scholarly journals Impact of Wind Veer and the Coriolis Force for an Idealized Farm to Farm Interaction Case

2019 ◽  
Vol 9 (5) ◽  
pp. 922 ◽  
Author(s):  
Ola Eriksson ◽  
Simon-Philippe Breton ◽  
Karl Nilsson ◽  
Stefan Ivanell
Keyword(s):  
Coriolis Force ◽  
Wind Shear ◽  
Source Term ◽  
Wind Farms ◽  
Long Distance ◽  
Large Eddy ◽  
Relative Production ◽  
The Mean ◽  
The Right ◽  
The Impact

The impact of the Coriolis force on the long distance wake behind wind farms is investigated using Large Eddy Simulations (LES) combined with a Forced Boundary Layer (FBL) technique. When using the FBL technique any mean wind shear and turbulent fluctuations can be added with body forces. The wind shear can also include the mean wind veer due to the Coriolis force. The variation of the Coriolis force due to local deviations from the mean profile, e.g., from wakes, is not taken into account in the FBL. This can be corrected for with an extra source term in the equations, hereon defined as the Coriolis correction. For a row of 4 turbines it is shown that the inclusion of the wind veer turns the wake to the right, while including the Coriolis correction turns it to the left. When including both wind veer and Coriolis correction the impact of wind veer dominates. For an idealized farm to farm interaction case, two farms of 4 ∗ 4 turbines with 6 km in between, it can be seen that when including wind veer and the Coriolis correction a approximately 3% increase in the relative production for a full wake direction can be seen and only a slightly smaller increase can be seen when including only wind veer. The results indicate that FBL can be used for studies of long distance wakes without including a Coriolis correction but efforts need to be taken to use a wind shear with a correct mean wind veer.

scholarly journals Comparison of branded rugby headguards on their effectiveness in reducing impact on the head

2018 ◽  
Vol 4 (1) ◽  
pp. e000361 ◽  
Author(s):  
Erin R A Frizzell ◽  
Graham P Arnold ◽  
Weijie Wang ◽  
Rami J Abboud ◽  
Tim S Drew
Keyword(s):  
Impact Force ◽  
Linear Acceleration ◽  
Baseline Measurement ◽  
Peak Acceleration ◽  
Impact Forces ◽  
Impact Attenuation ◽  
The Mean ◽  
Force Reduction ◽  
The Right ◽  
The Impact

AimTo compare the available brands of rugby headguards and evaluate their impact attenuation properties at various locations on the cranium, with regard to concussion prevention.MethodsSeven different branded headguards were fitted onto a rigid headform and drop-tested in three different positions. An accelerometer measured the linear acceleration the headform experienced on impact with the ground. Each test involved dropping the headform from a height that generated 103.8 g on average when bare, which is the closest acceleration to the upper limit of the concussion threshold of 100 g. A mean peak acceleration for each drop position was calculated and compared with the bare baseline measurement.ResultsEach headguard demonstrated a significant decrease in the mean peak acceleration from the baseline value (all p≤0.01). Overall the Canterbury Ventilator was the most effective headguard, decreasing the impact force on average by 47%. The least effective was the XBlades Elite headguard, averaging a force reduction of 27%. In five of the seven headguards, the right side of the headwear was the most effective at reducing impact force.ConclusionOverall, the results indicate that it would be beneficial to wear a headguard during rugby in order to reduce the impact forces involved in head collisions. There was also a clear difference in performance between the tested brands, establishing the Canterbury headguard as the most effective. However, only one model of headguard from each brand was tested, so further research evaluating all other models should be considered.

scholarly journals A pressure-driven atmospheric boundary layer model satisfying Rossby and Reynolds number similarity

2021 ◽  
Vol 6 (3) ◽  
pp. 777-790
Author(s):  
Maarten Paul van der Laan ◽  
Mark Kelly ◽  
Mads Baungaard
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Atmospheric Boundary Layer ◽  
Wind Farm ◽  
Three Dimensional ◽  
Computation Time ◽  
Wind Farms ◽  
The Mean ◽  
The Impact ◽  
Pressure Driven

Abstract. Idealized models of the atmospheric boundary layer (ABL) can be used to leverage understanding of the interaction between the ABL and wind farms towards the improvement of wind farm flow modeling. We propose a pressure-driven one-dimensional ABL model without wind veer, which can be used as an inflow model for three-dimensional wind farm simulations to separately demonstrate the impact of wind veer and ABL depth. The model is derived from the horizontal momentum equations and follows both Rossby and Reynolds number similarity; use of such similarity reduces computation time and allows rational comparison between different conditions. The proposed ABL model compares well with solutions of the mean momentum equations that include wind veer if the forcing variable is employed as a free parameter.

