Low Wind Conditions Research Articles

Catchment Based Aerodynamic Performance Analysis of Small Wind Turbine Using a Single Blade Concept for a Low Cost of Energy

For low and medium wind conditions, there is a possibility to harness maximum wind potential reducing the cost of energy by employing catchment-based wind turbine designs. This paper aims to study catchment-based small wind turbine aerodynamic performance for improved efficiency and reduced cost of energy. Hence, design parameters are considered based on specific conditions within a catchment area. The bins and statistical methods implemented with Weibull distribution of wind data for selected sites to characterize the wind conditions and a weighted average method proposed to create representative wind conditions implementing a single blade concept. The blade element method was applied using Matlab code (version R2017a, MathWorks Inc., Natick, MA, US) for aerodynamic design and analysis, and computational fluid dynamics employed using ANSYS—Fluent (version 18.1, ANSYS Inc., Canonsburg, PA, USA) for validation. The performance of the designed blade is evaluated based on annual energy production, capacity factor and power coefficient. Then, for site-specific wind conditions, yearly energy production, and relative cost of energy are examined against rated power. Appropriate rated power for a low cost of energy identified and performance measures evaluated for each site. As a result, a maximum power coefficient of around 51.8% achieved at a design wind speed of 10 m/s, and higher capacity factors of 28% and 50.9% respectively attained for the low and high wind conditions at the proposed rated powers. Therefore, for different wind condition sites, enhanced performance at a low cost of energy could be achieved using a single blade concept at properly selected rated powers employing suitable design conditions and procedures.

Experimental results of the cooperative operation of autonomous surface vehicles navigating in complex marine environment

Experimental results are presented of the cooperative operation of two maritime autonomous surface vehicles (ASVs) executing a pre-defined task in a complex marine environment. The ASVs are equipped with algorithms for motion-planning, path-following and motion control, where the motion-planning algorithm is based in the angle-guidance fast marching square method, the path-planning module is based in the vector-field path-following method and the controller is a PID. The ASVs are two self-propelled models of 2.5 m and 3.2 m length instrumented with several sensors, actuators and communication unit, such as, inertial measurement units, Global positioning system, anemometers, accelerometers, inclinometers, DC motors and Wi-Fi communication. To monitor and command the ASVs, a real-time program was coded in LabVIEW 2018®. Finally, in order to validate the developed system, experimental tests were carried out in an open-door pool with low wind conditions, and from these experiments good capabilities of the system were found.

A Novel Hybrid Solar-wind Energy Conversion System for Remote Area Electrification

Background: Remote area electrification is a social responsibility that needs to be catered by research fraternity. One of the most viable technology as a solution is the Renewable Energy Source (RES) based power generation. However, RES is intermittent and thus, mostly ineffective without an energy storage device. Energy storage device comes at increased cost and may not be a cost-effective solution to the problem. Introduction: One solution that has been frequently proposed to reduce the intermittency of RES is hybridization. Hybridization of RES such as Wind Energy Conversion System (WECS) with Solar Energy Conversion System (SECS) is the most basic solution offered owing to their complementary nature. Therefore, this paper sees SECS in the role of supporting WECS in regions with highly intermittent wind conditions. In this paper, a novel technique of hybridization of WECS with SECS has been proposed. Methods: The basic idea of the paper is to control the dc-link voltage from the generation side by regulating the power generated by RES as per load demand using minimum components. The underlined principle is the relative lower time constant of solar panel and battery system in comparison to a wind turbine. Results: The experimental results on the proposed system shows that the SECS supports the WECS at higher wind turbulence and low wind conditions. Conclusion: This unique feature of the proposed system enables a WECS supported by a small rated SECS to attain high power reliability and thus, suitable for application such as remote area electrification.

