Wind Asymmetry Research Articles

3D wind observations with a compact mobile lidar based on tropo- and stratospheric aerosol backscatter

Abstract. We present the first measurements of simultaneous horizontal and vertical winds using a new lidar system developed at the Leibniz Institute of Atmospheric Physics in Kühlungsborn, Germany (54.12° N, 11.77° E), for the concept of Vertical And Horizontal COverage by LIdars (VAHCOLI). We describe the technical details of a multi-field-of-view (MFOV) upgrade, which allows the measurement of wind dynamics in the transition region from microscale to mesoscale (103–104 m). The method was applied at the edge of a developing high-pressure region, covering altitudes between 3 and 25 km. Comparisons between the lidar measurements and data from the European Centre for Medium-Range Weather Forecasts (ECMWF) show excellent agreement for the meridional wind component along the north beam of the lidar, which is better than 0.30±0.33 m s−1, while along the south beam, a higher deviation with -0.93±0.73 m s−1 is observed. Measurements of vertical wind show a significant underestimation of this component by ECMWF. Comparison of Aeolus winds to the lidar winds projected to the Aeolus viewing direction shows good agreement, with results better than -0.12±3.31 m s−1. The capability of the MFOV lidar to explore small-scale asymmetries in the wind field is shown by a comparison of the north and south field of view, where we observe a wind asymmetry in the meridional winds, which is also present in ECMWF but underestimated by a factor of approximately 4.

Modulation of tropical cyclone rapid intensification by mesoscale asymmetries

AbstractComputer model simulations are one of the most important tools in current use for understanding tropical cyclone (TC) formation and rapid intensification (RI). These include “idealized” simulations in which a TC‐like vortex is placed in a hypothetical environment with predefined sea surface temperature and vertical profiles of temperature, humidity, and wind that are either constant or slowly varying across a large domain. The vast majority of such simulations begin with a perfectly circular vortex as the precursor to a TC. However, most real TCs form or intensify while interacting with asymmetric wind fields either within or external to the vortex circulation. This study introduces a method to initialize idealized TC simulations with asymmetries, and investigates the extent to which such asymmetries might delay RI in favorable environments. It is shown that mesoscale asymmetries can delay RI and reduce the fastest rates of intensification, and that these effects are statistically significantly increased when relatively low values of vertical shear of the horizontal wind are present. In some cases the asymmetries tilt the vortex directly through advection. In other cases, the wind asymmetries increase the disorganization of the convection or increase the size of the inner‐core wind field, and thus make the weaker TC more susceptible to environmental wind shear. The results suggest that mesoscale asymmetries of the wind field could be useful predictors for delay of RI in otherwise favorable environments.

Speckle imaging of γ2 Velorum: the inner wind possibly resolved

ABSTRACT Accurately quantifying the rates dM/dt at which massive stars lose mass is essential to any understanding of their evolution. All dM/dt estimates to date assume wind clumping factors; not allowing for clumping leads to overestimates of dM/dt and underestimates of lifetimes and masses when these stars explode as supernovae. Mid-infrared spectroscopy suggested that the wind of the nearest Wolf–Rayet (WR) star, γ2 Vel, is resolved with a full width at 10 per cent intensity of 0.5 arcsec, or 171 au at the 342 pc distance of the star. As the Zorro speckle imager on Gemini South is capable of ∼0.02 arcsec resolution, we have used it to image γ2 Vel at two orbital phases (0.30 and 0.44) with two narrow-band and two intermediate-band filters in an attempt to resolve its wind. Our observations demonstrate that γ2 Vel’s wind may be resolved as a ∼0.07 arcsec westward elongation through an 832 nm filter at orbital phase 0.3. If confirmed, this is the smallest scale (∼24 au) at which a WR star wind asymmetry has been directly imaged. Similar imaging at multiple phases is needed to determine if the asymmetry is due to stochastic wind clumping, co-rotating interaction regions or colliding-wind, cone-shaped shocks.

