Добірка наукової літератури з теми "Covariance turbulente"
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся зі списками актуальних статей, книг, дисертацій, тез та інших наукових джерел на тему "Covariance turbulente".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Статті в журналах з теми "Covariance turbulente":
1
Foken, T., F. Wimmer, M. Mauder, C. Thomas, and C. Liebethal. "Some aspects of the energy balance closure problem." Atmospheric Chemistry and Physics Discussions 6, no. 2 (April 27, 2006): 3381–402. http://dx.doi.org/10.5194/acpd-6-3381-2006.
Анотація:
Abstract. After briefly discussing several reasons for the energy balance closure problem in the surface layer, the paper focuses on the influence of the low frequency part of the turbulence spectrum on the residual. Changes in the turbulent fluxes in this part of the turbulence spectrum were found to have a significant influence on the changes of the residual. Using the ogive method, it was found that the eddy-covariance method underestimates turbulent fluxes in the case of ogives converging for measuring times longer than the typical averaging interval of 30 min. Additionally, the eddy-covariance method underestimates turbulent fluxes for maximal ogive functions within the averaging interval, both mainly due to advection and non-steady state conditions. This has a considerable influence on the use of the eddy-covariance method.
2
Foken, T., F. Wimmer, M. Mauder, C. Thomas, and C. Liebethal. "Some aspects of the energy balance closure problem." Atmospheric Chemistry and Physics 6, no. 12 (September 28, 2006): 4395–402. http://dx.doi.org/10.5194/acp-6-4395-2006.
Анотація:
Abstract. After briefly discussing several reasons for the energy balance closure problem in the surface layer, the paper focuses on the influence of the low frequency part of the turbulence spectrum on the residual. Changes in the turbulent fluxes in this part of the turbulence spectrum were found to have a significant influence on the changes of the residual. Using the ogive method, it was found that the eddy-covariance method underestimates turbulent fluxes in the case of ogives converging for measuring times longer than the typical averaging interval of 30 min. Additionally, the eddy-covariance method underestimates turbulent fluxes for maximal ogive functions within the averaging interval, both mainly due to advection and non-steady state conditions. This has a considerable influence on the use of the eddy-covariance method.
3
Krenk, Steen, and Randi N. Møller. "Turbulent wind field representation and conditional mean-field simulation." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 475, no. 2223 (March 2019): 20180887. http://dx.doi.org/10.1098/rspa.2018.0887.
Анотація:
The covariance structure of a homogeneous isotropic turbulent wind velocity field is derived in terms of modified Bessel functions for an extended form of the Kàrmàn velocity spectrum, including explicit expressions for the transverse coherence functions. A concept of transformed isotropic turbulence is introduced to account for differences in the axial, transverse and vertical fluctuating wind velocities and length scales in natural wind. A special form of the auto-regressive simulation format is developed for convected turbulence with exponentially increasing intervals to the regression planes. In each step, the wind velocity field in a transverse plane is represented by a conditional mean field and a stochastic contribution determined explicitly by the time–space covariances. Simulation results are presented for a square area of dimension less than the integral length scale, representative of buildings and wind turbines, and a horizontal line of length six times the length scale, representative of a long-span bridge. The simulations demonstrate high accuracy of simulated spectral densities, covariance functions and transverse coherence functions. The simulated results do not show visible dependence on the specific points used for the simulated records. The efficiency and the free simulation point configuration suggest high competitiveness compared to fast Fourier transform-based spectral methods.
4
Lenschow, Donald H., David Gurarie, and Edward G. Patton. "Modeling the diurnal cycle of conserved and reactive species in the convective boundary layer using SOMCRUS." Geoscientific Model Development 9, no. 3 (March 7, 2016): 979–96. http://dx.doi.org/10.5194/gmd-9-979-2016.
Анотація:
Abstract. We have developed a one-dimensional second-order closure numerical model to study the vertical turbulent transport of trace reactive species in the convective (daytime) planetary boundary layer (CBL), which we call the Second-Order Model for Conserved and Reactive Unsteady Scalars (SOMCRUS). The temporal variation of the CBL depth is calculated using a simple mixed-layer model with a constant entrainment coefficient and zero-order discontinuity at the CBL top. We then calculate time-varying continuous profiles of mean concentrations and vertical turbulent fluxes, variances, and covariances of both conserved and chemically reactive scalars in a diurnally varying CBL. The set of reactive species is the O3–NO–NO2 triad. The results for both conserved and reactive species are compared with large-eddy simulations (LES) for the same free-convection case using the same boundary and initial conditions. For the conserved species, we compare three cases with different combinations of surface fluxes, and CBL and free-troposphere concentrations. We find good agreement of SOMCRUS with LES for the mean concentrations and fluxes of both conserved and reactive species except near the CBL top, where SOMCRUS predicts a somewhat shallower depth, and has sharp transitions in both the mean and turbulence variables, in contrast to more smeared-out variations in the LES due to horizontal averaging. Furthermore, SOMCRUS generally underestimates the variances and species–species covariances. SOMCRUS predicts temperature–species covariances similar to LES near the surface, but much smaller magnitude peak values near the CBL top, and a change in sign of the covariances very near the CBL top, while the LES predicts a change in sign of the covariances in the lower half of the CBL. SOMCRUS is also able to estimate the intensity of segregation (the ratio of the species–species covariance to the product of their means), which can alter the rates of second-order chemical reactions; however, for the case considered here, this effect is small. The simplicity and extensibility of SOMCRUS means that it can be utilized for a broad range of turbulence-mixing scenarios and sets of chemical reactions in the planetary boundary layer; it therefore holds great promise as a tool to incorporate these processes within air quality and climate models.
