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Sample records for beddoes-leishman dynamic stall

  1. A Beddoes-Leishman type dynamic stall model in state-space and indicial formulations

    DEFF Research Database (Denmark)

    Hansen, M.H.; Gaunaa, Mac; Aagaard Madsen, Helge

    2004-01-01

    This report contains a description of a Beddoes-Leishman type dynamic stall model in both a state-space and an indicial function formulation. The model predicts the unsteady aerodynamic forces and moment on an airfoil section undergoing arbitrary motionin heave, lead-lag, and pitch. The model...... features, such as overshoot of the lift, in the stall region. The linearized model is shown to give identicalresults to the full model for small amplitude oscillations. Furthermore, it is shown that the response of finite thichkness airfoils can be reproduced to a high accuracy by the use of specific...

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

    Energy Technology Data Exchange (ETDEWEB)

    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)

  3. Comparing different dynamic stall models

    Energy Technology Data Exchange (ETDEWEB)

    Holierhoek, J.G. [Unit Wind Energy, Energy research Centre of the Netherlands, ZG, Petten (Netherlands); De Vaal, J.B.; Van Zuijlen, A.H.; Bijl, H. [Aerospace Engineering, Delft University of Technology, Delft (Netherlands)

    2012-07-16

    The dynamic stall phenomenon and its importance for load calculations and aeroelastic simulations is well known. Different models exist to model the effect of dynamic stall; however, a systematic comparison is still lacking. To investigate if one is performing better than another, three models are used to simulate the Ohio State University measurements and a set of data from the National Aeronautics and Space Administration Ames experimental study of dynamic stall and compare results. These measurements were at conditions and for aerofoils that are typical for wind turbines, and the results are publicly available. The three selected dynamic stall models are the ONERA model, the Beddoes-Leishman model and the Snel model. The simulations show that there are still significant differences between measurements and models and that none of the models is significantly better in all cases than the other models. Especially in the deep stall regime, the accuracy of each of the dynamic stall models is limited.

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

    DEFF Research Database (Denmark)

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

    2007-01-01

    on an 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...

  5. Dynamic stall model for wind turbine airfoils

    DEFF Research Database (Denmark)

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

    2007-01-01

    A model is presented for aerodynamic lift of wind turbine profiles under dynamic stall. The model combines memory delay effects under attached flow with reduced lift due to flow separation under dynamic stall conditions. The model is based on a backbone curve in the form of the static lift...... conditions, nonstationary effects are included by three mechanisms: a delay of the lift coefficient of fully attached flow via a second-order filter, a delay of the development of separation represented via a first-order filter, and a lift contribution due to leading edge separation also represented via...... during dynamic stall conditions. The proposed model is compared with five other dynamic stall models including, among others, the Beddoes-Leishman model and the ONERA model. It is demonstrated that the proposed model performs equally well or even better than more complicated models and that the included...

  6. DYNSTALL: Subroutine package with a dynamic stall model

    Energy Technology Data Exchange (ETDEWEB)

    Bjoerck, Anders [Aeronautical Research Inst. of Sweden, Bromma (Sweden)

    2001-03-01

    A subroutine package, called DYNSTALL, for the calculation of 2D unsteady airfoil aerodynamics is described. The subroutines are written in FORTRAN. DYNSTALL is basically an implementation of the Beddoes-Leishman dynamic stall model. This model is a semi-empirical model for dynamic stall. It includes, however, also models for attached flow unsteady aerodynamics. It is complete in the sense that it treats attached flow as well as separated flow. Semi-empirical means that the model relies on empirically determined constants. Semi because the constants are constants in equations with some physical interpretation. It requires the input of 2D airfoil aerodynamic data via tables as function of angle of attack. The method is intended for use in an aeroelastic code with the aerodynamics solved by blade/element method. DYNSTALL was written to work for any 2D angles of attack relative to the airfoil, e.g. flow from the rear of an airfoil.

  7. A Detailed Study of the Rotational Augmentation and Dynamic Stall Phenomena for Wind Turbines

    DEFF Research Database (Denmark)

    Guntur, Srinivas

    ), using rotationally augmented steady state polars as the input instead of the typically used 2D (stationary) data. The aim of this part of the work has been to investigate the differences between the stall phenomenon on harmonically pitching blades on a rotating wind turbine and the classic dynamic stall......This thesis presents investigations into the aerodynamics of wind turbine rotors, with a focus on the in-board sections of the rotor. Two important aerodynamic phenomena that have challenged scientists over nearly the last half a century are the so-called rotational augmentation and dynamic stall...... on wind turbine blades using the N-sequence data of the NREL UAE Phase VI experiment. The experimental data is compared with the results from unsteady Delayed Detached Eddy Simulations (DDES). The same conditions are also modelled using a Beddoes-Leishman type dynamic stall model by Hansen et al. (2004...

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

    Energy Technology Data Exchange (ETDEWEB)

    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)

  9. Dynamic stall in flapping flight

    Science.gov (United States)

    Hubel, Tatjana; Tropea, Cameron

    2007-11-01

    We report on experiments concerning unsteady effects in flapping flight, conducted in the low-speed wind tunnel of the TU Darmstadt using a mechanical flapping-wing model. Particle Image Velocimetry (PIV) was used for qualitative and quantitative analysis parallel and perpendicular to the flow field. A sensitivity analysis of the main flight parameters has been performed, with specific attention to the flight envelope of 26,500 dynamic stall effect could be verified by the direct force measurement as well as the flow visualization. The observation of the leading-edge vortex for typical bird flight reduced frequencies shows that this flow cannot be approximated as being quasi- steady. This in effect proves that adaptive wings are necessary to fully control these unsteady flow features, such as dynamic stall.

  10. The Relevance of the Dynamic Stall Effect for Transient

    DEFF Research Database (Denmark)

    Jauch, Clemens; Sørensen, Poul; Bak-Jensen, Birgitte

    2005-01-01

    This article describes a methodology to quantify the influence of dynamic stall on transient fault operations of active-stall turbines. The model of the dynamic stall effect is introduced briefly. The behaviour of the dynamic stall model during a transient fault operation is described...... mathematically, and from this its effect quantified. Two quantities are chosen to describe the influence of the dynamic stall effect: one is active power and the other is time delay. Subsequently a transient fault scenario is simulated with and without the dynamic stall effect and the differences discussed. From...... this comparison, the conclusion is drawn that the dynamic stall effect has some influence on the post-fault behaviour of the wind turbine, and it is hence suggested that the dynamic stall effect is considered if an active-stall wind turbine is to be modelled realistically....

  11. Dynamic stall and 3D effects

    Energy Technology Data Exchange (ETDEWEB)

    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

  12. Numerical Investigations of Dynamic Stall Control

    Directory of Open Access Journals (Sweden)

    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.

  13. Dynamic stall on a pitching and surging airfoil

    Science.gov (United States)

    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.

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

    Directory of Open Access Journals (Sweden)

    Han Wei

    2016-01-01

    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.

  15. Dynamic stall of an experimental wind turbine blade

    Science.gov (United States)

    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.

  16. The effects of leading edge roughness on dynamic stall

    Science.gov (United States)

    Hrynuk, John

    2016-11-01

    Dynamic stall is a fundamental flow phenomenon that is commonly observed for insect flight and rotorcraft. Under certain conditions a leading edge vortex forms generating large but temporary lift forces. Historically, computations studying dynamic stall on airfoil shapes have struggled to predict this vortex formation time and separation point. Reduced order models and CFD have performed well when experiments have been performed to develop separation models, but this has limited the development of robust design tools. The current study looks at the effect of leading edge surface roughness on the formation of the Dynamic Stall Vortex (DSV). Roughness elements were applied to the leading edge of a NACA 0012 airfoil and PIV data of the vortex formation process was recorded. Measurements were taken at a Reynolds number of Re = 12,000 and baseline smooth NACA 0012 data was also recorded for comparison. Surface roughness elements, below the typical scale modeled by CFD, are shown to change DSV formation angle and location.

  17. Investigation of compressibility effects on dynamic stall of pitching airfoil

    Science.gov (United States)

    Sangwan, Jyoti; Sengupta, Tapan K.; Suchandra, Prasoon

    2017-07-01

    In the present work, effects of compressibility on the dynamic stall of NACA 0012 airfoil, pitching sinusoidally from 5.03° to 24.79°, are investigated computationally using implicit large eddy simulations in a finite difference framework. Simulations of two-dimensional (2D), high Reynolds number, compressible flows are carried out without any transition or turbulence model to capture the physics of the dynamic stall process. The problem is formulated in a body-fixed, rotating, non-inertial frame. High accuracy, dispersion relation preserving optimized upwind compact scheme is used to compute convective flux derivatives, and an optimized three-stage Runge-Kutta method is used for time integration. Results are presented for free stream Mach number M∞ = 0.283, 0.4, and 0.5, where the Mach number is varied independent of the Reynolds number. The computations have been quite successful in capturing the essential features of the dynamic stall mechanism. It is observed that dynamic moment and lift stalls occur at smaller angles of attack as the Mach number increases. Reduction in the size of airload hysteresis loops and maximum attainable load coefficients are observed with increasing Mach number. Weak shock waves are observed near the leading edge (LE) at M∞ = 0.4, and lambda-shock is formed near the LE for M∞ = 0.5. It is observed that with increasing Mach number, the impact of dynamic stall on the aerodynamic loads (Cl, Cd, and Cm) becomes less dramatic as the maximum value attained by these aerodynamic loads decreases with an increase in the Mach number. An increase in positive damping area in the hysteresis loop is observed with an increase in the Mach number, inhibiting possible vulnerability to stall flutter.

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

    Data.gov (United States)

    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...

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

    Science.gov (United States)

    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 vibration, noise, and power output of the 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.

  20. Simulasi Numerik Dynamic Stall Pada Airfoil Yang Berosilasi

    Directory of Open Access Journals (Sweden)

    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.

  1. Effect of Mean Angle of Attack Modulation on Dynamic Stall

    Science.gov (United States)

    Heintz, Kyle; Corke, Thomas

    2016-11-01

    Wind tunnel experiments at M = 0 . 2 were conducted on a cambered airfoil instrumented with surface pressure transducers that was oscillated with two independent frequencies. The primary input, f1, corresponds to a range of reduced frequencies, while the slower, secondary input, f2, drives the modulation of the mean angle of attack, thus varying the stall-penetration angle, αpen. Various combinations transitioned different regimes of dynamic stall from "light" to "deep". Results suggest that when αpen is falling between consecutive cycles, the aerodynamic loads do not fully recover to the values seen when αpen is rising, even though the airfoil recedes to αpen load coefficients, aerodynamic damping, and their phase relationships to pitch angle. APS Fellow.

  2. Application of the ONERA model of dynamic stall

    Science.gov (United States)

    Mcalister, K. W.; Lambert, O.; Petot, D.

    1984-01-01

    A semiempirical model to predict the unsteady loads on an airfoil that is experiencing dynamic stall, is investigated. The mathematical model is described from an engineering point of view, demonstrates the procedure for obtaining various empirical parameters, and compares the loads predicted by the model with those obtained in the experiment. It is found that the procedure is straightforward, and the final calculations are in qualitative agreement with the experimental results. Comparisons between calculations and measurements also indicate that a decrease in accuracy results when the values of both the reduced frequency and the amplitude of oscillation are large. Potential quantitative improvements in the accuracy of the calculations are discussed for accounting of both the hysteresis in the static data and the effects of stall delay in the governing equations.

  3. Prediction of dynamic loads and induced vibrations in stall

    Energy Technology Data Exchange (ETDEWEB)

    Thirstrup Petersen, J.; Aagaard Madsen, H. [Risoe National Lab. (Denmark); Bjoerck, A. [Aeronautical Research Inst. of Sweden (Sweden); Enevoldsen, P. [Bonus Energy A/S (Denmark); Oeye, S. [The Technical Univ. of Denmark (Denmark); Ganander, H. [Teknikgruppen AB (Sweden); Winkelaar, D. [Netherlands Energy Research Foundation (Netherlands)

    1998-05-01

    Results from research in an EC Joule-III project and from national projects are presented. The objectives are improvement of design methods for stall regulated wind turbines with emphasis on stall induced vibrations and dynamic stall. The primary concern is limitation of the edgewise vibrations in the fundamental blade natural mode shape, which have caused trouble on modern wind turbines of approximate size 500 kW nominal power and 40 m rotor diameter. A theoretical study of quasi-steady aerodynamics confirms that the vibrations are driven basically by energy supplied from the aerodynamic forces during stalled operation. This energy exchange is equivalent to negative aerodynamic damping. The theoretical approach identifies the main parameters controlling the phenomenon. These parameters describe the steady and the dynamic airfoil characteristics, the overall aerodynamic layout of the blade, e.g. chord length and twist, the structural properties of the blade, e.g. structural damping and properties controlling the resulting vibration direction. Furthermore, full aeroelastic calculations and comparison with measurements show that the properties of the supporting structure, i.e. the main shaft, the nacelle and the tower, are important, as the global vibration of the rotor on its support may exchange energy with the blade vibration, when the blade natural frequency is close to one of the frequencies of the coupled rotor tilt-yaw mode shapes, usually denoted the global rotor whirl frequencies. It is confirmed that the influence of changing the primary design parameters can be determined by use of qualified aeroelastic calculations. Presented design guidelines therefore build on both the simple quasi-steady models, which can be used for the preliminary choice of the design variables mentioned above, and on full aeroelastic calculations. The aeroelastic calculations refine the design basis and should be used for choosing the final design variables and for final

  4. Fluid mechanics of dynamic stall. I - Unsteady flow concepts

    Science.gov (United States)

    Ericsson, L. E.; Reding, J. P.

    1988-01-01

    Advanced military aircraft 'supermaneuverability' requirements entail the sustained operation of airfoils at stalled flow conditions. The present work addresses the effects of separated flow on vehicle dynamics; an analytic method is presented which employs static experimental data to predict the separated flow effect on incompressible unsteady aerodynamics. The key parameters in the analytic relationship between steady and nonsteady aerodynamics are the time-lag before a change of flow conditions can affect the separation-induced aerodynamic loads, the accelerated flow effect, and the moving wall effect.

  5. Analysis of Dynamic Stall Through Chirp Signal Pitch Excursions

    Science.gov (United States)

    Heintz, Kyle; Coleman, Dustin; Wicks, Michael; Corke, Thomas; Thomas, Flint

    2013-11-01

    An augmentation of the typical pitching airfoil experiment has been performed where the pitching frequency and amplitude are dynamically varied in a short-time event to produce a ``chirp'' trajectory, α (t) =α0 +α1 (t) sin (tω (t)) . The frequency evolution followed a Schroeder-phase relation, ω (t) =ωmin + K (ωmax -ωmin) . The frequencies ranged from 0.5 Hz to 30 Hz, resulting in reduced frequencies from 0.02 to 0.1. The free-stream Mach number ranged from Mach 0.4 to 0.6, giving chord Reynolds numbers from 5 ×105 to 3 ×106 . The airfoil was a NACA 23012 section shape that was fully instrumented with 31 flush-mounted high-bandwidth pressure transducers. The pressure transducer outputs were simultaneously sampled with the instantaneous angle of attack, α (t) . The motivation for this study was to compare dynamic stall under non-equilibrium conditions. A particular interest is on the flow features that occur when dynamically passing between light and deep stall regimes. The results include phase analysis of aerodynamic loads, wavelet-based spectral analysis, and the determination of the intra-cycle aerodynamic damping factors.

  6. Analysis of compressible light dynamic stall flow at transitional Reynolds numbers

    DEFF Research Database (Denmark)

    Dyken, R.D. Van; Ekaterinaris, John A.; Chandrasekhara, M.S.;

    1996-01-01

    Numerical and experimental results of steady and light dynamic stall flow over an oscillating NACA 0012 airfoil at a freestream Mach number of 0.3 and Reynolds number of 0.54 x 10(6) are compared, The experimental observation that dynamic stall is induced from the bursting of a laminar separation...

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

    DEFF Research Database (Denmark)

    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...

  8. Dynamic Stall on Vertical Axis Wind Turbine Blades

    Science.gov (United States)

    Dunne, Reeve

    In this study the dynamics of flow over the blades of vertical axis wind turbines was investigated using a simplified periodic motion to uncover the fundamental flow physics and provide insight into the design of more efficient turbines. Time-resolved, two-dimensional velocity measurements were made with particle image velocimetry on a wing undergoing pitching and surging motion to mimic the flow on a turbine blade in a non-rotating frame. Dynamic stall prior to maximum angle of attack and a leading edge vortex development were identified in the phase-averaged flow field and captured by a simple model with five modes, including the first two harmonics of the pitch/surge frequency identified using the dynamic mode decomposition. Analysis of these modes identified vortical structures corresponding to both frequencies that led the separation and reattachment processes, while their phase relationship determined the evolution of the flow. Detailed analysis of the leading edge vortex found multiple regimes of vortex development coupled to the time-varying flow field on the airfoil. The vortex was shown to grow on the airfoil for four convection times, before shedding and causing dynamic stall in agreement with 'optimal' vortex formation theory. Vortex shedding from the trailing edge was identified from instantaneous velocity fields prior to separation. This shedding was found to be in agreement with classical Strouhal frequency scaling and was removed by phase averaging, which indicates that it is not exactly coupled to the phase of the airfoil motion. The flow field over an airfoil undergoing solely pitch motion was shown to develop similarly to the pitch/surge motion; however, flow separation took place earlier, corresponding to the earlier formation of the leading edge vortex. A similar reduced-order model to the pitch/surge case was developed, with similar vortical structures leading separation and reattachment; however, the relative phase lead of the separation mode

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

    Science.gov (United States)

    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.

  10. Compressible dynamic stall vorticity flux control using a dynamic camber airfoil

    Indian Academy of Sciences (India)

    M S Chandrasekhara

    2007-02-01

    This study reports control of compressible dynamic stall through management of its unsteady vorticity using a variable droop leading edge (VDLE) airfoil. Through dynamic adaptation of the airfoil edge incidence, the formation of a dynamic stall vortex was virtually eliminated for Mach numbers of up to 0·4. Consequently, the leading edge vorticity flux was redistributed enabling retention of the dynamic lift. Of even greater importance was the fact that the drag and pitching moment coefficients were reduced by nearly 50%. The camber variations introduced when the leading edge was drooped are explained to be the source of this benefit. Analysis of the peak vorticity flux levels allowed the determination of minimum necessary airfoil adaptation schedule.

  11. Dynamic-stall and structural-modeling effects on helicopter blade stability with experimental correlation

    Science.gov (United States)

    Barwey, D.; Gaonkar, Gopal H.

    1994-04-01

    The effects of blade and root-flexure elasticity and dynamic stall on the stability of hingeless rotor blades are investigated. The dynamic stall description is based on the ONERA models of lift, drag, and pitching moment. The structural analysis is based on three blade models that range from a rigid flap-lag model to two elastic flap-lag-torsion models, which differ in representing root-flexure elasticity. The predictions are correlated with the measured lag damping of an experimental isolated three-blade rotor; the correlation covers rotor operations from near-zero-thrust conditions in hover to highly stalled, high-thrust conditions in foward flight. That correlation shows sensitivity of lag-damping predictions to structural refinements in blade and root-flexure modeling. Moreover, this sensitivity increases with increasing control pitch angle and advance ratio. For high-advance-ratio and high-thrust conditions, inclusion of dynamic stall generally improves the correlation.

  12. Dynamic Characteristics of Rotating Stall in Mixed Flow Pump

    Directory of Open Access Journals (Sweden)

    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.

  13. Model improvements for evaluating the effect of tower tilting on the aerodynamics of a vertical axis wind turbine

    DEFF Research Database (Denmark)

    Wang, K.; Hansen, Martin Otto Laver; Moan, T.

    2015-01-01

    is quantified with respect to power, rotor torque, thrust force and the normal force and tangential force coefficients on the blades. Additionally, applications of Glauert momentum theory and pure axial momentum theory are compared to evaluate the effect of the velocity component parallel to the rotor shaft...... be investigated to more accurately predict the aerodynamic loads. This paper proposes certain modifications to the double multiple-streamtube (DMS) model to include the component of wind speed parallel to the rotating shaft. The model is validated against experimental data collected on an H-Darrieus wind turbine...... in skewed flow conditions. Three different dynamic stall models are also integrated into the DMS model: Gormont's model with the adaptation of Strickland, Gormont's model with the modification of Berg and the Beddoes-Leishman dynamic stall model. Both the small Sandia 17m wind turbine and the large Deep...

  14. Dynamics and Control of Three-Dimensional Perching Maneuver under Dynamic Stall Influence

    Science.gov (United States)

    Feroskhan, Mir Alikhan Bin Mohammad

    Perching is a type of aggressive maneuver performed by the class 'Aves' species to attain precision point landing with a generally short landing distance. Perching capability is desirable on unmanned aerial vehicles (UAVs) due to its efficient deceleration process that potentially expands the functionality and flight envelope of the aircraft. This dissertation extends the previous works on perching, which is mostly limited to two-dimensional (2D) cases, to its state-of-the-art threedimensional (3D) variety. This dissertation presents the aerodynamic modeling and optimization framework adopted to generate unprecedented variants of the 3D perching maneuver that include the sideslip perching trajectory, which ameliorates the existing 2D perching concept by eliminating the undesirable undershoot and reliance on gravity. The sideslip perching technique methodically utilizes the lateral and longitudinal drag mechanisms through consecutive phases of yawing and pitching-up motion. Since perching maneuver involves high rates of change in the angles of attack and large turn rates, introduction of three internal variables thus becomes necessary for addressing the influence of dynamic stall delay on the UAV's transient post-stall behavior. These variables are then integrated into a static nonlinear aerodynamic model, developed using empirical and analytical methods, and into an optimization framework that generates a trajectory of sideslip perching maneuver, acquiring over 70% velocity reduction. An impact study of the dynamic stall influence on the optimal perching trajectories suggests that consideration of dynamic stall delay is essential due to the significant discrepancies in the corresponding control inputs required. A comparative study between 2D and 3D perching is also conducted to examine the different drag mechanisms employed by 2D and 3D perching respectively. 3D perching is presented as a more efficient deceleration technique with respect to spatial costs and

  15. Simple theories of dynamic stall that are helpful in interpreting computational results

    Science.gov (United States)

    Jumper, E. J.; Hugo, R. J.

    1991-04-01

    This paper briefly reviews the phenomena of dynamic stall and comments on some of the theoretical work performed to help understand why the phenomena occurs for two-dimensional flow past an airfoil undergoing a pitching motion. A first look at how these understandings might be extended to three-dimensional flow fields past finite-span wings is also presented. In particular, a simple theory is developed that provides a rationale for why the experimental results from studies of finite-span wings undergoing dynamic stall closely resemble the dynamic-stall results for two-dimensional airfoils, while steady-flow results from finite-span wing studies are so dissimilar from those for two-dimensional airfoils.

  16. Fluid mechanics of dynamic stall. II - Prediction of full scale characteristics

    Science.gov (United States)

    Ericsson, L. E.; Reding, J. P.

    1988-01-01

    Analytical extrapolations are made from experimental subscale dynamics to predict full scale characteristics of dynamic stall. The method proceeds by establishing analytic relationships between dynamic and static aerodynamic characteristics induced by viscous flow effects. The method is then validated by predicting dynamic test results on the basis of corresponding static test data obtained at the same subscale flow conditions, and the effect of Reynolds number on the static aerodynamic characteristics are determined from subscale to full scale flow conditions.

  17. Fluid mechanics of dynamic stall. II - Prediction of full scale characteristics

    Science.gov (United States)

    Ericsson, L. E.; Reding, J. P.

    1988-01-01

    Analytical extrapolations are made from experimental subscale dynamics to predict full scale characteristics of dynamic stall. The method proceeds by establishing analytic relationships between dynamic and static aerodynamic characteristics induced by viscous flow effects. The method is then validated by predicting dynamic test results on the basis of corresponding static test data obtained at the same subscale flow conditions, and the effect of Reynolds number on the static aerodynamic characteristics are determined from subscale to full scale flow conditions.

  18. Control of unsteady separated flow associated with the dynamic stall of airfoils

    Science.gov (United States)

    Wilder, M. C.

    1995-01-01

    An effort to understand and control the unsteady separated flow associated with the dynamic stall of airfoils was funded for three years through the NASA cooperative agreement program. As part of this effort a substantial data base was compiled detailing the effects various parameters have on the development of the dynamic stall flow field. Parameters studied include Mach number, pitch rate, and pitch history, as well as Reynolds number (through two different model chord lengths) and the condition of the boundary layer at the leading edge of the airfoil (through application of surface roughness). It was found for free stream Mach numbers as low as 0.4 that a region of supersonic flow forms on the leading edge of the suction surface of the airfoil at moderate angles of attack. The shocks which form in this supersonic region induce boundary-layer separation and advance the dynamic stall process. Under such conditions a supercritical airfoil profile is called for to produce a flow field having a weaker leading-edge pressure gradient and no leading-edge shocks. An airfoil having an adaptive-geometry, or dynamically deformable leading edge (DDLE), is under development as a unique active flow-control device. The DDLE, formed of carbon-fiber composite and fiberglass, can be flexed between a NACA 0012 profile and a supercritical profile in a controllable fashion while the airfoil is executing an angle-of-attack pitch-up maneuver. The dynamic stall data were recorded using point diffraction interferometry (PDI), a noninvasive measurement technique. A new high-speed cinematography system was developed for recording interferometric images. The system is capable of phase-locking with the pitching airfoil motion for real-time documentation of the development of the dynamic stall flow field. Computer-aided image analysis algorithms were developed for fast and accurate reduction of the images, improving interpretation of the results.

  19. Bifurcation suppression of nonlinear systems via dynamic output feedback and its applications to rotating stall control

    Institute of Scientific and Technical Information of China (English)

    Pengnian CHEN; Huashu QIN; Shengwei MEI

    2005-01-01

    This paper deals with the problems of bifurcation suppression and bifurcation suppression with stability of nonlinear systems. Necessary conditions and sufficient conditions for bifurcation suppression via dynamic output feedback are presented;Sufficient conditions for bifurcation suppression with stability via dynamic output feedback are obtained. As an application, a dynamic compensator, which guarantees that the bifurcation point of rotating stall in axial flow compressors is stably suppressed, is constructed.

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

    Energy Technology Data Exchange (ETDEWEB)

    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

  1. Development of High Speed Imaging and Analysis Techniques Compressible Dynamics Stall

    Science.gov (United States)

    Chandrasekhara, M. S.; Carr, L. W.; Wilder, M. C.; Davis, Sanford S. (Technical Monitor)

    1996-01-01

    Dynamic stall has limited the flight envelope of helicopters for many years. The problem has been studied in the laboratory as well as in flight, but most research, even in the laboratory, has been restricted to surface measurement techniques such as pressure transducers or skin friction gauges, except at low speed. From this research, it became apparent that flow visualization tests performed at Mach numbers representing actual flight conditions were needed if the complex physics associated with dynamic stall was to be properly understood. However, visualization of the flow field during compressible conditions required carefully aligned and meticulously reconstructed holographic interferometry. As part of a long-range effort focused on exposing of the physics of compressible dynamic stall, a research wind tunnel was developed at NASA Ames Research Center which permits visual access to the full flow field surrounding an oscillating airfoil during compressible dynamic stall. Initially, a stroboscopic schlieren technique was used for visualization of the stall process, but the primary research tool has been point diffraction interferometry(PDI), a technique carefully optimized for use in th is project. A review of the process of development of PDI will be presented in the full paper. One of the most valuable aspects of PDI is the fact that interferograms are produced in real time on a continuous basis. The use of a rapidly-pulsed laser makes this practical; a discussion of this approach will be presented in the full paper. This rapid pulsing(up to 40,000 pulses/sec) produces interferograms of the rapidly developing dynamic stall field in sufficient resolution(both in space and time) that the fluid physics of the compressible dynamic stall flowfield can be quantitatively determined, including the gradients of pressure in space and time. This permits analysis of the influence of the effect of pitch rate, Mach number, Reynolds number, amplitude of oscillation, and other

  2. Combustion-Powered Actuation for Dynamic Stall Suppression - Simulations and Low-Mach Experiments

    Science.gov (United States)

    Matalanis, Claude G.; Min, Byung-Young; Bowles, Patrick O.; Jee, Solkeun; Wake, Brian E.; Crittenden, Tom; Woo, George; Glezer, Ari

    2014-01-01

    An investigation on dynamic-stall suppression capabilities of combustion-powered actuation (COMPACT) applied to a tabbed VR-12 airfoil is presented. In the first section, results from computational fluid dynamics (CFD) simulations carried out at Mach numbers from 0.3 to 0.5 are presented. Several geometric parameters are varied including the slot chordwise location and angle. Actuation pulse amplitude, frequency, and timing are also varied. The simulations suggest that cycle-averaged lift increases of approximately 4% and 8% with respect to the baseline airfoil are possible at Mach numbers of 0.4 and 0.3 for deep and near-deep dynamic-stall conditions. In the second section, static-stall results from low-speed wind-tunnel experiments are presented. Low-speed experiments and high-speed CFD suggest that slots oriented tangential to the airfoil surface produce stronger benefits than slots oriented normal to the chordline. Low-speed experiments confirm that chordwise slot locations suitable for Mach 0.3-0.4 stall suppression (based on CFD) will also be effective at lower Mach numbers.

  3. Interferometric Investigations of Compressible Dynamic Stall Over a Transiently Pitching Airfoil

    OpenAIRE

    Chandrasekhara, M.S.; Carr, L.W.; Wilder, M.C.

    1993-01-01

    The article of record as published may be found at http://dx.doi.org/10.2514/6.1993-211 The dynamic stall flow field over a NACA 0012 airfoil pitching transiently from 0 - 60 degrees at a constant rate under compressible flow conditions has been studied using the real-time technique of point diffraction interferometrv. This investigation using nonintrusive diagnostics-provides a quantitative description of the overall flow field, including the finer details of dynamic...

  4. Dynamic Stall Control on the Wind Turbine Airfoil via a Co-Flow Jet

    Directory of Open Access Journals (Sweden)

    He-Yong Xu

    2016-06-01

    Full Text Available Dynamic stall control of a S809 airfoil is numerically investigated by implementing a co-flow jet (CFJ. The numerical methods of the solver are validated by comparing results with the baseline experiment as well as a NACA 6415-based CFJ experiment, showing good agreement in both static and dynamic characteristics. The CFJ airfoil with inactive jet is simulated to study the impact that the jet channel imposes upon the dynamic characteristics. It is shown that the presence of a long jet channel could cause a negative effect of decreasing lift and increasing drag, leading to fluctuating extreme loads in terms of drag and moment. The main focus of the present research is the investigation of the dynamic characteristics of the CFJ airfoil with three different jet momentum coefficients, which are compared with the baseline, giving encouraging results. Dynamic stall can be greatly suppressed, showing a very good control performance of significantly increased lift and reduced drag and moment. Analysis of the amplitude of variation in the aerodynamic coefficients indicates that the fluctuating extreme aerodynamic loads are significantly alleviated, which is conducive to structural reliability and improved life cycle. The energy consumption analysis shows that the CFJ concept is applicable and economical in controlling dynamic stall.

  5. An Investigation of Airfoil Dynamic Stall with Large Amplitude Motions.

    Science.gov (United States)

    1983-10-01

    solid aluminum pieces and excavated to provide interior mounting locations for nineteen (19) miniature piezo -resistive pressure transducers. A side...PRESSURE MEASUREMENT SYSTEM Unsteady pressures were measured by miniature, dynamic piezo -resistive transducers possessing a high frequency response...motions introduces - another possible source of "contamination," namely, the influence of -. flow phenomena which are either multiples or subharmonics

  6. A Semi-Analytic dynamical friction model that reproduces core stalling

    CERN Document Server

    Petts, James A; Read, Justin I

    2015-01-01

    We present a new semi-analytic model for dynamical friction based on Chandrasekhar's formalism. The key novelty is the introduction of physically motivated, radially varying, maximum and minimum impact parameters. With these, our model gives an excellent match to full N-body simulations for isotropic background density distributions, both cuspy and shallow, without any fine-tuning of the model parameters. In particular, we are able to reproduce the dramatic core-stalling effect that occurs in shallow/constant density cores, for the first time. This gives us new physical insight into the core-stalling phenomenon. We show that core stalling occurs in the limit in which the product of the Coulomb logarithm and the local fraction of stars with velocity lower than the infalling body tends to zero. For cuspy backgrounds, this occurs when the infalling mass approaches the enclosed background mass. For cored backgrounds, it occurs at larger distances from the centre, due to a combination of a rapidly increasing minim...

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

    Energy Technology Data Exchange (ETDEWEB)

    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)

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

    DEFF Research Database (Denmark)

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

    2016-01-01

    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...... 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 combination...

  9. Dynamic Stall Prediction of a Pitching Airfoil using an Adjusted Two-Equation URANS Turbulence Model

    Directory of Open Access Journals (Sweden)

    Galih Bangga

    2017-01-01

    Full Text Available The necessity in the analysis of dynamic stall becomes increasingly important due to its impact on many streamlined structures such as helicopter and wind turbine rotor blades. The present paper provides Computational Fluid Dynamics (CFD predictions of a pitching NACA 0012 airfoil at reduced frequency of 0.1 and at small Reynolds number value of 1.35e5. The simulations were carried out by adjusting the k − ε URANS turbulence model in order to damp the turbulence production in the near wall region. The damping factor was introduced as a function of wall distance in the buffer zone region. Parametric studies on the involving variables were conducted and the effect on the prediction capability was shown. The results were compared with available experimental data and CFD simulations using some selected two-equation turbulence models. An improvement of the lift coefficient prediction was shown even though the results still roughly mimic the experimental data. The flow development under the dynamic stall onset was investigated with regards to the effect of the leading and trailing edge vortices. Furthermore, the characteristics of the flow at several chords length downstream the airfoil were evaluated.

  10. Numerical study on a single bladed vertical axis wind turbine under dynamic stall

    Energy Technology Data Exchange (ETDEWEB)

    Bangga, Galih [Institute of Aerodynamics and Gas Dynamics, University of Stuttgart, Stuttgart (Germany); Hutomo, Go; Sasongko, Herman [Dept. of Mechanical Engineering, Institut Teknologi Sepuluh Nopember, Surabaya (Indonesia); Wiranegara, Raditya [School of Mechanical Aerospace and Civil Engineering, University of Manchester, Manchester (United Kingdom)

    2017-01-15

    The aim of this study is to investigate the flow development of a single bladed vertical axis wind turbine using Computational fluid dynamics (CFD) methods. The blade is constructed using the NACA 0012 profile and is operating under stalled conditions at tip speed ratio of 2. Two dimensional simulations are performed using a commercial CFD package, ANSYS Fluent 15.0, employing the Menter-SST turbulence model. For the preliminary study, simulations of the NACA 0012 airfoil under static conditions are carried out and compared with available measurement data and calculations using the boundary layer code XFOIL. The CFD results under the dynamic case are presented and the resulting aerodynamic forces are evaluated. The turbine is observed to generate negative power at certain azimuth angles which can be divided into three main zones. The blade vortex interaction is observed to strongly influence the flow behavior near the blade and contributes to the power production loss. However, the impact is considered small since it covers only 6.4 % of the azimuth angle range where the power is negative compared to the dynamic stall impact which covers almost 22 % of the azimuth angle range.

  11. Dynamic stall development in the near-root region of a model wind turbine blade

    Science.gov (United States)

    Melius, Matthew; Cal, Raul Bayoan; Mulleners, Karen

    2014-11-01

    The dynamic behavior of atmospheric flows create highly variable operational conditions which affect the life expectancy of the turbine components and the power output of the turbine. To gain insight into the unsteady aerodynamics of wind turbine blades, wind tunnel experiments were conducted with a scaled three-dimensional NREL 5MW wind turbine blade model in the 2.2 m × 1.8 m cross-section closed loop wind tunnel DLR in Göttingen. The development of dynamic stall in response to a sudden change in the blades angle of attack are studied by means of time-resolved stereoscopic PIV in span-wisely distributed planes capturing the suction side of the blade. The change in angle of attack was obtained by varying the blade pitch angle to simulate a sudden change in wind speed or pitch angle regulation. Resulting time scales associated with flow separation and reattachment are determined at different radial positions ranging from r / R = 0 . 19 to r / R = 0 . 38 . The influence of the three-dimensionality of the blade geometry on the corresponding aerodynamic effects is captured by analyzing the radial flow component in neighboring measurement fields during stall development.

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

    Science.gov (United States)

    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.

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

    DEFF Research Database (Denmark)

    Castelein, D.; Ragni, D.; Tescione, G.;

    2015-01-01

    -based Reynolds number of 1.6e5 and 0.8e5. At both TSR, the velocity fields are presented in the mid (symmetry) plane of the blade for eight azimuthal positions. The velocity fields are directly derived from PIV, while the loads are obtained through an integral approach presented by Noca et...... al. The experimental data of the velocity fields around the airfoil and the loads on the blade are used for numerical validation. The aim of evaluating the two different TSR is identifying the effect of Dynamic Stall (DS), which is not present at the higher TSR, while dominant at the lower. The DS...... 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....

  14. Development of High Speed Interferometry Imaging and Analysis Techniques for Compressible Dynamic Stall

    Science.gov (United States)

    Chandrasekhara, M. S.; Carr, L. W.; Wilder, M. C.

    1998-01-01

    The development of a high-speed, phase-locked, realtime, point diffraction interferometry system for quantitative imaging unsteady separated flows is described. The system enables recording of up to 224 interferograms of the dynamic stall flow over an oscillating airfoil using a drum camera at rates of up to 40 KHz controlled by custom designed electronic interlocking circuitry. Several thousand interferograms of the flow have been obtained using this system. A comprehensive image analysis package has been developed for automatic processing of this large number of images. The software has been specifically tuned to address the special characteristics of airfoil flow interferograms. Examples of images obtained using the standard and the high-speed interferometry techniques are presented along with a demonstration of the image processing routine's ability to resolve the fine details present in these images.

  15. Low-Order Modeling of Dynamic Stall on Airfoils in Incompressible Flow

    Science.gov (United States)

    Narsipur, Shreyas

    Unsteady aerodynamics has been a topic of research since the late 1930's and has increased in popularity among researchers studying dynamic stall in helicopters, insect/bird flight, micro air vehicles, wind-turbine aerodynamics, and ow-energy harvesting devices. Several experimental and computational studies have helped researchers gain a good understanding of the unsteady ow phenomena, but have proved to be expensive and time-intensive for rapid design and analysis purposes. Since the early 1970's, the push to develop low-order models to solve unsteady ow problems has resulted in several semi-empirical models capable of effectively analyzing unsteady aerodynamics in a fraction of the time required by high-order methods. However, due to the various complexities associated with time-dependent flows, several empirical constants and curve fits derived from existing experimental and computational results are required by the semi-empirical models to be an effective analysis tool. The aim of the current work is to develop a low-order model capable of simulating incompressible dynamic-stall type ow problems with a focus on accurately modeling the unsteady ow physics with the aim of reducing empirical dependencies. The lumped-vortex-element (LVE) algorithm is used as the baseline unsteady inviscid model to which augmentations are applied to model unsteady viscous effects. The current research is divided into two phases. The first phase focused on augmentations aimed at modeling pure unsteady trailing-edge boundary-layer separation and stall without leading-edge vortex (LEV) formation. The second phase is targeted at including LEV shedding capabilities to the LVE algorithm and combining with the trailing-edge separation model from phase one to realize a holistic, optimized, and robust low-order dynamic stall model. In phase one, initial augmentations to theory were focused on modeling the effects of steady trailing-edge separation by implementing a non-linear decambering

  16. Validation of an Actuator Line Model Coupled to a Dynamic Stall Model for Pitching Motions Characteristic to Vertical Axis Turbines

    Science.gov (United States)

    Mendoza, Victor; Bachant, Peter; Wosnik, Martin; Goude, Anders

    2016-09-01

    Vertical axis wind turbines (VAWT) can be used to extract renewable energy from wind flows. A simpler design, low cost of maintenance, and the ability to accept flow from all directions perpendicular to the rotor axis are some of the most important advantages over conventional horizontal axis wind turbines (HAWT). However, VAWT encounter complex and unsteady fluid dynamics, which present significant modeling challenges. One of the most relevant phenomena is dynamic stall, which is caused by the unsteady variation of angle of attack throughout the blade rotation, and is the focus of the present study. Dynamic stall is usually used as a passive control for VAWT operating conditions, hence the importance of predicting its effects. In this study, a coupled model is implemented with the open-source CFD toolbox OpenFOAM for solving the Navier-Stokes equations, where an actuator line model and dynamic stall model are used to compute the blade loading and body force. Force coefficients obtained from the model are validated with experimental data of pitching airfoil in similar operating conditions as an H-rotor type VAWT. Numerical results show reasonable agreement with experimental data for pitching motion.

  17. Synthetic-jet-based dynamic stall control on a scaled finite span wind turbine S817 blade

    Science.gov (United States)

    Rice, Thomas; Taylor, Keith; Amitay, Michael

    2016-11-01

    As wind turbines increase in size, so do many of the adverse effects associated with unsteady flow fields. Yawed flow, unsteady gusts, atmospheric boundary layers, and even free stream turbulence can cause unsteady loading, which are detrimental to the blades' structure. In order to decrease unsteady loading, synthetic jet actuators were installed on a scaled finite span cantilevered wind turbine blade having an S817 airfoil shape. The S817 airfoil shape is of the blade tips on the NREL CART3, which will be used next year on full scale field testing of active flow control. The model has been tested in the wind tunnel with and without active flow control, using load, surface pressure, and PIV measurements to characterize the airfoil's stall behavior during static and dynamic conditions, and the effect of flow control on its aerodynamic performance. Surface-mounted microphones were also used to detect dominant frequencies in the flow field. Dynamic stall was also simulated by pitching the airfoil through stall in a sinusoidal pitching motion. Synthetic jets, placed near the leading edge, were shown to increase lift both in the static and dynamic cases, in addition to attaching the flow and reducing hysteresis during dynamic pitching, showing a decrease in structural loading.

  18. Experimental Investigation of Dynamic Stall on a Finite Span NACA 0012 Wing

    Science.gov (United States)

    Spellman, Wyatt; Bohl, Douglas

    2015-11-01

    In this work the velocity and vorticity fields around finite and ``infinite'' span wings with a NACA 0012 profile undergoing constant rate pitching were quantified using Molecular Tagging Velocimetry (MTV). The ``infinite'' span wing was bounded by walls to reduce the effects of the wing tip vortex while the finite span wing was bounded by a wall on one end and unbounded on the other. The wings were pitched from α = 0 to 55° with a constant non-dimensional pitch rate of Ω* = 0.1 at Rec = 12000. The Dynamic Stall Vortex (DSV) was identified and tracked using the `` Γ criteria.'' The results showed that the formation and trajectory of the DSV for the finite wing case varied with the spanwise location, with the location of the DSV remaining progressively closer to the airfoil surface towards the wingtip. These results were consistent with the ``Omega'' vortex structure previously observed in flow visualization. The DSV was also found to remain closer, and convect away from the airfoil surface slower, at all spanwise measurement planes when compared to the infinite span results. This work was supported by NSF Grant #845882.

  19. Advance Ratio Effects on the Dynamic-stall Vortex of a Rotating Blade in Steady Forward Flight

    Science.gov (United States)

    2014-08-06

    Office P.O. Box 12211 Research Triangle Park , NC 27709-2211 Leading-edge vortex, Dynamic stall vortex, Vortex flows, Rotating wing REPORT...observed on rotating insect wing investigations2,9–13. A common theme among most of these investigations is the existence of a strong span-wise flow...structures by considering only the topology of the flow field. It is specifically designed to identify a large scale vortex superposed on a small-scale

  20. Development of dynamic simulation of TF34-GE-100 turbofan engine with post-stall capability

    Science.gov (United States)

    Krosel, S. M.

    1984-01-01

    This paper describes the development of a hybrid computer simulation of a TF34-GE-100 turbofan engine with post-stall capability. The simulation operates in real-time and will be used to test and evaluate stall recovery control modes for this engine. The simulation calculations are performed by an analog computer with a peripheral multivariable function generation unit used for computing bivariate functions. Tabular listings of simulation variables are obtained by interfacing to a digital computer and using a custom software package for data collection and display.

  1. Airfoil drag elimination and stall suppression via piezoelectric dynamic tangential synthetic jet actuators

    NARCIS (Netherlands)

    Barrett, R.; Corpening, J.; Reasonover, C.

    2005-01-01

    This paper describes a new method for drag elimination and stall suppression via tangential synthetic jet actuators. This boundary layer control (BLC) method is shown to perform as well as continuous and normal synthetic jet BLC methods but without fouling difficulties, system-level complexity or ex

  2. A new method of dynamic and static stall detection using infrared thermography

    Science.gov (United States)

    Gardner, A. D.; Wolf, C. C.; Raffel, M.

    2016-09-01

    A new method of detecting flow separation for static and pitching airfoils is described, with application to the generation of stall maps for helicopter rotors. An airfoil is heated using a lamp, and a high-speed infrared camera monitors the surface temperature. Subtracting consecutive images and performing a spatial standard deviation over a region of interest yields a single σ {DIT} value which is used to detect boundary layer separation on the airfoil. The data can be analysed to identify attached flow (low values of σ {DIT}) and separated flow (high values of σ {DIT}). Although appropriate filtering can significantly improve the signal-to-noise ratio, the method is robust regarding the exact method of analysis and the unfiltered data are sufficiently clear to be analysed without additional processing. For the test airfoil used, stall was measured up to a pitching frequency of 5 Hz, and signal-to-noise ratios indicate that it should be possible to measure stall for a pitching frequency of 20 Hz for a carbon-fibre surface with the thermal properties used.

  3. Stall/surge dynamics of a multi-stage air compressor in response to a load transient of a hybrid solid oxide fuel cell-gas turbine system

    Science.gov (United States)

    Azizi, Mohammad Ali; Brouwer, Jacob

    2017-10-01

    A better understanding of turbulent unsteady flows in gas turbine systems is necessary to design and control compressors for hybrid fuel cell-gas turbine systems. Compressor stall/surge analysis for a 4 MW hybrid solid oxide fuel cell-gas turbine system for locomotive applications is performed based upon a 1.7 MW multi-stage air compressor. Control strategies are applied to prevent operation of the hybrid SOFC-GT beyond the stall/surge lines of the compressor. Computational fluid dynamics tools are used to simulate the flow distribution and instabilities near the stall/surge line. The results show that a 1.7 MW system compressor like that of a Kawasaki gas turbine is an appropriate choice among the industrial compressors to be used in a 4 MW locomotive SOFC-GT with topping cycle design. The multi-stage radial design of the compressor enhances the ability of the compressor to maintain air flow rate during transient step-load changes. These transient step-load changes are exhibited in many potential applications for SOFC/GT systems. The compressor provides sustained air flow rate during the mild stall/surge event that occurs due to the transient step-load change that is applied, indicating that this type of compressor is well-suited for this hybrid application.

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

    Energy Technology Data Exchange (ETDEWEB)

    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)

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

    Directory of Open Access Journals (Sweden)

    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.

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

    Institute of Scientific and Technical Information of China (English)

    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.

  7. Load prediction of stall regulated wind turbines

    Energy Technology Data Exchange (ETDEWEB)

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

    Energy Technology Data Exchange (ETDEWEB)

    Breton, Simon-Philippe

    2008-06-15

    the modeling of the stall phenomenon which involves very complex aerodynamics. The NREL wind tunnel results were further scrutinized in term of the root flapwise and edgewise bending moments. This allowed to study the dynamics of the NREL blades, at the same time as verifying the consistency between these moments and different loads measured in these tests. Measurements of these moments at the root of the rigid NREL blades in head-on flow showed vibrations corresponding to the two first oscillation modes of the blades, in respectively the flapwise and edgewise directions. These features observed in both an upwind and a downwind configuration were presumed to follow from the presence of the tower. In the downwind configuration, dynamic effects affecting one blade when going through the shadow of the tower were found to be transmitted to the other blade in both the teetered and the rigid configurations. Modelling of the root edgewise and flapwise bending moments was performed by calculating two dynamic estimates based on forces measured respectively along the blade and in the hub region. The simulations generally reproduced the dynamic effects well, and they suggested a systematic error in the measurement of the root flapwise bending moment in the upwind configuration. Inaccuracies in measuring the tangential forces on the blade at high wind speeds were also detected. Offshore wind energy, that is expected to soon lead the development of the wind energy technology, was thereafter studied, where downwind turbines that were given special attention in the dynamic analysis above might reveal themselves as a more adapted solution. The many advantages as well as challenges related to this technology were acknowledged. The status of this technology was investigated in both Europe and North America, and it revealed that Europe is in advance regarding all aspects of wind energy over North America, where it still is at a planning stage. Important plans were however found to exist

  9. Stall inception in a high-speed axial compressor

    Science.gov (United States)

    Cameron, Joshua David

    A research program designed to provide understanding of the fluid dynamic mechanisms that lead to rotating stall in the Notre Dame Stage 01 high-speed axial compressor is described. The stalling behavior of this compressor was studied with unsteady casing pressure measurements from a circumferentially spaced array of sensors. In addition, over rotor casing surface streak measurements were performed to investigate the time-averaged end-wall flow near the rotor at operating points near stall. Several investigative tools were applied to the analysis and interpretation of the unsteady casing pressure data. Traditional methods such as visual inspection, spatial Fourier decomposition, traveling wave energy and wavelet analysis were shown to be insufficient to characterize the pre-stall and stall inception behavior of the compressor. A new technique based on a windowed two-point correlation between adjacent sensors was developed and demonstrated to provide spatial and temporal resolution of both pre-stall and stall inception behavior. The spatial correlation technique was then applied to the analysis of stall inception data from experiments with asymmetric tip clearance. The non-uniform tip clearance was produced using the magnetic bearings which levitate the rotor shaft of the Notre Dame Transonic Axial Compressor facility. Both steady rotor centerline offset and rotor whirl were investigated. The results of these experiments, along with the surface streak measurements, provide evidence in support of recent computational observations (found in the literature) that predict that short length scale stall inception is related to specific features of the rotor tip clearance flow.

  10. POD based analysis of three-dimensional stall over a pitching wind turbine blade

    Science.gov (United States)

    Melius, Matthew; Bayoan Cal, Raul; Mulleners, Karen

    2015-11-01

    Aerodynamic performance of a wind turbine blade is a predominant factor in its power production. Under dynamic loading conditions, predicted aerodynamic loads often do not match operational loads. In the interest of gaining understanding of the complex flow over wind turbine blades, a three-dimensional scaled blade model has been designed and manufactured to be dynamically similar to a rotating full-scale NREL 5MW wind turbine blade. Time resolved particle image velocimetry (PIV) measurements collected over the suction surface of an inboard section of the experimental turbine blade. Flow characteristics are analyzed using coherent structure identification techniques to capture dynamic stall behavior. Proper orthogonal decomposition (POD) is applied to the velocity field providing information about separation point and stall development time scales based on the associated time coefficients and modes. Additionally, continuity and circulation calculations are used to capture three dimensional effects within stalled volumes during developing stall and re-attachment phases of dynamic stall.

  11. An experimental investigation of compressor stall using an on-line distortion indicator and signal conditioner

    Science.gov (United States)

    Costakis, W. G.; Wenzel, L. M.

    1975-01-01

    The relation of the steady-state and dynamic distortions and the stall margin of a J85-13 turbojet engine was investigated. A distortion indicator capable of computing two distortion indices was used. A special purpose signal conditioner was also used as an interface between transducer signals and distortion indicator. A good correlation of steady-state distortion and stall margin was established. The prediction of stall by using the indices as instantaneous distortion indicators was not successful. A sensitivity factor that related the loss of stall margin to the turbulence level was found.

  12. Fluid mechanics mechanisms in the stall process of helicopters

    Science.gov (United States)

    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.

  13. Identify the Rotating Stall in Centrifugal Compressors by Fractal Dimension in Reconstructed Phase Space

    Directory of Open Access Journals (Sweden)

    Le Wang

    2015-11-01

    Full Text Available Based on phase space reconstruction and fractal dynamics in nonlinear dynamics, a method is proposed to extract and analyze the dynamics of the rotating stall in the impeller of centrifugal compressor, and some numerical examples are given to verify the results as well. First, the rotating stall of an existing low speed centrifugal compressor (LSCC is numerically simulated, and the time series of pressure in the rotating stall is obtained at various locations near the impeller outlet. Then, the phase space reconstruction is applied to these pressure time series, and a low-dimensional dynamical system, which the dynamics properties are included in, is reconstructed. In phase space reconstruction, C–C method is used to obtain the key parameters, such as time delay and the embedding dimension of the reconstructed phase space. Further, the fractal characteristics of the rotating stall are analyzed in detail, and the fractal dimensions are given for some examples to measure the complexity of the flow in the post-rotating stall. The results show that the fractal structures could reveal the intrinsic dynamics of the rotating stall flow and could be considered as a characteristic to identify the rotating stall.

  14. 14 CFR 25.203 - Stall characteristics.

    Science.gov (United States)

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Stall characteristics. 25.203 Section 25.203 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Stalls § 25.203 Stall characteristics. (a) It...

  15. 14 CFR 25.207 - Stall warning.

    Science.gov (United States)

    2010-01-01

    ... sufficient margin to prevent inadvertent stalling with the flaps and landing gear in any normal position must... the pilot to prevent stalling (as defined in § 25.201(d)) when the pilot starts a recovery maneuver... non-icing and icing conditions to allow the pilot to prevent stalling when the pilot starts a...

  16. Supersonic stall flutter of high-speed fans

    Science.gov (United States)

    Adamczyk, J. J.; Stevans, W.; Jutras, R.

    1981-01-01

    An analytical model is proposed for predicting the onset of supersonic stall bending flutter in high-speed rotors. The analysis is based on a modified two-dimensional, compressible, unsteady actuator disk theory. The stability boundary predicted by the analysis is shown to be in good agreement with the measured boundary of a high speed fan. The prediction that the flutter mode would be a forward traveling wave sensitive to wheel speed and aerodynamic loading is confirmed by experimental measurements. In addition, the analysis shows that reduced frequency and dynamic head also play a significant role in establishing the supersonic stall bending flutter boundary of an unshrouded fan.

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

    DEFF Research Database (Denmark)

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

    2015-01-01

    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...

  18. Les stalles d’Entremont

    OpenAIRE

    Chassany, Chloé

    2010-01-01

    Les stalles sont un rare exemple de siège liturgique. On les trouve dans le chœur des sanctuaires où se réunissaient les communautés pour célébrer collectivement l’office. Les stalles datées du début du XVIe siècle, conservées dans l’église d’Entremont en Haute Savoie, n’ont jamais fait l’objet d’une étude approfondie. La première partie du mémoire réunit le bilan des recherches de première année de master, une synthèse historiographique du mobilier liturgique savoyard ainsi que l’histoire co...

  19. Literary Careers: Breaks and Stalls

    OpenAIRE

    Crozier, W. Ray

    2001-01-01

    In his article, "Literary Careers: Breaks and Stalls," W. Ray Crozier argues that biographical evidence points to considerable individual variation in writers' output over the life span even when allowance is made for longevity and length of writing career. This issue has been neglected by psychological accounts of creativity. Crozier outlines a theoretical framework for understanding variation in terms of an "artistic career." This is conceptualised as a sequence of projects, the success of ...

  20. Fluid mechanics mechanisms in the stall process of airfoils for helicopters

    Science.gov (United States)

    Young, W. H., Jr.

    1981-01-01

    Phenomena that control the flow during the stall portion of a dynamic stall cycle are analyzed, and their effect on blade motion is outlined. Four mechanisms by which dynamic stall may be initiated are identified: (1) bursting of the separation bubble, (2) flow reversal in the turbulent boundary layer on the airfoil upper surface, (3) shock wave-boundary layer interaction behind the airfoil crest, and (4) acoustic wave propagation below the airfoil. The fluid mechanics that contribute to the identified flow phenomena are summarized, and the usefulness of a model that incorporates the required fluid mechanics mechanisms is discussed.

  1. Evaluation of the concept of a stall limited rotor

    Energy Technology Data Exchange (ETDEWEB)

    Agius, P.; Bennett, I.; Christie, S.; Jamieson, P. (Howden (James) and Co. Ltd., Glasgow (United Kingdom))

    1990-01-01

    Stall regulation is of interest as a potentially low cost solution to the problem of regulating the output power of wind turbines in high winds. This report deals with a review of stall regulation; the problem of how to regulate overspeed of stall regulated wind turbines in fault conditions; and a modified kind of stall regulated operation described as stall limiting. (Author).

