic field during the activity cycle. It is commonly accepted that the terminal wind speed in a magnetic flux-tube is anti-correlated with its expansion ratio, which motivated the definition of widely-used semi-empirical scaling laws relating one to the other. In practice, such scaling laws require ad-hoc corrections. A predictive law based solely on physical principl...

  15. Performance of Pitch and Stall Regulated Tidal Stream Turbines

    Sujeet Swami

    2014-04-01

    Full Text Available Controllers for a pitch and a stall regulated horizontal axial flow, variable-speed tidal stream turbine are developed, and a performance comparison is carried out. Below rated flow speed, both turbines are operated in variable-speed mode so that the optimum tip-speed ratio is maintained. One of the turbines has variable pitch blades, which above rated speed are pitched to feather in order to regulate power. The other turbine has fixed pitch blades and uses speed-assisted stall to regulate power. The control system design behind both strategies is examined in MATLAB, with the performance under turbulent flows, loading and energy yield analysis being evaluated in GH Tidal Bladed. Both strategies provide a satisfactory performance, but the out-of-plane loads on the stall regulated turbine were higher over the entire range of operation. In addition, the dynamic characteristics of the stall regulated turbine require a more complex control design. The results suggest that the pitch regulated turbine would be a more attractive solution for turbine developers.

  16. Dynamic Characteristics of Rotating Stall in Mixed Flow Pump

    Xiaojun Li

    2013-01-01

    Full Text Available Rotating stall, a phenomenon that causes flow instabilities and pressure hysteresis by propagating at some fraction of the impeller rotational speed, can occur in centrifugal impellers, mixed impellers, radial diffusers, or axial diffusers. Despite considerable efforts devoted to the study of rotating stall in pumps, the mechanics of this phenomenon are not sufficiently understood. The propagation mechanism and onset of rotating stall are not only affected by inlet flow but also by outlet flow as well as the pressure gradient in the flow passage. As such, the complexity of these concepts is not covered by the classical explanation. To bridge this research gap, the current study investigated prerotation generated at the upstream of the impeller, leakage flow at the tip clearance between the casing and the impeller, and strong reserve flow at the inlet of the diffuser. Understanding these areas will clarify the origin of the positive slope of the head-flow performance curve for a mixed flow pump. Nonuniform pressure distribution and adverse pressure gradient were also introduced to evaluate the onset and development of rotating stall within the diffuser.

  17. Effects of injection frequency on the rotor stall margin

    2010-01-01

    The stall margin of compressor could be improved effectively by rotor tip injection,and the periodic injection is commonly used in the research.The purpose of this work is to investigate the influence of injection frequency on the rotor stall margin.An unsteady CFD code was employed to simulate the flow field of the rotor with injections of different frequencies.Comparing the stall margin of the rotor with injections of different frequencies,it is shown that there is an optimal injection frequency,around which the rotor stability enhancement is the largest.When the injection frequency is away form the optimal frequency,the improvement in stable flow range decreases correspondingly.For the rotor in this paper,the optimal frequency was 1.5 times the frequency of tip leakage vortex(for short,TLV) fluctuation.Time-averaged loading distribution at 98.5% span indicates that the loading of the rotor near the leading edge is decreased through injection with the optimal frequency,and therefore,the stall could be delayed.

  18. Stallings folds for CAT(0) cube complexes and quasiconvex subgroups

    Beeker, Benjamin; Lazarovich, Nir

    2016-01-01

    We describe a higher dimensional analogue of the Stallings folding sequence for group actions on CAT(0) cube complexes. We use it to give a characterization of quasiconvex subgroups of hyperbolic groups which act properly co-compactly on CAT(0) cube complexes via finiteness properties of their hyperplane stabilizers.

  19. DNA replication: stalling a fork for imprinting and switching

    Egel, Richard

    2004-01-01

    Mating-type switching in fission yeast has long been known to be directed by a DNA 'imprint'. This imprint has now been firmly characterized as a protected site-specific and strand-specific nick. New work also links the widely conserved Swi1-Swi3 complex to the protection of stalled replication...

