Bayesian method for estimating Weibull parameters for wind resource assessment in the Equatorial region: a comparison between two-parameter and three-parameter Weibull distributions

The two-parameter Weibull distribution has garnered much attention in the assessment of windenergy potential. The estimation of the shape and scale parameters of the distribution has broughtforth a successful tool for the wind energy industry. However, it may be inappropriate to use thetwo-parameter Weibull distribution to assess energy at every location, especially at sites wherelow wind speeds are frequent, such as the Equatorial region. In this work, a robust technique inwind resource assessment using a Bayesian approach for estimating Weibull parameters is firstproposed. Secondly, the wind resource assessment techniques using a two-parameter Weibulldistribution and a three-parameter Weibull distribution which is a generalized form of twoparameterWeibull distribution are compared. Simulation studies confirm that the Bayesianapproach seems a more robust technique for accurate estimation of Weibull parameters. Theresearch is conducted using data from seven sites in Equatorial region from 1o N of Equator to 19oSouth of Equator. Results reveal that a three-parameter Weibull distribution with non-zero shiftparameter is a better fit for wind data having a higher percentage of low wind speeds (0-1 m/s) andlow skewness. However, wind data with a smaller percentage of low wind speeds and highskewness showed better results with a two-parameter distribution that is a special case of threeparameterWeibull distribution with zero shift parameter. The results also demonstrate that theproposed Bayesian approach and application of a three-parameter Weibull distribution areextremely useful in accurate estimate of wind power and annual energy production.

CFD Comparative Study on Bended and 2D Airfoils on HAWT Performance

The design of a conventional horizontal axis wind turbine (HAWT) is based on the aerodynamic characteristics of a two-dimensional (2D) airfoil. The rotational motion and the consequent aerodynamic effects, of HAWT’s rotor, do not guarantee an optimal design point that matches the 2D airfoil characteristics. The present work studies the diversion of the flow due to the spanwise velocity component in a rotating reference frame. It suggests that a slight deviation in the flow away from the chordwise direction could alternate the characteristics of the airfoil profile. A bended profile with a circular arc was extracted from a baseline rotating blade, flattened, and modelled against the 2D S826 airfoil. The results show a substantial discrepancy in the airfoil characteristics which could influence the turbine efficiency. Therefore, it suggests using a pre-bended airfoil (3D) while modeling the blade, so the circular section will match the correct airfoil coordinates. The proposed bended-profile version was modeled against the baseline blade. This novel blade shows an augmentation in the power coefficient up to 5.4% starting from the design point to high tip speed ratios (TSR) and low wind speeds.

Assessment of scale of hazards due to pool fire for a fossil fired power plant in India

Hazards for a fossil fired power plant located at coastal Gujarat in India have been assessed. The trajectory and spread of the plume from tanks of fossil fired power plant were predicted using existing models named Carter, Mills, Briggs and Zonato during winter and summer seasons with low and high wind speeds observed in day and night hours. Results show that wide areas of habitation and human settlement to the northeast of the site may be potentially under hazards due to southwesterly and southerly winds during summer. Plume heights and widths are found high in the morning hours or late night when wind speeds are low. As wind speed increases around noon, low plume heights and widths are obtained. Length scales become low at low wind speeds and vice-versa. Lethal doses of thermal radiation beyond radial distance of 70 m are within the tolerable limit under hazardous condition.

Five Years (2014–2018) of Beta Activity Concentration and the Impact of Synoptic and Local Meteorological Conditions in Bilbao (Northern Spain)

The aim of this paper is to statistically characterize gross beta activity concentrations in ground-level air in Bilbao (northern Spain) by analysing five years (2014–2018) worth of weekly measurements in aerosols collected in filters to analyse the impact of local meteorological parameters on concentrations. In addition, synoptic meteorological scenarios associated with anomalous beta surface activity concentrations were identified. Over this five-year period, beta activity concentrations ranged from 35.45 µBq/m3 to 1778 µBq/m3 with a mean of 520.12 ± 281.77 µBq/m3. A positive correlation was found with the alpha concentrations (0.67), with an average of 0.138 for the alpha/beta ratio, and a low correlation was found with 7Be (0.16). Statistical analysis identified a seasonal component in the time series, increasing, on average, beta activity concentrations from winter to autumn. The highest beta activity concentrations were measured under the arrival of southerly land winds with low wind speeds, while the wind analysis (surface winds and air masses) of two different seasonal periods (autumn 2015 and winter 2017) have highlighted how small variations in synoptic and local winds highly influence beta activity concentrations. These results are relevant to understand the meteorological factors affecting beta activity concentrations in this area and hence to define meteorological scenarios that are in favour to high/anomalous surface activity concentrations that are harmful to the environmental and public health.