  2. Performance of Pitch and Stall Regulated Tidal Stream Turbines

    Directory of Open Access Journals (Sweden)

    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.

  3. Stalling chaos control accelerates convergence

    Science.gov (United States)

    Bick, Christian; Kolodziejski, Christoph; Timme, Marc

    2013-06-01

    Since chaos control has found its way into many applications, the development of fast, easy-to-implement and universally applicable chaos control methods is of crucial importance. Predictive feedback control has been widely applied but suffers from a speed limit imposed by highly unstable periodic orbits. We show that this limit can be overcome by stalling the control, thereby taking advantage of the stable directions of the uncontrolled chaotic map. This analytical finding is confirmed by numerical simulations, giving a chaos-control method that is capable of successfully stabilizing periodic orbits of high period.

  4. Transition Process from Diffuser Stall to Stage Stall in a Centrifugal Compressor with a Vaned Diffuser

    Directory of Open Access Journals (Sweden)

    Nobumichi Fujisawa

    2017-01-01

    Full Text Available The transition process from a diffuser rotating stall to a stage stall in a centrifugal compressor with a vaned diffuser was investigated by experimental and numerical analyses. From the velocity measurements, it was found that the rotating stall existed on the shroud side of the diffuser passage in the off-design flow condition. The numerical results revealed the typical vortical structure of the diffuser stall. The diffuser stall cell was caused by the systematic vortical structure which consisted of the tornado-type vortex, the longitudinal vortex at the shroud/suction surface corner (i.e., leading edge vortex (LEV, and the vortex in the throat area of the diffuser passages. Furthermore, the stage stall, which rotated within both the impeller and diffuser passages, occurred instead of the diffuser stall as the mass flow rate was decreased. According to the velocity measurements at the diffuser inlet, the diffuser stall which rotated on the shroud side was shifted to the hub side. Then, the diffuser stall moved into the impeller passages and formed the stage stall. Therefore, the stage stall was caused by the development of the diffuser stall, which transferred from the shroud side to the hub side in the vaneless space and expanded to the impeller passages.

  5. 飞行结冰后复杂系统动力学仿真与风险评估%Dynamic Simulation Study of Stalling in Wing Icing Conditions and Risk Evaluation

    Institute of Scientific and Technical Information of China (English)

    刘东亮; 徐浩军; 李嘉林; 薛源

    2011-01-01

    综合考虑结冰后气动参数的变化和驾驶员动态特性,建立了结冰后人-机-环复杂系统非线性动力学仿真模型,仿真出结冰后迎角、俯仰角和俯仰角速度的变化趋势。提出了结冰恶化速率因子的概念,以迎角为临界参数,提出了通过冰型、结冰强度来判断失速的方法,提出了综合评估飞机在某一航段结冰后飞行风险的思路和对防冰系统最大允许故障率进行计算的方法,最后给出算例验证了该方法的实用性。%Considering the change of aerodynamic parameters after icing and dynamic characters of pilot,the model of iced pilot-aircraft-environment nonlinear dynamical complex simulation system was built up,and then the simulation of the change of angle of attack,pitch angle,pitch rate along with time was completed.The concept of icing deterioration velocity factor was proposed.Using angle of attack as critical parameter,a method for judging stalling based on the type and velocity of incrassation of icing was brought forward.A thought for evaluating the flighting risk caused by icing in a given route and a calculating method of the highest permitted failure rate of anti-icing system were proposed.Finally,an example was given to validate the method's practicability.

  6. Basis for an Active Stall Avoidance System

    Directory of Open Access Journals (Sweden)

    Richard Schulze

    2000-01-01

    Full Text Available A single-stage subsonic compressor was examined with respect to compressor instabilities. During the inception of rotating stall, the transients of the pressure rise and mass flow were measured as well as their hysteresis. The development of the stall cell and the characteristics of the unstable operating range were determined.

  7. 14 CFR 23.49 - Stalling period.

    Science.gov (United States)

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Stalling period. 23.49 Section 23.49 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS... period. (a) VSOand VS1are the stalling speeds or the minimum steady flight speeds, in knots (CAS), at...

  8. Analysis of Low Speed Stall Aerodynamics of a Swept Wing with Laminar Flow Glove

    Science.gov (United States)

    Bui, Trong T.

    2014-01-01

    Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) analysis was conducted to study the low-speed stall aerodynamics of a GIII aircraft's swept wing modified with a laminar-flow wing glove. The stall aerodynamics of the gloved wing were analyzed and compared with the unmodified wing for the flight speed of 120 knots and altitude of 2300 ft above mean sea level (MSL). The Star-CCM+ polyhedral unstructured CFD code was first validated for wing stall predictions using the wing-body geometry from the First American Institute of Aeronautics and Astronautics (AIAA) CFD High-Lift Prediction Workshop. It was found that the Star-CCM+ CFD code can produce results that are within the scattering of other CFD codes considered at the workshop. In particular, the Star-CCM+ CFD code was able to predict wing stall for the AIAA wing-body geometry to within 1 degree of angle of attack as compared to benchmark wind-tunnel test data. Current results show that the addition of the laminar-flow wing glove causes the gloved wing to stall much earlier than the unmodified wing. Furthermore, the gloved wing has a different stall characteristic than the clean wing, with no sharp lift drop-off at stall for the gloved wing.

  9. Analysis of Low-Speed Stall Aerodynamics of a Swept Wing with Laminar-Flow Glove

    Science.gov (United States)

    Bui, Trong T.

    2014-01-01

    Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) analysis was conducted to study the low-speed stall aerodynamics of a GIII aircraft's swept wing modified with a laminar-flow wing glove. The stall aerodynamics of the gloved wing were analyzed and compared with the unmodified wing for the flight speed of 120 knots and altitude of 2300 ft above mean sea level (MSL). The Star-CCM+ polyhedral unstructured CFD code was first validated for wing stall predictions using the wing-body geometry from the First American Institute of Aeronautics and Astronautics (AIAA) CFD High-Lift Prediction Workshop. It was found that the Star-CCM+ CFD code can produce results that are within the scattering of other CFD codes considered at the workshop. In particular, the Star-CCM+ CFD code was able to predict wing stall for the AIAA wing-body geometry to within 1 degree of angle of attack as compared to benchmark wind-tunnel test data. Current results show that the addition of the laminar-flow wing glove causes the gloved wing to stall much earlier than the unmodified wing. Furthermore, the gloved wing has a different stall characteristic than the clean wing, with no sharp lift drop-off at stall for the gloved wing.

  10. Identification of vortices in a transonic compressor flow and the stall process

    Institute of Scientific and Technical Information of China (English)

    HUANGXu-dong; CHENHai-xin; FUSong; DavidWisler; AspiWadia; G.ScottMcNulty

    2007-01-01

    A novel vortex identification method for the visualization of the flow field is used for the study of the stall process of a transonic compressor. The parameter η4, which is one of the five invariants formed by the stain rate and vorticity tensors from the theory of modern rational mechanics, is found to have good ability to identify vortex stretching and vortex relaxation/breakdown processes, is introduced here to identify the tip leakage vortices. Compare with former generally used DPH(dynamic pressure head) contour, the new method reveals much more flow details which may advance our understanding of the compressor behaviors. The Vortices details are revealed in both peak efficiency and near stall condition. A possible stall process is also suggested based on the vortices analysis. The tip leakage flow from mid-chord, besides leading edge leakage flow, is also considered to play an important role in the stall process.

  11. Biomimetic Wind Turbine Design with Lift Enhancing Periodic Stall

    NARCIS (Netherlands)

    Stamhuis, Eize

    2017-01-01

    A wind turbine includes a rotor; a blade; and a periodic stall system. The periodic stall system selectively moves at least part of the blade in an oscillating motion whereby an angle of incidence continuously varies to invoke periodic stall. The periodic stall system can move the entire blade or

  12. 14 CFR 25.103 - Stall speed.

    Science.gov (United States)

    2010-01-01

    ... standard; (5) The center of gravity position that results in the highest value of reference stall speed... speed. VSR is expressed as: ER26NO02.001 where: VCL MAX = Calibrated airspeed obtained when the load...

  13. Prediction of induced vibrations in stall

    Energy Technology Data Exchange (ETDEWEB)

    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)

  14. Continued Experimental Investigation of Dynamic Stall.

    Science.gov (United States)

    1983-12-01

    pressure were measured using a standard hemispherical-head Pitot-static probe in conjunction with a Meriam A-937 water micromanometer. These pressures...and Meriam A-937 water micro- manometer normally used to measure test section velocity in the smoke tunnel. The probe was connected to the manometer...The Meriam A-937 water micromanometer provided a means of simultaneously generating and measur- ing a low magnitude, negative pressure for the

  15. Dynamic Stall Analysis Utilizing Interactive Computer Graphics

    Science.gov (United States)

    1988-03-01

    Blade-Vortex Interaction (BV[) studies. solkes the two-dimen i,)nal, unsteady, compressible Euler and Napier -Stokes equations in strong conservation...requirements, interactive computer graphics workstations have been evolved to complement the super -computer. Workstation capabilities, in terms of

  16. Comparison of driven and simulated "free" stall flutter in a wind tunnel

    Science.gov (United States)

    Culler, Ethan; Farnsworth, John; Fagley, Casey; Seidel, Jurgen

    2016-11-01

    Stall flutter and dynamic stall have received a significant amount of attention over the years. To experimentally study this problem, the body undergoing stall flutter is typically driven at a characteristic, single frequency sinusoid with a prescribed pitching amplitude and mean angle of attack offset. This approach allows for testing with repeatable kinematics, however it effectively decouples the structural motion from the aerodynamic forcing. Recent results suggest that this driven approach could misrepresent the forcing observed in a "free" stall flutter scenario. Specifically, a dynamically pitched rigid NACA 0018 wing section was tested in the wind tunnel under two modes of operation: (1) Cyber-Physical where "free" stall flutter was physically simulated through a custom motor-control system modeling a torsional spring and (2) Direct Motor-Driven Dynamic Pitch at a single frequency sinusoid representative of the cyber-physical motion. The time-resolved pitch angle and moment were directly measured and compared for each case. It was found that small deviations in the pitch angle trajectory between these two operational cases generate significantly different aerodynamic pitching moments on the wing section, with the pitching moments nearly 180o out of phase in some cases. This work is supported by the Air Force Office of Scientific Research through the Flow Interactions and Control Program and by the National Defense Science and Engineering Graduate Fellowship Program.

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

    Directory of Open Access Journals (Sweden)

    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.

  18. 16 CFR 1505.50 - Stalled motor testing.

    Science.gov (United States)

    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...

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

    NARCIS (Netherlands)

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

    2016-01-01

    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

  20. Chaotic Time Series Analysis Method Developed for Stall Precursor Identification in High-Speed Compressors

    Science.gov (United States)

    1997-01-01

    A new technique for rotating stall precursor identification in high-speed compressors has been developed at the NASA Lewis Research Center. This pseudo correlation integral method uses a mathematical algorithm based on chaos theory to identify nonlinear dynamic changes in the compressor. Through a study of four various configurations of a high-speed compressor stage, a multistage compressor rig, and an axi-centrifugal engine test, this algorithm, using only a single pressure sensor, has consistently predicted the onset of rotating stall.

  1. Measuring stall forces in vivo with optical tweezers through light momentum changes

    Science.gov (United States)

    Mas, J.; Farré, A.; López-Quesada, C.; Fernández, X.; Martín-Badosa, E.; Montes-Usategui, M.

    2011-10-01

    The stall forces of processive molecular motors have been widely studied previously in vitro. Even so, in vivo experiments are required for determining the actual performance of each molecular motor in its natural environment. We report the direct measurement of light momentum changes in single beam optical tweezers as a suitable technique for measuring forces inside living cells, where few alternatives exist. The simplicity of this method, which does not require force calibration for each trapped object, makes it convenient for measuring the forces involved in fast dynamic biological processes such us intracellular traffic. Here we present some measurements of the stall force of processive molecular motors inside living Allium cepa cells.

  2. EXPERIMENTAL INVESTIGATION OF ROTATING STALL FOR A LOW-SPEED CENTRIFUGAL COMPRESSOR

    Institute of Scientific and Technical Information of China (English)

    ZHU Xiaocheng; GUO Qiang; DU Zhaohui; CHEN Hua; ZHAO Yan

    2008-01-01

    Unsteady flows and rotating stall of a low-speed centrifugal compressor are investigated by measuring vaneless diffuser wall static pressure fluctuation and internal flow fields at different small flow fluxes. During the experiment, firstly the real time static pressure fluctuations on the vaneless diffuser shroud at different circumferential and radial position were acquired by high-frequency dynamic pressure transducers. Discrete Fourier transformation analysis and cross-correlation analysis were applied to the experimental results to ascertain the rotating stall beginning operation conditions and stall cells numbers and rotating speed. Secondly, the vaneless diffuser inlet flow angle distribution along diffuser width direction was acquired by single hotwire, which was compared with SENOO's analysis results. At last, the internal flow fields of the centrifugal compressor were investigated with a particle image velocimetry (PIV) system at different small flow fluxes. The flow field development of vaneless diffuser and blade flow passage are given at rotating stall conditions. The experiments enrich the understanding of rotating stall flow phenomenon of the low-speed centrifugal compressor and provide full experiment data for designing high performance centrifugal compressor.

  3. Nonlinear Aeroelastic Study of Stall Induced Oscillation in a Symmetric Airfoil

    NARCIS (Netherlands)

    Sarkar, S.; Bijl, H.

    2006-01-01

    In this paper the aeroelastic stability of a wind turbine rotor in the dynamic stall regime is investigated. Increased flexibility of modern turbine blades makes them more susceptible to aeroelastic instabilities. Complex oscillation modes like flap/lead-lag are of particular concern, which give way

  4. Nonlinear Aeroelastic Study of Stall Induced Oscillation in a Symmetric Airfoil

    NARCIS (Netherlands)

    Sarkar, S.; Bijl, H.

    2006-01-01

    In this paper the aeroelastic stability of a wind turbine rotor in the dynamic stall regime is investigated. Increased flexibility of modern turbine blades makes them more susceptible to aeroelastic instabilities. Complex oscillation modes like flap/lead-lag are of particular concern, which give way

  5. VIBRATION RESPONSE AND ITS CHARACTERISTICS OF CENTRIFUGAL COMPRESSOR WITH ROTATING STALL

    Institute of Scientific and Technical Information of China (English)

    Yan Xianguo; Guan Huiling; Zhang Youyun

    2004-01-01

    Based on the beginning, propagating and ending mechanism of rotating-stall cell, the relation between the pressure history signal and the pressure distribution along rotor circumference is proposed.The angular velocities of rotating-stall cell propagating are computed from time series picked by the pressure probes on a cross section.Self-relation calculating filtered the random noise of the pressure history data.The exciting load on rotor is computed by integral of filtered pressure signal along rotor circumference.By Prohl-Myklestad method, dynamical equations of rotor system are obtained.The dynamical response of rotor system is resolved by using Matlab system.Further more, the situation of more than one of stall cells is discussed.Two cases respectively from the natural gas compressor of some fertilizer plant and the CO2 compressor of some nitrogenous fertilizer plant demonstrate that both methods of calculating the load exerted on rotor by pressure fluctuation and resolving the dynamic response of rotor are available and the characteristics of frequency spectrum of rotating stall are correct.

  6. Inviscid double wake model for stalled airfoils

    DEFF Research Database (Denmark)

    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 sep......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...

  7. Field rotor measurements. Data sets prepared for analysis of stall hysteresis

    Energy Technology Data Exchange (ETDEWEB)

    Aagaard Madsen, H.; Thirstrup Petersen, J. [Risoe National Lab. (Denmark); Bruining, A. [Delft Univ. of Technology (Netherlands); Brand, A. [ECN (Netherlands); Graham, M. [Imperical College (United Kingdom)

    1998-05-01

    As part of the JOULE-3 project `STALLVIB` an analysis and synthesis of the data from the field rotor experiments at ECN, Delft University, Imperial College, NREL and Risoe has been carried out. This has been done in order to see to what extent the data could be used for further development and validation of engineering dynamic stall models. A detailed investigation of the influence of the post-processing of the different data sets has been performed. Further, important statistical functions such as PSD spectra, coherence and transfer functions have been derived for the data sets which can be used as basis for evaluation of the quality of the data seen relative to actual application of the data. The importance of using an appropriate low-pass filtering to remove high frequency noise has been demonstrated when the relation between instantaneous values of e.g. {alpha} and C{sub N} is considered. In general, the complicated measurement on a rotor of {alpha} and w and the interpretation of these parameters combined with the strongly three-dimensional, turbulent flow field around the rotating blade has the consequence that it seems difficult to derive systematic information from the different data sets about stall hysteresis. In particular, the measurement of {alpha}, which determination of the stagnation point gives reasonable data below stall but fails in stall. On the other hand, measurements of {alpha} with a five hole pitot tube can be used also in the stall region. Another main problem is the non-dimensionalization of the coefficients C{sub N} and C{sub r}. If the dynamic pressure used for the non-dimensionalization is not fully correlated with the aerodynamic pressure over the considered airfoil section due to e.g. influence of the gravity on the pressure pipes, the hysteresis loops will be distorted. However, using the data with caution and applying a suitable post-processing as described by the different participants, it will probably be possible to obtain some

  8. Stall force of a cargo driven by N interacting motor proteins

    Science.gov (United States)

    Bhat, Deepak; Gopalakrishnan, Manoj

    2017-01-01

    We study a generic one-dimensional model for an intracellular cargo driven by N motor proteins against an external applied force. The model includes motor-cargo and motor-motor interactions. The cargo motion is described by an over-damped Langevin equation, while motor dynamics is specified by hopping rates which follow a local detailed balance condition with respect to the change in energy per hopping event. Based on this model, we show that the stall force, the mean external force corresponding to zero mean cargo velocity, is completely independent of the details of the interactions and is, therefore, always equal to the sum of the stall forces of the individual motors. This exact result is arrived on the basis of a simple assumption: the (macroscopic) state of stall of the cargo is analogous to a state of thermodynamic equilibrium, and is characterized by vanishing net probability current between any two microstates, with the latter specified by motor positions relative to the cargo. The corresponding probability distribution of the microstates under stall is also determined. These predictions are in complete agreement with numerical simulations, carried out using specific forms of interaction potentials.

  9. Nonlinear analysis and control of an aircraft in the neighbourhood of deep stall

    Science.gov (United States)

    Kolb, Sébastien; Hétru, Laurent; Faure, Thierry M.; Montagnier, Olivier

    2017-01-01

    When an aircraft is locked in a stable equilibrium at high angle-of-attack, we have to do with the so-called deep stall which is a very dangerous situation. Airplanes with T-tail are mainly concerned with this phenomenon since the wake of the main wing flows over the horizontal tail and renders it ineffective but other aircrafts such as fighters can also be affected. First the phase portrait and bifurcation diagram are determined and characterized (with three equilibria in a deep stall prone configuration). It allows to diagnose the configurations of aircrafts susceptible to deep stall and also to point out the different types of time evolutions. Several techniques are used in order to determine the basin of attraction of the stable equilibrium at high angle-of-attack. They are based on the calculation of the stable manifold of the saddle-point equilibrium at medium angle-of-attack. Then several ways are explored in order to try to recover from deep stall. They exploits static features (such as curves of pitching moment versus angle-of-attack for full pitch down and full pitch up elevators) or dynamic aspects (excitation of the eigenmodes and improvement of the aerodynamic efficiency of the tail). Finally, some properties of a deep stall prone aircraft are pointed out and some control tools are also implemented. We try also to apply this mathematical results in a concrete situation by taking into account the captors specificities or by estimating the relevant variables thanks to other available information.

  10. 14 CFR 33.65 - Surge and stall characteristics.

    Science.gov (United States)

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Surge and stall characteristics. 33.65 Section 33.65 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT... stall characteristics. When the engine is operated in accordance with operating instructions required...

  11. Theoretical analysis of transcription process with polymerase stalling

    CERN Document Server

    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...

  12. A stochastic model for the simulation of wind turbine blades in static stall

    DEFF Research Database (Denmark)

    Bertagnolio, Franck; Rasmussen, Flemming; Sørensen, Niels N.;

    2010-01-01

    The aim of this work is to improve aeroelastic simulation codes by accounting for the unsteady aerodynamic forces that a blade experiences in static stall. A model based on a spectral representation of the aerodynamic lift force is defined. The drag and pitching moment are derived using a conditi......The aim of this work is to improve aeroelastic simulation codes by accounting for the unsteady aerodynamic forces that a blade experiences in static stall. A model based on a spectral representation of the aerodynamic lift force is defined. The drag and pitching moment are derived using...... a conditional simulation technique for stochastic processes. The input data for the model can be collected either from measurements or from numerical results from a Computational Fluid Dynamics code for airfoil sections at constant angles of attack. An analysis of such data is provided, which helps to determine...

  13. FBH1 Catalyzes Regression of Stalled Replication Forks

    DEFF Research Database (Denmark)

    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...... a model whereby FBH1 promotes early checkpoint signaling by remodeling of stalled DNA replication forks....... of a 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...

  14. Experimental Characterization of Stall Noise Toward its Modelling

    DEFF Research Database (Denmark)

    Bertagnolio, Franck; Aagaard Madsen, Helge; Fischer, Andreas;

    2015-01-01

    Wind tunnel measurements of three different airfoils are investigated using surface pressure microphones flush-mounted on the suction side of the airfoils. In stalled conditions, these microphones can be used to evaluate the convection velocity and the correlation length of the turbulent vortices...... that are generated in the separated region of the stalled flow. In addition, stall is characterized by the appearance of a spectral hump at relatively low frequencies that can be measured by the microphones located in the separated region. Using appropriate normalization and scaling, a nearly universal model...

  15. Simulation Model of an Active-stall Fixed-speed Wind Turbine Controller

    DEFF Research Database (Denmark)

    Jauch, Clemens; Hansen, Anca D.; Soerensen, Poul

    2004-01-01

    This paper describes an active-stall wind turbine controller. The objective is to develop a general model of an active stall controller in order to simulate the operation of grid connected active stall wind turbines. The active stall turbine concept and its control strategies are presented and ev...

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

    Institute of Scientific and Technical Information of China (English)

    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.

  17. Stalling HIV through social marketing: prospects in Pakistan.

    Science.gov (United States)

    Husain, Sara; Shaikh, Babar T

    2005-07-01

    Over the last two decades HIV/AIDS has evolved from a series of interesting case-reports to a growing epidemic that threatens the entire world. It is feared to cause devastation among large pockets of populations and may roll back more than thirty years of public health achievements. This killer disease has been more amenable to behavioral change than by provision of curative services and attempts are being made to educate the public about this threat. Various techniques of promotion have been tried through out the world including television dramas/soaps, mass media and school curricula. Social marketing is an evolving strategy used to influence human behavior and choices. By using the principles of marketing and promoting behavior as a product, social marketers attempt to understand the dynamics of human behaviour and devise messages and products to change, modify, accept or reject unsafe behaviors or practices. Thus, social marketers provide an effective force to combat the spread of HIV and may serve to be invaluable allies in health promotion efforts. In a complex and diversified cultural milieu of Pakistan, social marketing can have a significant impact on health determinants and the conditions that will facilitate the adoption of health-oriented behaviors and practices. This paper gives an account of the elements needed for the success of a health promotion strategy adopted in a developing country and makes a case for social marketing to be adopted as the lead strategy for stalling HIV/AIDS in Pakistan.

  18. Assessing lameness in cows kept in tie-stalls.

    Science.gov (United States)

    Leach, K A; Dippel, S; Huber, J; March, S; Winckler, C; Whay, H R

    2009-04-01

    Identifying lame cows and quantifying the prevalence of lameness are important elements of cattle welfare assessment that are generally achieved by methods involving observations of each animal walking. There is no published method for assessing lameness in cows confined in tie-stalls. The objective of this study (carried out within the European Commission's Welfare Quality(R) project) was to develop a suitable method and validate it for lameness detection against a published locomotion score. A series of indicators of lameness visible in tied cows was formalized into a stall assessment protocol. This was validated against a traditional locomotion score and tested for repeatability between 2 observers. A total of 98 cows on 4 farms were assessed. Overall interobserver agreement was 91%. Sensitivity compared with locomotion scoring was 0.54 to 0.77, dependent on observer and threshold definition. Assessment in the stall underestimated the herd prevalence of lameness revealed by locomotion scoring by 11 to 37% (mean 27%). The discrepancy between herd lameness prevalence assessed in the stall and by locomotion scoring was not affected significantly by farm or observer. The cases of lameness that were not detected in the stall tended to be the least severe. The proposed method for lameness detection in tie-stalls could be used for herd-level assessment of lameness and detection of individual lame animals by farmers and their advisors, but it is important to remember that it is less sensitive than locomotion scoring.

  19. A numerical strategy for modelling rotating stall in core compressors

    Science.gov (United States)

    Vahdati, M.

    2007-03-01

    The paper will focus on one specific core-compressor instability, rotating stall, because of the pressing industrial need to improve current design methods. The determination of the blade response during rotating stall is a difficult problem for which there is no reliable procedure. During rotating stall, the blades encounter the stall cells and the excitation depends on the number, size, exact shape and rotational speed of these cells. The long-term aim is to minimize the forced response due to rotating stall excitation by avoiding potential matches between the vibration modes and the rotating stall pattern characteristics. Accurate numerical simulations of core-compressor rotating stall phenomena require the modelling of a large number of bladerows using grids containing several tens of millions of points. The time-accurate unsteady-flow computations may need to be run for several engine revolutions for rotating stall to get initiated and many more before it is fully developed. The difficulty in rotating stall initiation arises from a lack of representation of the triggering disturbances which are inherently present in aeroengines. Since the numerical model represents a symmetric assembly, the only random mechanism for rotating stall initiation is provided by numerical round-off errors. In this work, rotating stall is initiated by introducing a small amount of geometric mistuning to the rotor blades. Another major obstacle in modelling flows near stall is the specification of appropriate upstream and downstream boundary conditions. Obtaining reliable boundary conditions for such flows can be very difficult. In the present study, the low-pressure compression (LPC) domain is placed upstream of the core compressor. With such an approach, only far field atmospheric boundary conditions are specified which are obtained from aircraft speed and altitude. A chocked variable-area nozzle, placed after the last compressor bladerow in the model, is used to impose boundary

  20. Supersonic Stall Flutter of High Speed Fans. [in turbofan engines

    Science.gov (United States)

    Adamczyk, J. J.; Stevens, W.; Jutras, R.

    1981-01-01

    An analytical model is developed for predicting the onset of supersonic stall bending flutter in axial flow compressors. The analysis is based on a modified two dimensional, compressible, unsteady actuator disk theory. It is applied to a rotor blade row by considering a cascade of airfoils whose geometry and dynamic response coincide with those of a rotor blade element at 85 percent of the span height (measured from the hub). The rotor blades are assumed to be unshrouded (i.e., free standing) and to vibrate in their first flexural mode. The effects of shock waves and flow separation are included in the model through quasi-steady, empirical, rotor total-pressure-loss and deviation-angle correlations. The actuator disk model predicts the unsteady aerodynamic force acting on the cascade blading as a function of the steady flow field entering the cascade and the geometry and dynamic response of the cascade. Calculations show that the present model predicts the existence of a bending flutter mode at supersonic inlet Mach numbers. This flutter mode is suppressed by increasing the reduced frequency of the system or by reducing the steady state aerodynamic loading on the cascade. The validity of the model for predicting flutter is demonstrated by correlating the measured flutter boundary of a high speed fan stage with its predicted boundary. This correlation uses a level of damping for the blade row (i.e., the log decrement of the rotor system) that is estimated from the experimental flutter data. The predicted flutter boundary is shown to be in good agreement with the measured boundary.

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

    DEFF Research Database (Denmark)

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

    2014-01-01

    This work presents an analysis of two-dimensional (2D) and three-dimensional (3D) non-moving, prescribed motion and elastically mounted airfoil computational fluid dynamics (CFD) computations. The elastically mounted airfoil computations were performed by means of a 2D structural model with two d...... are 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....

  2. FBH1 Catalyzes Regression of Stalled Replication Forks

    Directory of Open Access Journals (Sweden)

    Kasper Fugger

    2015-03-01

    Full Text Available 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 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 required for early phosphorylation of ATM substrates such as CHK2 and CtIP as well as hyperphosphorylation of RPA. These phosphorylations occur prior to apparent DNA double-strand break formation. Furthermore, FBH1-dependent signaling promotes checkpoint control and preserves genome integrity. We propose a model whereby FBH1 promotes early checkpoint signaling by remodeling of stalled DNA replication forks.

  3. Stall Recovery Guidance Algorithms Based on Constrained Control Approaches

    Science.gov (United States)

    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.

  4. Translation regulation via nascent polypeptide-mediated ribosome stalling.

    Science.gov (United States)

    Wilson, Daniel N; Arenz, Stefan; Beckmann, Roland

    2016-04-01

    As the nascent polypeptide chain is being synthesized, it passes through a tunnel within the large ribosomal subunit. Interaction between the nascent polypeptide chain and the ribosomal tunnel can modulate the translation rate and induce translational stalling to regulate gene expression. In this article, we highlight recent structural insights into how the nascent polypeptide chain, either alone or in cooperation with co-factors, can interact with components of the ribosomal tunnel to regulate translation via inactivating the peptidyltransferase center of the ribosome and inducing ribosome stalling.

  5. An examination of gas compressor stability and rotating stall

    Science.gov (United States)

    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.

  6. Study of casing treatment stall margin improvement phenomena. [for compressor rotor blade tips compressor blades rotating stalls

    Science.gov (United States)

    Prince, D. C., Jr.; Wisler, D. C.; Hilvers, D. E.

    1974-01-01

    The results of a program of experimental and analytical research in casing treatments over axial compressor rotor blade tips are presented. Circumferential groove, axial-skewed slot, and blade angle slot treatments were tested. These yielded, for reduction in stalling flow and loss in peak efficiency, 5.8% and 0 points, 15.3% and 2.0 points, and 15.0% and 1.2 points, respectively. These values are consistent with other experience. The favorable stalling flow situations correlated well with observations of higher-then-normal surface pressures on the rotor blade pressure surfaces in the tip region, and with increased maximum diffusions on the suction surfaces. Annular wall pressure gradients, especially in the 50-75% chord region, are also increased and blade surface pressure loadings are shifted toward the trailing edge for treated configurations. Rotor blade wakes may be somewhat thinner in the presence of good treatments, particularly under operating conditions close to the baseline stall.

  7. Some aspects of the stalling of modern low-lying monoplanes

    Science.gov (United States)

    Soule, Hartley A; GOUGH MELVIN N

    1938-01-01

    The factors affecting the stalling characteristics of modern airplanes are briefly discussed. The effect of present-day design trends is shown and means for improving the stalling characteristics of future airplanes are indicated.

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

    DEFF Research Database (Denmark)

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

    2009-01-01

    , 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 attached flow region and Hansen et al. The model is compared qualitatively to wind tunnel measurements of a Riso/ B1-18 blade section equipped with deformable trailing-edge flap devices in the form of piezoelectric devices. Copyright © 2009 John Wiley & Sons, Ltd....

  9. Stalling the Learning Process: Group Dynamics in Cyberspace.

    Science.gov (United States)

    Davis, Mike; Ralph, Sue

    2001-01-01

    Findings of a study of 10 graduate student sin an online course conducted via computer conferencing included (1) the need to familiarize participants with software and ensure access; (2) differences in online and face-to-face communication and participation; and (3) the need for careful structuring and attention to detail in online courses.…

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

    DEFF Research Database (Denmark)

    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...

  11. The Mechanical Impact of Aerodynamic Stall on Tunnel Ventilation Fans

    Directory of Open Access Journals (Sweden)

    A. G. Sheard

    2012-01-01

    Full Text Available This paper describes work aimed at establishing the ability of a tunnel ventilation fan to operate without risk of mechanical failure in the event of aerodynamic stall. The research establishes the aerodynamic characteristics of a typical tunnel ventilation fan when operated in both stable and stalled aerodynamic conditions, with and without an anti-stall stabilisation ring, with and without a “nonstalling” blade angle and at full, half, and one quarter design speed. It also measures the fan’s peak stress, thus facilitating an analysis of the implications of the experimental results for mechanical design methodology. The paper concludes by presenting three different strategies for tunnel ventilation fan selection in applications where the selected fan will most likely stall. The first strategy selects a fan with a low-blade angle that is nonstalling. The second strategy selects a fan with a high-pressure developing capability. The third strategy selects a fan with a fitted stabilisation ring. Tunnel ventilation system designers each have their favoured fan selection strategy. However, all three strategies can produce system designs within which a tunnel ventilation fan performs reliably in-service. The paper considers the advantages and disadvantages of each selection strategy and considered the strengths and weaknesses of each.

  12. Microbial studies of table scrapings from meat stalls in Ibadan ...

    African Journals Online (AJOL)

    USER

    2010-05-24

    May 24, 2010 ... must not exceed levels which could adversely affect the shelf life of the ... and salad dressing, cake mixes, cream-filled desserts and toppings, dried ... arise from lack of hygiene and sanitation in such abattoirs and meat stalls.

  13. Effects of injection frequency on the rotor stall margin

    Institute of Scientific and Technical Information of China (English)

    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.

  14. Stalling Out: The Relative Progress of African Americans.

    Science.gov (United States)

    Tidwell, Billy J.

    The socioeconomic progress of African Americans appears to be in a stalled state. This study analyzes the progress of African Americans toward parity with Whites over a 15- to 20-year period in the following areas: (1) employment; (2) economic development; (3) education; (4) health; (5) housing; and (6) political empowerment. For individual…

  15. Prediction of rotating stall and cavitation inception in pump turbines

    Energy Technology Data Exchange (ETDEWEB)

    Anciger, D; Jung, A; Aschenbrenner, T, E-mail: Danijel.Anciger@voith.co [Voith Hydro Holding GmbH and Co. KG Alexanderstr. 11, 89522 Heidenheim (Germany)

    2010-08-15

    The current development of modern pump storage plants aims towards a higher flexibility in operation, an extended operation range of the hydraulic machine, especially in the pumping mode, and a higher reliability. A major design target for state-of-the-art reversible Francis-type pump turbines is to find an optimal balance between pumping and generating performance. The pumping requirements are the crucial design drivers, since, even if the turbine mode performance is world class, the success of a project depends on the pump turbine delivering the required maximum pump head and starting reliably in pump mode. The proposed paper describes how advanced computational fluid dynamic (CFD) simulations can help the designer to evaluate his design with respect to hydraulic performance and dynamic phenomena occurring in pump turbines. A standard procedure today is to compute the flow by applying the Reynolds-averaged Navier-Stokes equations (RANS) on the steady-state flow in individual components or in multiple components which are coupled by mixing-plane interfaces (sometimes also called stage-interface). This standard approach gives fast turnaround times and is a good engineering tool. However, accuracy is limited due to necessary simplifications. Therefore methods are developed and evaluated which allow a more reliable prediction of the onset of rotating stall which is the operation limit of the pump under high heads and low flow rates. The behaviour a modern pump turbine design in this instability region is investigated in detail. Another important task in the design process is the proper prediction of cavitation phenomena in the runner. Predicting cavitating flows with multi-phase CFD computations is still a very challenging task. Some results of ongoing work in this field are presented and compared to single phase computations and results from model tests. The relevance and applicability of such computations is discussed. All the information gained from these kinds of

  16. A semi-empirical airfoil stall noise model based on surface pressure measurements

    DEFF Research Database (Denmark)

    Bertagnolio, Franck; Aagaard Madsen, Helge; Fischer, Andreas

    2017-01-01

    This work is concerned with the experimental study of airfoil stall and the modelling of stall noise. Using pressure taps and high-frequency surface pressure microphones flush-mounted on airfoils measured in wind tunnels and on an operating wind turbine blade, the characteristics of stall are ana...

  17. Stalled and stall-free performance of axial-flow compressor stage with three inlet-guide-vane and stator-blade settings

    Science.gov (United States)

    Urasek, D. C.; Steinke, R. J.; Cunnan, W. S.

    1977-01-01

    The performance of the first stage of a transonic, multistage compressor was mapped over a range of inlet-guide-vane and stator-blade settings. Both stall-free and deep-stall performance data were obtained. For the settings tested, as stall was encountered and flow was further reduced, a relatively sharp drop in pressure ratio occurred and was followed by a continuing but more gradual reduction in pressure ratio with reduced flow. The position of the stall line on the map of pressure ratio against equivalent weight flow was essentially unaffected over the range of inlet-guide-vane and stator-blade settings.

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

    Institute of Scientific and Technical Information of China (English)

    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.

  19. A method for localizing wing flow separation at stall to alleviate spin entry tendencies

    Science.gov (United States)

    Feistel, T. W.; Anderson, S. B.; Kroeger, R. A.

    1978-01-01

    A wing leading-edge modification has been developed, applicable at present to single-engine light aircraft, which produces stabilizing vortices at stall and beyond. These vortices have the effect of fixing the stall pattern of the wing such that the various portions of the wing upper surface stall nearly symmetrically. The lift coefficient produced is essentially constant to very high angles of attack above the stall angle of the unmodified wing. It is hypothesized that these characteristics will help prevent inadvertent spin entry after a stall. Results are presented from recent large-scale wind-tunnel tests of a complete light aircraft, both with and without the modification.

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

    Directory of Open Access Journals (Sweden)

    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.

  1. Experimental Methods Applied in a Study of Stall Flutter in an Axial Flow Fan

    Directory of Open Access Journals (Sweden)

    John D. Gill

    2004-01-01

    Full Text Available Flutter testing is an integral part of aircraft gas turbine engine development. In typical flutter testing blade mounted sensors in the form of strain gages and casing mounted sensors in the form of light probes (NSMS are used. Casing mounted sensors have the advantage of being non-intrusive and can detect the vibratory response of each rotating blade. Other types of casing mounted sensors can also be used to detect flutter of rotating blades. In this investigation casing mounted high frequency response pressure transducers are used to characterize the part-speed stall flutter response of a single stage unshrouded axial-flow fan. These dynamic pressure transducers are evenly spaced around the circumference at a constant axial location upstream of the fan blade leading edge plane. The pre-recorded experimental data at 70% corrected speed is analyzed for the case where the fan is back-pressured into the stall flutter zone. The experimental data is analyzed using two probe and multi-probe techniques. The analysis techniques for each method are presented. Results from these two analysis methods indicate that flutter occurred at a frequency of 411 Hz with a dominant nodal diameter of 2. The multi-probe analysis technique is a valuable method that can be used to investigate the initiation of flutter in turbomachines.

  2. Air Conditioning Stall Phenomenon Testing, Model Development, and Simulation

    Energy Technology Data Exchange (ETDEWEB)

    Irminger, Philip [ORNL; Rizy, D Tom [ORNL; Li, Huijuan [ORNL; Smith, Travis [ORNL; Rice, C Keith [ORNL; Li, Fangxing [ORNL; Adhikari, Sarina [ORNL

    2012-01-01

    Electric distribution systems are experiencing power quality issues of extended reduced voltage due to fault-induced delayed voltage recovery (FIDVR). FIDVR occurs in part because modern air conditioner (A/C) and heat pump compressor motors are much more susceptible to stalling during a voltage sag or dip such as a sub-transmission fault. They are more susceptible than older A/C compressor motors due to the low inertia of these newer and more energy efficient motors. There is a concern that these local reduced voltage events on the distribution system will become more frequent and prevalent and will combine over larger areas and challenge transmission system voltage and ultimately power grid reliability. The Distributed Energy Communications and Controls (DECC) Laboratory at Oak Ridge National Laboratory (ORNL) has been employed to (1) test, (2) characterize and (3) model the A/C stall phenomenon.

  3. Rotating Stall Suppression Using Oscillatory Blowing Actuation on Blades

    Science.gov (United States)

    2010-06-30

    AIAA Aerospace Sciences Meeting , Number 2009-1242, AIAA. Honors and Awards Received NONE AFRL Point of Contact Dr. Steven Puterbaugh and Dr. Todd...Rediniotis (2009, January). Internal plenum design and testing for an oscillatory blowing stall suppression system. In 47th AIAA Aerospace Sciences ...Meeting, Number 2009-1242. AIAA. Carter, C. J., S. A. Guillot, W. F. Ng, and W. W. Copenhaver (2001, July). Aerodynamic perfor- mace of a high-turning

  4. Performance traits of dairy cows stabled in tie stalls

    OpenAIRE

    Marková, Lenka

    2013-01-01

    The aim of this thesis was the evaluation of fertility and production traits stabled in tie stalls. 50 pure-bred Holstein cows were monitored and those traits were evaluated: interval of insemination, service period, calving interval, milk yield and content of milk protein and fat. All monitored cows finished standard lactation period (305 days) in year 2012. The evaluation was performed in relation to lactation order. Nearly all of fertility traits were evaluated as bad. The average interval...

  5. Flow and Performance Calculations of Axial Compressor near Stall Margin

    Science.gov (United States)

    Hwang, Yoojun; Kang, Shin-Hyoung

    2010-06-01

    Three-dimensional flows through a Low Speed Research Axial Compressor were numerically conducted in order to estimate the performance through unsteady and steady-state simulations. The first stage with the inlet guide vane was investigated at the design point to confirm that the rotor blade induced periodicity exists. Special attention was paid to the flow near the stall condition to inspect the flow behavior in the vicinity of the stall margin. The performance predicted under the steady-state assumption is in good agreement with the measured data. However, the steady-state calculations induce more blockage through the blade passage. Flow separations on the blade surface and end-walls are reduced when unsteady simulation is conducted. The negative jet due to the wake of the rotor blade periodically distorts the boundary layer on the surface of the stator blade and improves the performance of the compressor in terms of the pressure rise. The advantage of the unsteadiness increases as the flow rate reduces. In addition, the rotor tip leakage flow is forced downstream by the unsteadiness. Consequently, the behavior contributes to extending the range of operation by preventing the leakage flow from proceeding upstream near the stall margin.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  7. Study and Control of a Radial Vaned Diffuser Stall

    Directory of Open Access Journals (Sweden)

    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.

  8. Recent research in rotating stall chaos, fractals and attractors; Recherche recente en decrochage tournant chaos, fractales et attracteurs

    Energy Technology Data Exchange (ETDEWEB)

    Breugelmans, F.A.E. [Institut von Karman Rhode-St. Genese (Belgium). Dept. Turbomachines; Palomba, C. [Cagliari Univ. (Italy). Dept. de Mecanique

    1998-12-01

    As the mass flow is reduced at constant rotational speed, a fluid dynamic instability arises in axial-flow compressors, placing an upper limit to their operative range: rotating stall. When the compressor enters stall, the flow pattern shows quite a range of possible configurations depending not only on the specific machine built but also in the characteristic of the joined net and on the throttle operation. The particular behavior of this nonlinear complex-but-structured phenomenon has suggested a scientific approach with the tools of chaos theory. The phase space reconstruction technique has been applied to the time traces recorded during stalled operation of two different axial-flow compressors with the aid of five different sensors. The topological structure of the phase portraits is investigated through fractal analysis algorithms and the attractors are found have a fractal dimension typical of chaotic and strange attractors. Comparisons are made between same operating conditions but different sensors and similar operating conditions on the two rotors. The predictive aspect of an attractor is investigated. (authors) 27 refs.

  9. Predictions of the cycle-to-cycle aerodynamic loads on a yawed wind turbine blade under stalled conditions using a 3D empirical stochastic model

    Science.gov (United States)

    ELGAMMI, MOUTAZ; SANT, TONIO

    2016-09-01

    This paper investigates a new approach to model the stochastic variations in the aerodynamic loads on yawed wind turbines experienced at high angles of attack. The method applies the one-dimensional Langevin equation in conjunction with known mean and standard deviation values for the lift and drag data. The method is validated using the experimental data from the NREL Phase VI rotor in which the mean and standard deviation values for the lift and drag are derived through the combined use of blade pressure measurements and a free-wake vortex model. Given that direct blade pressure measurements are used, 3D flow effects arising from the co-existence of dynamic stall and stall delay are taken into account. The model is an important step towards verification of several assumptions characterized as the estimated standard deviation, Gaussian white noise of the data and the estimated drift and diffusion coefficients of the Langevin equation. The results using the proposed assumptions lead to a good agreement with measurements over a wide range of operating conditions. This provides motivation to implement a general fully independent theoretical stochastic model within a rotor aerodynamics model, such as the free-wake vortex or blade-element momentum code, whereby the mean lift and drag coefficients can be estimated using 2D aerofoil data with correction models for 3D dynamic stall and stall delay phenomena, while the corresponding standard derivations are estimated through CFD.

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

    Science.gov (United States)

    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

  11. Visualization and Analysis of Rotating Stall for Transonic Jet Engine Simulation.

    Science.gov (United States)

    Cher, Chun-Ming; Dutta, Soumya; Liu, Xiaotong; Heinlein, Gregory; Shen, Han-Wei; Chen, Jen-Ping

    2016-01-01

    Identification of early signs of rotating stall is essential for the study of turbine engine stability. With recent advancements of high performance computing, high-resolution unsteady flow fields allow in depth exploration of rotating stall and its possible causes. Performing stall analysis, however, involves Significant effort to process large amounts of simulation data, especially when investigating abnormalities across many time steps. In order to assist scientists during the exploration process, we present a visual analytics framework to identify suspected spatiotemporal regions through a comparative visualization so that scientists are able to focus on relevant data in more detail. To achieve this, we propose efficient stall analysis algorithms derived from domain knowledge and convey the analysis results through juxtaposed interactive plots. Using our integrated visualization system, scientists can visually investigate the detected regions for potential stall initiation and further explore these regions to enhance the understanding of this phenomenon. Positive feedback from scientists demonstrate the efficacy of our system in analyzing rotating stall.

  12. Effect of diffuser width on rotating stall in centrifugal blower with vaneless diffuser

    Energy Technology Data Exchange (ETDEWEB)

    Kim, J.H. [Small and Medium Industry Promotion Corporation (Korea); Cho, K.R. [Yonsei University, Seoul (Korea)

    2001-10-01

    It is generally known that radial vane blowers with vaneless diffuser may generate mostly only a rotating stall but backward curved vane blowers may do both an impeller and a diffuser rotating stalls. In this study, it was found from the numerical and experimental results that the diffuser rotating stall does not appear in a radial vane because of the suppression for the diffuser stall appearance by occuring of impeller rotating stall in a large flow rate coefficient. The diffuser rotating stalls occurring when the width of diffuser is broaden for a backward curved vane blower are classified definitely by the diffuser flow rate coefficient defined by adopting the varying diffuser width. (author). 12 refs., 9 figs.

  13. Experimental Investigation of High-Pressure Steam Induced Stall of a Transonic Rotor

    Science.gov (United States)

    2007-06-01

    disturbance can occur anywhere in a turbomachine and may be present during typical operation in small areas. When localized disturbances expand, stall...describe the flow breakdown over a particular stage of a turbomachine . Stall, however, often leads to a more damaging phenomenon known as surge. 3...Surge The cyclic stalling of a stage in a turbomachine is referred to as surge. Surge occurs when both the rotor and stator in a certain stage

  14. Structural basis for translational stalling by human cytomegalovirus and fungal arginine attenuator peptide

    OpenAIRE

    2010-01-01

    Specific regulatory nascent chains establish direct interactions with the ribosomal tunnel, leading to translational stalling. Despite a wealth of biochemical data, structural insight into the mechanism of translational stalling in eukaryotes is still lacking. Here we use cryo-electron microscopy to visualize eukaryotic ribosomes stalled during the translation of two diverse regulatory peptides: the fungal arginine attenuator peptide (AAP) and the human cytomegalovirus (hCMV) gp48 upstream op...

  15. Laser-Doppler velocimeter measurements in a cascade of controlled diffusion compressor blades at stall

    OpenAIRE

    Ganaim Rickel, Humberto Javier

    1994-01-01

    Approved for public release, distribution unlimited An incipient compressor blade stall has been generated and examined in the Low Speed Cascade Wind Tunnel at the Turbopropulsion Laboratory. The test blades were a controlled-diffusion design with solidity 1.67, and stalling occurred at 10 degrees of incidence above the design inlet air angle. Tufting and laser-sheet flow-visualization techniques showed that the stalling process was unsteady, and occurred over the whole cascade of 20 blade...

  16. Preferences of dairy cows for three stall surface materials with small amounts of bedding.

    Science.gov (United States)

    Norring, M; Manninen, E; de Passillé, A M; Rushen, J; Saloniemi, H

    2010-01-01

    Farmers' concerns about the economy, cost of labor, and hygiene have resulted in reduced use of organic bedding in stalls for dairy cows; however, the reduced use of organic bedding possibly impairs cow comfort. The effects of different stall surface materials were evaluated in an unheated building in which only a small amount of bedding was used. The lying time and preferences of 18 cows using 3 stall surface materials (concrete, soft rubber mat, and sand) were compared. All materials were lightly bedded with a small amount of straw, and the amount of straw added to each stall was measured. The cows only had access to stalls of one surface type while their lying time was observed. Lying times were longest on the rubber mats compared with other surfaces (rubber mat 768; concrete 727; sand 707+/-16 min/d). In a preference test, cows had access to 2 of the 3 types of stalls for 10 d and their stall preference was measured. Cows preferred stalls with rubber mats to stalls with a concrete floor (median 73 vs. 18 from a total of 160 observations per day; interquartile range was 27 and 12, respectively), but showed no preference for sand stalls compared with stalls with a concrete floor or with rubber mats. More straw was needed on sand stalls compared with concrete or mat (638+/-13 g/d on sand, 468+/-10 g/d on concrete, and 464+/-8 g/d on rubber mats). Lying times on bedded mats indicated that mats were comfortable for the cows. If availability or cost of bedding material requires limiting the amount of bedding used, rubber mats may help maintain cow comfort.

  17. Inception mechanism and suppression of rotating stall in an axial-flow fan

    Science.gov (United States)

    Nishioka, T.

    2013-12-01

    Inception patterns of rotating stall at two stagger-angle settings for the highly loaded rotor blades were experimentally investigated in a low-speed axial-flow fan. Rotor-tip flow fields were also numerically investigated to clarify the mechanism behind the rotating stall inception. The stall inception patterns depended on the rotor stagger-angle settings. The stall inception from a rotating instability was confirmed at the design stagger-angle settings. The stall inception from a short length-scale stall cell (spike) was also confirmed at the small stagger-angle setting. The spillage of tip-leakage flow and the tip-leakage vortex breakdown influence the rotating stall inception. An air-separator has been developed based on the clarified inception mechanism of rotating stall. The rotating stall was suppressed by the developed air-separator, and the operating range of fan was extended towards low flow rate. The effect of developed air-separator was also confirmed by application to a primary air fan used in a coal fired power plant. It is concluded from these results that the developed air-separator can provide a wide operating range for an axial-flow fan.

  18. Checkpoint responses to replication stalling: inducing tolerance and preventing mutagenesis

    Energy Technology Data Exchange (ETDEWEB)

    Kai, Mihoko; Wang, Teresa S.-F

    2003-11-27

    Replication mutants often exhibit a mutator phenotype characterized by point mutations, single base frameshifts, and the deletion or duplication of sequences flanked by homologous repeats. Mutation in genes encoding checkpoint proteins can significantly affect the mutator phenotype. Here, we use fission yeast (Schizosaccharomyces pombe) as a model system to discuss the checkpoint responses to replication perturbations induced by replication mutants. Checkpoint activation induced by a DNA polymerase mutant, aside from delay of mitotic entry, up-regulates the translesion polymerase DinB (Pol{kappa}). Checkpoint Rad9-Rad1-Hus1 (9-1-1) complex, which is loaded onto chromatin by the Rad17-Rfc2-5 checkpoint complex in response to replication perturbation, recruits DinB onto chromatin to generate the point mutations and single nucleotide frameshifts in the replication mutator. This chain of events reveals a novel checkpoint-induced tolerance mechanism that allows cells to cope with replication perturbation, presumably to make possible restarting stalled replication forks. Fission yeast Cds1 kinase plays an essential role in maintaining DNA replication fork stability in the face of DNA damage and replication fork stalling. Cds1 kinase is known to regulate three proteins that are implicated in maintaining replication fork stability: Mus81-Eme1, a hetero-dimeric structure-specific endonuclease complex; Rqh1, a RecQ-family helicase involved in suppressing inappropriate recombination during replication; and Rad60, a protein required for recombinational repair during replication. These Cds1-regulated proteins are thought to cooperatively prevent mutagenesis and maintain replication fork stability in cells under replication stress. These checkpoint-regulated processes allow cells to survive replication perturbation by preventing stalled replication forks from degenerating into deleterious DNA structures resulting in genomic instability and cancer development.

  19. Stalled replication forks within heterochromatin require ATRX for protection.

    Science.gov (United States)

    Huh, M S; Ivanochko, D; Hashem, L E; Curtin, M; Delorme, M; Goodall, E; Yan, K; Picketts, D J

    2016-05-12

    Expansive growth of neural progenitor cells (NPCs) is a prerequisite to the temporal waves of neuronal differentiation that generate the six-layered neocortex, while also placing a heavy burden on proteins that regulate chromatin packaging and genome integrity. This problem is further reflected by the growing number of developmental disorders caused by mutations in chromatin regulators. ATRX gene mutations cause a severe intellectual disability disorder (α-thalassemia mental retardation X-linked (ATRX) syndrome; OMIM no. 301040), characterized by microcephaly, urogenital abnormalities and α-thalassemia. Although the ATRX protein is required for the maintenance of repetitive DNA within heterochromatin, how this translates to disease pathogenesis remain poorly understood and was a focus of this study. We demonstrate that Atrx(FoxG1Cre) forebrain-specific conditional knockout mice display poly(ADP-ribose) polymerase-1 (Parp-1) hyperactivation during neurogenesis and generate fewer late-born Cux1- and Brn2-positive neurons that accounts for the reduced cortical size. Moreover, DNA damage, induced Parp-1 and Atm activation is elevated in progenitor cells and contributes to their increased level of cell death. ATRX-null HeLa cells are similarly sensitive to hydroxyurea-induced replication stress, accumulate DNA damage and proliferate poorly. Impaired BRCA1-RAD51 colocalization and PARP-1 hyperactivation indicated that stalled replication forks are not efficiently protected. DNA fiber assays confirmed that MRE11 degradation of stalled replication forks was rampant in the absence of ATRX or DAXX. Indeed, fork degradation in ATRX-null cells could be attenuated by treatment with the MRE11 inhibitor mirin, or exacerbated by inhibiting PARP-1 activity. Taken together, these results suggest that ATRX is required to limit replication stress during cellular proliferation, whereas upregulation of PARP-1 activity functions as a compensatory mechanism to protect stalled forks

  20. Just a Tea Stall Girl: Lessons from India

    Directory of Open Access Journals (Sweden)

    2005-05-01

    Full Text Available This article charts the learning of a female academic who travelled and volunteered in southern India during a sabbatical leave from her university. Opportunities to discover gender, race and class connections ranged from tea-stall conversations to academic symposia; from outings with impoverished Indian families to excursions with social justice organizations. The author explores topics that include dowry, politics, globalization, communalism, and poverty. To illustrate her learning, she draws on the work of such renowned Indian scholars as Ali Ashgar Engineer and Vandana Shiva.

  1. Experimental Investigations of Micro Air Injection to Control Rotating Stall

    Institute of Scientific and Technical Information of China (English)

    Chaoqun Nie; Zhiting Tong; Shaojuan Geng; Junqiang Zhu; Weiguang Huang

    2007-01-01

    Steady discrete micro air injection at the tip region in front of the first compressor rotor has been proved to be an effective method to delay the inception of rotating stall in a low speed axial compressor. Considering the practical application a new type of micro injector was designed and described in this paper, which was imbedded in the casing and could be moved along the chord. In order to verify its feasibility to other cases, such as high subsonic axial compressor or centrifugal compressor, some other cases have been studied. Experimental results of the same low speed axial compressor showed that the new injector could possess many other advantages besides successfully stabilizing the compressor. Experiments performed on a high subsonic axial compressor confirmed the effectiveness of micro air injection when the relative velocity at the blade tip is high subsonic. Meanwhile in order to explore its feasibility in centrifugal compressor, a similar micro injector was designed and tested on a low speed centrifugal compressor with vaned diffuser. The injected mass flow was a bit larger than that used in axial compressors and the results showed micro injection could also delay the onset of rotating stall in the centrifugal compressor.