5
Lenschow, D. H., D. Gurarie, and E. G. Patton. "Modeling the diurnal cycle of conserved and reactive species in the convective boundary layer." Geoscientific Model Development Discussions 8, no. 10 (October 29, 2015): 9323–72. http://dx.doi.org/10.5194/gmdd-8-9323-2015.
Анотація:
Abstract. We have developed a one-dimensional second-order closure numerical model to study the vertical turbulent transport of trace reactive species in the convective (daytime) planetary boundary layer (CBL), which we call the Second-Order Model for Conserved and Reactive Unsteady Scalars (SOMCRUS). The temporal variation of the CBL depth is calculated using a simple mixed-layer model with a constant entrainment coefficient and zero-order discontinuity at the CBL top. We then calculate time-varying continuous profiles of mean concentrations and vertical turbulent fluxes, variances, and covariances of both conserved and chemically-reactive scalars in a diurnally-varying CBL. The set of reactive species is the O3–NO–NO2 triad. The results for both conserved and reactive species are compared with large-eddy simulations (LES) for the same free-convection case using the same boundary and initial conditions. For the conserved species, we compare three cases with different combinations of surface fluxes, and CBL and free-troposphere concentrations. We find good agreement of SOMCRUS with LES for the mean concentrations and fluxes of both conserved and reactive species except near the CBL top, where SOMCRUS predicts a somewhat shallower depth, and has sharp transitions in both the mean and turbulence variables, in contrast to more smeared out variations in the LES due to horizontal averaging. Furthermore, SOMCRUS generally underestimates the variances and species-species covariances. SOMCRUS predicts temperature-species covariances similar to LES near the surface, but much smaller magnitude peak values near the CBL top, and a change in sign of the covariances very near the CBL top, while the LES predicts a change in sign of the covariances in the lower half of the CBL. SOMCRUS is also able to estimate the intensity of segregation (the ratio of the species-species covariance to the product of their means), which can alter the rates of second-order chemical reactions; however, for the case considered here, this effect is small. The simplicity and extensibility of SOMCRUS means that it can be utilized for a broad range of turbulence mixing scenarios and sets of chemical reactions in the planetary boundary layer; it therefore holds great promise as a tool to incorporate these processes within air quality and climate models.
6
Guerra, Maricarmen, and Jim Thomson. "Turbulence Measurements from Five-Beam Acoustic Doppler Current Profilers." Journal of Atmospheric and Oceanic Technology 34, no. 6 (June 2017): 1267–84. http://dx.doi.org/10.1175/jtech-d-16-0148.1.
Анотація:
AbstractTwo new five-beam acoustic Doppler current profilers—the Nortek Signature1000 AD2CP and the Teledyne RDI Sentinel V50—are demonstrated to measure turbulence at two energetic tidal channels within Puget Sound, Washington. The quality of the raw data is tested by analyzing the turbulent kinetic energy frequency spectra, the turbulence spatial structure function, the shear in the profiles, and the covariance Reynolds stresses. The five-beam configuration allows for a direct estimation of the Reynolds stresses from along-beam velocity fluctuations. The Nortek’s low Doppler noise and high sampling frequency allow for the observation of the turbulent inertial subrange in both the frequency spectra and the turbulence structure function. The turbulence parameters obtained from the five-beam acoustic Doppler current profilers are validated with turbulence data from simultaneous measurements with acoustic Doppler velocimeters. These combined results are then used to assess a turbulent kinetic energy budget in which depth profiles of the turbulent kinetic energy dissipation and production rates are compared. The associated codes are publicly available on the MATLAB File Exchange website.
7
Santos, Diego Jatobá, Celso Von Randow, and Pablo E. S. Oliveira. "Variabilidade temporal dos fluxos noturnos determinados a partir de duas diferentes metodologias no nível de 325 m acima da floresta Amazônica." Ciência e Natura 42 (August 28, 2020): e14. http://dx.doi.org/10.5902/2179460x45356.
Анотація:
The present study aimed to analyze and compare the temporal variability of the nocturnal fluxes of CO2, sensitive and latent heat, calculated from two different methodologies: one with a 5-minute temporal window (using the eddy covariance technique), and another with 109 minutes (from multiresolution decomposition). For this, night series of 25 nights were used between October and November 2015. The analyzes were made for two groups of distinct turbulence patterns: one with intermittent regime and the other with homogeneous turbulence. The results showed that the fluxes obtained by the classical method of eddy covariance were dependent on the intensity of the turbulence. On the other hand, the fluxes calculated from the multiresolution decomposition technique showed significant fluctuations in the temporal evolution of all scalars analyzed, with the largest percentage differences between the two approaches occurring in the homogeneous turbulence regime group, which was characterized by predominantly weak turbulent activity throughout the night. In the comparison made, the methodology employed in the 109-minute window showed greater efficiency in the estimates of exchanges at 325 m in the ATTO tower, especially during conditions of low turbulent activity.