  20. Investigation of flow behind vortex generators by stereo particle image velocimetry on a thick airfoil near stall

    Velte, Clara Marika; Hansen, Martin Otto Laver

    2013-01-01

    Stereoscopic Particle Image Velocimetry measurements investigating the effect of vortex generators (VGs) on the flow near stall were carried out in a purpose-built wind tunnel for airfoil investigations on a DU 91-W2-250 profile. Measurements were conducted at Re = 0.9⋅106, corresponding to free...... stream velocity U∞ = 15 m s−1. The objective was to investigate the flow structures induced by the vortex generators and study their separation controlling behavior on the airfoil. The uncontrolled flow (no VGs) displayed unsteady behavior with separation as observed from large streamwise velocity...

  1. Structural damage identification in wind turbine blades using piezoelectric active sensing with ultrasonic validation

    Claytor, Thomas N [Los Alamos National Laboratory; Ammerman, Curtt N [Los Alamos National Laboratory; Park, Gyu Hae [Los Alamos National Laboratory; Farinholt, Kevin M [Los Alamos National Laboratory; Farrar, Charles R [Los Alamos National Laboratory; Atterbury, Marie K [Los Alamos National Laboratory

    2010-01-01

    This paper gives a brief overview of a new project at LANL in structural damage identification for wind turbines. This project makes use of modeling capabilities and sensing technology to understand realistic blade loading on large turbine blades, with the goal of developing the technology needed to automatically detect early damage. Several structural health monitoring (SHM) techniques using piezoelectric active materials are being investigated for the development of wireless, low power sensors that interrogate sections of the wind turbine blade using Lamb wave propagation data, frequency response functions (FRFs), and time-series analysis methods. The modeling and sensor research will be compared with extensive experimental testing, including wind tunnel experiments, load and fatigue tests, and ultrasonic scans - on small- to mid-scale turbine blades. Furthermore, this study will investigate the effect of local damage on the global response of the blade by monitoring low-frequency response changes.

  2. Accretion disk winds in active galactic nuclei: X-ray observations, models, and feedback

    Tombesi, F.

    2016-05-01

    Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. A strong support of this ``quasar mode'' feedback came from the recent X-ray observation of a mildly relativistic accretion disk wind in a ultraluminous infrared galaxy (ULIRG) and its connection with a large-scale molecular outflow, providing a direct link between the SMBH and the gas out of which stars form. Spectroscopic observations, especially in the X-ray band, show that such accretion disk winds may be common in local AGN and quasars. However, their origin and characteristics are still not fully understood. Detailed theoretical models and simulations focused on radiation, magnetohydrodynamic (MHD) or a combination of these two processes to investigate the possible acceleration mechanisms and the dynamics of these winds. Some of these models have been directly compared to X-ray spectra, providing important insights into the wind physics. However, fundamental improvements on these studies will come only from the unprecedented energy resolution and sensitivity of the upcoming X-ray observatories, namely ASTRO-H (launch date early 2016) and Athena (2028).

  3. Aeroelastic instability problems for wind turbines

    Hansen, Morten Hartvig

    2007-01-01

    stiffness and chordwise position of the center of gravity along the blades are the main parameters for flutter. These instability characteristics are exemplified by aeroelastic stability analyses of different wind turbines. The review of each aeroelastic instability ends with a list of current research......This paper deals with the aeroelostic instabilities that have occurred and may still occur for modem commercial wind turbines: stall-induced vibrations for stall-turbines, and classical flutter for pitch-regulated turbines. A review of previous works is combined with derivations of analytical...... stability limits for typical blade sections that show the fundamental mechanisms of these instabilities. The risk of stall-induced vibrations is mainly related to blade airfoil characteristics, effective direction of blade vibrations and structural damping, whereas the blade tip speed, torsional blade...

  4. Wind from the black-hole accretion disk driving a molecular outflow in an active galaxy.

    Tombesi, F; Meléndez, M; Veilleux, S; Reeves, J N; González-Alfonso, E; Reynolds, C S

    2015-03-26

    Powerful winds driven by active galactic nuclei are often thought to affect the evolution of both supermassive black holes and their host galaxies, quenching star formation and explaining the close relationship between black holes and galaxies. Recent observations of large-scale molecular outflows in ultraluminous infrared galaxies support this quasar-feedback idea, because they directly trace the gas from which stars form. Theoretical models suggest that these outflows originate as energy-conserving flows driven by fast accretion-disk winds. Proposed connections between large-scale molecular outflows and accretion-disk activity in ultraluminous galaxies were incomplete because no accretion-disk wind had been detected. Conversely, studies of powerful accretion-disk winds have until now focused only on X-ray observations of local Seyfert galaxies and a few higher-redshift quasars. Here we report observations of a powerful accretion-disk wind with a mildly relativistic velocity (a quarter that of light) in the X-ray spectrum of IRAS F11119+3257, a nearby (redshift 0.189) optically classified type 1 ultraluminous infrared galaxy hosting a powerful molecular outflow. The active galactic nucleus is responsible for about 80 per cent of the emission, with a quasar-like luminosity of 1.5 × 10(46) ergs per second. The energetics of these two types of wide-angle outflows is consistent with the energy-conserving mechanism that is the basis of the quasar feedback in active galactic nuclei that lack powerful radio jets (such jets are an alternative way to drive molecular outflows). PMID:25810204