Bothersome Flies: How Free-Ranging Horses Reduce Harm While Maintaining Nutrition

The horses of Shackleford Banks, NC, United States are harassed by many species of biting flies. Apart from being a nuisance, their bites can lead to blood loss and transmit disease. As a result, these horses tend to avoid areas where fly abundances are high. Like other free-ranging horse populations, environmental factors such as low wind speeds and high temperatures increase fly loads per horse. Similarly, coat color matters since darker horses attract more flies than lighter ones, especially on hot sunny days. Many horse populations reduce per capita fly loads by living in large groups or by bunching tightly together. Shackleford horses do so, too, but also use wind speed differences among habitats to modulate fly numbers. By adopting a systematic pattern of moving between habitats such that they only visit a habitat when wind speed is high enough to keep fly harassment to a tolerable level, they can avoid being bitten while continuing to forage. Typically, they begin the day foraging on the salt marshes where fly abundance is inherently low and are lowered further by faint early morning breezes. Later in the morning, horses move to grassy patches (swales) when increasing wind speed reduces fly landings there to levels found on the marshes. Later still, when wind speeds peak, horses begin foraging among the sand dunes. At this point wind speeds are high enough so that horses using any habitat will be minimally harassed by flies, thus enabling them to freely choose where to feed based on which habitat meets particular dietary needs for protein, energy and nutrients on any particular day. Hence, Shackleford horses follow the breeze to solve a challenging dilemma of maintaining a high nutritional plane without succumbing to fly harassment. Other free-ranging horses populations appear to have a more limited “either-or” choice of “bite or be bitten,” thus limiting their decision-making options.

A Review of Solidity and Rotor Size Effects on Water-Pumping Windmills

The windmill is one of the important applications of wind energy and it is one of the best and the easiest ways to manipulate this wind power and use it for water pumping. The best feature of windmills is their high solidity, which gives high torque at the starting. Therefore, they will be able to lunch at low wind speeds like 2 m/s which gives a great possibility of utilizing, especially in the agricultural countries. This feature has been the focus of attention of researchers and developers over the long years. There are several factors affected by it, the most prominent of which is the number of blades and the diameter of the rotor. Some researchers have tested with different models of different diameters and others did on different numbers of blades. The challenge is how to find a model with an ideal number of blades and diameter that can give us the highest torque value under low wind conditions. In this paper, the multi-bladed horizontal axis wind turbines, which are used for water pumping, are discussed. Besides, the literature review is described, which presented the basic design requirements for windmill rotors as solidity, diameter, and tip speed ratio, also information given about materials that used in manufacture. The investigations of this paper are focused on the effect of the number of blades to reach the main goal and the best performance at located wind speeds.

The Effect of Windscreens and Walkways On Air-cooled Condenser Performance and Fan Blade Dynamic Loading

This paper presents a relative comparison of the impact of cruciform screens, perimeter screens and walkways on 3 × 6 cell forced draft air-cooled condenser's (ACC) thermal performance and dynamic fan blade loading under windy conditions. Numerical simulations were carried out for the three mitigation measures at two fan platform heights, four wind speeds and three wind directions. The results indicate that walkways are a robust solution to ACC wind effects and offer benefits in terms of thermal performance and dynamic blade loading under all wind conditions considered. Cruciform screens offered the most effective mitigation of wind-related thermal performance deterioration under certain wind conditions, but the impact of these screens is sensitive to the wind direction. The dynamic blade loading impact of cruciform screens is variable, and these screens are not recommended for dynamic blade loading mitigation. Perimeter screens offered the most effective mitigation of dynamic blade loading and were particularly effective at high wind speeds but often exacted a penalty in terms of thermal performance at moderate to low wind speeds. The results of this study indicate that a correctly configured wind mitigation system, potentially consisting of more than one individual mechanism, could help improve thermal performance and simultaneously reduce dynamic blade loading under windy conditions resulting in a robust, wind resistant condenser.