8
Chen, J., Y. Hu, Y. Yu, and S. Lü. "Ergodicity test of the eddy-covariance technique." Atmospheric Chemistry and Physics 15, no. 17 (September 4, 2015): 9929–44. http://dx.doi.org/10.5194/acp-15-9929-2015.
Анотація:
Abstract. The ergodic hypothesis is a basic hypothesis typically invoked in atmospheric surface layer (ASL) experiments. The ergodic theorem of stationary random processes is introduced to analyse and verify the ergodicity of atmospheric turbulence measured using the eddy-covariance technique with two sets of field observational data. The results show that the ergodicity of atmospheric turbulence in atmospheric boundary layer (ABL) is relative not only to the atmospheric stratification but also to the eddy scale of atmospheric turbulence. The eddies of atmospheric turbulence, of which the scale is smaller than the scale of the ABL (i.e. the spatial scale is less than 1000 m and temporal scale is shorter than 10 min), effectively satisfy the ergodic theorems. Under these restrictions, a finite time average can be used as a substitute for the ensemble average of atmospheric turbulence, whereas eddies that are larger than ABL scale dissatisfy the mean ergodic theorem. Consequently, when a finite time average is used to substitute for the ensemble average, the eddy-covariance technique incurs large errors due to the loss of low-frequency information associated with larger eddies. A multi-station observation is compared with a single-station observation, and then the scope that satisfies the ergodic theorem is extended from scales smaller than the ABL, approximately 1000 m to scales greater than about 2000 m. Therefore, substituting the finite time average for the ensemble average of atmospheric turbulence is more faithfully approximate the actual values. Regardless of vertical velocity or temperature, the variance of eddies at different scales follows Monin–Obukhov similarity theory (MOST) better if the ergodic theorem can be satisfied; if not it deviates from MOST. The exploration of ergodicity in atmospheric turbulence is doubtlessly helpful in understanding the issues in atmospheric turbulent observations and provides a theoretical basis for overcoming related difficulties.
9
RISTORCELLI, J. R. "A pseudo-sound constitutive relationship for the dilatational covariances in compressible turbulence." Journal of Fluid Mechanics 347 (September 25, 1997): 37–70. http://dx.doi.org/10.1017/s0022112097006083.
Анотація:
The mathematical consequences of a few simple scaling assumptions regarding the effects of compressibility are explored using a singular perturbation idea and the methods of statistical fluid mechanics. Representations for the pressure–dilatation and dilatational dissipation appearing in single-point moment closures for compressible turbulence are obtained. The results obtained, in as much as they come from the same underlying procedure, represent a unified development for both dilatational covariances. While the results are expressed in the context of a statistical turbulence closure they provide, with very few phenomenological assumptions, an interesting and clear mathematical model for the ‘scalar’ effects of compressibility. For homogeneous turbulence with quasi-normal large scales the expressions derived are – in the small turbulent Mach number squared isotropic limit – exact. The expressions obtained contain constants that have a precise physical significance and are defined in terms of integrals of the longitudinal velocity correlation. The pressure–dilatation covariance is found to be a non-equilibrium phenomenon related to the time rate of change of the kinetic energy and internal energy of the turbulence; it is seen to scale with α2M2t εs [Pk/ε−1] (Sk/εs)2. Implicit in the scaling is a dependence on the square of a gradient Mach number, S[lscr ]/c. A new feature indicated by the analysis is the appearance of the Kolmogorov scaling coefficient, α, suggesting that large-scale quantities embodied in the well-established ε∼u˜3/[lscr ] relationship provide a link to the structural dependence of the effects of compressibility. The expressions for the dilatational dissipation are found to depend on the turbulent Reynolds number and scale as M4t (Sk/εs)4R−1t. The scalings for the pressure–dilatation are found to produce an excellent collapse of the pressure–dilatation data from direct numerical simulation.
10
Liu, Lei, Yu Shi, and Fei Hu. "Characteristics of intrinsic non-stationarity and its effect on eddy-covariance measurements of CO<sub>2</sub> fluxes." Nonlinear Processes in Geophysics 29, no. 1 (March 24, 2022): 123–31. http://dx.doi.org/10.5194/npg-29-123-2022.
Анотація:
Abstract. Stationarity is a critical assumption in the eddy-covariance method that is widely used to calculate turbulent fluxes. Many methods have been proposed to diagnose non-stationarity attributed to external non-turbulent flows. In this paper, we focus on intrinsic non-stationarity (IN) attributed to turbulence randomness. The detrended fluctuation analysis is used to quantify IN of CO2 turbulent fluxes in the downtown of Beijing. Results show that the IN is common in CO2 turbulent fluxes and is a small-scale phenomenon related to the inertial sub-range turbulence. The small-scale IN of CO2 turbulent fluxes can be simulated by the Ornstein–Uhlenbeck (OU) process as a first approximation. Based on the simulation results, we find that the flux-averaging time should be greater than 27 s to avoid the effects of IN. Besides, the non-stationarity diagnosis methods that do not take into account IN would possibly make a wrong diagnosis with some parameters.
Дисертації з теми "Covariance turbulente":
1
Queiros-Condé, Diogo. "Covariance d'échelle et surface de flamme en combustion turbulente." Aix-Marseille 1, 1996. http://www.theses.fr/1996AIX11056.
