Transverse Wind Velocity Research Articles

Experimental study of spontaneous ignition of overloaded electrical wires under transverse wind

Spontaneous ignition of electrical wire caused by the Joule heat generated in core due to overloading or a short circuit is common, and is significantly influenced by wind velocity, but has been very limited addressed yet. This paper, for the first time, presents an experimental investigation in spontaneous ignition of overloaded wire under transverse wind (perpendicular to wire). Polyethylene (PE)-insulated wires with a NiCr core diameter of 0.8 mm and the insulation layer thickness of 0.3 mm and 0.15 mm are employed as samples. It can be found that with the increase of transverse wind velocity, the ignition delay time demonstrates a non-monotonic tendency (firstly decreases then increases, and decreases again, finally increases) until ignition limit, where four regimes are clarified according to different controlling mechanisms. The ignition delay time declines with the increase of electrical current. One of the most noteworthy findings is that the ignition delay time declines as the insulation thickness increases, which shows an opposite trend with the results of piloted ignition for thermally thin materials. In order to distinguish the ignition and non-ignition zones, an ignitability map considering both the gas phase kinetic effects and the solid phase heat loss effect is established based on two non-dimensional parameters [Damköhler number (Da) and Rloss]. A theoretical ignition model combining the effects of pyrolysis time, mixing time and chemical time is established, which well interprets the variation trend of ignition delay time and verifies the significant role of the chemical time in spontaneous ignition. This work provides essential knowledge on spontaneous ignition of overloaded electrical wires under practical transverse wind.

A Meandering-Capturing Wake Model Coupled to Rotor-Based Flow-Sensing for Operational Wind Farm Flow Prediction

The development of new wake models is currently one of the key approaches envisioned to further improve the levelized cost of energy of wind power. While the wind energy literature abounds with operational wake models capable of predicting in fast-time the behavior of a wind turbine wake based on the measurements available (e.g., SCADA), only few account for dynamic wake effects. The present work capitalizes on the success gathered by the Dynamic Wake Meandering formulation and introduces a new operational dynamic wake modeling framework aimed at capturing the wake dynamic signature at a low computational cost while relying only on information gathered at the wind turbine location. In order to do so, the framework brings together flow sensing and Lagrangian flow modeling into a unified framework. The features of the inflow are first inferred from the turbine loads and operating settings: a Kalman filter coupled to a Blade Element Momentum theory solver is used to determine the rotor-normal flow velocity while a Multi-Layer Perceptron trained on high-fidelity numerical data estimates of the transverse wind velocity component. The information recovered is in turn fed to a Lagrangian flow model as a source condition and is propagated in a physics-informed fashion across the domain. The ensuing framework is presented and then deployed within a numerical wind farm where its performances are assessed. The computational affordability of the proposed model is first confirmed: 7 × 10−4 wall-clock seconds per simulation second are required to simulate a small 12 turbines wind farm. Large Eddy Simulations of wind farm using advanced actuator disks are then used as a baseline and a strong focus is laid on the study of the wake meandering features. Comparison against the Large Eddy Simulation baseline reveals that the proposed model achieves good estimates of the flow state in both low and high Turbulence Intensity configurations. The model distinctly provides additional insight into the wake physics when compared to the traditional steady state approach: the wake recovery is consistently accounted for and the wake meandering signature is captured as far as 12D downstream with a correlation score ranging from 0.50 to 0.85.

Detection strategies for an optical communication system using Gaussian vortex beams.

In this paper, we describe the details of different detection strategies of a communication system using Gaussian vortex beams. These are listed as (a) simultaneous transmission of actual data symbol and reference signals (no multiplexing), (b) transmission of data symbol and reference signals in a wavelength division multiplexed manner, and (c) transmission of data symbol and reference signals in a time-division multiplexed manner. The performance of each one is evaluated for strong turbulence regimes with the help of an appropriately arranged random phase screen setup. It is found that the first two detection strategies work error-free within the source and propagation parameters chosen. In the last detection strategy, performance depends on the transverse wind velocity.

Role of location-dependent transverse wind on root-mean-square bandwidth of temporal light-flux fluctuations in the turbulent atmosphere.

