Air Density Variations Research Articles

Floating wind turbine stability and time response analysis with rotating modes

The periodic azimuthal time dependence of a linearized simple floating wind turbine model with four degrees of freedom is dealt with by developing a particular procedure that enables a stability analysis calculation and reduces computational efforts to calculate time responses. We apply Hill’s method for the aeroelastic stability analysis by generating a constant state-space hyper-matrix that takes into account the periodic azimuthal dependence of the system. It is used to compute precisely the time domain response and to solve an overall eigenvalue problem where natural frequency and modal damping are determined through the eigenvalues. For a varying rotational speed with a fixed air density, eigenfrequencies from Hill’s method are displayed on a Campbell diagram that is based on a waterfall plot of the frequencies obtained by decay tests peaks using the time domain model. Through the modal analysis as well, an investigation of the impact of aerodynamic damping is done following the same procedures by rather fixing the rotational speed and varying air density. In the end, a forcing moment of the platform pitch motion is added to analyze the accuracy of fast time response calculations compared to the time domain model benchmark results.

Feasibility of Wind Energy Utilization for Sustainable Power Generation in Ilorin, Kwara State, Nigeria's North-Central Region

The escalating energy demands across Nigeria, especially in remote rural areas, have outpaced the capacity of the national electricity grid, necessitating the development of independent and sustainable energy sources. Among the renewable options, wind energy stands out as a promising solution. This study focuses on assessing the potential of wind energy in Ilorin, located in Kwara State, within Nigeria's north-central region. Utilizing data collected from 2007 to 2021 by the Nigerian Meteorological Agency, the research examines monthly average wind speeds at two specific coordinates in Ilorin, considering variations in air density. The study utilizes a 15-year set of monthly average wind velocities obtained from the Nigerian Meteorological Agency (NiMet) Headquarters in Abuja, measured at a height of 10 meters above ground level. By employing the 2-coefficient Weibull statistical model and extrapolation principles across different altitudes ranging from 150 to 900 meters above ground level, the study reveals distinct seasonal patterns of wind speeds ranging from 1.1 to 5.1 m/s in Ilorin. Furthermore, wind power density values ranging from 6.7 to 39.20 W/m2 are identified, with optimal wind attributes observed at altitudes exceeding 900 meters. These findings provide valuable insights for assessing the feasibility of wind energy utilization and designing efficient systems in Nigeria's north-central regions, aiding in the sustainable energy transition.

On the Variation of Cup Anemometer Performance Due to Changes in the Air Density

In the present paper, the effect of air density variations on cup anemometer performance is analyzed. The effect on the sensor’s performance is mainly due to the difference between the altitude at which the cup anemometer is working and the altitude at which this instrument was calibrated. Data from the available literature are thoroughly analyzed, focusing on explaining the coupled effect of the air temperature on both the rotor’s friction torque and the air density (that is, related to the aerodynamic torque on the rotor). As a result, the effect of air density variation at constant temperature (that is, leaving aside any variation of friction forces at the anemometer rotor shaft) on the sensor transfer function (i.e., on the calibration constants) is evaluated. The analysis carried out revealed a trend change in the variation with air density of the transfer function of the cup anemometer. For densities greater than 0.65, the calibration constants of the instrument have a variation with density that must necessarily change suddenly as the start-up speed, represented by the calibration constant B, becomes zero around this value of air density. To highlight the relevance of the present research, some estimations of the effect of wind speed measurement errors associated with air density changes on the Annual Energy Production (AEP) of wind turbines are included. A 1.5% decrease in the AEP forecast at air density corresponding to 2917 m above sea level is estimated for 3000–4500 kW wind turbines.

Simple Experiment to Show Gravity Does Not Affect the Velocity of Sound

In the present work, we have designed an electronic setup to experimentally verify that gravity does not directly affect the velocity of sound as stated by Lord Rayleigh. For this purpose, we have designed a setup comprising of two sensors namely ultrasonic sensor and accelerometer and a microcontroller Raspberry Pi to determine the values of sound velocity and acceleration due to gravity. The setup was then carefully enclosed in a box with bubble pack and dropped from a height of [Formula: see text]. At this height, there is no variation in air pressure and density, thus, the only parameter which is being varied is acceleration due to gravity. Under the free fall condition, the Raspberry Pi was programmed to control the working of both the sensors and store their responses in the memory card. The results show that the acceleration due to gravity acting upon the setup becomes negligible soon after it is dropped but the velocity of sound remains unaffected.