Guidelines for first responders based on results from deploying a mockup radiological dispersal device

During the past 7th Security Framework Program the European Commission funded a research project called CATO (CBRN Crisis management, Architectures, Technologies and Operational procedures) to develop a prototype decision support system for crisis management in addition to providing a suite of guidelines for first responders and incident commanders when dealing with chemical, biological, radiological or nuclear incidents. In order to derive these guidelines a proof-of-concept experiment was setup during which several passive agent (Stable CsCl) dispersions with improvised explosive devices and vehicle-borne improvised explosive devices were carried out. Each dispersion was thoroughly characterised by a number of monitoring devices, including high-volume air samplers and size-segregated air samplers. All environmental and forensic samples were collected by the UK counter terrorism police, following strict labelling and chain-of-custody protocols. The samples were analysed at the Belgian Nuclear Research Center suing the k0 method for instrumental neutron activation technique. A full consequence assessment analysis was carried out assuming that the observed concentration of Cs-133 in samples was Cs-137 instead and use was made of the specific activity of Cs-137. Due to the sensitivity of the information the European Commission classified this research. The resulted reported on in this work have been unclassified and are released to assist emergency planners and first responders to take the necessary precautions. The results indicate that, up to distances of 50 m from ground zero radiation levels will be considerable and therefore live-saving actions must be performed by fire/rescue wearing full protective gear. In addition, low-wind conditions will favor a long airborne residence time and therefore the use of full-face protective gear is a must. In order to protect first responders, a radiation protection specialist is to determine how long people can enter and remain in the contaminated area. The recovery of evidence in the case of a car-bomb will be hard or even impossible due to the high level of radioactive material remaining inside the vehicle.

Measurement report: Short-term variation in ammonia concentrations in an urban area increased by mist evaporation and emissions from a forest canopy with bird droppings

Abstract. Local meteorological conditions and natural and anthropogenic sources affect atmospheric NH3 concentrations in urban areas. To investigate potential sources and processes of NH3 variation in urban areas, hourly NH3 and NH4+ concentrations were measured during November 2017–October 2019 in Nagoya, a central Japanese megacity. Average NH3 concentrations are high in summer and low in winter. Daily minimum NH3 concentrations are linearly correlated with daily minimum air temperatures. By contrast, daily maximum NH3 concentrations increase exponentially with temperature, suggesting that different nighttime and daytime processes and air temperatures affect concentrations. Short-term increases in NH3 concentrations of two types were examined closely. Infrequent but large increases (11 parts per billion (ppb) for 2 h) occurred after mist evaporation during daytime. During 2 years of observations, only one event of this magnitude was identified in Nagoya, although evaporation of mist and fog occurs frequently after rains. Also, short-term increases occur with a large morning peak in summer. Amplitudes of diurnal variation in NH3 concentration (daily maximum minus minimum) were analyzed on days with nonwet and low wind conditions. Amplitudes were small (ca. 2 ppb) in winter, but they increased from early summer along with new leaf growth. Amplitudes peaked in summer (ca. 20 ppb) because of droppings from hundreds of crows before roosting in trees on the campus. High daily maximum NH3 concentrations were characterized by a rapid increase occurring 2–4 h after local sunrise. In summer, peak NH3 concentrations at around 08:00 local time (LT) in sunny weather were greater than in cloudy weather, suggesting that direct sunlight particularly boosts the morning peak. Daily and seasonal findings related to the morning peak imply that stomatal emission at the site causes the increase. Differences between daily amplitudes during the two summers was explained by the different input amounts of reactive nitrogen from bird droppings and rain, suggesting that bird droppings, a temporary rich source of NH3, affected the small forest canopy.

The Comparison of the Efficiency of Small Wind Turbine Generators with Horizontal and Vertical Axis Under Low Wind Conditions

Abstract The authors perform a comparative analysis of the efficiency of two types of low-power wind energy conversion systems with horizontal and vertical axis in the meteorological conditions of Latvia. The analysis is based on long-term wind speed measurements over the period of two years conducted by a network of 22 observation stations at the height of 10 m above the ground. The study shows that in the conditions of Latvia wind turbines with a horizontal axis are expected to work with greater efficiency than similar installations with a vertical axis. The paper presents the models of the spatial distribution of average wind speed, Weibull wind speed frequency distribution parameters and the values of the expected operational efficiency for small wind turbine generators. The modelling results are presented in the form of colour contour maps. Overall, the results of the study can serve as a tool for forecasting annual energy production and for estimating the feasibility of commercial use of wind energy at the height of 10 m in the territory of Latvia.

