Speed-up Effect Research Articles

An Experimental Investigation of Streamwise and Vertical Wind Fields on a Typical Three-Dimensional Hill

To study the streamwise and vertical wind fields on a typical three-dimensional hill, wind tunnel tests were performed. The mean values and turbulence intensities of the streamwise and vertical wind speeds of the typical positions above the hill were measured, and they are presented in the form of contour maps for design. Furthermore, the speed-up of the mean wind speeds in the streamwise direction was compared with codes. Finally, the windage yaw of a jumper cable was examined as an example of how to take into account the streamwise and vertical wind field influence on the wind load in the analysis of wind-induced responses. The results show that the most significant speed-up effect in the streamwise direction occurs on the hill crest, and the wind speed-up decreases with the increase of the height. Overall, the wind speed-up along the crosswind center line is larger than that along the along-wind center line of the hill. In the codes, the speed-up effect specified for the structure at half the height of the upstream side of the hill is relatively conservative. With regard to the mean wind speed in the vertical direction, the wind climbing effect located at half the height of the upstream side of the hill is the most significant. The area with the stronger turbulence intensity appears at the foot of the upstream and downstream sides of the hill. The influence of the vertical wind on the jumper cable is remarkable where the wind climbing effect is the most significant, which is worthy of attention in the design of the structure immersed in a hilly terrain-disturbed wind field.

Wind Farm Simulation and Layout Optimization in Complex Terrain

This work reports on incorporating complex terrain into wind farm simulations for the purpose of layout optimization. Adding complex terrain boundary conditions to NREL’s medium fidelity Reynolds averaged Navier-Stokes flow model, WindSE, produces significant separation, flow curvature, and speedup effects that would otherwise be difficult to capture with lower-fidelity models or a flat-terrain assumption. These flow features, in turn, can significantly impact the optimal turbine array layout. We demonstrate the addition of complex terrain improves agreement with SCADA data by 34.8% in mean average error. Additionally, we discuss modifications to the code that enable gradient-based layout optimization using terrainaware adjoints with arbitrary topography. Through several optimization case studies, we show that the layout optimization process takes advantage of speedup effects on terrain high points, and leverages flow curvature effects that modify wake trajectories. This yields substantial power improvements over gridded layouts, and hints at future research directions in simulation and optimization for wake trajectories in complex terrain.

Running safety of metro train over a high-pier bridge subjected to fluctuating crosswind in mountain city

Due to the rugged terrain, metro lines in mountain city across numerous wide rivers and deep valleys, resulting in instability of high-pier bridge and insecurity of metro train subjected to fluctuating crosswind. To ensure the safe operation in metro lines in mountain cities, running safety of the metro train over the high-pier bridge under crosswind is analyzed in this paper. Firstly, the dynamic model of the wind-train-bridge (WTB) system is built, in which the speed-up effect of crosswind is fully considered. On the basis of time domain analysis, the basic characteristics of the WTB system with high-pier are analyzed. Afterwards, the dynamic responses varies with train speed and wind speed are calculated, and the safety zone of metro train over a high-pier bridge subjected to fluctuating crosswind in mountain city is determined. The results indicate that, fluctuating crosswind triggers drastic vibration to the metro train and high-pier bridges, which in turn causes running instability of the train. For this reason, the corresponding safety zone for metro train running on the high-pier is proposed, and the metro traffic on the high-pier bridge should be closed as the mean wind speed of standard height reaches 9 m/s (15.6 m/s for the train).

Advanced methodology for wind resource assessment near hydroelectric dams in complex mountainous areas

To increase renewable energy generation in some hydroelectric dams, a solution consisting in installing wind turbines close to dams is proposed. Indeed, dam surroundings are prone to benefit from wind speed-up effect, extra wind generation associated with thermal winds, and existing electrical infrastructure. Identifying the most suitable locations for turbines, that is, areas of relatively high-speed and low-turbulence wind, is fundamental to maximize this complementary power. Easy accessibility to turbines and minimum distance to dam electrical infrastructure are also essential to reduce the costs. Thus, a methodology is proposed to improve wind resource assessment in complex mountainous areas. First, potentially interesting dams are chosen using statistical local wind data. Second, weighted results of wind speed and turbulence intensity, considering all wind directions are presented based on CFD simulations. Finally, wind power density and annual energy production maps are generated, along with accessibility maps, to identify suitable sites. The Camarasa dam in the north-east of the Iberian Peninsula is chosen as case study to show and test the proposed methodology. Error estimations are provided, along with validation against Wind Atlas data and WAsP simulations.