  5. Activity of Wind-Blown Sand and the Formation of Feathered Sand Ridges in the Kumtagh Desert, China

    Liao, Kongtai; Qu, Jianjun; Tang, Jinnian; Ding, Feng; Liu, Hujun; Zhu, Shujuan

    2010-05-01

    We study the activity of wind-blown sand and its effects on the evolution of feathered sand ridges in the Kumtagh Desert, China, and attempt to reveal the formation process of feathered sand ridges using wind-tunnel experiments, remote sensing data, and detailed field observations from 2005 to 2008. The prevailing wind direction in the Kumtagh Desert is easterly in winter and north-easterly in other seasons. The average annual wind speed is 5.9 ms-1, and winds sufficiently strong to entrain sand occur on 143 days per annum. The sand transport rate within 0.4 m of the ground is strongly influenced by local landforms, and is related to wind speed by a power function. Wind erosion occurs on the crest, the windward slope of crescent sand ridges and inter-ridge sand strips, where the blowing sand cloud is in an unsaturated state; in contrast, sand accumulation occurs on the leeward slope of the crescent sand ridges, where the blowing sand cloud is in an over-saturated state. These results indicate that the development of feathered sand ridges in the Kumtagh Desert is mainly controlled by the local wind regime. The dominant winds (from the north, north-north-east and north-east) and additional winds (from the east-north-east, east and east-south-east) determine the development of crescent sand ridges, but winds that are approximately parallel to sand ridges form the secondary inter-ridge sand strips.

  6. DeepWind - from Idea to 5 MW Concept

    Schmidt Paulsen, Uwe; Aagaard Madsen, Helge; Kragh, Knud Abildgaard;

    2014-01-01

    The DeepWind concept has been described previously on challenges and potentials, this new offshore floating technology can offer to the wind industry [1]. The paper describes state of the art design improvements, new simulation results of the DeepWind floating vertical axis wind turbine concept, ...... both the generator and the aerodynamic rotor. Another example is aerofoil design affecting energy capture, stall behaviour, structural dynamics and control design. Finally, the potential for up-scaling to 20 MW is discussed....

  7. Dynamic lift measurements on a FX79W151A airfoil via pressure distribution on the wind tunnel walls

    We report on an experimental setup for measurements of dynamic stall for airfoils via the pressure distribution over wind tunnel walls. This measuring technique, hitherto used for lift measurements under static conditions, is also an adequate method for dynamic conditions until stall occurs. A step motor is used, allowing for sinusoidal as well as non-sinusoidal and stochastic pitching to simulate fast fluctuating flow conditions. Measurements with sinusoidal pitching and constant angular velocities were done and show dynamic stall characteristics. Under dynamic stall conditions, maximum lift coefficients were up to 80% higher than the maximum for static lift

  8. Active Power Optimal Control of Wind Turbines with Doubly Fed Inductive Generators Based on Model Predictive Control

    Guo Jiuwang

    2015-01-01

    Full Text Available Because of the randomness and fluctuation of wind energy, as well as the impact of strongly nonlinear characteristic of variable speed constant frequency (VSCF wind power generation system with doubly fed induction generators (DFIG, traditional active power control strategies are difficult to achieve high precision control and the output power of wind turbines is more fluctuated. In order to improve the quality of output electric energy of doubly fed wind turbines, on the basis of analyzing the operating principles and dynamic characteristics of doubly fed wind turbines, this paper proposes a new active power optimal control method of doubly fed wind turbines based on predictive control theory. This method uses state space model of wind turbines, based on the prediction of the future state of wind turbines, moves horizon optimization, and meanwhile, gets the control signals of pitch angle and generator torque. Simulation results show that the proposed control strategies can guarantee the utilization efficiency for wind energy. Simultaneously, they can improve operation stability of wind turbines and the quality of electric energy.