Анотація:
Une symetrie fondamentale, la covariance d'echelle, est mise en evidence experimentalement sur un corpus de flammes turbulentes appartenant au regime des flammelettes. Elle implique l'existence d'une courbe unique caracterisant le plissement d'une flamme par la turbulence et integrant dans une meme description toutes nos flammes qu'elles soient faiblement ou fortement plissees. Une consequence directe de ce resultat est la possibilite de definir de maniere deterministe, la construction echelle par echelle d'une flamme par un ecoulement turbulent. La notion de transition d'un objet euclidien vers un objet fractal est ainsi introduite ; elle permet, mieux que la geometrie fractale, de decrire la forme d'une flamme turbulente. Toujours experimentalement, une deuxieme etude a permis de montrer sur nos fronts l'existence d'une intermittence geometrique ; par le biais de l'autosimilarite etendue, les exposants d'echelle ont ete mesures. Nous sommes ainsi parvenu, par voie geometrique, a des resultats comparables a ceux existant en turbulence mais decoulant de mesures de vitesse ; ceci signifie que le phenomene d'intermittence releverait d'une generalite plus grande que l'hydrodynamique pure. Enfin, une derniere etude suggere l'eventuelle utilisation de la flamme comme marqueur de l'ecoulement
2
Sa, Leonardo Deane de Abreu. "Les flux turbulents dans la couche limite de surface analysés à partir de mesures aéroportées : validation d'une méthode dissipative-inertielle et étude de variabilité." Toulouse 3, 1992. http://www.theses.fr/1992TOU30088.
Анотація:
La methode des covariances est generalement utilisee pour la mesure des flux turbulents par moyen aeroporte. Cependant elle necessite des equipements sophistiques pour calculer la vitesse verticale de l'air. On propose une methode dissipative-inertielle bien connue pour calculer les flux lorsque les mesures avion sont realisees a basse altitude. Ceci necessite la seule connaissance des caracteristiques du domaine inertiel pour la vitesse et les scalaires. La methode est validee en comparant les flux calcules par la methode dissipative avec les flux calcules par la methode des covariances. L'accord entre les deux est tres bon. Il est ensuite montre comment le taux de dissipation d'energie cinetique turbulente peut etre facilement calcule en utilisant une seule mesure dynamique simple. Ceci permet la mesure a l'aide d'un avion legerement equipe. La deuxieme partie du travail a porte sur l'etude de la variabilite spatiale des flux turbulents calcules par les deux methodes et l'incertitude associee a leur determination. La variabilite spatiale des flux augmente lorsqu'on diminue la longueur d'integration (l#p) et l'erreur evolue suivant une loi voisine de 1/l#p. Les estimations des flux par la methode dissipative-inertielle montrent une plus grande stabilite que celles obtenues par la methode des covariances. Elle peut etre utilisee sur des echantillons plus courts
3
Herig, Coimbra Pedro Henrique. "A whirlwind journey of wavelet turbulent flux mapping : estimation of spatialized turbulent flux on tall towers and its uncertainties." Electronic Thesis or Diss., université Paris-Saclay, 2024. https://theses.hal.science/tel-04637523.
Анотація:
Le climat et l'activité humaine sont étroitement liés. Les émissions de gaz à effet de serre (GES) impactent la dynamique climatique et la qualité de l'air, affectant des millions de personnes dans le monde. La surveillance efficace des GES est essentielle pour des décisions politiques éclairées, mais elle est complexe en raison de la variabilité des sources et puits, ainsi que du transport atmosphérique. Les réseaux de surveillance abordent cette variabilité en déployant des capteurs dans des lieux géographiques divers, échantillonnant en continu sur le temps.Les zones urbaines sont des points d'émission clés. Cependant, directement surveiller les changements de GES sur > 5 km2 avec des sources variées et des zones végétalisées manque d'une méthode standard. La méthode de covariance turbulente (eddy covariance, EC) offre une surveillance directe et continue du flux net de GES. L'EC basée sur les ondelettes fonctionne sur les mêmes principes mais ne nécessite pas de stationnarité, laissant plus de données exploitables pour l'analyse, ce qui est particulièrement bénéfique dans les environnements urbains complexes.Démêler les composantes anthropiques et biogéniques d'un flux net de CO2 est reconnu comme un problème clé à résoudre dans les zones urbanisées. Les modèles écosystémiques conventionnels utilisés pour partitionner la productivité primaire brute (GPP) et la respiration de l'écosystème (Reco) ne sont pas appropriés pour les zones urbanisées. La partition directe en utilisant des corrélations haute fréquence entre les gaz traceurs peut aider à surmonter les limitations des méthodes de partitionnement standard.Bien que l'EC reste la norme pour les études locales, l'estimation des flux de surface à plus grande échelle implique souvent d'assimiler des mesures de concentration de fond à des estimations antérieures à l'aide de modèles de transport. Les méthodes d'inversion utilisant les données de flux de tour sont encore rares et il serait intéressant de les tester dans les zones urbanisées.L'objectif de cette thèse était d'évaluer l'EC basée sur les ondelettes combinée à des méthodes d'inversion bayésiennes pour la cartographie des flux de CO2. Au cours de la thèse, j'ai découvert une nouvelle méthode de partitionnement direct qui a été utilisée pour améliorer l'inversion globale dans la zone suburbaine du plateau de Saclay.Dans le premier article de la thèse, nous avons proposé la nouvelle méthode de partitionnement direct basée sur l'analyse en