Modelo de pluma segmento com velocidades estocásticas para dispersão atmosférica em condições de vento fraco

This work presents an analytical solution for the transient three-dimensional advection-diffusion equation. This solution, obtained from a combination of the variable separation method and GILTT (Generalized Integral Laplace Transform Technique) is used to simulate the pollutant dispersion in the atmosphere. The new solution has the advantage of not requiring a numerical inversion performed in the temporal variable in works using only GILTT technique. The model was tested in low wind condition, with diffusion in transverse and longitudinal directions and stochastic speeds. Simulations were performed for the INEL experiment. The analytical character of the model makes it simple, which represents advantages in its development and implementation, as well as in the computational cost for execution.

Fenômeno de meandro do vento e a função de autocorrelação calculada com base na concentração de poluentes simulada pelo modelo transiente 3D-GILTT

The aim of this work is to present a pollutants dispersion transient model in low wind conditions to simulate the behavior of the pollutants plume in the atmosphere, considering in the model the u e v horizontal wind components simulated by the LES-PALM model. The dispersion model is based in the advection-diffusion equation and represent by this methodology the wind meandering phenomenon. The Generalized Integral Laplace Transform Technique in three dimensions (3D- GILTT) solves the transient advection-diffusion equation. The data utilized to initialize the simulations are data of the low wind INEL (Idaho National Engineering Laboratory) experiment accomplished in EUA. The results show that the dispersion model reproduces the wind meandering phenomenon, in other words, the autocorrelation function of the concentration simulated over an hour presents the negative lobule, similarly to observed lobules in the u and v wind components. Therefore, the model simulates the pollutants plume in a satisfactory way and can be used to air quality regulatory applications in low wind and wind meandering conditions.

Simulation of three-dimensional transient pollutant dispersion in low wind conditions using the 3D-GILTT technique

The aim of this work is to present a transient model in low wind conditionsto simulate the pollutants dispersion in the atmosphere. The dispersion model is based in the advection-diffusion equation and it considers the zonal and meridional components of the wind. The transient advection-diffusion equation is solved using integral transform techniques. In this work, the generalized integral transform and Laplace techniques are used, known in the literature as GILTT and which applied to the three-dimensional problem is called 3D-GILTT (Three-dimensional Generalized Integral Laplace Transform Technique). To validate the model, data from INEL experiment (Idaho National Engineering Laboratory) carried out in the USA were used. The model simulates the observed concentrations in a satisfactory way and can be used for regulatory air quality applications

Coordinated Control of Parallel DR-HVDC and MMC-HVDC Systems for Offshore Wind Energy Transmission

Parallel operation of a diode rectifier-based high-voltage direct current (DR-HVDC) and modular multilevel converter (MMC)-based HVDC (MMC-HVDC) for transmitting offshore wind energy is investigated in this article. An enhanced active power control scheme of the offshore MMC station is proposed to improve the power flow distribution between the MMC-HVDC and DR-HVDC links which are both connected to the offshore wind farm (OWF) ac network. By regulating the offshore voltage, all the wind powers are transmitted via the DR-HVDC link in low wind conditions while the offshore MMC power is controlled around zero to reduce transmission losses, considering the efficiency superiority of DR-HVDC over its MMC counterpart. When the DR-HVDC is out of service, wind energy is transferred via the MMC-HVDC and the wind turbine (WT) generated power is automatically limited by slightly increasing the offshore ac voltage to avoid potential MMC-HVDC overload. A power curtailment control is also proposed which slightly increases the dc voltage of the DR-HVDC to enable autonomous reduction of the generated wind power so as to avoid DR-HVDC overload during MMC-HVDC outage. The proposed coordinated control only uses local measurements and, without the need for communication, can seamlessly handle transitions including various faults. The proposed scheme enables fault ride-through operation and provides a high efficient solution with flexible operation for integrating large OWFs. Simulation results confirm the proposed control strategy.