  9. FANCD2-Controlled Chromatin Access of the Fanconi-Associated Nuclease FAN1 Is Crucial for the Recovery of Stalled Replication Forks

    Chaudhury, Indrajit; Stroik, Daniel R.

    2014-01-01

    Fanconi anemia (FA) is a cancer predisposition syndrome characterized by cellular hypersensitivity to DNA interstrand cross-links (ICLs). Within the FA pathway, an upstream core complex monoubiquitinates and recruits the FANCD2 protein to ICLs on chromatin. Ensuing DNA repair involves the Fanconi-associated nuclease 1 (FAN1), which interacts selectively with monoubiquitinated FANCD2 (FANCD2Ub) at ICLs. Importantly, FANCD2 has additional independent functions: it binds chromatin and coordinates the restart of aphidicolin (APH)-stalled replication forks in concert with the BLM helicase, while protecting forks from nucleolytic degradation by MRE11. We identified FAN1 as a new crucial replication fork recovery factor. FAN1 joins the BLM-FANCD2 complex following APH-mediated fork stalling in a manner dependent on MRE11 and FANCD2, followed by FAN1 nuclease-mediated fork restart. Surprisingly, APH-induced activation and chromatin recruitment of FAN1 occur independently of the FA core complex or the FAN1 UBZ domain, indicating that the FANCD2Ub isoform is dispensable for functional FANCD2-FAN1 cross talk during stalled fork recovery. In the absence of FANCD2, MRE11 exonuclease-promoted access of FAN1 to stalled forks results in severe FAN1-mediated nucleolytic degradation of nascent DNA strands. Thus, FAN1 nuclease activity at stalled replication forks requires tight regulation: too little inhibits fork restart, whereas too much causes fork degradation. PMID:25135477

  10. Semianalytic Models of Two-Phase Disk Winds in Active Galactic Nuclei with Combined Hydromagnetic and Radiative Driving

    Everett, John E.

    2002-01-01

    (abridged) We present a semianalytic model of steady-state magnetically and radiatively driven disk outflows in Active Galactic Nuclei (AGNs) consisting of a continuous wind with embedded clouds. The continuous outflow is launched from the disk surface as a centrifugally driven wind, whereas the clouds are uplifted from the disk by the ram pressure of the continuous outflow. In addition, the continuous wind and clouds are subject to both line and continuum radiative acceleration. We describe ...

  11. Numerical Simulation of Rotating Stall in a Centrifugal Compressor with Vaned Diffuser

    Weiguang Huang; Shaojuan Geng; Junqiang Zhu; Hongwu Zhang

    2007-01-01

    This paper reports a numerical study on the process from normal operating conditions to rotating stall in a centrifugal compressor with vaned diffuser. The purpose is to better understand the flow characteristics near stall point under the interactions between centrifugal impeller and vaned diffuser. Numerical results show that under certain conditions just preceding stall point the tip leakage vortex begins to fluctuate at roughly half of the blade passing frequency. This phenomenon is similar to rotating instability in axial compressors. With the flow rate reduced further the impeller stalls and five stall cells propagating at a frequency of 85 percent of impeller rotation speed are found.

  12. Flow and Noise Characteristics of Centrifugal Fan under Different Stall Conditions

    Lei Zhang

    2014-01-01

    Full Text Available An implicit, time-accurate 3D Reynolds-averaged Navier-Stokes (RANS solver is used to simulate the rotating stall phenomenon in a centrifugal fan. The goal of the present work is to shed light on the flow field and particularly the aerodynamic noise at different stall conditions. Aerodynamic characteristics, frequency domain characteristics, and the contours of sound power level under two different stall conditions are discussed in this paper. The results show that, with the decrease of valve opening, the amplitude of full pressure and flow fluctuations tends to be larger and the stall frequency remains the same. The flow field analysis indicates that the area occupied by stall cells expands with the decrease of flow rate. The noise calculation based on the simulation underlines the role of vortex noise after the occurrence of rotating stall, showing that the high noise area rotates along with the stall cell in the circumferential direction.

  13. Active region plasma outflows as sources of slow/intermediate solar wind

    van Driel-Gesztelyi, Lidia M.

