Air Density Research Articles

Probabilistic design and optimization of thermal protection system with variable thickness based on non-uniform aerodynamic heating

Thermal Protection System (TPS) is a critical component of space vehicles to protect them from damage by extreme aerothermal heating conditions. The uncertainty of the aerothermal heating conditions, including approaching velocities, atmospheric density, pressure, etc., significantly affects the aerothermal heating imposed on the TPS, vastly changing the initial design conditions. In this study, we developed a new uncertainty quantitative (UQ) analysis method to comprehensively consider all the uncertainty of TPS materials, structures, and aerothermal heating conditions. To address the challenges of a massive amount of input and determined optimization parameters, we first induced the response surface method and Monte Carlo algorithm to produce a large number of analysis samples for Probabilistic Design. Then, the key affecting factors, not all the input design parameters, were chosen for optimization with sequential optimization and reliability assessment (SORA) strategy by a sensitivity analysis. With such improvements, the optimization for UQ analysis becomes practical. We used this new UQ method to analyze the effects of uncertainty of the aerothermal heating conditions on the thermal protection layer. A variable thickness design is proposed to adapt the non-uniform aerothermal heating conditions for the TPS. The results show that significant light-weighting can be achieved without the reliability penalty. The optimized structure also reduces internal temperature gradients and facilitates a more uniform temperature field distribution for the TPS. This study provides a new UQ engineering design approach for the system with many designed parameters.

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.

Research on the hazards of gas leakage and explosion in a full-scale residential building

The gas explosion in residential building has always been a highly concerned problem. Explosions in homogeneous mixtures have been extensively studied. However, mixtures are often inhomogeneous in the practical scenarios due to the differences in the densities of methane and air. In order to investigate the effects of gas explosions in inhomogeneous mixtures, experimental studies involving gas leakage and explosion are conducted in a full-scale residential building to reproduce the process of gas explosion. By fitting the dimensionless buoyancy as a function of dimensionless height and dimensionless time, a distribution model of gas in large-scale spaces is established, and the mechanism of inhomogeneous distribution of methane is also be revealed. Furthermore, the stratified reconstruction method (SRM) is introduced for efficiently setting up inhomogeneous concentration fields in FLACS. The simulation results highlight that for the internal overpressure, the distribution of methane has no effect on the first overpressure peak (ΔP1), while it significantly influences the subsequent overpressure peak (ΔP2), and the maximum difference between the overpressure of homogeneous and inhomogeneous distribution is 174.3%. Moreover, the initial concentration distribution also has a certain impact on the external overpressure.

Effects of the 2007 Martian Global Dust Storm on Boundary Positions in the Induced Magnetosphere

Mars's magnetosphere is a sensitive system, varying due to external and internal factors, such as solar wind conditions and crustal magnetic fields. A signature of this influence can be seen in the position of two boundaries; the bow shock and the induced magnetospheric boundary (IMB). The bow shock moves closer to Mars during times of high solar activity, and both the bow shock and IMB bulge away from Mars over crustal magnetic fields in the southern hemisphere. This study investigates whether large-scale atmospheric events at Mars have any signature in these two magnetic boundaries, by investigating the 2007 storm. The 2007 global storm lasted for several months and increased atmospheric temperatures and densities of both water vapor and carbon dioxide in the atmosphere, leading to an increase in atmospheric escape. Using Mars Express, we identified boundary locations before, during, and after the event, and compared these to modeled boundary locations and areographical locations on Mars. We find that, while it is unclear whether the bow shock position is impacted by the storm, the IMB location does change significantly, despite the orbital bias introduced by Mars Express. The terminator distance for the IMB peaks at longitudes 0°–40° and 310°–360°, leaving a depression around 180° longitude, where the boundary usually extends to higher altitudes due to the crustal magnetic fields. We suggest this may be due to the confinement of ionospheric plasma over crustal fields preventing mixing with the dust, creating a dip in ionospheric pressure here.