Investigation of wind turbine performance coupling wake and topography effects based on LiDAR measurements and SCADA data

This paper investigates the power generations of four wind turbines coupling the wake and topography effects with field measurements and SCADA (Supervisory Control and Data Acquisition) data. Two LiDARs (Light Detection and Ranging) were adopted for the four turbines’ wake detections which lasted for 6 months. Based on the wake interference degrees depending on the incoming wind directions and relative locations of turbines, three scenarios were observed, i.e. full wake effects (at the incoming wind direction from the top view), part wake effects and separated wake effects. Results show that the altitude is not the only significant influence factor on wind velocities. Larger gradient with a longer distance of mountain slop can conduct more obvious “Speed-up effect”. The increase of power generation from full wake effect to part wake effect can reach 15% and the terrain effect amplifies the increasement of the power generation. Meanwhile, significant wake recoveries are observed with the multi-wake interactions. Results in this paper can provide guidelines for the micro-sing and turbines’ operating of wind farm in complex terrain.

Detached eddy simulation of flow characteristics around railway embankments and the layout of anemometers

Anemometers are usually set up along railway embankments to monitor wind speeds, and the layout for them has to be investigated. This work used an improved delayed detached eddy simulation (IDDES) approach to explore the flow properties around railway embankments, and then a proposal was put forward for the layout of anemometers. The numerical method was validated against previous wind tunnel tests on the speed-up ratios of the flow around a 1/300 scale two-dimensional embankment with the slope gradient of 1:2. The effects of inlet velocity profiles, i.e., uniform velocity and atmospheric boundary layer velocity profiles, on the speed-up ratios around a 5 m high railway embankment were compared. The study indicates that using a uniform velocity profile to assess the operational safety of trains running across strong wind regions could be favourable, especially when complex local terrains contribute to different wind characteristics. The anemometers should be set upstream, i.e., at a well defined distance in locations with sufficient extent of open ground and on the electrification masts along railway lines. This is not in line with the anemometer layout of the existing SWEWS (Strong Wind Early Warning Systems), the difference being due to the speed-up effect of the railway embankment, which is usually not considered explicitly. Formulas have been developed on the basis of regression of the simulation results to express the relationships between e.g. top wind speed over the embankment (located in an area where it is not possible to install anemometers) and measured wind speeds. In this way it is possible to take into account the speed-up effect encountered by the wind passing over the embankment, which needs to be considered in the operational rules in order to ensure safe operations.

Mathematical modeling of a horizontal axis shrouded wind turbine

In this work, an accurate mathematical modeling of a shrouded wind turbine is presented. This work claims new equations to predict the power coefficient and speed-up ratio effects. In the proposed model, the duct-based pressure drop is considered and the velocity in the far-wake is not suggested to be the same as the bare wind turbines. The mathematical model revealed that any shroud with an optimum design hardly can provide a CP=1 for a wind turbine. However, using a properly designed duct, CP=0.93 can be reached practically. This work also reveals that the speed-up ratio should be 0.6<γ<1.7; in order to exceed Betz limit and work in the optimum condition. The developed model presents a clear relation between the duct efficiency (ηd), duct exit area ratio (β) and its pressure loss coefficient (Kpd). Finally, a practical limitation for duct parameters is suggested in order to exceed the Betz limit. Further, a physical assumption is applied to approximate the power coefficient, which indicated that the power coefficient growth never can reach the speed-up ratio scale.

On-Demand Processing of Data Cubes from Satellite Image Collections with the gdalcubes Library

Earth observation data cubes are increasingly used as a data structure to make large collections of satellite images easily accessible to scientists. They hide complexities in the data such that data users can concentrate on the analysis rather than on data management. However, the construction of data cubes is not trivial and involves decisions that must be taken with regard to any particular analyses. This paper proposes on-demand data cubes, which are constructed on the fly when data users process the data. We introduce the open-source C++ library and R package gdalcubes for the construction and processing of on-demand data cubes from satellite image collections, and show how it supports interactive method development workflows where data users can initially try methods on small subsamples before running analyses on high resolution and/or large areas. Two study cases, one on processing Sentinel-2 time series and the other on combining vegetation, land surface temperature, and precipitation data, demonstrate and evaluate this implementation. While results suggest that on-demand data cubes implemented in gdalcubes support interactivity and allow for combining multiple data products, the speed-up effect also strongly depends on how original data products are organized. The potential for cloud deployment is discussed.