Geomagnetic activity dependence and dawn-dusk asymmetry of thermospheric winds from 9-year measurements with a Fabry–Perot interferometer in Tromsø, Norway

Ion drag associated with the ionospheric plasma convection plays an important role in the high-latitude thermospheric dynamics, yet changes in the thermospheric wind with geomagnetic activity are not fully understood. We performed a statistical analysis of the thermospheric wind measurements with a Fabry–Perot interferometer (FPI; 630 nm wavelength) in Tromsø, Norway, in the winter months for 9 years. The measurements were sorted by a SuperMAG (SME) index, and a quiet-time wind pattern was defined as an hourly mean under SME ≤ 40 nT. The quiet-time wind pattern can be expected to be represented by a pressure gradient associated with the solar radiation and a geostrophic force balance. With an increase in the geomagnetic activity level, the thermospheric wind turned over from eastward to westward at dusk and increased the equatorward magnitude from midnight to dawn. Deviations from the quiet-time wind presented similar patterns in the direction with the ionospheric plasma convection but were larger in magnitude at dusk than at dawn. This is the first study to report a dawn-dusk asymmetry of the thermospheric wind acceleration feature and signatures of the eastward wind acceleration at dawn by ion drag.Graphical

A Simple Modified Deadbeat Direct Thrust Control for Permanent Magnet Linear Synchronous Machine Considering Parameter Asymmetry

Permanent magnet linear synchronous machine (PMLSM) has the inherent drawbacks of end effect which would cause phase winding asymmetry, viz., electromagnetic parameter asymmetry (EMPA). In order to achieve fast and precise thrust response, traditional deadbeat direct thrust control (DB-DTC) is suitable for PMLSM, however it cannot be directly applied to PMLSM since it is constructed based on symmetrical machine mathematical model. Moreover, if EMPA is considered in traditional DB-DTC strategy, it is hard to calculate the required change of load angle since the primary flux linkage should be kept constant, especially when the salient-pole effect exists. Based on this, this paper proposed a simple modified DB-DTC strategy for a salient-pole PMLSM considering EMPA. Firstly, the mathematical model with and without considering asymmetrical inductance are derived. Then the influence of EMPA on traditional deadbeat direct thrust control (DB-DTC) is fully investigated. In order to compensate the effect of EMPA, this paper proposes a simple modified DB-DTC by compensating the error in both prediction and deadbeat control processes. Finally, the prototype experiments are carried out to validate the proposed control strategy. The results show that the phase current unbalance that caused by EMPA is largely suppressed controlled with the proposed control strategy. Moreover, both good steady and transient performances can be obtained compared with traditional DB-DTC strategy. The effectiveness of the proposed control strategy is validated.

Operational Diagnostics System for Asymmetric Emergency Modes in Traction Drives with Direct Torque Control

This article presents an analysis of the causes behind the development of asymmetric modes in a traction drive system that features direct torque control (DTC) of a rolling stock with asynchronous traction motors. The development of asymmetric modes in the traction drive system was found to be caused by the asymmetry of the supply voltage system, the asymmetry of the traction motor windings, and transient processes triggered by a change in the inverter supply voltage and variation in the traction motor load. At the same time, the asymmetric modes caused by the asymmetry of the feed voltage system and the windings of the traction motor are the emergency modes. The influence of the asymmetry of the feed voltage system and asymmetry of the windings of traction motor on the starting characteristics of the phase currents and flux linkages of the stator in the steady-state mode was investigated. In these cases, the ratio of the amplitudes of phase currents and flux linkages of the stator of different phases was found to be constant. The effect of a variation in the feed voltage and load acting on the motor shaft on the starting characteristics of phase currents and flux linkages of the stator was investigated in the case of absence of the emergency modes. In these cases, the ratio of the amplitudes of phase currents and flux linkages of the stator of different phases was found to not be constant. The amplitudes of the phase current and stator flux linkage were proposed as criteria for diagnosis and identification of asymmetric emergency modes. An algorithm and a structural scheme have been proposed for the diagnosis of emergency asymmetric modes in the traction drive system with direct torque control. Modifications to the traction drive system with direct torque control are suggested in order to diagnose the presence of faulty asymmetric modes and identify the damaged traction drive element.

