Letteratura scientifica selezionata sul tema "Complex realistic atmospheres"
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Articoli di riviste sul tema "Complex realistic atmospheres":
1
Kravchenko, K., S. Van Eck, A. Chiavassa, A. Jorissen, B. Freytag e B. Plez. "Tomography of cool giant and supergiant star atmospheres". Astronomy & Astrophysics 610 (febbraio 2018): A29. http://dx.doi.org/10.1051/0004-6361/201731530.
Abstract (sommario):
Context. Cool giant and supergiant star atmospheres are characterized by complex velocity fields originating from convection and pulsation processes which are not fully understood yet. The velocity fields impact the formation of spectral lines, which thus contain information on the dynamics of stellar atmospheres. Aim. The tomographic method allows to recover the distribution of the component of the velocity field projected on the line of sight at different optical depths in the stellar atmosphere. The computation of the contribution function to the line depression aims at correctly identifying the depth of formation of spectral lines in order to construct numerical masks probing spectral lines forming at different optical depths. Methods. The tomographic method is applied to one-dimensional (1D) model atmospheres and to a realistic three-dimensional (3D) radiative hydrodynamics simulation performed with CO5BOLD in order to compare their spectral line formation depths and velocity fields. Results. In 1D model atmospheres, each spectral line forms in a restricted range of optical depths. On the other hand, in 3D simulations, the line formation depths are spread in the atmosphere mainly because of temperature and density inhomogeneities. Comparison of cross-correlation function profiles obtained from 3D synthetic spectra with velocities from the 3D simulation shows that the tomographic method correctly recovers the distribution of the velocity component projected on the line of sight in the atmosphere.
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Burley, Jarred L., Steven T. Fiorino, Brannon J. Elmore e Jaclyn E. Schmidt. "A Remote Sensing and Atmospheric Correction Method for Assessing Multispectral Radiative Transfer through Realistic Atmospheres and Clouds". Journal of Atmospheric and Oceanic Technology 36, n. 2 (1 febbraio 2019): 203–16. http://dx.doi.org/10.1175/jtech-d-18-0078.1.
Abstract (sommario):
Abstract The ability to quickly and accurately model actual atmospheric conditions is essential to remote sensing analyses. Clouds present a particularly complex challenge, as they cover up to 70% of Earth’s surface, and their highly variable and diverse nature necessitates physics-based modeling. The Laser Environmental Effects Definition and Reference (LEEDR) is a verified and validated atmospheric propagation and radiative transfer code that creates physically realizable vertical and horizontal profiles of meteorological data. Coupled with numerical weather prediction (NWP) model output, LEEDR enables analysis, nowcasts, and forecasts for radiative effects expected for real-world scenarios. A recent development is the inclusion of the U.S. Air Force’s World-Wide Merged Cloud Analysis (WWMCA) cloud data in a new tool set that enables radiance calculations through clouds from UV to radio frequency (RF) wavelengths. This effort details the creation of near-real-time profiles of atmospheric and cloud conditions and the resulting radiative transfer analysis for virtually any wavelength(s) of interest. Calendar year 2015 data are analyzed to establish climatological limits for diffuse transmission in the 300–1300-nm band, and the impacts of various geometry, cloud microphysical, and atmospheric conditions are examined. The results show that 80% of diffuse band transmissions are estimated to fall between 0.248 and 0.889 under the assumptions of cloud homogeneity and maximum overlap and are sufficient for establishing diffuse transmission percentiles. The demonstrated capability provides an efficient way to extend optical wavelength cloud parameters across the spectrum for physics-based multiple-scattering effects modeling through cloudy and clear atmospheres, providing an improvement to atmospheric correction for remote sensing and cloud effects on system performance metrics.
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Gimeno García, S., T. Trautmann e V. Venema. "Reduction of radiation biases by incorporating the missing cloud variability by means of downscaling techniques: a study using the 3-D MoCaRT model". Atmospheric Measurement Techniques 5, n. 9 (20 settembre 2012): 2261–76. http://dx.doi.org/10.5194/amt-5-2261-2012.