Indoor Environmental Quality (IEQ) Analysis of a Two-Sided Windcatcher Integrated with Anti-Short-Circuit Device for Low Wind Conditions

Windcatchers are considered as promising passive ventilation and cooling strategy, but the ventilation performance of this system is still of concern in areas with low speed and unpredictable winds. The air short circuiting in windcatchers can reduce its ventilation performance and ability to introduce clean air and remove stale air. The current work aimed to evaluate the indoor environmental quality (IEQ) performance of a two-sided windcatcher fitted with an anti-short-circuit device (ASCD) for improving its performance in low wind speed conditions. Computational Fluid Dynamics (CFD) simulations were performed for different ASCD configurations. The CFD method was verified using grid-sensitivity analysis and validated by comparing the simulation results with wind tunnel data. The results indicated that the average difference between CFD results and previous experimentation was below 10%, therefore indicating good agreement. Building on the findings of the previous research, the study focused on evaluating the impact of the length of ASCD on the achieved fresh air supply rates and air change rate. The length of the ASCD was varied between 5 cm to 50 cm, while the angle was maintained at 80°. The shorter ASCD was still able to minimize the fresh supply airflow short-circuiting to the exhaust stream, and at the same time, it would also require a smaller ceiling space for installation and lower material cost. Hence, the 15 cm ASCD with 80° angle was selected for further analysis in this study. Then, consideration of low wind speed and various directions were studied to evaluate the ventilation performance of windcatcher with ASCD. The study simulated wind speeds between 0.5–2 m/s and two wind directions. Based on the assessment of IEQ factors, including mean age of air and percentage of dead zone, a 0° incident angle demonstrated slightly better results. The achieved fresh air supply rates ranged between 180 L/s to 890 L/s in 45° wind angle, while, for 0°, these values were from 160 L/s to 642 L/s. Likewise, the range of air change rates (ACH) was from 8 ACH to 32 ACH in 0° wind angle and increased to 9 ACH and then to 45 ACH in 45° wind angle.

PM10 source identification using the trajectory based potential source apportionment (TraPSA) toolkit at Kochi, India

A recently developed open source tool kit named the Trajectory based Potential Source Apportionment (TraPSA) was used to identify the sources of respirable particulates at Kochi, India. Using 24-h average particulate matter data from samples collected at five regulatory monitoring stations over the five-year period from January 2011 to October 2016, local and regional scale analyses were made. Concentration field analysis was performed using back trajectories generated by Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model with inputs from atmospheric reanalysis data. Conditional bivariate probability function analyses were made using local meteorology data to identify the influence of local sources. Most of the stations indicated the contribution from local traffic activities during low wind conditions and from a nearby industrial area especially during high speed winds. Back trajectory analysis identified potential source areas in Kerala as well as in nearby state of Tamil Nadu as contributing to the air quality at Kochi. Arabian sea on the western side was also observed to be a potential source area for Kochi. The study demonstrated the utility of TrapSA as a tool for deriving information about the potential source areas affecting particulate matter mass concentrations.

Deriving L-Band Tilting Ocean Surface Roughness From Measurements by Operational Systems

Waves much shorter than those measured by operational systems make significant contribution to the ocean surface roughness. This article describes a method to obtain the L-band tilting ocean surface roughness using wind speed and windsea dominant wave period coupled with a wind-wave spectrum model. Examples are presented with wind and dominant wave data from ocean buoys and hurricane hunters. Several related issues are discussed: high-frequency wave spectrum, integration limit, swell contribution, and measurements in extreme winds: 1) it is well known since the 1970s that with stationary sensors, extending the frequency range in measuring elevation spectrum does not yield useful short-wave information because of the low signal level and large Doppler frequency shift involved in measuring short waves. 2) Low-pass mean square slopes (LPMSSs) integrated to 5 and 11 rad/m are computed to quantify their difference as a function of wind speed and inverse wave age (IWA). The normalized difference decreases with increasing wind speed and decreasing IWA. 3) Swell contribution to the L-band LPMSS is almost negligible for wind speed greater than 5 m/s (less than 5% in 99% of observations). In low-wind conditions (wind speed less than 5 m/s), the swell contribution is difficult to assess because of inaccuracy in identifying the weak windsea system. 4) The coarse resolution in National Data Buoy Center (NDBC) wave spectra causes large data scatter in the computed LPMSS in very high winds (greater than 20 m/s). A mitigating solution is offered.