Revisiting the Cox and Munk wave-slope statistics using IASI observations of the sea surface

We use radiances collected from space by the Infrared Atmospheric Sounder Interferometer (IASI) when looking down at ocean surfaces during the day to remotely determine the probability distribution of wave slopes. This is achieved by using about 300 channels between 3.6 and 4.0μm and a physically-based approach which properly takes the contribution of the reflected solar radiation into account. Based on about 150 millions observations, the same number of wave-slope probabilities are retrieved for wind speeds (at 10 m) up to 15 m/s. We revisit and discuss the methodology proposed by Cox and Munk (CM) to derive their celebrated wave-slope probability distribution function (pdf) from photographs of the sun glitter. We propose an original and robust approach for accurate retrievals of the 7 parameters appearing in the Gram–Charlier representation of the pdf. Our results for the mean square slopes (MSSs) are fully compatible with those of CM, and with the more recent results by Bréon and Henriot, but our lower uncertainties enable to point out departures from the linear wind-speed dependencies and a slight overestimation of the upwind MSS described by the linear fit of CM at moderate wind speed. Our skewness and kurtosis coefficients show clear influences of the wind speed, with a steady decrease of the former and the alongwind kurtosis coefficient being maximal at moderate wind speeds, features that CM could not point out due to the limitations of their measurements. We revisit the renormalization procedure employed by CM to obtain the complete variances from truncated pdfs and show that it imposes stringent conditions on the kurtosis coefficients that allow to determine them accurately, with wind-dependent values specific to the local sea state. We also provide measurements of the shifted position of the most probable slope as well as a demonstration of a qualitative change of regime in the updown wind asymmetry of the wave-slope probability when the wind speed increases.

Simulation of transients in an autonomous power system considering the generator and transformer magnetic core saturation

The paper considers transients in an autonomous power system consisting of a generator, a transformer, and a general load. The numerical method for simulating transients includes the possibility of the asymmetry of stator windings and magnetic core saturation of a generator and a transformer. The asymmetry is usually observed under synchronous machine faults such as turn-to-turn short circuits in the stator winding. The method is based on the solution of differential equations for the equilibrium of electromotive force and voltage drops in windings in phase coordinates in combination with the rotor rotation equation. In this case, a circuit of each phase stator winding is described by an equation that considers the difference in phase parameters. The mathematical model is developed in MATLAB. The model includes an unequal number of turns in phase windings that allows simulating the turn-to-turn short circuits without considering the occurrence of additional short-circuited circuits. The analysis of simulation results was performed under no-load operating conditions and in the presence of load. The obtained results demonstrated the influence of the saturation of magnetic systems on the parameters of normal and abnormal operating conditions in the power system.

Investigation of Tropical Cyclone Wind Models With Application to Storm Tide Simulations

AbstractThe hazards induced by tropical cyclones (TCs), for example, high winds, extreme precipitation, and storm tides, are closely related to the TC surface wind field. Parametric models for TC surface wind distribution have been widely used for hazards and risk analysis due to their simplicity and efficiency in application. Here we revisit the parametric modeling of TC wind fields, including the symmetrical and asymmetrical components, and its applications in storm tide modeling in the North Atlantic. The asymmetrical wind field has been related to TC motion and vertical wind shear; however, we find that a simple and empirical background‐wind model, based solely on a rotation and scaling of the TC motion vector, can largely capture the observed surface wind asymmetry. The implicit inclusion of the wind shear effect can be understood with the climatological relationship between the general TC motion and wind shear directions during hurricane seasons. For the symmetric wind field, the widely used Holland wind profile is chosen as a benchmark model, and we find that a physics‐based complete wind profile model connecting the inner core and outer region performs superiorly compared to a wind analysis data set. When used as wind forcing for storm tide simulations, the physics‐based complete wind profile integrated with the background‐wind asymmetry model can reproduce the observed storm tides with lower errors than the often‐used Holland model coupled with a translation‐speed‐based method.