Abstract (sommario):
Abstract. Handling complexity to the smallest detail in atmospheric radiative transfer models is unfeasible in practice. On the one hand, the properties of the interacting medium, i.e., the atmosphere and the surface, are only available at a limited spatial resolution. On the other hand, the computational cost of accurate radiation models accounting for three-dimensional heterogeneous media are prohibitive for some applications, especially for climate modelling and operational remote-sensing algorithms. Hence, it is still common practice to use simplified models for atmospheric radiation applications. Three-dimensional radiation models can deal with complex scenarios providing an accurate solution to the radiative transfer. In contrast, one-dimensional models are computationally more efficient, but introduce biases to the radiation results. With the help of stochastic models that consider the multi-fractal nature of clouds, it is possible to scale cloud properties given at a coarse spatial resolution down to a higher resolution. Performing the radiative transfer within the cloud fields at higher spatial resolution noticeably helps to improve the radiation results. We present a new Monte Carlo model, MoCaRT, that computes the radiative transfer in three-dimensional inhomogeneous atmospheres. The MoCaRT model is validated by comparison with the consensus results of the Intercomparison of Three-Dimensional Radiation Codes (I3RC) project. In the framework of this paper, we aim at characterising cloud heterogeneity effects on radiances and broadband fluxes, namely: the errors due to unresolved variability (the so-called plane parallel homogeneous, PPH, bias) and the errors due to the neglect of transversal photon displacements (independent pixel approximation, IPA, bias). First, we study the effect of the missing cloud variability on reflectivities. We will show that the generation of subscale variability by means of stochastic methods greatly reduce or nearly eliminate the reflectivity biases. Secondly, three-dimensional broadband fluxes in the presence of realistic inhomogeneous cloud fields sampled at high spatial resolutions are calculated and compared to their one-dimensional counterparts at coarser resolutions. We found that one-dimensional calculations at coarsely resolved cloudy atmospheres systematically overestimate broadband reflected and absorbed fluxes and underestimate transmitted ones.
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Forget, F., e J. Leconte. "Possible climates on terrestrial exoplanets". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, n. 2014 (28 aprile 2014): 20130084. http://dx.doi.org/10.1098/rsta.2013.0084.
Abstract (sommario):
What kind of environment may exist on terrestrial planets around other stars? In spite of the lack of direct observations, it may not be premature to speculate on exoplanetary climates, for instance, to optimize future telescopic observations or to assess the probability of habitable worlds. To begin with, climate primarily depends on (i) the atmospheric composition and the volatile inventory; (ii) the incident stellar flux; and (iii) the tidal evolution of the planetary spin, which can notably lock a planet with a permanent night side. The atmospheric composition and mass depends on complex processes, which are difficult to model: origins of volatiles, atmospheric escape, geochemistry, photochemistry, etc. We discuss physical constraints, which can help us to speculate on the possible type of atmosphere, depending on the planet size, its final distance for its star and the star type. Assuming that the atmosphere is known, the possible climates can be explored using global climate models analogous to the ones developed to simulate the Earth as well as the other telluric atmospheres in the solar system. Our experience with Mars, Titan and Venus suggests that realistic climate simulators can be developed by combining components, such as a ‘dynamical core’, a radiative transfer solver, a parametrization of subgrid-scale turbulence and convection, a thermal ground model and a volatile phase change code. On this basis, we can aspire to build reliable climate predictors for exoplanets. However, whatever the accuracy of the models, predicting the actual climate regime on a specific planet will remain challenging because climate systems are affected by strong positive feedbacks. They can drive planets with very similar forcing and volatile inventory to completely different states. For instance, the coupling among temperature, volatile phase changes and radiative properties results in instabilities, such as runaway glaciations and runaway greenhouse effect.
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Medina, Fabian, Hugo Ruiz, Jorge Espíndola e Eduardo Avendaño. "Deploying IIoT Systems for Long-Term Planning in Underground Mining: A Focus on the Monitoring of Explosive Atmospheres". Applied Sciences 14, n. 3 (29 gennaio 2024): 1116. http://dx.doi.org/10.3390/app14031116.
Abstract (sommario):
This paper presents a novel methodology for deploying wireless sensor nodes in the Industrial Internet of Things (IIoT) to address the safety and efficiency challenges in underground coal mining. The methodology is intended to support long-term planning on mitigating the risks in occupational health and safety policies. To ensure realistic and accurate deployment, we propose a software tool that generates mine models based on geolocation data or blueprints in image format, allowing precise adaptation to the specific conditions of each mine. Furthermore, the process is based on sensing and communication range values obtained through simulations and on-site experiments. The deployment strategy is articulated in two complementary steps: a deterministic deployment, where nodes are strategically placed according to the structure of the tunnels, followed by a random stage to include additional nodes that ensure optimal coverage and connectivity inside the mine by comparing different methodologies for deploying sensor networks using coverage density as a performance metric. We analyze coverage and connectivity based on the three probability density functions (PDFs) for the random deployment of nodes: uniform, normal, and exponential, evaluating both the degree of coverage (k-coverage) and the degree of connectivity (k-connectivity). The results show that our proposed methodology stands out for its lower density of sensors per square meter, which translates into a reduction of between 20.81% and 23.46% for uniform and exponential PDFs, respectively, concerning the number of sensors compared to the analyzed methodologies. In this way, it is possible to determine which distribution is suitable to cover the elongated area with the smallest number of nodes, considering the coverage and connectivity requirements, to reduce the deployment cost. The uniform PDF minimizes the number of sensors needed by 44.70% in small mines and 46.27% in medium ones compared to the exponential PDF. These findings provide valuable information to optimize node deployment regarding cost and efficiency; a uniform function is a good option depending on prices. The exponential distribution reached the highest values of k-coverage and k-connectivity for small and medium-sized mines; in addition, it has greater robustness and tolerance to faults like signal network intermittence. This methodology not only improves the collection of critical information for the mining operation but also plays a vital role in reducing the risks to the health and safety of workers by providing a more robust and adaptive monitoring system. The approach can be used to plan IIoT systems based on Wireless Sensor Networks (WSN) for underground mining exploitation, offering a more reliable and adaptable strategy for monitoring and managing complex work environments.