Every Data Point Counts: Stellar Flares as a Case Study of Atmosphere-aided Studies of Transients in the LSST Era

Due to their short timescale, stellar flares are a challenging target for the most modern synoptic sky surveys. The upcoming Vera C. Rubin Legacy Survey of Space and Time (LSST), a project designed to collect more data than any precursor survey, is unlikely to detect flares with more than one data point in its main survey. We developed a methodology to enable LSST studies of stellar flares, with a focus on flare temperature and temperature evolution, which remain poorly constrained compared to flare morphology. By leveraging the sensitivity expected from the Rubin system, differential chromatic refraction (DCR) can be used to constrain flare temperature from a single-epoch detection, which will enable statistical studies of flare temperatures and constrain models of the physical processes behind flare emission using the unprecedentedly high volume of data produced by Rubin over the 10 yr LSST. We model the refraction effect as a function of the atmospheric column density, photometric filter, and temperature of the flare, and show that flare temperatures at or above ∼4000 K can be constrained by a single g-band observation at air mass X ≳ 1.2, given the minimum specified requirement on the single-visit relative astrometric accuracy of LSST, and that a surprisingly large number of LSST observations are in fact likely be conducted at X ≳ 1.2, in spite of image quality requirements pushing the survey to preferentially low X. Having failed to measure flare DCR in LSST precursor surveys, we make recommendations on survey design and data products that enable these studies in LSST and other future surveys.

An Index Description of the General Characteristics of Thermospheric Density Based on the Two‐Line‐Element Data Sets and the Spectral Whitening Method

AbstractThe thermospheric density and its variations are crucial to aerospace activities as well as space weather research and operation. However, due to the difficulties in observing the thermosphere, there has been a lack of effective descriptions for the general characteristics of thermospheric density. In this paper, the Two‐Line‐Element data sets (TLEs) from multi‐target low Earth orbit satellites are used to derive a proxy of the daily average atmospheric density in the thermospheric shell located in the vicinity of LEOs' orbital altitude. It captures the overall characteristics of the thermosphere and exhibits good correlations (∼0.9) with modeled and observed thermospheric density. By applying the spectral whitening method to this proxy, a new index is derived to describe non‐periodic perturbation of the density where the specific satellite passed by. The fact that the obtained from different satellites within the same thermospheric shell presents significant consistency to each other means that the new index is a good indicator for the overall feature of the variations of thermospheric density, and it is possible to define a unified regional index to describe density disturbances for the thermospheric shell where these satellites fly through. Moreover, the at different altitudes also present good consistency suggesting the possibility of defining a global index , capable of describing the density variation of the entire thermosphere.

Design of an electric tilt-wing Martian aircraft

Aerial vehicles increase the range and versatility of resources that can be researched on exterritorial bodies that possess an atmosphere. These vehicles provide significant advantages over traditional landers and rovers in their ability to travel through complicated terrain and obstacles as well as their ability to obtain gas samples at different altitudes. Currently, there has already been an aircraft present on Mars. Ingenuity, the Martian helicopter deployed by NASA Jet Propulsion Laboratory as part of the Mars 2020 mission, has become the first human aircraft to make a powered extraterrestrial flight and is still conducting flying experiments to date. This research aims to explore the possibilities of designs for future aircraft used for Mars explorations as well as technologies that can improve on the existing designs and concepts. This research also proposes possible solutions to the challenges posed by the Martian environment such as the low atmospheric density and terrain restrictions for take-off by utilising existing technology developed for eVTOL such as tilt-wing design to gain the ability to take-off and land vertically. Other aspects such as the selection and accommodation of the spacecraft to launch vehicles have also been covered in the scope of this research.

Wake forces in a background of quadratically coupled mediators

Two particles can exert forces on each other when embedded in a sea of weakly coupled particles. These “wake forces” occur whenever the source and target particles have quadratic interactions with the mediating particles; they are proportional to the ambient energy density and typically have a range of order the characteristic de Broglie wavelength of the background. The effect can be understood as source particles causing a disturbance in the background waves—a wake—which subsequently interacts with the target particles. Wake forces can be mediated by bosons or fermions, can have spin dependence, may be attractive or repulsive, and have a generally anisotropic spatial profile and range that depends on the phase-space distribution of the ambient particles. In this work, I investigate the application of wake forces to dark matter searches, recast existing limits on short-range forces into leading constraints on dark matter with quadratic couplings, and sketch out potential experimental modifications to optimize sensitivity. Wake forces occur in the Standard Model: the presence of the cosmic neutrino background induces a millimeter-range force about 22 orders of magnitude weaker than gravity. Wake forces may also be relevant in condensed-matter and atomic physics. Published by the American Physical Society 2024