  2. Flap/Lag Stall Flutter Control of Large-Scale Wind Turbine Blade Based on Robust H2 Controller

    Directory of Open Access Journals (Sweden)

    Tingrui Liu

    2016-01-01

    Full Text Available Flap/lag stall nonlinear flutter and active control of anisotropic composite wind turbine blade modeled as antisymmetric beam analysis have been investigated based on robust H2 controller. The blade is modeled as single-cell thin-walled beam structure, exhibiting flap bending moment-lag transverse shear deformation, and lag bending moment-flap transverse shear deformation, with constant pitch angle set. The stall flutter control of dynamic response characteristics of composite blade incorporating nonlinear aerodynamic model is investigated based on some structural and dynamic parameters. The aeroelastic partial differential equations are reduced by Galerkin method, with the aerodynamic forces decomposed by strip theory. Robust H2 optimal controller is developed to enhance the vibrational behavior and dynamic response to aerodynamic excitation under extreme wind conditions and stabilize structures that might be damaged in the absence of control. The effectiveness of the control algorithm is demonstrated in both amplitudes and frequencies by description of time responses, extended phase planes, and frequency spectrum analysis, respectively.

  3. Sufficient conditions for the additivity of stall forces generated by multiple filaments or motors

    Science.gov (United States)

    Bameta, Tripti; Das, Dipjyoti; Das, Dibyendu; Padinhateeri, Ranjith; Inamdar, Mandar M.

    2017-02-01

    Molecular motors and cytoskeletal filaments work collectively most of the time under opposing forces. This opposing force may be due to cargo carried by motors or resistance coming from the cell membrane pressing against the cytoskeletal filaments. Some recent studies have shown that the collective maximum force (stall force) generated by multiple cytoskeletal filaments or molecular motors may not always be just a simple sum of the stall forces of the individual filaments or motors. To understand this excess or deficit in the collective force, we study a broad class of models of both cytoskeletal filaments and molecular motors. We argue that the stall force generated by a group of filaments or motors is additive, that is, the stall force of N number of filaments (motors) is N times the stall force of one filament (motor), when the system is reversible at stall. Conversely, we show that this additive property typically does not hold true when the system is irreversible at stall. We thus present a novel and unified understanding of the existing models exhibiting such non-addivity, and generalise our arguments by developing new models that demonstrate this phenomena. We also propose a quantity similar to thermodynamic efficiency to easily predict this deviation from stall-force additivity for filament and motor collectives.

  4. Simulation of Entropy Generation under Stall Conditions in a Centrifugal Fan

    Directory of Open Access Journals (Sweden)

    Lei Zhang

    2014-06-01

    Full Text Available Rotating stalls are generally the first instability met in turbomachinery, before surges. This 3D phenomenon is characterized by one or more stalled flow cells which rotate at a fraction of the impeller speed. The goal of the present work is to shed some light on the entropy generation in a centrifugal fan under rotating stall conditions. A numerical simulation of entropy generation is carried out with the ANSYS Fluent software which solves the Navier-Stokes equations and user defined function (UDF. The entropy generation characteristics in the centrifugal fan for five typical conditions are presented and discussed, involving the design condition, conditions on occurrence and development of stall inception, the rotating stall conditions with two throttle coefficients. The results show that the entropy generation increases after the occurrence of stall inception. The high entropy generation areas move along the circumferential and axial directions, and finally merge into one stall cell. The entropy generation rate during circumferential propagation of the stall cell is also discussed, showing that the entropy generation history is similar to sine curves in impeller and volute, and the volute tongue has a great influence on entropy generation in the centrifugal fan.

  5. An Examination of Stallings'"Implementation and Child Effects of Teaching Practices in Follow Through Classrooms."

    Science.gov (United States)

    Adolf, Jane W.

    The purpose of this paper is to critique Stallings' 1975 evaluation of Project Follow Through (PFT) in order to examine methodological issues inherent in evaluation research. Following a summary of the objectives, methods, and conclusions of Stallings' study, the critique focuses on four elements of research evaluation: internal validity, external…

  6. An experimental study on the rotating stall in vaneless diffuser of centrifugal blower with radial type impeller

    Energy Technology Data Exchange (ETDEWEB)

    Kim, J.H. [Yonsei University Graduate School, Seoul (Korea, Republic of); Cho, K.R. [Yonsei University, Seoul (Korea, Republic of)

    1998-09-01

    The vaneless diffusers are widely used in industrial centrifugal compressors which are required to operate within a wide flow range. When very high pressure gases are handled by centrifugal compressor, rotating stall is a serious problem because of the occurrence of large aerodynamic exciting forces. Rotating stall mostly often occurs in the impellers but it can occur in vaneless diffusers as well. In this experimental study, the rotating stall in vaneless diffuser with radial type centrifugal impeller was measured by changing the flow rate with I-type, X-type hot-wire. As the result, it was cleared which type of rotating stall of the impeller stall would occur and how many stall cells would appear relating with the flow rate. As the flow rate reduced, the propagation speed of rotating stall was reduced. But the stall cell number unchanged with respect to the flow rate. (author). 7 refs., 13 figs.

  7. Wider stall space affects behavior, lesion scores, and productivity of gestating sows.

    Science.gov (United States)

    Salak-Johnson, J L; DeDecker, A E; Levitin, H A; McGarry, B M

    2015-10-01

    Limited space allowance within the standard gestation stall is an important welfare concern because it restricts the ability of the sow to make postural adjustments and hinders her ability to perform natural behaviors. Therefore, we evaluated the impacts of increasing stall space and/or providing sows the freedom to access a small pen area on sow well-being using multiple welfare metrics. A total of 96 primi- and multiparous crossbred sows were randomly assigned in groups of 4 sows/treatment across 8 replicates to 1 of 3 stall treatments (TRT): standard stall (CTL; dimensions: 61 by 216 cm), width-adjustable stall (flex stall [FLX]; dimensions: adjustable width of 56 to 79 cm by 216 cm), or an individual walk-in/lock-in stall with access to a small communal open-pen area at the rear of the stall (free-access stall [FAS]; dimensions: 69 by 226 cm). Lesion scores, behavior, and immune and productivity traits were measured at various gestational days throughout the study. Total lesion scores were greatest for sows in FAS and least for sows in FLX ( sows in FAS had the most severe lesion scores (TRT × parity, sows in FLX had the least severe scores ( sows in CTL ( Sow BW and backfat (BF) were greater for sows in FLX and FAS ( sows in FAS than the same parity sows in CTL (TRT × parity, sows as assessed by changes in postural behaviors, lesion severity scores, and other sow traits. Moreover, compromised welfare measures found among sows in various stall environments may be partly attributed to the specific constraints of each stall system such as restricted stall space in CTL, insufficient floor space in the open-pen area of the FAS system, and gate design of the FLX (e.g., direction of bars and feeder space). These results also indicate that parity and gestational day are additional factors that may exacerbate the effects of restricted stall space or insufficient pen space, further compromising sow well-being.

  8. Large Eddy Simulation of Surface Pressure Fluctuations on a Stalled Airfoil

    Science.gov (United States)

    Lele, Sanjiva; Kocheemoolayil, Joseph

    2016-11-01

    The surface pressure fluctuations beneath the separated flow over a turbine blade are believed to be responsible for a phenomenon known as Other Amplitude Modulation (OAM) of wind turbine noise. Developing the capability to predict stall noise from first-principles is a pacing item within the context of critically evaluating this conjecture. We summarize the progress made towards using large eddy simulations to predict stall noise. Successful prediction of pressure fluctuations on the airfoil surface beneath the suction side boundary layer is demonstrated in the near-stall and post-stall regimes. Previously unavailable two-point statistics necessary for characterizing the surface pressure fluctuations more completely are documented. The simulation results indicate that the space-time characteristics of pressure fluctuations on the airfoil surface change drastically in the near-stall and post-stall regimes. The changes are not simple enough to be accounted for by straight-forward scaling laws. The eddies responsible for surface pressure fluctuations and hence far-field noise are significantly more coherent across the span of the airfoil in the post-stall regime relative to the more canonical attached configurations.

  9. Effects of laminar separation bubbles and turbulent separation on airfoil stall

    Energy Technology Data Exchange (ETDEWEB)

    Dini, P. [Carleton College, Northfield, MN (United States); Coiro, D.P. [Universita di Napoli (Italy)

    1997-12-31

    An existing two-dimensional, interactive, stall prediction program is extended by improving its laminar separation bubble model. The program now accounts correctly for the effects of the bubble on airfoil performance characteristics when it forms at the mid-chord and on the leading edge. Furthermore, the model can now predict bubble bursting on very sharp leading edges at high angles of attack. The details of the model are discussed in depth. Comparisons of the predicted stall and post-stall pressure distributions show excellent agreement with experimental measurements for several different airfoils at different Reynolds numbers.

  10. Research on Aero-Thermodynamic Distortion Induced Structural Dynamic Response of Multistage Compressor Blading

    Science.gov (United States)

    1992-03-01

    compresor operating point. Also, the reduced steady surface pressure distributions and steady lift for thesolidity has much higher pressure differences and...including stall flutter and dynamic stall , Received May 9. 198 revision received Oct. 10. 1988. Copyright also have been addressed. Thus, oscillating...function, with the last ’ 2Yashima. S., and Tanaka. H.. "Torsional Flutter in Stalled stage stator vane row replaced with isolated instrumented Cascade

  11. Roaming About the Ground Stalls ——A Special Scene in Beijing

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    NOT quite as overwhelming as the GreatWall, Forbidden City or Chinese Opera,roaming amongst the stalls scattered on theground at markets like Beijing’s Panjiayuanis nevertheless a cultural experience uniqueto China.

  12. A study of casing treatment stall margin improvement phenomena. [for axial compressor rotor blade tips

    Science.gov (United States)

    Prince, D. C., Jr.; Wisler, D. C.; Hilvers, D. E.

    1975-01-01

    The results of a program of experimental and analytical research in casing treatments over axial compressor rotor blade tips are presented. Circumferential groove, axial-skewed slot and blade angle slot treatments were tested at low speeds. With the circumferential groove treatment the stalling flow was reduced 5.8% at negligible efficiency sacrifice. The axial-skewed slot treatment improved the stalling flow by 15.3%; 1.8 points in peak efficiency were sacrificed. The blade angle slot treatment improved the stalling flow by 15.0%; 1.4 points in peak efficiency were sacrificed. The favorable stalling flow situations correlated well with observations of higher-than-normal surface pressures on the rotor blade pressure surfaces in the tip region, and with increased maximum diffusions on the suction surfaces. Annulus wall pressure gradients, especially in the 50 to 75% chord region, are also increased and blade surface pressure loadings are shifted toward the trailing edge for treated configurations.

  13. An experimental and analytical investigation of stall effects on flap-lag stability in forward flight

    Science.gov (United States)

    Nagabhushanam, J.; Gaonkar, Gopal H.; Mcnulty, Michael J.

    1987-01-01

    Experiments have been performed with a 1.62 m diameter hingeless rotor in a wind tunnel to investigate flap-lag stability of isolated rotors in forward flight. The three-bladed rotor model closely approaches the simple theoretical concept of a hingeless rotor as a set of rigid, articulated flap-lag blades with offset and spring restrained flap and lag hinges. Lag regressing mode stability data was obtained for advance ratios as high as 0.55 for various combinations of collective pitch and shaft angle. The prediction includes quasi-steady stall effects on rotor trim and Floquet stability analyses. Correlation between data and prediction is presented and is compared with that of an earlier study based on a linear theory without stall effects. While the results with stall effects show marked differences from the linear theory results, the stall theory still falls short of adequate agreement with the experimental data.

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

    Energy Technology Data Exchange (ETDEWEB)

    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)

  15. BRCA1 controls homologous recombination at Tus/Ter-stalled mammalian replication forks.

    Science.gov (United States)

    Willis, Nicholas A; Chandramouly, Gurushankar; Huang, Bin; Kwok, Amy; Follonier, Cindy; Deng, Chuxia; Scully, Ralph

    2014-06-26

    Replication fork stalling can promote genomic instability, predisposing to cancer and other diseases. Stalled replication forks may be processed by sister chromatid recombination (SCR), generating error-free or error-prone homologous recombination (HR) outcomes. In mammalian cells, a long-standing hypothesis proposes that the major hereditary breast/ovarian cancer predisposition gene products, BRCA1 and BRCA2, control HR/SCR at stalled replication forks. Although BRCA1 and BRCA2 affect replication fork processing, direct evidence that BRCA gene products regulate homologous recombination at stalled chromosomal replication forks is lacking, due to a dearth of tools for studying this process. Here we report that the Escherichia coli Tus/Ter complex can be engineered to induce site-specific replication fork stalling and chromosomal HR/SCR in mouse cells. Tus/Ter-induced homologous recombination entails processing of bidirectionally arrested forks. We find that the Brca1 carboxy (C)-terminal tandem BRCT repeat and regions of Brca1 encoded by exon 11-two Brca1 elements implicated in tumour suppression-control Tus/Ter-induced homologous recombination. Inactivation of either Brca1 or Brca2 increases the absolute frequency of 'long-tract' gene conversions at Tus/Ter-stalled forks, an outcome not observed in response to a site-specific endonuclease-mediated chromosomal double-strand break. Therefore, homologous recombination at stalled forks is regulated differently from homologous recombination at double-strand breaks arising independently of a replication fork. We propose that aberrant long-tract homologous recombination at stalled replication forks contributes to genomic instability and breast/ovarian cancer predisposition in BRCA mutant cells.

  16. Process and apparatus for recovery from rotating stall in axial flow fans and compressors

    OpenAIRE

    1997-01-01

    Active recovery from a rotating stall operating condition in an axial flow compression system is accomplished by altering the temperature and/or density of the working fluid flowing in the inlet of the compression system once rotating stall is detected. A burner is used to increase the compressor inlet flow temperature and concomitantly reduce the inlet flow density. Alternatively, a low density gas such as helium is injected into the compressor inlet. The ingestion of high temperature gases ...

  17. Precursors of stall and surge processes in gas turbines revealed by wavelet analysis

    Energy Technology Data Exchange (ETDEWEB)

    Dremin, I.M.; Ivanov, O.V.; Nechitailo, V.A. [P.N. Lebedev Physical Institute, Moscow (Russian Federation); Furletov, V.I. [Central Institute for Aviation Motors, Moscow (Russian Federation); Terziev, V.G. [TEKO, Moscow (Russian Federation)

    2002-06-01

    Multiresolution wavelet analysis of pressure variations in a gas turbine compressor reveals the existence of precursors of stall and surge processes. Signals from eight pressure sensors positioned at various places within the compressor were recorded and digitized in three different operating modes in stationary conditions with a recording interval of 1 ms during 5-6 s. It has been discovered that there exists a scale of 32 intervals over which the dispersion (variance) of the wavelet coefficients shows a remarkable drop of about 40% for more than 1 s prior to the development of the malfunction. A shuffled sample of the same values of the pressure does not show such a drop demonstrating the dynamical origin of this effect. Higher order correlation moments reveal different slopes in these two regions differing by the variance values. The log-log dependence of the moments does not show clear fractal behavior because the scales of 16 and 32 intervals are not on the straight line of monofractals. This is a clear indication of the nonlinear response of the system at this scale. These results provide a means for automatic regulation of an engine, preventing possible failures. (author)

  18. Identification of a small molecule inhibitor that stalls splicing at an early step of spliceosome activation

    Science.gov (United States)

    Sidarovich, Anzhalika; Will, Cindy L; Anokhina, Maria M; Ceballos, Javier; Sievers, Sonja; Agafonov, Dmitry E; Samatov, Timur; Bao, Penghui; Kastner, Berthold; Urlaub, Henning; Waldmann, Herbert; Lührmann, Reinhard

    2017-01-01

    Small molecule inhibitors of pre-mRNA splicing are important tools for identifying new spliceosome assembly intermediates, allowing a finer dissection of spliceosome dynamics and function. Here, we identified a small molecule that inhibits human pre-mRNA splicing at an intermediate stage during conversion of pre-catalytic spliceosomal B complexes into activated Bact complexes. Characterization of the stalled complexes (designated B028) revealed that U4/U6 snRNP proteins are released during activation before the U6 Lsm and B-specific proteins, and before recruitment and/or stable incorporation of Prp19/CDC5L complex and other Bact complex proteins. The U2/U6 RNA network in B028 complexes differs from that of the Bact complex, consistent with the idea that the catalytic RNA core forms stepwise during the B to Bact transition and is likely stabilized by the Prp19/CDC5L complex and related proteins. Taken together, our data provide new insights into the RNP rearrangements and extensive exchange of proteins that occurs during spliceosome activation. DOI: http://dx.doi.org/10.7554/eLife.23533.001 PMID:28300534

  19. Numerical study of the static and pitching RISOe-B1-18 airfoil[STALL

    Energy Technology Data Exchange (ETDEWEB)

    Bertagnolio, F.

    2004-01-01

    The objective of this report is the better understanding of the physics of the aeroelastic motion of wind turbine blades in order to improve the numerical models used for their design. In this study, the case of the RISOe-B1-18 airfoil which was equipped and measured in an open jet wind tunnel is studied. Two and three dimensional Navier-Stokes calculations using the k-w SST and Detached Eddy Simulation turbulence models are conducted. An engineering semi-empirical dynamic stall model is also used for performing calculations. Computational results are compared to the experimental results that are available both for the static airfoil and in the case of pitching motions. It is shown that the Navier-Stokes simulations can reproduced the main characteristic features of the flow. The DES model seems also to be able to reproduce some details of the unsteady aerodynamics. The Navier-Stokes computations can then be used to improve the performance of the engineering model. (au)

  20. Parameter Estimation from Near Stall Flight Data using Conventional and Neural-based Methods

    Directory of Open Access Journals (Sweden)

    S. Saderla

    2016-12-01

    Full Text Available The current research paper is an endeavour to estimate the parameters from near stall flight data of manned and unmanned research flight vehicles using conventional and neural based methods. For an aircraft undergoing stall, the aerodynamic model at these high angles of attack becomes non linear due to the influence of unsteady, transient and flow separation phenomena. In order to address these issues the Kirchhoff’s flow separation theory was used to incorporate the nonlinearity in the aerodynamic model in terms of flow separation point and stall characteristic parameters. The classical Maximum Likelihood (MLE method and Neural Gauss-Newton (NGN method have been employed to estimate the nonlinear parameters of two manned and one unmanned research aircrafts. The estimated static stall parameter and the break point, for the flight vehicles under consideration, were observed to be consistent from both the methods. Moreover the efficacy of the methods is also evident from the consistent estimates of post stall hysteresis time constant. It can also be inferred that the considered quasi steady model is able to adequately capture the drag and pitching moment coefficients in the post stall regime. The confidence in these estimates have been significantly enhanced with the observed lower values of Cramer-Rao bounds. Further the estimated nonlinear parameters were validated by performing a proof of match exercise for the considered flight vehicles. Interestingly the NGN method, which doesn’t involve solving equations of motion, was able to perform on a par with the MLE method.

  1. A New Simplified Model of Post Stall Transients in Axial Compression Systems

    Institute of Scientific and Technical Information of China (English)

    JunHu; LeonhardFottner

    1999-01-01

    Based on the theory developed by Moore and Greitzer,a new simplifying approximation,which takes into account the influence of higher harmonics of rotating waves,is proposed in this paper of get a simplified model of post stall transients in axial compression systems.This approximation leads to a set of three simultaneous nonlinear first order partial differential equations.The further investigation of post stall behavior for different response modes of instabilities(rotating stall and /or surge) recoverability,prestall period during stall inception,and the effect of compression system parameters on them can be carried out by this model and has been discussed in detail in the present paper,It has been found that stall inception exhibits a large prestall period in the region with small slope of compressor characteristic,and in this region,final throttle stting,compressor characteristic and time-lag parameters have a strong influence on the period.The inertia parameters of blade rows have a strong influence on the recoverability of compression systems and the blockage of stall cell at recovery point Some qualitative comparisons with available experimental results and experience are made ,and it shows that the proposed model is very simple and reliable.

  2. Stalled RNAP-II molecules bound to non-coding rDNA spacers are required for normal nucleolus architecture.

    Science.gov (United States)

    Freire-Picos, M A; Landeira-Ameijeiras, V; Mayán, María D

    2013-07-01

    The correct distribution of nuclear domains is critical for the maintenance of normal cellular processes such as transcription and replication, which are regulated depending on their location and surroundings. The most well-characterized nuclear domain, the nucleolus, is essential for cell survival and metabolism. Alterations in nucleolar structure affect nuclear dynamics; however, how the nucleolus and the rest of the nuclear domains are interconnected is largely unknown. In this report, we demonstrate that RNAP-II is vital for the maintenance of the typical crescent-shaped structure of the nucleolar rDNA repeats and rRNA transcription. When stalled RNAP-II molecules are not bound to the chromatin, the nucleolus loses its typical crescent-shaped structure. However, the RNAP-II interaction with Seh1p, or cryptic transcription by RNAP-II, is not critical for morphological changes.

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

    Institute of Scientific and Technical Information of China (English)

    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.

  4. Numerical Simulation of Active Suppression of Rotating Stall in Axial Compression Systems

    Institute of Scientific and Technical Information of China (English)

    JunHu; LeonhardFottner

    1996-01-01

    In the present paper,a theoretical model is proposed to analyze the transient behavior of suppression of rotating stall in axial compression systems through the use of an additional distubance,The governing equations of the model are a set of simultaneous nonlinear first order partial differential equations,and for numerical calculations,a simple explicit time marching method can be used.The influence of system parameters on the suppression effectiveness and the interaction between rotating stall and surge have been discussed initially.The anslysis of the influence of system parameters presents that both the B parameter and axisymmetric comprssor characteristic have significant effect on the stabilization effectiveness of a control strategy.The effectiveness decreases as the value of B and the number of stages or stage loading of the compressor increase,It has been found that the onset flow rate of rotating stall and surge in a compression system may be different,and there is a strong interaction between these two kinds of instabilities.The onset flow rate of pure one dimensional surge depends on the value of B and axisymmetric compressor characteristic,besides the slope of the compressor characteristic.In some cases,when rotating stall which is the natural mode of instability in a compression system is suppressed one dimensional surge can occur,It often limits the effectiveness of a control strategy to suppress rotating stall.But when surge is intiated by ratating stall,it is also possible to inhibit the occurrence of surge by suppressing rotating stall in a compression system.

  5. Development and implementation of spin to stall resin at Anglo Americans Australian underground coal operations

    Institute of Scientific and Technical Information of China (English)

    Emery J.; Canbulat I.; Craig P.; Naylor J.; Sykes A.

    2016-01-01

    Longwall mining is by far the most common method of underground coal extraction in Australia. The industry trends and expectations are placing increasing emphasis on the reliability and productivity of these operations. The longwalls are becoming wider and longer while retreat rates are continuously increasing due to significant improvements achieved in longwall equipment reliability and automation. This increased longwall productivity is placing significant emphasis on the reliability of longwall panel development. Although there have been significant improvements in the reliability of continuous miners and hydraulic drill rigs, the traditional resin encapsulated bolt installation is still the principal method used in all major coal-producing countries around the world. Anglo American realised an opportunity existed to introduce an alternative roof bolt installation technique called ‘spin to stall” in Australia. Spin to stall was first introduced in Anglo American Coal in South Africa where it has been successfully used for over a decade, though implementation of South African spin to stall resin in Australia has proven to be near impossible due to a significant difference in geotechnical conditions, mining method, and, sub-sequently, roof bolting equipment. Therefore, a new spin to stall development project was initiated between Anglo American Coal and Jennmar Australia (SPIN2STALL?). This paper summarises the journey of this project, the results, and the successful implementation of spin to stall achieved at Grasstree Mine.

  6. An experimental description of the flow in a centrifugal compressor from alternate stall to surge

    Science.gov (United States)

    Moënne-Loccoz, V.; Trébinjac, I.; Benichou, E.; Goguey, S.; Paoletti, B.; Laucher, P.

    2017-08-01

    The present paper gives the experimental results obtained in a centrifugal compressor stage designed and built by SAFRAN Helicopter Engines. The compressor is composed of inlet guide vanes, a backswept splittered unshrouded impeller, a splittered vaned radial diffuser and axial outlet guide vanes. Previous numerical simulations revealed a particular S-shape pressure rise characteristic at partial rotation speed and predicted an alternate flow pattern in the vaned radial diffuser at low mass flow rate. This alternate flow pattern involves two adjacent vane passages. One passage exhibits very low momentum and a low pressure recovery, whereas the adjacent passage has very high momentum in the passage inlet and diffuses efficiently. Experimental measurements confirm the S-shape of the pressure rise characteristic even if the stability limit experimentally occurs at higher mass flow than numerically predicted. At low mass flow the alternate stall pattern is confirmed thanks to the data obtained by high-frequency pressure sensors. As the compressor is throttled the path to instability has been registered and a first scenario of the surge inception is given. The compressor first experiences a steady alternate stall in the diffuser. As the mass flow decreases, the alternate stall amplifies and triggers the mild surge in the vaned diffuser. An unsteady behavior results from the interaction of the alternate stall and the mild surge. Finally, when the pressure gradient becomes too strong, the alternate stall blows away and the compressor enters into deep surge.

  7. Stall Margin Improvement in a Centrifugal Compressor through Inducer Casing Treatment

    Directory of Open Access Journals (Sweden)

    V. V. N. K. Satish Koyyalamudi

    2016-01-01

    Full Text Available The increasing trend of high stage pressure ratio with increased aerodynamic loading has led to reduction in stable operating range of centrifugal compressors with stall and surge initiating at relatively higher mass flow rates. The casing treatment technique of stall control is found to be effective in axial compressors, but very limited research work is published on the application of this technique in centrifugal compressors. Present research was aimed to investigate the effect of casing treatment on the performance and stall margin of a high speed, 4 : 1 pressure ratio centrifugal compressor through numerical simulations using ANSYS CFX software. Three casing treatment configurations were developed and incorporated in the shroud over the inducer of the impeller. The predicted performance of baseline compressor (without casing treatment was in good agreement with published experimental data. The compressor with different inducer casing treatment geometries showed varying levels of stall margin improvement, up to a maximum of 18%. While the peak efficiency of the compressor with casing treatment dropped by 0.8%–1% compared to the baseline compressor, the choke mass flow rate was improved by 9.5%, thus enhancing the total stable operating range. The inlet configuration of the casing treatment was found to play an important role in stall margin improvement.

  8. A semi-empirical airfoil stall noise model based on surface pressure measurements

    Science.gov (United States)

    Bertagnolio, Franck; Madsen, Helge Aa.; Fischer, Andreas; Bak, Christian

    2017-01-01

    This work is concerned with the experimental study of airfoil stall and the modelling of stall noise. Using pressure taps and high-frequency surface pressure microphones flush-mounted on airfoils measured in wind tunnels and on an operating wind turbine blade, the characteristics of stall are analyzed. This study shows that the main quantities of interest, namely convection velocity, spatial correlation and surface pressure spectra, can be scaled highlighting the universal nature of stall independently of airfoil shapes and flow conditions, although within a certain range of experimental conditions. Two main regimes for the scaling of the correlation lengths and the surface pressure spectra, depending on the Reynolds number of the flow, can be distinguished. These results are used to develop a model for the surface pressure spectra within the detached flow region valid for Reynolds numbers ranging from 1 ×106 to 6 ×106. Subsequently, this model is used to derive a model for stall noise. Modelled noise spectra are compared with experimental data measured in anechoic wind tunnels with reasonably satisfactory agreement.

  9. Structural basis for translational stalling by human cytomegalovirus and fungal arginine attenuator peptide.

    Science.gov (United States)

    Bhushan, Shashi; Meyer, Helge; Starosta, Agata L; Becker, Thomas; Mielke, Thorsten; Berninghausen, Otto; Sattler, Michael; Wilson, Daniel N; Beckmann, Roland

    2010-10-08

    Specific regulatory nascent chains establish direct interactions with the ribosomal tunnel, leading to translational stalling. Despite a wealth of biochemical data, structural insight into the mechanism of translational stalling in eukaryotes is still lacking. Here we use cryo-electron microscopy to visualize eukaryotic ribosomes stalled during the translation of two diverse regulatory peptides: the fungal arginine attenuator peptide (AAP) and the human cytomegalovirus (hCMV) gp48 upstream open reading frame 2 (uORF2). The C terminus of the AAP appears to be compacted adjacent to the peptidyl transferase center (PTC). Both nascent chains interact with ribosomal proteins L4 and L17 at tunnel constriction in a distinct fashion. Significant changes at the PTC were observed: the eukaryotic-specific loop of ribosomal protein L10e establishes direct contact with the CCA end of the peptidyl-tRNA (P-tRNA), which may be critical for silencing of the PTC during translational stalling. Our findings provide direct structural insight into two distinct eukaryotic stalling processes.

  10. A time-varying subjective quality model for mobile streaming videos with stalling events

    Science.gov (United States)

    Ghadiyaram, Deepti; Pan, Janice; Bovik, Alan C.

    2015-09-01

    Over-the-top mobile video streaming is invariably influenced by volatile network conditions which cause playback interruptions (stalling events), thereby impairing users' quality of experience (QoE). Developing models that can accurately predict users' QoE could enable the more efficient design of quality-control protocols for video streaming networks that reduce network operational costs while still delivering high-quality video content to the customers. Existing objective models that predict QoE are based on global video features, such as the number of stall events and their lengths, and are trained and validated on a small pool of ad hoc video datasets, most of which are not publicly available. The model we propose in this work goes beyond previous models as it also accounts for the fundamental effect that a viewer's recent level of satisfaction or dissatisfaction has on their overall viewing experience. In other words, the proposed model accounts for and adapts to the recency, or hysteresis effect caused by a stall event in addition to accounting for the lengths, frequency of occurrence, and the positions of stall events - factors that interact in a complex way to affect a user's QoE. On the recently introduced LIVE-Avvasi Mobile Video Database, which consists of 180 distorted videos of varied content that are afflicted solely with over 25 unique realistic stalling events, we trained and validated our model to accurately predict the QoE, attaining standout QoE prediction performance.

  11. Analysis of blade vibration response induced by rotating stall in axial compressor

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    An experimental and numerical study was conducted to investigate the forced response of blade vibration induced by rotating stall in a low speed axial compressor.Measurements have been made of the transient stalling process in a low speed axial compressor stage.The CFD study was performed using solution of 3-dimensional Navier-Stokes equations,coupled with structure finite element models for the blades to identify modal shapes and structural deformations simultaneously.Interactions between fluid and structure were managed in a coupled manner,based on the interface information exchange until convergence in each time step.Based on the rotating stall measurement data obtained from a low speed axial compressor,the blade aeroelastic response induced by the rotating stall flow field was analyzed to study the vibration characteristics and the correlation between the phenomena.With this approach,good agreement between the numerical results and the experimental data was observed.The flow phenomena were well captured,and the results indicate that the rotating field stall plays a significant role in the blade vibration and stress affected by the flow excitation.

  12. The role of tip clearance in high-speed fan stall

    Energy Technology Data Exchange (ETDEWEB)

    Adamczyk, J.J. (NASA Lewis Research Center, Cleveland, OH (United States)); Celestina, M.L. (Sverdrup Tech., Inc., Cleveland, OH (United States)); Greitzer, E.M. (Massachusetts Institute of Technology, Cambridge, MA (United States))

    1993-01-01

    A numerical experiment has been carried out to define the near-stall casing endwall flow field of a high-speed fan rotor. The experiment used a simulation code incorporating a simple clearance model, whose calibration is presented. The results of the simulation show that the interaction of the tip leakage vortex and the in-passage shock plays a major role in determining the fan flow range. More specifically, the computations imply that it is the area increase of this vortex as it passes through the in-passage shock that is the source of the blockage associated with stall. In addition, for fans of this type, it is the clearance over the forward portion of the fan blade that controls the flow processes leading to stall.

  13. The role of tip clearance in high-speed fan stall

    Science.gov (United States)

    Adamczyk, J. J.; Celestina, M. L.; Greitzer, E. M.

    1991-01-01

    A numerical experiment has been carried out to define the near-stall casing endwall flowfield of a high-speed fan rotor. The experiment used a simulation code incorporating a simple clearance model, whose calibration is presented. The results of the simulation show that the interaction of the tip leakage vortex and the in-pasage shock plays a major role in determining the fan flow range. More specifically, the computations imply that it is the area increase of this vortex as it passes through the in-passage shock, which is the source of the blockage associated with stall. In addition, for fans of this type, it is the clearance over the forward portion of the fan blade which controls the flow processes leading to stall.

  14. Local Voltage Support from Distributed Energy Resources to Prevent Air Conditioner Motor Stalling

    Energy Technology Data Exchange (ETDEWEB)

    Baone, Chaitanya A [ORNL; Xu, Yan [ORNL; Kueck, John D [ORNL

    2010-01-01

    Microgrid voltage collapse often happens when there is a high percentage of low inertia air-conditioning (AC) motors in the power systems. The stalling of the AC motors results in Fault Induced Delayed Voltage Recovery (FIDVR). A hybrid load model including typical building loads, AC motor loads, and other induction motor loads is built to simulate the motoring stalling phenomena. Furthermore, distributed energy resources (DE) with local voltage support capability are utilized to boost the local bus voltage during a fault, and prevent the motor stalling. The simulation results are presented. The analysis of the simulation results show that local voltage support from multiple DEs can effectively and economically solve the microgrid voltage collapse problem.

  15. Further studies of stall flutter and nonlinear divergence of two-dimensional wings

    Science.gov (United States)

    Dugundji, J.; Chopra, I.

    1975-01-01

    An experimental investigation is made of the purely torsional stall flutter of a two-dimensional wing pivoted about the midchord, and also of the bending-torsion stall flutter of a two-dimensional wing pivoted about the quarterchord. For the purely torsional flutter case, large amplitude limit cycles ranging from + or - 11 to + or - 160 degrees were observed. Nondimensional harmonic coefficients were extracted from the free transient vibration tests for amplitudes up to 80 degrees. Reasonable nondimensional correlation was obtained for several wing configurations. For the bending-torsion flutter case, large amplitude coupled limit cycles were observed with torsional amplitudes as large as + or - 40 degrees. The torsion amplitudes first increased, then decreased with increasing velocity. Additionally, a small amplitude, predominantly torsional flutter was observed when the static equilibrium angle was near the stall angle.

  16. Chloramphenicol induction of cat-86 requires ribosome stalling at a specific site in the leader.

    Science.gov (United States)

    Alexieva, Z; Duvall, E J; Ambulos, N P; Kim, U J; Lovett, P S

    1988-05-01

    The plasmid gene cat-86 specifies chloramphenicol-inducible chloramphenicol acetyltransferase in Bacillus subtilis. Induction by the antibiotic is primarily due to activation of the translation of cat-86-encoded mRNA. It has been suggested that the inducer stalls ribosomes at a discrete location in the leader region of cat-86 mRNA, which causes the destabilization of a downstream RNA secondary structure that normally sequesters the cat-86 ribosome binding site. It is the destabilization of this RNA secondary structure that permits translation of the cat-86 coding sequence. In the present report, we show that ribosomes that were stalled in the cat-86 leader by starvation of host cells for the amino acid specified by leader codon 6 induced gene expression to a level above that detected when cells were starved for the amino acids specified by leader codons 7 and 8. Starvation for amino acids specified by leader codons 3, 4, or 5 failed to activate cat-86 expression. These results indicate that the stalled ribosome that is most active in cat-86 induction has its aminoacyl site occupied by leader codon 6. To determine if chloramphenicol also stalled ribosomes in the cat-86 regulatory leader such that the aminoacyl site was occupied by codon 6, we separately changed leader codons 3, 4, 5, and 6 to the translation termination (ochre) codon TAA. Each of the mutated genes was tested for its ability to be induced by chloramphenicol. The results show that replacement of leader codons 3, 4, or 5 by the ochre codon blocked induction, whereas replacement of leader codon 6 by the ochre codon permitted induction. Collectively, these observations lead to the conclusion that cat-86 induction requires ribosome stalling in leader mRNA, and they identify leader codon 6 as the codon most likely to be occupied by the aminoacyl site of a stalled ribosome that is active in the induction.

  17. Unsteady numerical analysis of the rotating stall in pump- turbine geometry

    Science.gov (United States)

    Ješe, U.; Fortes-Patella, R.

    2016-11-01

    Main challenges in energy sector nowadays are storing and recovering of a large amount of energy in a short time. Pumped Storage Power Plants (PSP), using reversible pump- turbines are among the most cost-efficient solution to answer these needs. To provide a rapid adjustment to the electrical grid, pump-turbines are subjects of quick switching between pumping and generating modes and to extended operation under off-design conditions. To maintain the stability of the grid, the continuous operating area of reversible pump-turbines must be free of hydraulic instabilities. One of the main sources of pumping mode instabilities is the presence of the rotating stall that occurs at the part load. It can be observed as periodic occurrence and decay of recirculation zones in the distributor regions. Consequently, the machine can be exposed to uncontrollable shift between the operating points with the significant discharge modification and the drop of the efficiency. The phenomenon is very complex, three-dimensional and demanding for the investigation. The paper presents cost- efficient numerical methodology that enables the accurate prediction and analysis of the rotating stall. The investigations were made on a reduced-scaled high head pump-turbine design. Unsteady numerical calculations were performed using code FINE/TurboTM and URANS equations. Local flow study was done to describe in details the governing mechanisms of the rotating stall. The analyses enable the investigations of the rotating stall frequencies, the number of stalled cells and the intensity of the rotating stall. Moreover, the unsteady calculations give very good prediction of the pump-turbine performance for both, stable and unstable operating regions. Numerical results show very good qualitative and quantitative agreement with the available experimental data.

  18. The Expression of Antibiotic Resistance Methyltransferase Correlates with mRNA Stability Independently of Ribosome Stalling.

    Science.gov (United States)

    Dzyubak, Ekaterina; Yap, M N

    2016-12-01

    Members of the Erm methyltransferase family modify 23S rRNA of the bacterial ribosome and render cross-resistance to macrolides and multiple distantly related antibiotics. Previous studies have shown that the expression of erm is activated when a macrolide-bound ribosome stalls the translation of the leader peptide preceding the cotranscribed erm Ribosome stalling is thought to destabilize the inhibitory stem-loop mRNA structure and exposes the erm Shine-Dalgarno (SD) sequence for translational initiation. Paradoxically, mutations that abolish ribosome stalling are routinely found in hyper-resistant clinical isolates; however, the significance of the stalling-dead leader sequence is largely unknown. Here, we show that nonsense mutations in the Staphylococcus aureus ErmB leader peptide (ErmBL) lead to high basal and induced expression of downstream ErmB in the absence or presence of macrolide concomitantly with elevated ribosome methylation and resistance. The overexpression of ErmB is associated with the reduced turnover of the ermBL-ermB transcript, and the macrolide appears to mitigate mRNA cleavage at a site immediately downstream of the ermBL SD sequence. The stabilizing effect of antibiotics on mRNA is not limited to ermBL-ermB; cationic antibiotics representing a ribosome-stalling inducer and a noninducer increase the half-life of specific transcripts. These data unveil a new layer of ermB regulation and imply that ErmBL translation or ribosome stalling serves as a "tuner" to suppress aberrant production of ErmB because methylated ribosome may impose a fitness cost on the bacterium as a result of misregulated translation.

  19. Effect of summer grazing on welfare of dairy cows reared in mountain tie-stall barns

    Directory of Open Access Journals (Sweden)

    Simonetta Dovier

    2010-09-01

    Full Text Available Traditional mountain farms have an important economic, social and environmental role. The Alps management system for dairy cows consists of animals kept indoors from autumn to spring, mostly in tie-stalls, and moved to mountain pasture in summer. The aim of our study was to assess the effect of mountain summer grazing on the welfare of dairy cows housed in tie-stall barns. Twenty-four farms were considered. In twelve of them, animals were reared in tie-stalls and moved to mountain pasture for three months in summer; they were visited three times: (i four weeks before grazing during the indoor period in the stall; (ii about three weeks after the start of grazing; and (iii in the stall, in autumn, at least three weeks after returning from grazing. The other twelve farms kept the animals in tie-stalls all year; they were visited once in autumn. Data were collected following a protocol that considers animal-based measures and structure information on the basis of Quality Welfare Consortium® indications. Data allowed the calculation of both the Animal Needs Index score (ANI 35L and an overall assessment of the cows’ welfare obtained from three general aspects: housing, animal’s physical condition, and animal’s behaviour. Summer grazing had a significant positive effect on injuries, lameness and animal’s rising duration but a negative effect on faeces consistency. Moreover, a reduction of tongue playing was observed. The ANI 35L and the overall assessment did not show significant differences linked to summer grazing, which tended to have a positive but temporary effect on animal behaviour.

  20. Analysis of supersonic stall bending flutter in axial-flow compressor by actuator disk theory

    Science.gov (United States)

    Adamczyk, J. J.

    1978-01-01

    An analytical model was developed for predicting the onset of supersonic stall bending flutter in axial-flow compressors. The analysis is based on two-dimensional, compressible, unsteady actuator disk theory. It is applied to a rotor blade row by considering a cascade of airfoils. The effects of shock waves and flow separation are included in the model. Calculations show that the model predicts the onset, in an unshrouded rotor, of a bending flutter mode that exhibits many of the characteristics of supersonic stall bending flutter. The validity of the analysis for predicting this flutter mode is demonstrated.

  1. Stall flutter and nonlinear divergence of a two-dimensional flat plate wing

    Science.gov (United States)

    Dugundji, J.; Aravamudan, K.

    1976-01-01

    Tests were conducted in a small wind tunnel to study the torsional stall flutter behavior of a two-dimensional flat-plate wing pivoted about the midchord. The nonlinear static divergence equilibrium properties of the wing were well predicted from the measured static moment characteristics. Large amplitude limit cycles ranging from plus or minus 11 degrees to plus or minus 100 degrees were observed. Stall flutter occurred above a critical value of a reduced frequency of about 2. Self-excitation occurred for initial angles of attack between 0 and 8 degrees. Nondimensional harmonic coefficients were extracted from the free transient vibration tests for amplitudes up to 80 degrees.

  2. Power control of a wind farm with active stall wind turbines and AC grid connection

    DEFF Research Database (Denmark)

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

    This paper describes the design of a centralised wind farm controller for a wind farm made-up exclusively of active stall wind turbines with AC grid connection. The overall aim of such controller is to enable the wind farms to provide the best grid support. The designed wind farm control involves...... both the control on wind turbine level as well as the central control on the wind farm level. The ability of active stall wind farms with AC grid connection to regulate the power production to the reference power ordered by the operators is assessed and discussed by means of simulations....

  3. Propeller swirl effect on single-engine general-aviation aircraft stall-spin tendencies

    Science.gov (United States)

    Katz, Joseph; Feistel, Terry W.

    1987-01-01

    An investigation is conducted of the effect of a single engine, untapered low wing general aviation aircraft propeller's swirl on the craft's stall pattern. The asymmetrical character of the propeller's swirl can trigger an early stall of one of the wings, aggravating the spin-entry condition. It is shown that the combination of this propeller-induced effect with adverse sideslip can result in large and abrupt changes in the rolling moment, in such conditions as uncoordinated low speed turning maneuvers where the pilot yaws the aircraft with wings level, rather than rolling it.

  4. Low-Frequency Flow Oscillations on Stalled Wings Exhibiting Cellular Separation Topology

    Science.gov (United States)

    Disotell, Kevin James

    One of the most pervasive threats to aircraft controllability is wing stall, a condition associated with loss of lift due to separation of air flow from the wing surface at high angles of attack. A recognized need for improved upset recovery training in extended-envelope flight simulators is a physical understanding of the post-stall aerodynamic environment, particularly key flow phenomena which influence the vehicle trajectory. Large-scale flow structures known as stall cells, which scale with the wing chord and are spatially-periodic along the span, have been previously observed on post-stall airfoils with trailing-edge separation present. Despite extensive documentation of stall cells in the literature, the physical mechanisms behind their formation and evolution have proven to be elusive. The undertaken study has sought to characterize the inherently turbulent separated flow existing above the wing surface with cell formation present. In particular, the question of how the unsteady separated flow may interact with the wing to produce time-averaged cellular surface patterns is considered. Time-resolved, two-component particle image velocimetry measurements were acquired at the plane of symmetry of a single stall cell formed on an extruded NACA 0015 airfoil model at chord Reynolds number of 560,000 to obtain insight into the time-dependent flow structure. The evolution of flow unsteadiness was analyzed over a static angle-of-attack range covering the narrow post-stall regime in which stall cells have been observed. Spectral analysis of velocity fields acquired near the stall angle confirmed a low-frequency flow oscillation previously detected in pointwise surface measurements by Yon and Katz (1998), corresponding to a Strouhal number of 0.042 based on frontal projected chord height. Probability density functions of the streamwise velocity component were used to estimate the convective speed of this mode at approximately half the free-stream velocity, in agreement

  5. Features of Rotating Stall Cell in a Diagonal Flow Fan(in Case of Mid-loading Rotor)

    Institute of Scientific and Technical Information of China (English)

    N. SHIOMI; K. KANEKO; Y. KINOUE; T. SETOGUCHI

    2006-01-01

    The structure and behavior of rotating stall cell were experimentally clarified in a diagonal flow fan. The specific-speed of the fan was 1140 (r/min, m3/min, m), and the total pressure-rise coefficient at design flow-rate was 0.345. The static pressure on outer casing wall and the total pressure at rotor inlet and outlet were measured using a high response pressure transducer. The measured data were processed by the use of DPLA technique, and the structure and behavior of rotating stall cell were obtained. As a result, the stall cell extent for circumferential and spanwise direction and the pressure distributions inside stall cell were clarified. The details of stall cell propagation were also shown.

  6. Corner separation and the onset of stall in an axial compressor

    Science.gov (United States)

    Thiam, Aicha; Whittlesey, Robert; Wark, Candace; Williams, David

    2007-11-01

    Axial compressor performance is limited by the onset of stall between the diffusing passageways of the rotors and stators. The flow physics responsible for the stall depends on the blade geometry of the machine, and in this experiment stall develops from a blade-hub corner separation. The 1.5 stage axial compressor consists of inlet guide vanes, a rotor and stator section. Separate motors drive the downstream fan and rotor, which makes it possible to change the compressor pressure ratio and flow coefficient by changing either the wheel speed or the bulk flow rate through the machine. Detailed maps of the flow behind the stators and in front of the rotors were obtained using a Kulite stagnation pressure probe. Mean pressure measurements show the growth of the corner flow separation and divergence of the ``through flow'' toward the outer casing. Spectra show a sensitivity of the separated region to small amplitude external disturbances, in this case originating from the downstream fan. The onset of rotating stall appears as the first subharmonic of the rotor frequency, 0.5 fr, then shifts to a slightly lower frequency 0.45 fr as the flow coefficient is decreased.

  7. Power reduction and the radial limit of stall delay in revolving wings of different aspect ratio

    NARCIS (Netherlands)

    Kruyt, J.W.; Heijst, Van G.F.; Altshuler, D.L.; Lentink, David

    2015-01-01

    Airplanes and helicopters use high aspect ratio wings to reduce the power required to fly, but must operate at low angle of attack to prevent flow separation and stall. Animals capable of slow sustained flight, such as hummingbirds, have low aspect ratio wings and flap their wings at high angle o

  8. EVALUATION OF STYRENE EMISSIONS FROM A SHOWER STALL/BATHTUB MANUFACTURING FACILITY

    Science.gov (United States)

    The report gives results of emissions measurements carried out at a representative facility (Eljer Plumbingware in Wilson, NC) that manufactures polyester-resin-reinforced shower stalls and bathtubs by spraying styrene-based resins onto molds in vented, open, spray booths. Styren...

  9. Stall Recovery in a Centrifuge-Based Flight Simulator With an Extended Aerodynamic Model

    NARCIS (Netherlands)

    Ledegang, W.D.; Groen, E.L.

    2015-01-01

    We investigated the performance of 12 airline pilots in recovering from an asymmetrical stall in a flight simulator featuring an extended aerodynamic model of a transport-category aircraft, and a centrifuge-based motion platform capable of generating enhanced buffet motion and g-cueing. All pilots h

  10. Power reduction and the radial limit of stall delay in revolving wings of different aspect ratio

    NARCIS (Netherlands)

    Kruyt, J.W.; Heijst, Van G.F.; Altshuler, D.L.; Lentink, David

    2015-01-01

    Airplanes and helicopters use high aspect ratio wings to reduce the power required to fly, but must operate at low angle of attack to prevent flow separation and stall. Animals capable of slow sustained flight, such as hummingbirds, have low aspect ratio wings and flap their wings at high angle o

  11. 76 FR 77452 - Advisory Circular for Stall and Stick Pusher Training

    Science.gov (United States)

    2011-12-13

    ... recommendations and best practices for academic training, job performance training, and instructor training... Federal Aviation Administration 14 CFR Parts 121, 135 and 142 Advisory Circular for Stall and Stick Pusher... read at http://www.regulations.gov at any time. Follow the online instructions for accessing the...

  12. Pilot Human Factors in Stall/Spin Accidents of Supersonic Fighter Aircraft

    Science.gov (United States)

    Anderson, S. B.; Enevoldson, E. K.; Nguyen, L. T.

    1983-01-01

    A study has been made of pilot human factors related to stall/spin accidents of supersonic fighter aircraft. The military specifications for flight at high angles of attack are examined. Several pilot human factors problems related to stall/spin are discussed. These problems include (1) unsatisfactory nonvisual warning cues; (2) the inability of the pilot to quickly determine if the aircraft is spinning out of control, or to recognize the type of spin; (3) the inability of the pilot to decide on and implement the correct spin recovery technique; (4) the inability of the pilot to move, caused by high angular rotation; and (5) the tendency of pilots to wait too long in deciding to abandon the irrecoverable aircraft. Psycho-physiological phenomena influencing pilot's behavior in stall/spin situations include (1) channelization of sensory inputs, (2) limitations in precisely controlling several muscular inputs, (3) inaccurate judgment of elapsed time, and (4) disorientation of vestibulo-ocular inputs. Results are given of pilot responses to all these problems in the F14A, F16/AB, and F/A-18A aircraft. The use of departure spin resistance and automatic spin prevention systems incorporated on recent supersonic fighters are discussed. These systems should help to improve the stall/spin accident record with some compromise in maneuverability.

  13. Implementation of the Stallings Classroom Management Staff Development Demonstration Project in Putnam County, West Virginia.

    Science.gov (United States)

    Sullivan, Debra K.; And Others

    The primary objective of the Stallings Classroom Management Staff Development Model is to help teachers change so that they can manage their classrooms more effectively. In this model, classroom observations and specific recommendations for teaching behaviors are made for each teacher, and a series of teacher training sessions helps them to change…

  14. Evaluation of the Stallings Classroom Management Staff Development Demonstration Project in Putnam County, West Virginia.

    Science.gov (United States)

    Meehan, Merrill L.

    An evaluation is presented of the Stallings Classroom Management Staff Development Demonstration Project, designed to increase student achievement in basic skills through the use of research-based, systematic change in teachers' classroom management and organizational techniques. One objective of the evaluation was to utilize techniques and to…

  15. Reevaluating Data Stall Time with the Consideration of Data Access Concurrency

    Institute of Scientific and Technical Information of China (English)

    刘宇航; 孙贤和

    2015-01-01

    Data access delay has become the prominent performance bottleneck of high-end computing systems. The key to reducing data access delay in system design is to diminish data stall time. Memory locality and concurrency are the two essential factors influencing the performance of modern memory systems. However, existing studies in reducing data stall time rarely focus on utilizing data access concurrency because the impact of memory concurrency on overall memory system performance is not well understood. In this study, a pair of novel data stall time models, the L-C model for the combined effort of locality and concurrency and the P-M model for the effect of pure miss on data stall time, are presented. The models provide a new understanding of data access delay and provide new directions for performance optimization. Based on these new models, a summary table of advanced cache optimizations is presented. It has 38 entries contributed by data concurrency while only has 21 entries contributed by data locality, which shows the value of data concurrency. The L-C and P-M models and their associated results and opportunities introduced in this study are important and necessary for future data-centric architecture and algorithm design of modern computing systems.

  16. Vortical structures responsible for delayed stall in an idealized humpback whale flipper model

    Science.gov (United States)

    Kim, Heesu; Kim, Jooha; Choi, Haecheon

    2016-11-01

    In this study, we investigate how the tubercles on the leading edge of an idealized humpback whale flipper model delay the stall. Oil-surface visualization is performed to see the surface flow pattern on the suction surface, and PIV is conducted in several streamwise and crossflow planes at different attack angles (α). Without tubercles, leading edge separation first occurs near the tip region and progresses inboard with increasing α. With tubercles, however, two types of vortical motions are observed at the mid-span. The first is streamwise vortex arrays which are dominant at α 9° , and these structures appear near the trailing edge. These two types of vortical motions delay flow separation at the peak regions of the mid-span, eliminating the spanwise stall progression and resulting in delayed stall. At α = 16° at which the tubercle model stalls, a large-scale streamwise vortex is originated from flow separation near the root region. This structure delays flow separation at the mid-span, leading to higher lift coefficient. Supported by NRF-2014M3C1B1033848.

  17. Conical Magnetic Bearings Developed for Active Stall Control in Gas Turbine Engines

    Science.gov (United States)

    Trudell, Jeffrey J.; Kascak, Albert F.; Provenza, Andrew J.; Buccieri, Carl J.

    2004-01-01

    Active stall control is a current research area at the NASA Glenn Research Center that offers a great benefit in specific fuel consumption by allowing the gas turbine to operate beyond the onset of stall. Magnetic bearings are being investigated as a new method to perform active stall control. This enabling global aviation safety technology would result in improved fuel efficiency and decreased carbon dioxide emissions, as well as improve safety and reliability by eliminating oil-related delays and failures of engine components, which account for 40 percent of the commercial aircraft departure delays. Active stall control works by perturbing the flow in front of the compressor stage such that it cancels the pressure wave, which causes the compressor to go into stall. Radial magnetic bearings are able to whirl the shaft so that variations in blade tip leakage would flow upstream causing a perturbation wave that could cancel the rotating stall cell. Axial or thrust magnetic bearings cannot be used to cancel the surge mode in the compressor because they have a very low bandwidth and thus cannot modulate at a high enough frequency. Frequency response is limited because the thrust runner cannot be laminated. To improve the bandwidth of magnetic thrust bearings, researchers must use laminations to suppress the eddy currents. A conical magnetic bearing can be laminated, resulting in increased bandwidth in the axial direction. In addition, this design can produce both radial and thrust force in a single bearing, simplifying the installation. The proposed solution combines the radial and thrust bearing into one design that can be laminated--a conical magnetic bearing. The new conical magnetic bearing test rig, funded by a Glenn fiscal year 2002 Director's Discretionary Fund, was needed because none of the existing rigs has an axial degree of freedom. The rotor bearing configuration will simulate that of the main shaft on a gas turbine engine. One conical magnetic bearing

  18. Internal Flow of a High Specific-Speed Diagonal-Flow Fan (Rotor Outlet Flow Fields with Rotating Stall

    Directory of Open Access Journals (Sweden)

    Norimasa Shiomi

    2003-01-01

    Full Text Available We carried out investigations for the purpose of clarifying the rotor outlet flow fields with rotating stall cell in a diagonal-flow fan. The test fan was a high–specific-speed (ns=1620 type of diagonal-flow fan that had 6 rotor blades and 11 stator blades. It has been shown that the number of the stall cell is 1, and its propagating speed is approximately 80% of its rotor speed, although little has been known about the behavior of the stall cell because a flow field with a rotating stall cell is essentially unsteady. In order to capture the behavior of the stall cell at the rotor outlet flow fields, hot-wire surveys were performed using a single-slant hotwire probe. The data obtained by these surveys were processed by means of a double phase-locked averaging technique, which enabled us to capture the flow field with the rotating stall cell in the reference coordinate system fixed to the rotor. As a result, time-dependent ensemble averages of the three-dimensional velocity components at the rotor outlet flow fields were obtained. The behavior of the stall cell was shown for each velocity component, and the flow patterns on the meridional planes were illustrated.