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Prentice, I. C., X. Liang, B. E. Medlyn e Y. P. Wang. "Reliable, robust and realistic: the three R's of next-generation land surface modelling". Atmospheric Chemistry and Physics Discussions 14, n. 17 (26 settembre 2014): 24811–61. http://dx.doi.org/10.5194/acpd-14-24811-2014.
Abstract (sommario):
Abstract. Land surface models (LSMs) are increasingly called upon to represent not only the exchanges of energy, water and momentum across the land-atmosphere interface (their original purpose in climate models), but also how ecosystems and water resources respond to climate and atmospheric environment, and how these responses in turn influence land-atmosphere fluxes of carbon dioxide (CO2), trace gases and other species that affect the composition and chemistry of the atmosphere. However, the LSMs embedded in state-of-the-art climate models differ in how they represent fundamental aspects of the hydrological and carbon cycles, resulting in large inter-model differences and sometimes faulty predictions. These "third-generation" LSMs respect the close coupling of the carbon and water cycles through plants, but otherwise tend to be under-constrained, and have not taken full advantage of robust hydrological parameterizations that were independently developed in offline models. Benchmarking, combining multiple sources of atmospheric, biospheric and hydrological data, should be a required component of LSM development, but this field has been relatively poorly supported and intermittently pursued. Moreover, benchmarking alone is not sufficient to ensure that models improve. Increasing complexity may increase realism but decrease reliability and robustness, by increasing the number of poorly known model parameters. In contrast, simplifying the representation of complex processes by stochastic parameterization (the representation of unresolved processes by statistical distributions of values) has been shown to improve model reliability and realism in both atmospheric and land-surface modelling contexts. We provide examples for important processes in hydrology (the generation of runoff and flow routing in heterogeneous catchments) and biology (carbon uptake by species-diverse ecosystems). We propose that the way forward for next-generation complex LSMs will include: (a) representations of biological and hydrological processes based on the implementation of multiple internal constraints; (b) systematic application of benchmarking and data assimilation techniques to optimize parameter values and thereby test the structural adequacy of models; and (c) stochastic parameterization of unresolved variability, applied in both the hydrological and the biological domains.
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Prentice, I. C., X. Liang, B. E. Medlyn e Y. P. Wang. "Reliable, robust and realistic: the three R's of next-generation land-surface modelling". Atmospheric Chemistry and Physics 15, n. 10 (29 maggio 2015): 5987–6005. http://dx.doi.org/10.5194/acp-15-5987-2015.
Abstract (sommario):
Abstract. Land-surface models (LSMs) are increasingly called upon to represent not only the exchanges of energy, water and momentum across the land–atmosphere interface (their original purpose in climate models), but also how ecosystems and water resources respond to climate, atmospheric environment, land-use and land-use change, and how these responses in turn influence land–atmosphere fluxes of carbon dioxide (CO2), trace gases and other species that affect the composition and chemistry of the atmosphere. However, the LSMs embedded in state-of-the-art climate models differ in how they represent fundamental aspects of the hydrological and carbon cycles, resulting in large inter-model differences and sometimes faulty predictions. These "third-generation" LSMs respect the close coupling of the carbon and water cycles through plants, but otherwise tend to be under-constrained, and have not taken full advantage of robust hydrological parameterizations that were independently developed in offline models. Benchmarking, combining multiple sources of atmospheric, biospheric and hydrological data, should be a required component of LSM development, but this field has been relatively poorly supported and intermittently pursued. Moreover, benchmarking alone is not sufficient to ensure that models improve. Increasing complexity may increase realism but decrease reliability and robustness, by increasing the number of poorly known model parameters. In contrast, simplifying the representation of complex processes by stochastic parameterization (the representation of unresolved processes by statistical distributions of values) has been shown to improve model reliability and realism in both atmospheric and land-surface modelling contexts. We provide examples for important processes in hydrology (the generation of runoff and flow routing in heterogeneous catchments) and biology (carbon uptake by species-diverse ecosystems). We propose that the way forward for next-generation complex LSMs will include: (a) representations of biological and hydrological processes based on the implementation of multiple internal constraints; (b) systematic application of benchmarking and data assimilation techniques to optimize parameter values and thereby test the structural adequacy of models; and (c) stochastic parameterization of unresolved variability, applied in both the hydrological and the biological domains.