Tracking of High-Order Stray-Flux Harmonics Under Starting for the Detection of Winding Asymmetries in Wound-Rotor Induction Motors

Wound rotor induction motors (WRIM) are widely used in a vast number of high output power industrial applications due to their capability of reaching high start torques while maintaining low inrush currents. Nonetheless, these machines are very prone to require early maintenance, and the possibility of presenting rotor winding asymmetry failures is high due to their more complex rotor circuit. Although some recent works have proposed techniques that overcome the drawbacks of conventional methods, an additional research effort for the development of alternative approaches able to enhance their performance and reliability is desirable. In this work, a new method for the diagnosis of rotor asymmetries in WRIM is presented. The proposed methodology is based on a feed-forward neural network fed by suitable fault severity indicators, which rely on the maximum energy density of higher order harmonics (amplified by the failure) at strategic regions of the time-frequency maps obtained from stray flux signals under startup transient. Experimental results for three different levels of rotor asymmetries in a 11-KW WRIM prove the reliability of the enhanced proposed system in comparison to conventional approaches that only rely on the main sideband fault-harmonic amplitudes.

Simple hurricane model: asymmetry and dynamics

In recent decades, the development of several products and hurricane-related models has attempted to predict the dynamic conditions of these systems and regions beyond they can impact. Thus, this article presents a parametric model to describe wind asymmetry in these systems. For this, the analysis of this model was applied in Hurricane Ike, which occurred in September 2008. In this model, the tangential wind field above the boundary layer was considered in balance with the thermal wind. It was possible to identify that as Hurricane Ike evolves, tangential velocity also evolves. Thus, there was a change in static, baroclinic, and inertial stability. An exponential radial reduction was included for maximum speed, and, therefore, the maximum winds always to the right of the hurricane displacement were identified. In addition, pumping near the surface had an influx into this system induced caused by drag between the air and the surface.

Method for Determining the Degree of Damage to the Stator Windings of an Induction Electric Motor with an Asymmetric Power System

A method is proposed for determining the number of damaged stator windings in the presence of an asymmetric power supply system for an induction electric motor based on the Park vector hodograph. As a result of the experiments on the simulation model, it was found that with the symmetry of the system of supply voltages and stator windings, the hodograph of the Park vector describes a circle; in all other cases it is an ellipse. It has been established that the presence of asymmetry in the supply voltage system is indicated by the angle of inclination of the ellipse, and the indicator of the presence of the asymmetry of the stator windings is the angle of ellipticity. In order to identify the presence of asymmetry of the stator windings in the conditions of asymmetry of the supply voltage system, an algorithm for recalculating the ellipse parameters for the condition of the symmetry of the supply voltage system was proposed. Recalculation errors did not exceed 6%. It has been established that the dependence of the increment of the amplitudes of the phase and angles of the phase currents of the stator on the number of damaged turns of the stator winding is linear. Based on this fact, an algorithm for determining the number of damaged turns was proposed. The results of this work can be used to build systems for diagnosing the interturn short circuit of the stator of an induction electric motor built into the drive.

Aircraft and Satellite Observations of Vortex Evolution and Surface Wind Asymmetry of Concentric Eyewalls in Hurricane Irma

We compare the vortex evolutions of eyewall replacement cycles (ERCs) between the sea-surface and the free-atmosphere levels and investigate the asymmetric structure of concentric eyewalls (CEs) by examining a combination of aircraft observations and surface wind fields derived from C-band spaceborne synthetic aperture radar (SAR) images during Hurricane Irma (2017) from 4 September 2017 to 8 September 2017. A total of 116 radial wind profiles measured by an aircraft were collected and showed that ERCs occur at both the sea-surface and the free-atmosphere levels. The outer eyewall was shown to form at the free atmospheric level (~3 km) with a narrow structure at the sea-surface level and an outward tilt with height in the cross-section. In our study, four ERC events were determined from wind profile parameters fitted by a modified Rankine vortex model, which was validated by 328 radial legs collected from six hurricanes. The outer eyewall did not replace the inner eyewall at the sea-surface level in the third ERC, due to the maintenance of a short duration and intense original eyewall. Additionally, Irma’s intensity weakened during the fourth ERC rather than re-intensified, because of the generation of a third wind maximum outside the secondary eyewall. Comparisons of five SAR-derived surface wind fields in Irma and another two hurricane cases illustrated that the location of the secondary eyewall generation is a key point in the interpretation of anomaly intensity changes in the fourth ERC.