Use of High-Resolution Numerical Models and Statistical Approaches to Understand New Zealand Historical Wind Speed and Gust Climatologies

AbstractThis paper describes how a combination of high-resolution numerical modeling, a robust homogenization algorithm, and local pressure observations have been used to understand and reconcile time series of daily, seasonal, and annual peak wind gusts recorded at observing sites in the Cook Strait region of New Zealand. The homogenization algorithm consists of corrections for the relocation of masts, changes in instrumentations, data acquisition and signal processing, surrounding surface roughness, and measurement heights. In addition, a statistical method, penalized maximal F test (PMFT), was used to assess the homogeneity of the wind speed time series and detect and eliminate all remaining, undocumented, artificial (i.e., nonclimatic) breakpoints. A three-dimensional time-dependent computational fluid dynamics (CFD) simulation was carried out using the Gerris model to characterize the turbulence environment at the mast sites and to estimate topographic speedup effects. Trends in magnitudes and frequencies of the homogenized seasonal and annual peak wind gusts are evaluated and presented for the Cook Strait region. The pressure gradients between pairs of stations were used to study the correlation between the gust wind speeds and the pressure field. A high-resolution convection-resolving numerical weather prediction model [the New Zealand Convective-Scale Model (NZCSM)] was employed to aid the interpretation of results and analyze wind trends. The trend in gust speeds is also shown to be consistent with larger-scale NCEP–NCAR reanalysis pressure trends. The homogenization algorithm showed promising results in eliminating the artificial breakpoints and trends. Overall, strong correlations were found between the homogenized gust speeds, the pressure field across the region, and NZCSM predictions.

Density-Dependent Speed-up of Particle Transport in Channels

Collective transport through channels shows surprising properties under one-dimensional confinement: particles in a single file exhibit subdiffusive behavior, while liquid confinement causes distance-independent correlations between the particles. Such interactions in channels are well studied for passive Brownian motion, but driven transport remains largely unexplored. Here, we demonstrate gating of transport due to a speed-up effect for actively driven particle transport through microfluidic channels. We prove that particle velocity increases with particle density in the channel due to hydrodynamic interactions under electrophoretic and gravitational forces. Numerical models demonstrate that the observed speed-up of transport originates from a hydrodynamic pistonlike effect. Our discovery is fundamentally important for understanding protein channels and transport through porous materials and for designing novel sensors and filters.

Behavior Aware Service Staffing

Empirical studies of service systems have shown that workers exhibit different service rates depending on their assigned workload. In contrast, staffing models typically assume a constant service rate. To address this issue, we model two commonly observed behavioral effects, speedup and slowdown, in a general way that allows us to study their joint impact on service staffing. We fit our behavioral model to a hospital dataset and show that both effects are present across a variety of departments. Given these findings, we incorporate speedup and slowdown behavior into a multiperiod workforce staffing model and show that a workload (defined as the number of jobs assigned to each worker) that maximizes the service rate is typically not optimal. As expected, the effectiveness of the widely practiced single‐ratio workload staffing policy depends on the strength of the speedup and slowdown effects. Interestingly, we find that in the presence of slowdown, weak behavioral effects (where workers work at a relatively constant rate) are the cases where the single‐ratio policy performs the worst; the optimal workload instead varies the most as system demand changes. This result differs from practice in many services such as healthcare, where fixed patient‐to‐nurse ratio workloads are commonly used. We show that the strength of behavioral effects modulates the trade‐off between a steady workload and the number of schedule adjustments.

Nuclear Bragg reflection of 57FeBO3 in radio-frequency magnetic field observed with Si-APD linear array detector

We observed nuclear Bragg reflection by 57FeBO3 (333) with an external radio frequency (RF) magnetic field using a 64 pixel silicon avalanche photodiode linear array detector. The reflection was caused by γ rays resonantly emitted from 57Fe nuclei using synchrotron X-rays of 14.413 keV. When an RF magnetic field of only 1.0 Oe at 8.0 MHz was applied to an 57FeBO3 single crystal, a stripe structure of 0.12 mm pitch was distinguished from the intensity distribution with a 30 μm spatial resolution (full width at half-maximum (FWHM)) of the detector system. Simultaneously, the detector revealed that a decay time of the reflection increased from 15.0 to 35.6 ns with a 0.5 ns time resolution (FWHM). We consider that a magneto-acoustic wave excited on the crystal surface slightly changed the energy of the atomic vibration to partly collapse the speed-up effect caused by the nuclear multiple scattering.