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Kitiashvili, Irina N., Alan A. Wray, Viacheslav Sadykov, Alexander G. Kosovichev e Nagi N. Mansour. "Realistic 3D MHD modeling of self-organized magnetic structuring of the solar corona". Proceedings of the International Astronomical Union 15, S354 (giugno 2019): 346–50. http://dx.doi.org/10.1017/s1743921320001532.
Abstract (sommario):
AbstractThe dynamics of solar magnetoconvection spans a wide range of spatial and temporal scales and extends from the interior to the corona. Using 3D radiative MHD simulations, we investigate the complex interactions that drive various phenomena observed on the solar surface, in the low atmosphere, and in the corona. We present results of our recent simulations of coronal dynamics driven by underlying magnetoconvection and atmospheric processes, using the 3D radiative MHD code StellarBox (Wray et al. 2018). In particular, we focus on the evolution of thermodynamic properties and energy exchange across the different layers from the solar interior to the corona.
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Lavail, A., O. Kochukhov e G. A. J. Hussain. "Characterising the surface magnetic fields of T Tauri stars with high-resolution near-infrared spectroscopy". Astronomy & Astrophysics 630 (26 settembre 2019): A99. http://dx.doi.org/10.1051/0004-6361/201935695.
Abstract (sommario):
Aims. In this paper, we aim to characterise the surface magnetic fields of a sample of eight T Tauri stars from high-resolution near-infrared spectroscopy. Some stars in our sample are known to be magnetic from previous spectroscopic or spectropolarimetric studies. Our goals are firstly to apply Zeeman broadening modelling to T Tauri stars with high-resolution data, secondly to expand the sample of stars with measured surface magnetic field strengths, thirdly to investigate possible rotational or long-term magnetic variability by comparing spectral time series of given targets, and fourthly to compare the magnetic field modulus ⟨B⟩ tracing small-scale magnetic fields to those of large-scale magnetic fields derived by Stokes V Zeeman Doppler Imaging (ZDI) studies. Methods. We modelled the Zeeman broadening of magnetically sensitive spectral lines in the near-infrared K-band from high-resolution spectra by using magnetic spectrum synthesis based on realistic model atmospheres and by using different descriptions of the surface magnetic field. We developped a Bayesian framework that selects the complexity of the magnetic field prescription based on the information contained in the data. Results. We obtain individual magnetic field measurements for each star in our sample using four different models. We find that the Bayesian Model 4 performs best in the range of magnetic fields measured on the sample (from 1.5 kG to 4.4 kG). We do not detect a strong rotational variation of ⟨B⟩ with a mean peak-to-peak variation of 0.3 kG. Our confidence intervals are of the same order of magnitude, which suggests that the Zeeman broadening is produced by a small-scale magnetic field homogeneously distributed over stellar surfaces. A comparison of our results with mean large-scale magnetic field measurements from Stokes V ZDI show different fractions of mean field strength being recovered, from 25–42% for relatively simple poloidal axisymmetric field topologies to 2–11% for more complex fields.
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Rutten, Robert J. "Dynamical Behavior of the Upper Solar Photosphere". Symposium - International Astronomical Union 210 (2003): 221–31. http://dx.doi.org/10.1017/s0074180900133388.
Abstract (sommario):
The dynamical behavior of upper cool-star photospheres constitutes the next step in realistic atmosphere modeling after the successful numerical implementation of low-photosphere granulation. The solar example shows that this behavior is complex even when magnetism is ignored. Acoustic waves are a principal ingredient, but so are atmospheric gravity waves. Acoustic events provide less pistoning than expected. Correlation and Fourier analyses of image sequences from TRACE demonstrate the ubiquity of gravity waves.
Tesi sul tema "Complex realistic atmospheres":
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Blayac, Marion. "Impacts de la pollution atmosphérique sur le phénotype pulmonaire de la mucoviscidose : étude expérimentale sur deux modèles précliniques". Electronic Thesis or Diss., Paris 12, 2022. http://www.theses.fr/2022PA120045.