scholarly journals Three-Dimensional Salt Dynamics in Well-Mixed Estuaries: Influence of Estuarine Convergence, Coriolis, and Bathymetry

2017 ◽  
Vol 47 (7) ◽  
pp. 1843-1871 ◽  
Author(s):  
Xiaoyan Wei ◽  
Mohit Kumar ◽  
Henk M. Schuttelaars
Keyword(s):  
Coriolis Force ◽  
Three Dimensional ◽  
Temporal Correlation ◽  
Salt Transport ◽  
Residual Circulation ◽  
Three Dimensional Model ◽  
Coriolis Effects ◽  
Set Up ◽  
The Right ◽  
The Impact

AbstractA semianalytical three-dimensional model is set up to dynamically calculate the coupled water motion and salinity for idealized well-mixed estuaries and prognostically investigate the influence of each physical mechanism on the residual salt transport. As a study case, a schematized estuary with an exponentially converging width and a channel–shoal structure is considered. The temporal correlation between horizontal tidal velocities and tidal salinities is the dominant process for the landward residual salt transport. The residual salt transport induced by residual circulation is locally significant, but the induced salt transport integrated over the cross section is small. The impacts of the estuarine geometry, Coriolis force, and bathymetry on the salt dynamics are studied using three dedicated experiments, in which the impact of each of these factors is studied separately. To assess the impact of width convergence, a convergent estuary without bathymetric variations or Coriolis force is considered. In this experiment, the temporal correlation between tidal velocities and salinities is the only landward salt transport process. In the second experiment, Coriolis effects are included. This results in a significant residual salt transport cell due to the advection of the tidally averaged salinity by residual circulation, with salt imported into the estuary from the left side and exported on the right (looking seaward). In the last experiment, a lateral channel–shoal structure is included while the Coriolis effects are excluded. This results in a significant landward salt transport through the deeper channel and a seaward salt transport over the shoals due to the advection of the tidally averaged salinity by residual circulation.

scholarly journals Wind speed analysis based on the logarithmic wind shear model: a case study for some brazilian cities

2020 ◽  
Vol 9 (7) ◽  
pp. e298973984
Author(s):  
Anny Key de Souza Mendonça ◽  
Antonio Cezar Bornia
Keyword(s):  
Wind Speed ◽  
Wind Power ◽  
Wind Shear ◽  
Wind Farms ◽  
Shear Model ◽  
The Public ◽  
Wind Speeds ◽  
Generating Capacity ◽  
Mean Wind Speed ◽  
The Mean

The wind power’ share in electricity generating capacity has increased significantly in recent years. Due to the variability in wind power generation, given the variations in wind speed and considering the increase in wind participation in the Brazilian energy matrix, a fact that reinforces the relevance of the source, this article aims to present the methods used to analyze the wind speed more used in the literature and to analyze the wind speed in several Brazilian cities. The logarithmic wind shear model was used to analyze mean wind speeds based on historical data of twelve Brazilian cities available to the public on the ESRL database for a period of eight years 2010 to 2018. The study showed that in localities such as Uruguaiana/RS, Campo Grande/MS, Uberlândia/MG, São Luiz/MA and Corumba/MS, mean wind speeds are strong in all altitudes of reference, with a gain of ± 2m/s of wind speed as the operational altitude increases. The logarithmic wind gain in high altitudes or low altitudes can be seen in z = 100 meters, where the mean wind speed found was Wn ≈ 8 m/s in Uruguaiana/RS and Campo Grande/MS, whereas in Manaus it was Wn ≈ 5 m/s. In Porto Alegre (RS), Florianópolis (SC), Curitiba/PR and Brasília/DF, the mean wind speed in altitudes ≥ 250 m becomes significant, allowing the implementation of wind farms if the technology proves to be economically feasible.

scholarly journals Extracting Microphysical Impacts in Large-Eddy Simulations of Shallow Convection

2014 ◽  
Vol 71 (12) ◽  
pp. 4493-4499 ◽  
Author(s):  
Wojciech W. Grabowski
Keyword(s):  
Traditional Approach ◽  
Cloud Droplet ◽  
Cloud Microphysics ◽  
Natural Variability ◽  
Large Eddy Simulations ◽  
Shallow Convection ◽  
Liquid Water Path ◽  
Large Eddy ◽  
The Mean ◽  
The Impact