Go with the flow: The extent of drag reduction as epiphytic bromeliads reorient in wind

Vascular epiphytes represent almost 10% of all terrestrial plant diversity. Being structurally dependent on trees, epiphytes live at the interface of vegetation and atmosphere, making them susceptible to atmospheric changes. Despite the extensive research on vascular epiphytes, little is known about wind disturbance on these plants. Therefore, this study investigated the wind-epiphyte mechanical interactions by quantifying the drag forces on epiphytic bromeliads when subjected to increasing wind speeds (5–22 m s-1) in a wind tunnel. Drag coefficients (Cd) and Vogel exponents (B) were calculated to quantify the streamlining ability of different bromeliad species. Bromeliads’ reconfiguration occurred first via bending and aligning leaves in the flow direction. Then leaves clustered and reduced the overall plant frontal area. This reconfiguration caused drag forces to increase at a slower rate as wind velocity increased. In the extreme case, drag force was reduced by 50% in a large Guzmania monostachia individual at a wind velocity of 22 m s-1, compared to a stiff model. This species had one of the smallest Cd (0.58) at the highest wind velocity, and the largest negative mean B (-0.98), representing the largest reconfiguration capacity amongst the tested bromeliads. The streamlining ability of bromeliads was mainly restricted by the rigidity of the lower part of the plant where the leaves are already densely clustered. Wind speeds used in this study were generally low as compared to storm force winds. At these low wind speeds, reconfiguration was an effective mechanism for drag reduction in bromeliads. This mechanism is likely to lose its effectiveness at higher wind speeds when continuous vigorous fluttering results in leaf damage and aspects such as root-attachment strength and substrate stability become more relevant. This study is a first step towards an understanding of the mechanical bottleneck in the epiphyte-tree-system under wind stress.

Traffic Density-Related Black Carbon Distribution: Impact of Wind in a Basin Town

Black carbon is one of the riskiest particle matter pollutants that is harmful to human health. Although it has been increasingly investigated, factors that depend on black carbon distribution and concentration are still insufficiently researched. Variables, such as traffic density, wind speeds, and ground levels can lead to substantial variations of black carbon concentrations and potential exposure, which is even riskier for people living in less-airy sites. Therefore, this paper “fills the gaps” by studying black carbon distribution variations, concentrations, and oscillations, with special emphasis on traffic density and road segments, at multiple locations, in a small city located in a basin, with frequent temperature inversions and infrequent low wind speeds. As wind speed has a significant impact on black carbon concentration trends, it is critical to present how low wind speeds influence black carbon dispersion in a basin city, and how black carbon is dependent on traffic density. Our results revealed that when the wind reached speeds of 1 ms−1, black carbon concentrations actually increased. In lengthy wind periods, when wind speeds reached 2 or 3 ms−1, black carbon concentrations decreased during rush hour and in the time of severe winter biomass burning. By observing the results, it could be concluded that black carbon persists longer in higher altitudes than near ground level. Black carbon concentration oscillations were also seen as more pronounced on main roads with higher traffic density. The more the traffic decreases and becomes steady, the more black carbon concentrations oscillate.

Dependence of Power Characteristics on Savonius Rotor Segmentation

Savonius rotors are large and heavy because they use drag force for propulsion. This leads to a larger investment in comparison to horizontal axis wind turbine (HAWT) rotors using lift forces. A simple construction of the Savonius rotor is preferred to reduce the production effort. Therefore, it is proposed here to use single-segment rotors of high elongation. Nevertheless, this rotor type must be compared with a multi-segment rotor to prove that the simplification does not deteriorate the effectiveness. The number of segments affects the aerodynamic performance of the rotor, however, the results shown in the literature are inconsistent. The paper presents a new observation that the relation between the effectiveness of single- and multi-segment rotors depends on the wind velocity. A single-segment rotor becomes significantly more effective than a four-segment rotor at low wind speeds. At high wind speeds, the effectiveness of both rotors becomes similar.