quadrants des flux décomposés en fréquence de CO2 et de vapeur d'eau. Nous avons montré que cette méthode pouvait fournir des estimations impartiales de GPP et Reco. Nous avons également constaté que l'EC basée sur les ondelettes a gardé jusqu'à ~30% plus des données exploitables.Dans le deuxième article, nous avons utilisé une grande tour équipée d'analyseurs à haute précision mais lents. Malgré des fréquences d'acquisition plus lentes, l'atténuation était limitée à ~20 % par une plus faible contribution de hautes fréquences à cette hauteur. Les résultats encouragent une collaboration entre les réseaux atmosphériques et écosystémiques.Dans le troisième article, nous avons combiné la méthode de partitionnement proposée dans le premier article avec les instruments d'une tour atmosphérique du deuxième article. Le flux de CO2 partionné en biogéniques et anthropiques ont été assimilé dans des estimations spatialisées des flux à quelques km2. Les cartes de flux obtenues offrent l'avantage de reposer sur des mesures de flux directes à l'échelle du paysage et peuvent être utilisées pour informer les inversions à grande échelle à des échelles plus larges.Les résultats centrés sur la région parisienne fournissent des bases pour les mesures de flux à l'échelle du paysage et à definir des stratégies de surveillance des émissions. Ces avancées contribuent à la compréhension et à la résolution des défis environnementaux aux échelles temporelles et spatiales où les décisions sont prisesClimate and human activity are closely linked. Greenhouse gas (GHGs) emissions impact climate dynamics and air quality, affecting millions globally. Effective GHG monitoring is essential for informed policy decisions, yet it is complex due to spatial and temporal variability of sources and sinks, and atmospheric transport. Monitoring networks address this variability by deploying sensors across diverse geographic locations sampling continuously over time.Urban areas are key emission points, driving climate change. However, monitoring direct GHG changes over >5 km2 with varied sources and vegetated areas lacks a standard method. Eddy Covariance (EC) offers direct, continuous GHG net flux monitoring. Wavelet-based EC operates on the same principles as the standard method but calculates covariance using frequency decomposed time series. This approach does not require stationarity, leaving more data available for analysis, particularly beneficial in complex urban environments where non-stationary fluxes are common.Disentangling anthropogenic and biogenic components of a net CO2 flux is recognised as a key issue yet to be resolved in urbanised areas. Conventional ecosystem models used to partition gross primary productivity (GPP) and ecosystem respiration (Reco) are not appropriate for urbanised areas. Direct partitioning using high-frequency correlations between tracer gases may help overcoming the limitations of standard partitioning methods.While Eddy Covariance remains standard for local studies, estimating larger-scale surface fluxes often involves assimilating background concentration measurements to prior estimations using transport models. The progress in satellite imagery and detailed inventories provides a new basis that helps improve these methods. However, inversion methods using tower flux data are still sparse and would be interesting to test in urbanised areas.The objective of this PhD was to evaluate wavelet-based EC combined with Bayesian inversion methods for CO2 flux mapping. During the course of the PhD I discovered a new direct partitioning method that was used with a combination of CH4 and CO to improve the overall inversion in the suburban area of the Saclay plateau.In the first paper of the PhD, we hypothesised that decomposing concentration and wind signals by frequency can capture individual gusts within each frequency, typically mixed in the original signal. We leveraged this feature to propose a new parameter-free direct partitioning method based on quadrant analysis of CO2 and water vapour frequency decomposed fluxes. We showed that this method could indeed provide unbiased estimates of GPP and Reco at a crop and a forest ecosystem site near Paris. We also found that wavelet eddy covariance further saved up to 30% of the non-stationary data in these sites.In the second paper, we proposed using tall towers equipped with high-precision but slow analysers for measuring fluxes. Despite slower acquisition frequencies, attenuation was limited to 20 % by a lower contribution of high frequencies at this height. Results encourage further collaboration between atmospheric and ecosystem networks for in-situ measurements.In the third paper, we combined the partitioning method proposed in the first paper with the flux from the second paper, including now more gases measured to partition CO2 fluxes in biogenic and anthropogenic components and assimilate them in previous spatially-explicit estimations of fluxes at few km2. The obtained flux maps offer the advantage of relying on direct flux measurements at the landscape scale and may be used to informing large-scale inversions at broader scales.Results focused on the Parisian region provide valuable insights for flux measurements at the landscape scale and beyond, and contributing to emission monitoring strategies. These advancements contribute to understanding and addressing environmental challenges at the temporal and spatial scales where decisions are made
4
Nilsson, Charlotta. "Beräkning av turbulenta flödenenligt inertial dissipationsmetodenmed mätdata från enspecialkonstrueradlättviktsanemometer samtjämförelsemed turbulenta utbytesmetoden." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-303161.