Abstract (sommario):
La mucoviscidose est une maladie génétique due à une mutation du gène CFTR qui code pour un canal chlorure épithélial. La pathologie se caractérise par une diminution progressive de la fonction respiratoire qui conditionne l’essentiel de la morbidité et de la mortalité de la maladie. Il existe une grande diversité génétique des patients qui s’accompagne d’une grande variabilité phénotypique, ceci même entre des individus présentant les mêmes mutations. Cela laisse supposer la mise en jeu d’autres facteurs d’origine génétique ou environnementale. Parmi les pistes évoquées, le rôle de la pollution atmosphérique nous a paru intéressant à considérer, celle-ci représentant le risque environnemental le plus important pour la santé. L'objectif de cette thèse était d'étudier par une approche expérimentale les effets de la pollution atmosphérique sur le phénotype pulmonaire de la mucoviscidose chez deux modèles murins dédiés. Pour cela, j’ai utilisé la chambre de simulation atmosphérique CESAM permettant de simuler au laboratoire des atmosphères multiphasiques réalistes. Cette chambre est couplée à des isolateurs permettant l’exposition d’organismes vivants aux atmosphères simulées. Nous avons ainsi simulé différents types d’atmosphères urbaines de niveau de pollution différents, représentatives des villes de Paris et de Pékin en été et en hiver, auxquelles nous avons exposé les modèles murins pendant 18H et 72H. Les effets biologiques ont ensuite été caractérisés par l’étude des structures et de la fonction pulmonaires, de la production de mucus et de la réponse inflammatoire et oxydative. Une exposition aux différentes atmosphères semblerait ainsi entraîner une stimulation de la sécrétion de mucus associée à une augmentation de la sécrétion de cytokines pro-inflammatoires, du stress oxydant et de l’expression de protéases pulmonaires. Les effets observés étaient plus importants chez les souris atteintes de mucoviscidose par rapport aux souris saines, le type de réponse dépendant de la composition chimique de l’atmosphère considérée. Suite à ces constats, la pollution atmosphérique est donc fortement suspectée de contribuer à la physiopathologie de la mucoviscidose en augmentant la sévérité de la maladieCystic Fibrosis (CF) is a genetic disease due to a mutation of the CFTR gene encoding for an epithelial chloride channel. The disease is characterized by a progressive loss of respiratory function responsible for most of the morbidity and mortality of the disease. CF patients show an important genotypic variability along with a great phenotypic diversity between patients with the same mutations. This suggests the implication of other factors, either genetic or environmental. Among these factors, one that is of interest is air pollution, indeed representing the most important environmental risk for health. The objective of this thesis was to study, using an experimental approach, the effects of air pollution on CF pulmonary phenotype in two dedicated murine models. I used CESAM atmospheric simulation chamber to simulate at the laboratory multiphasic realistic atmospheres. This chamber is coupled to mice isolators allowing to expose living organisms to the simulated atmospheres. We simulated different types of urban atmospheres, with different levels of air pollutants, representative of Paris and Beijing atmospheres in summer and winter conditions. Mice were exposed to these atmospheres for 18H and 72H. Biological effects were then characterized by studying lung structure and function, mucus production as well as inflammatory and oxidative response. Exposure to urban atmospheres tended to stimulate mucus secretion and increased inflammatory biomarkers, oxidative stress, and expression of pulmonary proteinases. The effects were more important in CF mice compared to healthy mice and the type of response induced depended on the chemical composition of the considered atmosphere. Based on these effects, air pollution is highly suspected to contribute to CF physiopathology by increasing the severity of the disease
Capitoli di libri sul tema "Complex realistic atmospheres":
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Su, Jingyao, e Steffen Schön. "Bounding the Residual Tropospheric Error by Interval Analysis". In International Association of Geodesy Symposia. Berlin, Heidelberg: Springer Berlin Heidelberg, 2022. http://dx.doi.org/10.1007/1345_2022_184.
Abstract (sommario):
AbstractGNSS integrity monitoring requires proper bounding to characterize all ranging error sources. Unlike classical approaches based on probabilistic assumptions, our alternative integrity approach depends on deterministic interval bounds as inputs. The intrinsically linear uncertainty propagation with intervals is adequate to describe remaining systematic uncertainty, the so-called imprecision. In this contribution, we make a proposal on how to derive the required intervals in order to quantify and bound the residual error for empirical troposphere models, based on the refined sensitivity analysis via interval arithmetic. We evaluated experimentally the Saastamoinen model with (i) a priori ISO standard atmosphere, and (ii) on-site meteorological measurements from IGS and Deutscher Wetterdienst (DWD) stations as inputs. We obtain consistent and complete enclosure of residual ZPD errors w.r.t IGS ZPD products. Thanks to the DWD dense network, interval maps for meteorological parameters and residual ZPD errors are generated for Germany as by-products. These experimental results and products are finally validated, taking advantage of the high-quality tropospheric delays estimated by the Vienna Ray Tracer. Overall, the results indicate that our strategy based on interval analysis successfully bounds tropospheric model uncertainty. This will contribute to a realistic uncertainty assessment of GNSS-based single point positioning.
Atti di convegni sul tema "Complex realistic atmospheres":
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Hummel, John R. "Inverting Lidar Data Using Realistic Atmospheric Data". In Optical Remote Sensing of the Atmosphere. Washington, D.C.: Optica Publishing Group, 1990. http://dx.doi.org/10.1364/orsa.1990.md12.
Abstract (sommario):
Laser radars, or lidars, are powerful tools for probing the atmosphere. Inverting the lidar equation, however, suffers, from the problem of having more unknowns than equations. Numerous studies have focused on how to reduce the problem to a complete set of equations. Many of the solution schemes have major limitations as a result of the unrealistic assumptions required to complete the set of equations.