    2015-08-01

    L. van Driel-Gesztelyi (1,2,3), D. Baker (1), P. Démoulin (2), Culhane, J.L. (1), M.L. DeRosa (4) C.H. Mandrini (5,6), D.H. Brooks (7), A.N. Fazakerley (1), L.K. Harra (1), L. Zhao (7), T.H. Zurbuchen (7), F.A. Nuevo (5,6), A.M. Vásquez (5,6), G.D. Cristiani (5,6) M. Pick (2)1) UCL/MSSL, UK, (2) Paris Observatory, LESIA, CNRS, France, (3) Konkoly Observatory, Hungary, (4) Lockheed Martin Solar and Astrophysics Laboratory, USA, (5) IAFE, CONICET-UBA, Argentina (6) FCEN, UBA, Argentina (7) Dept. of Atmospheric, Oceanic and Earth Sciences, Univ. of Michigan, USAWe analyse plasma upflows of tens of km/s from the edges of solar active regions discovered by Hinode/EIS and investigate whether or not they become outflows, i.e. find their way into the solar wind. We analyse two magnetic configurations: bipolar and quadrupolar and find that the active region plasma may be directly channeled into the solar wind via interchange reconnection at a high-altitude null point above the active region especially when active regions are located besides coronal holes or in a more complex way via multiple reconnections even from under a closed helmet streamer. We relate the solar observations to in-situ slow/intermediate solar wind streams.

  14. The duelling wind model for the emission line region of active nuclei

    The consequences of the duelling wind model for the nuclear properties of active galaxies and quasars are investigated. Detailed predictions can be made as a result of the clear postulates for the origins of both the nuclear and disc winds. We demonstrate how predictions for a single source can be extracted from the model by using IUE data of the Seyfert galaxy NGC 4151. A central mass of ∼ 2 x 106 solar masses, an active phase λ ∼ 1, and a broad-line density maximum ∼ 1012 cm-3 at a radius ∼ 2 x 1016 cm are required to produce the line intensities, widths and response times. The delayed response of the line emission to the continuum can be used to test the model. (author)

  15. Wind tunnel test on airfoil Riso-B1-18 with an Active Trailing Edge Flap

    Bak, Christian; Gaunaa, Mac; Andersen, Peter Bjørn;

    2010-01-01

    A wind tunnel test of the wind turbine airfoil Risø-B1-18 equipped with an Active Trailing Edge Flap (ATEF) was carried out. The ATEF was 9% of the total chord, made of piezo electric actuators attached to the trailing edge of a non-deformable airfoil and actuated using an (electric) amplifier. The...

  16. Cooling systems of the resting area in free stall dairy barn

    Calegari, F.; Calamari, L.; Frazzi, E.

    2016-04-01

    A study during the summer season evaluated the effect of different cooling systems on behavioral and productive responses of Italian Friesian dairy cows kept in an experimental-free stall barn located in the Po Valley in Italy. The study involved 30 lactating dairy cows subdivided into two groups kept in two pens with external hard court paddock in each free stall. The same cooling system was applied in the feeding area in both pens. A different cooling system in the resting area was applied to the two pens: in the pen SW, the resting area was equipped with fans and misters; in the other, there was simple ventilation (SV). Breathing rate, rectal temperature, milk yield, and milk characteristics (fat, protein, and somatic cell count) were measured. Behavioral activities (standing and lying cows in the different areas, as well as the animals in the feed bunk) were recorded. Mild to moderate heat waves during the trial were observed. On average, the breathing rate was numerically greater in SV compared with SW cows (60.2 and 55.8 breath/min, respectively), and mean rectal temperature remained below 39 °C in both groups during the trial (on average 38.7 and 38.8 °C in SV and SW, respectively. During the hotter periods of the trial, the time spent lying indoor in the free stall was greater in SW (11.8 h/day) than SV (10.7 h/day). Conversely, the time spent standing indoor without feeding was greater in SV (4.3 h/day) than SW (3.8 h/day). Milk yield was slightly better maintained during hotter period in SW compared with SV and somatic cell count was also slightly greater in the former. In conclusion, the adoption of the cooling system by means of evaporative cooling also in the resting area reduces the alteration of time budget caused by heat stress.

  17. Wind Turbine Measurement Technique—an Open Laboratory for Educational Purposes

    Pedersen, Knud Ole Helgesen; Hansen, Kurt Schaldemose; Schmidt Paulsen, Uwe;

    2008-01-01

    As part of the International Master of Science Programme in Wind Energy at the Technical University of Denmark (DTU),a complete interactive wind turbine measurement laboratory (WTMLAB) was developed. A 500 kW stall regulated wind turbine was instrumented with sensors for recording (i) turbine ope...