Анотація:
För att ta reda på användbarheten av en specialkonstruerad lättviktsanemometer när det gälleratt beräkna turbulenta flöden, har mätdata från instrumentet använts i den så kallade inertialdissipationsmetoden. Resultatet har jämförts med direkta flödesberäkningar från enljudanemometer enligt turbulenta utbytesmetoden, vilka antas vara korrekta. Resultatanalyshar utförts från mätningar på höjderna 8, 16 och 20 m. Lättviktssanemometern (inertialdissipationsmetoden) visade sig stämma bra överens med ljudanemometern (turbulentautbytesmetoden) under nära neutrala förhållanden och vid höga vindhastigheter. Resultatenvisar ett inflytande av havsvågor och den bör därför användas vid uppbyggande sjö för attundvika detta. I rapporten presenteras en rekommendation med nödvändiga korrektioner föranvändning av lättviktsanemometern till turbulenta flödesberäkningar enligt inertialdissipationsmetoden.In order to evaluate a combined cup anemometer/wind vane profile instrument, measurementsfrom the instrument has been used in the so called inertial-dissipation method to derive itsability to measure turbulent fluxes. The result was compared to data from a sonic anemometercalculated with eddy-correlation method, which is assumed to be correct. Analysis of theresult was made from measurements at levels 8, 16 and 20 m. The profile instrument (inertialdissipationmethod) agreed well with the sonic anemometer (eddy-correlation method) duringnear neutral conditions and at high wind speed. The profile instrument also proved to be mostaccurate at conditions of growing sea, otherwise the result was affected by waves. In thereport there is also a recommendation for specific corrections when the profile instrument isused for calculating turbulent fluxes according to the inertial-dissipation method.
5
Inubushi, Masanobu. "Covariant Lyapunov Analysis of Navier-Stokes Turbulence." 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/175095.
6
Vendrame, Nadia. "Study of vegetation-atmosphere interactions over vineyards: CO2 fluxes and turbulent transport mechanics." Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3425729.
Анотація:
The study of vegetation‒atmosphere exchanges is today of great interest in order to understand and model plant responses to environmental conditions and their potential influence on global climate change. A special attention is usually given to carbon dioxide (CO2) fluxes and, in general, natural ecosystems such as forests received more attention. In the present work we investigated vegetation‒atmosphere interactions over vineyards, focusing on the annual carbon budget and turbulent transport processes driving exchanges of mass and energy.
Vineyard is a complex ecosystem with distributed sources/sinks of scalars (water vapour, carbon dioxide, heat), where vines and soil surface combine to give the overall flux of the canopy. In Northern Italy vineyard inter-row is often grassed, playing then an important role in the whole carbon budget. In this context, the partitioning of net ecosystem CO2 exchange (NEE) into soil and vine components deserves a special attention. We monitored vineyard NEE applying the eddy covariance (EC) method for three years, while soil CO2 flux measurements have been carried on using soil chambers (transparent and dark). In 2015, the annual carbon budget of the vineyard was about ‒ 80 g C m‒2 y‒1, however the largest part of carbon assimilation was due to grassed soil compartment (‒ 60 g C m‒2 y‒1). The interannual variability of seasonal carbon budget showed to be high and significantly affected by heat waves and drought spells in summer. During the growing season of 2014, characterized by plenty of rainfall, NEE reached its maximum value of about ‒ 250 g C m‒2.
The organization in rows of the vineyard determines a peculiar turbulent transport dynamics within the canopy. However, the morphological structure of the vineyard is greatly variable over the year, shifting from an empty canopy during vine dormancy to dense foliage in summer. We investigated the influence of foliage development on turbulence statistics deploying a vertical array of sonic anemometers. Turbulent flow showed to be greatly influenced by canopy structure. Without leaves, turbulent regime is typical of a rough‒wall boundary layer flow, whereas at full foliage development it assumes the features of a mixing‒layer flow, even if the inflection point at canopy top is weak, due to sparseness of the vineyard. Coherent structures involved in momentum transport and their temporal scales have been also investigated, showing the increasing importance of sweeps throughout the growing season. The average duration of dominating coherent structures was in the order of 6 ‒ 10 s and no clear influence by canopy structure evolution was detected.