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Rasheed, Adil, Mandar Tabib e Jørn Kristiansen. "Wind Farm Modeling in a Realistic Environment Using a Multiscale Approach". In ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/omae2017-61686.
Abstract (sommario):
We present a multiscale approach to model a windfarm under real meteorological conditions. The multiscale model consists of a mesoscale atmospheric code coupled to a stochastic ocean wave model, a microscale model and a super-microscale model. The mesoscale model (with 2.5km × 2.5km horizontal resolution) forces the microscale model (with finer 100m × 100m horizontal resolution). The microscale model is capable of resolving surface variations both on wavy and complex terrain surfaces. Finally, the computed wind, temperature and turbulent kinetic energy from microscale model are used to provide boundary conditions to a super-microscale model, which has features to resolve turbine wakes using actuator line model. The three classes of models are validated using a very diverse array of observational data obtained from satellites, radiosondes and a wind tunnel. Towards the end, performance of an operational onshore wind farm under realistic meteorological conditions is evaluated.
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Jana, R., P. S. Rajagopal, A. Vinod Kumar, V. D. Puranik e A. Runchal. "Limited Area Air Quality Modeling in Geographic Scale Through Flow Field Validation in Hilly Terrain". In ASME 2013 Heat Transfer Summer Conference collocated with the ASME 2013 7th International Conference on Energy Sustainability and the ASME 2013 11th International Conference on Fuel Cell Science, Engineering and Technology. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/ht2013-17681.
Abstract (sommario):
The turbulent motion of atmosphere adjoined to the earth’s surface is caused by the surface friction and buoyancy force in a short time scale which is of the order of few seconds to minutes. This interactive layer is atmospheric boundary layer with several detailed features viz., roughness layer, surface layer for small eddies, mixed layer for large eddies, which may extend vertically more than a kilometer under deep convective condition. The surface layer is primarily characterised through several scaling parameters, viz., roughness length, momentum flux and sensible heat flux as triggering force of turbulence and its maintenance through eddy formation and dissipation. Air dispersion and hence the distribution of atmospheric pollutants from various sources follow flow path and its turbulent characteristics, which is dependent on geometry of the terrain specially for complex terrain, meteorological conditions and source term inventories. In the present study, an virtual environment is designed in a computational fluid dynamics based solver for limited area/local scale air quality modelling by incorporating digital elevation model of intermediate valley zone of Sahyadri Range of Western Ghats of India as site. Finite volume method and mass flux transfer approach is followed by the solver to estimate 3D atmospheric or ground level concentration of atmospheric non-reactive pollutants for unit discharge per second from a hypothetical 100 m tall stack for 72 hours. Flow field is computed for various realistic cases for which initial and boundary conditions are incorporated from larger scale model, viz., Mesoscale Model (MM5) developed by the National Centre for Atmospheric Research, USA and also from measured local data taken from distributed micro-meteorological observatories. Computed flow field is validated with independent observation not utilised in computation giving a validation to the estimated contaminant concentration so. The uncertainty in diffusion is also studied when Lagrangian particle movement is driven fully by flow field and its turbulent phenomena in comparison to random walk model.
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Draper, Douglas C., J. Fred Holmes e John Peacock. "An Unwrapped Phase Distribution Model for Speckle/Turbulence". In Optical Remote Sensing of the Atmosphere. Washington, D.C.: Optica Publishing Group, 1990. http://dx.doi.org/10.1364/orsa.1990.tud24.
Abstract (sommario):
Several models have been proposed for the probability density function (p.d.f.) of phase for a speckle field created by a coherent beam and a diffuse object1-5 and also for a coherent beam propagating through a random medium such as clear air turbulence6-7. The p.d.f. models for speckle as well as many of the p.d.f. models for turbulence are given for the wrapped phase since the models are based on extracting phase information from the complex field amplitudes representing the radiation. Wrapped phase refers to phase angles that are limited to principal values (0-2π radians). The phase fluctuations really represent the optical path length variations which can greatly exceed 2π when represented as phase changes. Path length variations are linearly related to unwrapped phase variations by the relationship ϕ = 2πΔL/λ where ΔL represents path length variations. Consequently in a realistic situation phase is not limited to principal values. In addition the wrapped p.d.f. expressions are mathematically complicated and it would be difficult to extend them to the case where a speckle field and a turbulence field are combined (ie. where a speckle field is propagating through turbulence). Consequently simple Gaussian unwrapped phase p.d.f. models for both speckle alone and turbulence alone and a model for the combined speckle field in turbulence using the simpler unwrapped models are proposed. It will be shown using a standard technique for calculating a wrapped p.d.f. from an unwrapped p.d.f5 that the wrapped p.d.f.’s obtained from unwrapped Gaussian models are approximately equivalent to the known wrapped p.d.f.’s for speckle phase. It will also be shown from our experimental work that the measured unwrapped phase is approximately Gaussian.