A Numerical Study for Tropical Cyclone Atsani (2020) Past Offshore of Southern Taiwan under Topographic Influences

Tropical Cyclone Atsani occurred in late October 2020 and moved westward offshore south of Taiwan. During its offshore passage, the cyclone deflects northward as it closes to the southern end of Taiwan. A global model MPAS at a multi-resolution of 60-15-3-km is applied to explore the track responses of Atsani and identify the topographic effects of the Central Mountain Range (CMR) on the cyclone circulation and the associated track deflection. With a 3-km resolution targeted at the Taiwan area, the cyclone track deflection can be reasonably simulated, with more sensitivity to physics schemes and dynamic vortex initialization and less sensitivity to initial environmental perturbations. When the Taiwan terrain is removed, the cyclone indeed deflects more northward earlier, in particular for simulations with a stronger cyclone that tends to generate stronger east-west wind asymmetry in the absence of the terrain. Idealized simulations with a regional model WRF at 3-km resolution are also utilized to contrast the track deflection of different departing cyclones, similar to the real case. It was found that northward deflection will be induced near south of the CMR-like terrain for both stronger and weaker westbound cyclones departing at different latitudes south of the terrain. We have explained why a further northward track at earlier stages is induced in the absence of the terrain effects in regard to model initial states. In both real and idealized cases, the track deflection of the cyclone moving around the terrain is dominated by the wavenumber-one horizontal potential vorticity (PV) advection that is somewhat offset by both vertical PV advection and differential diabatic heating.

Impact of Actual Wind Speed Distribution on the Fault Characteristic of DFIG Rotor Winding Asymmetry

Studies show that in industrial wind turbines (WTs), the wind speed may significantly vary across the rotor disk area. This variation may originate from different parameters, including wind shear (WS) and tower shadow (TS), which affect the mechanical load and the generated electrical power. However, the influence of wind speed variation on the fault characteristics of WTs has rarely been investigated so far. As an improvement, this study made an attempt to investigate the impact of spatiotemporal distribution (STD) of wind speed on the fault characteristic of the doubly fed induction generator (DFIG). The primary contribution of this article lies in two aspects: 1) establishment of a new equivalent wind speed (EWS) model comprehensively considering the affecting parameters, including WS, TS, and turbulence, and 2) reanalysis of the rotor winding asymmetry (RWA) fault characteristics under EWS, and thus new characteristics of fault were obtained. Simulations and experiments were also carried out to evaluate the accuracy of the theoretical analysis. The obtained results reveal that in addition to the original characteristic frequency, which is correlated with RWA fault, other modulation frequencies are also correlated with wind speed distribution. It is concluded that the RWA fault characteristics of DFIG are different from those of the ordinary induction generator considering the STD of the wind speed. Importantly, the obtained results are expected to improve the fault diagnosis of DFIG.

Automatic Classification of Winding Asymmetries in Wound Rotor Induction Motors Based on Bicoherence and Fuzzy C-Means Algorithms of Stray Flux Signals

Wound rotor induction motors are used in a certain number of industrial applications due to their interesting advantages, such as the possibility of inserting external rheostats in series with the rotor winding to enhance the torque characteristics under starting and to decrease the high inrush currents. However, the more complex structure of the rotor winding, compared to cage induction motors, is a source for potential maintenance problems. In this regard, several anomalies can lead to the occurrence of asymmetries in the rotor winding that may yield terrible repercussions for the machine's integrity. Therefore, monitoring the levels of asymmetry in the rotor winding is of paramount importance to ensure the correct operation of the motor. This work proposes the use of bicoherence of the stray flux signal, as an indicator to obtain an automatic classification of the rotor winding condition. For this, the Fuzzy C-Means machine learning algorithm is used, which starts with the bicoherence calculation and generates the different clusters for grouping and classification, according to the level of winding asymmetry. In addition, an analysis regarding the influence of the flux sensor position on the automatic classification and the failure detection is carried out. The results are highly satisfactory and prove the potential of the method for its future incorporation in autonomous condition monitoring systems that can be satisfactorily applied to determine the health of these machines.