The research demonstrated the importance of long‒term monitoring of vegetation‒atmosphere exchanges, and also the complexity of turbulent transport dynamics in the canopy space. However, only a thorough comprehension of this mechanics could lead to a solid interpretation of the role of vegetation in fundamental biogeochemical cycles.Lo studio delle interazioni tra vegetazione e atmosfera è oggi un tema di grande interesse nell’ottica di migliorare la comprensione della risposta delle piante alle variabili ambientali e la modellizzazione del loro ruolo nel cambiamento climatico globale. Particolare attenzione è di solito rivolta ai flussi di anidride carbonica (CO2) e, in genere, gli ecosistemi naturali come le foreste hanno ricevuto una maggiore attenzione. In questa ricerca sono state studiate le interazioni vegetatione-atmosfera su una coltura agraria importante per il bacino mediterraneo, quale il vigneto, focalizzandosi sul monitoraggio del bilancio annuale di carbonio e approfondendo lo studio della meccanica del trasporto turbulento che è alla base degli scambi di energia e materia. Il vigneto è un sistema complesso con diverse sorgenti e sink di scalari (vapore d’acqua, anidride carbonica, calore), in cui le due principali componenti, vite e suolo, compongono il flusso totale della canopy in un rapporto che varia nel corso dell’anno. Nei vigneti del Nord Italia, l’interfila è solitamente non lavorata e inerbita, giocando un ruolo importante nel bilancio del carbonio del sistema. In questo contesto, risulta cruciale la ripartizione dello scambio netto di CO2 dell’ecosistema (Net Ecosystem Exchange, NEE) nelle componenti suolo e vite. Nel corso di questa indagine, la NEE di un vigneto è stata monitorata per tre anni utilizzando la tecnica micrometeorologica dell’ eddy covariance (EC), mentre la misura dei flussi di CO2 al suolo è stata effettuata con camere (a cupola trasparente e oscura). Nel 2015, il bilancio annuale di carbonio del vigneto è stato di circa ‒ 80 g C m‒ 2 a‒ 1, dimostrando quindi la capacità di agire da sink, ma la maggior parte dell’assimilazione è risultata legata al suolo inerbito (‒ 60 g C m‒2 a‒1). In ogni caso, il sistema ha dimostrato un’elevata variabilità interannuale del bilancio del carbonio stagionale, in cui ondate di calore e periodi di siccità estivi hanno giocato un ruolo primario. Nella stagione 2014, caratterizzata da un regime di precipitazione abbondante, la NEE ha raggiunto il valore massimo di circa ‒ 250 g C m‒2. L’organizzazione del vigneto in filari determina una particolare dinamica del trasporto turbolento dentro canopy. Inoltre, la struttura morfologica del vigneto è altamente variabile durante il corso dell’anno, passando da una canopy praticamente vuota nel periodo di dormienza della vite a una situazione dove il fogliame è denso e concentrato nelle file al culmine della stagione vegetativa. L’influenza dello sviluppo della densità fogliare sulle statistiche della turbolenza è stato studiato installando un profilo verticale di anemometri ad ultrasuoni. Il flusso turbolento è risultato fortemente influenzato dalla struttura della canopy. Senza foglie, il regime turbolento è caratteristico di un flusso di parete, mentre con lo sviluppo completo del fogliame assume le proprietà tipiche di un flusso con mixing‒layer, sebbene il flesso al limite superiore della canopy sia poco accentuato, a causa della bassa densità fogliare del vigneto. Infine, è stata condotta un’analisi specifica delle strutture coerenti coinvolte nel trasporto di quantità di moto e sulle loro scale temporali. L’importanza di eventi discendenti che trasportano aria più veloce del flusso medio (sweeps) è aumentata nel corso della stagione. La durata media delle strutture coerenti dominanti è stato nell’ordine di 6 ‒ 10 s e, in questo caso, non è stata riscontrata nessuna chiara correlazione con lo sviluppo della struttura della canopy. Lo studio ha messo in evidenza l’importanza del monitoraggio a lungo termine degli scambi tra vegetazione e atmosfera, ma anche la complessità dei fenomeni di trasporto turbolento che li caratterizzano. Tuttavia, solo la piena comprensione della meccanica di questi processi può portare alla corretta interpretazione del ruolo della vegetazione nei cicli biogeochimici più fondamentali.
7
Carneiro, Janaína Viário. "Fluxos turbulentos de CO2 em uma área de arroz irrigado no RS." Universidade Federal de Santa Maria, 2007. http://repositorio.ufsm.br/handle/1/9185.
Анотація:
Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThis thesis quantifies the net change of CO2 (NEE) in an irrigated rice crop cultivation in RS (Brazil). The research is part of the project CT-HIDRO, which presents as main purpose the description of surface conditions for different ecosystems in the country. Data were gathered during the cultivation period, from October 2003 to March 2004. During this time, the average air temperature and the incident radiation were suitable for the development of the culture in such an area. The turbulent flows, calculated by the eddy covariance method, overestimated the NEE value, probably due to the low estimate of breathing tax, because, during some night-times, sensor registered little turbulence. Moreover, other factor could have interfered in the result of the flows, for instance, the time in which the flows are calculated. The Webb correction was applied in the curve of NEE, and a value smaller than 1% was found. Such result didn't modify the previous result significantly. The behavior of CO2 flow during the whole analyzed period showed a maximum of -0,47mgCO2 m−2 s −1 in January 2004, what demonstrates the largest absorption of CO2 from the atmosphere by the plant during the day and a smaller liberation at night, due to the development phase in which the plant is. In this case, the Webb correction was also little emphasized, not interfering in the obtained result. The curves that demonstrate the three phases of development of the rice presented a larger absorption of CO 2 during the reproductive phase. The behavior of the flow of CO 2 showed a negative flow during the day, when the plant absorbs CO2 from the atmosphere, and a positive flow during the night, when the inverse process occurs, what was waited for. The latent heat flow presented larger diary average values from January to February, always with positive values, consequence of the rice crop irrigation. Two days with high values of flow of latent heat were obtained, what motivated the analysis of the energy balance. The closing of the energy balance was not reached in both days. A possible reason for that could be the low estimate of flows when the eddy covariance method was applied.