An Experimental Study on the Flash Boiling Characteristics of Liquid Ammonia Spray in a Constant Volume Chamber under High Injection Pressure

The spray characteristics of liquid ammonia under various ambient pressures and temperatures were analyzed in a constant volume chamber to cover a wide range of superheat degrees. The injection pressure was set as 70 and 80 MPa with ambient pressure ranging from 0.2 to 4 MPa. The ambient temperature was 500 K. The results showed that the higher the injection pressure, the greater the kinetic energy obtained. The droplet fragmentation was enhanced, and the phenomenon of gradual separation of the gas–liquid region occurred with increasing injection pressure. Under flash boiling spray conditions, the spray developed faster than non-flash boiling and transition flash boiling spray under the same injection pressure. In addition, the flash boiling spray tip penetration of the gas and liquid increased more than that of cold spray, and the fluctuation of the late stage of the injection was relatively large. Therefore, the injection pressure has a greater effect on the spray tip penetration of flash boiling spray. Moreover, ambient pressure greatly influences the flare flash boiling spray. The spray resistance phenomenon was found during the spray development in the flare flash boiling condition. With the increase in ambient pressure, the spray tip penetration of flash boiling spray decreases due to the reduction in the pressure difference inside and outside the spray hole and the restriction of ambient gas. Meanwhile, owing to the low ambient pressure and ambient density, the liquid penetration in the initial phase of the flare flash boiling spray will be abnormally shorter than that of the non-flash boiling spray.

MRO overview: Sixteen years in Mars orbit

Launched on August 12, 2005, the Mars Reconnaissance Orbiter (MRO) entered Mars orbit on March 10, 2006. Following a period of aerobraking, MRO completed its entry into its primary science orbit in September 2006, initiating a program of systematic observations of Mars that still continues. Five providers, including the Italian Space Agency, provided 6 instruments for flight, observing the surface, atmosphere, and subsurface of Mars with greater spatial resolution and systematic coverage than ever before. Two investigations utilized the spacecraft accelerometers and tracking of the orbiter via the Deep Space Network to study upper atmosphere densities and the gravity field of the planet. The data acquired by MRO have revealed a dynamic planet whose change from an ancient wetter climate to the drier climate of today was a complex transition and not a simple “drying out”. Furthermore, that climate continues to change even today. The diversity of the early habitable environments, the ice ages recorded in the polar cap layering and subsurface ice deposits, the repeating patterns of dust storms, and the revelation of new features at the limit of resolution are all part of the scientific return from MRO during nearly a decade of Mars years. The story of that mission, of the evolution of its capabilities, and its contributions to our current understanding of Mars are the subject of nearly two dozen papers in the Icarus special issue, MRO: Sixteen Years at Mars. Three papers describe in more detail the evolution of instrument operations and data products over the mission; several papers describe new analysis techniques for the radar, including construction of 3-dimensional views, and for the atmospheric sounder, enabling better retrievals in a dusty lower atmosphere. Other papers report on recent research including, but not limited to, dune movement, the roles of water and carbon dioxide ice in surface change, and attempts to understand the formation and fading of the enigmatic recurring slope lineae. This paper describes general aspects of the MRO spacecraft, payload, and mission as context for the special issue papers; it also summarizes scientific results and mission support events on a mission phase by mission phase basis to give a time history of discovery and effort.