Abstract A simple methodology is proposed to extract impacts of cloud microphysics on macrophysical cloud-field properties in large-eddy simulations of shallow convection. These impacts are typically difficult to assess because of natural variability of the simulated cloud field. The idea is to use two sets of thermodynamic variables driven by different microphysical schemes or by a single scheme with different parameters as applied here. The first set is coupled to the dynamics as in the standard model, and the second set is applied diagnostically—that is, driven by the flow but without the feedback on the flow dynamics. Having the two schemes operating in the same flow pattern allows for extracting the impact with high confidence. For illustration, the method is applied to simulations of precipitating shallow convection applying a simple bulk representation of warm-rain processes. Because of natural variability, the traditional approach provides an uncertain estimate of the impact of cloud droplet concentration on the mean cloud-field rainfall even with an ensemble of simulations. In contrast, the impact is well constrained while applying the new methodology. The method can even detect minuscule changes of the mean cloud cover and liquid water path despite their large temporal fluctuations and different evolutions within the ensemble.

scholarly journals A Comparison of Selected Assessment Results before and during the COVID-19 Pandemic in One University in South Africa

2021 ◽  
Vol 10 (7) ◽  
pp. 74
Author(s):  
Tafirenyika Mafugu
Keyword(s):  
Professional Development ◽  
Cognitive Skills ◽  
Quantitative Research ◽  
Research Approach ◽  
Student Knowledge ◽  
Science Courses ◽  
Online Assessments ◽  
The Mean ◽  
The Right ◽  
The Impact

The study examined the impact of coursework-only assessment, as made necessary at the onset of the COVID-19 pandemic, adopting a quantitative research approach with 1013 students. The data obtained were analysed using SPSS version 27.0 to obtain descriptive and inferential statistics. The results revealed significant differences between the 2019- and 2020 marks for the same courses. In two of the science courses (T2 and T3), the mean scores for 2019 were significantly higher than the mean scores for 2020. In the mathematics course, the 2020 marks were significantly higher than the marks for 2019. While a normal distribution was assumed for the science courses, the mathematic course showed marks that were skewed to the right. A higher number of distinctions in the F1 course and a significant decline in the mean scores for T1 and T2 implies that there is a need for professional development of lecturers teaching in the online space. It is, therefore, recommended that higher education lecturers need adequate professional development on setting and administering online assessments. The assessment should test adequate lower- and higher-order cognitive skills for sufficient testing of student knowledge during online assessments. Furthermore, a variety of assessment methods and a diversity of tasks may be used to ensure the reliability of the assessment outcomes.

scholarly journals Effect of Reynolds number and inflow parameters on mean and turbulent flow over complex topography

2016 ◽  
Vol 1 (2) ◽  
pp. 237-254 ◽  
Author(s):  
Ryan Kilpatrick ◽  
Horia Hangan ◽  
Kamran Siddiqui ◽  
Dan Parvu ◽  
Julia Lange ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Wind Shear ◽  
Large Scale ◽  
Flow Behaviour ◽  
Complex Topography ◽  
Mean Flow ◽  
Effective Roughness ◽  
The Mean ◽  
The Impact

Abstract. A characterization of mean and turbulent flow behaviour over complex topography was conducted using a large-scale (1 : 25) model in the WindEEE Dome at Western University. The specific topographic feature considered was the Bolund Hill escarpment facing westerly winds. A total of eight unique inflow conditions were tested in order to isolate the impact of key parameters such as Reynolds number, inflow shear profile, and effective roughness, on flow behaviour over the escarpment. The results show that the mean flow behaviour was generally not affected by the Reynolds number; however, a slight increase in speed-up over the escarpment was observed for cases with lower inflow roughness. The shape of the inflow wind shear profile also had a minor impact on the mean flow near the escarpment. More significant effects were observed in the turbulent flow behaviour, where the turbulent kinetic energy (TKE) over the escarpment was found be a strong function of inflow roughness and a weak function of the Reynolds number. The local change in the inflow wind shear was found to have the most significant influence on the TKE magnitude, which more closely approximated the full-scale TKE data, a result which had not been previously observed in wind tunnel modelling of this topography.

scholarly journals Strongly sheared stratocumulus convection: an observationally based large-eddy simulation study

2012 ◽  
Vol 12 (2) ◽  
pp. 4941-4977
Author(s):  
S. Wang ◽  
X. Zheng ◽  
Q. Jiang
Keyword(s):  
Large Eddy Simulation ◽  
Turbulence Intensity ◽  
Wind Shear ◽  
Marine Boundary Layer ◽  
Turbulence Structure ◽  
Heating Rates ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wind Shears ◽  
The Impact