Author Correction: A changeable day in the life of Venus

In the version of this Sketch-Up originally published, labels describing atmospheric torques acting on Venus were incorrect. The sketch suggested that the speed-up effect of mountain waves is balanced by a slow-down from thermal tides; instead, both mountain waves and thermal tides speed up the rotation, and this effect is balanced by a slow-down from the solar gravitational torque on the solid body, which is transmitted to the atmosphere. This error has now been corrected in the online versions by adjusting the relevant labels; that is, “Mountain waves speed the planet up” has been changed to “Mountain waves and thermal tides speed the planet up”, and “Thermal tide slows the planet down” has been changed to “Solar gravitational torques slow the planet down”.

An Empirical Study on Green Innovation Efficiency in the Green Institutional Environment

Previous studies have found that reverse technology spillover effects can promote industrial technology modernization in developing countries. However, it is still unknown whether reverse technology spillover effects can improve green innovation efficiency in developing countries. In particular, institutional uncertainties characteristic of transition economies have a significant impact on industrial modernization. Therefore, researching the impact of the institutional environment on the relationship between reverse technology spillover effects and green innovation efficiency is of great significance. In this paper, we use data from G20 countries as well as China’s foreign direct investment (FDI) data to measure the effects of reverse technology spillovers and adopt the threshold effect model to explore the relationship between reverse technology spillover effects and green innovation efficiency as well as the influence of the institutional environment on this relationship, based on China’s provincial panel data from 2003 to 2015. The empirical results show that the reverse technology spillover effects can effectively improve green innovation efficiency. There is a threshold for the influence of the institutional environment on the relationship between reverse technology spillover effects and green innovation efficiency. When the institutional development level surpasses the threshold value, an acceleration effect is generated. In addition, we find that the legal system is the key bottleneck in terms of improving green innovation efficiency. How to improve and perfect the path of institutional construction in China and how to enable institutions to gain threshold speed-up effects have become the major problems the Chinese government faces in institutional construction. The research results of this paper offer a reference to developing countries in regard to improving their institutions and enhancing their green innovation efficiency.

Recursive Local Summation of RX Detection for Hyperspectral Image Using Sliding Windows

Anomaly detection has received considerable interest for hyperspectral data exploitation due to its high spectral resolution. Fast processing and good detection performance are practically significant in real world problems. Aiming at these requirements, this paper develops a recursive local summation RX anomaly detection approach by virtue of sliding windows. This paper develops a recursive local summation RX anomaly detection approach by virtue of sliding windows. A causal sample covariance/correlation matrix is derived for local window background. As for the real-time sliding windows, the W o o d b u r y identity is used in recursive update equations, which could avoid the calculation of historical information and thus speed up the processing. Furthermore, a background suppression algorithm is also proposed in this paper, which removes the current under test pixel from the recursively update processing. Experiments are implemented on a real hyperspectral image. The experiment results demonstrate that the proposed anomaly detector outperforms the traditional real-time local background detector and has a significant speed-up effect on calculation time compared with the traditional detectors.

Computational Simulations of Wind Loads of Super Tall Buildings in Hilly Terrain

The wind loads could be increased by the complex hilly terrain. In order to consider this threat, computational simulations about wind pressures in buildings in hilly terrain and surrounding buildings were finished. In the CFD model, surrounding buildings within 500 meters and hilly terrain within 700 meters were established, and total 16 cases including different sensitive wind directions were simulated. The results showed that, because of the complex situation of surrounding hilly terrain and interfered buildings, wind loads in the building group under different direction show opposite characteristics. The speed-up effects by the hilly terrain increased the windward mean pressures when the flow comes from the north, while the interference effects by the surrounding buildings decreased them when the flow comes from the south.

An experimental investigation on the aeromechanics and wake interferences of wind turbines sited over complex terrain

An experimental study was conducted to investigate the aeromechanics and wake interferences of wind turbines sited on two-dimensional hills with different slopes. First, detailed flow field measurements were correlated with dynamic wind load measurements to reveal the effect of topography on the performance of an individual wind turbine sited at different locations on hilly terrains. Compared to a flat surface, wind turbines sited on a hilltop not only generate more power due to the speed-up effect but also experience reduced fatigue loads due to the decreased level of the turbulence on a hilltop. It was also found that a wind turbine located downstream of a steep hill has a greater likelihood of experiencing extreme wind loads compared to one on a gentle hill. Second, wind turbine wake characteristics and their effects on the dynamic wind loads of downstream wind turbines were also assessed. The effect of an upstream turbine wake on the wind turbine sited on a hilltop was found to be much less significant compared to a wind turbine on a flat surface. In addition, while the wake of an upstream turbine sited on hilltop has a significant influence on the dynamic wind loads of a downstream turbine sited behind a gentle hill, the effect of an upstream turbine wake on a downstream turbine placed behind a steep hill was found to be almost negligible. The quantitative measurement results of the present study not only provide a database for the validation of wake models and numerical simulations but can also be used to optimize the layout of wind turbines sited on complex terrain for higher power yield and better durability.