Electron cyclotron maser instability by evolving fast electron beams in the flare loops

The electron cyclotron maser instability (ECMI) stands as a pivotal coherent radio emission mechanism widely implicated in various astrophysical phenomena. In the context of solar activity, ECMI is primarily instigated by energetic electrons generated during solar eruptions, notably flares. These electrons, upon leaving the acceleration region, traverse the solar atmosphere, forming fast electron beams (FEBs) along magnetic field lines. It is widely accepted that as these FEBs interact with the ambient plasma and magnetic fields, they give rise to radio and hard X-ray emission. Throughout their journey in the plasma, FEBs undergo modifications in their energy spectrum and velocity spatial distribution due to diverse energy loss mechanisms and changes in ambient plasma parameters. In this study, we delve into the impact of the evolving energy spectrum and velocity anisotropic distribution of FEBs on ECMI during their propagation in flare loops. Our findings indicate that if we solely consider the progressively flattened lower energy cutoff behavior as FEBs descend along flare loops, the growth rates of ECMI decrease accordingly. However, when accounting for the evolution of ambient magnetic plasma parameters, the growth rates of ECMI increase as FEBs delve into denser atmosphere. This underscores the significant influence of the energy spectrum and velocity anisotropy distribution evolution of FEBs on ECMI. Our study sheds light on a more comprehensive understanding of the dynamic spectra of solar radio emissions.

Power Augmentation of Gas Turbine Using Exhaust Flue Gas Operated Vapor Absorption Machine

Industrial gas turbines (GT) that operate at constant speed are constant-volume-flow combustion machines. As the specific volume of air is directly proportional to the temperature, an increase in air density results in a higher air mass flow rate at low air ambient temperatures. This results more mass of air is now passes through same volume gas turbine space. Consequently, the gas turbine power output increases proportionally with the increase in air mass flow rate. For geographic regions where warm and humid months are predominant throughout the year, significant power loss occurs during these months, and a higher rate of expensive fuel is fired at reduced power output. A gas turbine inlet air cooling technique is a useful option to enhance GT output. One of the innovative options for power augmentation of gas turbine is inlet air conditioning using a vapor absorption machine (VAM). Using VAM for GT intake air conditioning has the advantage over other systems in that it can be operated from waste heat. Many gas turbine machines, particularly natural gas pumping stations, are operated without heat recovery steam generator (HRSG) or heat recovery option. Valuable heat energy is escaped with exhaust flue gas in these systems. This paper demonstrates how GT exhaust waste heat can be utilized for its own power generation enhancement. In this study, a flue gas-based vapor absorption machine is selected for cooling the inlet air of a 26 MW gas turbine, which is used to drive the booster compressor of a natural gas pumping station. The capacity of the VAM for the required cooling effect has been calculated. The expected GT power enhancement from intake air gas conditioning has also been estimated in this paper.

Aeolian saltation over plateau gobi: Field studies in the Zhongzaohuo gobi area, northeastern Tibetan plateau, China

Aeolian sand movement, affected by low air density, exhibits special characteristics. Our understanding of saltation, especially in plateau gobi regions, is limited. Here, we report results of aeolian saltation processes over gobi in the Zhongzaohuo area of the northeastern Tibetan Plateau using high-frequency saltation measurement. The key findings include: (1) In turbulent winds, aeolian sand saltation on plateau gobi occurs intermittently. As the aeolian sand transport activity parameter increases, the threshold wind speed Ut for sand movement decreases exponentially. Concurrently, the threshold wind speed required to move sand particles shows a significant increase, being 49%–68% higher than that in lower altitude gobi regions. (2) The average saltation height zq in plateau gobi ranges from 0.25 to 0.40 m, with a mean value of 0.36 ± 0.04 m, which is approximately 2.3–2.6 times higher than that in lower altitude gobi areas. (3) Sand transport rate in the plateau gobi is significantly reduced, being 57%–94% lower than that in lower altitude gobi areas. This research will deepen our knowledge of how turbulent winds affect aeolian sand movements in plateau gobi regions.

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.