Temporal and spatial analysis of traffic – Related pollutant under the influence of the seasonality and meteorological variables over an urban city in Peru

A four yearlong air monitoring data (since 2015 to 2018) was collected to assess the impact of meteorological parameters such as temperature, relative humidity, wind speed and wind direction on the spatial and temporal variability of CO (carbon monoxide), NO2 (nitrogen oxide), O3 (ozone), SO2 (sulfur dioxide), PM10 and PM2.5 (particulate matter with diameter aerodynamic less than 2.5 μm and 10 μm respectively) in Lima Metropolitan Area (LMA). Data from eight air quality monitoring stations, currently under the supervision of the National Meteorological and Hydrological Service (SENAMHI), was used to capture traffic – related pollutants concentrations under various local traffic conditions. Effects on meteorological events on seasonal traffic-related pollutants concentration variability were identified. Using average data from the eight stations, it was found that the monthly mean traffic-related pollutants since 2015 to 2018 were higher in spring and winter and lower in autumn and summer. Low-wind speed was associated with events that contribute to elevated seasonal PM2.5 levels. Correlation coefficients between PM2.5 concentrations and meteorological variables fluctuated significaly across different seasons. High PM2.5 concentrations were associated with low relative humidity and high wind conditions in spring. Results suggest that there exist a seasonal variation of PM2.5 concentration, and set the need of future work on the understanding of the air pollution effects on human health.

EXTREMELY LOW FREQUENCY ELECTROMAGNETIC FIELD EXPOSURE MEASUREMENT IN THE VICINITY OF WIND TURBINES.

There is an exponential growth of public concern worldwide regarding the exposure to electromagnetic fields (EMF) generated by wind turbines. The high concern of the general population enhances the fact that EMF exposure remains a crucial issue that demands specific actions and reliable data to evaluate possible health hazards. EMF exposure measurements were conducted in two wind farm (W/F) areas in Greece. The magnetic field strength concentrated in the proximity of 22 wind turbines (20 type of Gamesa Eolica Siemens of total power of 17MW and 2 type of E53 Enercon, 800 KW each). Measurements were conducted using a Narda-NBM-550 basic unit (Narda Safety Test Solutions Company) using EHP-50F probe. The EMF exposure measurements were processed applying the weighted peak method (WPM), according to the 2013/35/EU Directive. WPM provides correction of the measured value of pulse signals, taking into account the phases of the various frequency components. The data were classified under two scenarios of EMF exposure: 'high wind' and 'low wind' conditions. The variation of the magnetic field strength was calculated between 1.13 and 1.42% (WPM). Measurements indicate that the intensity of the emitted magnetic field at the base of the wind turbines, in both high and low wind conditions, was relatively low (mean=0.146 μT), while decreasing rapidly with increasing distance and reaching background values 6m from the base. The results of the present study indicate that EMF levels are similar or even lower compared to those in urban areas and well below the national and international safety limits.

Influence of Storm Events on Chlorophyll Distribution Along the Oligotrophic Continental Shelf Off South-Western Australia

The role of storm events in controlling chlorophyll distribution along the oligotrophic Rottnest continental shelf is examined data collected by autonomous ocean gliders combined with meteorological data. Spatial and temporal distribution of chlorophyll concentrations were obtained from a repeated transect across the shallow continental shelf that revealed complex relationships among wind events (e.g. differences in wind speed and direction) and chlorophyll concentrations. Data indicated that the water column responded rapidly to changes in wind speeds alternating between stratification, de-stratification and vice-versa over 1-3 days. Under low wind conditions (wind speeds 15 ms-1) higher chlorophyll values were present throughout the vertically mixed water column. Maximum chlorophyll concentrations, more than double that due to climatology, were observed 1-3 days after the passage of storms subsequent to sediment re-suspension. Storm events, with an onshore component, promoted downwelling, the water column retained vertical stratification, and DSWC was present across the shelf. Here, DSWC intensified with higher chlorophyll in the cascaded water extending further offshore. It is concluded that wind speed and direction are the dominant parameters controlling the distribution of chlorophyll particularly during storm events.