  19. Investigation of the Flow Physics Driving Stall-Side Flutter in Advanced Forward Swept Fan Designs

    Science.gov (United States)

    Sanders, Albert J.; Liu, Jong S.; Panovsky, Josef; Bakhle, Milind A.; Stefko, George; Srivastava, Rakesh

    2003-01-01

    Flutter-free operation of advanced transonic fan designs continues to be a challenging task for the designers of aircraft engines. In order to meet the demands of increased performance and lighter weight, these modern fan designs usually feature low-aspect ratio shroudless rotor blade designs that make the task of achieving adequate flutter margin even more challenging for the aeroelastician. This is especially true for advanced forward swept designs that encompass an entirely new design space compared to previous experience. Fortunately, advances in unsteady computational fluid dynamic (CFD) techniques over the past decade now provide an analysis capability that can be used to quantitatively assess the aeroelastic characteristics of these next generation fans during the design cycle. For aeroelastic applications, Mississippi State University and NASA Glenn Research Center have developed the CFD code TURBO-AE. This code is a time-accurate three-dimensional Euler/Navier-Stokes unsteady flow solver developed for axial-flow turbomachinery that can model multiple blade rows undergoing harmonic oscillations with arbitrary interblade phase angles, i.e., nodal diameter patterns. Details of the code can be found in Chen et al. (1993, 1994), Bakhle et al. (1997, 1998), and Srivastava et al. (1999). To assess aeroelastic stability, the work-per-cycle from TURBO-AE is converted to the critical damping ratio since this value is more physically meaningful, with both the unsteady normal pressure and viscous shear forces included in the work-per-cycle calculation. If the total damping (aerodynamic plus mechanical) is negative, then the blade is unstable since it extracts energy from the flow field over the vibration cycle. TURBO-AE is an integral part of an aeroelastic design system being developed at Honeywell Engines, Systems & Services for flutter and forced response predictions, with test cases from development rig and engine tests being used to validate its predictive

  20. Modelling and Quasilinear Control of Compressor Surge and Rotating Stall Vibrations

    Directory of Open Access Journals (Sweden)

    Ranjan Vepa

    2010-01-01

    Full Text Available An unsteady nonlinear and extended version of the Moore-Greitzer model is developed to facilitate the synthesis of a quasilinear stall vibration controller. The controller is synthesised in two steps. The first step defines the equilibrium point and ensures that the desired equilibrium point is stable. In the second step, the margin of stability at the equilibrium point is tuned or increased by an appropriate feedback of change in the mass flow rate about the steady mass flow rate at the compressor exit. The relatively simple and systematic non-linear modelling and linear controller synthesis approach adopted in this paper clearly highlights the main features on the controller that is capable of inhibiting compressor surge and rotating stall vibrations. Moreover, the method can be adopted for any axial compressor provided its steady-state compressor and throttle maps are known.

  1. Hydrodynamic Optimization Method and Design Code for Stall-Regulated Hydrokinetic Turbine Rotors

    Energy Technology Data Exchange (ETDEWEB)

    Sale, D.; Jonkman, J.; Musial, W.

    2009-08-01

    This report describes the adaptation of a wind turbine performance code for use in the development of a general use design code and optimization method for stall-regulated horizontal-axis hydrokinetic turbine rotors. This rotor optimization code couples a modern genetic algorithm and blade-element momentum performance code in a user-friendly graphical user interface (GUI) that allows for rapid and intuitive design of optimal stall-regulated rotors. This optimization method calculates the optimal chord, twist, and hydrofoil distributions which maximize the hydrodynamic efficiency and ensure that the rotor produces an ideal power curve and avoids cavitation. Optimizing a rotor for maximum efficiency does not necessarily create a turbine with the lowest cost of energy, but maximizing the efficiency is an excellent criterion to use as a first pass in the design process. To test the capabilities of this optimization method, two conceptual rotors were designed which successfully met the design objectives.

  2. The fail-safe system to rescue the stalled ribosomes in Escherichia coli.

    Science.gov (United States)

    Abo, Tatsuhiko; Chadani, Yuhei

    2014-01-01

    Translation terminates at stop codon. Without stop codon, ribosome cannot terminate translation properly and reaches and stalls at the 3'-end of the mRNA lacking stop codon. Bacterial tmRNA-mediated trans-translation releases such stalled ribosome and targets the protein product to degradation by adding specific "degradation tag." Recently two alternative ribosome rescue factors, ArfA (YhdL) and ArfB (YaeJ), have been found in Escherichia coli. These three ribosome rescue systems are different each other in terms of molecular mechanism of ribosome rescue and their activity, but they are mutually related and co-operate to maintain the translation system in shape. This suggests the biological significance of ribosome rescue.

  3. Two-Dimensional Rotating Stall Analysis in a Wide Vaneless Diffuser

    Directory of Open Access Journals (Sweden)

    2006-01-01

    Full Text Available We report a numerical study on the vaneless diffuser core flow instability in centrifugal compressors. The analysis is performed for the purpose of better understanding of the rotating stall flow mechanism in radial vaneless diffusers. Since the analysis is restricted to the two-dimensional core flow, the effect of the wall boundary layers is neglected. A commercial code with the standard incompressible viscous flow solver is applied to model the vaneless diffuser core flow in the plane parallel to the diffuser walls. At the diffuser inlet, rotating jet-wake velocity pattern is prescribed and at the diffuser outlet constant static pressure is assumed. Under these circumstances, two-dimensional rotating flow instability similar to rotating stall is found to exist. Performed parameter analysis reveals that this instability is strongly influenced by the diffuser geometry and the inlet and outlet flow conditions.

  4. Wave energy plants: Control strategies for avoiding the stalling behaviour in the Wells turbine

    Energy Technology Data Exchange (ETDEWEB)

    Amundarain, Modesto; Alberdi, Mikel; Garrido, Aitor J.; Garrido, Izaskun; Maseda, Javier [Dept. of Automatic Control and Systems Engineering, EUITI Bilbao, University of the Basque Country, Plaza de la Casilla 3, 48012 Bilbao (Spain)

    2010-12-15

    This study analyzes the problem of the stalling behaviour in Wells turbines, one of the most widely used turbines in wave energy plants. For this purpose two different control strategies are presented and compared. In the first one, a rotational speed control system is employed to appropriately adapt the speed of the double-fed induction generator coupling to the turbine, according to the pressure drop entry. In the second control strategy, an airflow control regulates the power generated by the turbine generator module by means of the modulation valve avoiding the stalling behaviour. It is demonstrated that the proposed rotational speed control design adequately matches the desired relationship between the slip of the double-fed induction generator and the pressure drop input, whilst the valve control using a traditional PID controller successfully governs the flow that modulates the pressure drop across the turbine. (author)

  5. Grid support of a wind farm with active stall wind turbines and AC grid connection

    DEFF Research Database (Denmark)

    Hansen, Anca Daniela; Sørensen, Poul Ejnar; Iov, F.

    2006-01-01

    One of the main concerns in the grid integration of large wind farms is their ability to behave as active controllable components in the power system. This article presents the design of a new integrated power control system for a wind farm made up exclusively of active stall wind turbines with AC...... grid connection. The designed control system has the task of enabling such a wind farm to provide the best grid support. It is based on two control levels: a supervisory control level, which controls the power production of the whole farm by sending out reference signals to each individual wind turbine......, and a local control level, which ensures that the reference power signals at the wind turbine level are reached. The ability of active stall wind farms with AC grid connection to control the power production to the reference power ordered by the operators is assessed and discussed by means of simulations....

  6. Characterization of Stall Inception in High-Speed Single-Stage Compressors

    Science.gov (United States)

    1992-12-01

    Institute of Technology Air University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Aeronautical Engineering AJeaidsft...other members of my thesis committee, Professor William Elrod and Captain Thomas Buter. For their contributions, Dr Bill Copenhaver and the entire... Copenhaver [14], and Gorrell [15]. As was mentioned in section 1.4, the majority of stall 11 investigations performed to date (both analytical and

  7. A Method to Predict Compressor Stall in the TF34-100 Turbofan Engine Utilizing Real-Time Performance Data

    Science.gov (United States)

    2015-06-01

    an innovative method to forecast the probability of compressor stall, according to individual engine sensor data which has recently become...maintenance. By utilizing an innovative method to forecast the probability of compressor stall, according to individual engine sensor data which has recently...scenario? How to predict the fault event probability by utilizing an ARIMA model? Should the forecasting function of the ARIMA model be used to set an

  8. Group space allowance has little effect on sow health, productivity, or welfare in a free-access stall system

    Science.gov (United States)

    Free-access stalls allow sows to choose the protection of a stall or use of a shared group space. This study investigated the effect of group space width: 0.91 (SS), 2.13 (IS), and 3.05 (LS) m on the health, production, behavior, and welfare of gestating sows. At gestational day (GD) 35.4 ± 2.3, 21 ...

  9. Stall Characteristics and Tip Clearance Effects in Forward Swept Axial Compressor Rotors

    Institute of Scientific and Technical Information of China (English)

    Ramakrishna PV; Govardhan M

    2009-01-01

    Tilting the blade sections to the flow direction (blade sweep) would increase the operating range of an axial com-pressor due to modifications in the pressure and velocity fields on the suction surface. On the other hand, blade tip gap, though finite, has great influence on the performance of a turbomachine. The present paper investigates the combined effect of these two factors on various flow characteristics in'a low speed axial flow compressor. For this present study, nine computational domains were modeled; three rotor sweep configurations (0°, 20° and 30°) and for three different clearance levels for each rotor. Commercial CFD solver ANSYS CFX 11.0 is used for the simulations. Results indicated that tip chordline sweep is found to improve the stall margin of the compressor by modifying the suction surface boundary layer migration phenomenon. Diffusion Factor (DF) contours showed the severity of stalling with unswept rotor. For the swept rotors, the zones of high probable stall are less severe and they become less in size with increasing sweep. Increment in the tip gap is found to gradually affect the perform-ance of unswept rotor, while the effect is very high for the two swept rotors for the earlier increments. As a mini-mum clearance is unavoidable, swept rotors suffer relatively higher deviation from the idealistic behavior than the unswept rotor due to tip clearance.

  10. An automatic system for the detection of dairy cows lying behaviour in free-stall barns

    Directory of Open Access Journals (Sweden)

    Simona M.C. Porto

    2013-09-01

    Full Text Available In this paper, a method for the automatic detection of dairy cow lying behaviour in free-stall barns is proposed. A computer visionbased system (CVBS composed of a video-recording system and a cow lying behaviour detector based on the Viola Jones algorithm was developed. The CVBS performance was tested in a head-to-head free stall barn. Two classifiers were implemented in the software component of the CVBS to obtain the cow lying behaviour detector. The CVBS was validated by comparing its detection results with those generated from visual recognition. This comparison allowed the following accuracy indices to be calculated: the branching factor (BF, the miss factor (MF, the sensitivity, and the quality percentage (QP. The MF value of approximately 0.09 showed that the CVBS missed one cow every 11 well detected cows. Conversely, the BF value of approximately 0.08 indicated that one false positive was detected every 13 well detected cows. The high value of approximately 0.92 obtained for the sensitivity index and that obtained for QP of about 0.85 revealed the ability of the proposed system to detect cows lying in the stalls.

  11. DksA Guards Elongating RNA Polymerase Against Ribosome-Stalling-Induced Arrest

    Science.gov (United States)

    Zhang, Yan; Mooney, Rachel A.; Grass, Jeffrey A.; Sivaramakrishnan, Priya; Herman, Christophe; Landick, Robert; Wang, Jue D.

    2014-01-01

    Summary In bacteria, translation-transcription coupling inhibits RNA polymerase (RNAP) stalling. We present evidence suggesting that, upon amino acid starvation, inactive ribosomes promote rather than inhibit RNAP stalling. We developed an algorithm to evaluate genome-wide polymerase progression independently of local noise, and used it to reveal that the transcription factor DksA inhibits promoter-proximal pausing and increases RNAP elongation when uncoupled from translation by depletion of charged tRNAs. DksA has minimal effect on RNAP elongation in vitro and on untranslated RNAs in vivo. In these cases, transcripts can form RNA structures that prevent backtracking. Thus, the effect of DksA on transcript elongation may occur primarily upon ribosome slowing/stalling or at promoter-proximal locations that limit the potential for RNA structure. We propose that inactive ribosomes prevent formation of backtrack-blocking mRNA structures and that, in this circumstance, DksA acts as a transcription elongation factor in vivo. PMID:24606919

  12. Aire unleashes stalled RNA polymerase to induce ectopic gene expression in thymic epithelial cells.

    Science.gov (United States)

    Giraud, Matthieu; Yoshida, Hideyuki; Abramson, Jakub; Rahl, Peter B; Young, Richard A; Mathis, Diane; Benoist, Christophe

    2012-01-10

    Aire is a transcriptional regulator that induces expression of peripheral tissue antigens (PTA) in thymic medullary epithelial cells (MECs), driving immunological self-tolerance in differentiating T cells. To elucidate its mechanistic pathways, we examined its transcriptional impact in MECs in vivo by microarray analysis with mRNA-spanning probes. This analysis revealed initiation of Aire-activated genes to be comparable in Aire-deficient and wild-type MECs, but with a block to elongation after 50-100 bp in the absence of Aire, suggesting activation by release of stalled polymerases by Aire. In contrast, patterns of activation by transcription factors such as Klf4 were consistent with regulation of initiation. Mapping of Aire and RNA polymerase-II (Pol-II) by ChIP and high-throughput sequencing (ChIP-seq) revealed that Aire bound all Pol-II-rich transcriptional start sites (TSS), irrespective of its eventual effect. However, the genes it preferentially activated were characterized by a relative surfeit of stalled polymerases at the TSS, which resolved once Aire was introduced into cells. Thus, transcript mapping and ChIP-seq data indicate that Aire activates ectopic transcription not through specific recognition of PTA gene promoters but by releasing stalled polymerases.

  13. The Relationships between Selection and Processing Food with Escherichia coli Contaminant on Food Stall Serving

    Directory of Open Access Journals (Sweden)

    Tris Eryando

    2014-04-01

    Full Text Available Escherichia coli in food stalls surrounding the X Campuss in Depok, year 2012. The research conducted to examine food safety, which were served in surrounding the campus X in Depok. Escherichia coli (E. coli existence was used to indicate the quality of hygiene and sanitation of the food that was served. Using the cross sectional method, the research examined the persons who served the food to be sold in the food stalls in the campus. There were 173 food servers chosen as the respondents from 10 different food stalls around the university. The existence of E. coli examined in the microbiology laboratory in the Faculty of Public Health. Using the most probable number (MPN method found that 59.54% of the food served in the campus were contaminated E. coli. Factors affecting the existence of E. coli were the raw materials (vegetables treated and the length of cooking of the materials (rice/beens. The improper treatment such as washing with no running water or even unwashed vegetables had 5 times risk of the E. coli contamination. Cooking less than 15 minutes was also more risky than cooking more than 15 minutes. As a result, this is very important to find a method to improve knowledge and to increase practical skills in food safety. Furthermore, in this research area may give contribution to avoid E. coli contamination which will prevent unnecessary illness among students in the campus.

  14. Replisome stall events have shaped the distribution of replication origins in the genomes of yeasts

    Science.gov (United States)

    Newman, Timothy J.; Mamun, Mohammed A.; Nieduszynski, Conrad A.; Blow, J. Julian

    2013-01-01

    During S phase, the entire genome must be precisely duplicated, with no sections of DNA left unreplicated. Here, we develop a simple mathematical model to describe the probability of replication failing due to the irreversible stalling of replication forks. We show that the probability of complete genome replication is maximized if replication origins are evenly spaced, the largest inter-origin distances are minimized, and the end-most origins are positioned close to chromosome ends. We show that origin positions in the yeast Saccharomyces cerevisiae genome conform to all three predictions thereby maximizing the probability of complete replication if replication forks stall. Origin positions in four other yeasts—Kluyveromyces lactis, Lachancea kluyveri, Lachancea waltii and Schizosaccharomyces pombe—also conform to these predictions. Equating failure rates at chromosome ends with those in chromosome interiors gives a mean per nucleotide fork stall rate of ∼5 × 10−8, which is consistent with experimental estimates. Using this value in our theoretical predictions gives replication failure rates that are consistent with data from replication origin knockout experiments. Our theory also predicts that significantly larger genomes, such as those of mammals, will experience a much greater probability of replication failure genome-wide, and therefore will likely require additional compensatory mechanisms. PMID:23963700

  15. Estimating the probabilities of making a smoking quit attempt in Italy: stall in smoking cessation levels, 1986-2009

    Directory of Open Access Journals (Sweden)

    Carreras Giulia

    2012-03-01

    Full Text Available Abstract Background No data on annual smoking cessation probability (i.e., the probability of successfully quit in a given year are available for Italy at a population level. Mathematical models typically used to estimate smoking cessation probabilities do not account for smoking relapse. In this paper, we developed a mathematical model to estimate annual quitting probabilities, taking into account smoking relapse and time since cessation. Methods We developed a dynamic model describing the evolution of current, former, and never smokers. We estimated probabilities of smoking cessation by fitting the model with observed smoking prevalence in Italy, 1986-2009. Results Annual cessation probabilities were higher than 5% only in elderly persons and in women aged Conclusions Over the last 20 years, cessation probabilities among Italian smokers, particularly for those aged 30-59 years, have been very low and stalled. Quitting in Italy is considered as a practicable strategy only by women in the age of pregnancy and by elderly persons, when it’s likely that symptoms of tobacco-related diseases have already appeared. In order to increase cessation probabilities, smoking cessation treatment policies (introducing total reimbursement of cessation treatments, with a further development of quitlines and smoking cessation services should be empowered and a country-wide mass media campaign targeting smokers aged 30-59 years and focusing on promotion of quitting should be implemented.

  16. The DNA-Binding Domain of S. pombe Mrc1 (Claspin Acts to Enhance Stalling at Replication Barriers.

    Directory of Open Access Journals (Sweden)

    Juergen Zech

    Full Text Available During S-phase replication forks can stall at specific genetic loci. At some loci, the stalling events depend on the replisome components Schizosaccharomyces pombe Swi1 (Saccharomyces cerevisiae Tof1 and Swi3 (S. cerevisiae Csm3 as well as factors that bind DNA in a site-specific manner. Using a new genetic screen we identified Mrc1 (S. cerevisiae Mrc1/metazoan Claspin as a replisome component involved in replication stalling. Mrc1 is known to form a sub-complex with Swi1 and Swi3 within the replisome and is required for the intra-S phase checkpoint activation. This discovery is surprising as several studies show that S. cerevisiae Mrc1 is not required for replication barrier activity. In contrast, we show that deletion of S. pombe mrc1 leads to an approximately three-fold reduction in barrier activity at several barriers and that Mrc1's role in replication fork stalling is independent of its role in checkpoint activation. Instead, S. pombe Mrc1 mediated fork stalling requires the presence of a functional copy of its phylogenetically conserved DNA binding domain. Interestingly, this domain is on the sequence level absent from S. cerevisiae Mrc1. Our study indicates that direct interactions between the eukaryotic replisome and the DNA are important for site-specific replication stalling.

  17. Review of delta wing space shuttle vehicle dynamics

    Science.gov (United States)

    Reding, J. P.; Ericsson, L. E.

    1972-01-01

    The unsteady aerodynamics of the delta planform, high cross range, shuttle orbiter were investigated. It has been found that these vehicles are subject to five unsteady flow phenomena that could compromise the flight dynamics. They are: (1) leeside shock induced separation, (2) sudden leading edge stall, (3) vortex burst, (4) bow shock-flap shock interaction, (5) forebody vorticity. Trajectory shaping is seen as the most powerful means of avoiding the detrimental effects of the stall phenomena. However, stall must be fixed or controlled when traversing the stall region. The other phenomena may be controlled by carefully programmed control deflections and some configuration modification. Ways to alter the occurrence of the various flow conditions are explored.

  18. Computational Investigation of the Compressible Dynamic Stall Characteristics of the Sikorsky SSC-A09 Airfoil

    Science.gov (United States)

    1993-09-01

    convergence is obtained. Procedures: * Run bl2d * Run gnuplot * Load ’dis’ and check CF for convergence * If diverged solution, change the upper transition...progressively aft. Find the point where BL2D will just converge. This is the Transition Point. R. VISUALIZATION ROUTINES Data output is viewed using Gnuplot ...batch files. Gnuplot is a plotting routine available on the Indigos. Procedures to view or print your results: 173 Appendix A g Activates gnuplot

  19. Time-and-Spatially Adapting Simulations for Efficient Dynamic Stall Predictions

    Science.gov (United States)

    2015-09-01

    URANS) turbulence models are statistical closures. Two-equation models have been shown by numerous researchers to be superior to one- equation... algebraic error) descend below a spec- ified fraction of the temporal error norm Et . A drop of at least one order of magnitude is typically rec

  20. Pressure-Based High-Order TVD Methodology for Dynamic Stall Control

    Science.gov (United States)

    1992-01-31

    Shari M. Shea and Ms. Jennifer L. Swann of CFDRC for their skillful preparation of the typescript of this report. I I I I I I I I ii I TABLE OF CONTENTS...sectional lift coefficient. Ashworth , et al.52 studied three-dimensional flow field about a forward swept NACA 0015 wing. They found that strong helical tip...occurred in the cycle. Ashworth , et al. 56,57, Luttges and M.C. Robinson 58, and Adler and Luttges59 have I made a series of studies on three

  1. Schlieren Studies of Compressibility Effects on Dynamic Stall of Airfoils in Transient Pitching Motion

    OpenAIRE

    Chandrasekhara, M.S.; Ahmed, S; Carr, L.W.

    1990-01-01

    Compressibility effects on the flowfield of an airfoil executing rapid transient pitching motion from 0 - 60 degrees over a wide range of Mach numbers and pitching rates were studied using a stroboscopic schlieren flow visualization technique. The studies have led to the first direct experiments] documentation of multiple shocks on the airfoil upper surface flow for certain conditions. Also, at low Mach numbers, additional coherent vortical structures were found to be ...

  2. Schlieren Studies of Compressibility Effects on Dynamic Stall on Transiently Pitching Airfoils

    OpenAIRE

    Chandrasekhara, M.S.; Ahmed, S; Carr, L.W.

    2016-01-01

    The article of record as published may be found at http://dx.doi.org/10.2514/3.48268 Compressibility effects on the flowfield of an airfoil executing rapid transient pitching motion from 0-60 deg over a wide range of Mach numbers and pitching rates were studied using a stroboscopic schlieren flow visualization technique. The studies have led to the first direct experimental documentation of multiple shocks on the airfoil upper surface flow for certain conditions. Also, at low Mach...

  3. Predictability of rotating stall and surge in a centrifugal compressor stage with dynamic simulations

    NARCIS (Netherlands)

    González Díez, N.; Smeulers, J.P.M.; Tapinassi, L.; Scotti del Greco, A.; Toni, L.

    2014-01-01

    A testing campaign performed on a centrifugal compressor test-loop showed that multiple areas of stable operation existed that were not expected. It was shown during the tests that after a first region of instability at low flow rates, a second stable region would appear at even lower flow rates. Dy

  4. Dynamic Stall Predictions by CFD Method%CFD法中的动态失速模拟

    Institute of Scientific and Technical Information of China (English)

    陈文轩

    2008-01-01

    本文介绍了CFD动态失速模拟所需要捕捉的关键物理,CFD法一般情况和较先进的CFD法,最后重点介绍了CFD法动态失速模拟的当前水平.总的来说在动态失速预测方面,CFD法优于综合法,CFD/CSD耦合结果与试验结果之间的吻合度还是可以接受的.俯仰力矩曲线的相位、大小和形状与试验数据吻合得较好,耦合解与试验数据之间的主要偏差在于法向力预测上.

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

    DEFF Research Database (Denmark)

    Castelein, D.; Ragni, D.; Tescione, G.;

    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-ba...

  6. Effects of rotating frame turbulence and dynamic stall on gust response of helicopter blades

    Science.gov (United States)

    Madhavan, R.; Gaonkar, G. H.

    1989-01-01

    The instantaneous or frequency-time spectrum of rotating frame turbulence (RFT) is presented. This spectrum makes it possible to predict the transfer of energy with respect to frequencies and the periodically varying nonstationarity with respect to time. Attention is also given to the RFT effects on the response statistics of an isolated rotor blade for low-advance-ratio and low-altitude conditions. It is noted that spectral density, rms values, and threshold-crossing expectation rates are significantly influenced by RFT.

  7. Dynamic stall control by plasma actuators with combined energy/momentum action

    Science.gov (United States)

    Starikovskiy, Andrey; Miles, Richard; PU Team

    2016-09-01

    Increased interest in plasma assisted flow control is reflected by a dramatic increase in publication rate over the past decade, including numerous demonstrations of plasma-assisted flow control. Many of these have been summarized in several topical reviews published recently. As an alternative to AC voltage inputs, nanosecond pulse driven plasma actuators in which voltage is applied in pulses at a specific frequency and with a specific on-time have been proposed for separated flow control. Nanosecond pulsed periodic dielectric barrier devices have been experimentally demonstrated to affect separated flows over a range of Mach numbers (0 . 03 >= M >= 0 . 85) and Reynolds numbers (10-4 >= Re >= 2 ×10-6) that are consistent with retreating blade flows. Furthermore, the nanosecond pulsed actuators tested to date have required less than 10 Watt per cm. of wing span, and therefore are energy efficient.

  8. 轴流压气机失速特征识别%Identification of stall characteristics of axial flow compressor

    Institute of Scientific and Technical Information of China (English)

    王春瑞; 岳林

    2011-01-01

    为了能够准确识别压气机旋转失速过程中失速团的数目,将压气机旋转失速过程中脉动压力波动的相位和幅值特征绘制在极坐标中,然后根据其在极坐标图中表现出来的特征来确定失速团的数目.经过与传统方法对比说明该分析方法对于失速团数目的确定优于原有的方法,具有抗噪性和一定的精度.另外,使用该方法可以可视化周向失速分布区域,并能可视化压气机失速先兆的发生和发展.%In order to identify the number of stall cells during rotating stall process, a method was presented in this paper. Firstly, the phase and amplitude characteristics of pres sure fluctuation during stall process were drew in the polar coordinate, and then the number of stall cells was obtained by judging the waveform displayed. After comparison with the traditional method, it shows that this method for determining the number of stall cell is better than original one thanks to its noise immunity and certain degree of precision. Besides, the method can also visualize the areas of stall in circumference and occurrence and development of stall inception in compressor.

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

    Science.gov (United States)

    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.

  10. Replication Stalling and Heteroduplex Formation within CAG/CTG Trinucleotide Repeats by Mismatch Repair

    KAUST Repository

    Viterbo, David

    2016-03-16

    Trinucleotide repeat expansions are responsible for at least two dozen neurological disorders. Mechanisms leading to these large expansions of repeated DNA are still poorly understood. It was proposed that transient stalling of the replication fork by the repeat tract might trigger slippage of the newly-synthesized strand over its template, leading to expansions or contractions of the triplet repeat. However, such mechanism was never formally proven. Here we show that replication fork pausing and CAG/CTG trinucleotide repeat instability are not linked, stable and unstable repeats exhibiting the same propensity to stall replication forks when integrated in a yeast natural chromosome. We found that replication fork stalling was dependent on the integrity of the mismatch-repair system, especially the Msh2p-Msh6p complex, suggesting that direct interaction of MMR proteins with secondary structures formed by trinucleotide repeats in vivo, triggers replication fork pauses. We also show by chromatin immunoprecipitation that Msh2p is enriched at trinucleotide repeat tracts, in both stable and unstable orientations, this enrichment being dependent on MSH3 and MSH6. Finally, we show that overexpressing MSH2 favors the formation of heteroduplex regions, leading to an increase in contractions and expansions of CAG/CTG repeat tracts during replication, these heteroduplexes being dependent on both MSH3 and MSH6. These heteroduplex regions were not detected when a mutant msh2-E768A gene in which the ATPase domain was mutated was overexpressed. Our results unravel two new roles for mismatch-repair proteins: stabilization of heteroduplex regions and transient blocking of replication forks passing through such repeats. Both roles may involve direct interactions between MMR proteins and secondary structures formed by trinucleotide repeat tracts, although indirect interactions may not be formally excluded.

  11. Effect of softer flooring in tie stalls on resting behavior and leg injuries of lactating cows.

    Science.gov (United States)

    Rushen, J; Haley, D; de Passillé, A M

    2007-08-01

    To test the advantages of softer flooring in tie stalls, we compared the behavior and injuries of dairy cows housed in tie stalls with either soft rubber mats (n = 12) or concrete flooring (n = 12), both lightly covered with straw. Data were collected for 112 d beginning at 14 DIM (+/-4 d). Cows' general activity was observed continuously for 24 h every 28 d. Behavior was also scored by a scan sampling technique every 14 d such that each cow was observed for a period of 3 min every 12 min. We scored the occurrence of leg lesions and other injuries every 7 d throughout the study. Cows on rubber mats had shorter bouts of lying but the frequency of bouts was higher, leading them to tend to spend more time lying compared with cows housed on concrete. Cows on concrete spent more time standing idle, but there was no difference in the time spent eating. There was no effect of stall flooring on the number of minor abrasions to the legs and body. There was a significantly higher incidence of swelling of the carpus joints for cows housed on concrete. Cows housed on soft rubber flooring appeared to be less hesitant to change posture from lying to standing (and vice versa), and as a result changed posture more frequently and spent more time lying than cows on concrete flooring. The decreased incidence of swelling of the carpus joint for cows on soft rubber mats may have important long-term effects in preventing a variety of leg problems.

  12. Formation of a stalled early intermediate of pseudouridine synthesis monitored by real-time FRET.

    Science.gov (United States)

    Hengesbach, Martin; Voigts-Hoffmann, Felix; Hofmann, Benjamin; Helm, Mark

    2010-03-01

    Pseudouridine is the most abundant of more than 100 chemically distinct natural ribonucleotide modifications. Its synthesis consists of an isomerization reaction of a uridine residue in the RNA chain and is catalyzed by pseudouridine synthases. The unusual reaction mechanism has become the object of renewed research effort, frequently involving replacement of the substrate uridines with 5-fluorouracil (f(5)U). f(5)U is known to be a potent inhibitor of pseudouridine synthase activity, but the effect varies among the target pseudouridine synthases. Derivatives of f(5)U have previously been detected, which are thought to be either hydrolysis products of covalent enzyme-RNA adducts, or isomerization intermediates. Here we describe the interaction of pseudouridine synthase 1 (Pus1p) with f(5)U-containing tRNA. The interaction described is specific to Pus1p and position 27 in the tRNA anticodon stem, but the enzyme neither forms a covalent adduct nor stalls at a previously identified reaction intermediate of f(5)U. The f(5)U27 residue, as analyzed by a DNAzyme-based assay using TLC and mass spectrometry, displayed physicochemical properties unaltered by the reversible interaction with Pus1p. Thus, Pus1p binds an f(5)U-containing substrate, but, in contrast to other pseudouridine synthases, leaves the chemical structure of f(5)U unchanged. The specific, but nonproductive, interaction demonstrated here thus constitutes an intermediate of Pus turnover, stalled by the presence of f(5)U in an early state of catalysis. Observation of the interaction of Pus1p with fluorescence-labeled tRNA by a real-time readout of fluorescence anisotropy and FRET revealed significant structural distortion of f(5)U-tRNA structure in the stalled intermediate state of pseudouridine catalysis.

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

    Science.gov (United States)

    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.

  14. Prediction of RNA Polymerase II recruitment, elongation and stalling from histone modification data

    DEFF Research Database (Denmark)

    Chen, Yun; Jørgensen, Mette; Kolde, Raivo

    2011-01-01

    ABSTRACT: BACKGROUND: Initiation and elongation of RNA polymerase II (RNAPII) transcription is regulated by both DNA sequence and chromatin signals. Recent breakthroughs make it possible to measure the chromatin state and activity of core promoters genome-wide, but dedicated computational...... in the gene body, the mRNA production originating from the promoter and finally also the stalling characteristics of RNAPII by considering both quantitative and spatial features of histone modifications around the transcription start site (TSS). As the model framework can also pinpoint the signals...

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  16. Analytical Calculation of Stall-inception and Surge Points for an Axial-flow Compresor Rotor

    OpenAIRE

    Moreno Benavides, Efren; López Juste, Gregorio

    2012-01-01

    Recently, a theoretical criterion to calculate the stability of an axial-flow compressor rotor has been presented in the scientific literature. This theoretical criterion was used for determining the locus of the stability line over the rotor map and for predicting the post-stall evolution of the constant-speed line of a rotor. The main objective of this paper is to improve the predictions of such a model. To do that, the paper proposes a different characterization of the characteristic az...

  17. Fixed-speed active-stall wind turbines in offshore applications

    DEFF Research Database (Denmark)

    Akhmatov, Vladislav; Nielsen, Arne Hejde

    2005-01-01

    A large offshore wind farm in the East Danish power system was commissioned in 2003 at Rodsand. The power capacity of the wind farm is 165 MW divided between 72 wind turbines. For this large offshore application, robust and well-known wind technology has been chosen in the form of fixed-speed, ac......-speed, active-stall wind turbines equipped with induction generators. In this paper, maintaining and improving the short-term voltage stability is discussed and systematized in terms of this wind technology. Copyright (C) 2004 John Wiley Sons, Ltd....

  18. The Role of Tip Leakage Flow in Triggering Rotating Stall of a Low Speed Compressor under Inlet Distortion

    Institute of Scientific and Technical Information of China (English)

    Jingxuan Zhang; Feng Lin; Jingyi Chen; Chaoqun Nie

    2009-01-01

    The stall behavior in a single-stage low-speed axial compressor under rotating inlet distortion (RID) is investi-gated in the first half of this paper. The tests demonstrate that the tip leakage flow (TLF) plays an important rolein triggering rotating stall. The tracking of the spike-like disturbances caused by the spillage of TLV indicates that most of such spike-like disturbances will be smeared by non-distorted sector and the growth of the spike-like dis-turbances actually relate closely to how and how often the path of the propagating disturbances come across the path of the rotating distorted sector. In the second half of this paper, micro air injections are applied to test the ef-fect behavior of TLF on stall inception. Contrasts to without micro air injections, the spike-like disturbances are much fewer, so the possibilities that spike-like disturbances may trigger rotating stall are fewer too. As a result, the compressor gets a lower mass flow rate at stall for both co-rotating inlet distortion and counter-rotating inlet distortion.

  19. Effects of Vortex Generator Jet on Corner Separation/Stall in High-Turning Compressor Cascade

    Institute of Scientific and Technical Information of China (English)

    刘华坪; 李得英; 陈焕龙; 张东飞

    2016-01-01

    The effects of the vortex generator jet(VGJ)attached at the endwall on the corner separation/stall con-trol are investigated by numerical simulation in a high-turning linear compressor cascade. The results show that the corner separation could be reduced significantly, which results in a wider operation range as well as a more uniform exit flow angle and total pressure profile. At the near-stall operation point, the maximum relative reduction of the total pressure loss is up to 32.5%,, whereas the jet mass ratio is less than 0.4%,. Based on the analysis of the detailed flow structure, three principal effects of the VGJ on the endwall cross flow and corner separation are identified. One is to increase the tangential velocity component opposite to cross flow, thus inhibiting the endwall secondary flow near the jet exit. The second is to suppress the pitchwise extension of the passage vortex as an air fence. The third is to sweep the low energy fluids towards the mainstream on the up-washed side and to transport the mainstream flu-ids to the endwall to reenergize the boundary layer on the down-washed side.

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

    Directory of Open Access Journals (Sweden)

    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.

  1. A Model to Predict Stall Inception of Transonic Axial Flow Fan/Compressors

    Institute of Scientific and Technical Information of China (English)

    SUN Xiaofeng; SUN Dakun; YU Weiwei

    2011-01-01

    A stall inception model for transonic fan/compressors is presented in this paper.It can be shown that under some assumptions the solution of unsteady flow field consists of pressure wave which propagates upstream or downstream,vortex wave and entropy wave convected with the mean flow speed.By further using the mode-matching technique and applying the conservation law and conditions reflecting the loss characteristics of a compressor in the inlet and outlet of the rotor or stator blade rows,a group of homogeneous equations can be obtained from which the stability equation can be derived.Based on the analysis of the unsteady phenomenon caused by casing treatments,the function of casing treatments has been modeled by a wall impedance condition which has been included in the stability model through the eigenvalues and the corresponding eigenfunctions of the system.Besides,the effect of shock waves in cascade channel on the stability prediction is also considered in the stall inception model.Finally,some numerical analysis and experimental investigation are also conducted with emphasis on the mutual comparison.

  2. Ethnic Dimensions of Guatemala's Stalled Transition: A Parity-Specific Analysis of Ladino and Indigenous Fertility Regimes.

    Science.gov (United States)

    Grace, Kathryn; Sweeney, Stuart

    2016-02-01

    In some contemporary populations, fertility levels appear to plateau, with women maintaining a consistently high level of fertility for a relatively extended period. Because this plateau does not reflect the historical patterns observed in Europe, the focus of most studies on fertility patterns, mechanisms underlying the plateau and the reinstatement of a decline have not been fully explored and are not fully understood. Through the construction of fertility histories of 25,000 women using multiple years of health survey data, we analyze some of the components of stalled fertility as they pertain to Guatemala, the only Central American country to have experienced a stalled fertility decline.

  3. Influence of free-stall flooring on comfort and hygiene of dairy cows during warm climatic conditions.

    Science.gov (United States)

    De Palo, P; Tateo, A; Zezza, F; Corrente, M; Centoducati, P

    2006-12-01

    An evaluation of behavioral and hygienic conditions was carried out with 4 materials used as free-stall flooring for dairy cows: polyethylene vinyl acetate (EVA) and polypropylene vinyl acetate (PVA) mats, wood shavings, and solid manure. The free-stall type selected by cows was evaluated in response to changes in environmental temperature and humidity. Two tests were used: 1) a preference test, in which 8 cows were housed in a pen with 32 free stalls and 4 types of flooring; and 2) an aversion test, in which 32 cows were placed in 4 pens, each with 8 free stalls. The free stalls in each pen had a single type of bedding material. These tests showed that the comfort of dairy cows was predominantly influenced by environmental conditions. The preference test for lying showed that cows preferred free-stall floors with EVA mats over those with PVA mats, wood shavings, and solid manure (332.4 +/- 24.0 vs. 130.8 +/- 6.2, 160.9 +/- 23.7, and 102.6 +/- 23.2 min/d, respectively), but under conditions of heat stress, with a temperature-humidity index > 80, they chose wood shavings and solid manure lying areas. These results were confirmed by the aversion test. In all experimental and environmental conditions, the PVA mats were the least suitable. The mats contaminated with organic manure and the free stalls bedded with wood shavings and organic solids did not differ in either the coliform load on the lying surfaces (EVA mats: 290 +/- 25; PVA mats: 306 +/- 33; wood shavings: 290 +/- 39; and solid manure: 305 +/- 23 log(10) cfu/mL) or the total bacterial count in the raw milk (EVA mats: 232 +/- 22; PVA mats: 233 + 24; wood shavings: 221 +/- 24; and solid manure: 220 +/- 25 log(10) cfu/mL). These results demonstrate that the comfort of dairy cows housed in barns with free stalls as resting areas does not depend only on the material used, but also on the value of the material in microenvironmental conditions.

  4. Association of airborne concentration of virulent Rhodococcus equi with location (stall versus paddock) and month (January through June) on 30 horse breeding farms in central Kentucky.

    Science.gov (United States)

    Cohen, Noah D; Kuskie, Kyle R; Smith, Jacqueline L; Slovis, Nathan M; Brown, Stuart E; Stepusin, Randolph S; Chaffin, M Keith; Takai, Shinji; Carter, Craig N

    2012-10-01

    To determine whether the concentration of airborne virulent Rhodococcus equi varied by location (stall vs paddock) and month on horse farms. Air samples from stalls and paddocks used to house mares and foals on 30 horse breeding farms in central Kentucky. Air samples from 1 stall and 1 paddock were obtained monthly from each farm from January through June 2009. Concentrations of airborne virulent R equi were determined via a modified colony immunoblot assay. Random-effects logistic regression was used to determine the association of the presence of airborne virulent R equi with location from which air samples were obtained and month during which samples were collected. Of 180 air samples, virulent R equi was identified in 49 (27%) and 13 (7%) obtained from stalls and paddocks, respectively. The OR of detecting virulent R equi in air samples from stalls versus paddocks was 5.2 (95% confidence interval, 2.1 to 13.1). Of 60 air samples, virulent R equi was identified in 25 (42%), 18 (30%), and 6 (10%) obtained from stalls during January and February, March and April, and May and June, respectively. The OR of detecting virulent R equi from stall air samples collected during May and June versus January and February was 0.22 (95% confidence interval, 0.08 to 0.63). Foals were more likely to be exposed to airborne virulent R equi when housed in stalls versus paddocks and earlier (January and February) versus later (May and June) during the foaling season.

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

    DEFF Research Database (Denmark)

    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...

  6. Survey on welfare of dairy cow in tie-stalls in mountain area

    Directory of Open Access Journals (Sweden)

    Stefano Bovolenta

    2010-01-01

    Full Text Available The aim of the survey was to study the effect of Alpine pasture and breed on welfare of dairy cattle bred in tie-stalls in mountain area of Friuli Venezia Giulia Region. Twenty-four representative farms were divided into 4 groups following a factorial design: 2 managements (with vs. without summer grazing x 2 breeds (Italian Simmental vs. Italian Brown. Data were collected following a protocol that considers direct animals’ measures or remarks, buildings and equipments information. The results showed that summer grazing affected some physical parameters - BCS, claw conformation and injuries - and some behaviour parameters such as rising movements. In this trial the breed did not seem to markedly influence cows’ welfare, except for BCS and lie down time.

  7. Numerical Simulation of Stall Flow Control Using a DBD Plasma Actuator in Pulse Mode

    Science.gov (United States)

    Khoshkhoo, R.; Jahangirian, A.

    2016-09-01

    A numerical simulation method is employed to investigate the effects of the unsteady plasma body force over the stalled NACA 0015 airfoil at low Reynolds number flow conditions. The plasma body force created by a dielectric barrier discharge actuator is modeled with a phenomenological method for plasma simulation coupled with the compressible Navier-Stokes equations. The governing equations are solved using an efficient implicit finitevolume method. The responses of the separated flow field to the effects of an unsteady body force in various inter-pulses and duty cycles as well as different locations and magnitudes are studied. It is shown that the duty cycle and inter-pulse are key parameters for flow separation control. Additionally, it is concluded that the body force is able to attach the flow and can affect boundary layer grow that Mach number 0.1 and Reynolds number of 45000.

  8. Spins, Stalls, and Shutdowns: Pitfalls of Qualitative Policing and Security Research

    Directory of Open Access Journals (Sweden)

    Randy K. Lippert

    2015-11-01

    Full Text Available This article explores key elements of qualitative research on policing and security agencies, including barriers encountered and strategies to prevent them. While it is oft-assumed that policing/security agencies are difficult to access due to their clandestine or bureaucratic nature, this article demonstrates this is not necessarily the case, as access was gained for three distinct qualitative research projects. Yet, access and subsequent research were not without pitfalls, which we term security spins, security stalls, and security shutdowns. We illustrate how each was encountered and argue these pitfalls are akin to researchers falling into risk categories, not unlike those used by policing/security agents in their work. Before concluding we discuss methodological strategies for scholars to avoid these pitfalls and to advance research that critically interrogates the immense policing/security realm. URN: http://nbn-resolving.de/urn:nbn:de:0114-fqs1601108

  9. Milk yield affects time budget in daiyr cows kept in tie-stalls

    DEFF Research Database (Denmark)

    Norring, M.; Valros, A.; Munksgaard, Lene

    2012-01-01

    compared with multiparous cows. Multiparous cows ruminated more while lying than primiparous cows. High milk yield cows spent a shorter time lying and they fell asleep (lay with neck relaxed) sooner. The degree of daily milk yield was associated with modifications in behavior and cows with high milk......Effective selection in breeding programs and improved management has increased the milk production per cow. However, the effects of the increased yield on behavior have not yet been clarified. We investigated the effect of milk yield on the time budget of 29 Finnish Ayrshire cows in the same stage...... of lactation kept in tie-stalls. The time spent lying, eating, ruminating, lying inactive without ruminating, and lying with the neck muscles relaxed, as well as the milk yield of primiparous and multiparous cows were recorded for 2d. The effects of milk yield and parity on behavior were analyzed with mixed...

  10. Low speed axial compressor stall margin improvement by unsteady plasma actuation

    Science.gov (United States)

    Li, Gang; Xu, Yanji; Yang, Lingyuan; Du, Wei; Zhu, Junqiang; Nie, Chaoqun

    2014-04-01

    This research investigates the use of single dielectric barrier discharge (SDBD) actuators for energizing the tip leakage flow to suppress rotating stall inception and extend the stable operating range of a low speed axial compressor with a single rotor. The jet induced by the plasma actuator adds momentum to the flow in the tip region and has a significant impact on the tip-gap flow. Experiments are carried out on a low speed axial compressor with a single rotor. The static pressure is measured at both the rotor inlet and outlet. The flow coefficient and pressure rise coefficient are calculated. Then the characteristic line is acquired to show the overall performance of the compressor. With unsteady plasma actuation of 18kV and 60W the compressor stability range improvement is realized at rotor speed of 1500 r/min — 2400 r/min.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  12. Fan cooling of the resting area in a free stalls dairy barn.

    Science.gov (United States)

    Calegari, Ferdinando; Calamari, Luigi; Frazzi, Ermes

    2014-08-01

    This summer study evaluated the effect of providing additional fans (cooling) in the resting area within a free-stall dairy barn that had fans and sprinklers in the feeding area and paddock availability. Thirty cows were divided into two homogenous groups and kept in two pens: one had the resting area equipped with two fans (FAN) while no fans were added to the other resting area (CON). Microclimatic parameters, rectal temperature (RT), breathing rate (BR), milk yield, and milk pH traits were recorded. Time budgeting and the behaviour of the cows (time spent in the feeding area, standing and lying in other areas) were also recorded using digital video technology. Two slight-to-moderate heat waves were observed. During the hottest period the daily maximum temperature recorded was 33.5 °C and the daily maximum THI was 81.6. During this period, the BR and RT increased only slightly in both groups, with lower BR (n.s.) in FAN compared with CON. Milk yield was better maintained (n.s.) in FAN compared with CON during the hottest period. The FAN cows showed a greater (Pfree stalls (9.5 and 8.6 h/day in FAN and CON, respectively), whereas CON cows made greater (P<0.05) use of the paddock during evening and late evening hours. Consequently, the total daily lying time was 13.5 h/day in both groups. In conclusion, the results suggest that using fans in the resting area improves cow comfort, which increases use of the resting area. The lying time results also suggest that the benefits of providing ventilation in the resting area might be more evident in barns where there is no paddock.

  13. Climate trends account for stalled wheat yields in Australia since 1990.

    Science.gov (United States)

    Hochman, Zvi; Gobbett, David L; Horan, Heidi

    2017-01-24

    Global food security requires that grain yields continue to increase to 2050, yet yields have stalled in many developed countries. This disturbing trend has so far been only partially explained. Here, we show that wheat yields in Australia have stalled since 1990 and investigate the extent to which climate trends account for this observation. Based on simulation of 50 sites with quality weather data, that are representative of the agro-ecological zones and of soil types in the grain zone, we show that water-limited yield potential declined by 27% over a 26 year period from 1990 to 2015. We attribute this decline to reduced rainfall and to rising temperatures while the positive effect of elevated atmospheric CO2 concentrations prevented a further 4% loss relative to 1990 yields. Closer investigation of three sites revealed the nature of the simulated response of water-limited yield to water availability, water stress and maximum temperatures. At all three sites, maximum temperature hastened time from sowing to flowering and to maturity and reduced grain number per m(2) and average weight per grain. This 27% climate-driven decline in water-limited yield is not fully expressed in actual national yields. This is due to an unprecedented rate of technology-driven gains closing the gap between actual and water-limited potential yields by 25 kg ha(-1)  yr(-1) enabling relative yields to increase from 39% in 1990 to 55% in 2015. It remains to be seen whether technology can continue to maintain current yields, let alone increase them to those required by 2050.

  14. Study of Near-Stall Flow Behavior in a Modern Transonic Fan with Composite Sweep

    Science.gov (United States)

    Hah, Chunill; Shin, Hyoun-Woo

    2011-01-01

    Detailed flow behavior in a modern transonic fan with a composite sweep is investigated in this paper. Both unsteady Reynolds-averaged Navier-Stokes (URANS) and Large Eddy Simulation (LES) methods are applied to investigate the flow field over a wide operating range. The calculated flow fields are compared with the data from an array of high-frequency response pressure transducers embedded in the fan casing. The current study shows that a relatively fine computational grid is required to resolve the flow field adequately and to calculate the pressure rise across the fan correctly. The calculated flow field shows detailed flow structure near the fan rotor tip region. Due to the introduction of composite sweep toward the rotor tip, the flow structure at the rotor tip is much more stable compared to that of the conventional blade design. The passage shock stays very close to the leading edge at the rotor tip even at the throttle limit. On the other hand, the passage shock becomes stronger and detaches earlier from the blade passage at the radius where the blade sweep is in the opposite direction. The interaction between the tip clearance vortex and the passage shock becomes intense as the fan operates toward the stall limit, and tip clearance vortex breakdown occurs at near-stall operation. URANS calculates the time-averaged flow field fairly well. Details of measured RMS static pressure are not calculated with sufficient accuracy with URANS. On the other hand, LES calculates details of the measured unsteady flow features in the current transonic fan with composite sweep fairly well and reveals the flow mechanism behind the measured unsteady flow field.

  15. Reducing Respiratory Health Risks to Horses and Workers: A Comparison of Two Stall Bedding Materials

    Directory of Open Access Journals (Sweden)

    Markku Saastamoinen

    2015-10-01

    Full Text Available Stable air quality and the choice of bedding material are an important health issue both in horses and people working or visiting horse stables. Risks of impaired respiratory health are those that can especially be avoided by improving air quality in the stable. The choice of bedding material is particularly important in cold climate conditions; where horses are kept most of the day and year indoors throughout their life. This study examined the effect of two bedding materials; wood shavings and peat; on stable air quality and health of horses. Ammonia and dust levels were also measured to assess conditions in the stable. Ammonia was not detected or was at very low levels (<0.25 ppm in the boxes in which peat was used as bedding; but its concentration was clearly higher (1.5–7.0 ppm in stalls with wood shavings as bedding. Personal measurements of workers revealed quite high ammonia exposure (5.9 ppm8h in the boxes in which wood shavings were used; but no exposure was Animals 2015, 5 966 observed in stalls bedded with peat. The respiratory symptoms in horses increased regardless of the bedding material at the beginning of the study. The health status of the horses in the peat bedding group returned to the initial level in the end of the trial but horses bedded with wood shavings continued to be symptomatic. The hooves of the horses with peat bedding had a better moisture content than those of the horses bedded with wood shavings. The results suggest that peat is a better bedding material for horses than wood shavings regarding the health of both horses and stable workers.

  16. Has Uganda experienced any stalled fertility transitions? Reflecting on the last four decades (1973-2011).

    Science.gov (United States)

    Kabagenyi, Allen; Reid, Alice; Rutaremwa, Gideon; Atuyambe, Lynn M; Ntozi, James P M

    2015-09-23

    Persistent high fertility is associated with mother and child mortality. While most regions in the world have experienced declines in fertility rates, there are conflicting views as to whether Uganda has entered a period of fertility transition. There are limited data available that explicitly detail the fertility trends and patterns in Uganda over the last four decades, from 1973 to 2011. Total fertility rate (TFR) is number of live births that a woman would have throughout her reproductive years if she were subject to the prevailing age specific fertility patterns. The current TFR for Uganda stands at 6.2 children born per woman, which is one of the highest in the region. This study therefore sought to examine whether there has been a fertility stall in Uganda using all existing Demographic Health Survey data, to provide estimates for the current fertility levels and trends in Uganda, and finally to examine the demographic and socioeconomic factors responsible for fertility levels in Uganda. This is a secondary analysis of data from five consecutive Ugandan Demographic Health Surveys (UDHS); 1988/1989, 1995, 2000/2001, 2006 and 2011. Using pooled data to estimate for fertility levels, patterns and trends, we applied a recently developed fertility estimation approach. A Poisson regression model was also used to analyze fertility differentials over the study period. Over the studied period, fertility trends and levels fluctuated from highs of 8.8 to lows of 5.7, with no specific lag over the study period. These findings suggest Uganda is at the pre-transitional stage, with indications of imminent fertility rate reductions in forthcoming years. Marital status remained a strong predictor for number of children born, even after controlling for other variables. This study suggests there is no evidence of a fertility stall in Uganda, but demonstrates an onset of fertility transition in the country. If this trend continues, Uganda will experience a low fertility rate in

  17. Associations of soft flooring materials in free stalls with milk yield, clinical mastitis, teat lesions, and removal of dairy cows.

    Science.gov (United States)

    Ruud, L E; Bøe, K E; Osterås, O

    2010-04-01

    The objective was to test if there was an association between free-stall base softness and milk yield, incidence of clinical mastitis (CM), teat lesions, and removal of cows. In a questionnaire sent to 1,923 dairy farms presumed to be using free-stall housing, farmers were asked for information regarding housing and stall base; for example, the year of installation and the product name or brand of their mats or mattresses. This information was merged with data for milk yield, CM, teat lesions, and removal of cows extracted from the Norwegian Dairy Herd Recording System for the years after installation of mats or mattresses. After exclusion of invalid contributions, the data set consisted of 29,326 lactations for milk yield distributed over 363 free-stalled herds in Norway. The farms were stratified into 5 categories according to the softness of the stall surface measured as millimeter impact of a sphere with a diameter of 120 mm at 2-kN load: 1=concrete, softness of 0mm; 2=rubber, softness of 1 to 8mm; 3=soft mats, softness of 9 to 16 mm; 4=multilayer mats, softness of 17 to 24 mm; and 5=mattresses, softness over 24 mm. Lactation curves were estimated as modified Wood's lactation curves using test-day data and mixed models with repeated measurements, adjusting for days in milk, parity, and softness of free-stall flooring. Herds on concrete free-stall bases yielded 6,727+/-146 kg of milk from 5 to 305 days in milk. In comparison, herds showed a decrease of 0.3% on rubber, an increase of 2.4% on soft mats, an increase of 4.5% on multilayer mats, and an increase of 3.9% on mattresses. Compared with concrete, the hazard ratio (HR) of CM was less on rubber, multilayer mats, and mattresses [HR=0.89 (0.79-0.99), 0.85 (0.73-0.996), and 0.80 (0.73-0.88), respectively]. Compared with concrete, the HR of teat lesions was less on rubber, soft mats, multilayer mats, and mattresses [HR=0.41 (0.26-0.65), 0.33 (0.24-0.44), 0.12 (0.04-0.38), and 0.47 (0.33-0.67), respectively]. The

  18. Scientific Investigations of a 16th Century Stall Belonging to the Evangelic Church in Bistriţa, Bistriţa-Năsăud County, Romania

    Directory of Open Access Journals (Sweden)

    C. Marutoiu

    2013-01-01

    Full Text Available The Evangelic Church in Bistriţa city is one of the important gothic monuments in Romania. Inside the church there have been preserved a series of furniture pieces from different centuries, and the stall that has been analysed in this study is one of them. The study presents the investigations that were made on the occasion of restoring the stall. The nature and the status of the wooden supports and also the composition of the painting layer which covers the front side of the stall were investigated by several methods: Fourier transform infrared (FTIR spectroscopy, X-ray diffraction (XRD, and differential scanning calorimetry (DSC analyses. The back side of the stall was made of spruce fir wood and its status was also investigated. The nature of the component elements and the heritage value of the ensemble were also established.

  19. Why commercialization of gene therapy stalled; examining the life cycles of gene therapy technologies.

    Science.gov (United States)

    Ledley, F D; McNamee, L M; Uzdil, V; Morgan, I W

    2014-02-01

    This report examines the commercialization of gene therapy in the context of innovation theories that posit a relationship between the maturation of a technology through its life cycle and prospects for successful product development. We show that the field of gene therapy has matured steadily since the 1980s, with the congruent accumulation of >35 000 papers, >16 000 US patents, >1800 clinical trials and >$4.3 billion in capital investment in gene therapy companies. Gene therapy technologies comprise a series of dissimilar approaches for gene delivery, each of which has introduced a distinct product architecture. Using bibliometric methods, we quantify the maturation of each technology through a characteristic life cycle S-curve, from a Nascent stage, through a Growing stage of exponential advance, toward an Established stage and projected limit. Capital investment in gene therapy is shown to have occurred predominantly in Nascent stage technologies and to be negatively correlated with maturity. Gene therapy technologies are now achieving the level of maturity that innovation research and biotechnology experience suggest may be requisite for efficient product development. Asynchrony between the maturation of gene therapy technologies and capital investment in development-focused business models may have stalled the commercialization of gene therapy.