Precise Analysis of the Differences in the Laser-Activated Energy Density of Aluminum Nitride Ceramics under Various Gas Bath Environments

Laser activation can lead to the formation of a layer of aluminum on the surface of aluminum nitride ceramics, thereby preparing metal circuits. Under various gas environments, there are differences in the aluminum layers precipitated by laser-activated aluminum nitride ceramics. The existing literature uses the width of the metal layer to characterize this difference, and these data are very imprecise. Usually, laser energy density is used to describe this processing difference. However, the existing concept of laser energy density is an average value and is not suitable for the threshold of laser activation, because the intensity gradient of the focused Gaussian beam is large, and different intensity distributions represent different energy levels. This article applied a precise concept of laser energy density that sees it as being proportional to light intensity and can be used to evaluate the difference in laser energy density required for the decomposition of aluminum nitride ceramics under various gas bath conditions precisely. Due to the strong energy of a focused Gaussian beam, it is not possible to directly obtain the intensity distribution. Here, the intensity distribution of the collimated beam was used to indirectly obtain the intensity distribution of the focused Gaussian beam, and the threshold values for laser activation under different gas baths were calculated. It was found that the minimum energy density in air increased by 12.5%, and the minimum energy density in nitrogen increased by 3%, using the minimum energy density required for laser activation in argon as the reference.

Simulation of a Pulsed Metastable Helium Lidar

Measurements of atmosphere density in the upper thermosphere and exosphere are of great significance for studying space–atmosphere interactions. However, the region from 200 km to 1000 km has been a blind area for traditional ground-based active remote sensing techniques due to the limitation of facilities and the paucity of neutral atmosphere. To fulfill this gap, the University of Science and Technology of China is developing a powerful metastable helium resonance fluorescent lidar incorporating a 2 m aperture telescope, a high-energy 1083 nm pulsed laser, as well as a superconducting nanowire single-photon detector (SNSPD) with high quantum efficiency and low dark noise. The system is described in detail in this work. To evaluate the performance of the lidar system, numerical simulation is implemented. The results show that metastable helium density measurements can be achieved with a relative error of less than 20% above 370 km in winter and less than 200% in 270–460 km in summer, demonstrating the feasibility of metastable helium lidar.

Plasma electron acceleration driven by a long-wave-infrared laser

Laser-driven plasma accelerators provide tabletop sources of relativistic electron bunches and femtosecond x-ray pulses, but usually require petawatt-class solid-state-laser pulses of wavelength λL ~ 1 μm. Longer-λL lasers can potentially accelerate higher-quality bunches, since they require less power to drive larger wakes in less dense plasma. Here, we report on a self-injecting plasma accelerator driven by a long-wave-infrared laser: a chirped-pulse-amplified CO2 laser (λL ≈ 10 μm). Through optical scattering experiments, we observed wakes that 4-ps CO2 pulses with < 1/2 terawatt (TW) peak power drove in hydrogen plasma of electron density down to 4 × 1017 cm−3 (1/100 atmospheric density) via a self-modulation (SM) instability. Shorter, more powerful CO2 pulses drove wakes in plasma down to 3 × 1016 cm−3 that captured and accelerated plasma electrons to relativistic energy. Collimated quasi-monoenergetic features in the electron output marked the onset of a transition from SM to bubble-regime acceleration, portending future higher-quality accelerators driven by yet shorter, more powerful pulses.

Prototipo de aplicativo Android para el dimensionamiento electromecánico de cadenas de aisladores de vidrio bajo norma IEC-60071 Y IEC-60815 (2008)

In this study, a new Android application was developed to help users accurately determine the dimensioning of a string insulator through the analysis of the evaluation of two methods based on IEC-60071 and IEC-60815 (2008) standards. The first method uses equations from IEC-60815-2 (2008), while the second method considers parameters such as relative air density and pressure. To ensure reliability, both methods are evaluated: the first through the creepage factor to determine if the chosen profile is suitable, and the second through lightning and switching critical flashover voltages to avoid insulator flashover. Tests were carried out using data from real projects, and those results were compared with the results obtained from the application. The number of string insulators obtained from the tests was exactly the same as the number obtained from the application, except in two cases. Of the three evaluations, all cases complied satisfactorily with at least two tests.

Approximation of the statistical distributions of atmospheric air density in the surface layer

Approximation of the statistical distributions of atmospheric air density in the surface layer

Approximation of the statistical distributions of atmospheric air density in the surface layer

Approximation of the statistical distributions of atmospheric air density in the surface layer