  18. Optimal Active Power Control of A Wind Farm Equipped with Energy Storage System based on Distributed Model Predictive Control

    Zhao, Haoran; Wu, Qiuwei; Guo, Qinglai;

    2016-01-01

    This paper presents the Distributed Model Predictive Control (D-MPC) of a wind farm equipped with fast and short-term Energy Storage System (ESS) for optimal active power control using the fast gradient method via dual decomposition. The primary objective of the D-MPC control of the wind farm is...... power reference tracking from system operators. Besides, by optimal distribution of the power references to individual wind turbines and the ESS unit, the wind turbine mechanical loads are alleviated. With the fast gradient method, the convergence rate of the DMPC is significantly improved which leads...... to a reduction of the iteration number. Accordingly, the communication burden is reduced. Case studies demonstrate that the additional ESS unit can lead to a larger wind turbine load reduction, compared to the conventional wind farm control without ESS. Moreover, the efficiency of the developed D...

  19. Robust Active Disturbance Rejection Control Approach to Maximize Energy Capture in Variable-Speed Wind Turbines

    Horacio Coral-Enriquez; John Cortés-Romero; Ramos, Germán A.

    2013-01-01

    This paper proposes an alternative robust observer-based linear control technique to maximize energy capture in a 4.8 MW horizontal-axis variable-speed wind turbine. The proposed strategy uses a generalized proportional integral (GPI) observer to reconstruct the aerodynamic torque in order to obtain a generator speed optimal trajectory. Then, a robust GPI observer-based controller supported by an active disturbance rejection (ADR) approach allows asymptotic tracking of the generator speed opt...

  20. Electric vehicle battery charging algorithm using PMSM windings and an inverter as an active rectifier

    Zaja, Mario; Oprea, Matei-lon; Suárez, Carlos Gómez; Mathe, Laszlo

    2014-01-01

    A major setback for large scale electric vehicle market expansion compared to their internal combustion competitors consists in their high price and low driving range. One way of reducing the cost, dimensions and mass of electric vehicles is to eliminate the dedicated AC/DC converter used for battery charging. Alternatively, charging could be done using the motor windings as grid side inductors and controlling the inverter to operate as an active boost rectifier. The challenge in this approac...

  1. Wind for Schools: A National Data and Curricula Development Activity for Schools (Poster)

    Baring-Gould, I.

    2011-05-01

    As the United States dramatically expands wind energy deployment, the industry is challenged with developing a skilled workforce and addressing public resistance. Wind Powering America?s Wind for Schools project addresses these issues by: 1) Developing Wind Application Centers (WACs) at universities; WAC students assist in implementing school wind turbines and participate in wind courses. 2) Installing small wind turbines at community 'host' schools. 3) Implementing teacher training with interactive curricula at each host school.

  2. Study and Control of a Radial Vaned Diffuser Stall

    Aurélien Marsan; Isabelle Trébinjac; Sylvain Coste; Gilles Leroy

    2012-01-01

    International audience The aim of the present study is to evaluate the efficiency of a boundary layer suction technique in case of a centrifugal compressor stage in order to extend its stable operating range. First, an analysis of the flow pattern within the radial vaned diffuser is presented. It highlights the stall of the diffuser vanes when reaching a low massflow. A boundary layer separation in the hub-suction side corner grows when decreasing the massflow from the nominal operating po...

  3. Open books supporting overtwisted contact structures and Stallings twist

    Yamamoto, Ryosuke

    2006-01-01

    We study open books (or open book decompositions) of a closed oriented 3-manifold which support overtwisted contact structures. We focus on a simple closed curve along which one can perform Stallings twist, called ``twisting loop''. We show that the existence of a twisting loop on the fiber surface of an open book is equivalent up to positive stabilization to the existence of an overtwisted disk in the contact manifold supported by the open book. We also show a criterion for overtwistedness u...

  4. Study and Control of a Radial Vaned Diffuser Stall

    Aurélien Marsan

    2012-01-01

    Full Text Available The aim of the present study is to evaluate the efficiency of a boundary layer suction technique in case of a centrifugal compressor stage in order to extend its stable operating range. First, an analysis of the flow pattern within the radial vaned diffuser is presented. It highlights the stall of the diffuser vanes when reaching a low massflow. A boundary layer separation in the hub-suction side corner grows when decreasing the massflow from the nominal operating point to the surge and finally leads to a massive stall. An aspiration strategy is investigated in order to control the stall. The suction slot is put in the vicinity of the saddle that originates the main separating skin-friction line, identified thanks to the analysis of the skin-friction pattern. Several aspiration massflow rates are tested, and two different modelings of the aspiration are evaluated. Finally, an efficient control is reached with a removal of only 0,1% of the global massflow and leads—from a steady-state calculations point of view—to an increase by 40% of the compressor operating range extent.