  20. RNA polymerase stalls in a post-translocated register and can hyper-translocate

    Science.gov (United States)

    Nedialkov, Yuri A.; Nudler, Evgeny; Burton, Zachary F.

    2012-01-01

    Exonuclease (Exo) III was used to probe translocation states of RNA polymerase (RNAP) ternary elongation complexes (TECs). Escherichia coli RNAP stalls primarily in a post-translocation register that makes relatively slow excursions to a hyper-translocated state or to a pre-translocated state. Tagetitoxin (TGT) strongly inhibits hyper-translocation and inhibits backtracking, so, as indicated by Exo III mapping, TGT appears to stabilize both the pre- and probably a partially post-translocation state of RNAP. Because the pre-translocated to post-translocated transition is slow at many template positions, these studies appear inconsistent with a model in which RNAP makes frequent and rapid (i.e., millisecond phase) oscillations between pre- and post-translocation states. Nine nucleotides (9-nt) and 10-nt TECs, and TECs with longer nascent RNAs, have distinct translocation properties consistent with a 9–10 nt RNA/DNA hybrid. RNAP mutant proteins in the bridge helix and trigger loop are identified that inhibit or stimulate forward and backward translocation. PMID:23132506

  1. Welfare assessment of dairy cows housed in a tie-stall system

    Directory of Open Access Journals (Sweden)

    Marija Vučemilo

    2012-03-01

    Full Text Available Welfare assessment methods and techniques developed as a result of great interest of scientific and consumer populations regarding the welfare of animals housed in farms. In view of the fact that welfare by definition includes both physical and mental health, the welfare quality assessment includes an extensive number of measures. Welfare assessment was performed in two stables in which cows are kept in tie-stall by using the specific method described in the Welfare Quality® Assessment Protocol for Cattle. The measures included body condition score, qualitative behaviour assessment and body hygiene. The welfare assessment confirmed the importance of quality housing for ensuring better performance from animals, thus also affecting their health and productivity. It also pointed out the necessity of freeing animals by providing them with the possibility of free movement, whereat they can exhibit their physiological behaviour. It is definitely important to continue research, expand the number of researched measures in order to confirm the most useful indicators for welfare assessment and to identify the factors that within the animals’ physical and social environment affect the increase of their welfare.

  2. ETAA1 acts at stalled replication forks to maintain genome integrity.

    Science.gov (United States)

    Bass, Thomas E; Luzwick, Jessica W; Kavanaugh, Gina; Carroll, Clinton; Dungrawala, Huzefa; Glick, Gloria G; Feldkamp, Michael D; Putney, Reid; Chazin, Walter J; Cortez, David

    2016-11-01

    The ATR checkpoint kinase coordinates cellular responses to DNA replication stress. Budding yeast contain three activators of Mec1 (the ATR orthologue); however, only TOPBP1 is known to activate ATR in vertebrates. We identified ETAA1 as a replication stress response protein in two proteomic screens. ETAA1-deficient cells accumulate double-strand breaks, sister chromatid exchanges, and other hallmarks of genome instability. They are also hypersensitive to replication stress and have increased frequencies of replication fork collapse. ETAA1 contains two RPA-interaction motifs that localize ETAA1 to stalled replication forks. It also interacts with several DNA damage response proteins including the BLM/TOP3α/RMI1/RMI2 and ATR/ATRIP complexes. It binds ATR/ATRIP directly using a motif with sequence similarity to the TOPBP1 ATR-activation domain; and like TOPBP1, ETAA1 acts as a direct ATR activator. ETAA1 functions in parallel to the TOPBP1/RAD9/HUS1/RAD1 pathway to regulate ATR and maintain genome stability. Thus, vertebrate cells contain at least two ATR-activating proteins.

  3. Parametric analyses for synthetic jet control on separation and stall over rotor airfoil

    Institute of Scientific and Technical Information of China (English)

    Zhao Guoqing; Zhao Qijun

    2014-01-01

    Numerical simulations are performed to investigate the effects of synthetic jet control on separation and stall over rotor airfoils. The preconditioned and unsteady Reynolds-averaged Navier-Stokes equations coupled with akxshear stream transport turbulence model are employed to accomplish the flowfield simulation of rotor airfoils under jet control. Additionally, a velocity boundary condition modeled by a sinusoidal function is developed to fulfill the perturba-tion effect of periodic jets. The validity of the present CFD procedure is evaluated by the simulated results of an isolated synthetic jet and the jet control case for airfoil NACA0015. Then, parametric analyses are conducted specifically for an OA213 rotor airfoil to investigate the effects of jet param-eters (forcing frequency, jet location and momentum coefficient, jet direction, and distribution of jet arrays) on the control effect of the aerodynamic characteristics of a rotor airfoil. Preliminary results indicate that the efficiency of jet control can be improved with specific frequencies (the best lift-drag ratio at F+=2.0) and jet angles (40? or 75?) when the jets are located near the separation point of the rotor airfoil. Furthermore, as a result of a suitable combination of jet arrays, the lift coefficient of the airfoil can be improved by nearly 100%, and the corresponding drag coefficient decreased by 26.5%in comparison with the single point control case.

  4. Exceptionally strong easterly wind burst stalling El Niño of 2014.

    Science.gov (United States)

    Hu, Shineng; Fedorov, Alexey V

    2016-02-23

    Intraseasonal wind bursts in the tropical Pacific are believed to affect the evolution and diversity of El Niño events. In particular, the occurrence of two strong westerly wind bursts (WWBs) in early 2014 apparently pushed the ocean-atmosphere system toward a moderate to strong El Niño--potentially an extreme event according to some climate models. However, the event's progression quickly stalled, and the warming remained very weak throughout the year. Here, we find that the occurrence of an unusually strong basin-wide easterly wind burst (EWB) in June was a key factor that impeded the El Niño development. It was shortly after this EWB that all major Niño indices fell rapidly to near-normal values; a modest growth resumed only later in the year. The easterly burst and the weakness of subsequent WWBs resulted in the persistence of two separate warming centers in the central and eastern equatorial Pacific, suppressing the positive Bjerknes feedback critical for El Niño. Experiments with a climate model with superimposed wind bursts support these conclusions, pointing to inherent limits in El Niño predictability. Furthermore, we show that the spatial structure of the easterly burst matches that of the observed decadal trend in wind stress in the tropical Pacific, suggesting potential links between intraseasonal wind bursts and decadal climate variations.

  5. Lameness and Claw Lesions of the Norwegian Red Dairy Cattle Housed in Free Stalls in Relation to Environment, Parity and Stage of Lactation

    Directory of Open Access Journals (Sweden)

    Østerås O

    2005-12-01

    Full Text Available Approximately 88% of Norwegian dairy cattle are housed in tie stalls. Free stall housing for all dairy cattle will be implemented within 20 years. This means that the majority of existing stalls will be rebuilt in the near future. Fifty-seven free stall herds of the Norwegian Red breed were randomly selected and 1547 cows and 403 heifers were trimmed by 13 claw trimmers during the late winter and spring of 2002. The claw trimmers had been taught diagnosing and recording of claw lesions. Environment, management- and feeding routines were also recorded. Fifty-three herds had concrete slatted alleys while 4 had solid concrete. Thirty-five herds had concrete as a stall base, while 17 had rubber mats, 2 had wood and 3 had deep litter straw beds. The prevalence of lameness was 1.6% in hind claws. Models for lameness and claw lesions were designed to estimate the influence of different risk factors and to account for the cluster effects within herd and claw trimmer. Detected risk factors for lameness were: parity three and above and narrow cubicles; for heel horn erosions: lactation stage around 5–7 months after calving and solid concrete alleys; for haemorrhages of the white line: lactation stage around 3–5 months after calving and solid concrete alleys; for haemorrhages of the sole: parity one, lactation stage around 5–7 months after calving and short cubicles, for white line fissures: slatted concrete alleys; for asymmetrical claws: parities two and above and for corkscrewed claws: solid concrete alleys. The prevalence of lameness in heifers was low, however 29% had one or more claw lesions. Heifers that were housed in pens or free stalls had more heel-horn erosions, haemorrhages of the sole and white-line fissures than heifers in tie stalls. As new free stalls are being built, it is important to optimise the conditions for claw health.

  6. Lameness and Claw Lesions of the Norwegian Red Dairy Cattle Housed in Free Stalls in Relation to Environment, Parity and Stage of Lactation

    Directory of Open Access Journals (Sweden)

    Sogstad ÅM

    2006-12-01

    Full Text Available Approximately 88% of Norwegian dairy cattle are housed in tie stalls. Free stall housing for all dairy cattle will be implemented within 20 years. This means that the majority of existing stalls will be rebuilt in the near future. Fifty-seven free stall herds of the Norwegian Red breed were randomly selected and 1547 cows and 403 heifers were trimmed by 13 claw trimmers during the late winter and spring of 2002. The claw trimmers had been taught diagnosing and recording of claw lesions. Environment, management- and feeding routines were also recorded. Fifty-three herds had concrete slatted alleys while 4 had solid concrete. Thirty-five herds had concrete as a stall base, while 17 had rubber mats, 2 had wood and 3 had deep litter straw beds. The prevalence of lameness was 1.6% in hind claws. Models for lameness and claw lesions were designed to estimate the influence of different risk factors and to account for the cluster effects within herd and claw trimmer. Detected risk factors for lameness were: parity three and above and narrow cubicles; for heel horn erosions: lactation stage around 5–7 months after calving and solid concrete alleys; for haemorrhages of the white line: lactation stage around 3–5 months after calving and solid concrete alleys; for haemorrhages of the sole: parity one, lactation stage around 5–7 months after calving and short cubicles, for white line fissures: slatted concrete alleys; for asymmetrical claws: parities two and above and for corkscrewed claws: solid concrete alleys. The prevalence of lameness in heifers was low, however 29% had one or more claw lesions. Heifers that were housed in pens or free stalls had more heel-horn erosions, haemorrhages of the sole and white-line fissures than heifers in tie stalls. As new free stalls are being built, it is important to optimise the conditions for claw health.

  7. Oligodeoxynucleotide binding to (CTG) · (CAG) microsatellite repeats inhibits replication fork stalling, hairpin formation, and genome instability.

    Science.gov (United States)

    Liu, Guoqi; Chen, Xiaomi; Leffak, Michael

    2013-02-01

    (CTG)(n) · (CAG)(n) trinucleotide repeat (TNR) expansion in the 3' untranslated region of the dystrophia myotonica protein kinase (DMPK) gene causes myotonic dystrophy type 1. However, a direct link between TNR instability, the formation of noncanonical (CTG)(n) · (CAG)(n) structures, and replication stress has not been demonstrated. In a human cell model, we found that (CTG)(45) · (CAG)(45) causes local replication fork stalling, DNA hairpin formation, and TNR instability. Oligodeoxynucleotides (ODNs) complementary to the (CTG)(45) · (CAG)(45) lagging-strand template eliminated DNA hairpin formation on leading- and lagging-strand templates and relieved fork stalling. Prolonged cell culture, emetine inhibition of lagging-strand synthesis, or slowing of DNA synthesis by low-dose aphidicolin induced (CTG)(45) · (CAG)(45) expansions and contractions. ODNs targeting the lagging-strand template blocked the time-dependent or emetine-induced instability but did not eliminate aphidicolin-induced instability. These results show directly that TNR replication stalling, replication stress, hairpin formation, and instability are mechanistically linked in vivo.

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

    Science.gov (United States)

    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.

  9. Bloom syndrome complex promotes FANCM recruitment to stalled replication forks and facilitates both repair and traverse of DNA interstrand crosslinks.

    Science.gov (United States)

    Ling, Chen; Huang, Jing; Yan, Zhijiang; Li, Yongjiang; Ohzeki, Mioko; Ishiai, Masamichi; Xu, Dongyi; Takata, Minoru; Seidman, Michael; Wang, Weidong

    2016-01-01

    The recruitment of FANCM, a conserved DNA translocase and key component of several DNA repair protein complexes, to replication forks stalled by DNA interstrand crosslinks (ICLs) is a step upstream of the Fanconi anemia (FA) repair and replication traverse pathways of ICLs. However, detection of the FANCM recruitment has been technically challenging so that its mechanism remains exclusive. Here, we successfully observed recruitment of FANCM at stalled forks using a newly developed protocol. We report that the FANCM recruitment depends upon its intrinsic DNA translocase activity, and its DNA-binding partner FAAP24. Moreover, it is dependent on the replication checkpoint kinase, ATR; but is independent of the FA core and FANCD2-FANCI complexes, two essential components of the FA pathway, indicating that the FANCM recruitment occurs downstream of ATR but upstream of the FA pathway. Interestingly, the recruitment of FANCM requires its direct interaction with Bloom syndrome complex composed of BLM helicase, Topoisomerase 3α, RMI1 and RMI2; as well as the helicase activity of BLM. We further show that the FANCM-BLM complex interaction is critical for replication stress-induced FANCM hyperphosphorylation, for normal activation of the FA pathway in response to ICLs, and for efficient traverse of ICLs by the replication machinery. Epistasis studies demonstrate that FANCM and BLM work in the same pathway to promote replication traverse of ICLs. We conclude that FANCM and BLM complex work together at stalled forks to promote both FA repair and replication traverse pathways of ICLs.

  10. Coexisting state of surge and rotating stall in a two-stage axial flow compressor using a double-phase-locked averaging technique

    Science.gov (United States)

    Sakata, Yuu; Ohta, Yutaka

    2017-02-01

    The interaction between surge and rotating stall in an axial flow compressor was investigated from the viewpoint of an unsteady inner flow structure. The aim of this study was to identify the key factor that determines the switching phenomenon of a surge cycle. The main feature of the tested compressor is a shock tube connected in series to the compressor outlet through a diaphragm, slits, and a concentric duplex pipe: this system allows surge and rotating stall to be generated by connecting the shock tube with the compressor, or enables the compression plane wave injection. The unsteady characteristics and the internal flow velocity fluctuations were measured in detail, and the stall cell structure was averaged and visualized along the movement of the operation point under a coexisting state of surge. A coefficient of the cell scale fluctuation was calculated using the result of the averaging, and it confirmed that the processes of inner flow structure change differed from each other according to the next cycle of the surge. The result suggests that the key factor that determines the next cycle is the transformation of the internal flow structure, particularly between the stall cell and the entire circumferential stall, in both the recovering and stalling processes.

  11. Dynamics

    CERN Document Server

    Goodman, Lawrence E

    2001-01-01

    Beginning text presents complete theoretical treatment of mechanical model systems and deals with technological applications. Topics include introduction to calculus of vectors, particle motion, dynamics of particle systems and plane rigid bodies, technical applications in plane motions, theory of mechanical vibrations, and more. Exercises and answers appear in each chapter.

  12. Evaluation of free-stall mattress bedding treatments to reduce mastitis bacterial growth

    Energy Technology Data Exchange (ETDEWEB)

    Kristula, M.A.; Dou, Z.; Toth, J.D.; Smith, B.I.; Harvey, N.; Sabo, M. [University of Penn, Kennett Square, PA (United States)

    2008-05-15

    Bacterial counts were compared in free-stall mattresses and teat ends exposed to 5 treatments in a factorial study design on 1 dairy farm. Mattresses in five 30-cow groups were subjected to 1 of 5 bedding treatments every other day: 0.5 kg of hydrated limestone, 120 mL of commercial acidic conditioner, 1 kg of coal fly ash, 1 kg of kiln-dried wood shavings, and control (no bedding). Counts of coliforms, Klebsiella spp., Escherichia coli, and Streptococcus spp. were lowest on mattresses bedded with lime. Mattresses bedded with the commercial acidic conditioner had the next lowest counts for coliforms, Klebsiella spp., and Streptococcus spp. Wood shavings and the no-bedding control had the highest counts for coliform and Klebsiella spp. Compared with wood shavings or control, fly ash reduced the counts of coliforms, whereas for the other 3 bacterial groups, the reduction was not always significant. Streptococcus spp. counts were greatest in the control group and did not differ among the shavings and fly ash groups. Teat swab results indicated that hydrated lime was the only bedding treatment that significantly decreased the counts of both coliforms and Klebsiella spp. There were no differences in Streptococcus spp. numbers on the teats between any of the bedding treatments. Bacterial populations grew steadily on mattresses and were generally higher at 36 to 48 h than at 12 to 24 h, whereas bacterial populations on teats grew rapidly by 12 h and then remained constant. Hydrated lime was the only treatment that significantly reduced bacterial counts on both mattresses and teat ends, but it caused some skin irritation.

  13. An experimental and numerical investigation on the formation of stall-cells on airfoils

    Science.gov (United States)

    Manolesos, M.; Papadakis, G.; Voutsinas, S.

    2014-12-01

    Stall Cells (SCs) are large scale three-dimensional structures of separated flow that have been observed on the suction side of airfoils designed for or used on wind turbine blades. SCs are unstable in nature but can be stabilised by means of a localized disturbance; here in the form of a zigzag tape covering 10% of the wing span. Based on extensive tuft flow visualisations, the resulting flow was found macroscopically similar to the undisturbed flow. Next a combined investigation was carried out including pressure recordings, Stereo-PIV measurements and CFD simulations. The investigation parameters were the aspect ratio, the angle of attack and the Re number. Tuft and pressure data were found in good agreement. The 3D CFD simulations reproduced the structure of the SCs in qualitative agreement with the experimental data but had a delay of ~3deg in capturing the first appearance of a SC. The error in Cl max prediction was 7% compared to 19% for the 2D cases. Tests show that SCs grow with Re number and angle of attack. Also analysis of the time averaged computational results indicated the presence of three types of vortices: (a) the trailing edge line vortex (TELV) in the wake, (b) the separation line vortex (SLV) over the wing and (c) the SC vortices. The TELV and SLV run parallel to the trailing edge and are of opposite sign, while the SC vortices start normal to the wing suction surface, then bend towards the SC centre and later extend downstream, with their vorticity parallel to the free stream.

  14. The Quest for the Largest Depleted Galaxy Core: Supermassive Black Hole Binaries and Stalled Infalling Satellites

    Science.gov (United States)

    Bonfini, Paolo; Graham, Alister W.

    2016-10-01

    Partially depleted cores are practically ubiquitous in luminous early-type galaxies (M B ≲ -20.5 mag) and are typically smaller than 1 kpc. In one popular scenario, supermassive black hole (SMBH) binaries—established during dry (i.e., gas-poor) galaxy mergers—kick out the stars from a galaxy’s central region via three-body interactions. Here, this “binary black hole scouring scenario” is probed at its extremes by investigating the two galaxies reported to have the largest partially depleted cores found to date: 2MASX J09194427+5622012 and 2MASX J17222717+3207571 (the brightest galaxy in Abell 2261). We have fit these galaxy’s two-dimensional light distribution using the core-Sérsic model and found that the former galaxy has a core-Sérsic break radius {R}b,{cS}=0.55 {{kpc}}, which is three times smaller than the published value. We use this galaxy to caution that other reportedly large break radii may too have been overestimated if they were derived using the “sharp-transition” (inner core)-to-(outer Sérsic) model. In the case of 2MASX J17222717+3207571, we obtain R b,cS = 3.6 kpc. While we confirm that this is the biggest known partially depleted core of any galaxy, we stress that it is larger than expected from the evolution of SMBH binaries—unless one invokes substantial gravitational-wave-induced (black hole-)recoil events. Given the presence of multiple nuclei located (in projection) within the core radius of this galaxy, we explored and found support for the alternative “stalled infalling perturber” core-formation scenario, in which this galaxy’s core could have been excavated by the action of an infalling massive perturber.

  15. CFD study of a NACA 63-415 aerofoil fitted with stall strips

    Energy Technology Data Exchange (ETDEWEB)

    Zahle, F.; Soerensen, N.N.; Johansen, J.

    2002-09-01

    The present work describes a thorough investigation of 2D computations of the flow around a NACA 63-415 aerofoil fitted with stall strips (SS). A mesh study as well as a time step study is carried out and all computations are compared with experiments. Two different SS, 5mm and 7mm are investigated at several positions. Furthermore the influence of laminar to turbulent transition and the effect of a rounded SS were tested. There is not sufficient agreement between the experimental results and the simulations to draw any conclusions of optimum position and geometry of the SS. The 7mm SS's placed at P00 and P-02 has the greatest effect on the max lift followed by SS P02. The 5mm SS's does, as in the experiment, not change the lift curve noticeably. Even though this investigation does not conclusively succeed in verifying the experimental results with CFD, many useful conclusions can be drawn from the results. It is observed in the experiment that the vertical force fluctuates at higher angles of attack. This indicates that small bubbles are being shed off the profile causing the force to vary. This property is observed when transition is included in the model and also when the tip of the SS is rounded. From this result it could be concluded that the level of turbulence produced on the tip of the SS is very important for the development of the flow downstream. In the sharp tip calculations using fully turbulent computations, this is most likely too high, which resulted in the fine structures being damped out, with only one bubble appearing. (au)

  16. Revival of The Stalled Core-Collapse Supernova Shock Triggered by Precollapse Asphericity in the Progenitor Star

    CERN Document Server

    Couch, Sean M

    2013-01-01

    Multi-dimensional simulations of advanced nuclear burning stages of massive stars suggest that the Si/O layers of presupernova stars harbor large deviations from the spherical symmetry typically assumed for presupernova stellar structure. We carry out three-dimensional core-collapse supernova simulations with and without aspherical velocity perturbations to assess their potential impact on the supernova hydrodynamics in the stalled shock phase. Our results show that realistic perturbations can qualitatively alter the postbounce evolution, triggering an explosion in a model that fails to explode without them. This finding underlines the need for a multi-dimensional treatment of the presupernova stage of stellar evolution.

  17. Stall margin improvement of an axial flow fan with end wall injection and suction; Hekimen fukidashi suidashi ni yoru han'yo jikuryu sofuki no shissoku kaizen

    Energy Technology Data Exchange (ETDEWEB)

    Nishioka, K.; Kuroda, H.; Obata, S.; Chimura, O. [National Defense Academy, Kanagawa (Japan)

    1999-06-25

    The experimental studies are conducted to reveal the mechanism of stall margin improvement of an axial flow fan by injection or suction from the end wall. In case of injection, the largest improvement is obtained by the injection at about 0. 14 {approx} 0 .21 times axial chord length downstream from leading edge. The reason for large improvement is that stall vortex, shed intermittent separation vortex and tip leakage vortex are dissipated by this injection, and also that this blowing suppresses the separation of boundary layer. In case of suction, the largest improvement is found for the suction from the end wall near leading edge. The amplitude of periodic static pressure after stall inception becomes smaller in comparison with injection cases. These effects are increased with the increase of suction flow rate, because the discharge of the vortex occurs more easily. On the other hand, the suction from the upstream of leading edge reduces the axial velocity near rotor tip, and then it induces stall. Also we tried to visualize the tip region flow, The suppression mechanism is discussed based on the visualization. The suppression of stall is successfully photographed. (author)

  18. Spatial variability of air temperature in a free-stall in the Northeastern semi-arid region of Brazil

    Directory of Open Access Journals (Sweden)

    Indira C. M. Gonçalves

    2016-01-01

    Full Text Available ABSTRACT The knowledge on the spatial variability of climatic attributes and the building of Kriging maps can assist in the design and management of confined animal facilities, by allowing a spatial visualization that is helpful for the planning and control of information from the production environment. The study aimed to characterize the spatial variability of air temperature in a free-stall barn used for dairy cattle confinement located in Petrolina-PE, Brazil, in different seasons and at different times. The variable air temperature was recorded at 136 points distributed in the areas under the shed and the shade cloth for the study of spatial variability and the construction of maps by Kriging. Air temperature data was collected in the winter and in the summer, in the months of July and August (2013 and January and February (2014, at different times (9 and 15 h. According to the results, the use of geostatistics enabled to define areas with different spatial variabilities in air temperature and specific areas in the free-stall with values higher than the recommended levels for thermal comfort. In addition, the central part of the facility is the region with the lowest values of air temperatures, due to the presence of a ridge vent.

  19. Wall-resolved LES of high Reynolds number airfoil flow near stall condition for wall modeling in LES: LESFOIL revisited

    Science.gov (United States)

    Asada, Kengo; Kawai, Soshi

    2016-11-01

    Wall-resolved large-eddy simulation (LES) of an airfoil flow involving a turbulent transition and separations near stall condition at a high Reynolds number 2.1 x 106 (based on the freestream velocity and the airfoil chord length) is conducted by using K computer. This study aims to provide the wall-resolved LES database including detailed turbulence statistics for near-wall modeling in LES and also to investigate the flow physics of the high Reynolds number airfoil flow near stall condition. The LES well predicts the laminar separation bubble, turbulent reattachment and turbulent separation. The LES also clarified unsteady flow features associated with shear-layer instabilities: high frequency unsteadiness at St = 130 at the laminar separation bubble near the leading edge and low frequency unsteadiness at St = 1.5 at the separated turbulent shear-layer near the trailing edge. Regarding the near-wall modeling in LES, the database indicates that the pressure term in the mean streamwise-momentum equation is not negligible at the laminar and turbulent separated regions. This fact suggests that widely used equilibrium wall model is not sufficient and the inclusion of the pressure term is necessary for wall modeling in LES of such flow. This research used computational resources of the K computer provided by the RIKEN Advanced Institute for Computational Science through the HPCI System Research project (Project ID: hp140028). This work was supported by KAKENHI (Grant Number: 16K18309).

  20. Effect of 3D stall-cells on the pressure distribution of a laminar NACA64-418 wing

    Science.gov (United States)

    Ragni, Daniele; Ferreira, Carlos

    2016-08-01

    A 3D stall-cell flow-field has been studied in a 4.8 aspect-ratio wing obtained by linear extrusion of a laminar NACA64-418 airfoil profile. The span-wise change in the velocity and pressure distribution along the wing has been quantified with respect to the development of cellular structures from 8° to 20° angle of attack. Oil-flow visualizations help localizing the regular cellular pattern in function of the angle of attack. Multi-plane stereoscopic PIV measurements obtained by traversing the entire setup along the wing span show that the flow separation is not span-wise uniform. The combination of different stereoscopic fields into a 3D volume of velocity data allows studying the global effect of the stall-cell pattern on the wing flow. Integration of the experimentally computed pressure gradient from the Navier-Stokes equation is employed to compute the span-wise distribution of the mean surface pressure. Comparison of the results with the ones obtained from pressure taps installed in the wing evidences a span-wise periodic loading on the wing. The periodic loading has maxima confined in the stream-wise direction between the location of the highest airfoil curvature and the one of the airfoil flow separation. Estimation of the periodic loading is found within 2-6 % of the sectional wing lift.

  1. Numerical study on the influence mechanism of inlet distortion on the stall margin in a transonic axial rotor

    Science.gov (United States)

    Du, Juan; Lin, Feng; Chen, Jingyi; Morris, Scott C.; Nie, Chaoqun

    2012-06-01

    A numerical study is conducted to investigate the influence of inlet flow condition on tip leakage flow (TLF) and stall margin in a transonic axial rotor. A commercial software package FLUENT, is used in the simulation. The rotor investigated in this paper is ND_TAC rotor, which is the rotor of one-stage transonic compressor in the University of Notre Dame. Three varied inlet flow conditions are simulated. The inlet boundary condition with hub distortion provides higher axial velocity for the incoming flow near tip region than that for the clean inflow, while the incoming main flow possesses lower axial velocity near the tip region at tip distortion inlet boundary condition. Among the total pressure ratio curves for the three inlet flow conditions, it is found that the hub distorted inlet boundary condition improves the stall margin, while the tip distorted inlet boundary condition deteriorates compressor stability. The axial location of interface between tip leakage flow (TLF) and incoming main flow (MF) in the tip gap and the axial momentum ratio of TLF to MF are further examined. It is demonstrated that the axial momentum balance is the mechanism for interface movement. The hub distorted inflow could decrease the axial momentum ratio, suppress the movement of the interface between TLF and MF towards blade leading edge plane and thus enhance compressor stability.

  2. Topic 1.1.2, Unsteady Aerodynamics: Time-Varying Compressible Dynamic Stall Mechanisms Due to Freestream Mach Oscillations

    Science.gov (United States)

    2014-12-31

    25 Figure 10: SSC-A09 Airfoil used in this work: (a) isometric view and (b) side view showing tap distribution...above the airfoil. Each sensor orifice is connected to a miniature pressure transducer via a short length of plastic tubing. Pneumatic corrections are...yielding an aspect ratio equal to 1. One end of the model mates with a “rectangular side block” which is used to rigidly mount the airfoil in the

  3. A model for roll stall and the inherent stability modes of low aspect ratio wings at low Reynolds numbers

    Science.gov (United States)

    Shields, Matt

    The development of Micro Aerial Vehicles has been hindered by the poor understanding of the aerodynamic loading and stability and control properties of the low Reynolds number regime in which the inherent low aspect ratio (LAR) wings operate. This thesis experimentally evaluates the static and damping aerodynamic stability derivatives to provide a complete aerodynamic model for canonical flat plate wings of aspect ratios near unity at Reynolds numbers under 1 x 105. This permits the complete functionality of the aerodynamic forces and moments to be expressed and the equations of motion to solved, thereby identifying the inherent stability properties of the wing. This provides a basis for characterizing the stability of full vehicles. The influence of the tip vortices during sideslip perturbations is found to induce a loading condition referred to as roll stall, a significant roll moment created by the spanwise induced velocity asymmetry related to the displacement of the vortex cores relative to the wing. Roll stall is manifested by a linearly increasing roll moment with low to moderate angles of attack and a subsequent stall event similar to a lift polar; this behavior is not experienced by conventional (high aspect ratio) wings. The resulting large magnitude of the roll stability derivative, Cl,beta and lack of roll damping, Cl ,rho, create significant modal responses of the lateral state variables; a linear model used to evaluate these modes is shown to accurately reflect the solution obtained by numerically integrating the nonlinear equations. An unstable Dutch roll mode dominates the behavior of the wing for small perturbations from equilibrium, and in the presence of angle of attack oscillations a previously unconsidered coupled mode, referred to as roll resonance, is seen develop and drive the bank angle? away from equilibrium. Roll resonance requires a linear time variant (LTV) model to capture the behavior of the bank angle, which is attributed to the

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

    Science.gov (United States)

    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.

  5. 3D wake dynamics of the VAWT: experimental and numerical investigation

    NARCIS (Netherlands)

    Ferreira, C.; Hofemann, C.; Dixon, K.; Van Kuik, G.A.M.; Van Bussel, G.J.W.

    2010-01-01

    The Vertical Axis Wind Turbine, in its 2D form, is characterized by a complex unsteady aerodynamic flow, including dynamic stall and blade vortex interaction. Adding to this complexity, the 3D flow causes spanwise effects and the presence of trailing vorticity and tip vortices. The objective of the

  6. Research on aerodynamic characteristics of transport aircraft with stall strips%某运输机加装失速条气动特性研究

    Institute of Scientific and Technical Information of China (English)

    刘毅; 赵晓霞; 欧阳绍修; 袁志敏

    2016-01-01

    为改善某运输机着陆襟翼构型失速急剧滚转问题,采用数值计算和风洞实验方法优选了机翼失速条的外形参数,并对气动力和流场特性进行了研究分析。以失速条高度H和安装位置距离前缘的长度S 为设计变量,采用求解 RANS方程的方法研究了失速条对着陆构型翼型二维特性的影响,表明S越小(即越靠近上翼面)失速迎角提前越多,H增大也能使失速迎角提前但敏感性小于S。失速条后方产生了分离气泡且随迎角增加而逐渐增大增长,在破裂后导致翼型失速提前,使升力线出现圆弧形的失速特征。设计了4种失速条在机翼上的平面布局方案,通过缩比模型风洞实验验证表明:40%半展长处展向长度2m,S=0的失速条使升力线由急剧失速变为平顶型失速并消除了失速后的不对称滚转力矩,将此失速条展长缩小一半的2种方案也不同程度地改善了失速形态,15%半展长处失速条对失速特性无明显改善,主要原因是气流分离从约40%半展长处开始发生,失速条安装在这一展向位置时才能发挥作用。%In order to alleviate the violent roll motion during stall of a transport aircraft with landing flap configuration,the geometric parameters of stall strips are optimized and selected by numerical simulations and wind tunnel tests,and the aerodynamic force and flow field character-istics are studied.The height H and the install distance S from the leading edge are selected as design parameters for stall strips,and are evaluated by solving Reynolds Averaged Navior-Stokes (RANS)equations for the airfoil section of the landing flap configuration.The calculation indicates that smaller S value (installed closer to the upper surface)promotes earlier stall,while the larger H has sim-ilar but weaker effect.Separation bubble emerges after the stall strips when the angle of attack (AOA) of the airfoil becomes large,which grows larger and longer with

  7. Analysis of the Unsteady Flow Field in a Centrifugal Compressor from Peak Efficiency to Near Stall with Full-Annulus Simulations

    Directory of Open Access Journals (Sweden)

    Yannick Bousquet

    2014-01-01

    Full Text Available This study concerns a 2.5 pressure ratio centrifugal compressor stage consisting of a splittered unshrouded impeller and a vaned diffuser. The aim of this paper is to investigate the modifications of the flow structure when the operating point moves from peak efficiency to near stall. The investigations are based on the results of unsteady three-dimensional simulations, in a calculation domain comprising all the blade. A detailed analysis is given in the impeller inducer and in the vaned diffuser entry region through time-averaged and unsteady flow field. In the impeller inducer, this study demonstrates that the mass flow reduction from peak efficiency to near stall leads to intensification of the secondary flow effects. The low momentum fluid accumulated near the shroud interacts with the main flow through a shear layer zone. At near stall condition, the interface between the two flow structures becomes unstable leading to vortices development. In the diffuser entry region, by reducing the mass flow, the high incidence angle from the impeller exit induces a separation on the diffuser vane suction side. At near stall operating point, vorticity from the separation is shed into vortex cores which are periodically formed and convected downstream along the suction side.

  8. Stochastic model for aerodynamic force dynamics on wind turbine blades in unsteady wind inflow

    CERN Document Server

    Luhur, Muhammad Ramzan; Kühn, Martin; Wächter, Matthias

    2015-01-01

    The paper presents a stochastic approach to estimate the aerodynamic forces with local dynamics on wind turbine blades in unsteady wind inflow. This is done by integrating a stochastic model of lift and drag dynamics for an airfoil into the aerodynamic simulation software AeroDyn. The model is added as an alternative to the static table lookup approach in blade element momentum (BEM) wake model used by AeroDyn. The stochastic forces are obtained for a rotor blade element using full field turbulence simulated wind data input and compared with the classical BEM and dynamic stall models for identical conditions. The comparison shows that the stochastic model generates additional extended dynamic response in terms of local force fluctuations. Further, the comparison of statistics between the classical BEM, dynamic stall and stochastic models' results in terms of their increment probability density functions gives consistent results.

  9. Design of a 21 m blade with Risø-A1 airfoils for active stall controlled wind turbines

    DEFF Research Database (Denmark)

    Fuglsang, Peter; Sangill, O.; Hansen, P.

    2002-01-01

    the characteristics of the new blade. Airfoil characteristics, power curve and fatigue loads were derived onbasis of the measurements. Most of the design criteria for the new blade were met. The new blade had a reduced weight of 4% reducing blade cost compared with LM 21.0P. The measurements showed that the wind......This is the final report, from the project, "Design of a Rotor/Airfoil Family for Active Stall-regulated Wind Turbines by Use of Multi-point Optimization". It describes the full scale testing of a 21 m wind turbine blade specially designed for active stallregulation. Design objectives were...... increased ratio of produced energy to turbine loads and more stable power control characteristics. Both were taken directly into account during the design of the blade using numerical optimization. The blade used theRisø-A1 airfoil family, which was specially designed for operation on wind turbine blades...

  10. Injury scores and locomotor disorders of Holstein cows in a free-stall facility with different beds

    Directory of Open Access Journals (Sweden)

    Daiane Cecchin

    2015-12-01

    Full Text Available The aim of the present study was to evaluate hock and knee injuries and locomotor disorders in 36 multiparous Holstein cows confined in a free-stall model system with two types of beds at Embrapa Dairy Cattle in the city of Coronel Pacheco / MG. Rubber composite beds and sand beds were compared and the hock and knee injuries and locomotor disorders were assessed for severity scores. There was no difference between the scores or hock lesions observed at the beginning and end of the trial period for knee injuries in both beds. The two beds offer the same conditions of comfort, injury rates, and hull health, at least in the short term.

  11. 组合压气机旋转失速特征的小波分析%Wavelet analysis of features of rotating stall in a combined compressor

    Institute of Scientific and Technical Information of China (English)

    单晓明; 姚峥嵘; 岳林; 黄金泉

    2012-01-01

    采用高频响动态压力探针测量了小流量轴流/离心组合压气机的旋转失速和喘振,并采用基于Morlet小波时频分析和小波系数奇异分解的方法分析了压气机失速信号.研究结果表明:稳定工况下,频率分量较多、幅值较小.失速工况下,特征频率能量较大、且成倍频关系.在该组合压气机的失稳过程中,并没有引起大幅度的压力脉动.压气机光滑地从失速前出现的模态波过渡到完全失速.周向存在2个失速团,失速团传播速度约为44.8%~45.9%转速.%A fast response pressure probe was applied to test the rotating stall and surge of an axial and centrifugal combined compressor.The pressure signals were analyzed by utilizing the method of the time-frequency analysis based on the Morlet and singular value decomposition.The experimental results indicate that,at the stable condition,there are many main frequency components in the frequency domain but the amplitude is small,while,at the stall condition,the energy of the frequency components becomes larger.In the process of unstall to stall,the larger amplitude of the pressure fluctuation does not produced by the stall cell in this compressor.The compressor enters smoothly into the full stall condition from the modal wave.2 stall cells are measured around annulus and the propagation speed of the stall cell is from 44.8% to 45.9% rotor speed.

  12. A ruthenium polypyridyl intercalator stalls DNA replication forks, radiosensitizes human cancer cells and is enhanced by Chk1 inhibition

    Science.gov (United States)

    Gill, Martin R.; Harun, Siti Norain; Halder, Swagata; Boghozian, Ramon A.; Ramadan, Kristijan; Ahmad, Haslina; Vallis, Katherine A.

    2016-08-01

    Ruthenium(II) polypyridyl complexes can intercalate DNA with high affinity and prevent cell proliferation; however, the direct impact of ruthenium-based intercalation on cellular DNA replication remains unknown. Here we show the multi-intercalator [Ru(dppz)2(PIP)]2+ (dppz = dipyridophenazine, PIP = 2-(phenyl)imidazo[4,5-f][1,10]phenanthroline) immediately stalls replication fork progression in HeLa human cervical cancer cells. In response to this replication blockade, the DNA damage response (DDR) cell signalling network is activated, with checkpoint kinase 1 (Chk1) activation indicating prolonged replication-associated DNA damage, and cell proliferation is inhibited by G1-S cell-cycle arrest. Co-incubation with a Chk1 inhibitor achieves synergistic apoptosis in cancer cells, with a significant increase in phospho(Ser139) histone H2AX (γ-H2AX) levels and foci indicating increased conversion of stalled replication forks to double-strand breaks (DSBs). Normal human epithelial cells remain unaffected by this concurrent treatment. Furthermore, pre-treatment of HeLa cells with [Ru(dppz)2(PIP)]2+ before external beam ionising radiation results in a supra-additive decrease in cell survival accompanied by increased γ-H2AX expression, indicating the compound functions as a radiosensitizer. Together, these results indicate ruthenium-based intercalation can block replication fork progression and demonstrate how these DNA-binding agents may be combined with DDR inhibitors or ionising radiation to achieve more efficient cancer cell killing.

  13. Suppression of inducer stall based on inlet recirculation in a centrifugal impeller. 1st Report. Improvement in stall limit by ring groove arrangement; Enshin haneguruma iriguchi junkanryu ni yoru inducer shissoku no yokusei. 1. kanjoko ni yoru shissoku genkai no kaizen

    Energy Technology Data Exchange (ETDEWEB)

    Ueki, H.; Ishida, M.; Sakaguchi, D.; Sun, Z. [Nagasaki University, Nagasaki (Japan). Faculty of Engineering

    2000-07-25

    A ring groove arrangement is proposed to suppress unstable flow or surge in a centrifugal blower. The ring groove arrangement connects the upstream position of impeller inlet and the inducer throat tip through a bypass. The recirculation flow 'vas formed by the pressure difference between the two positions, and the recirculation flow rate was changed by increasing the ring groove widths. The inlet recirculation results in a decrease in the flow rate of unstable flow inception, and an up to 800 improvement in stall limit was obtained by the ring groove arrangement at a small expense of the delivery pressure drop. The improvement of stall limit in the present experiment seems to be mainly due to decrease in flow incidence based on the inlet recirculation flow. Tre flow incidence decreases more as the recirculation flow rate increases, thus resulting in a larger improvement in stall limit. (author)

  14. 某型尾吊高平尾飞机失速特性试飞方法研究%Research on Flight Test Methods of Stall Characteristics of a Rear-Mount Engine and High Horizontal Tail Civil Airplane

    Institute of Scientific and Technical Information of China (English)

    邹灿东; 王育平; 徐南波; 付琳

    2012-01-01

    某型尾吊高平尾飞机通过安装失速保护系统改善失速特性,满足了适航条例的要求。介绍了失速保护系统的设计,从保障试飞安全的失速试飞准备工作、失速保护系统研制试飞与失速特性验证试飞三个方面研究了安装失速保护系统飞机的失速试飞方法。%Stall characteristics ot a rear-mourn engine airworthiness requirements are met by implementing stall protection system. The design of stall protection system is presented. Stall characteristics flight test methods of airplane with stall protection system are studied, including preparations for the flight test safety before stall flight test, stall protection system development flight test and airworthiness certification test.

  15. 运输类飞机平尾失速敏感性及其试飞技术研究%Transport aircraft tailplane stall susceptibility and flight test technique

    Institute of Scientific and Technical Information of China (English)

    张建; 李勤红; 屈飞舟; 焦连跃

    2011-01-01

    This paper studies the tailplane stall flight test technique, which starts from the tailplane stall theoretical mechanism, the possible tailplane stall flight condition is researched, and finally summarizes the methods used to conduct the tailplane stall susceptibility flight test. Meanwhile, the difference between wing stall and tailplane stall is also studied, helping the pilot to adopt a distinct judgement, which can guarantee the appropriate recovery method and flight safety. The achievements in this paper can lay a strong foundation for the future large transport category aircraft stall susceptibility flight test.%从平尾失速理论研究出发,探讨了可能产生平尾失速的飞行状态,总结了可用于运输类飞机平尾失速敏感性研究的飞行试验技术,研究了平尾失速和机翼失速的相互区别,帮助飞行员在遇到机翼失速或平尾失速时进行必要的清晰判断,并采取适当的改出方法,从而保证飞机飞行安全.研究结果可为未来大型运输类飞机平尾失速敏感性试飞提供很好的技术支持.

  16. System identification modeling and unstable behavior of the dynamics of flows within the tip region of an axial compressor blade passage

    Science.gov (United States)

    Sterbentz, Dane M.; Prasai, Sujan; Hofle, Mary M.; Walters, Thomas; Lin, Feng; Li, Ji-chao; Bosworth, Ken; Schoen, Marco P.

    2016-04-01

    In recent years, the correlation coefficient of pressure data from the same blade passage in an axial compressor unit has been used to characterize the state of flow in the blade passage. In addition, the correlation coefficient has been successfully used as an indicator for active control action using air injection. In this work, the correlation coefficient approach is extended to incorporate system identification algorithms in order to extract a mathematical model of the dynamics of the flows within a blade passage. The dynamics analyzed in this research focus on the flow streams and pressure along the rotor blades as well as on the unsteady tip leakage flow from the rotor tip gaps. The system identification results are used to construct a root locus plot for different flow coefficients, starting far away from stall to near stall conditions. As the compressor moves closer to stall, the poles of the identified models move towards the imaginary axis of the complex plane, indicating an impending instability. System frequency data is captured using the proposed correlation based system identification approach. Additionally, an oscillatory tip leakage flow is observed at a flow coefficient away from stall and how this oscillation changes as the compressor approaches stall is an interesting result of this research. Comparative research is analyzed to determine why the oscillatory flow behavior occurs at a specific sensor location within the tip region of the rotor blade.

  17. A Novel Approach to Contrast-Enhanced Breast Magnetic Resonance Imaging for Screening: High-Resolution Ultrafast Dynamic Imaging

    NARCIS (Netherlands)

    Mann, R.M.; Mus, R.D.M.; Zelst, J. van; Geppert, C.; Karssemeijer, N.; Platel, B.

    2014-01-01

    The use of breast magnetic resonance imaging (MRI) as screening tool has been stalled by high examination costs. Scan protocols have lengthened to optimize specificity. Modern view-sharing sequences now enable ultrafast dynamic whole-breast MRI, allowing much shorter and more cost-effective procedur

  18. Computational Fluid Dynamic Model of Steam Ingestion into a Transonic Compressor

    Science.gov (United States)

    2009-06-01

    DYNAMIC MODEL OF STEAM INGESTION INTO A TRANSONIC COMPRESSOR by Collin R. Hedges June 2009 Thesis Advisor: Anthony J. Gannon Second...TYPE AND DATES COVERED Master’s Thesis 4. TITLE AND SUBTITLE Computational Fluid Dynamic Model of Steam Ingestion into a Transonic Compressor 6...flight deck. When ingested into jet engines, this steam may increase the engines’ susceptibility to stall. The serpentine air inlet ducts and single

  19. Collective dynamics of active cytoskeletal networks

    CERN Document Server

    Köhler, Simone; Bausch, Andreas R

    2011-01-01

    Self organization mechanisms are essential for the cytoskeleton to adapt to the requirements of living cells. They rely on the intricate interplay of cytoskeletal filaments, crosslinking proteins and molecular motors. Here we present an in vitro minimal model system consisting of actin filaments, fascin and myosin-II filaments exhibiting pulsative collective long range dynamics. The reorganizations in the highly dynamic steady state of the active gel are characterized by alternating periods of runs and stalls resulting in a superdiffusive dynamics of the network's constituents. They are dominated by the complex competition of crosslinking molecules and motor filaments in the network: Collective dynamics are only observed if the relative strength of the binding of myosin-II filaments to the actin network allows exerting high enough forces to unbind actin/fascin crosslinks. The feedback between structure formation and dynamics can be resolved by combining these experiments with phenomenological simulations base...

  20. Analysis on Stall of Double Stage Adjustable-blade AXial Flow Induced Draft Fan in High-load Operation%双级动叶可调式轴流引风机高负荷失速分析

    Institute of Scientific and Technical Information of China (English)

    王军民

    2016-01-01

    Through the elaboration on the mechanism of axial flow fan stall and in combination with double stage adjustable-blade axial flow induced draft fan stall in actual production of a power plant, the paper ana-lyzes the deep-seated causes of the stall and thus puts forward the principle of stall handling of induced draft fan in high load and effective measures for install prevention.%通过阐述轴流通风机失速的机理,结合某发电厂实际生产中双级动叶可调式轴流引风机失速的现象,分析发生失速的深层次原因,提出机组高负荷下处理引风机失速异常的原则以及防止失速的有效措施。

  1. Detection of Mycobacterium avium subspecies paratuberculosis in tie-stall dairy herds using a standardized environmental sampling technique and targeted pooled samples.

    Science.gov (United States)

    Arango-Sabogal, Juan C; Côté, Geneviève; Paré, Julie; Labrecque, Olivia; Roy, Jean-Philippe; Buczinski, Sébastien; Doré, Elizabeth; Fairbrother, Julie H; Bissonnette, Nathalie; Wellemans, Vincent; Fecteau, Gilles

    2016-07-01

    Mycobacterium avium ssp. paratuberculosis (MAP) is the etiologic agent of Johne's disease, a chronic contagious enteritis of ruminants that causes major economic losses. Several studies, most involving large free-stall herds, have found environmental sampling to be a suitable method for detecting MAP-infected herds. In eastern Canada, where small tie-stall herds are predominant, certain conditions and management practices may influence the survival and transmission of MAP and recovery (isolation). Our objective was to estimate the performance of a standardized environmental and targeted pooled sampling technique for the detection of MAP-infected tie-stall dairy herds. Twenty-four farms (19 MAP-infected and 5 non-infected) were enrolled, but only 20 were visited twice in the same year, to collect 7 environmental samples and 2 pooled samples (sick cows and cows with poor body condition). Concurrent individual sampling of all adult cows in the herds was also carried out. Isolation of MAP was achieved using the MGIT Para TB culture media and the BACTEC 960 detection system. Overall, MAP was isolated in 7% of the environmental cultures. The sensitivity of the environmental culture was 44% [95% confidence interval (CI): 20% to 70%] when combining results from 2 different herd visits and 32% (95% CI: 13% to 57%) when results from only 1 random herd visit were used. The best sampling strategy was to combine samples from the manure pit, gutter, sick cows, and cows with poor body condition. The standardized environmental sampling technique and the targeted pooled samples presented in this study is an alternative sampling strategy to costly individual cultures for detecting MAP-infected tie-stall dairies. Repeated samplings may improve the detection of MAP-infected herds.

  2. Structural basis of error-prone replication and stalling at a thymine base by human DNA polymerase

    Energy Technology Data Exchange (ETDEWEB)

    Kirouac, Kevin N.; Ling, Hong; (UWO)

    2009-06-30

    Human DNA polymerase iota (pol iota) is a unique member of Y-family polymerases, which preferentially misincorporates nucleotides opposite thymines (T) and halts replication at T bases. The structural basis of the high error rates remains elusive. We present three crystal structures of pol complexed with DNA containing a thymine base, paired with correct or incorrect incoming nucleotides. A narrowed active site supports a pyrimidine to pyrimidine mismatch and excludes Watson-Crick base pairing by pol. The template thymine remains in an anti conformation irrespective of incoming nucleotides. Incoming ddATP adopts a syn conformation with reduced base stacking, whereas incorrect dGTP and dTTP maintain anti conformations with normal base stacking. Further stabilization of dGTP by H-bonding with Gln59 of the finger domain explains the preferential T to G mismatch. A template 'U-turn' is stabilized by pol and the methyl group of the thymine template, revealing the structural basis of T stalling. Our structural and domain-swapping experiments indicate that the finger domain is responsible for pol's high error rates on pyrimidines and determines the incorporation specificity.

  3. Using Nature-Based Rehabilitation to Restart a Stalled Process of Rehabilitation in Individuals with Stress-Related Mental Illness

    Directory of Open Access Journals (Sweden)

    Eva Sahlin

    2015-02-01

    Full Text Available After a period of decrease, sick leave in Sweden due to psychiatric diagnoses is on the increase. The lack of established rehabilitation programmes for patients with stress-related mental disorders (SRMD has opened up for the use of garden/nature in a multimodal rehabilitation context (Nature-Based Rehabilitation, NBR. Region Västra Götaland (VGR started an NBR to offer additional rehabilitation for its employees on long-term sick leave due to SRMD, where initial care had not been sufficient. The aim was to explore whether the mental health and well-being of NBR participants had improved at the end of the NBR and at three follow-ups, and to explore the development of sick leave and health care utilization according to the NBR model (n = 57 and an occupational health service (OHS model (n = 45. Self-assessment instruments for measuring burnout, depression, anxiety and wellbeing, and data from regional and national registers were used. Results showed decreased scores on burnout, depression and anxiety, and increased well-being scores and significantly reduced health care utilization in the NBR group. A large movement from ordinary sickness benefit to rehabilitation benefit was observed, which was not observed in the OHS group. The two groups were in different rehabilitation phases, which limited comparisons. The results point to beneficial effects of using NBR for this patient group and for enhancing a stalled rehabilitation process.

  4. The RecQ DNA helicase Rqh1 constrains Exonuclease 1-dependent recombination at stalled replication forks.

    Science.gov (United States)

    Osman, Fekret; Ahn, Jong Sook; Lorenz, Alexander; Whitby, Matthew C

    2016-03-09

    DNA double-strand break (DSB) repair by homologous recombination (HR) involves resection of the break to expose a 3' single-stranded DNA tail. In budding yeast, resection occurs in two steps: initial short-range resection, performed by Mre11-Rad50-Xrs2 and Sae2; and long-range resection catalysed by either Exo1 or Sgs1-Dna2. Here we use genetic assays to investigate the importance of Exo1 and the Sgs1 homologue Rqh1 for DNA repair and promotion of direct repeat recombination in the fission yeast Schizosaccharomyces pombe. We find that Exo1 and Rqh1 function in alternative redundant pathways for promoting survival following replication fork breakage. Exo1 promotes replication fork barrier-induced direct repeat recombination but intriguingly limits recombination induced by fork breakage. Direct repeat recombination induced by ultraviolet light depends on either Exo1 or Rqh1. Finally, we show that Rqh1 plays a major role in limiting Exo1-dependent direct repeat recombination induced by replication fork stalling but only a minor role in constraining recombination induced by fork breakage. The implications of our findings are discussed in the context of the benefits that long-range resection may bring to processing perturbed replication forks.

  5. Long inverted repeat transiently stalls DNA replication by forming hairpin structures on both leading and lagging strands.

    Science.gov (United States)

    Lai, Pey Jiun; Lim, Chew Theng; Le, Hang Phuong; Katayama, Tsutomu; Leach, David R F; Furukohri, Asako; Maki, Hisaji

    2016-02-01

    Long inverted repeats (LIRs), often found in eukaryotic genomes, are unstable in Escherichia coli where they are recognized by the SbcCD (the bacterial Mre11/Rad50 homologue), an endonuclease/exonuclease capable of cleaving hairpin DNA. It has long been postulated that LIRs form hairpin structures exclusively on the lagging-strand template during DNA replication, and SbcCD cleaves these hairpin-containing lagging strands to generate DNA double-strand breaks. Using a reconstituted oriC plasmid DNA replication system, we have examined how a replication fork behaves when it meets a LIR on DNA. We have shown that leading-strand synthesis stalls transiently within the upstream half of the LIR. Pausing of lagging-strand synthesis at the LIR was not clearly observed, but the pattern of priming sites for Okazaki fragment synthesis was altered within the downstream half of the LIR. We have found that the LIR on a replicating plasmid was cleaved by SbcCD with almost equal frequency on both the leading- and lagging-strand templates. These data strongly suggest that the LIR is readily converted to a cruciform DNA, before the arrival of the fork, creating SbcCD-sensitive hairpin structures on both leading and lagging strands. We propose a model for the replication-dependent extrusion of LIRs to form cruciform structures that transiently impede replication fork movement.

  6. The Slx4-Dpb11 scaffold complex: coordinating the response to replication fork stalling in S-phase and the subsequent mitosis.

    Science.gov (United States)

    Princz, Lissa N; Gritenaite, Dalia; Pfander, Boris

    2015-01-01

    Replication fork stalling at DNA lesions is a common problem during the process of DNA replication. One way to allow the bypass of these lesions is via specific recombination-based mechanisms that involve switching of the replication template to the sister chromatid. Inherent to these mechanisms is the formation of DNA joint molecules (JMs) between sister chromatids. Such JMs need to be disentangled before chromatid separation in mitosis and the activity of JM resolution enzymes, which is under stringent cell cycle control, is therefore up-regulated in mitosis. An additional layer of control is facilitated by scaffold proteins. In budding yeast, specifically during mitosis, Slx4 and Dpb11 form a cell cycle kinase-dependent complex with the Mus81-Mms4 structure-selective endonuclease, which allows efficient JM resolution by Mus81. Furthermore, Slx4 and Dpb11 interact even prior to joining Mus81 and respond to replication fork stalling in S-phase. This S-phase complex is involved in the regulation of the DNA damage checkpoint as well as in early steps of template switch recombination. Similar interactions and regulatory principles are found in human cells suggesting that Slx4 and Dpb11 may have an evolutionary conserved role organizing the cellular response to replication fork stalling.