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Cooper, Jared, Jeremy Hopwood, Stephan Wekker, Michael DeVore e Craig Woolsey. "Intelligent Wind Estimation for Chemical Source Localization". In Vertical Flight Society 79th Annual Forum & Technology Display. The Vertical Flight Society, 2023. http://dx.doi.org/10.4050/f-0079-2023-18194.
Abstract (sommario):
This paper presents a methodology to sense ambient wind conditions to assist in localizing the source of a released agent using small unmanned aerial systems (sUAS). The technology and methods to detect, localize, and model release and dispersion of chemical, biological, radiological, or nuclear (CBRN) agents have been enhanced by integrating cross-disciplinary solutions using advances from sensor design, intelligent signal processing, control systems, vehicle design, chemical modeling, and atmospheric modeling. The miniaturization of sensors and sUAS has enabled the application of sUAS with a chemical sensor payload to detect and localize the source of CBRN agents. In many instances, this chemotaxis operation can be performed faster and more accurately with the addition of atmospheric information, such as ambient wind condition. The paper provides an overview of chemical source localization and current challenges which motivated this work, including operation in complex settings and turbulence. Analysis of these challenges from an atmospheric science perspective is summarized along with strategies to obtain accurate and useful wind estimates that assist in localizing the source quickly and efficiently. A description of the wind estimation approach, based on Bayesian estimation, is provided along with results from simulation studies utilizing realistic vehicle dynamics, wind, turbulence, and chemical plume models.
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Barcarolo, Daniel, Yann Andrillon, Erwan Jacquin e Alain Ledoux. "Evaluation of Wind Loads on FPSO Topsides Using a Numerical Wind Tunnel". In ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/omae2016-54346.
Abstract (sommario):
The accurate evaluation of wind loads applied on floating offshore structures is extremely important as they are in specific conditions one of the dimensioning criteria for the mooring design. Nowadays these loads are mainly assessed through wind tunnel tests performed at model scale. Estimating realistic wind loads however, remains a big challenge. The complexity and associated simplification level of FPSO topside structures, the scale effects and the establishment of the atmospheric boundary layer imply that many simplifications are to be made. Typically, the FPSO topside is greatly simplified and equivalent blocs of wired frame are used. Today with the evolution of CFD software, and the increase of the meshing capacity, new scopes open to CFD. Aerodynamic simulations on complex FPSO structures are therefore now possible, but need specific developments and validations that are presented in this paper. The main objective of the work presented is to investigate the ability of CFD to evaluate wind loads on complex FPSOs topsides and to provide information on the impact of model simplifications made in wind tunnels. In a first stage, the numerical model was intensively validated by comparing its results to a wind tunnel test case. The numerical model was developed in order to ensure the quality of the results and enable a relevant comparison that was obtained with grids density up to 30 million cells. For this purpose, the geometric model used corresponds to the one used in wind tunnel. The same Atmospheric Boundary Layer was simulated and a thorough effort was performed to ensure the mesh convergence. In a second stage, more physical aspects of the wind tunnel methodology were investigated. Typically the accuracy of the blockage effect correction was evaluated by performing computations with and without blockage, and results were compared with classical corrections applied in wind tunnel. The impacts of the Atmospheric Boundary Layer on wind loads have also been investigated. Finally, the wind load contribution of each component of the FPSO was evaluated.
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Řezníček, Hynek, Jan Geletič, Martin Bureš, Pavel Krč, Jaroslav Resler, Kateřina Vrbová, Arsenii Trush, Petr Michálek, Luděk Beneš e Matthias Sühring. "Different boundary conditions for LES solver Palm 6.0 used for ABL in tunnel experiment". In Programs and Algorithms of Numerical Mathematics 21. Institute of Mathematics, Czech Academy of Sciences, 2023. http://dx.doi.org/10.21136/panm.2022.19.
Abstract (sommario):
We tried to reproduce results measured in the wind tunnel experiment with a CFD simulation provided by numerical model PALM. A realistic buildings layout from the Prague-Dejvice quarter has been chosen as a testing domain because solid validation campaign for PALM simulation of Atmospheric Boundary Layer (ABL) over this quarter was documented in the past. The question of input data needed for such simulation and capability of the model to capture correctly the inlet profile and its turbulence structure provided by the wind-tunnel is discussed in the study. The PALM dynamical core contains a solver for the Navier-Stokes equations. By default, the model uses the Large Eddy Simulation (LES) approach in which the bulk of the turbulent motions is explicitly resolved. It is well validated tool for simulations of the complex air-flow within the real urban canopy and also within its reduced scale provided by wind tunnel experiments. However the computed flow field between the testing buildings did not correspond well to the measured wind velocity in some points. Different setting of the inlet boundary condition was tested but none of them gave completely developed turbulent flow generated by vortex generators and castellated barrier wall place at the entrance of the aerodynamic section of the wind tunnel.