  5. Simulasi Numerik Dynamic Stall Pada Airfoil Yang Berosilasi

    Galih S.T.A. Bangga

    2012-09-01

    Full Text Available Kebutuhan analisa pada sudu helikopter, kompresor, kincir angin dan struktur streamline lainya yang beroperasi pada angle of attack yang tinggi dan melibatkan instationary effects yang disebut dynamic stall menjadi semakin penting. Fenomena ini ditandai dengan naiknya dynamic lift melewati static lift maksimum pada critical static stall angle, vortex yang terbentuk pada leading edge mengakibatkan naiknya suction contribution yang kemudian terkonveksi sepanjang permukaan hingga mencapai trailling edge diikuti terbentuknya trailling edge vortex yang menunjukkan terjadinya lift stall. Fenomena ini sangat berbahaya terhadap struktur airfoil itu sendiri. Secara umum, beban fatique yang ditimbulkan oleh adanya efek histerisis karena fluktuasi gaya lift akibat induksi vibrasi lebih besar dibandingkan kondisi statis. Simulasi numerik dilakukan secara 2D dengan menggunakan profil Boeing-Vertol V23010-1.58 pada α0 = 14.92°. Standard-kω dan SST-kω digunakan sebagai URANS turbulence modelling. Model osilasi dari airfoil disusun dalam suatu user defined function (UDF. Gerakan meshing beserta airfoil diakomodasi dengan menggunakan dynamic mesh approach. Simulasi numerik menunjukkan bahwa, model SST-kω menunjukkan performa yang lebih baik dibandingkan dengan Standard-kω. Fenomena travelling vortex yang terjadi mampu ditangkap dengan baik, meski pada angle of attack yang tinggi URANS turbulence model gagal memprediksikan fenomena yang terjadi karena dominasi efek 3D.

  6. Vorticity Transport on a Flexible Wing in Stall Flutter

    Akkala, James; Buchholz, James; Farnsworth, John; McLaughlin, Thomas

    2014-11-01

    The circulation budget within dynamic stall vortices was investigated on a flexible NACA 0018 wing model of aspect ratio 6 undergoing stall flutter. The wing had an initial angle of attack of 6 degrees, Reynolds number of 1 . 5 ×105 and large-amplitude, primarily torsional, limit cycle oscillations were observed at a reduced frequency of k = πfc / U = 0 . 1 . Phase-locked stereo PIV measurements were obtained at multiple chordwise planes around the 62.5% and 75% spanwise locations to characterize the flow field within thin volumetric regions over the suction surface. Transient surface pressure measurements were used to estimate boundary vorticity flux. Recent analyses on plunging and rotating wings indicates that the magnitude of the pressure-gradient-driven boundary flux of secondary vorticity is a significant fraction of the magnitude of the convective flux from the separated leading-edge shear layer, suggesting that the secondary vorticity plays a significant role in regulating the strength of the primary vortex. This phenomenon is examined in the present case, and the physical mechanisms governing the growth and evolution of the dynamic stall vortices are explored. This work was supported by the Air Force Office of Scientific Research through the Flow Interactions and Control Program monitored by Dr. Douglas Smith, and through the 2014 AFOSR/ASEE Summer Faculty Fellowship Program (JA and JB).

  7. Experiences and results from Elkraft 1 MW wind turbine

    Raben, N.; Jensen, F.V. [SEAS Distribution A.m.b.A., Wind Power Dept., Haslev (Denmark); Oeye, S. [DTU, Inst. for Energiteknik, Lyngby (Denmark); Markkilde Petersen, S.; Antoniou, I. [Risoe National Lab., Wind Energy and Atmospheric Physics Dept., Roskilde (Denmark)

    1999-03-01

    The Elkraft 1 MW Demonstration wind turbine was at the time of installation in 1993 the largest stall controlled wind turbine in the world. It was constructed to allow accurate comparison of two different forms of operation: pitch control and stall control. A comprehensive programme for the investigation of the two operation modes was established. This paper presents the main experiences from five years of operation and measurements. For a three-year period the wind turbine was in operation in stall controlled mode. During this period the turbine faced problems of various significance. Especially lightning strikes and unusually poor wind conditions caused delays of the project. In early 1997, the wind turbine was modified to enable pitch controlled operation. The gearbox ratio was changed in order to allow higher rotor speed, the hydraulic system was altered and new control software was installed. Tests were carried out successfully during the spring of 1997 and the wind turbine has since been operating as a pitch controlled wind turbine. The most significant events and problems are presented and commented in this paper along with results from the measurement programme. The results cover both stall and pitch controlled operation and include power curves, annual energy production, structural loads, fatigue loads etc. (au) 10 refs.