  7. AERODYNAMIC DAMPING ANALYSIS OF HORIZONTAL AXIS WIND TURBINE BLADE IN STEADY STALL%水平轴风力机叶片稳态失速气动阻尼分析

    Institute of Scientific and Technical Information of China (English)

    陈严; 王小虎; 刘雄; 叶枝全; 吴涛

    2011-01-01

    By analyzing on steady aerodynamic forces on an airfoil section of the wind turbine blade, combining with the blade modal analysis of the structural dynamics, a model for analyzing steady aerodynamic damping of wind turbine blade was established. Then, based on the accurate calculation on the aerodynamic damping of an airfoil section and a single blade, an effective analysis method of aerodynamic damping was established, and the key parameters which influence aerodynamic damping change were researched. Taking the negative aerodynamic damping which can easily initiate stall vibration of blade as the key point of the research, using a typical blade model as a sample, calculating on it, this paper modifies the parameters of blade model according to the established analysis method of aerodynamic damping. So that the negative aerodynamic damping in stall situation is improved, these can offer a more accurate realistic basis for aerodynamic optimization and vibration restraining design of wind turbine blade.%通过对风力机叶片翼型截面进行稳态气动力分析,同时结合整个叶片的结构动力学模态分析,创建风力机叶片稳态气动阻尼分析模型.从而在准确计算单翼型和单叶片气动阻尼的基础上,建立有效的气动阻尼分析方法,探究影响气动阻尼变化的关键参数.并以容易引发叶片失速振动的负气动阻尼为研究重点,采用典型的叶片模型进行实例计算,进而应用建立的气动阻尼分析方法进行叶片模型参数修正,旨在改善失速工况下的负气动阻尼,从而为风力机叶片的气动优化和抑振设计提供较准确的现实依据.

  8. Caracterização do microambiente em secção transversal de um galpão do tipo "free-stall" orientado na direção norte-sul Environment characterization in transversal direction in a free-stall housing oriented to north-south direction

    Directory of Open Access Journals (Sweden)

    Alessandro T. Campos

    2004-04-01

    Full Text Available O trabalho teve o objetivo de caracterizar o microambiente climático das baias de um galpão de confinamento para gado leiteiro, modelo "free-stall", no sentido transversal da instalação. O "free-stall" é orientado na direção norte-sul, localizado em Marechal Cândido Rondon, região Oeste do Paraná, com capacidade para abrigar 40 vacas em lactação (40 baias. Visando à determinação do Índice de Temperatura do Globo e Umidade (ITGU e da Carga Térmica de Radiação (CTR, foram instalados quatro globos negros, no centro de baias dispostas no sent ido transversal, dispondo dois globos no lado oeste e dois globos no lado leste (separados pelo corredor de alimentação. Lateralmente ao galpão, no lado leste, havia vegetação a 4 m da instalação, que promovia sombreamento nas primeiras horas do dia. Pode-se concluir que, nas primeiras horas do dia, não há diferença significativa entre os valores de ITGU e CTR encontrados, indicando que o sombreamento, devido à vegetação, foi capaz de amenizar os efeitos da radiação solar. Às 17 h 30 min, verificou-se que há ocorrência de maiores valores, tanto de ITGU quanto de CTR, nas baias localizadas no lado oeste do "free-stall".This work aimed to characterize the microclimatic conditions of the stalls of a free-stall model confinement building for dairy cattle in the transversal direction of the installation. Free-stall building was oriented to north-south direction, located in Marechal Cândido Rondon, west of Paraná State -Brazil, with a capacity of 40 dairy cows (40 stalls. In order to determine the Black-Globe-Humidity Index (BGHI and Radiant Heat Load (RHL, four black globes were installed in the center of stalls disposed in the transversal direction, disposing two globes in the west side and two globes in the east side (separated by the feed alley. At the building sidelong, east side, there was a four meter distant vegetation, that promoted shading in the first hours of the day

  9. Robust control of post-stall pitching maneuver based on finite-time observer.

    Science.gov (United States)

    Wu, Dawei; Chen, Mou; Gong, Huajun

    2017-09-01

    This article presents a robust finite-time maneuver control scheme for the longitudinal attitude dynamic of the aircraft with unsteady aerodynamic disturbances and input saturation. To efficiently eliminate the influence of unsteady aerodynamic disturbances, nonlinear finite-time observers are developed. Despite the existence of the nonlinearity and the coupling between aircraft states and unsteady aerodynamic disturbances, the proposed observers can still precisely estimate the unmeasurable unsteady aerodynamic disturbances in finite time. To attenuate the effect caused by input saturation, a finite-time auxiliary system is constructed. With the error between the desired control input and saturation input as the input of the auxiliary system, the additional signals are generated to compensate for the effect of input saturation. Combined with the finite-time observers and the finite-time auxiliary system, a robust finite-time backstepping attitude control design is developed. The finite-time convergence of all closed-loop system signals is rigorously proved via Lyapunov analysis method under the developed robust attitude control schemes. Finally, simulation results are presented to illustrate the effectiveness of the proposed attitude control approaches. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

  10. A semi-analytic dynamical friction model for cored galaxies

    CERN Document Server

    Petts, James A; Gualandris, Alessia

    2016-01-01

    We present a dynamical friction model based on Chandrasekhar's formula that reproduces the fast inspiral and stalling experienced by satellites orbiting galaxies with a large constant density core. We show that the fast inspiral phase does not owe to resonance. Rather, it owes to the background velocity distribution function for the constant density cores being dissimilar from the usually-assumed Maxwellian distribution. Using the correct background velocity distribution function and the semi-analytic model from Petts et al. (2015), we are able to correctly reproduce the infall rate in both cored and cusped potentials. However, in the case of large cores, our model is no longer able to correctly capture core-stalling. We show that this stalling owes to the tidal radius of the satellite approaching the size of the core. By switching off dynamical friction when rt(r) = r (where rt is the tidal radius at the satellite's position) we arrive at a model which reproduces the N-body results remarkably well. Since the...

  11. Aeroelastic research programme EFP-2001[YAW;STALL]; Forskning i aeroelasticitet EFP-2001

    Energy Technology Data Exchange (ETDEWEB)

    Aagaard Madsen, H. (ed.)

    2002-12-01

    The project covers the one year period from mid 2001 to mid 2002 and is the last part of a 5 years research programme on aeroelasticity. The overall objectives of the project are to improve the load and design basis for wind turbines and to ensure in collaboration with industry a continu-ously running process on development of new designs and solution of actual problems. Specifi-cally the main objectives for the present period are the following: a) development of a design tool for analysis of dynamic stability b) investigations of blade tip aerodynamics and blade tip design on basis of 3D CFD computa-tions c) publication of an airfoil catalogue d) load reduction using new control strategies e) aeroacoustic modelling of noise propagation During the present project period the computer code HAWCModal has been finished. The code computes the modal characteristics for a turbine as function of rotational speed. It is based on the structural modelling in the aeroelastic code HAWC and uses the same input files. The computed eigen frequencies are shown in a Campbell diagram and the corresponding modal forms can be shown graphically for an operating turbine. Finally, the structural damping is also computed by the code. HAWCModal is the basis for the stability analysis tool HAWCStab which is now under devel-opment. With HAWCStab the aeroelastic stability of a turbine can be analysed. The complex aerodynamics at three different blade tip shapes have been analysed with the three-dimensional CFD code EllipSys3D. The tip vortex was visualised and the lift and drag coef-ficients in the tip region were analysed in order to study the influence of the tip geometry on the performance and aerodynamic damping. An airfoil catalogue containing computations on 28 different airfoils for wind turbine applica-tion in comparison with experimental data has been developed and is available via the internet. Besides the main themes of the project as mentioned above there have been research

  12. 叶片数对离心泵叶轮失速特性影响研究%Study on Effects of Blade Number on Stall Characteristics for Centrifugal Pump Impeller

    Institute of Scientific and Technical Information of China (English)

    周佩剑; 王福军; 姚志峰

    2016-01-01

    为研究叶片数对离心泵叶轮失速特性的影响,以4种不同叶片数的离心泵叶轮为研究对象,采用改进的亚格子模型(Sub-grid scale model, SGS)对叶轮的内部流场进行数值模拟,得到不同叶片数的失速团的运动规律,以及失速频率、失速团个数、转速等特性参数。研究表明,叶片数对叶轮内部失速团的类型有显著影响,当叶片数为偶数时,会发生“交替失速”流动现象;当叶片数为奇数时,会发生“旋转失速”流动现象。另外,叶片数对失速团特征参数也有一定影响。当发生“交替失速”时,叶片数增多,失速团的数量也随之增多,失速频率也随之变化,4叶片叶轮失速团的失速频率约是6叶片的2.4倍;而当发生“旋转失速”时,叶片数增多,失速团的数量也随之增多,转速也随之增大,7叶片叶轮失速团的转速约是5叶片的1.8倍,失速频率是它的3.8倍。%In order to investigate the effects of blade number on stall characteristics for a centrifugal pump impeller, a developed Sub-grid scale model is applied to a centrifugal pump impeller with different blade number. The motion rule and characteristic parameters of stall cells are obtained, including the number, stall frequency and rotation speed. The results show that the blade number has significant effects on stall types. As the blade number is even, the alternative stall phenomenon occurs. Otherwise, when it is odd, the rotating stall phenomenon appears. Furthermore, the blade number also has influence on the characteristic parameters of stall cells. Under the alternative stall condition, as the increase of blade number, the number of stall cells increases, while the stall frequency decreases. The stall frequency of 4 blades is 2.4 times as large as that of 6 blades. Under the rotating stall condition, with the increase of blade number, the number of stall cells also increased. The speed of

  13. Effects of dietary calcium and phosphorus on reproductive performance and markers of bone turnover in stall- or group-housed sows.

    Science.gov (United States)

    Tan, F P Y; Kontulainen, S A; Beaulieu, A D

    2016-10-01

    Increasing productivity and new housing standards necessitate a reevaluation of nutrient requirements for sows, including minerals. The objective of this study was to determine if the recommended levels of dietary Ca and P are adequate for sows housed in groups and that, therefore, have the potential for increased mobility. A total of 180 multiparous sows and gilts were assigned to 1 of 6 treatments. Treatments, arranged as a 3 × 2 factorial, included the main effects of dietary Ca:P-0.70:0.55% Ca:P (as-fed basis; control), 0.60:0.47% Ca:P (as-fed basis; Low CaP), and 0.81:0.63% Ca:P (as-fed basis; High CaP)-and housing-stalls or groups. The trial was initiated when sows were moved from the breeding stalls to the gestation room at wk 4 or 5 after breeding. Sows were initially fed 2.3 kg/d. This allotment was increased to 3.0 kg/d 2 wk prior to farrowing. Group-housed sows, fed in individual stalls, were allowed access to a loafing area after feeding. Serum samples were collected at the start of the trial and on d 100 of gestation, and both serum and milk samples were collected at mid lactation and prior to weaning. Neither diet nor housing had an effect on the total number of piglets born, ADG from birth to weaning, or weaning weight ( > 0.10). The number of live-born piglets and birth weight were unaffected by diet ( > 0.10) but were improved by group housing relative to stalls ( sows fed the Low CaP diet had reduced serum Ca (diet × housing interaction, = 0.02), and the greatest reduction (between d 28 and 100 of gestation) in serum P level was observed in group-housed sows fed the Low CaP diet (diet × housing interaction, = 0.04). Osteocalcin and pyridinoline, markers of bone formation and resorption, respectively, were unaffected by diet or housing ( > 0.10). Results from these studies imply that the level of dietary Ca and P recommended by the NRC is adequate for sows of modern genetics, whether housed in stalls or groups.

  14. Effect of rubber flooring on claw health in lactating dairy cows housed in free-stall barns.

    Science.gov (United States)

    Vanegas, J; Overton, M; Berry, S L; Sischo, W M

    2006-11-01

    Multiparous dairy cows between 10 to 30 d in milk (DIM) were enrolled in a clinical trial to evaluate the effects of rubber flooring on the development of claw lesions, locomotion scores, clinical lameness, and rates of hoof growth and wear. Two groups of cows were housed in identical free-stall facilities, except that 1 pen (rubber, n = 84) had rubber alley mats covering the entire concrete floor of the pen, whereas cows in the second pen were exposed to concrete flooring (concrete, n = 82) without rubber alley mats. All cows were evaluated 3 times between 10 and 30, 74 and 94, and 110 and 130 DIM for 1) the presence of claw lesions on their rear feet, 2) the occurrence of clinical lameness based on a locomotion score, and 3) rates of claw growth and wear as observed on the dorsal wall of the right lateral claw. No differences between flooring groups at the time of enrollment were detected for lactation number, mean DIM at first examination, body condition score, and proportion of cows with claw lesions at the first examination. Odds of developing claw lesions between examinations were not different for cows exposed to the rubber surface compared with those exposed to concrete. Cows on concrete, however, had greater odds of developing or exacerbating existing heel erosion than cows on rubber flooring. Regardless of the flooring surface, the lateral claw was more likely to develop lesions than the medial claw. Odds of becoming lame by the third examination and the proportion of cows requiring therapeutic hoof trimming because of lameness were greater for concrete-exposed cows than those on rubber. Cows on rubber flooring had decreased claw growth and wear between the first and last examination compared with cows on concrete. Regardless of flooring surface, second-lactation cows had greater wear rates than those in third or greater parities. Results of our study suggest that a soft flooring surface, such as interlocking rubber, is beneficial for hoof health.

  15. Ribosome stalling and antibiotic resistance%核糖体停靠与抗生素耐药

    Institute of Scientific and Technical Information of China (English)

    郑薇; 凌保东; 贾旭; 李显志

    2014-01-01

    蛋白质在核糖体的合成受多个分子层面的精细调控,包括核糖体停靠(ribosome stalling,亦称为核糖体延宕)机制,即核糖体可与tRNA及氨基酸、肽或其它化合物如抗生素持久结合形成复合物,使核糖体停靠在正在转录的前导肽mRNA的开放阅读框内,并促使前导肽下游未翻译结构基因如耐药基因mRNA的表达.核糖体停靠需要前导肽参与,可分为非抗生素依赖和抗生素依赖两种类型,后者诱导多种作用于核糖体靶位抗生素(如大环内酯类、氯霉素类及四环素类等)的耐药性形成.对大环内酯类介导的核糖体停靠已有深入了解,这些研究有助于了解抗生素耐药机制及进化,并从干扰蛋白质表达的角度探索控制耐药性和研发新型抗菌化合物.本文也讨论了影响蛋白质表达的核糖体拯救(ribosme rescue)和核糖开关(riboswitch)机制.

  16. Complex rearrangements in patients with duplications of MECP2 can occur by fork stalling and template switching

    Science.gov (United States)

    Carvalho, Claudia M.B.; Zhang, Feng; Liu, Pengfei; Patel, Ankita; Sahoo, Trilochan; Bacino, Carlos A.; Shaw, Chad; Peacock, Sandra; Pursley, Amber; Tavyev, Y. Jane; Ramocki, Melissa B.; Nawara, Magdalena; Obersztyn, Ewa; Vianna-Morgante, Angela M.; Stankiewicz, Pawel; Zoghbi, Huda Y.; Cheung, Sau Wai; Lupski, James R.

    2009-01-01

    Duplication at the Xq28 band including the MECP2 gene is one of the most common genomic rearrangements identified in neurodevelopmentally delayed males. Such duplications are non-recurrent and can be generated by a non-homologous end joining (NHEJ) mechanism. We investigated the potential mechanisms for MECP2 duplication and examined whether genomic architectural features may play a role in their origin using a custom designed 4-Mb tiling-path oligonucleotide array CGH assay. Each of the 30 patients analyzed showed a unique duplication varying in size from ∼250 kb to ∼2.6 Mb. Interestingly, in 77% of these non-recurrent duplications, the distal breakpoints grouped within a 215 kb genomic interval, located 47 kb telomeric to the MECP2 gene. The genomic architecture of this region contains both direct and inverted low-copy repeat (LCR) sequences; this same region undergoes polymorphic structural variation in the general population. Array CGH revealed complex rearrangements in eight patients; in six patients the duplication contained an embedded triplicated segment, and in the other two, stretches of non-duplicated sequences occurred within the duplicated region. Breakpoint junction sequencing was achieved in four duplications and identified an inversion in one patient, demonstrating further complexity. We propose that the presence of LCRs in the vicinity of the MECP2 gene may generate an unstable DNA structure that can induce DNA strand lesions, such as a collapsed fork, and facilitate a Fork Stalling and Template Switching event producing the complex rearrangements involving MECP2. PMID:19324899

  17. 低速增升装置失速特性预测研究%Prediction Research on Stall Characteristic for Low-speed High-lift System

    Institute of Scientific and Technical Information of China (English)

    成水燕; 李中武; 聂智军; 梁益华

    2014-01-01

    民机低速增升装置失速特性是具有挑战性的空气动力学难题之一,决定着飞机起、降阶段机翼处于流动分离或尾迹干扰状态时的操纵稳定性,是气动设计必须关注的重要方面。利用基于N-S方程的自研多块结构网格计算软件和混合网格计算软件,对NASA高升力梯形机翼标准模型开展了失速特性计算研究,系统评估了计算软件、计算网格、湍流模型等主要因素对失速特性的影响,获得了有效预测高升力构型失速特性的计算方案,并将其成功应用于工程实际,为增升装置失速特性计算评估提供了有意义的参考。%Stall characteristic of civil aircraft low-speed high-lift device is one of the challenging aerody-namics problems .It determines the control stability of wing in the flow separation or wake interference state when airplane is taking off and landing .It is an important aspect that aerodynamic design must be paying attention to .In this paper ,CFD computational study is performed on the standard model of NASA high-lift trapezoidal wing by using our in-house multi-block structured mesh solver and unstructured mesh solver based on RANS equation .Predictive capabilities for stall characteristic from solvers ,meshes and turbulence models are systematically evaluated .Calculation scheme which can effectively predict stall characteristic of high-lift configurations is obtained and it was applied in practical engineering successful-ly .The aim is to provide a meaningful guideline for stall characteristic prediction of civil aircraft high-lift system .

  18. The Frequency Domain Characteristics and Gradual Process Analysis of Rotating Stall of Centrifugal Fan%离心风机旋转失速时频特性及渐进过程分析

    Institute of Scientific and Technical Information of China (English)

    舒畅

    2015-01-01

    To analysis the time-frequency characteristics and the gradual process characteristics of stall, the experi-ment of rotating stall was carried out on the centrifugal fan, which is widely used in domestic power plant. Te develop-ment pressure signals from the normal to the stall are ex-tracted. Then, the pressure signals are analyzed about the time-frequency characteristics and the gradual process char-acteristics of stall. Thus, a foundation to the further research of the rotating stall to centrifugal fan is laid.%为了对风机失速时频特性进行分析,利用国内电站广泛应用的离心风机,进行了旋转失速实验,提取风机从正常状态到旋转失速发展过程的压力信号,运用Fourier变换以及小波包分析对压力信号的时频特性以及失速渐进过程进行分析,从而在一定程度上为失速的检测和控制奠定基础。

  19. Mutagenesis of active site residues in type I dehydroquinase from Escherichia coli. Stalled catalysis in a histidine to alanine mutant.

    Science.gov (United States)

    Leech, A P; James, R; Coggins, J R; Kleanthous, C

    1995-10-27

    mutant is able to slowly transform substrate to product but that the hydrolytic release of the product is stalled. The proposed dual role of His-143 in the mechanism of type I dehydroquinase may explain why the elimination reaction catalyzed by the enzyme proceeds with syn stereochemistry.

  20. Quasi-periodic dynamics of a high angle of attack aircraft

    Science.gov (United States)

    Rohith, G.; Sinha, Nandan K.

    2017-01-01

    High angle of attack maneuvers closer to stall is a commonly accessed flight regime especially in case of fighter aircrafts. Stall and post-stall dynamics are dominated by nonlinearities which make the analysis difficult. Presence of external factors such as wind makes the system even more complex. Rich nonlinearities point to the possibility of existence of chaotic solutions. Past studies in this area confirm the development of such solutions. These studies are mainly concentrated on very high angle of attack regimes, which may not be practically easily accessible. This paper examines the possibility of existence of chaotic solutions in the lower, more accessible areas in the post stall domain. The analysis is composed of the study of effect of external wind as an agent to drive the system towards the possibility of a chaotic solution. Investigations reveal presence of quasi-periodic solutions, which are characterized by two incommensurate frequencies. This solution appears in the time simulation by varying the control parameter viz., wind. The solutions correspond to the values in the lower region of the angle of attack versus elevator bifurcation curve in the post-stall region. A steady wind is considered for the analysis and explores the possibility of chaotic motion by increasing the wind in a step wise manner. It is found that wind adds extra energy to the system which in turn drives the system in to chaos. The analysis is done with the help of phase portrait, Poincare map and amplitude spectrum and a quasi-periodic route to chaos via torus doubling is also presented.

  1. THE STALLING POINT

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    A series of disputes cause another rift in the strained relationship between the two Koreas The uneasy relations between Pyongyang and Seoul grew even tenser recently.South Korean Unification Minister Kim Ha Joong said that the jointly run industrial park in Kaesong would not be expanded until progress on the North Korean nuclear issue was made.Later,General Kim Tae Young,South Korea’s new Chairman of the Joint Chiefs of Staff,told a parliamentary hearing that the military would attack a suspected North Korean nuclear weapons site if it believed the country was going to launch a nuclear attack on South Korea.

  2. Wetting dynamics of a collapsing fluid hole

    Science.gov (United States)

    Bostwick, J. B.; Dijksman, J. A.; Shearer, M.

    2017-01-01

    The collapse dynamics of an axisymmetric fluid cavity that wets the bottom of a rotating bucket bound by vertical sidewalls are studied. Lubrication theory is applied to the governing field equations for the thin film to yield an evolution equation that captures the effect of capillary, gravitational, and centrifugal forces on this converging flow. The focus is on the quasistatic spreading regime, whereby contact-line motion is governed by a constitutive law relating the contact-angle to the contact-line speed. Surface tension forces dominate the collapse dynamics for small holes with the collapse time appearing as a power law whose exponent compares favorably to experiments in the literature. Gravity accelerates the collapse process. Volume dependence is predicted and compared with experiment. Centrifugal forces slow the collapse process and lead to complex dynamics characterized by stalled spreading behavior that separates the large and small hole asymptotic regimes.

  3. Dynamic response of Hovercraft lift fans

    Science.gov (United States)

    Moran, D. D.

    1981-08-01

    Hovercraft lift fans are subjected to varying back pressure due to wave action and craft motions when these vehicles are operating in a seaway. The oscillatory back pressure causes the fans to perform dynamically, exhibiting a hysteresis type of response and a corresponding degradation in mean performance. Since Hovercraft motions are influenced by variations in lift fan pressure and discharge, it is important to understand completely the nature of the dynamic performance of lift fans in order to completely solve the Hovercraft seakeeping problem. The present study was performed to determine and classify the instabilities encountered in a centrifugal fan operating against time-varying back pressure. A model-scale experiment was developed in which the fan discharge was directed into a flow-measuring device, terminating in a rotating valve which produced an oscillatory back pressure superimposed upon a mean aerodynamic resistance. Pressure and local velocity were measured as functions of time at several locations in the fan volute. The measurements permitted the identification of rotating (or propagating) stall in the impeller. One cell and two cell configurations were classified and the transient condition connecting these two configurations was observed. The mechanisms which lead to rotating stall in a centrifugal compressor are presented and discussed with specific reference to Hovercraft applications.

  4. A combined cryo-EM and molecular dynamics approach reveals the mechanism of ErmBL-mediated translation arrest

    Science.gov (United States)

    Arenz, Stefan; Bock, Lars V.; Graf, Michael; Innis, C. Axel; Beckmann, Roland; Grubmüller, Helmut; Vaiana, Andrea C.; Wilson, Daniel N.

    2016-07-01

    Nascent polypeptides can induce ribosome stalling, regulating downstream genes. Stalling of ErmBL peptide translation in the presence of the macrolide antibiotic erythromycin leads to resistance in Streptococcus sanguis. To reveal this stalling mechanism we obtained 3.6-Å-resolution cryo-EM structures of ErmBL-stalled ribosomes with erythromycin. The nascent peptide adopts an unusual conformation with the C-terminal Asp10 side chain in a previously unseen rotated position. Together with molecular dynamics simulations, the structures indicate that peptide-bond formation is inhibited by displacement of the peptidyl-tRNA A76 ribose from its canonical position, and by non-productive interactions of the A-tRNA Lys11 side chain with the A-site crevice. These two effects combine to perturb peptide-bond formation by increasing the distance between the attacking Lys11 amine and the Asp10 carbonyl carbon. The interplay between drug, peptide and ribosome uncovered here also provides insight into the fundamental mechanism of peptide-bond formation.

  5. Development of Protection System Preventing 60 000 m3 Air Compressor from Stall%60000m3空压机喘振保护系统的研发

    Institute of Scientific and Technical Information of China (English)

    李学波

    2014-01-01

    This article describes the reason and harm of air compressor stall in detail ,and elaborates the principle of the anti-stall control system .A protection system for 60 000 m3 air compressor is set up .By using the function of DCS and PLC ,we can make the control of compressor fast and reliable .This work has important reference value to the other anti-stall control systems .%简述了喘振的原理及危害。详细阐述了防喘振系统的控制原理,并建立了60000 m3空压机的保护系统,利用DCS和PLC的强大功能实现快速可靠的控制,对其他系统的防喘振控制有着重要的参考价值。

  6. Wet Compression Performance of a Transonic Compressor Rotor at its Near Stall Point%失速点上湿压缩对于跨音速压气机转子性能的影响

    Institute of Scientific and Technical Information of China (English)

    杨怀丰; 郑群; 罗铭聪; 孙兰昕; Rakesh Bhargava

    2011-01-01

    In order to study the effects of wet compression on a transonic compressor, a full 3-D steady numerical simulation was carried out under varying conditions. Different injected water flow rates and droplet diameters were considered. The effect of wet compression on the shock, separated flow, pressure ratio, and efficiency was investigated. Additionally, the effect of wet compression on the tip clearance when the compressor runs in the near-stall and stall situations was emphasized. Analysis of the results shows that the range of stable operation is extended, and that the pressure ratio and inlet air flow rate are also increased at the near-stall point. In addition, it seems that there is an optimum size of the droplet diameter.

  7. Incidence of error in oestrus detection based on secondary oestrus signs in a 24-h tie-stalled dairy herd with low fertility.

    Science.gov (United States)

    Ranasinghe, R M S B K; Nakao, T; Kobayashi, A

    2009-08-01

    Oestrus detection error and conception rates after AI based only on secondary oestrus signs were evaluated in a high yielding, 24-h tie-stalled dairy herd with low fertility, using milk progesterone profiles. Oestrus detection was based on the secondary oestrus signs such as restlessness, swelling, congestion of vulva and clear mucus discharge. Sixty eight AI conducted after observing the secondary oestrus signs in 44 animals were included in the study. Of the 68 AI, 53 (77.9%) were conducted in the follicular phase, and 13 (19.1%) and 2 (2.9%) were carried out in the luteal phase and during pregnancy, respectively. The overall error in oestrus detection based on milk progesterone profiles was 22.1%. The oestrus detection error did not differ significantly among different secondary oestrus signs. None of the AI conducted in the luteal phase resulted in conception, whereas 20.8% of AI conducted in the follicular phase resulted in conception. No significant difference in the conception rates among the groups of cows with different secondary oestrus signs was shown. The high incidence of oestrus detection error in this study might have been caused by the detection of cows in oestrus based only on secondary oestrus signs due to the confinement of animals. In conclusion, there was a high incidence of heat detection error in the 24-h tie-stalled dairy herd and oestrus detection based only on secondary oestrus signs resulted in low conception rate.

  8. The Effect of Different Types of Physical Exercise on the Behavioural and Physiological Parameters of Standardbred Horses Housed in Single Stalls

    Directory of Open Access Journals (Sweden)

    Barbara Padalino

    2014-01-01

    Full Text Available The aim of this study was to investigate the impacts of three different physical exercises on the physiological and behavioural patterns of Standardbred trotters housed in single stalls. Twelve racing mares were observed twice during each different exercise: daily training (DT consisted of forty minutes at slow trot (4-5 m/s in a small track; maximal exercise (ME consisted of 1600 m run at maximal velocity; race (R was a real race of 1600 m. The mares were examined at rest in their stall (Time I, soon after the completion of the exercise (Time II, one hour (Time III, and two hours (Time IV after the exercise. Their heart rate, respiratory rate, and rectal temperature were recorded and they were videotaped in order to complete a focal animal sampling ethogram. All physiological parameters increased after exercise, in accordance with its intensity. After R and ME horses spent more time drinking, eating, and standing. The incidence of abnormal behaviours was very low and it was not affected by the different types of exercise. Overall, the assessment of horse behaviour after physical exercise by means of a focal animal sampling ethogram represents a useful tool to monitor equine welfare.

  9. The effect of different types of physical exercise on the behavioural and physiological parameters of standardbred horses housed in single stalls.

    Science.gov (United States)

    Padalino, Barbara; Zaccagnino, Paola; Celi, Pietro

    2014-01-01

    The aim of this study was to investigate the impacts of three different physical exercises on the physiological and behavioural patterns of Standardbred trotters housed in single stalls. Twelve racing mares were observed twice during each different exercise: daily training (DT) consisted of forty minutes at slow trot (4-5 m/s) in a small track; maximal exercise (ME) consisted of 1600 m run at maximal velocity; race (R) was a real race of 1600 m. The mares were examined at rest in their stall (Time I), soon after the completion of the exercise (Time II), one hour (Time III), and two hours (Time IV) after the exercise. Their heart rate, respiratory rate, and rectal temperature were recorded and they were videotaped in order to complete a focal animal sampling ethogram. All physiological parameters increased after exercise, in accordance with its intensity. After R and ME horses spent more time drinking, eating, and standing. The incidence of abnormal behaviours was very low and it was not affected by the different types of exercise. Overall, the assessment of horse behaviour after physical exercise by means of a focal animal sampling ethogram represents a useful tool to monitor equine welfare.

  10. Recent structural studies on Dom34/aPelota and Hbs1/aEF1α: important factors for solving general problems of ribosomal stall in translation.

    Science.gov (United States)

    Kobayashi, Kan; Ishitani, Ryuichiro; Nureki, Osamu

    2013-01-01

    In the translation process, translating ribosomes usually move on an mRNA until they reach the stop codon. However, when ribosomes translate an aberrant mRNA, they stall. Then, ribosomes are rescued from the aberrant mRNA, and the aberrant mRNA is subsequently degraded. In eukaryotes, Pelota (Dom34 in yeast) and Hbs1 are responsible for solving general problems of ribosomal stall in translation. In archaea, aPelota and aEF1α, homologous to Pelota and Hbs1, respectively, are considered to be involved in that process. In recent years, great progress has been made in determining structures of Dom34/aPelota and Hbs1/aEF1α. In this review, we focus on the functional roles of Dom34/aPelota and Hbs1/aEF1α in ribosome rescue, based on recent structural studies of them. We will also present questions to be answered by future work.

  11. Contribution to a dynamic wind turbine model validation from a wind farm islanding experiment

    DEFF Research Database (Denmark)

    Pedersen, Jørgen Kaas; Pedersen, Knud Ole Helgesen; Poulsen, Niels Kjølstad;

    2003-01-01

    and possible discrepancies are explained. The work with the wind turbine model validation relates to the dynamic stability investigations on incorporation of large amount of wind power in the Danish power grid, where the dynamic wind turbine model is applied.......Measurements from an islanding experiment on the Rejsby Hede wind farm, Denmark, are used for the validation of the dynamic model of grid-connected, stall-controlled wind turbines equipped with induction generators. The simulated results are found to be in good agreement with the measurements...

  12. Fuel cell-gas turbine hybrid system design part II: Dynamics and control

    Science.gov (United States)

    McLarty, Dustin; Brouwer, Jack; Samuelsen, Scott

    2014-05-01

    Fuel cell gas turbine hybrid systems have achieved ultra-high efficiency and ultra-low emissions at small scales, but have yet to demonstrate effective dynamic responsiveness or base-load cost savings. Fuel cell systems and hybrid prototypes have not utilized controls to address thermal cycling during load following operation, and have thus been relegated to the less valuable base-load and peak shaving power market. Additionally, pressurized hybrid topping cycles have exhibited increased stall/surge characteristics particularly during off-design operation. This paper evaluates additional control actuators with simple control methods capable of mitigating spatial temperature variation and stall/surge risk during load following operation of hybrid fuel cell systems. The novel use of detailed, spatially resolved, physical fuel cell and turbine models in an integrated system simulation enables the development and evaluation of these additional control methods. It is shown that the hybrid system can achieve greater dynamic response over a larger operating envelope than either individual sub-system; the fuel cell or gas turbine. Results indicate that a combined feed-forward, P-I and cascade control strategy is capable of handling moderate perturbations and achieving a 2:1 (MCFC) or 4:1 (SOFC) turndown ratio while retaining >65% fuel-to-electricity efficiency, while maintaining an acceptable stack temperature profile and stall/surge margin.

  13. Dynamic wind turbine models in power system simulation tool

    DEFF Research Database (Denmark)

    Hansen, Anca D.; Iov, Florin; Sørensen, Poul

    This report presents a collection of models and control strategies developed and implemented in the power system simulation tool PowerFactory DIgSILENT for different wind turbine concepts. It is the second edition of Risø-R-1400(EN) and it gathers and describes a whole wind turbine model database...... strategies have different goals e.g. fast response over disturbances, optimum power efficiency over a wider range of wind speeds, voltage ride-through capability including grid support. A dynamic model of a DC connection for active stall wind farms to the grid including the control is also implemented...

  14. In Search of Nonlinear Process-Product Functions in Existing Schooling Effects Data: I. A Reanalysis of the First Grade Reading and Mathematics Data From the Stallings and Kaskowitz Follow Through Study.

    Science.gov (United States)

    Rim, Eui-Do; Coller, Alan R.

    As an attempt to confirm the view that the relationships between certain classroom process variables and student achievement are curvilinear, first grade reading and mathematics data from the Stallings and Kaskowitz (1974) Project Follow Through Classroom Observation Evaluation were reanalyzed using orthogonal polynomial regression methods.…

  15. Identification of Proteins at Active, Stalled, and Collapsed Replication Forks Using Isolation of Proteins on Nascent DNA (iPOND) Coupled with Mass Spectrometry*

    Science.gov (United States)

    Sirbu, Bianca M.; McDonald, W. Hayes; Dungrawala, Huzefa; Badu-Nkansah, Akosua; Kavanaugh, Gina M.; Chen, Yaoyi; Tabb, David L.; Cortez, David

    2013-01-01

    Both DNA and chromatin need to be duplicated during each cell division cycle. Replication happens in the context of defects in the DNA template and other forms of replication stress that present challenges to both genetic and epigenetic inheritance. The replication machinery is highly regulated by replication stress responses to accomplish this goal. To identify important replication and stress response proteins, we combined isolation of proteins on nascent DNA (iPOND) with quantitative mass spectrometry. We identified 290 proteins enriched on newly replicated DNA at active, stalled, and collapsed replication forks. Approximately 16% of these proteins are known replication or DNA damage response proteins. Genetic analysis indicates that several of the newly identified proteins are needed to facilitate DNA replication, especially under stressed conditions. Our data provide a useful resource for investigators studying DNA replication and the replication stress response and validate the use of iPOND combined with mass spectrometry as a discovery tool. PMID:24047897

  16. Studies on the power output of a MADE AE-30 operating on complex terrain. Annual Energy Production estimation and Multivariable analysis. A case of multi-stall effect

    Energy Technology Data Exchange (ETDEWEB)

    Cuerva, A.

    1996-12-01

    The main need of the EWTS-II Sub-project IV group is to have a suitable data-base which allows it to reach proper conclusions on the characteristics of power performance of wind turbines in complex terrain. With this aim, this document presents an analysis on the power output of the MADE AE-30 Wind turbine operating at Tarifa (also data from flat terrain are enclosed as a reference). An application of the bin method and AEP estimation for energy production method, in the two last issues a directional analysis and an study for two different turbulence intensity ranges are enclosed. Finally the Stepwise multirregression method is applied on the measurements to identify the stored parameters that have influence on the power output. A brief description of multi stall effect is enclosed. (Author)

  17. The Correlation between Eating Utensils and Place of Sales in the Contamination of Escherichia coli in Food Sold at Campus Food Stalls

    Directory of Open Access Journals (Sweden)

    Dewi Susanna

    2015-04-01

    Full Text Available Up to now, in general, the safety of food that is sold at any canteens in the campuses, the eating utensils are handled and the food stalls are managed are still uncertain. This research was aimed to understand the correlation between the eating utensils handling and the contamination of Escherichia coli (E. coli in the food sold by the food vendors in the campus. The cross-sectional design research applied on the food stalls in the university campus in Depok with a total number of 173 consumers as respondents. The variables observed as independent variables were the sanitation of the eating utensils and the sanitation of the dining place. The examination method of the Most Probable Number (MPN for E. coli was conducted to assess the food’s hygiene. The data analyzed using the chi-square test and followed by the logistic regression. The result showed that more than half of the food samples (59.54% were contaminated by E. coli. The storage place of the eating utensils was most significantly correlated with the E. coli contamination of the served food with an OR=0.45 (0.21-0.87. Therefore, it is necessary to promote the awareness of this risk and reinforce supervision by the Health Authorities and by the management of the place of sales to provide guidance to the food vendors and to the consumers as well. Further research is recommended to observe the E. coli contamination through clean water, eating utensils, the hands of the consumers and the napkins used to wipe dry the eating utensils.

  18. Transonic Wind Tunnel Modernization for Experimental Investigation of Dynamic Stall in a Wide Range of Mach Numbers by Plasma Actuators with Combined Energy/Momentum Action

    Science.gov (United States)

    2015-01-02

    operate with pulsed NS, PS or combined voltage up to 200 kV (Figure 3). Figure 4. 3D positioning system and Kollmorgen DDR servomotor below the test...section. DDR motor is connected to the model through the 6-component ATI-IA transducer. Pitching mechanism A new pitching mechanism consists of a...to right: UPS power supply; 24-V power supply; NI cRIO 9068 real-time control module; Kollmorgen DDR servomotor interface; main control computer

  19. How milk-fed dairy calves perform in stable versus dynamic groups

    DEFF Research Database (Denmark)

    Pedersen, Rikke Engelbrecht; Sørensen, Jan Tind; Skjøth, F;

    2009-01-01

    The objective of the present field trial was to compare calf performance among pre-weaned calves in two different group housing systems, stable groups ("all in-all out") and dynamic groups (continuous introduction). Performance data was collected from 484 calves randomly assigned to the two systems...... at six large (230-450 cows) commercial Danish dairy herds. All six farms had both systems simultaneously in the same stall, and under identical management and feeding regimes. Calves in stable groups had significantly higher daily live weight gain than calves in dynamic groups (870 vs. 810 g...

  20. Dynamic Gust Load Analysis for Rotors

    Directory of Open Access Journals (Sweden)

    Yuting Dai

    2016-01-01

    Full Text Available Dynamic load of helicopter rotors due to gust directly affects the structural stress and flight performance for helicopters. Based on a large deflection beam theory, an aeroelastic model for isolated helicopter rotors in the time domain is constructed. The dynamic response and structural load for a rotor under the impulse gust and slope-shape gust are calculated, respectively. First, a nonlinear Euler beam model with 36 degrees-of-freedoms per element is applied to depict the structural dynamics for an isolated rotor. The generalized dynamic wake model and Leishman-Beddoes dynamic stall model are applied to calculate the nonlinear unsteady aerodynamic forces on rotors. Then, we transformed the differential aeroelastic governing equation to an algebraic one. Hence, the widely used Newton-Raphson iteration algorithm is employed to simulate the dynamic gust load. An isolated helicopter rotor with four blades is studied to validate the structural model and the aeroelastic model. The modal frequencies based on the Euler beam model agree well with published ones by CAMRAD. The flap deflection due to impulse gust with the speed of 2m/s increases twice to the one without gust. In this numerical example, results indicate that the bending moment at the blade root is alleviated due to elastic effect.

  1. Single DNA molecule jamming and history-dependent dynamics during motor-driven viral packaging

    Science.gov (United States)

    Keller, Nicholas; Grimes, Shelley; Jardine, Paul J.; Smith, Douglas E.

    2016-08-01

    In many viruses, molecular motors forcibly pack single DNA molecules to near-crystalline density into ~50-100 nm prohead shells. Unexpectedly, we found that packaging frequently stalls in conditions that induce net attractive DNA-DNA interactions. Here, we present findings suggesting that this stalling occurs because the DNA undergoes a nonequilibrium jamming transition analogous to that observed in many soft-matter systems, such as colloidal and granular systems. Experiments in which conditions are changed during packaging to switch DNA-DNA interactions between purely repulsive and net attractive reveal strongly history-dependent dynamics. An abrupt deceleration is usually observed before stalling, indicating that a transition in DNA conformation causes an abrupt increase in resistance. Our findings suggest that the concept of jamming can be extended to a single polymer molecule. However, compared with macroscopic samples of colloidal particles we find that single DNA molecules jam over a much larger range of densities. We attribute this difference to the nanoscale system size, consistent with theoretical predictions for jamming of attractive athermal particles.

  2. A structural perspective on the dynamics of kinesin motors

    CERN Document Server

    Hyeon, Changbong

    2011-01-01

    Despite significant fluctuation under thermal noise, biological machines in cells perform their tasks with exquisite precision. Using molecular simulation of a coarse-grained model and theoretical arguments we envisaged how kinesin, a prototype of biological machines, generates force and regulates its dynamics to sustain persistent motor action. A structure based model, which can be versatile in adapting its structure to external stresses while maintaining its native fold, was employed to account for several features of kinesin dynamics along the biochemical cycle. This analysis complements our current understandings of kinesin dynamics and connections to experiments. We propose a thermodynamic cycle for kinesin that emphasizes the mechanical and regulatory role of the neck-linker and clarify issues related the motor directionality, and the difference between the external stalling force and the internal tension responsible for the head-head coordination. The comparison between the thermodynamic cycle of kines...

  3. 有限翼展机翼失速特性控制研究%Researches of a finite-span wing stall control

    Institute of Scientific and Technical Information of China (English)

    白亚磊; 李鹏

    2013-01-01

    For controlling the flow separation on the wing at high angle of attack, an innovative technique for a finites-span wing stall control, flow deflector, is studied in the present paper.Wind tunnel experiments are conducted to validate the reliability of the numerical simulation.The comparison between them indicates that the flow deflector can control the stall of a wing and restrain the flow separation effectively at high angle of attack.Deep research of flow direction changing trend and boundary layer are carried out to investigate the mechanism of flow deflector.The results indicate that the flow deflector increase the angle of flow around the leading edge of the wing and decrease the angle of the coming flow to make it deflect to the upside of the wing.The flow deflector can suppress the three dimensional effects and maintain the two-dimensional flow characteristics to some extent.Furthermore, the flow deflector can easily change the velocity profile in the boundary layer and make it more "fuller".It decreases the shape factor and increases the stability of the boundary layer to restrain the flow separation.%针对有限翼展机翼大迎角下的流动分离情况,研究了一种新型流动控制技术——流动偏转器.通过风洞实验和数值计算相结合的方法,既验证了计算的准确性,又阐述了流动偏转器可改善机翼大迎角失速特性的作用.通过对流动方向变化规律和翼面边界层的深入研究,探寻了流动偏转器的控制原理:使来流向机翼吸力面偏转;削弱机翼前缘附近流动的三维效应使流动趋近二元化;使边界层内速度型变得饱满,减小速度型形状因子H12,增大速度型的稳定性,抑制流动分离.

  4. Analysis of the Start Stall Failure of CFM56-5B Engine%CFM56-5B发动机启动失速故障分析

    Institute of Scientific and Technical Information of China (English)

    熊善果

    2015-01-01

    本文通过CFM56-5B发动机在启动过程中出现“ENG 1 START STALL”故障信息(非高原机场)排故全过程进行分析,提出了对启动过程中出现“ENG 1 START STALL”故障信息(非高原机场)排故建议和维护提示。%This article analyzes the troubleshooting process of the CFM56-5B engine which shows "ENG 1 START STALL" during start up (non-plateau airport), and proposes suggestions and maintenance tips for troubleshooting of "ENG 1 START STALL" during start up.

  5. Dynamic Response of Flexible Wind Turbine Blade

    Directory of Open Access Journals (Sweden)

    Yu-qiao Zheng

    2013-07-01

    Full Text Available 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 using the finite element method under the transient load environment. A 29.2 m rotor blade, previously reported in specialized literature, was chosen as a case study to validate dynamic behaviour predicted by a Timoshenko beam model. It is concluded that despite its simplicity, The cross-sectional shear-deformation  has great influence on  dynamic response of the blade.Dynamic model is sufficiently accurate to serve as a design tool for the recursive analyses required during design and optimization stages of wind turbines using only readily available computational tools.

  6. Phenolic extract of Parkia biglobosa fruit pulp stalls aflatoxin B1 – mediated oxidative rout in the liver of male rats

    Directory of Open Access Journals (Sweden)

    Taofeek O. Ajiboye

    2014-12-01

    Full Text Available The effect of phenolic extract of Parkia biglobosa (Jacq. R. Br. ex G. Don, Fabaceae, pulp on aflatoxin B1 induced oxidative imbalance in rat liver was evaluated. Thirty-five male rats were randomized into seven groups of five animals each. Rats in group A served as control and received vehicle for drug administration (0.5% DMSO once daily at 24 h intervals for six weeks. Rats in groups B, D, E, F and G, received aflatoxin B1 (167 μg/kg body weight in 0.5% DMSO for three weeks, starting from the third week of the experimental period. Rats in Group C received 400 mg/kg bodyweight of the extract for six weeks, while groups D, E and F rats were treated with 100, 200 and 400 mg/kg bodyweight of the extract for six weeks respectively. Group G rats received 100 mg/kg body weight of vitamin C. Aflatoxin B1-mediated decrease in the activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and glucose-6-phosphate dehydrogenase were significantly attenuated. Aflatoxin B1 mediated the elevation in malondialdehyde, conjugated dienes, lipid hydroperoxides, protein carbonyl, and significantly lowered DNA fragmentation percentage. Overall, the phenolic extract of P. biglobosa pulp stalls aflatoxin B1-mediated oxidative rout by enhancing antioxidant enzyme activities leading to decreased lipid peroxidation, protein oxidation and DNA fragmentation.

  7. Postarrest stalling rather than crawling favors CD8(+) over CD4(+) T-cell migration across the blood-brain barrier under flow in vitro.

    Science.gov (United States)

    Rudolph, Henriette; Klopstein, Armelle; Gruber, Isabelle; Blatti, Claudia; Lyck, Ruth; Engelhardt, Britta

    2016-09-01

    Although CD8(+) T cells have been implied in the pathogenesis of multiple sclerosis (MS), the molecular mechanisms mediating CD8(+) T-cell migration across the blood-brain barrier (BBB) into the central nervous system (CNS) are ill defined. Using in vitro live cell imaging, we directly compared the multistep extravasation of activated CD4(+) and CD8(+) T cells across primary mouse brain microvascular endothelial cells (pMBMECs) as a model for the BBB under physiological flow. Significantly higher numbers of CD8(+) than CD4(+) T cells arrested on pMBMECs under noninflammatory and inflammatory conditions. While CD4(+) T cells polarized and crawled prior to their diapedesis, the majority of CD8(+) T cells stalled and readily crossed the pMBMEC monolayer preferentially via a transcellular route. T-cell arrest and crawling were independent of G-protein-coupled receptor signaling. Rather, absence of endothelial ICAM-1 and ICAM-2 abolished increased arrest of CD8(+) over CD4(+) T cells and abrogated T-cell crawling, leading to the efficient reduction of CD4(+) , but to a lesser degree of CD8(+) , T-cell diapedesis across ICAM-1(null) /ICAM-2(-/-) pMBMECs. Thus, cellular and molecular mechanisms mediating the multistep extravasation of activated CD8(+) T cells across the BBB are distinguishable from those involved for CD4(+) T cells.

  8. Tracking the Fragile X Mental Retardation Protein in a Highly Ordered Neuronal RiboNucleoParticles Population: A Link between Stalled Polyribosomes and RNA Granules

    Science.gov (United States)

    Tremblay, Sandra; Jaglin, Xavier; Dury, Alain; Robert, Claude; De Koninck, Paul; Khandjian, Edouard W.

    2016-01-01

    Local translation at the synapse plays key roles in neuron development and activity-dependent synaptic plasticity. mRNAs are translocated from the neuronal soma to the distant synapses as compacted ribonucleoparticles referred to as RNA granules. These contain many RNA-binding proteins, including the Fragile X Mental Retardation Protein (FMRP), the absence of which results in Fragile X Syndrome, the most common inherited form of intellectual disability and the leading genetic cause of autism. Using FMRP as a tracer, we purified a specific population of RNA granules from mouse brain homogenates. Protein composition analyses revealed a strong relationship between polyribosomes and RNA granules. However, the latter have distinct architectural and structural properties, since they are detected as close compact structures as observed by electron microscopy, and converging evidence point to the possibility that these structures emerge from stalled polyribosomes. Time-lapse video microscopy indicated that single granules merge to form cargoes that are transported from the soma to distal locations. Transcriptomic analyses showed that a subset of mRNAs involved in cytoskeleton remodelling and neural development is selectively enriched in RNA granules. One third of the putative mRNA targets described for FMRP appear to be transported in granules and FMRP is more abundant in granules than in polyribosomes. This observation supports a primary role for FMRP in granules biology. Our findings open new avenues for the study of RNA granule dysfunctions in animal models of nervous system disorders, such as Fragile X syndrome. PMID:27462983

  9. 襟缝翼对民用飞机失速特性的影响%Effect of Slat and Flap on Stall Characteristic of Civil Aircraft

    Institute of Scientific and Technical Information of China (English)

    周涛; 李亚林; 梁益华; 陈迎春

    2012-01-01

    To detect factors of affecting stall characteristic and stability of aircraft, slot parameter of out board slat, separation face of inboard slat and fuselage, slot between slat and pylon, and slot parameter of flap were investigated. The results indicate that, root and tip of slat may affect pitching moment character- istic, slot between slat and pylon may improve lift coefficient, but no contribution for pitching moment characteristic, and, adjusting deploy angle of flap may not improve separation characteristic on main wing, because effective camber of wing is not changed.%从外侧缝翼缝道参数、内侧缝翼分离面、缝翼与挂架间隙以及后缘襟翼缝道参数等方面考虑,分析了民用飞机失速特性和失稳特性的影响因素.结果表明,前缘缝翼根部和梢部细节对力矩特性有较大影响,缝翼挂架堵缝可提高升力,不影响力矩特性,调整襟翼偏角,可改变机翼有效弯度,不改变主翼分离特性.

  10. Identification of genes involved in low aminoglycoside-induced SOS response in Vibrio cholerae: a role for transcription stalling and Mfd helicase.

    Science.gov (United States)

    Baharoglu, Zeynep; Babosan, Anamaria; Mazel, Didier

    2014-02-01

    Sub-inhibitory concentrations (sub-MIC) of antibiotics play a very important role in selection and development of resistances. Unlike Escherichia coli, Vibrio cholerae induces its SOS response in presence of sub-MIC aminoglycosides. A role for oxidized guanine residues was observed, but the mechanisms of this induction remained unclear. To select for V. cholerae mutants that do not induce low aminoglycoside-mediated SOS induction, we developed a genetic screen that renders induction of SOS lethal. We identified genes involved in this pathway using two strategies, inactivation by transposition and gene overexpression. Interestingly, we obtained mutants inactivated for the expression of proteins known to destabilize the RNA polymerase complex. Reconstruction of the corresponding mutants confirmed their specific involvement in induction of SOS by low aminoglycoside concentrations. We propose that DNA lesions formed on aminoglycoside treatment are repaired through the formation of single-stranded DNA intermediates, inducing SOS. Inactivation of functions that dislodge RNA polymerase leads to prolonged stalling on these lesions, which hampers SOS induction and repair and reduces viability under antibiotic stress. The importance of these mechanisms is illustrated by a reduction of aminoglycoside sub-MIC. Our results point to a central role for transcription blocking at DNA lesions in SOS induction, so far underestimated.

  11. "If we can just 'stall' new unfriendly legislations, the scoreboard is already in our favour": transnational tobacco companies and ingredients disclosure in Thailand.

    Science.gov (United States)

    MacKenzie, R; Collin, J; Sriwongcharoen, K; Muggli, M E

    2004-12-01

    To review the strategies employed by overseas cigarette manufacturers operating in Thailand to obstruct the passage and subsequent enforcement of national public health legislation, specifically the ingredients disclosure provision of the 1992 Tobacco Products Control Act. Analysis of previously confidential tobacco industry documents relevant to non-compliance with the ingredients disclosure legislation. Requirement for disclosure of ingredients contained in cigarettes contained in the Tobacco Products Control Act was identified by transnational tobacco companies (TTCs) not only as a significant threat to their operations in Thailand, but as a dangerous global precedent. Industry documents reveal a determined campaign to block, stall, or amend the proposed regulation during the legislative process. Industry representatives petitioned the Ministry of Health to revise the requirement from by brand disclosure to a more palatable by company submission. Strategies were adapted in the wake of the passage of the Act. Most significantly, the industry in concert with embassies in Bangkok threatened the Thai government with appeals to international trade bodies on the grounds of violation of international agreements. Industry documents also reveal that as submission of ingredient lists appeared unavoidable, leading companies operating in Thailand endeavoured to confound the disclosure requirement by disguising ingredients and reformulating brand recipes. The evidence presented highlights the importance of ingredients regulation and demonstrates how health policy can be transformed during its implementation. A greater understanding of trade agreements emerges as a priority for global tobacco control.

  12. "If we can just ‘stall' new unfriendly legislations, the scoreboard is already in our favour": transnational tobacco companies and ingredients disclosure in Thailand

    Science.gov (United States)

    MacKenzie, R; Collin, J; Sriwongcharoen, K; Muggli, M

    2004-01-01

    Objectives: To review the strategies employed by overseas cigarette manufacturers operating in Thailand to obstruct the passage and subsequent enforcement of national public health legislation, specifically the ingredients disclosure provision of the 1992 Tobacco Products Control Act. Methods: Analysis of previously confidential tobacco industry documents relevant to non-compliance with the ingredients disclosure legislation. Results: Requirement for disclosure of ingredients contained in cigarettes contained in the Tobacco Products Control Act was identified by transnational tobacco companies (TTCs) not only as a significant threat to their operations in Thailand, but as a dangerous global precedent. Industry documents reveal a determined campaign to block, stall, or amend the proposed regulation during the legislative process. Industry representatives petitioned the Ministry of Health to revise the requirement from by brand disclosure to a more palatable by company submission. Strategies were adapted in the wake of the passage of the Act. Most significantly, the industry in concert with embassies in Bangkok threatened the Thai government with appeals to international trade bodies on the grounds of violation of international agreements. Industry documents also reveal that as submission of ingredient lists appeared unavoidable, leading companies operating in Thailand endeavoured to confound the disclosure requirement by disguising ingredients and reformulating brand recipes. Conclusions: The evidence presented highlights the importance of ingredients regulation and demonstrates how health policy can be transformed during its implementation. A greater understanding of trade agreements emerges as a priority for global tobacco control. PMID:15564225

  13. Numerical Study for Effects of End Wall Behavior on Transonic Compressor Stall%端区流动对跨声速压气机失速影响的数值研究

    Institute of Scientific and Technical Information of China (English)

    傅文广; 孙鹏; 徐佳汇; 钟兢军

    2016-01-01

    In order to study the complex flow structure in rotor clearance and stator corner at near stall condition and explore the main factors inducing compressor stall,a highly loaded compressor was simu⁃lated. Characteristics of the compressor and single rotor were obtained. The compressor flow fields were analyzed in detail. Results show,for the compressor in this paper,stall incept in the stator top corner. The completion of transition from open separation to closed separation can be regarded as the signal of stall inception in stator. At near stall point,tip leakage vortex breaks down in bubble type in rotor. The separation bubble plugs the rotor flow field. The plugging effect caused by leakage vortex breakdown has been extended from the tip to about 70% of the blade height.%为了揭示近失速工况下动叶间隙和静叶角区的复杂流动结构,探索诱发压气机失速的主要因素,对高负荷跨声速压气机开展数值研究,获得了整级压气机和单转子的特性曲线,进而对压气机的流场进行了详细分析。结果表明:对于研究对象,失速最先起始于静叶上角区。上角区完成由开式分离到闭式分离的转变过程,可以认为是静叶发生失速的标志。在近失速工况下,动叶叶尖泄漏涡发生“泡式破裂”堵塞流道,泄漏涡破裂引起的堵塞作用一直从叶顶延伸至70%叶高左右。

  14. Nuclear insulin-like growth factor 1 receptor phosphorylates proliferating cell nuclear antigen and rescues stalled replication forks after DNA damage.