Exploring influence of air density deviation on power production of wind energy conversion system: Study on correction method

Thousands of wind turbines are already installed, providing renewable energy to meet the growing energy demand of consumers. This article investigates the effect of air density deviation, which depends on weather conditions, on power production of operational wind turbines, and examines strategy to mitigate this effect. Throughout the year, the air density in the area where the wind turbines are installed experiences continuous variations. It affects the annual power production of the wind turbine. Therefore, it is essential to discover a method that can reduce the effect of air density changes on power production of the wind turbine without adding extra extender blade. The effect of air density deviation on parameter of the wind turbines is investigated using four years measurement data (with a 10-minute interval) as well as simulation data. To reduce air density effect, the pitch angle and torque gain are readjusted rather than setting it constant based on the air density value. The analysis and simulation study were conducted in Matlab/Simulink® software. The results revealed that the suggested correction in pitch angle and torque gain according air density effectively alleviated the effect of air density variations, and the power production of the wind turbine was increased.

Path Planning of Electric VTOL UAV Considering Minimum Energy Consumption in Urban Areas

As a new mode of transportation in the future, electric vertical take-off and landing unmanned aerial vehicles (eVTOL UAV) can undertake the task of logistics distribution and carry people in urban areas. It is challenging to carry out research designed to plan the path of eVTOL UAVs which can have a safe and sustainable operation mode in urban areas. Therefore, this work proposes a method for planning an obstacle-free path for eVTOL UAVs in urban areas with the goal of minimizing energy consumption. It aims to improve the safety and sustainability of eVTOL UAV operations. Based on variations of air density with height, a more accurate formula for calculating battery energy consumption of eVTOL UAV is derived. It is used in the vertical takeoff and landing phase and horizontal flight phase, respectively. Considering the influence of buildings on eVTOL UAV operation, a path planning method applicable to complex urban environments is proposed. The safe nodes of eVTOL UAV flight are obtained by using Voronoi diagrams based on building locations. Then, the complete shortest and obstacle-free path is obtained by using a Dubins geometric path and Floyd algorithm. After obtaining the obstacle-free paths for all flight height zones, the battery energy consumption of the eVTOL UAV in each flight height zone is calculated. Then, the flight height with the minimum energy consumption is obtained. The simulation results show that the path length obtained by the proposed path planning method is shorter than that obtained by particle swarm optimization; the total battery energy consumption changes in the same pattern in the low-altitude areas and high-altitude areas; the difference between the maximum and minimum energy consumption in the small area enables the eVTOL UAV to cover about 350 m more, and about 420 m more in the large area. Therefore, in future high-frequency UAV mission flights, choosing the altitude with the lowest energy consumption can reduce UAV operator costs. It can also significantly increase UAV transport range and make UAVs operate more sustainably.

МАТЕМАТИЧЕСКАЯ МОДЕЛЬ РАВНОВЕСИЯ СТОЛБА СЖИМАЕМОЙ АТМОСФЕРЫ. ЧАСТЬ 1: СТАЦИОНАРНЫЕ РЕШЕНИЯ ДЛЯ ТЕМПЕРАТУРЫ

An analytical model of mathematical physics, which is implemented for an unbounded column of compressible atmosphere, is discussed. For the column, there are two equilibrium conditions, which are written in the form of a system of aerodynamic equations. The first condition is the classical condition of hydrostatic, which is derived from the equations of motion. The second one is derived from the continuity equation and arises due to temporal variations of air density. Two boundary conditions are selected near the solid surface: one is the magnitude of temperature and second condition is the magnitude of its vertical gradient. This allows us to consider the column without any restrictive conditions at some upper boundary. The analytical solution for adiabatic temperature can contain a sharp minimum at some height, above which the temperature rises with altitude. Herewith the temperature profile depends on the altitude linearly near the surface. The physical interpretation of the solutions based on the data of experimental measurements in the Earth's atmosphere is discussed. The analytical solution can be used to describe adiabatic atmospheric column, which is important for some applications. The research results improve understanding of processes in atmosphere and can be used for scientific and educational purposes.