  8. Linear active disturbance rejection-based load frequency control concerning high penetration of wind energy

    Highlights: • A disturbance rejection solution to the load frequency control issue is proposed. • Several power systems with wind energy conversation system have been tested. • A tuning algorithm of the controller parameters was proposed. • The performance of the proposed approach is better than traditional controllers. - Abstract: A new grid load frequency control approach is proposed for the doubly fed induction generator based wind power plants. The load frequency control issue in a power system is undergoing fundamental changes due to the rapidly growing amount of wind energy conversation system, and concentrating on maintaining generation-load balance and disturbance rejection. The prominent feature of the linear active disturbance rejection control approach is that the total disturbance can be estimated and then eliminated in real time. And thus, it is a feasible solution to deal with the load frequency control issue. In this paper, the application of the linear active disturbance rejection control approach in the load frequency control issue for a complex power system with wind energy conversation system based on doubly fed induction generator is investigated. The load frequency control issue is formulated as a decentralized multi-objective optimization control problem, the solution to which is solved by the hybrid particle swarm optimization technique. To show the effectiveness of the proposed control scheme, the robust performance testing based on Monte-Carlo approach is carried out. The performance superiority of the system with the proposed linear active disturbance rejection control approach over that with the traditional proportional integral and fuzzy-proportional integral-based controllers is validated by the simulation results

  9. Economic evaluation of stall stocking density of lactating dairy cows.

    De Vries, Albert; Dechassa, Hailegziabher; Hogeveen, Henk

    2016-05-01

    An increase in stall stocking density (SSD), as measured by the number of lactating cows per stall in a freestall barn, reduces cow performance, such as milk yield and fertility, but may increase farm profitability. Our objectives were to calculate effects of varying SSD on profit per stall for a range of effects on cow performances and external farm factors and store results in regression metamodels. The literature on quantified effects of SSD on cow performance that directly affects cash flow was found to be weak. We assumed effects of SSD on milk yield, probability of conception, and probability of culling. External farm factors were probability of insemination, feed price, and milk price. A herd budget-simulation model was used which mimics the performance of cows in a herd and calculates profit per stall per year and other results. The SSD varied from 100 (no overstocking) to 150% (severe overstocking) in steps of 10%. Sensitivity analyses for effects of SSD on cow performance and effects of external farm factors were performed. Three regression metamodels were developed. The first metamodel accurately predicted profitability at 100% SSD for all variations in the external farm factors. Optimal SSD varied from 100 to 150% SSD, depending on the combination of inputs, and was very sensitive to changes in the size of the milk loss and milk and feed prices. Average optimal SSD of all 2,187 combinations of inputs was 120% SSD and average maximum increase in profit was $99/stall per year. Of the 2,187 combinations of inputs, 18% were ascending (maximum increase in profit >150% SSD), 33% were descending (maximum profit at 100% SSD), and 50% had a maximum increase in profit between 100 and 150% SSD. The second metamodel accurately captured changes in profit for all combinations of biological and external inputs and SSD. A third metamodel captured breakeven daily milk losses which would result in the same profit as at 100% SSD given the same external farm factors. In

  10. Development of Control Structure for Hybrid Wind Generators with Active Power Capability

    Mehdi Niroomand

    2014-01-01

    Full Text Available A hierarchical control structure is proposed for hybrid energy systems (HES which consist of wind energy system (WES and energy storage system (ESS. The proposed multilevel control structure consists of four blocks: reference generation and mode select, power balancing, control algorithms, and switching control blocks. A high performance power management strategy is used for the system. Also, the proposed system is analyzed as an active power filter (APF with ability to control the voltage, to compensate the harmonics, and to deliver active power. The HES is designed with parallel DC coupled structure. Simulation results are shown for verification of the theoretical analysis.