    Science.gov (United States)

    Waraky, Ahmed; Lin, Yingbo; Warsito, Dudi; Haglund, Felix; Aleem, Eiman; Larsson, Olle

    2017-09-18

    We have previously shown that the insulin like growth factor 1 receptor (IGF1R) translocates to the cell nucleus, where it binds to enhancer like regions and increases gene transcription. Further studies have demonstrated that nuclear IGF1R (nIGF1R) physically and functionally interacts with some nuclear proteins, i.e. the lymphoid enhancer binding factor 1 (Lef1), histone H3, and Brahma related gene 1 proteins. In the present study, we identified the proliferating cell nuclear antigen (PCNA) as a nIGF1R binding partner. PCNA is a pivotal component of the replication fork machinery and a main regulator of the DNA damage tolerance (DDT) pathway. We found that IGF1R interacts with and phosphorylates PCNA in human embryonic stem cells and other cell lines. In vitro MS analysis of PCNA coincubated with the IGF1R kinase indicated tyrosine residues 60, 133, and 250 in PCNA as IGF1R targets, and PCNA phosphorylation was followed by mono and poly ubiquitination. Coimmunoprecipitation experiments suggested that these ubiquitination events may be mediated by DDT dependent E2/E3 ligases (e.g. RAD18 and SHPRH/HLTF). Absence of IGF1R or mutation of Tyr60, Tyr133, or Tyr250 in PCNA abrogated its ubiquitination. Unlike in cells expressing IGF1R, externally induced DNA damage in IGF1R negative cells caused G1 cell cycle arrest and S phase fork stalling. Taken together, our results suggest a role of IGF1R in DDT. Copyright © 2017, The American Society for Biochemistry and Molecular Biology.

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

    DEFF Research Database (Denmark)

    Hansen, Anca Daniela; Iov, F.; Sørensen, Poul Ejnar

    This report presents a collection of models and control strategies developed and implemented in the power system simulation tool PowerFactory DIgSILENT for different wind turbine concepts. It is the second edition of Risø-R-1400(EN) and it gathers and describes a whole wind turbine model database...... strategies have different goals e.g. fast response over disturbances, optimum power efficiency over a wider range of wind speeds, voltage ride-through capability including grid support. A dynamic model of a DC connection for active stall wind farms to the grid including the control is also implemented...

  16. Taxa de gestação em fêmeas da raça Holandesa confinadas em free stall, no verão e inverno Gestation rate of Holstein females confined in free stall, during the summer and winter

    Directory of Open Access Journals (Sweden)

    M.F.A. Pires

    2002-02-01

    Full Text Available A taxa de gestação de vacas em lactação e de novilhas confinadas em free stall foi avaliada durante o inverno e o verão, nos anos de 1993, 1994 e 1995. A temperatura ambiente (TA e a umidade relativa do ar (UR foram acompanhadas diariamente, durante quatro meses de verão (dezembro a março e três meses de inverno (junho a agosto. Em cada estação mediram-se semanalmente às 9, 15 e 21h a temperatura retal (TR e a freqüência respiratória (FR de 50% das vacas em lactação, sorteadas ao acaso, separadas em quatro grupos de acordo com a produção de leite. A TA e o índice de temperatura e umidade (ITU médios foram mais elevados (P The gestation rate was used to evaluate the reproductive performance of dairy cows and heifers confined in a free stall barn during the winter and summer seasons of 1993, 1994 and 1995. The temperature (T and relative humidity (RH were monitored daily during the summer (December, January, February and March and winter (June, July and August. The rectal temperature (RT and respiration rate (RR were measured weekly at 9AM and 3 and 9PM, in each season, in 50% of the animals randomly selected and sorted in four groups based on their milk production. The averages of T and the temperature and humidity index (THI were higher in the summer (25.6ºC e 75.8 than in the winter (19.0ºC e 65.3, while the RH were the same in both seasons (80.0%. The averages of RT and RR were always higher in the summer and at 3PM when compared to 9AM RT and RR (39.47ºC and 64.76 mov/min vs 38.89ºC and 44.21 mov/min. Gestation rate for milking cows was smaller in summer than in the winter. Conversely 85.4% of heifers became pregnant during the summer and 78.5% during the winter season.

  17. Custo e resultados do tratamento de seqüelas de laminite bovina: relato de 112 casos em vacas em lactação no sistema free-stall Results and costs of treatment for bovine laminitis sequelae: study of 112 lameness cases in lactating cows in free-stall system

    Directory of Open Access Journals (Sweden)

    P.M. Ferreira

    2004-10-01

    Full Text Available Os resultados e o custo do tratamento de seqüelas podais da laminite subclínica são descritos em 112 casos de manqueira em vacas em lactação mantidas no sistema free-stall. As observações feitas durante um ano abrangeram animais de 2,5 a 10 anos de idade, da primeira à sexta lactação e com média de produção de 8.000±2.000kg de leite. O protocolo de tratamento, descrito detalhadamente para cada uma das afecções podais, foi eficiente na reversão de todas elas. O custo total do tratamento para o rebanho foi de US$5,005.23, equivalente ao custo médio de US$44.68 por animal. O tratamento das úlceras de sola foi o mais dispendioso (US$72.58 e o mais demorado (26,8 dias. As afecções mais comuns foram os abscessos de sola e do talão e as lesões da linha branca (64/112 ou 57,2%.The results and costs of treatments of feet sequelae of subclinic dairy cattle laminitis were described in 112 cases of lameness in lactating cows maintained in free stall system. The analyses were performed in an one-year-period using 2.5 to 10 year-old, first to sixth parity cows. Average milk yield was 8,000±2,000kg. The treatment protocol was described in details for each digit lesion and it was very successful to reverse all kinds of lesions. The total treatment cost for the herd was US$5,005.23 and the mean cost/animal was US$44.68. The ulcer treatments were costly (US$72.58 and longer (26.8 days. Sole and heel abscesses and white line disease at the foe (64/112 or 57.2% were most commonly observed.

  18. Unsteady aerodynamics modeling for flight dynamics application

    Science.gov (United States)

    Wang, Qing; He, Kai-Feng; Qian, Wei-Qi; Zhang, Tian-Jiao; Cheng, Yan-Qing; Wu, Kai-Yuan

    2012-02-01

    In view of engineering application, it is practicable to decompose the aerodynamics into three components: the static aerodynamics, the aerodynamic increment due to steady rotations, and the aerodynamic increment due to unsteady separated and vortical flow. The first and the second components can be presented in conventional forms, while the third is described using a one-order differential equation and a radial-basis-function (RBF) network. For an aircraft configuration, the mathematical models of 6-component aerodynamic coefficients are set up from the wind tunnel test data of pitch, yaw, roll, and coupled yawroll large-amplitude oscillations. The flight dynamics of an aircraft is studied by the bifurcation analysis technique in the case of quasi-steady aerodynamics and unsteady aerodynamics, respectively. The results show that: (1) unsteady aerodynamics has no effect upon the existence of trim points, but affects their stability; (2) unsteady aerodynamics has great effects upon the existence, stability, and amplitudes of periodic solutions; and (3) unsteady aerodynamics changes the stable regions of trim points obviously. Furthermore, the dynamic responses of the aircraft to elevator deflections are inspected. It is shown that the unsteady aerodynamics is beneficial to dynamic stability for the present aircraft. Finally, the effects of unsteady aerodynamics on the post-stall maneuverability are analyzed by numerical simulation.

  19. Unsteady aerodynamics modeling for flight dynamics application

    Institute of Scientific and Technical Information of China (English)

    Qing Wang; Kai-Feng He; Wei-Qi Qian; Tian-Jiao Zhang; Yan-Qing Cheng; Kai-Yuan Wu

    2012-01-01

    In view of engineering application,it is practicable to decompose the aerodynamics into three components:the static aerodynamics,the aerodynamic increment due to steady rotations,and the aerodynamic increment due to unsteady separated and vortical flow.The first and the second components can be presented in conventional forms,while the third is described using a one-order differential equation and a radial-basis-function (RBF) network. For an aircraft configuration,the mathematical models of 6-component aerodynamic coefficients are set up from the wind tunnel test data of pitch,yaw,roll,and coupled yawroll large-amplitude oscillations.The flight dynamics of an aircraft is studied by the bifurcation analysis technique in the case of quasi-steady aerodynamics and unsteady aerodynamics,respectively.The results show that:(1) unsteady aerodynamics has no effect upon the existence of trim points,but affects their stability; (2) unsteady aerodynamics has great effects upon the existence,stability,and amplitudes of periodic solutions; and (3) unsteady aerodynamics changes the stable regions of trim points obviously.Furthermore,the dynamic responses of the aircraft to elevator deflections are inspected.It is shown that the unsteady aerodynamics is beneficial to dynamic stability for the present aircraft.Finally,the effects of unsteady aerodynamics on the post-stall maneuverability are analyzed by numerical simulation.

  20. Heritability of gross feed efficiency and associations with yield, intake, residual intake, body weight, and body condition score in 11 commercial Pennsylvania tie stalls.

    Science.gov (United States)

    Vallimont, J E; Dechow, C D; Daubert, J M; Dekleva, M W; Blum, J W; Barlieb, C M; Liu, W; Varga, G A; Heinrichs, A J; Baumrucker, C R

    2011-04-01

    The objectives of this study were to calculate the heritability of feed efficiency and residual feed intake, and examine the relationships between feed efficiency and other traits of productive and economic importance. Intake and body measurement data were collected monthly on 970 cows in 11 tie-stall herds for 6 consecutive mo. Measures of efficiency for this study were: dry matter intake efficiency (DMIE), defined as 305-d fat-corrected milk (FCM)/305-d DMI, net energy for lactation efficiency (NELE), defined as 305-d FCM/05-d NEL intake, and crude protein efficiency (CPE), defined as 305-d true protein yield/305-d CP intake. Residual feed intake (RFI) was calculated by regressing daily DMI on daily milk, fat, and protein yields, body weight (BW), daily body condition score (BCS) gain or loss, the interaction between BW and BCS gain or loss, and days in milk (DIM). Data were analyzed with 3- and 4-trait animal models and included 305-d FCM or protein yield, DM, NEL, or CP intake, BW, BCS, BCS change between DIM 1 and 60, milk urea nitrogen, somatic cell score, RFI, or an alternative efficiency measure. Data were analyzed with and without significant covariates for BCS and BCS change between DIM 1 and 60. The average DMIE, NELE, and CPE were 1.61, 0.98, and 0.32, respectively. Heritability of gross feed efficiency was 0.14 for DMIE, 0.18 for NELE, and 0.21 for CPE, and heritability of RFI was 0.01. Body weight and BCS had high and negative correlations with the efficiency traits (-0.64 to -0.70), indicating that larger and fatter cows were less feed efficient than smaller and thinner cows. When BCS covariates were included in the model, cows identified as being highly efficient produced 2.3 kg/d less FCM in early lactation due to less early lactation loss of BCS. Results from this study suggest that selection for higher yield and lower BW will increase feed efficiency, and that body tissue mobilization should be considered. Copyright © 2011 American Dairy Science

  1. Home Was a Horse Stall.

    Science.gov (United States)

    Carnes, Jim

    1995-01-01

    This story of the internment of a Japanese American family during World War II is 1 of 14 stories of intolerance in America in "Us and Them," the text component of a "Teaching Tolerance" curriculum kit, "The Shadow of Hate." The kit includes a video, teacher's guide, and lesson plans. (SLD)

  2. Stalled ERP at Random Textiles

    Science.gov (United States)

    Brumberg, Robert; Kops, Eric; Little, Elizabeth; Gamble, George; Underbakke, Jesse; Havelka, Douglas

    2016-01-01

    Andre Raymond, Executive Vice President of Sales and Marketing for Random Textiles Co. Inc. (RTC), stood in front of the podium to address his team of 70 sales consultants in Las Vegas, NV. The organization had increased market share and achieved record sales over the past three years; however, in the shadow of this success lurked an obstacle that…

  3. Beijing’s Stalled Traffic

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Beijing authorities recently announced the extension of the city’s vehicle restrictions for another year, from April 11, 2009 to April 10, 2010, excluding legal holidays. According to the first round of auto restrictions designed for the Beijing Olympics, private vehicles were banned from roads from 6 a.m. to 9 p.m. daily, alternating

  4. Escova dental e dedeira na remoção da placa bacteriana dental em cães The dental brush and thumb-stall in the removal of the dental plaque in dogs

    Directory of Open Access Journals (Sweden)

    Tânia Berbert Ferreira Lima

    2004-02-01

    Full Text Available A placa bacteriana é fator primário na formação de gengivite, cálculo dentário, halitose e doença periodontal. Objetivou-se avaliar a quantidade de placa bacteriana dental removida pela escova dental e dedeira. Foram utilizados 60 cães machos e fêmeas de diferentes raças, idade e peso, divididos em dois grupos. O índice Logan & Boyce foi utilizados para quantificar a placa bacteriana antes e após a escovação. Observou-se diferença estatística (p0,05 entre a utilização da escova dental e a dedeira.The dental plaque is the primary factor for gingivitis formation, dental calculus, oral malodor and periodontal disease. To evaluate the amount of dental plaque removed by the dental brush and thumb-stall, 60 male and female dogs of different races, age and weight were divided in two groups and studies. The index of Logan & Boyce was used to quantify the dental plaque before and after the toothbrush. Statistical difference was observed (p 0.05 between the use of the dental brush and the thumb-stall.

  5. Collapse dynamics of a fluid hole in a rotating thin film

    CERN Document Server

    Bostwick, Joshua

    2015-01-01

    We study the collapse dynamics of an axisymmetric fluid cavity that wets the bottom of a rotating bucket bound by vertical sidewalls. Lubrication theory is applied to the governing field equations for the thin film to yield an evolution equation that captures the effect of capillary, gravitational and centrifugal forces on this converging flow. We focus on the quasi-static spreading regime, whereby contact-line motion is governed by a constitutive law relating the contact-angle to the contact-line speed. We report the collapse time, as it depends upon the initial hole size, showing that gravity accelerates the collapse process. Surface tension forces dominate the collapse dynamics for small holes leading to a universal power law whose exponent compares favorably to experiments reported in the literature. Centrifugal forces slow the collapse process and lead to complex dynamics characterized by stalled spreading behavior that separates the large and small hole asymptotic regimes.

  6. The Role of Molecular Microtubule Motors and the Microtubule Cytoskeleton in Stress Granule Dynamics

    Directory of Open Access Journals (Sweden)

    Kristen M. Bartoli

    2011-01-01

    Full Text Available Stress granules (SGs are cytoplasmic foci that appear in cells exposed to stress-induced translational inhibition. SGs function as a triage center, where mRNAs are sorted for storage, degradation, and translation reinitiation. The underlying mechanisms of SGs dynamics are still being characterized, although many key players have been identified. The main components of SGs are stalled 48S preinitiation complexes. To date, many other proteins have also been found to localize in SGs and are hypothesized to function in SG dynamics. Most recently, the microtubule cytoskeleton and associated motor proteins have been demonstrated to function in SG dynamics. In this paper, we will discuss current literature examining the function of microtubules and the molecular microtubule motors in SG assembly, coalescence, movement, composition, organization, and disassembly.

  7. Dynamical System Analysis of Unsteady Phenomena in Centrifugal Compressor

    Institute of Scientific and Technical Information of China (English)

    YasuyukiKomatsubara; ShimpeiMizuki

    1997-01-01

    Surge and rotating stall occurring in a centrifugal compressor system are investigated by using a phase portrait reconstruction method.From experimentally measured time series of data,the method clarified the cyclic behavior of surge.For rotating stall,there still remain problems in the phase portrait due to the chaotic behavior.However,the results obtained by the present method are able to provide new insights to the modelings for surge and rotating stall.Surge and roatting stall occurring in a centrifugal compressor system are investigated by using a phase portrait reconstruction method.From experimentally measured time series of data,the method clarified the cylcic behavior of surge.For rotating stall,there still remain problems in the phase portrait due to the chaotic behavior.However,the results obtained by the present method are able to provide new insights to the modelings for surge and rotating stall.

  8. 螺旋桨飞机升力失速特性研究%Investigation on lift stall characteristics of propeller aircraft

    Institute of Scientific and Technical Information of China (English)

    刘毅; 赵晓霞; 欧阳绍修

    2015-01-01

    The maximum lift coefficient CLmax is directly connected to the selection of wing loading,which further affects aircraft’s mass and economy.CLmax of propeller aircraft is improved with increased slipstream intensity at powered condition,however the conventional theory trends to some conservative and smaller power-off value,hence does not utilize the full potential per-formance of aircraft.Combining the airworthiness regulations and the actual flight condition of an aircraft with four turbo-prop engines,a new concept is proposed to find the optimal CLmax based on engine standby condition.The power-on CLmax is separated into four parts:power-off CLmax , propeller thrust component,propeller normal force and lift due to slipstream,which are simula-ted,measured and corrected by power-off and multi-balance power-on wind tunnel tests.The calculation shows that the propeller aircraft with four engines has slipstream intensity in the order of 0.1 at stall flight test condition with engines standby.The slipstream effect is the major factor of lift increment even at small slipstream intensity,and the increment increases as flap angle or slipstream intensity increase.The four engines at standby condition also generate considerable thrust and normal force due to lift.The power effect of turbo-prop engine increases the CLmax of different flap configurations up to 8%~9%.The CLmax obtained by the method agrees well with flight test,and the low speed performance of the aircraft is well utilized.The research can be an important reference for propeller aircraft design.%飞机的最大升力系数 CLmax 直接影响翼载的选取,进而影响飞机的重量和经济性。螺旋桨飞机在带动力条件下 CLmax 随滑流强度增加而提高,但按照常规理论采用无动力 CLmax 数据选取的翼载偏小偏保守,没有充分发掘飞机的性能潜力。结合适航规定以及某四发螺旋桨飞机飞行实际情况,提出了一种基

  9. Dynamic Logics of Dynamical Systems

    CERN Document Server

    Platzer, André

    2012-01-01

    We survey dynamic logics for specifying and verifying properties of dynamical systems, including hybrid systems, distributed hybrid systems, and stochastic hybrid systems. A dynamic logic is a first-order modal logic with a pair of parametrized modal operators for each dynamical system to express necessary or possible properties of their transition behavior. Due to their full basis of first-order modal logic operators, dynamic logics can express a rich variety of system properties, including safety, controllability, reactivity, liveness, and quantified parametrized properties, even about relations between multiple dynamical systems. In this survey, we focus on some of the representatives of the family of differential dynamic logics, which share the ability to express properties of dynamical systems having continuous dynamics described by various forms of differential equations. We explain the dynamical system models, dynamic logics of dynamical systems, their semantics, their axiomatizations, and proof calcul...

  10. Local Dynamic Reactive Power for Correction of System Voltage Problems

    Energy Technology Data Exchange (ETDEWEB)

    Kueck, John D [ORNL; Rizy, D Tom [ORNL; Li, Fangxing [ORNL; Xu, Yan [ORNL; Li, Huijuan [University of Tennessee, Knoxville (UTK); Adhikari, Sarina [ORNL; Irminger, Philip [ORNL

    2008-12-01

    Distribution systems are experiencing outages due to a phenomenon known as local voltage collapse. Local voltage collapse is occurring in part because modern air conditioner compressor motors are much more susceptible to stalling during a voltage dip than older motors. These motors can stall in less than 3 cycles (.05s) when a fault, such as on the sub-transmission system, causes voltage to sag to 70 to 60%. The reasons for this susceptibility are discussed in the report. During the local voltage collapse, voltages are depressed for a period of perhaps one or two minutes. There is a concern that these local events are interacting together over larger areas and may present a challenge to system reliability. An effective method of preventing local voltage collapse is the use of voltage regulation from Distributed Energy Resources (DER) that can supply or absorb reactive power. DER, when properly controlled, can provide a rapid correction to voltage dips and prevent motor stall. This report discusses the phenomenon and causes of local voltage collapse as well as the control methodology we have developed to counter voltage sag. The problem is growing because of the use of low inertia, high efficiency air conditioner (A/C) compressor motors and because the use of electric A/C is growing in use and becoming a larger percentage of system load. A method for local dynamic voltage regulation is discussed which uses reactive power injection or absorption from local DER. This method is independent, rapid, and will not interfere with conventional utility system voltage control. The results of simulations of this method are provided. The method has also been tested at the ORNL s Distributed Energy Communications and Control (DECC) Laboratory using our research inverter and synchronous condenser. These systems at the DECC Lab are interconnected to an actual distribution system, the ORNL distribution system, which is fed from TVA s 161kV sub-transmission backbone. The test results

  11. 交流牵引机车库内移车矢量控制系统研究%On the Vector Control System for the Stall Parking of AC Traction Locomotives

    Institute of Scientific and Technical Information of China (English)

    张帅; 易吉良; 程焰; 刘小文; 杨晓芳

    2016-01-01

    Based on the operating mode of the stall parking of AC traction electric locomotives, a vector control system, with DC 110 V accumulator its power source, has been designed of a fuzzy self-adaptive PI speed controller. By controlling the rotational speed of the induction motor, a slow and steady movement of the AC traction locomotives has been realized in the process of stall parking. The final result of a modeling and simulation test for the control system based on MATLAB/Simulink shows that the vector control system based on the fuzzy self-adaptive PI has the following advantages:more efficient voltage utilization, less rotational speed errors and smaller overshoot, greater self-adaptive capacity for the system speed regulator, etc.%针对交流牵引电力机车在库内低速移动的工况,提出以机车DC 110 V蓄电池作为动力源,采用基于模糊自适应PI速度控制器的矢量控制系统。通过控制异步电机的转速,从而控制交流牵引电力机车在库内低速、稳定移动。最后,利用MATLAB/Simulink对本控制系统进行建模和仿真实验。仿真结果表明,基于模糊自适应PI速度控制器的矢量控制系统具有电压利用率高、转速误差及超调小、系统速度调节的自适应能力强等优点。

  12. Dynamical friction in constant density cores: a failure of the Chandrasekhar formula

    CERN Document Server

    Read, J I; Moore, B; Pontzen, A P; Lake, J S G; Goerdt, Tobias; Moore, Ben; Lake, Joachim Stadel & George

    2006-01-01

    Using analytic calculations and N-body simulations we show that in constant density (harmonic) cores, sinking satellites undergo an initial phase of very rapid (super-Chandrasekhar) dynamical friction, after which they experience no dynamical friction at all. For density profiles with a central power law profile of log-slope, $-\\alpha$, the infalling satellite heats the background and causes $\\alpha$ to decrease. For $\\alpha < 0.5$ initially, the satellite generates a small central constant density core and stalls as in the $\\alpha = 0$ case. We discuss some astrophysical applications of our results to decaying satellite orbits, galactic bars and mergers of supermassive black hole binaries. In a companion paper we show that a central constant density core can provide a natural solution to the timing problem for Fornax's globular clusters.

  13. Dynamic surface measurements on a model helicopter rotor during blade slap at high angles of attack

    Science.gov (United States)

    Hubbard, J. E., Jr.; Harris, W. L.

    1982-01-01

    The modern helicopter offers a unique operational capability to both the public and private sectors. However, the use of the helicopter may become severely limited due to the radiated noise generated by the rotor system. A description is presented of some of the experimental results obtained with a model helicopter rotor in an anechoic wind tunnel with regard to blade stall as a source mechanism of blade slap. Attention is given to dynamic rotor blade surface phenomena and the resulting far field impulsive noise from the model helicopter rotor at high angles of attack and low tip speed. The results of the investigation strongly implicates the boundary layer as playing an important role in blade slap due to blade/vortex interaction (BVI) in a highly loaded rotor. Intermittent stall cannot be ruled out as a possible source mechanism for blade slap. This implies that blade surface characteristics, airfoil shape and local Reynolds number may now be used as tools to reduce the resultant far-field sound pressure levels in helicopters.

  14. Static and Dynamic Characteristics of Coupled Nonlinear Aeroelasticity and Flight Dynamics of Flexible Aircraft%柔性飞机非线性气动弹性与飞行动力学耦合静、动态特性

    Institute of Scientific and Technical Information of China (English)

    张健; 向锦武

    2011-01-01

    High-altitude long-endurance (HALE) aircraft features slender and flexible structures, which under nominal operation conditions may result in large structural deformation, aerodynamic stall, and coupling between the low-frequency structural vibration and the rigid body motion of the aircraft. These nonlinearities and interactions affect dramatically the static and dynamic behaviors of a HALE flexible aircraft. This paper developed a coupled model of aeroelasticity and flight dynamics for high-aspect-ratio flexible aircraft based on the geometrically exact, fully intrinsic beam theory, ONERA aerodynamic stall model, and a six degree of freedom model of the rigid body motion. This model takes into consideration the geometrical non-linearities, dynamic stall and material anisotropy, etc. Two case models of the conventional configuration and the flying-wing configuration are used to investigate the characteristics of the trim, dynamic stability and time-domain response of the high-aspect-ratio flexible aircraft with nonlinear aeroelasticity and flight dynamics coupled. The results obtained indicate that when the wing deformation is relatively small, the angle of attack required for the trim of the flexible aircraft is smaller than that for a rigid aircraft, and stall may occur along the whole wing span, which may cause altitude decrease quickly due to the dramatic reduction in the total lift of the complete aircraft. When the wing deformation is relatively large, the angle of attack required for the trim of the flexible aircraft is larger than that for a rigid aircraft, and stall occurs in a limited region near the wing tip. In addition, the motion of a flexible aircraft may become unstable due to large deformation of its wings, which can be improved by applying aeroelastic tailoring.%高空长航时(HALE)飞机结构细长、具有柔性,在常规飞行条件下可发生结构大变形、气动失速以及结构低频振动与刚体运动耦合,这些现象显著影

  15. Dynamical Languages

    Science.gov (United States)

    Xie, Huimin

    The following sections are included: * Definition of Dynamical Languages * Distinct Excluded Blocks * Definition and Properties * L and L″ in Chomsky Hierarchy * A Natural Equivalence Relation * Symbolic Flows * Symbolic Flows and Dynamical Languages * Subshifts of Finite Type * Sofic Systems * Graphs and Dynamical Languages * Graphs and Shannon-Graphs * Transitive Languages * Topological Entropy

  16. The Science of Cow Comfort: Building Better Barns-Seeing the Free Stall from the Cow's Perspective%奶牛舒适度的科学:设计更好的卧床——奶牛感觉舒适的卧床

    Institute of Scientific and Technical Information of China (English)

    王艳明; 边四辈; 崔春涛; 于磊

    2013-01-01

    不管是躺卧区域还是站立区域,奶牛都喜欢柔软的表面.深槽卧床是最舒适的卧床,但需要很好的维护.当设计散放场自由卧床时,物理屏障越少越好.限制性硬件投入越多,奶牛越不喜欢.卧床的一些限制硬件可以保持牛床干净,但是为了避免肢蹄病的发生,这些硬件是必须配备好的,如软的、干的地面.饲喂区域的设计和管理很重要.饲养密度过高会增加牛只间的攻击性,使得从属地位的牛远离采食区域.牛只间的物理屏障,包括颈夹和采食槽,能够降低竞争、增加采食时间.%Cows like softer surfaces,for both lying down and for standing upon.Deep-bedded stalls work well for cow comfort,but require maintenance.When it comes to the physical structures used to build freestalls,less is more-the hardware we place in the stall is for our benefit and not the cows.The more restrictive we design stalls the less attractive they become for the cow.Use of restrictive stall designs can help keep stalls clean,but to avoid problems with hoof health these designs need to be accompanied by better flooring options,such as softer and drier flooring.The design and management of the feeding area important.High stocking densities at the feed bunk increase aggressive competition and keep subordinate cows away from feed.Physical barrier between cows,including head lockers and feed stalls,can help reduce this competition and increase feeding time.

  17. Realistic initiation and dynamics of the Madden-Julian Oscillation in a coarse resolution aquaplanet GCM

    Science.gov (United States)

    Ajayamohan, R. S.; Khouider, Boualem; Majda, Andrew J.

    2013-12-01

    The main mechanisms for the initiation and propagation of the Madden-Julian Oscillation (MJO) are still widely debated. The capacity of operational global climate models (GCMs) to correctly simulate the MJO is hindered by the inadequacy of the underlying cumulus parameterizations. Here we show that a coarse resolution GCM, coupled to a simple multicloud model parameterization mimicking the observed dynamics and physical structure of organized tropical convection, simulates the MJO in an idealized setting of an aquaplanet without ocean dynamics. We impose a fixed nonhomogeneous sea-surface temperature replicating the Indian Ocean/Western Pacific warm pool. This results in a succession of MJOs with realistic phase speed, amplitude, and physical structure. Each MJO event is initiated at a somewhat random location over the warm pool and dies sometimes near the eastern boundary of the warm pool and sometimes at a random location way beyond the warm pool. Also occasionally the MJO events stall at the center of maximum heating. This is reminiscent of the fact that in nature some MJOs stall over the maritime continent while others reach the central Pacific Ocean and beyond. The initiation mechanism in the model is believed to be a combination of persistent intermittent convective events interacting with observed large-scale flow patterns and internal tropical dynamics. The large-scale flow patterns are associated with planetary-scale dry Kelvin waves that are triggered by preceding MJO events and circle the globe, while congestus cloud decks on the flanks of the warm pool are believed to force Rossby gyres which then funnel moisture toward the equatorial region.

  18. Análise do investimento em climatização para bovinos de leite em sistema de alojamento free-stall Analysis of the investment in climatization for dairy cows in freestall

    Directory of Open Access Journals (Sweden)

    Silvia R. L. Souza

    2004-08-01

    Full Text Available A dificuldade de adaptação das raças leiteiras européias no Brasil afeta diretamente o setor produtivo de leite. As condições climáticas do País são desfavoráveis, e o desenvolvimento de novas tecnologias é imprescindível para que o potencial genético e a capacidade de conversão alimentar sejam evidenciados nos animais. Dessa forma, a análise econômica do investimento na climatização de instalações do tipo free-stall torna-se necessária para estimar os aspectos relacionados à rentabilidade, capacidade de pagamento e tempo necessário para recuperar o capital investido. O objetivo deste trabalho foi o de avaliar a influência da climatização no processo produtivo de bovinos de leite e realizar uma análise econômica do investimento. Foram utilizadas 470 vacas com características genéticas e morfológicas homogêneas, de alta produção, analisadas em dois períodos semelhantes. Os cálculos do investimento foram efetuados por meio do programa Excell®. Os resultados das análises indicam que deve haver retorno do capital investido em curto prazo (57 dias.The difficulty in adapting European dairy cows breeds in Brazil affect considerably the milk production sector. Brazilian climatic conditions are not totally favorable and the development of new tecnologies is needed for the animals express their genetic potential, as well as their best feed conversion. An economical analysis of the applied investment in the free-stall climatization equipment in dairy housing, for estimating studies related to profit, possibility of return investment as well as time for this return is necessary. The objective of this research was to evaluate the influence of climatization investment in the milk production process and analyze the economical aspect of this investment. There were used 470 high productive dairy cows with genetic and morphologic homogeneous characteristics, and analyzed in two similar periods. Investment calculations were

  19. Molecular dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Ladd, A.J.C.

    1988-08-01

    The basic methodology of equilibrium molecular dynamics is described. Examples from the literature are used to illustrate how molecular dynamics has been used to resolve theoretical controversies, provide data to test theories, and occasionally to discover new phenomena. The emphasis is on the application of molecular dynamics to an understanding of the microscopic physics underlying the transport properties of simple fluids. 98 refs., 4 figs.

  20. Dynamics Laboratory

    Data.gov (United States)

    Federal Laboratory Consortium — The Dynamics Lab replicates vibration environments for every Navy platform. Testing performed includes: Flight Clearance, Component Improvement, Qualification, Life...

  1. Dynamical systems

    CERN Document Server

    Sternberg, Shlomo

    2010-01-01

    Celebrated mathematician Shlomo Sternberg, a pioneer in the field of dynamical systems, created this modern one-semester introduction to the subject for his classes at Harvard University. Its wide-ranging treatment covers one-dimensional dynamics, differential equations, random walks, iterated function systems, symbolic dynamics, and Markov chains. Supplementary materials offer a variety of online components, including PowerPoint lecture slides for professors and MATLAB exercises.""Even though there are many dynamical systems books on the market, this book is bound to become a classic. The the

  2. Overexpression of OsKTN80a, a katanin P80 ortholog, caused the repressed cell elongation and stalled cell division mediated by microtubule apparatus defects in primary root in Oryza sativa

    Institute of Scientific and Technical Information of China (English)

    Lei Wan; Xiuwen Wang; Shaoqing Li; Jun Hu; Wenchao Huang; Yingguo Zhu

    2014-01-01

    Katanin, a microtubule-severing enzyme, consists of two subunits:the catalytic subunit P60, and the regulatory subunit P80. In several species, P80 functions in meiotic spindle organization, the flagella biogenesis, the neuronal development, and the male gamete production. However, the P80 function in higher plants remains elusive. In this study, we found that there are three katanin P80 orthologs (OsKTN80a, OsKTN80b, and OsKTN80c) in Oryza sativa L. Overexpression of OsKTN80a caused the retarded root growth of rice seedlings. Further investigation indicates that the retained root growth was caused by the repressed cell elongation in the elongation zone and the stalled cytokinesis in the division zone in the root tip. The in vivo examination suggests that OsKTN80a acts as a microtubule stabilizer. We prove that OsKTN80a, possibly associated with OsKTN60, is involved in root growth via regulating the cell elongation and division.

  3. Validation of fixed speed wind turbine dynamic models with measured data

    Energy Technology Data Exchange (ETDEWEB)

    Martins, M.; Perdana, A.; Agneholm, E.; Carlson, O. [Department of Electric Power Engineering, Chalmers University of Technology, S-412 96 Goeteborg (Sweden); Ledesma, P. [Departamento de Ingenieria Electrica, Universidad Carlos III de Madrid, Butarque 15, 28911 Leganes (Spain)

    2007-07-15

    Power system dynamics studies involving fixed-speed wind turbines normally use a wind turbine model consisting of two lumped masses, an elastic coupling and a induction generator model which neglects stator transients. However, validations of this model with measured data are rarely reported in the literature. This paper validates the model using a recorded case obtained in a fixed speed, stall regulated 180kW wind turbine through a voltage dip. The work analyses the performance of the reduced order induction generator model which neglects stator transients, compared to the detailed induction generator model. It also includes a study of the convenience of representing mechanical damping in the drive train, and an evaluation of the single mass mechanical model. (author)

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

    DEFF Research Database (Denmark)

    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...

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

    Directory of Open Access Journals (Sweden)

    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.

  6. Molecular dynamics

    NARCIS (Netherlands)

    Bergstra, J.A.; Bethke, I.

    2002-01-01

    Molecular dynamics is a model for the structure and meaning of object based programming systems. In molecular dynamics the memory state of a system is modeled as a fluid consisting of a collection of molecules. Each molecule is a collection of atoms with bindings between them. A computation is model

  7. Dynamic Squares

    NARCIS (Netherlands)

    Blackburn, P.; Venema, Y.

    2008-01-01

    This paper examines various propositional logics in which the dynamic implication connective (discussed in Groenendijk and Stokhof's (1992) Dynamic Predicate Logic and Kamp's (1981) Discourse Representation Theory) plays the central role. Our approach is modal: the basic idea is to view as a binary

  8. Record dynamics

    DEFF Research Database (Denmark)

    Robe, Dominic M.; Boettcher, Stefan; Sibani, Paolo

    2016-01-01

    When quenched rapidly beyond their glass transition, colloidal suspensions fall out of equilibrium. The pace of their dynamics then slows down with the system age, i.e., with the time elapsed after the quench. This breaking of time translational invariance is associated with dynamical observables...

  9. Fluid Dynamics

    DEFF Research Database (Denmark)

    Brorsen, Michael

    These lecture notes are intended mainly for the 7th semester course "Fluid Dynamics" offered by the Study Committee on Civil Engineering, Aalborg University.......These lecture notes are intended mainly for the 7th semester course "Fluid Dynamics" offered by the Study Committee on Civil Engineering, Aalborg University....

  10. Persuasion dynamics

    Science.gov (United States)

    Weisbuch, Gérard; Deffuant, Guillaume; Amblard, Frédéric

    2005-08-01

    We here discuss a model of continuous opinion dynamics in which agents adjust continuous opinions as a result of random binary encounters whenever their difference in opinion is below a given threshold. We concentrate on the version of the model in the presence of few extremists which might drive the dynamics to generalized extremism. A network version of the dynamics is presented here, and its results are compared to those previously obtained for the full-mixing case. The same dynamical regimes are observed, but in rather different parameter regions. We here show that the combination of meso-scale features resulting from the first interaction steps determines the asymptotic state of the dynamics.

  11. Dynamic Optimization

    Science.gov (United States)

    Laird, Philip

    1992-01-01

    We distinguish static and dynamic optimization of programs: whereas static optimization modifies a program before runtime and is based only on its syntactical structure, dynamic optimization is based on the statistical properties of the input source and examples of program execution. Explanation-based generalization is a commonly used dynamic optimization method, but its effectiveness as a speedup-learning method is limited, in part because it fails to separate the learning process from the program transformation process. This paper describes a dynamic optimization technique called a learn-optimize cycle that first uses a learning element to uncover predictable patterns in the program execution and then uses an optimization algorithm to map these patterns into beneficial transformations. The technique has been used successfully for dynamic optimization of pure Prolog.

  12. Dynamic triggering

    Science.gov (United States)

    Hill, David P.; Prejean, Stephanie; Schubert, Gerald

    2015-01-01

    Dynamic stresses propagating as seismic waves from large earthquakes trigger a spectrum of responses at global distances. In addition to locally triggered earthquakes in a variety of tectonic environments, dynamic stresses trigger tectonic (nonvolcanic) tremor in the brittle–plastic transition zone along major plate-boundary faults, activity changes in hydrothermal and volcanic systems, and, in hydrologic domains, changes in spring discharge, water well levels, soil liquefaction, and the eruption of mud volcanoes. Surface waves with periods of 15–200 s are the most effective triggering agents; body-wave trigger is less frequent. Triggering dynamic stresses can be < 1 kPa.

  13. Galactic dynamics

    CERN Document Server

    Binney, James

    2008-01-01

    Since it was first published in 1987, Galactic Dynamics has become the most widely used advanced textbook on the structure and dynamics of galaxies and one of the most cited references in astrophysics. Now, in this extensively revised and updated edition, James Binney and Scott Tremaine describe the dramatic recent advances in this subject, making Galactic Dynamics the most authoritative introduction to galactic astrophysics available to advanced undergraduate students, graduate students, and researchers. Every part of the book has been thoroughly overhauled, and many section

  14. Dynamic capabilities

    DEFF Research Database (Denmark)

    Grünbaum, Niels Nolsøe; Stenger, Marianne

    2013-01-01

    it was dominated by a lack of systematism, assessment, monitoring, marketing speculations and feasibility calculation. Furthermore, the sphere was dictated by asymmetric supplier-customer relationships and negotiation power leading, among other possible factors, to meager profitability.......The consequences of dynamic capabilities (i.e. innovation performance and profitability) is an under researched area in the growing body of literature on dynamic capabilities and innovation management. This study aims to examine the relationship between dynamic capabilities, innovation performance...... and profitability of small and medium sized manufacturing enterprises operating in volatile environments. A multi-case study design was adopted as research strategy. The findings reveal a positive relationship between dynamic capabilities and innovation performance in the case companies, as we would expect. It was...

  15. Prokaryotic expression and purification of human soluble sTALL-2 mutants%人可溶性TALL-2突变体的原核表达及纯化

    Institute of Scientific and Technical Information of China (English)

    刘宝英; 郑英如; 何凤田; 李蓉芬; 龚薇; 黄刚

    2006-01-01

    目的 制备人可溶性(soluble TNF and apoptosisligand-relatedleukocyte-expressedligand 2,sTALL-2)的3种突变体,为寻找sTALL-2的竞争抑性制剂创造条件.方法 采用一步反向PCR,将编码sTALL-2第187位谷氨酰胺(Gln)的核苷酸序列分别置换为丝氨酸(Ser)、天冬氨酸(Asp)、精氨酸(Arg)的编码序列,测序正确后,亚克隆到原核表达载体pQE-80L;经IPTG诱导表达,SDS-PAGE和Western blotting鉴定表达产物,Ni2+-NTA柱层析纯化目和蛋白,进而经Sepha-dex G-75柱层析,获得同源三聚体分子.结果 经一步反向PCR扩增后均得到441bp的DNA片段,测序分析表明分别为sTALL-2第187位谷氨酰胺残基置换为Ser、Asp、Arg的序列,3种突变体蛋白在大肠杆DH5α中获得成功表达,并得以有效纯化.结论 成功制备了sTALL-2的3种突变体蛋白,为进一步探讨sTALL-2结构与功能的关系及寻找基于sTALL-2突变体的抗肿瘤分子奠定了基础.

  16. Fully Coupled Three-Dimensional Dynamic Response of a TLP Floating Wind Turbine in Waves and Wind

    DEFF Research Database (Denmark)

    Ramachandran, Gireesh Kumar V.R.; Bredmose, Henrik; Sørensen, Jens Nørkær

    2013-01-01

    A dynamic model for a tension-leg platform (TLP) floating offshore wind turbine is proposed. The model includes threedimensional wind and wave loads and the associated structural response. The total system is formulated using 17 degrees of freedom (DOF), 6 for the platform motions and 11 for the ...... and discussed. As a next step (which is not presented here), the dynamic model for the substructure is therefore being coupled to an advanced aero-elastic code Flex5, Øye (1996), which has a higher number of DOFs and a controller module.......A dynamic model for a tension-leg platform (TLP) floating offshore wind turbine is proposed. The model includes threedimensional wind and wave loads and the associated structural response. The total system is formulated using 17 degrees of freedom (DOF), 6 for the platform motions and 11......, including Glauert correction for high values of axial induction factor, dynamic stall, dynamic wake and dynamic yaw. The aerodynamic model takes into account the wind shear and turbulence effects. For a representative geographic location, platform responses are obtained for a set of wind and wave climatic...

  17. Nonequilibrium dynamics and ultraslow relaxation of confined DNA during viral packaging.

    Science.gov (United States)

    Berndsen, Zachary T; Keller, Nicholas; Grimes, Shelley; Jardine, Paul J; Smith, Douglas E

    2014-06-10

    Many viruses use molecular motors that generate large forces to package DNA to near-crystalline densities inside preformed viral proheads. Besides being a key step in viral assembly, this process is of interest as a model for understanding the physics of charged polymers under tight 3D confinement. A large number of theoretical studies have modeled DNA packaging, and the nature of the molecular dynamics and the forces resisting the tight confinement is a subject of wide debate. Here, we directly measure the packaging of single DNA molecules in bacteriophage phi29 with optical tweezers. Using a new technique in which we stall the motor and restart it after increasing waiting periods, we show that the DNA undergoes nonequilibrium conformational dynamics during packaging. We show that the relaxation time of the confined DNA is >10 min, which is longer than the time to package the viral genome and 60,000 times longer than that of the unconfined DNA in solution. Thus, the confined DNA molecule becomes kinetically constrained on the timescale of packaging, exhibiting glassy dynamics, which slows the motor, causes significant heterogeneity in packaging rates of individual viruses, and explains the frequent pausing observed in DNA translocation. These results support several recent hypotheses proposed based on polymer dynamics simulations and show that packaging cannot be fully understood by quasistatic thermodynamic models.

  18. Design of a Parallel Robot with a Large Workspace for the Functional Evaluation of Aircraft Dynamics beyond the Nominal Flight Envelope

    Directory of Open Access Journals (Sweden)

    Umar Asif

    2012-08-01

    Full Text Available This paper summarizes the development of a robotic system for the analysis of aircraft dynamics within and beyond the nominal flight envelope. The paper proposes the development of a parallel robot and its motion cueing algorithm to attain a reasonable workspace with adequate motion capabilities to facilitate the testing of aircraft stall and fault manoeuvrability scenarios. The proposed design combines two parallel mechanisms and aims to provide six degrees of freedom motion with a much larger motion envelope than the conventional hexapods in order to realize the manoeuvrability matching of aircraft dynamics near and beyond the upset flight envelopes. Finally the paper draws a comparative evaluation of motion capabilities between the proposed motion platform and a conventional hexapod based on Stewart configuration in order to emphasize the significance of the design proposed herein.

  19. Jumping Dynamics

    DEFF Research Database (Denmark)

    Sannino, Francesco

    2013-01-01

    We propose an alternative paradigm to the conjectured Miransky scaling potentially underlying the physics describing the transition from the conformally broken to the conformally restored phase when tuning certain parameters such as the number of flavors in gauge theories. According to the new...... paradigm the physical scale and henceforth also the massive spectrum of the theory jump at the lower boundary of the conformal window. In particular we propose that a theory can suddenly jump from a Quantum Chromodynamics type spectrum, at the lower boundary of the conformal window, to a conformal one...... without particle interpretation. The jumping scenario, therefore, does not support a near-conformal dynamics of walking type. We will also discuss the impact of jumping dynamics on the construction of models of dynamical electroweak symmetry breaking....

  20. Dynamic Bifurcations

    CERN Document Server

    1991-01-01

    Dynamical Bifurcation Theory is concerned with the phenomena that occur in one parameter families of dynamical systems (usually ordinary differential equations), when the parameter is a slowly varying function of time. During the last decade these phenomena were observed and studied by many mathematicians, both pure and applied, from eastern and western countries, using classical and nonstandard analysis. It is the purpose of this book to give an account of these developments. The first paper, by C. Lobry, is an introduction: the reader will find here an explanation of the problems and some easy examples; this paper also explains the role of each of the other paper within the volume and their relationship to one another. CONTENTS: C. Lobry: Dynamic Bifurcations.- T. Erneux, E.L. Reiss, L.J. Holden, M. Georgiou: Slow Passage through Bifurcation and Limit Points. Asymptotic Theory and Applications.- M. Canalis-Durand: Formal Expansion of van der Pol Equation Canard Solutions are Gevrey.- V. Gautheron, E. Isambe...

  1. Dynamical systems

    CERN Document Server

    Birkhoff, George D

    1927-01-01

    His research in dynamics constitutes the middle period of Birkhoff's scientific career, that of maturity and greatest power. -Yearbook of the American Philosophical Society The author's great book€¦is well known to all, and the diverse active modern developments in mathematics which have been inspired by this volume bear the most eloquent testimony to its quality and influence. -Zentralblatt MATH In 1927, G. D. Birkhoff wrote a remarkable treatise on the theory of dynamical systems that would inspire many later mathematicians to do great work. To a large extent, Birkhoff was writing about his o

  2. Forest dynamics.

    Science.gov (United States)

    Frelich, Lee

    2016-01-01

    Forest dynamics encompass changes in stand structure, species composition, and species interactions with disturbance and environment over a range of spatial and temporal scales. For convenience, spatial scale is defined as individual tree, neighborhood, stand, and landscape. Whether a given canopy-leveling disturbance will initiate a sequence of development in structure with little change in composition or initiate an episode of succession depends on a match or mismatch, respectively, with traits of the dominant tree species that allow the species to survive disturbance. When these match, certain species-disturbance type combinations lock in a pattern of stand and landscape dynamics that can persist for several generations of trees; thus, dominant tree species regulate, as well as respond to, disturbance. A complex interaction among tree species, neighborhood effects, disturbance type and severity, landform, and soils determines how stands of differing composition form and the mosaic of stands that compose the landscape. Neighborhood effects (e.g., serotinous seed rain, sprouting, shading, leaf-litter chemistry, and leaf-litter physical properties) operate at small spatial extents of the individual tree and its neighbors but play a central role in forest dynamics by contributing to patch formation at stand scales and dynamics of the entire landscape. Dominance by tree species with neutral to negative neighborhood effects leads to unstable landscape dynamics in disturbance-prone regions, wherein most stands are undergoing succession; stability can only occur under very low-severity disturbance regimes. Dominance by species with positive effects leads to stable landscape dynamics wherein only a small proportion of stands undergo succession at any one time. Positive neighborhood effects are common in temperate and boreal zones, whereas negative effects are more common in tropical climates. Landscapes with positive dynamics have alternate categories of dynamics

  3. Study of 3-D Dynamic Roughness Effects on Flow Over a NACA 0012 Airfoil Using Large Eddy Simulations at Low Reynolds Numbers

    Science.gov (United States)

    Guda, Venkata Subba Sai Satish

    There have been several advancements in the aerospace industry in areas of design such as aerodynamics, designs, controls and propulsion; all aimed at one common goal i.e. increasing efficiency --range and scope of operation with lesser fuel consumption. Several methods of flow control have been tried. Some were successful, some failed and many were termed as impractical. The low Reynolds number regime of 104 - 105 is a very interesting range. Flow physics in this range are quite different than those of higher Reynolds number range. Mid and high altitude UAV's, MAV's, sailplanes, jet engine fan blades, inboard helicopter rotor blades and wind turbine rotors are some of the aerodynamic applications that fall in this range. The current study deals with using dynamic roughness as a means of flow control over a NACA 0012 airfoil at low Reynolds numbers. Dynamic 3-D surface roughness elements on an airfoil placed near the leading edge aim at increasing the efficiency by suppressing the effects of leading edge separation like leading edge stall by delaying or totally eliminating flow separation. A numerical study of the above method has been carried out by means of a Large Eddy Simulation, a mathematical model for turbulence in Computational Fluid Dynamics, owing to the highly unsteady nature of the flow. A user defined function has been developed for the 3-D dynamic roughness element motion. Results from simulations have been compared to those from experimental PIV data. Large eddy simulations have relatively well captured the leading edge stall. For the clean cases, i.e. with the DR not actuated, the LES was able to reproduce experimental results in a reasonable fashion. However DR simulation results show that it fails to reattach the flow and suppress flow separation compared to experiments. Several novel techniques of grid design and hump creation are introduced through this study.

  4. Selection bias in dynamically-measured super-massive black hole samples: consequences for pulsar timing arrays

    CERN Document Server

    Sesana, A; Bernardi, M; Sheth, R K

    2016-01-01

    Supermassive black hole -- host galaxy relations are key to the computation of the expected gravitational wave background (GWB) in the pulsar timing array (PTA) frequency band. It has been recently pointed out that standard relations adopted in GWB computations are in fact biased-high. We show that when this selection bias is taken into account, the expected GWB in the PTA band is a factor of about three smaller than previously estimated. Compared to other scaling relations recently published in the literature, the median amplitude of the signal at $f=1$yr$^{-1}$ drops from $1.3\\times10^{-15}$ to $4\\times10^{-16}$. Although this solves any potential tension between theoretical predictions and recent PTA limits without invoking other dynamical effects (such as stalling, eccentricity or strong coupling with the galactic environment), it also makes the GWB detection more challenging.

  5. Internetwork dynamics

    NARCIS (Netherlands)

    Rutten, R.J.

    1995-01-01

    This review places current research in quiet-Sun chromospheric dynamics in the context of past and future work, concentrating on observational aspects of three-minute oscillations and Ca II K2V grains. The subject is of interest at present because observations and simulations come together to permit

  6. Structural dynamics

    CERN Document Server

    Strømmen, Einar N

    2014-01-01

    This book introduces to the theory of structural dynamics, with focus on civil engineering structures that may be described by line-like beam or beam-column type of systems, or by a system of rectangular plates. Throughout this book the mathematical presentation contains a classical analytical description as well as a description in a discrete finite element format, covering the mathematical development from basic assumptions to the final equations ready for practical dynamic response predictions. Solutions are presented in time domain as well as in frequency domain. Structural Dynamics starts off at a basic level and step by step brings the reader up to a level where the necessary safety considerations to wind or horizontal ground motion induced dynamic design problems can be performed. The special theory of the tuned mass damper has been given a comprehensive treatment, as this is a theory not fully covered elsewhere. For the same reason a chapter on the problem of moving loads on beams has been included.

  7. Coastal Dynamics

    NARCIS (Netherlands)

    Bakker, W.T.

    1998-01-01

    This book deals on "Coastal Dynamics", which will be defined in a narrow sense as a mathematical theory, which starts from given equations of motion for the sediment, which leads with the continuity equation and given boundary conditions to a calculated (eventually schematized) coastal topography,

  8. Membrane dynamics

    DEFF Research Database (Denmark)

    Bendix, Pól Martin

    2015-01-01

    Current topics include membrane-protein interactions with regard to membrane deformation or curvature sensing by BAR domains. Also, we study the dynamics of membrane tubes of both cells and simple model membrane tubes. Finally, we study membrane phase behavior which has important implications...... for the lateral organization of membranes as wells as for physical properties like bending, permeability and elasticity...

  9. Glassy Dynamics

    DEFF Research Database (Denmark)

    Jensen, Henrik J.; Sibani, Paolo

    2007-01-01

    The term glassy dynamics is often used to refer to the extremely slow relaxation observed in several types of many component systems. The time span needed to reach a steady, time independent, state will typically be far beyond experimentally accessible time scales. When melted alloys are cooled d...

  10. Dynamic LIMIDS

    NARCIS (Netherlands)

    Díez, F.J.; Gerven, M.A.J. van

    2011-01-01

    One of the objectives of artificial intelligence is to build decision-support models for systems that evolve over time and include several types of uncertainty. Dynamic limited-memory influence diagrams (DLIMIDs) are a new type of model proposed recently for this kind of problems. DLIMIDs are simila

  11. Dynamic LIMIDS

    NARCIS (Netherlands)

    Díez, F.J.; Gerven, M.A.J. van

    2011-01-01

    One of the objectives of artificial intelligence is to build decision-support models for systems that evolve over time and include several types of uncertainty. Dynamic limited-memory influence diagrams (DLIMIDs) are a new type of model proposed recently for this kind of problems. DLIMIDs are simila

  12. Record dynamics

    DEFF Research Database (Denmark)

    Robe, Dominic M.; Boettcher, Stefan; Sibani, Paolo

    2016-01-01

    -facto irreversible and become increasingly harder to achieve. Thus, a progression of record-sized dynamical barriers are traversed in the approach to equilibration. Accordingly, the statistics of the events is closely described by a log-Poisson process. Originally developed for relaxation in spin glasses...

  13. System Dynamics

    Science.gov (United States)

    Morecroft, John

    System dynamics is an approach for thinking about and simulating situations and organisations of all kinds and sizes by visualising how the elements fit together, interact and change over time. This chapter, written by John Morecroft, describes modern system dynamics which retains the fundamentals developed in the 1950s by Jay W. Forrester of the MIT Sloan School of Management. It looks at feedback loops and time delays that affect system behaviour in a non-linear way, and illustrates how dynamic behaviour depends upon feedback loop structures. It also recognises improvements as part of the ongoing process of managing a situation in order to achieve goals. Significantly it recognises the importance of context, and practitioner skills. Feedback systems thinking views problems and solutions as being intertwined. The main concepts and tools: feedback structure and behaviour, causal loop diagrams, dynamics, are practically illustrated in a wide variety of contexts from a hot water shower through to a symphony orchestra and the practical application of the approach is described through several real examples of its use for strategic planning and evaluation.

  14. Classical dynamics

    CERN Document Server

    Greenwood, Donald T

    1997-01-01

    Graduate-level text for science and technology students provides strong background in the more abstract and intellectually satisfying areas of dynamical theory. Topics include d'Alembert's principle and the idea of virtual work, Hamilton's equations, Hamilton-Jacobi theory, canonical transformations, more. Problems and references at chapter ends.

  15. Internetwork dynamics

    NARCIS (Netherlands)

    Rutten, R.J.

    2001-01-01

    This review places current research in quiet-Sun chromospheric dynamics in the context of past and future work, concentrating on observational aspects of three-minute oscillations and Ca II K2V grains. The subject is of interest at present because observations and simulations come together to permit

  16. Mitotic dynamics

    Institute of Scientific and Technical Information of China (English)

    唐孝威

    1996-01-01

    A new model for mitotic dynamics of eukaryotic cells is proposed. In the kinetochore mo-tor-midzone motor model two kinds of motors, the kinetochore motors and the midzone motors, play important roles in chromosome movement. Using this model the chromosome congression during prometaphase, the chromosome oscillation during metaphase and the chromatid segregation during anaphase are described in a unified way.