Whole Genome Sequencing Reveals the Structure of Environment-Associated Divergence in a Broadly Distributed Montane Bumble Bee, Bombus vancouverensis

Abstract Broadly distributed species experience divergent abiotic conditions across their ranges that may drive local adaptation. Montane systems where populations are distributed across both latitudinal and elevational gradients are especially likely to produce local adaptation due to spatial variation in multiple abiotic factors, including temperature, oxygen availability, and air density. We use whole-genome resequencing to evaluate the landscape genomics of Bombus vancouverensis Cresson (Hymenoptera: Apidae), a common montane bumble bee that is distributed throughout the western part of North America. Combined statistical approaches revealed several large windows of outlier SNPs with unusual levels of differentiation across the region and indicated that isothermality and elevation were the environmental features most strongly associated with these variants. Genes found within these regions had diverse biological functions, but included neuromuscular function, ion homeostasis, oxidative stress, and hypoxia that could be associated with tolerance of temperature, desiccation, or high elevation conditions. The whole-genome sequencing approach revealed outliers occurred in genome regions with elevated linkage disequilibrium, elevated mean FST, and low intrapopulation nucleotide diversity. Other kinds of structural variations were not widely associated with environmental predictors but did broadly match geographic separation. Results are consistent with other studies suggesting that regions of low recombination may harbor adaptive variation in bumble bees within as well as between species and refine our understanding of candidate genes that could be further investigated as possible targets of selection across the B. vancouverensis range.

Spatiotemporal variation in air density and associated effects on the wind-induced response of high-rise buildings

It is widely acknowledged that the density of the atmosphere noticeably varies with space and time. However, the effects of spatiotemporal variation in air density on the wind-induced response of building structures, especially of high-rise buildings, have usually been neglected in practice. This paper presents a field study on the spatiotemporal variation in air density based on meteorological records collected from weather stations at various latitudes and ground elevations. The vertical profile of air density in a typhoon’s core region is highlighted, and a data-driven profile model is proposed. The dependence of wind-induced response of high-rise buildings on air density is then investigated via a wind tunnel test. A pressure model for a high-rise building with a square cross-section is tested, and the wind-induced acceleration response of the building is estimated. The results suggest that if the proposed profile of the typhoon air density is adopted, the estimation of the wind-induced structural response would be below the permitted level, while if a scheme with a constant air density is adopted, the structural response would exceed the limit. This means that taking the spatiotemporal variation in air density into account in wind-resistant building design can sometimes lead to considerable economic benefits.

A revised offshore wind resource assessment and site selection along the Indian coast using ERA5 near-hub-height wind products

The present study aims to re-assess offshore wind resources and analyse the wind climate along the Indian coast using the latest ERA5 near-hub-height wind products. Further, proposed an index to identify the hotspots for offshore wind farm (OWF) establishment. The effect of air density variation is considered while estimating wind power density (WPD) and actual power generation with the two latest wind turbines. Results show that maximum wind speed (7–10 m/s) and WPD (500–650 W/m2) are along the southern coast. The peak frequency of exploitable wind energy (>60%) is observed along the Tamil Nadu coast. Further, it is observed that consideration of standard air density overestimates the WPD with 5–7.5%, and wind turbines power output (2.5–5.1%) than actual air density. The suggested hotspots for OWFs have the potential of generating 1.84–3.96 GWh/year with a V164/9500 wind turbine. The methodology presented in this study will aid decision-makers in rapidly identifying and characterising OWF sites for the Indian coast and other regions.

Impact of Air Density Variation on a Simulated Earth-to-Air Heat Exchanger’s Performance

Due to their simple design and reliable operation, earth-to-air heat exchangers (EAHE) are used in modern buildings to reduce ventilation heat losses. EAHE operation in atmospheric conditions results in variation in ambient air temperature and pressure affecting air density. The paper presents the study on the impact of ambient air density variation on the calculated hourly air temperature at the EAHE outlet and the resulting energy use for space heating and cooling of an exemplary residential building. The ground temperature was computed from the model given in EN 16798-5-1. Then, air density was obtained using five various methods. Energy use for space heating and cooling of the building was computed using the 5R1C thermal network model of EN ISO 13790. Depending on the chosen method and concerning the base case without EAHE, a reduction in annual heating and cooling needs was obtained from 7.5% to 8.8% in heating and from 15.3% to 19% in cooling. Annual heating and cooling gain from EAHE were 600.9 kWh and 628.3 kWh for heating and 616.9 kWh and 603.5 kWh for cooling for the Typical Meteorological Years (TMY) and International Weather for Energy Calculation (IWEC) files, respectively. Unit heating and cooling gains per heat exchanger area were from 34.9 kWh/m2 to 36.8 kWh/m2 and from −35.1 kWh/m2 to −36.3 kWh/m2. Density variation with temperature from the relevant typical Polish meteorological year at constant pressure, in comparison to the method of EN 16798-5-1, resulted in an hourly difference of that unit gain up to 4.3 W/m2 and 2.0 W/m2 for heating and cooling, respectively. The same was true inthe case of IWEC files that resulted in differences of 5.5 W/m2 and 1.1 W/m2.