Modeling and control of unmanned finless airship with robotic arms

This paper presents the mathematical modeling and control of a finless airship that can fly at low altitudes in low wind conditions. Slow speed symmetrical airships can move freely in 3-dimensional air space with a vector propulsion system. The forces/moments of robotic arm are derived at center of gravity (CG) of the airship, and controllers are designed using classical control theory. An inner-outer loop strategy is proposed here in this paper; LQR based longitudinal and lateral controllers are designed for inner control loops while PI-based controllers are proposed for the height and velocity in outer guidance loop. The performance of the proposed scheme is validated through 6-degree of freedom nonlinear simulation having actuator dynamics and sensor models including measurement noises. Different scenarios are generated in nonlinear simulation to check the performance and robustness of the proposed scheme; simulation results validated the effectiveness of proposed scheme.

Sources of error in open-path FTIR measurements of N<sub>2</sub>O and CO<sub>2</sub> emitted from agricultural fields

Abstract. Open-path Fourier transform infrared spectroscopy (OP-FTIR) is susceptible to environmental variables which can become sources of errors for gas quantification. In this study, we assessed the effects of water vapour, temperature, path length, and wind speed on quantitative uncertainties of nitrous oxide (N2O) and carbon dioxide (CO2) derived from OP-FTIR spectra. The presence of water vapour in spectra underestimated N2O mole fractions by 3 % and 12 %, respectively, from both lab and field experiments using a classical least squares (CLS) model when the reference and sample spectra were collected at the same temperature (i.e. 30 ∘C). Differences in temperature between sample and reference spectra also underestimated N2O mole fractions due to temperature broadening and the increased interferences of water vapour in spectra of wet samples. Changes in path length resulted in a non-linear response of spectra and bias (e.g. N2O and CO2 mole fractions were underestimated by 30 % and 7.5 %, respectively, at the optical path of 100 m using CLS models). For N2O quantification, partial least squares (PLS) models were less sensitive to water vapour, temperature, and path length and provided more accurate estimations than CLS. Uncertainties in the path-averaged mole fractions increased in low-wind conditions (<2 m s−1). This study identified the most common interferences that affect OP-FTIR measurements of N2O and CO2, which can serve as a quality assurance/control guide for current or future OP-FTIR users.

Hierarchical model predictive control of wind farm with energy storage system for frequency regulation during black-start

In high wind power penetration power system, using wind farm equipped with energy storage system (WF-ESS) as black-start (BS) source needs to maintain system frequency stability when starting up ancillary machine or picking up load. A hierarchical model predictive control (HMPC) method of WF-ESS for frequency regulation during BS is proposed in this paper, which consists of two control modes: frequency regulation mode and reserve recovery mode. For the first control mode, a PI controller is used to generate reference power for WF-ESS and to recover system frequency to 50 Hz. The proposed HMPC is divided into WF level and wind turbine (WT) level to accurately track the reference power and guarantee secure operation of each WT. Considering WTs’ different operation conditions, WF level MPC distributes reference power to WTs according to the proportion of single WT reserve to total WF reserve. The ESS power is utilized as supplementary when WF output power is insufficient. The rotor speed and pitch angle constraints are included in the WT level MPC while providing frequency response. After frequency deviation is eliminated, WF and ESS are coordinated by the second control mode to avoid a second frequency drop meanwhile reserve a certain proportion of WF available power for managing potential frequency disturbances in the future. A case study is conducted to show the effectiveness of the proposed control method under both low and high wind conditions.

Shape effects on aerodynamic loading of heliostats

The effect of the shape of the mirror of a heliostat is studied through wind tunnel tests in uniform smooth and turbulent flow conditions. Three shapes are investigated: square (reference case), octagonal and circular geometries. The forces and moments are measured on reduced scale models of heliostats in low, medium and strong turbulence wind conditions in a uniform wind profile. The turbulence intensity of the flow is adjusted in the wind tunnel test section by the adjunction of passive grids upstream the model. The experimental results are presented for several elevation and azimuth angles. The results showed that: in smooth flow conditions, the geometry of the mirror has very limited effect on the mean force coefficient, while impacting the fluctuating part of the aerodynamic loads. In turbulence flow conditions, the circular mirror/panel is advantageous for the aerodynamic design of the elevation drive and mirror support structure.