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Haq, M. Z., e M. R. Mohiuddin. "Thermodynamic Analysis of a Multi-Fueled Single Cylinder SI Engine". In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-62423.
Abstract (sommario):
The paper presents a thermodynamic analysis of a single cylinder four-stroke spark-ignition (SI) engine fuelled by four fuels namely iso-octane, methane, methanol and hydrogen. In SI engines, due to phenomena like ignition delay and finite flame speed manifested by the fuels, the heat addition process is not instantaneous, and hence ‘Weibe function’ is used to address the realistic heat release scenario of the engine. Empirical correlations are used to predict the heat loss from the engine cylinder. Physical states and chemical properties of gaseous species present inside the cylinder are determined using first and second law of thermodynamics, chemical kinetics, JANAF thermodynamic data-base and NASA polynomials. The model is implemented in FORTRAN 95 using standard numerical routines and some simulation results are validated against data available in literature. The second law of thermodynamics is applied to estimate the change of exergy i.e. the work potential or quality of the in-cylinder mixture undergoing various phases to complete the cycle. Results indicate that, around 4 to 24% of exergy initially possessed by the in-cylinder mixture is reduced during combustion and about 26 to 42% is left unused and exhausted to the atmosphere.
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von Langenthal, Thomas, Nikolaos Zarzalis e Marco Konle. "Experimental and Numerical Investigation of Different Flame Types Inside a Laboratory Scale RQL Combustion Chamber". In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-90127.
Abstract (sommario):
Abstract RQL (rich burn, quick quench, lean burn) combustion chambers are common in modern aero engines due to their low NOx emissions and good stability. The rich primary zone leads to lower flame temperatures and in combination with the lack of oxygen, the NOx production is low. The mixing of the secondary air must be quick in order to avoid stoichiometric conditions and at the same time must ensure the oxidation of the soot produced in the fuel rich primary zone to keep soot emissions to a minimum. However, the design of such a combustion chamber is complicated due to the complex interaction between the swirling primary flow and the jets of the secondary airflow. In this paper, we present a new test rig, which was designed to study combustion processes inside RQL combustion chambers at atmospheric conditions. The test rig features liquid kerosene combustion and a realistic quenching zone as well as good access for optical and conventional measurement techniques. For realistic engine like conditions the combustion air is preheated to 600 K and the fuel–air equivalence ratio in the primary combustion zone is set to be between Φ = 1.66 and Φ = 1.25, resulting in an overall thermal power between 80 kW and 110 kW. To get insights into the complex flow field inside the combustion chamber unsteady RANS simulations of both the reacting and the non-reacting case were performed using OpenFOAM. The turbulent flow field was modeled using the k-ω-SST model and the combustion was simulated using the Partially Stirred Reactor model. The experimental investigations showed two stable flame types for the same operating conditions with considerable differences in the visible flame structure and soot radiation. The flow field of both of these flame types were measured using a 1.5 kHz 2D PIV System. The numerical simulations showed good overall agreement with the experimental results but could not represent the change in flame type. In order to understand the underlying effects of the flame change the OH* chemiluminescence was recorded and the two-phase flow near the nozzle exit was investigated. This showed that the change in flame structure might arise due to spray dispersion of the pilot fuel nozzle and the recirculation of the secondary air into the primary zone.
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Dias, Filipe, José Páscoa e Carlos Xisto. "Numerical Analysis of a Multi-Species MHD Model for Plasma Layer Control of Re-Entry Vehicles". In ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-87467.
Abstract (sommario):
Several critical aspects control the successful reentry of vehicles on the earth’s atmosphere: continuous communication, GPS signal reception and real-time telemetry. However, there are some common issues that can interfere with the instruments operation, the most typical being the radio blackout, in which the plasma layer frequency modifies the electromagnetic waves in a way that makes communications to and from the spacecraft impossible. So far, there have been several proposed techniques to mitigate radio blackout, one of which is the usage of electromagnetic fields. Previous studies have proven the effectiveness of the usage of an electric and/or magnetic fields to manipulate plasma layers. Experiments on plasma layer manipulation during hypersonic flight regime are extremely costly. Therefore, there has been a continuous interest in the development of cheaper solutions, that can guarantee a reliable degree of accuracy, such as the development of complex multiphysics computational models. These models are becoming increasingly realistic and accurate, as more and more physical aspects can be considered, greatly increasing the accuracy and range of models. However, those models need to be validated with recourse to experimental data. In this paper we propose a model that uses a Low Magnetic Reynolds number, and accounts for five common neutral species: N2, O2, NO, N and O, along with several of their respective reactions: dissociation of molecular nitrogen and oxygen, and exchange. The model chemistry is then validated based on experimental data gathered by several authors.