Abstract. Unusually large wind shears across the inversion in the stratocumulus-topped marine boundary layer (MBL) were frequently observed during VOCALS-REx. To investigate the impact of wind shear on the MBL turbulence structure, a large-eddy simulation (LES) model is used to simulate the strongly sheared MBL observed from Twin-Otter RF 18 on 13 November 2008. The LES simulated turbulence statistics agree in general with those derived from the measurements, with the MBL exhibiting a decoupled structure characterized by an enhanced entrainment and a turbulence intensity minimum just below the clouds. Sensitivity simulations show that the shear tends to reduce the dynamic stability of the inversion, enhance the entrainment mixing, and decrease the cloud water. Consequently, the turbulence intensity in the MBL is significantly weakened by the intense wind shear. The inversion thickens considerably and the MBL top separates from the cloud top, creating a finite cloud-free sublayer of 10–50 m thickness within the inversion, depending on the shear intensity. The wind shear enhances the turbulence buoyant consumption within the inversion, and simultaneously weakens the buoyant production in the cloud layer. These effects may result in different heating rates between the cloud and subcloud layer, leading to a process that tends to decouple the cloud from the subcloud layer. The decoupling process occurs even without solar radiation in the case of an intense wind shear similar to the observations.

scholarly journals Investigation of the effect of Reynolds number and inflow parameters on mean and turbulent flow over complex topography

2016 ◽  
Author(s):  
Ryan Kilpatrick ◽  
Horia Hangan ◽  
Kamran Siddiqui ◽  
Dan Parvu ◽  
Julia Lange ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Wind Shear ◽  
Large Scale ◽  
Flow Behaviour ◽  
Complex Topography ◽  
Mean Flow ◽  
Effective Roughness ◽  
The Mean ◽  
The Impact

Abstract. A characterization of mean and turbulent flow behaviour over complex topography was conducted using a large-scale (1:25) model of Bolund Hill in the WindEEE Dome at Western University. The specific topographic feature considered was an escarpment. A total of eight unique inflow conditions were tested in order to isolate the impact of key parameters such as Reynolds number, inflow shear profile and upstream effective roughness, on flow behaviour over the escarpment. The results show that the mean flow behaviour was generally not affected by the Reynolds number, however a slight increase in speed-up over the escarpment was observed for cases with lower upstream roughness. The shape of the inflow wind shear profile also had a minor impact on the mean flow near the escarpment. More significant effects were observed in the turbulent flow behaviour, where the turbulent kinetic energy (TKE) over the escarpment was found be a strong function of upstream roughness and a weak function of the Reynolds number. The local change in the upstream wind shear was found to have the most significant influence on the TKE magnitude, which more closely approximated the full-scale TKE data, and had not been previously observed in wind tunnel modelling of this topography.

scholarly journals LES study of the impact of moist thermals on the oxidative capacity of the atmosphere in southern West Africa

2017 ◽  
Author(s):  
Fabien Brosse ◽  
Maud Leriche ◽  
Céline Mari ◽  
Fleur Couvreux
Keyword(s):  
Turbulent Mixing ◽  
Reaction Rate ◽  
Reaction Rates ◽  
Oxidative Capacity ◽  
Detailed Chemistry ◽  
Substantial Modification ◽  
Large Eddy ◽  
On Line ◽  
The Mean ◽  
The Impact

Abstract. The hydroxyl radical (OH) is a highly reactive specie and plays a key role in the oxidative capacity of the atmosphere. The total OH reactivity, corresponding to the inverse of OH lifetime, may have a significant fraction non-attributable to commonly measured compounds. The turbulence-driven segregation of OH and its reactants can cause substantial modification of averaged reaction rates, and thus of the total OH reactivity, when compared to a perfectly mixed assumption. We study the impact of turbulent mixing on the OH reactivity with Large-Eddy Simulations from the Meso-NH model coupled on-line with a detailed chemistry mechanism in two contrasted regimes. Our findings show that the non-mixing of isoprene (resp. aldehydes) and OH leads to 30 % decrease (resp. 16 % increase) of the mean reaction rate at the top of the boundary layer and consequently to 9 % decrease (resp. 5 % increase) of the OH total reactivity in a biogenic (resp. anthropogenic) environment. Moreover, the total OH reactivity is highest inside thermals in both cases.

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