Features of an induction motor design taking into account the possible operation in the mode of electrical asymmetry of the windings resistances

The paper examines the operation of large high-voltage induction motors used as an electric drive of critical installations in enterprises with a continuous production cycle. The theoretical foundations of the appearance of a dip in the mechanical characteristic of an induction motor in the mode of winding resistances asymmetry are considered. The developed power supply device for an induction motor with torque dip compensation at electrical asymmetry of phase windings appears is presented. The necessity of introducing a service factor is formulated to take into account the decrease in the total level of the electromagnetic torque in such operating modes, which is carried out at the stage of the motor design beginning.

Development of mathematical models of energy conversion processes in an induction motor supplied from an autonomous induction generator with parametric non-symmetry

The paper presents studies of the system "induction generator-induction motor" with parametric asymmetry on a mathematical model to determine the quality of generated electricity in load operating modes. A mathematical model of the "induction generator-induction motor" system has been developed taking into account losses in steel and parametric asymmetry. The analysis of the transient characteristics of an induction generator when a motor load is connected in symmetrical and asymmetrical modes of operation is carried out. The results of changes in the main characteristics of an induction motor at various degrees of parametric asymmetry in the generator are presented. The quality of the generated electricity was analyzed based on the calculations of the unbalance coefficients for each of the operating modes. The assessment of the thermal state in steady-state conditions was carried out using an equivalent thermal equivalent circuit. Thermal transients were investigated when starting an induction motor from an autonomous energy source based on an induction generator. On a thermal mathematical model, the study of the effect of the output voltage asymmetry on the heating of the connected induction motor was carried out. It is shown that the asymmetry of the output voltage of an induction generator reaches 3–10 % and causes overheating of the windings in excess of the permissible values. A regression model has been developed for studying the operating conditions of an induction motor when powered by an induction generator with an asymmetry of the stator windings. The use of the obtained equations will make it possible to determine the most rational combination of factors affecting the heating of the stator windings of induction machines, in which they will not overheat above the maximum permissible temperature values of the corresponding insulation classes

On the bipolarity of Wolf–Rayet nebulae

ABSTRACT Wolf–Rayet stars are amongst the rarest but also most intriguing massive stars. Their extreme stellar winds induce famous multiwavelength circumstellar gas nebulae of various morphologies, spanning from circles and rings to bipolar shapes. This study is devoted to the investigation of the formation of young, asymmetric Wolf–Rayet gas nebulae and we present a 2.5-dimensional magneto-hydrodynamical toy model for the simulation of Wolf–Rayet gas nebulae generated by wind–wind interaction. Our method accounts for stellar wind asymmetries, rotation, magnetization, evolution, and mixing of materials. It is found that the morphology of the Wolf–Rayet nebulae of blue supergiant ancestors is tightly related to the wind geometry and to the stellar phase transition time interval, generating either a broadened peanut-like or a collimated jet-like gas nebula. Radiative transfer calculations of our Wolf–Rayet nebulae for dust infrared emission at $24\, \mu \rm m$ show that the projected diffuse emission can appear as oblate, bipolar, ellipsoidal, or ring structures. Important projection effects are at work in shaping observed Wolf–Rayet nebulae. This might call a revision of the various classifications of Wolf–Rayet shells, which are mostly based on their observed shape. Particularly, our models question the possibility of producing pre-Wolf–Rayet wind asymmetries, responsible for bipolar nebulae like NGC 6888, within the single red supergiant evolution channel scenario. We propose that bipolar Wolf–Rayet nebulae can only be formed within the red supergiant scenario by multiple/merged massive stellar systems, or by single high-mass stars undergoing additional, e.g. blue supergiant, evolutionary stages prior to the Wolf–Rayet phase.

Investigation on Winding Theory for Short Primary Linear Machines

The winding theory is a crucial tool for analyzing the electric machines. However, some special phenomena in short primary linear machines (SPLMs) cannot be explained by the traditional theory, which is commonly applied in rotary machines (RMs). In this paper, an improved winding theory for SPLMs is presented. Starting with the magnetic field produced by a single conductor, the difference between winding theory for SPLMs and RMs is analyzed. According to the proposed theory, the pulsating magneto-motive force (MMF) and the asymmetry of the three-phase windings can be analyzed and calculated in details. It is very useful for perceiving, analysis and optimal design for the winding in SPLMs. The proposed theory is verified by 2-D finite-element analysis (FEA) and experiment.