  17. Nonlinear Dynamic Analysis of Disordered Bladed-Disk Assemblies

    Science.gov (United States)

    McGee, Oliver G., III

    1997-01-01

    In a effort to address current needs for efficient, air propulsion systems, we have developed some new analytical predictive tools for understanding and alleviating aircraft engine instabilities which have led to accelerated high cycle fatigue and catastrophic failures of these machines during flight. A frequent cause of failure in Jets engines is excessive resonant vibrations and stall flutter instabilities. The likelihood of these phenomena is reduced when designers employ the analytical models we have developed. These prediction models will ultimately increase the nation's competitiveness in producing high performance Jets engines with enhanced operability, energy economy, and safety. The objectives of our current threads of research in the final year are directed along two lines. First, we want to improve the current state of blade stress and aeromechanical reduced-ordered modeling of high bypass engine fans, Specifically, a new reduced-order iterative redesign tool for passively controlling the mechanical authority of shroudless, wide chord, laminated composite transonic bypass engine fans has been developed. Second, we aim to advance current understanding of aeromechanical feedback control of dynamic flow instabilities in axial flow compressors. A systematic theoretical evaluation of several approaches to aeromechanical feedback control of rotating stall in axial compressors has been conducted. Attached are abstracts of two .papers under preparation for the 1998 ASME Turbo Expo in Stockholm, Sweden sponsored under Grant No. NAG3-1571. Our goals during the final year under Grant No. NAG3-1571 is to enhance NASA's capabilities of forced response of turbomachines (such as NASA FREPS). We with continue our development of the reduced-ordered, three-dimensional component synthesis models for aeromechanical evaluation of integrated bladeddisk assemblies (i.e., the disk, non-identical bladeing etc.). We will complete our development of component systems design

  18. 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

    Institute of Scientific and Technical Information of China (English)

    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.

  19. Effects of Dynamic Pitching on Wind Turbine Blade Performance

    Science.gov (United States)

    Naughton, Jonathan; Babbitt, Ashli; Strike, John; Hind, Michael; Magstadt, Andrew; Nikoueeyan, Pourya

    2012-11-01

    Due to turbulence in the wind and the rotation of the blade through a shear layer, wind turbine blade flows are inherently unsteady. Over the past five years, a number of wind turbine blade sections used for inboard, mid-span, and tip regions of the blade (including flatback airfoils) have been tested at a Reynolds number of 225,000. The airfoils have been tested at reduced frequencies cω / 2 U , where c is the chord length, ω is the oscillation frequency (radians/sec), and U is the air velocity ahead of the blade, relevant to commercial wind turbines. Unsteady pressure measurements and Particle Image Velocimetry (PIV) have provided information about the surface properties and surrounding flow field and their relationship. The results have shown that, depending on the reduced frequency, a lag in pressure and flow-field structures is experienced by the blade. When the blade is operating at angles above the static stall angle, delayed separation is experience as expected. The reattachment of the flow is also delayed, and, at higher reduced frequencies, the flow can remain separated throughout the entire downward pitching movement. Such dynamic data result in a better understanding of the unsteady flow physics necessary for improved designs. Support from DOE and BP is acknowledged.

  20. Competitive Overdrive Stalls High Achieving Teens.

    Science.gov (United States)

    Bernardo, Debra

    1990-01-01

    This article discusses findings by pediatric psychologists studying destructive stress responses and other psychological costs of overdriven competitiveness in gifted students. Warning signs indicative of depression or antisocial withdrawal are described, as are contributing factors such as parental expectations. Suggestions for avoiding…

  1. Fan Stall Flutter Flow Mechanism Studied

    Science.gov (United States)

    Lepicovsky, Jan

    2002-01-01

    Modern turbofan engines employ a highly loaded fan stage with transonic or low-supersonic velocities in the blade-tip region. The fan blades are often prone to flutter at off-design conditions. Flutter is a highly undesirable and dangerous self-excited mode of blade oscillations that can result in high-cycle fatigue blade failure. The origins of blade flutter are not fully understood yet. Experimental data that can be used to clarify the origins of blade flutter in modern transonic fan designs are very limited. The Transonic Flutter Cascade Facility at the NASA Glenn Research Center was developed to experimentally study the details of flow mechanisms associated with fan flutter. The cascade airfoils are instrumented to measure high-frequency unsteady flow variations in addition to the steady flow data normally recorded in cascade tests. The test program measures the variation in surface pressure in response to the oscillation of one or more of the cascade airfoils. However, during the initial phases of the program when all airfoils were in fixed positions, conditions were found where significant time variations in the pressures near the airfoil leading edges could be observed.

  2. wethers under stall-feeding conditions

    African Journals Online (AJOL)

    Discussion. According to Forbes (1995), selection of food may be euphagic, i.e. implying nutritional wisdom, ... Although the aim of this study was not to investigate behaviour, the goats showed a tendency to eat more in ... Similarly, pen-fed goats in Malaysia drank ... Water intake and consumption in sheep differing in growth.

  3. 14 CFR 25.201 - Stall demonstration.

    Science.gov (United States)

    2010-01-01

    ...; or (3) The pitch control reaches the aft stop and no further increase in pitch attitude occurs when... Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS... steady rate of speed reduction can be established, apply the longitudinal control so that the speed...

  4. Stall/Spin Problems of Military Aircraft

    Science.gov (United States)

    1976-06-01

    6galement repr~sent6 un parachute 1 on peut traiter son c en conaiddrant, qu’A priori, son action eat du mtme type Quo celul d’una fus~e agissant en...10 pour looquolo 10 sons d’action du dicentrage vera Vaila axtdriouro nest pas Is mime quo celul des autros cas i pour ceo deux points il y a Moins de

  5. The Stalled Recovery of the Iraqi Marshes

    Directory of Open Access Journals (Sweden)

    Richard H. Becker

    2014-01-01

    Full Text Available The Iraqi (Mesopotamian Marshes, an extensive wetlands system in Iraq, has been heavily impacted by both human and climate forces over the past decades. In the period leading up to the Second Gulf War in 2002, the marshlands were shrinking due to both a policy of draining and water diversion in Iraq and construction of dams upstream on the Tigris and Euphrates rivers. Following the war through 2006, this trend was reversed as the diversions were removed and active draining stopped. A combination of MODIS and GRACE datasets were used to determine the change in surface water area (SWA in the marshes, marshland extent and change in mass both upriver in the Tigris and Euphrates watersheds and in the marshlands. Results suggest that the post war dam removal and decreased pumping in 2003 provided only temporary respite for the marshlands (2003–2006 SWA: 1,477 km2 increase (600%, water equivalent depth (WED: +2.0 cm/yr.; 2006–2009: −860 km2 (−41% WED: −3.9 cm/yr.. Unlike in the period 2003–2006, from 2006 forward the mass variations in the marshes are highly correlated with those in the upper and middle watershed (R = 0.86 and 0.92 respectively, suggesting that any recovery due to that removal is complete, and that all future changes are tied more strongly to any climate changes that will affect recharge in the upper Tigris-Euphrates system. Precipitation changes in the watershed show a reduction of an average of 15% below the 15 yr mean in 2007–2011 This corresponds with published ensemble predictions for the 2071–2099 time period, that suggested similar marshland shrinkage should be expected in that time period.

  6. Discrete dynamics versus analytic dynamics

    DEFF Research Database (Denmark)

    Toxværd, Søren

    2014-01-01

    For discrete classical Molecular dynamics obtained by the “Verlet” algorithm (VA) with the time increment h there exists a shadow Hamiltonian H˜ with energy E˜(h) , for which the discrete particle positions lie on the analytic trajectories for H˜ . Here, we proof that there, independent...

  7. Applied dynamics

    CERN Document Server

    Schiehlen, Werner

    2014-01-01

    Applied Dynamics is an important branch of engineering mechanics widely applied to mechanical and automotive engineering, aerospace and biomechanics as well as control engineering and mechatronics. The computational methods presented are based on common fundamentals. For this purpose analytical mechanics turns out to be very useful where D’Alembert’s principle in the Lagrangian formulation proves to be most efficient. The method of multibody systems, finite element systems and continuous systems are treated consistently. Thus, students get a much better understanding of dynamical phenomena, and engineers in design and development departments using computer codes may check the results more easily by choosing models of different complexity for vibration and stress analysis.

  8. Fluid dynamics

    CERN Document Server

    Bernard, Peter S

    2015-01-01

    This book presents a focused, readable account of the principal physical and mathematical ideas at the heart of fluid dynamics. Graduate students in engineering, applied math, and physics who are taking their first graduate course in fluids will find this book invaluable in providing the background in physics and mathematics necessary to pursue advanced study. The book includes a detailed derivation of the Navier-Stokes and energy equations, followed by many examples of their use in studying the dynamics of fluid flows. Modern tensor analysis is used to simplify the mathematical derivations, thus allowing a clearer view of the physics. Peter Bernard also covers the motivation behind many fundamental concepts such as Bernoulli's equation and the stream function. Many exercises are designed with a view toward using MATLAB or its equivalent to simplify and extend the analysis of fluid motion including developing flow simulations based on techniques described in the book.

  9. Dynamic capabilities

    DEFF Research Database (Denmark)

    Grünbaum, Niels Nolsøe; Stenger, Marianne

    2013-01-01

    and profitability of small and medium sized manufacturing enterprises operating in volatile environments. A multi-case study design was adopted as research strategy. The findings reveal a positive relationship between dynamic capabilities and innovation performance in the case companies, as we would expect. It was...... it was dominated by a lack of systematism, assessment, monitoring, marketing speculations and feasibility calculation. Furthermore, the sphere was dictated by asymmetric supplier-customer relationships and negotiation power leading, among other possible factors, to meager profitability....

  10. Cybersecurity Dynamics

    Science.gov (United States)

    2014-08-20

    envisioned) Science of Cybersecurity:  Soul: Security (concepts)  Brain: Cybersecurity Dynamics (kind of Complexity Science)  Muscle & Blood ...Complexity Science)  Muscle & Blood : Probability Theory, Number Theory, Abstract Algebra, etc.  Thrust I: Building a systematic theory of...Under-specification, composition and emergent properties. In Proc. NSPW’97, pp. 83–93. [11] A. Kubík. Toward a formalization of emergence. Artif . Life

  11. Hamiltonian dynamics

    CERN Document Server

    Vilasi, Gaetano

    2001-01-01

    This is both a textbook and a monograph. It is partially based on a two-semester course, held by the author for third-year students in physics and mathematics at the University of Salerno, on analytical mechanics, differential geometry, symplectic manifolds and integrable systems. As a textbook, it provides a systematic and self-consistent formulation of Hamiltonian dynamics both in a rigorous coordinate language and in the modern language of differential geometry. It also presents powerful mathematical methods of theoretical physics, especially in gauge theories and general relativity. As a m

  12. PREFACE: Cooperative dynamics Cooperative dynamics

    Science.gov (United States)

    Gov, Nir

    2011-09-01

    The dynamics within living cells are dominated by non-equilibrium processes that consume chemical energy (usually in the form of ATP, adenosine triphosphate) and convert it into mechanical forces and motion. The mechanisms that allow this conversion process are mostly driven by the components of the cytoskeleton: (i) directed (polar) polymerization of filaments (either actin or microtubules) and (ii) molecular motors. The forces and motions produced by these two components of the cytoskeleton give rise to the formation of cellular shapes, and drive the intracellular transport and organization. It is clear that these systems present a multi-scale challenge, from the physics of the molecular processes to the organization of many interacting units. Understanding the physical nature of these systems will have a large impact on many fundamental problems in biology and break new grounds in the field of non-equilibrium physics. This field of research has seen a rapid development over the last ten years. Activities in this area range from theoretical and experimental work on the underlying fundamental (bio)physics at the single-molecule level, to investigations (in vivo and in vitro) of the dynamics and patterns of macroscopic pieces of 'living matter'. In this special issue we have gathered contributions that span the whole spectrum of length- and complexity-scales in this field. Some of the works demonstrate how active forces self-organize within the polymerizing cytoskeleton, on the level of cooperative cargo transport via motors or due to active fluxes at the cell membrane. On a larger scale, it is shown that polar filaments coupled to molecular motors give rise to a huge variety of surprising dynamics and patterns: spontaneously looping rings of gliding microtubules, and emergent phases of self-organized filaments and motors in different geometries. All of these articles share the common feature of being out-of-equilibrium, driven by metabolism. As demonstrated here

  13. Complex dynamics

    CERN Document Server

    Carleson, Lennart

    1993-01-01

    Complex dynamics is today very much a focus of interest. Though several fine expository articles were available, by P. Blanchard and by M. Yu. Lyubich in particular, until recently there was no single source where students could find the material with proofs. For anyone in our position, gathering and organizing the material required a great deal of work going through preprints and papers and in some cases even finding a proof. We hope that the results of our efforts will be of help to others who plan to learn about complex dynamics and perhaps even lecture. Meanwhile books in the field a. re beginning to appear. The Stony Brook course notes of J. Milnor were particularly welcome and useful. Still we hope that our special emphasis on the analytic side will satisfy a need. This book is a revised and expanded version of notes based on lectures of the first author at UCLA over several \\Vinter Quarters, particularly 1986 and 1990. We owe Chris Bishop a great deal of gratitude for supervising the production of cour...

  14. Conforto térmico para matrizes suínas em fase de gestação, alojadas em baias individuais e coletivas Thermal comfort for pregnant sows housed in individual and group stalls

    Directory of Open Access Journals (Sweden)

    Héliton Pandorfi

    2008-06-01

    Full Text Available Este experimento foi realizado no período compreendido entre 04/01 e 11/03/2005, em uma propriedade de produção industrial de suínos, localizada no município de Elias Fausto, estado de São Paulo. O objetivo da pesquisa consistiu na avaliação de diferentes sistemas de alojamento para matrizes gestantes, verificando-se as influências dos elementos meteorológicos e os aspectos relacionados à qualidade química do ar e seus reflexos no conforto animal na fase de gestação, determinando-se as condições favoráveis ao melhor desempenho animal, com base nas respostas ao ambiente de criação. O estudo foi desenvolvido no setor de gestação, com 24 matrizes primíparas, 12 fêmeas alojadas em baias individuais (T1 e 12 animais em baias coletivas (T2. O trabalho foi dividido em duas etapas: análise bioclimática e análise da qualidade química do ar. O delineamento experimental foi em blocos casualizados, com dois tratamentos e 67 blocos, e as médias comparadas pelo teste de Tukey. As variáveis meteorológicas (T, °C e h, kJ kg-1 apontam o sistema de alojamento em baias coletivas como aquele que permitiu melhor condicionamento térmico natural às matrizes em gestação apresentando valores da ordem de 25,03 °C e 62,02 kJ kg-1. As concentrações dos teores de gases não superaram as concentrações consideradas críticas para as matrizes.The experiment was carried out from January 4 to March 11, 2005 in a farm specialized in industrial production of pork, located in Elias Fausto, São Paulo State. This study evaluated different housing systems for pregnant sows looking at meteorological element influences and aspects of air chemical quality on the animal thermal comfort. The optimal conditions for animal performance improvement were determined by analyzing behavioral data taken in the breeding environment. In the gestation facility 24 gilts were allocated: 12 in individual stalls (T1 and 12 in group housings (T2. This study was

  15. Population dynamics

    Directory of Open Access Journals (Sweden)

    Cooch, E. G.

    2004-06-01

    Full Text Available Increases or decreases in the size of populations over space and time are, arguably, the motivation for much of pure and applied ecological research. The fundamental model for the dynamics of any population is straightforward: the net change over time in the abundance of some population is the simple difference between the number of additions (individuals entering the population minus the number of subtractions (individuals leaving the population. Of course, the precise nature of the pattern and process of these additions and subtractions is often complex, and population biology is often replete with fairly dense mathematical representations of both processes. While there is no doubt that analysis of such abstract descriptions of populations has been of considerable value in advancing our, there has often existed a palpable discomfort when the ‘beautiful math’ is faced with the often ‘ugly realities’ of empirical data. In some cases, this attempted merger is abandoned altogether, because of the paucity of ‘good empirical data’ with which the theoretician can modify and evaluate more conceptually–based models. In some cases, the lack of ‘data’ is more accurately represented as a lack of robust estimates of one or more parameters. It is in this arena that methods developed to analyze multiple encounter data from individually marked organisms has seen perhaps the greatest advances. These methods have rapidly evolved to facilitate not only estimation of one or more vital rates, critical to population modeling and analysis, but also to allow for direct estimation of both the dynamics of populations (e.g., Pradel, 1996, and factors influencing those dynamics (e.g., Nichols et al., 2000. The interconnections between the various vital rates, their estimation, and incorporation into models, was the general subject of our plenary presentation by Hal Caswell (Caswell & Fujiwara, 2004. Caswell notes that although interest has traditionally

  16. Nonlinear dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Turchetti, G. (Bologna Univ. (Italy). Dipt. di Fisica)

    1989-01-01

    Research in nonlinear dynamics is rapidly expanding and its range of applications is extending beyond the traditional areas of science where it was first developed. Indeed while linear analysis and modelling, which has been very successful in mathematical physics and engineering, has become a mature science, many elementary phenomena of intrinsic nonlinear nature were recently experimentally detected and investigated, suggesting new theoretical work. Complex systems, as turbulent fluids, were known to be governed by intrinsically nonlinear laws since a long time ago, but received purely phenomenological descriptions. The pioneering works of Boltzmann and Poincare, probably because of their intrinsic difficulty, did not have a revolutionary impact at their time; it is only very recently that their message is reaching a significant number of mathematicians and physicists. Certainly the development of computers and computer graphics played an important role in developing geometric intuition of complex phenomena through simple numerical experiments, while a new mathematical framework to understand them was being developed.

  17. Superconductor Dynamics

    CERN Document Server

    Gömöry, F

    2014-01-01

    Superconductors used in magnet technology could carry extreme currents because of their ability to keep the magnetic flux motionless. The dynamics of the magnetic flux interaction with superconductors is controlled by this property. The cases of electrical transport in a round wire and the magnetization of wires of various shapes (circular, elliptical, plate) in an external magnetic field are analysed. Resistance to the magnetic field penetration means that the field produced by the superconducting magnet is no longer proportional to the supplied current. It also leads to a dissipation of electromagnetic energy. In conductors with unequal transverse dimensions, such as flat cables, the orientation with respect to the magnetic field plays an essential role. A reduction of magnetization currents can be achieved by splitting the core of a superconducting wire into fine filaments; however, new kinds of electrical currents that couple the filaments consequently appear. Basic formulas allowing qualitative analyses ...

  18. Locomotion Disorders and Skin and Claw Lesions in Gestating Sows Housed in Dynamic versus Static Groups

    Science.gov (United States)

    Bos, Emilie-Julie; Maes, Dominiek; van Riet, Miriam M. J.; Millet, Sam; Ampe, Bart; Janssens, Geert P. J.; Tuyttens, Frank A. M.

    2016-01-01

    Lameness and lesions to the skin and claws of sows in group housing are commonly occurring indicators of reduced welfare. Typically, these problems are more common in group housing than in individual housing systems. Group management type (dynamic versus static) and stage of gestation influence the behavior of the animals, which in turn influences the occurrence of these problems. The present study compared prevalence, incidence and mean scores of lameness and skin and claw lesions in static versus dynamic group housed sows at different stages of gestation during three consecutive reproductive cycles. A total of 10 Belgian sow herds were monitored; 5 in which dynamic groups and 5 in which static groups were utilized. All sows were visually assessed for lameness and skin lesions three times per cycle and the claws of the hind limbs were assessed once per cycle. Lameness and claw lesions were assessed using visual analogue scales. Static groups, in comparison with dynamic groups, demonstrated lower lameness scores (Psows demonstrating claw lesions regardless of group management. Prevalences of lameness (22.4 vs. 8.9%, P<0.05) and skin lesions (46.6 vs. 4.4%, P<0.05) were highest during the group-housed phase compared to the individually housed phases. Although the prevalence of lameness and skin lesions did not differ three days after grouping versus at the end of the group-housing phase, their incidence peaked during the first three days after moving from the insemination stalls to the group. In conclusion, the first three days after grouping was the most risky period for lameness incidence, but there was no significant difference between static or dynamic group management. PMID:27680675

  19. Dynamic stability test results on an 0.024 scale B-1 air vehicle

    Science.gov (United States)

    Beeman, R. R.

    1972-01-01

    Dynamic longitudinal and lateral-directional stability characteristics of the B-1 air vehicle were investigated in three wind tunnels at the Langley Research Center. The main rotary derivatives were obtained for an angle of attack range of -3 degrees to +16 degrees for a Mach number range of 0.2 to 2.16. Damping in roll data could not be obtained at the supersonic Mach numbers. The Langley 7 x 10 foot high speed tunnel, the 8 foot transonic pressure tunnel, and the 4 foot Unitary Plan wind tunnel were the test sites. An 0.024 scale light-weight model was used on a forced oscillation type balance. Test Reynolds number varied from 474,000/ft to 1,550,000/ft. through the Mach number range tested. The results showed that the dynamic stability characteristics of the model in pitch and roll were generally satisfactory up to an angle attack of about +6 degrees. In the wing sweep range from 15 to 25 degrees the positive damping levels in roll deteriorated rapidly above +2 degrees angle of attack. This reduction in roll damping is believed to be due to the onset of separation over the wing as stall is approached.

  20. Dynamic Analysis for a Geared Turbofan Engine with Variable Area Fan Nozzle

    Science.gov (United States)

    Csank, Jeffrey T.; Thomas, George L.

    2017-01-01

    Aggressive design goals have been set for future aero-propulsion systems with regards to fuel economy, noise, and emissions. To meet these challenging goals, advanced propulsion concepts are being explored and current operating margins are being re-evaluated to find additional concessions that can be made. One advanced propulsion concept being evaluated is a geared turbofan with a variable area fan nozzle (VAFN), developed by NASA. This engine features a small core, a fan driven by the low pressure turbine through a reduction gearbox, and a shape memory alloy (SMA)-actuated VAFN. The VAFN is designed to allow both a small exit area for efficient operation at cruise, while being able to open wider at high power conditions to reduce backpressure on the fan and ensure a safe level of stall margin is maintained. The VAFN is actuated via a SMA-based system instead of a conventional system to decrease overall weight of the system, however, SMA-based actuators respond relatively slowly, which introduces dynamic issues that are investigated in this work. This paper describes both a control system designed specifically for issues associated with SMAs, and dynamic analysis of the geared turbofan VAFN with the SMA actuators. Also, some future recommendations are provided for this type of propulsion system.

  1. Fluid dynamics

    CERN Document Server

    Ruban, Anatoly I

    This is the first book in a four-part series designed to give a comprehensive and coherent description of Fluid Dynamics, starting with chapters on classical theory suitable for an introductory undergraduate lecture course, and then progressing through more advanced material up to the level of modern research in the field. The present Part 1 consists of four chapters. Chapter 1 begins with a discussion of Continuum Hypothesis, which is followed by an introduction to macroscopic functions, the velocity vector, pressure, density, and enthalpy. We then analyse the forces acting inside a fluid, and deduce the Navier-Stokes equations for incompressible and compressible fluids in Cartesian and curvilinear coordinates. In Chapter 2 we study the properties of a number of flows that are presented by the so-called exact solutions of the Navier-Stokes equations, including the Couette flow between two parallel plates, Hagen-Poiseuille flow through a pipe, and Karman flow above an infinite rotating disk. Chapter 3 is d...

  2. Dynamic Processes

    Science.gov (United States)

    Klingshirn, C.

    The purpose of this chapter is to present the results of the dynamics of exciton (polariton)s or more generally of electron-hole pairs. For a recent review of this topic concentrating on quantum wells, see Davies and Jagadish (Laser Photon. Rev. 3(1), 1(2008)). We neither consider the dynamics of carriers, for example, their relaxation time entering in Hall mobility or electrical conductivity, nor the dynamics of phonons or spins, respectively. We give here only a very small selection of references to these topics (Baxter and Schmuttenmaer, J. Phys. Chem. B, 110:25229, 2006; Queiroz et al. Superlattice Microstruct. 42:270, 2007; Niehaus and Schwarz, Superlattice Microstruct. 42:299, 2007; Lee et al., J. Appl. Phys. 93:4939, 2003; A. K Azad, J. Han, W. Zhang, Appl. Phys. Lett. 88:021103, 2006; Janssen et al., QELS 2008 IEEE 2; D. Lagarde et al., Phys. Stat. Sol. C 4:472, 2007; S. Gosh et al., Appl. Phys. Lett. 86:232507, 2005; W. K. Liu et al. Phys. Rev. Lett. 98:186804, 2007). The main characteristic time constants relevant to optical properties close to the fundamental absorption edge are the dephasing time T 2, (i.e. the time after which the polarization amplitude of the optically excited electron-hole pair loses the coherence with the driving light field), the intra band or inter sub band relaxation times T 3 (i.e. the time it takes for the electron-hole pairs to relax from their initial state of excitation to a certain other state e.g. to a thermal distribution with a temperature equal to or possibly still above lattice temperature) and finally the lifetime T 1 (i.e. the time until the electron-hole pairs recombine). The characteristic time constants T 2 and T 1 are also known as transverse and longitudinal relaxation times, respectively. Their inverses are the corresponding rate constants. T 2 is inversely proportional to the homogeneous width Γ, and T 1 includes both the radiative and the generally dominating non-radiative recombination (Hauser et al., Appl

  3. Internet dynamics

    Science.gov (United States)

    Lukose, Rajan Mathew

    The World Wide Web and the Internet are rapidly expanding spaces, of great economic and social significance, which offer an opportunity to study many phenomena, often previously inaccessible, on an unprecedented scale and resolution with relative ease. These phenomena are measurable on the scale of tens of millions of users and hundreds of millions of pages. By virtue of nearly complete electronic mediation, it is possible in principle to observe the time and ``spatial'' evolution of nearly all choices and interactions. This cyber-space therefore provides a view into a number of traditional research questions (from many academic disciplines) and creates its own new phenomena accessible for study. Despite its largely self-organized and dynamic nature, a number of robust quantitative regularities are found in the aggregate statistics of interesting and useful quantities. These regularities can be understood with the help of models that draw on ideas from statistical physics as well as other fields such as economics, psychology and decision theory. This thesis develops models that can account for regularities found in the statistics of Internet congestion and user surfing patterns and discusses some practical consequences. practical consequences.

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

    Energy Technology Data Exchange (ETDEWEB)

    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

  5. Void Dynamics

    Science.gov (United States)

    Padilla, Nelson D.; Paz, Dante; Lares, Marcelo; Ceccarelli, Laura; Lambas, Diego Garcí A.; Cai, Yan-Chuan; Li, Baojiu

    2016-10-01

    Cosmic voids are becoming key players in testing the physics of our Universe.Here we concentrate on the abundances and the dynamics of voids as these are among the best candidatesto provide information on cosmological parameters. Cai, Padilla & Li (2014)use the abundance of voids to tell apart Hu & Sawicki f(R) models from General Relativity. An interestingresult is that even though, as expected, voids in the dark matter field are emptier in f(R) gravity due to the fifth force expellingaway from the void centres, this result is reversed when haloes are used to find voids. The abundance of voids in this casebecomes even lower in f(R) compared to GR for large voids. Still, the differences are significant and thisprovides a way to tell apart these models. The velocity field differences between f(R) and GR, on the other hand, arethe same for halo voids and for dark matter voids.Paz et al. (2013), concentrate on the velocity profiles around voids. First they show the necessityof four parameters to describe the density profiles around voids given two distinct voidpopulations, voids-in-voids and voids-in-clouds. This profile is used to predict peculiar velocities around voids,and the combination of the latter with void density profiles allows the construction of modelvoid-galaxy cross-correlation functions with redshift space distortions. When these modelsare tuned to fit the measured correlation functions for voids and galaxies in the SloanDigital Sky Survey, small voids are found to be of the void-in-cloud type, whereas largerones are consistent with being void-in-void. This is a novel result that is obtaineddirectly from redshift space data around voids. These profiles can be used toremove systematics on void-galaxy Alcock-Pacinsky tests coming from redshift-space distortions.

  6. Coupled nonlinear aeroelasticity and flight dynamics of fully flexible aircraft

    Science.gov (United States)

    Su, Weihua

    of the framework. Gust responses of the Flying-Wing configuration subject to stall effects are investigated. A bilinear torsional stiffness model is introduced to study the skin wrinkling due to large bending curvature of the Flying-Wing. The numerical studies illustrate the improvements of the existing reduced-order formulation with new capabilities of both structural modeling and coupled aeroelastic and flight dynamic analysis of fully flexible aircraft.

  7. Tonala skillnader mellan ett tryckande stall och ett limmat stall. : -hos en bouzouki

    OpenAIRE

    Nordwall, Mats

    2006-01-01

    Summary I have a great interest in bouzoukis and since I, during my education in guitar making, mainly have focused on building bouzoukis and other traditional folk instruments, I have chosen the bouzouki as the object of my degree project. In connection to the making of these instruments, I started to consider the construction of the bouzouki and why the bouzouki has such a characteristic sound. One of my theories is based on the fact that most bouzoukis are made with floating bridges instea...

  8. Investigation of Rotating Stall Phenomena in Axial Flow Compressors. Volume I. Basic Studies of Rotating Stall

    Science.gov (United States)

    1976-06-01

    Hz at -800 screen rpm (26.7 Hz). Inspection of thc inlet dyna- mic pressure, q, , records at rotating sta.l inception shows that as negative screen...of tma .’nes% of these 4iszu~ancrei. - - -_ ~ I- S. . . .. In the following analysis, we will consider the response of the blade row to a distortion

  9. A novel approach to contrast-enhanced breast magnetic resonance imaging for screening: high-resolution ultrafast dynamic imaging.

    Science.gov (United States)

    Mann, Ritse M; Mus, Roel D; van Zelst, Jan; Geppert, Christian; Karssemeijer, Nico; Platel, Bram

    2014-09-01

    The use of breast magnetic resonance imaging (MRI) as screening tool has been stalled by high examination costs. Scan protocols have lengthened to optimize specificity. Modern view-sharing sequences now enable ultrafast dynamic whole-breast MRI, allowing much shorter and more cost-effective procedures. This study evaluates whether dynamic information from ultrafast breast MRI can be used to replace standard dynamic information to preserve accuracy. We interleaved 20 ultrafast time-resolved angiography with stochastic trajectory (TWIST) acquisitions (0.9 × 1 × 2.5 mm, temporal resolution, 4.3 seconds) during contrast inflow in a regular high-resolution dynamic MRI protocol. A total of 160 consecutive patients with 199 enhancing abnormalities (95 benign and 104 malignant) were included. The maximum slope of the relative enhancement versus time curve (MS) obtained from the TWIST and curve type obtained from the regular dynamic sequence as defined in the breast imaging reporting and data system (BIRADS) lexicon were recorded. Diagnostic performance was compared using receiver operating characteristic analysis. All lesions were visible on both the TWIST and standard series. Maximum slope allows discrimination between benign and malignant disease with high accuracy (area under the curve, 0.829). Types of MS were defined in analogy to BIRADS curve types: MS type 3 implies a high risk of malignancy (MS >13.3%/s; specificity, 85%), MS type 2 yields intermediate risk (MS 6.4%/s), and MS type 1 implies a low risk (MS BIRADS curve type analysis does (area under the curve, 0.812 vs 0.692; P = 0.0061). Ultrafast dynamic breast MRI allows detection of breast lesions and classification with high accuracy using MS. This allows substantial shortening of scan protocols and hence reduces imaging costs, which is beneficial especially for screening.

  10. Dynamical system synchronization

    CERN Document Server

    Luo, Albert C J

    2013-01-01

    Dynamical System Synchronization (DSS) meticulously presents for the first time the theory of dynamical systems synchronization based on the local singularity theory of discontinuous dynamical systems. The book details the sufficient and necessary conditions for dynamical systems synchronizations, through extensive mathematical expression. Techniques for engineering implementation of DSS are clearly presented compared with the existing techniques.  This book also:  Presents novel concepts and methods for dynamical system synchronization Extends beyond the Lyapunov theory for dynamical system synchronization Introduces companion and synchronization of discrete dynamical systems Includes local singularity theory for discontinuous dynamical systems Covers the invariant domains of synchronization Features more than 75 illustrations Dynamical System Synchronization is an ideal book for those interested in better understanding new concepts and methodology for dynamical system synchronization, local singularity...

  11. Fundamentals of structural dynamics

    CERN Document Server

    Craig, Roy R

    2006-01-01

    From theory and fundamentals to the latest advances in computational and experimental modal analysis, this is the definitive, updated reference on structural dynamics.This edition updates Professor Craig's classic introduction to structural dynamics, which has been an invaluable resource for practicing engineers and a textbook for undergraduate and graduate courses in vibrations and/or structural dynamics. Along with comprehensive coverage of structural dynamics fundamentals, finite-element-based computational methods, and dynamic testing methods, this Second Edition includes new and e

  12. OTTO MOTOR DYNAMICS

    OpenAIRE

    Petrescu, Florian Ion Tiberiu; Polytechnic University of Bucharest; Petrescu, Relly Victoria Virgil; Polytechnic University of Bucharest

    2016-01-01

    Otto engine dynamics are similar in almost all common internal combustion engines. We can speak so about dynamics of engines: Lenoir, Otto, and Diesel. The dynamic presented model is simple and original. The first thing necessary in the calculation of Otto engine dynamics, is to determine the inertial mass reduced at the piston. It uses then the Lagrange equation. The dynamic equation of motion of the piston, obtained by integrating the Lagrange equation, takes a new form. It presents a new r...

  13. Dynamical systems theory for music dynamics

    CERN Document Server

    Boon, J P

    1994-01-01

    Abstract:We show that, when music pieces are cast in the form of time series of pitch variations, the concepts and tools of dynamical systems theory can be applied to the analysis of {\\it temporal dynamics} in music. (i) Phase space portraits are constructed from the time series wherefrom the dimensionality is evaluated as a measure of the {\\pit global} dynamics of each piece. (ii) Spectral analysis of the time series yields power spectra (\\sim f^{-\

  14. Influence of Icing on the Modal Behavior of Wind Turbine Blades

    Directory of Open Access Journals (Sweden)

    Sudhakar Gantasala

    2016-10-01

    Full Text Available Wind turbines installed in cold climate sites accumulate ice on their structures. Icing of the rotor blades reduces turbine power output and increases loads, vibrations, noise, and safety risks due to the potential ice throw. Ice accumulation increases the mass distribution of the blade, while changes in the aerofoil shapes affect its aerodynamic behavior. Thus, the structural and aerodynamic changes due to icing affect the modal behavior of wind turbine blades. In this study, aeroelastic equations of the wind turbine blade vibrations are derived to analyze modal behavior of the Tjaereborg 2 MW wind turbine blade with ice. Structural vibrations of the blade are coupled with a Beddoes-Leishman unsteady attached flow aerodynamics model and the resulting aeroelastic equations are analyzed using the finite element method (FEM. A linearly increasing ice mass distribution is considered from the blade root to half-length and thereafter constant ice mass distribution to the blade tip, as defined by Germanischer Lloyd (GL for the certification of wind turbines. Both structural and aerodynamic properties of the iced blades are evaluated and used to determine their influence on aeroelastic natural frequencies and damping factors. Blade natural frequencies reduce with ice mass and the amount of reduction in frequencies depends on how the ice mass is distributed along the blade length; but the reduction in damping factors depends on the ice shape. The variations in the natural frequencies of the iced blades with wind velocities are negligible; however, the damping factors change with wind velocity and become negative at some wind velocities. This study shows that the aerodynamic changes in the iced blade can cause violent vibrations within the operating wind velocity range of this turbine.

  15. for hybrid dynamical systems

    Directory of Open Access Journals (Sweden)

    Wassim M. Haddad

    2001-01-01

    Full Text Available In this paper we develop a unified dynamical systems framework for a general class of systems possessing left-continuous flows; that is, left-continuous dynamical systems. These systems are shown to generalize virtually all existing notions of dynamical systems and include hybrid, impulsive, and switching dynamical systems as special cases. Furthermore, we generalize dissipativity, passivity, and nonexpansivity theory to left-continuous dynamical systems. Specifically, the classical concepts of system storage functions and supply rates are extended to left-continuous dynamical systems providing a generalized hybrid system energy interpretation in terms of stored energy, dissipated energy over the continuous-time dynamics, and dissipated energy over the resetting events. Finally, the generalized dissipativity notions are used to develop general stability criteria for feedback interconnections of left-continuous dynamical systems. These results generalize the positivity and small gain theorems to the case of left-continuous, hybrid, and impulsive dynamical systems.

  16. Transitory Control of the Aerodynamic Loads on an Airfoil in Dynamic Pitch and Plunge

    Science.gov (United States)

    Tan, Yuehan; Crittenden, Thomas; Glezer, Ari

    2016-11-01

    Transitory control and regulation of trapped vorticity concentrations are exploited in wind tunnel experiments for control of the aerodynamic loads on an airfoil moving in time-periodic 2-DOF (pitch and plunge) beyond the dynamic stall margin. Actuation is effected using a spanwise array of integrated miniature chemical (combustion based) high-impulse actuators that are triggered intermittently relative to the airfoil's motion. Each actuation pulse has sufficient control authority to alter the global aerodynamic performance throughout the motion cycle on a characteristic time scale that is an order of magnitude shorter than the airfoil's convective time scale. The effects of the actuation on the aerodynamic characteristics of the airfoil are assessed using time-dependent measurements of the lift force and pitching moment coupled with time-resolved particle image velocimetry that is acquired phased-locked to the motion of the airfoil. It is shown that the aerodynamic loads can be significantly altered using actuation programs based on multiple actuation pulses during the time-periodic pitch/plunge cycle. Superposition of such actuation programs leads to enhancement of cycle lift and pitch stability, and reduced cycle hysteresis and peak pitching moment. Supported by GT-VLRCOE.

  17. Dynamic Remodeling of the Magnetosome Membrane Is Triggered by the Initiation of Biomineralization

    Directory of Open Access Journals (Sweden)

    Elias Cornejo

    2016-02-01

    Full Text Available Magnetotactic bacteria produce chains of membrane-bound organelles that direct the biomineralization of magnetic nanoparticles. These magnetosome compartments are a model for studying the biogenesis and subcellular organization of bacterial organelles. Previous studies have suggested that discrete gene products build and assemble magnetosomes in a stepwise fashion. Here, using an inducible system, we show that the stages of magnetosome formation are highly dynamic and interconnected. During de novo formation, magnetosomes first organize into discontinuous chain fragments that are subsequently connected by the bacterial actin-like protein MamK. We also find that magnetosome membranes are not uniform in size and can grow in a biomineralization-dependent manner. In the absence of biomineralization, magnetosome membranes stall at a diameter of ~50 nm. Those that have initiated biomineralization then expand to significantly larger sizes and accommodate mature magnetic particles. We speculate that such a biomineralization-dependent checkpoint for membrane growth establishes the appropriate conditions within the magnetosome to ensure successful nucleation and growth of magnetic particles.

  18. Cell cycle coordination and regulation of bacterial chromosome segregation dynamics by polarly localized proteins.

    Science.gov (United States)

    Schofield, Whitman B; Lim, Hoong Chuin; Jacobs-Wagner, Christine

    2010-09-15

    What regulates chromosome segregation dynamics in bacteria is largely unknown. Here, we show in Caulobacter crescentus that the polarity factor TipN regulates the directional motion and overall translocation speed of the parS/ParB partition complex by interacting with ParA at the new pole. In the absence of TipN, ParA structures can regenerate behind the partition complex, leading to stalls and back-and-forth motions of parS/ParB, reminiscent of plasmid behaviour. This extrinsic regulation of the parS/ParB/ParA system directly affects not only division site selection, but also cell growth. Other mechanisms, including the pole-organizing protein PopZ, compensate for the defect in segregation regulation in ΔtipN cells. Accordingly, synthetic lethality of PopZ and TipN is caused by severe chromosome segregation and cell division defects. Our data suggest a mechanistic framework for adapting a self-organizing oscillator to create motion suitable for chromosome segregation.

  19. The force generated by biological membranes on a polymer rod and its response: Statics and dynamics

    Science.gov (United States)

    Daniels, D. R.; Turner, M. S.

    2004-10-01

    We propose a theory for the force exerted by a fluctuating membrane on a polymer rod tip. Using statistical mechanical methods, the expression for the generated force is written in terms of the distance of the rod tip from the membrane "frame." We apply the theory in calculating the stall force and membrane displacement required to cease the growth of a growing fiber induced by membrane fluctuations, as well as the membrane force and membrane displacement required for rod/fiber buckling. We also consider the dynamics of a growing fiber tip under the influence of a fluctuation-induced membrane force. We discuss the importance of our results in various biological contexts. Finally, we present a method to simultaneously extract both the rigidity of the semiflexible rod and the force applied by, e.g., the membrane from the measurements of the bending fluctuations of the rod. Such a measurement of the force would give information about the thermodynamics of the rod polymerization that involves the usual Brownian ratchet mechanism.

  20. A dynamic wall model for Large-Eddy simulations of wind turbine dedicated airfoils

    Science.gov (United States)

    J, Calafell; O, Lehmkuhl; A, Carmona; D, Pérez-Segarra C.; A, Oliva

    2014-06-01

    This work aims at modelling the flow behavior past a wind turbine dedicated airfoil at high Reynolds number and large angle of attack (AoA). The DU-93-W-210 airfoil has been selected. To do this, Large Eddy Simulations (LES) have been performed. Momentum equations have been solved with a parallel unstructured symmetry preserving formulation while the wall-adapting local-eddy viscosity model within a variational multi-scale framework (VMS- WALE) is used as the subgrid-scales model. Since LES calculations are still very expensive at high Reynolds Number, specially at the near-wall region, a dynamic wall model has been implemented in order to overcome this limitation. The model has been validated with a very unresolved Channel Flow case at Reτ = 2000. Afterwards, the model is also tested with the Ahmed Car case, that from the flow physics point of view is more similar to an stalled airfoil than the Channel Flow is, including flow features as boundary layer detachment and recirculations. This case has been selected because experimental results of mean velocity profiles are available. Finally, a flow around a DU-93-W-210 airfoil is computed at Re = 3 x 106 and with an AoA of 15°. Numerical results are presented in comparison with Direct Numerical Simulation (DNS) or experimental data for all cases.

  1. Vibro-impact dynamics

    CERN Document Server

    Luo, Albert C J

    2012-01-01

    Presents a systematic view of vibro-impact dynamics based on the nonlinear dynamics analysis Comprehensive understanding of any vibro-impact system is critically impeded by the lack of analytical tools viable for properly characterizing grazing bifurcation. The authors establish vibro-impact dynamics as a subset of the theory of discontinuous systems, thus enabling all vibro-impact systems to be explored and characterized for applications.  Vibro-impact Dynamics presents an original theoretical way of analyzing the behavior of vibro-impact dynamics that can be extended to discontinuous dynamic

  2. Dynamic statistical information theory

    Institute of Scientific and Technical Information of China (English)

    XING; Xiusan

    2006-01-01

    In recent years we extended Shannon static statistical information theory to dynamic processes and established a Shannon dynamic statistical information theory, whose core is the evolution law of dynamic entropy and dynamic information. We also proposed a corresponding Boltzmman dynamic statistical information theory. Based on the fact that the state variable evolution equation of respective dynamic systems, i.e. Fokker-Planck equation and Liouville diffusion equation can be regarded as their information symbol evolution equation, we derived the nonlinear evolution equations of Shannon dynamic entropy density and dynamic information density and the nonlinear evolution equations of Boltzmann dynamic entropy density and dynamic information density, that describe respectively the evolution law of dynamic entropy and dynamic information. The evolution equations of these two kinds of dynamic entropies and dynamic informations show in unison that the time rate of change of dynamic entropy densities is caused by their drift, diffusion and production in state variable space inside the systems and coordinate space in the transmission processes; and that the time rate of change of dynamic information densities originates from their drift, diffusion and dissipation in state variable space inside the systems and coordinate space in the transmission processes. Entropy and information have been combined with the state and its law of motion of the systems. Furthermore we presented the formulas of two kinds of entropy production rates and information dissipation rates, the expressions of two kinds of drift information flows and diffusion information flows. We proved that two kinds of information dissipation rates (or the decrease rates of the total information) were equal to their corresponding entropy production rates (or the increase rates of the total entropy) in the same dynamic system. We obtained the formulas of two kinds of dynamic mutual informations and dynamic channel

  3. Solar Dynamics Observatory

    Data.gov (United States)

    National Aeronautics and Space Administration — A searchable database of all Solar Dynamics Observatory data including EUV, magnetograms, visible light and X-ray. SDO: The Solar Dynamics Observatory is the first...

  4. Dynamic Interactive Learning Systems

    Science.gov (United States)

    Sabry, Khaled; Barker, Jeff

    2009-01-01

    This paper reviews and discusses the notions of interactivity and dynamicity of learning systems in relation to information technologies and design principles that can contribute to interactive and dynamic learning. It explores the concept of dynamic interactive learning systems based on the emerging generation of information as part of a…

  5. Intramolecular and nonlinear dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Davis, M.J. [Argonne National Laboratory, IL (United States)

    1993-12-01

    Research in this program focuses on three interconnected areas. The first involves the study of intramolecular dynamics, particularly of highly excited systems. The second area involves the use of nonlinear dynamics as a tool for the study of molecular dynamics and complex kinetics. The third area is the study of the classical/quantum correspondence for highly excited systems, particularly systems exhibiting classical chaos.

  6. Dynamics of Carroll particles

    NARCIS (Netherlands)

    Bergshoeff, Eric; Gomis, Joaquim; Longhi, Giorgio

    2014-01-01

    We investigate particles whose dynamics are invariant under the Carroll group. Although a single, free such Carroll particle has no non-trivial dynamics (the Carroll particle does not move), we show that non-trivial dynamics exists for a set of interacting Carroll particles. Furthermore, we gauge th

  7. The dynamics of scaffolding

    NARCIS (Netherlands)

    Van Geert, P. L. C.; Steenbeek, H.W.

    2005-01-01

    In this article we have reinterpreted a relatively standard definition of scaffolding in the context of dynamic systems theory. Our main point is that scaffolding cannot be understood outside the context of a dynamic approach of learning and (formal or informal) teaching. We provide a dynamic system

  8. Dynamics at Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Sylvia Ceyer, Nancy Ryan Gray

    2010-05-04

    The 2009 Gordon Conference on Dynamics at Surfaces is the 30th anniversary of a meeting held every two years that is attended by leading researchers in the area of experimental and theoretical dynamics at liquid and solid surfaces. The conference focuses on the dynamics of the interaction of molecules with either liquid or solid surfaces, the dynamics of the outermost layer of liquid and solid surfaces and the dynamics at the liquid-solid interface. Specific topics that are featured include state-to-state dynamics, non-adiabatic interactions in molecule-metal systems, photon induced desorption from semiconductor and metal surfaces, ultrafast x-ray and electron diffraction as probes of the dynamics of ablation, ultrafast vibrational spectroscopy of water surface dynamics, dynamics of a single adsorbate, growth at nano-scale mineral surfaces, dynamics of atom recombination on interstellar dust grains and the dynamics of the interaction of water with lipid bilayers. The conference brings together investigators from a variety of scientific disciplines including chemistry, physics, materials science, geology and biophysics.

  9. Variable Dynamic Testbed Vehicle: Dynamics Analysis

    Science.gov (United States)

    Lee, A. Y.; Le, N. T.; Marriott, A. T.

    1997-01-01

    The Variable Dynamic Testbed Vehicle (VDTV) concept has been proposed as a tool to evaluate collision avoidance systems and to perform driving-related human factors research. The goal of this study is to analytically investigate to what extent a VDTV with adjustable front and rear anti-roll bar stiffnesses, programmable damping rates, and four-wheel-steering can emulate the lateral dynamics of a broad range of passenger vehicles.

  10. Complexity and Dynamical Depth

    Directory of Open Access Journals (Sweden)

    Terrence Deacon

    2014-07-01

    Full Text Available We argue that a critical difference distinguishing machines from organisms and computers from brains is not complexity in a structural sense, but a difference in dynamical organization that is not well accounted for by current complexity measures. We propose a measure of the complexity of a system that is largely orthogonal to computational, information theoretic, or thermodynamic conceptions of structural complexity. What we call a system’s dynamical depth is a separate dimension of system complexity that measures the degree to which it exhibits discrete levels of nonlinear dynamical organization in which successive levels are distinguished by local entropy reduction and constraint generation. A system with greater dynamical depth than another consists of a greater number of such nested dynamical levels. Thus, a mechanical or linear thermodynamic system has less dynamical depth than an inorganic self-organized system, which has less dynamical depth than a living system. Including an assessment of dynamical depth can provide a more precise and systematic account of the fundamental difference between inorganic systems (low dynamical depth and living systems (high dynamical depth, irrespective of the number of their parts and the causal relations between them.

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

    Energy Technology Data Exchange (ETDEWEB)

    Hansen, A.C.; Jauch, C.; Soerensen, P.; Iov, F.; Blaabjerg, F.

    2003-12-01

    The present report describes the dynamic wind turbine models implemented in the power system simulation tool DIgSILENT (Version 12.0). The developed models are a part of the results of a national research project, whose overall objective is to create a model database in different simulation tools. This model database should be 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 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. However, the main attention in this report is drawn to the modelling at the system level of two wind turbine concepts: 1. Active stall wind turbine with induction generator 2. Variable speed, variable pitch wind turbine with doubly fed induction generator. 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. For both these two concepts, control strategies are developed and implemented, their performance assessed and discussed by means of simulations. (au)

  12. Synchronization dynamics of two different dynamical systems

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Albert C.J., E-mail: aluo@siue.edu [Department of Mechanical and Industrial Engineering, Southern Illinois University Edwardsville, Edwardsville, IL 62026-1805 (United States); Min Fuhong [Department of Mechanical and Industrial Engineering, Southern Illinois University Edwardsville, Edwardsville, IL 62026-1805 (United States)

    2011-06-15

    Highlights: > Synchronization dynamics of two distinct dynamical systems. > Synchronization, de-synchronization and instantaneous synchronization. > A controlled pendulum synchronizing with the Duffing oscillator. > Synchronization invariant set. > Synchronization parameter map. - Abstract: In this paper, synchronization dynamics of two different dynamical systems is investigated through the theory of discontinuous dynamical systems. The necessary and sufficient conditions for the synchronization, de-synchronization and instantaneous synchronization (penetration or grazing) are presented. Using such a synchronization theory, the synchronization of a controlled pendulum with the Duffing oscillator is systematically discussed as a sampled problem, and the corresponding analytical conditions for the synchronization are presented. The synchronization parameter study is carried out for a better understanding of synchronization characteristics of the controlled pendulum and the Duffing oscillator. Finally, the partial and full synchronizations of the controlled pendulum with periodic and chaotic motions are presented to illustrate the analytical conditions. The synchronization of the Duffing oscillator and pendulum are investigated in order to show the usefulness and efficiency of the methodology in this paper. The synchronization invariant domain is obtained. The technique presented in this paper should have a wide spectrum of applications in engineering. For example, this technique can be applied to the maneuvering target tracking, and the others.

  13. Multiscale Gentlest Ascent Dynamics

    CERN Document Server

    Zhou, Xiang

    2016-01-01

    The gentlest ascent dynamics (E and Zhou in {\\it Nonlinearity} vol 24, p1831, 2011) locally converges to a nearby saddle point with one dimensional unstable manifold. Here we present a multiscale gentlest ascent dynamics for stochastic slow-fast systems in order to compute saddle point associated with the effective dynamics of the slow variable. Such saddle points, as the candidates of transition states, are important in non-equilibrium transitions for the coarse-grained slow variables; they are also helpful to explore free energy surface. We derive the expressions of the gentlest ascent dynamics for the averaged system, and propose the multiscale numerical methods to efficiently solve the multiscale gentlest ascent dynamics for search of saddle point. The examples of stochastic ordinary and partial differential equations are presented to illustrate the performance of this multiscale gentlest ascent dynamics.

  14. Dynamics of Media Attention

    CERN Document Server

    Traag, V A; Hicks, J; van Klinken, G

    2014-01-01

    Studies of human attention dynamics analyses how attention is focused on specific topics, issues or people. In online social media, there are clear signs of exogenous shocks, bursty dynamics, and an exponential or powerlaw lifetime distribution. We here analyse the attention dynamics of traditional media, focussing on co-occurrence of people in newspaper articles. The results are quite different from online social networks and attention. Different regimes seem to be operating at two different time scales. At short time scales we see evidence of bursty dynamics and fast decaying edge lifetimes and attention. This behaviour disappears for longer time scales, and in that regime we find Poissonian dynamics and slower decaying lifetimes. We propose that a cascading Poisson process may take place, with issues arising at a constant rate over a long time scale, and faster dynamics at a shorter time scale.

  15. Dynamic Boiler Performance

    DEFF Research Database (Denmark)

    Sørensen, Kim

    Traditionally, boilers have been designed mainly focussing on the static operation of the plant. The dynamic capability has been given lower priority and the analysis has typically been limited to assuring that the plant was not over-stressed due to large temperature gradients. New possibilities...... for buying and selling energy has increased the focus on the dynamic operation capability, efciency, emissions etc. For optimizing the design of boilers for dynamic operation a quantication of the dynamic capability is needed. A framework for optimizing design of boilers for dynamic operation has been...... developed. Analyzing boilers for dynamic operation gives rise to a number of opposing aims: shrinking and swelling, steam quality, stress levels, control system/philosophy, pressurization etc. Common for these opposing aims is that an optimum can be found for selected operation conditions. The framework has...

  16. Dynamic Capabilities and Performance

    DEFF Research Database (Denmark)

    Wilden, Ralf; Gudergan, Siegfried P.; Nielsen, Bo Bernhard

    2013-01-01

    Dynamic capabilities are widely considered to incorporate those processes that enable organizations to sustain superior performance over time. In this paper, we argue theoretically and demonstrate empirically that these effects are contingent on organizational structure and the competitive...... are contingent on the competitive intensity faced by firms. Our findings demonstrate the performance effects of internal alignment between organizational structure and dynamic capabilities, as well as the external fit of dynamic capabilities with competitive intensity. We outline the advantages of PLS...

  17. Dynamical Constraints on Exoplanets

    CERN Document Server

    Horner, Jonti; Tinney, Chris; Hinse, Tobias C; Marshall, Jonathan P

    2013-01-01

    Dynamical studies of new exoplanet systems are a critical component of the discovery and characterisation process. Such studies can provide firmer constraints on the parameters of the newly discovered planets, and may even reveal that the proposed planets do not stand up to dynamical scrutiny. Here, we demonstrate how dynamical studies can assist the characterisation of such systems through two examples: QS Virginis and HD 73526.

  18. ON NONDETERMINISTIC DYNAMIC PROGRAMMING

    OpenAIRE

    2008-01-01

    R. Bellman left a lot of research problems in his work “Dynamic Programming" (1957). Having received ideas from Bellman, S. Iwamoto has extracted, out of his problems, a problem on nondeterministic dynamic programming (NDP). Instead of stochastic dynamic programming which has been well studied, Iwamoto has opened a gate to NDP. This report presents speci_c optimal solutions for NDPs on continuous state and decision spaces.

  19. Dynamical Systems Conference

    CERN Document Server

    Gils, S; Hoveijn, I; Takens, F; Nonlinear Dynamical Systems and Chaos

    1996-01-01

    Symmetries in dynamical systems, "KAM theory and other perturbation theories", "Infinite dimensional systems", "Time series analysis" and "Numerical continuation and bifurcation analysis" were the main topics of the December 1995 Dynamical Systems Conference held in Groningen in honour of Johann Bernoulli. They now form the core of this work which seeks to present the state of the art in various branches of the theory of dynamical systems. A number of articles have a survey character whereas others deal with recent results in current research. It contains interesting material for all members of the dynamical systems community, ranging from geometric and analytic aspects from a mathematical point of view to applications in various sciences.

  20. Dynamics of machinery

    CERN Document Server

    Dresig, Hans

    2010-01-01

    Dynamic loads and disturbing oscillations increase with higher speed of the machines and more lightweight constructions. Industrial safety standards require better oscillation reduction and noise control. The book by Dresig/Holzweissig deals with these topics. It presents the classical areas of modeling, dynamics of rigid bodies, balancing, torsional and bending vibrations, problems of vibration isolation and the dynamic behavior of complex vibrating systems. Typical dynamic effects, i.e., the gyroscopic effect, the damping of oscillations, resonances of k-th order, subharmonic and nonlinear f