Baudrillard Between Benjamin and McLuhan: ‘the Narcissistic Seduction’ of the Media Society

This paper aims to further investigate some aspects of Baudrillard’s analysis of the media society, influenced by Benjamin’s aesthetic teaching and McLuhan’s mediological legacy. His purpose is to probe the effects of the symbolic speedup fueled by the repeatability of messages and contents, constantly substituted by their immanent abstractions. The dominion of the signifier upon the signified, the replacement of the referendum with its referential highlights, the emphasis on the semiotic complexity of contemporary myths (as already remarked by Barthes), all this is destined to turn media into body extensions. Hence follows the ‘narcissistic seduction’ of television, as McLuhan outlines in reference to the tautological nature of mainstream media. In this sense, Baudrillard does not neglect the heuristic relevance of daily experience, conceived as an ‘open work’ by Eco. To the fore are the expressive shifts engendered by the cultural industry in the age of consumer fever. The result is Baudrillard’s syncretistic analysis of our communicative uncertainty. The latter stems from the meaningful and repeatable objects permeating the social act, increasingly influenced by the ‘narcissistic seduction’ of media.

OPTIMIZATION OF TIMES OF RUNNING AND BRAKING OF POSITION FREQUENCY-REGULATED ASYNCHRONOUS ELECTRIC DRIVES

Purpose. Obtaining analytical dependencies for calculating the optimum speedup and speeddown times for a frequencycontrolled asynchronous motor that minimize the main electromagnetic energy losses of the engine for small displacements of its shaft, and also the estimation of the influence of these optimal speedup and speeddown times on the value of the main electromagnetic energy losses in the frequency-controlled asynchronous motor various types of engine tachograms (with linear and parabolic forms or hyperbolic sine form).Methodology. Methods of optimal control and simulation modelling.Findings. Analytical dependencies are obtained and a graphoanalytical method proposed for calculating the optimum speedup and speedown times for the frequency-controlled asynchronous motor that minimizes the main electromagnetic energy losses of the motor with small displacements of its shaft. The effect of these optimal speedup and speeddown times on the value of the main electromagnetic energy losses in the frequency-controlled asynchronous motor under different types of motor tachograms (with linear and parabolic forms or the form of the hyperbolic sine) are estimated. Originality. For the first time, analytical dependencies are obtained for calculating the optimal speedup and spedddown times for small displacements of the frequency-controlled asynchronous motor, by which the electromagnetic losses in the motor is minimized. For the first time, a graphoanalytical method developed to determine these optimum speedup and speeddown times for the frequency-controlled asynchronous motor when was working out small displacements.Practical value. An approach to energy saving in positional frequency-controlled asynchronous electric drives is proposed, by optimizing their speedup and speeddown times, which allows in practice without significant capital costs to reduce power losses in these electric drives

Sound propagation from a ridge wind turbine across a valley.

Sound propagation outdoors can be strongly affected by ground topography. The existence of hills and valleys between a source and receiver can lead to the shielding or focusing of sound waves. Such effects can result in significant variations in received sound levels. In addition, wind speed and air temperature gradients in the atmospheric boundary layer also play an important role. All of the foregoing factors can become especially important for the case of wind turbines located on a ridge overlooking a valley. Ridges are often selected for wind turbines in order to increase their energy capture potential through the wind speed-up effects often experienced in such locations. In this paper, a hybrid calculation method is presented to model such a case, relying on an analytical solution for sound diffraction around an impedance cylinder and the conformal mapping (CM) Green's function parabolic equation (GFPE) technique. The various aspects of the model have been successfully validated against alternative prediction methods. Example calculations with this hybrid analytical-CM-GFPE model show the complex sound pressure level distribution across the valley and the effect of valley ground type. The proposed method has the potential to include the effect of refraction through the inclusion of complex wind and temperature fields, although this aspect has been highly simplified in the current simulations.This article is part of the themed issue 'Wind energy in complex terrains'.