The Influence of Fly Ash on the Mechanical Performance of Cementitious Materials Produced with Recycled Cement

Concrete is the most widely used construction material in the world; as such, the best way to promote a more sustainable construction industry is to improve the environmental performance of this material. Since cement production is the main source of the high environmental impact of concrete, due to the high calcination temperature that clinker requires, replacing this binder with recycled cement would allow for the establishment of a new concrete design with a much lower ecological footprint. This research intends to analyse the mechanical performance of mortars with recycled cement and fly ash. Mixes with two replacement ratios of recycled cement (5% and 10%) were studied separately or in combination with fly ash (10% and 20%). An exhaustive experimental programme was designed to assess the variation in air content, density, compressive and flexural strengths, modulus of elasticity, and ultrasonic pulse velocity. The results suggest that the simultaneous use of recycled cement and fly ash improves the mechanical performance of mortars relative to those with recycled cement only or fly ash only.

Seismic and Newtonian Noise in the GW Detectors

Gravitational wave detectors aim to measure relative length variations of the order of ΔL/L≃10−21, or less. Thus, any mechanism that is able to reproduce such a tiny variation can, in principle, threaten the sensitivity of these instruments, representing a source of noise. There are many examples of such noise, and seismic and Newtonian noise are among these and will be the subject of this review. Seismic noise is generated by the incessant ground vibration that characterizes Earth. Newtonian noise is instead produced by the tiny fluctuations of the Earth’s gravitational field. These fluctuations are generated by variations of air and soil density near the detector test masses. Soil density variations are produced by the same seismic waves comprising seismic noise. Thus, it makes sense to address these two sources of noise in the same review. An overview of seismic and Newtonian noise is presented, together with a review of the strategies adopted to mitigate them.

Assessment and validation of wind power potential at convection-permitting resolution for the Caribbean region of Colombia

High-resolution wind power assessments, validated with ground data, are key for wind energy projects in regions of promising potential such as the Colombian Caribbean. This study assesses the annual wind power for this region at convection-permitting resolution, using the Weather Research and Forecasting (WRF) model with two nested domains (9 km and 3 km) and 50 vertical levels with 15 min outputs for the northern coast of South America. WRF simulations with three planetary boundary layer schemes (YSU, MYJ and QNSE) perform considerably better than ERA5 reanalysis at representing ground observations of near surface winds in the months with the strongest and weakest winds. WRF accurately simulates phase and amplitude of observed wind diurnal cycles, extreme values, and hodographs in terms of correlations, standard deviations, bias and Weibull distributions. The QNSE scheme served to validate the Wind Power Density (WPD) observed at ground stations, using variations of air density to improve the calculations. The assessment shows areas within the domain with WPD at 100 m up to 1200 Wm-2 onshore and 2000 Wm-2 offshore, with annual values above 400 Wm-2. In this regard, WRF provides a more detailed framework of the atmospheric dynamics for this part of the Caribbean region.

Attempt to quantify the impact of seasonal air density variation on operating tip-speed ratio of small wind turbines

This study presents the impact of seasonal variation in air density on the operating tip-speed ratio of small wind turbines. The air density, which varies depending on the temperature, atmospheric pressure, and relative humidity, has an annual amplitude of about 5% in Tokyo, Japan. This study quantified this impact using the rotational speed equation of motion in a small wind turbine informed by previous work. This governing equation has been simplified by expanding the aerodynamic torque coefficient profile for a wind turbine rotor to the tip-speed ratio. Furthermore, this governing equation is simplified by using nondimensional forms of the air density, inflow wind velocity, and rotational speed with their characteristic values. In this study, the generator’s load is set to be constant based on a previous analysis of a small wind turbine. By considering the equilibrium between the aerodynamic torque and the load torque of the governing equation at the optimum tip-speed ratio, the impact of the variation in the air density on the operating tip-speed ratio was expressed using a simple mathematical form. As shown in this derived form, the operating tip-speed ratio was found to be less sensitive to a variation in air density than that in inflow wind velocity.