The root-mean-square (RMS) bandwidth of temporal light-flux fluctuations is formulated for both plane and spherical waves propagating in the turbulent atmosphere with location-dependent transverse wind. Two path weighting functions characterizing the joint contributions of turbulent eddies and transverse winds at various locations toward the RMS bandwidth are derived. Based on the developed formulations, the roles of variations in both the direction and magnitude of transverse wind velocity with locations over a path on the RMS bandwidth are elucidated. For propagation paths between ground and space, comparisons of the RMS bandwidth computed based on the Bufton wind profile with that calculated by assuming a nominal constant transverse wind velocity are made to exemplify the effect that location dependence of transverse wind velocity has on the RMS bandwidth. Moreover, an expression for the weighted RMS transverse wind velocity has been derived, which can be used as a nominal constant transverse wind velocity over a path for accurately determining the RMS bandwidth.

Atmospheric turbulence-induced fading channel model for space-to-ground laser communications links

The fading channel model for generating a random time-varying signal based on the atmospheric turbulence spectrum for space-to-ground laser links is discussed. The temporal frequency characteristics of the downlink are theoretically derived based on the von Karman spectrum. The rms wind speed based on the Bufton wind model is used as the transverse wind velocity, which makes the simulation simple. The time-varying signal is generated as functions of the receiver aperture diameter and the rms wind speed. The simulated result of the time-varying signal is presented and compared with the gamma-gamma distribution based on the scintillation theory in a moderate-to-strong-turbulence regime.

Numerical Analysis of the Induced Corona Vibrations on High-Voltage Transmission Lines Affected by Rainfall

Droplets formation on high-voltage transmission lines affected by rainfall amplifies the corona discharges from the conductors. The induced corona vibrations intensify the fatigue of high-voltage conductors and supporting elements. The alternating presence of space charge and the ionic wind associated with the corona discharge are the main causes of this phenomenon. The objective of this paper is to validate a numerical simulation method to investigate the effects of different parameters (electric field strength and polarity, rain intensity, transverse wind velocity) on the amplitude of the induced corona vibrations. The finite element method was used to develop the numerical model of the conductor movement under the action of mechanical and electrical forces, while time discretization was made with the finite difference method. The numerical simulation results were in good agreement with the experimental data available in the literature. The model enables better comprehension of the induced corona vibration mechanism.

On the possibility to determine the transverse wind velocity from the correlation of coherent images of an atmospheric layer

A method for determining the transverse wind velocity from the correlation of images of a scattering atmospheric layer illuminated by the laser radiation is proposed and justified in computer experiments.

Remote sensing of atmospheric turbulence and transverse winds from wave-front slope measurements from crossed optical paths

In the theory of atmospheric turbulence, the strength of the spatial variations of the index of refraction n is proportional to a parameter known as the atmospheric-structure constant. The atmosphericstructure constant is denoted C(2)(n)(z) and is a function of position along the optical path z. The characteristics of the temporal variations of the index of refraction are related to both C(2)(n)(z) and to the transverse wind velocity V(z). Current optical techniques for remotely sensing C(2)(n)(z) and V(z) rely primarily on the spatial or temporal cross-correlation properties of the intensity of the optical field. In the remote-sensing technique proposed here, we exploit the correlation properties of the wave-front slope measured from two point sources to obtain profiles of C(2)(n)(z) and V(z). The two sources are arranged to give crossed optical paths. The geometry of the crossed paths and the characteristics of the wave-front slope sensor determine the achievable resolution. The signal-to-noise ratio calculationsindicate the need for multiple measurements to obtain useful estimates of the desired quantities.

Effects of the intensity of precipitation and transverse wind on the corona-induced vibration of HV conductors

The effects of rainfall intensity, electric field strengths, alternating and both polarities of direct voltage, and the velocity of an ACSR conductor were studied. The results obtained showed that the amplitude of the vibration was linearly proportional to the intensity of precipitation up to 24 mm/h. When the intensity of precipitation was higher than 24 mm/h, the amplitude of the vibration remained constant. At a constant intensity of precipitation and a steady vibration, the amplitude of the vibration was generally highest with negative DC fields and lowest with AC fields. The effects of transverse wind velocity upon the vibration were studied under a constant precipitation rate using a wind tunnel generating winds with velocities up to 50 km/h. As a result, two critical wind velocities, V/sub C1/ and V/sub C2/, were established. V/sub C1/ represented the point at which the corona-induced vibration began to decrease and V/sub C2/ the point at which the vibration stopped. Under both alternating and direct voltages, V/sub C1/ decreased with an increase in the applied field, while V/sub C2/ remained at about 25 km/h. Photographs of water droplets hanging from the conductor were taken in order to document the effect of wind velocity on the shape of the hanging drops. >

Aperture size and bandwidth requirements for measuring strong scintillation in the atmosphere

Irradiance statistics were simultaneously measured with five apertures of four different sizes and also with five different bandwidths under conditions of strong path-integrated turbulence to determine aperture size and bandwidth requirements. The probability density function and the second and third moments are considered. Good measurements of these statistics can be made with detector apertures near the wave coherence length and with bandwidths near the ratio of the transverse wind velocity to the wave coherence length under these conditions.