Estimation of the influences of spatiotemporal variations in air density on wind energy assessment in China based on deep neural network

This study proposes a deep neural network-based wind energy assessment method, aiming to systematically evaluate the effects of the spatiotemporal variations in air density on wind energy assessment in China. On this basis, the spatiotemporal patterns of air density are modelled on a high-spatial-resolution scale (1000 m × 1000 m). The influence of the spatiotemporal distribution characteristics of air density on the wind energy production is quantified, and the spatiotemporal variability of the corresponding wind energy production is estimated. The results demonstrate that changes in air density during the year present typical periodic characteristics. The mean air density value in January is 1.079 kg/m3, the highest throughout the year. The difference in mean air density between cold and warm seasons in the study area shows a decreasing law of higher in the northeast and lower in the southwest. When the elevation is less than 3500 m, it reaches 5.06%. The observed spatiotemporal variability in annual energy production exhibits a distinct seasonal cycle, with the highest production appears in spring (2.968 GWh/yr). The total annual energy production in the cold season is 16.08 GWh/yr, whereas the annual energy production decreases by higher than 23.46% when it comes to the warm season.

A Simple Way to Demonstrate and Explain Different Facets of Mirages

As intriguing optical phenomena that occur in nature, mirages are widely known and often mentioned in physics classes when introducing the basics of optics. In the atmosphere, a mirage occurs under the condition of vertical variations in air density, which are usually caused by a temperature gradient. The light rays are continuously refracted and follow a curved path when passing through the air, because the refractive index of air changes with its density. Hence, the image observed in an optical manner is displaced from the location of the object. An upward-shifted image is known as a superior mirage, whereas a downward-shifted one is known as an inferior mirage. There are several simple experiments that can create both superior and inferior mirages, using a non-uniform liquid solution to simulate the refractive index gradient in the air. These experiments not only demonstrate the curved paths of light rays, but also produce artificial multiple-image mirages. This paper introduces a simplified method of creating inferior mirages in a liquid solution. Using this method, we further demonstrate several different facets of mirages and explain their origins through computer simulations.

V-Tail flutter analysis of wing-in-surface-effect (WISE) aircraft using a structural analysis software

Flutter is a dynamic aeroelastic instability that may cause structural failure and limits flight envelope of an aircraft. A passenger aircraft is required to be free from flutter and other aeroelastic instability phenomena, as stated in the regulations such as FAR 25. 33 / FAR 23.33. This paper presents the flutter analyses of the WISE aircraft using MSC Nastran. The analyses were carried out to the V-tail, one of the component where flutter might occur, by assuming rigid fuselage. Results of each analysis, in the form of velocity-damping and velocity-frequency curves, were evaluated to determine the critical flutter speed and frequency. First the analysis were conducted for sea level operation using KE, PK and PKNL methods which predict respectively the flutter speed of 1036 knot, 1037 knot, and 1037 knot. The three methods also consistently predict that the mode shapes involved in the flutter are the 5th mode and the 3rd mode. Then by using the PK-method, the analysis were repeated for air density variation. It is shown that the lower the air density, the higher the flutter speed is. It is concluded that tail flutter does not occur during the operation of the WISE craft with max operating speed of 80 knot.

Dynamic mode decomposition based predictive model performance on supersonic and transonic aero-optical wavefront measurements.

Air density variations around an airborne directed energy system distort a beam's wavefront, resulting in degraded performance after propagation into the far field. Adaptive optics (AO) can be used to correct for these rapidly evolving aero-optical aberrations; however, in some conditions, the inherent latency between measurement and correction in state-of-the-art AO systems results in significantly reduced performance. Predictive AO control methods utilize future state predictions to compensate for rapidly evolving distortions and are promising techniques for mitigating this limitation. This paper demonstrates an application of the dynamic mode decomposition (DMD) method on turbulent boundary layer wavefront data from supersonic and transonic wind tunnel flow from the Air Force Research Laboratory's Aero-Effects Laboratory. DMD is a lightweight algorithm used to isolate spatiotemporal patterns in a dataset into physically meaningful modes with associated dynamics, which were used to predict future states from a given wavefront. This method showed notable improvements in simulated wavefront correction, providing a reduction of residual wavefront distortion, measured as root mean square over the aperture, by up to 25.4% over a simulated latency model, which could accordingly result in higher laser system performance.

Ventilation heat loss in a multifamily building under varying air density

Ventilation heat loss in a multifamily building under varying air density