A meteorological data-acquisition system for atmospheric propagation studies

Instrumentation for studying the propagation of near-millimeter waves has been designed and implemented at 1-mile-long test site in Sandusky, OH. Measurements of the atmospheric structure functions and the transverse wind velocity along the propagation path is accomplished with a custom-built meteorological data-acquisition network consisting of six towers linked together with fiber-optic data lines. Each tower is microprocessor controlled and includes a three-axis anemometer, a Lyman-alpha hydrometer, and a differential temperature probe, with other meteorological parameters obtained at various locations along the path. A modified ISO-OSI reference model is used as the controlling protocol.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Remote atmospheric probing on a line‐of‐sight path, using spatial filter concepts: 1. Theory

A rigorous treatment is given to a spatial filtering method for remotely determining the transverse wind velocity and the atmospheric structure constant along a line‐of‐sight path, assuming a Kolmogorov spectrum of refractivity and weak scattering. The results are applicable from the millimeter‐wave range to the optical range for linear array configurations at either one end or both ends of the path. Various methods of signal detection are considered, such as coherent, quasi‐coherent (knowledge of relative phases), and incoherent. In order to determine the two parameters the integral for the time covariance or the spectrum of the wave fluctuations must be inverted. For simple arrangements of single elements or pairs of elements at the transmitting and receiving locations the inversion is ill conditioned and yields only three or four resolution cells along the path. A statement of the problem in spectral form for line apertures representing narrow bandpass‐type spatial filters leads to optimal orthogonality of the inversion problem. In the limiting case of ideally sharp spatial filters, the inversion is shown to degenerate into a simple one‐to‐one relationship between spectral measurements of the spatially filtered wave fluctuations and the values of the parameters at a specified location along the path. A subsequent paper will be devoted to an experimental application of the principle in the mm‐wave region.

The effect of wind velocity on the amplitude scintillations of millimetre radio waves

The effect of transverse wind velocity on the amplitude scintillations of millimetre radio waves is studied. Scintillation data obtained on two line-of-sight microwave links at 36 GHz and 110 GHz on a common 4.1 km path are used to estimate the wind velocity perpendicular to the propagation path. The estimated wind velocity is within 20% of the value obtained from direct measurements using a conventional anemometer.

Bandwidth specification for adaptive optics systems*

A simplified expression for the bandwidth of an adaptive optics system is found to depend on a weighted path integral of the turbulence strength, where the weighting is transverse wind velocity to the 5/3 power. The wave-front corrector is conservatively assumed to match the phase perfectly, at least spatially, if not temporally. For the case of astronomical imaging from a mountaintop observatory, the necessary bandwidth is found to be less than 200 Hz.

Remote determination of the profiles of the atmospheric structure constant and wind velocity along a line-of-sight path by a statistical inversion procedure

A statistical inversion procedure is developed for remotely determining the average transverse wind velocity and the atmospheric structure constant at N arbitrary points along a line-of-sight path. Linear integral equations are given relating the amplitude correlation function and the amplitude and phase structure functions with the unknown structure constant and wind velocity. It is shown that the standard matrix inversion leads to large variations, as high as 10^{11} percent errors, in the unknown for small data error of one percent; thus the problem is ill posed. The errors are reduced to a suitable level by a statistical procedure that is dependent upon a priori knowledge of the statistics of the unknowns. For the structure constant, a procedure developed by Franklin and others is used, while the wind velocity is determined by modifying the method to include the errors in the structure constant. Computer simulation is used to estimate the error. It is shown that, with an input error of one percent, the rms error in the unknown is only on the order of ten percent. To show the effectiveness of the method, experimental data obtained by a Stanford group are used to determine the wind velocity and the structure constant along the path, yielding reasonable results.