Este trabalho quantifica a troca líquida de CO2 (NEE) em uma área de cultivo de arroz irrigado no RS, como parte do projeto CT-HIDRO, projeto este que tem como finalidade descrever condições de superfície para diferentes ecossistemas do país. Os dados utilizados foram coletados durante o período de cultivo, entre outubro de 2003 e março de 2004. Neste período a temperatura média do ar e a radiação incidente são adequadas para o desenvolvimento da cultura nesta região. Os fluxos turbulentos, calculados pelo método de covariância de vórtices (eddy covariance), superestimaram o valor da NEE, provavelmente devido, a subestimativa da taxa de respiração, pois em alguns períodos noturnos os sensores registraram pouca turbulência. Além disso, outro fator que pode interferir no resultado dos fluxos, como por exemplo, o intervalo em que os fluxos são calculados. Foi aplicada a correção de Webb na curva de NEE e encontrou-se um valor menor que 1%, fato este que não modificou significativamente o resultado encontrado. O comportamento do fluxo de CO 2 durante todo o período analisado, mostrou um pico de -0,47mgCO2 m−2 s −1 , em janeiro de 2004, o que demonstra a maior captura de CO2 da atmosfera pela planta durante o dia e uma menor liberação à noite, devido a fase de desenvolvimento em que a planta se encontra. Neste caso, a correção de Webb também foi pouco acentuada, não interferindo no resultado obtido. As curvas que demonstram as três fases de desenvolvimento do arroz mostraram claramente uma maior absorção de CO 2 durante a fase reprodutiva. O comportamento do fluxo de CO 2 mostra um fluxo negativo durante à dia, quando a planta absorve CO2 da atmosfera e um fluxo positivo durante à noite quando ocorre o processo inverso, o que era esperado. O fluxo de calor latente apresentou maiores valores médios diários entre os meses de janeiro e fevereiro, apresentando sempre valores positivos, conseqüência da irrigação do campo de arroz. Obtivemos dois dias com valores elevados de fluxo de calor latente, o que fez com que analisássemos o balanço de energia. O fechamento do balanço de energia não foi alcançado em ambos os dias. Uma possível razão para isto pode ser o devido à subestimativa dos fluxos quando aplicado o método de covariância de vórtices.
8
Stauch, Vanessa Juliane. "Data-led methods for the analysis and interpretation of eddy covariance observations." Phd thesis, kostenfrei, 2006. http://opus.kobv.de/ubp/volltexte/2007/1238/.
9
Zimermann, Hans Rogério. "Diferentes técnicas de condicionamento em séries temporais turbulentas." Universidade Federal de Santa Maria, 2005. http://repositorio.ufsm.br/handle/1/9211.
Анотація:
Conselho Nacional de Desenvolvimento Científico e TecnológicoThe dynamics process of the atmosphere near Earth ground is controled by two main forcings, termical and machanics. These process are reponsible for the atmospheric flow variability in this layer, and this variability characterizes the atmospheric turbulence. The presence of turbulence phenomena drives to distinguish it from the rest of atmosphere, such layer is commom called Atmospheric Boundary Layer (ABL). So, the importance of studying ABL is the fact of that turbulence represents an effective transport process near the ground surface. Adequate treating of the experimental data gives more truthful so qualitative as quantitavie when we are interpreting and understading these transports. This is very impportant for suitable trustful charaterizing the turbulent fluxes. This dissertation shows an overview about some basics turbulent data treatment techics. The dataset, colected experimentaly and separed into 27 minutes window samples, were subjected to simple mean, running mean through digital recursive filter e and linear detrending. Our focus are the implications of applying this technics and how each of this acts in turbulent time series of temperature and vertical velocity of the wind data, showing and discussing about the results in the estimating fluxes of sensible heat by Eddy Covariance method and also spectral densities estimates of temperature and vertical wind velocity. The main goal of the study done in this dissertation, was identifying that applying corrections on fase lag, not considered in older digital recursive filter (FDR as proposed by McMillen 1988) and, present into the model (FFDR proposed by Franceschi e Zardi 2003) leads for trusties estimatives, mainly for turbulent temperature spectra, which are the hardest ones for minimizing the non statinarity effects. Clearly, observing the graphical results of temperature spectra, we see that those low frequencies were better removed than the others technics, giving to spectral shape the classics espected shape.
A dinâmica da atmosfera próxima á superfície é regida por dois forçantes principais, um mecânico e outro térmico. Esses processos são responsáveis pela variabilidade dos escoamentos na baixa atmosfera e, é essa variabilidade que caracteriza a turbulência atmosférica. A presença do fenômeno de turbulência, permite distinguir uma camada do restante da atmosfera, esta é chamada de Camada Limite Atmosférica ( CLA). A importância de estudos nessa camada, está relacionada com o fato da turbulência representar um processo efetivo de transporte próximo à superfície. O tratamento adequado dos dados experimentais permite maior contabilidade, tanto qualitativa quanto quantitativas, na interpretação e entendimento desse transporte, ou seja, é necessário para uma adequada caracterização dos fluxos turbulentos. Nesta dissertação são investigadas algumas, das principais técnicas básicas, no tratamento de dados e condicionamento em séries temporais turbulentas. Os dados, experimentalmente coletados e separados em conjuntos de amostras com 27 minutos, são submetidos aos tratamentos com técnicas de média simples, média instantânea através de filtros digitais recursivos e remoção linear de tendência. Obeserva-se as implicações da aplicação destas técnicas, como cada uma delas age nas séries temporais turbulentas de temperatura e velocidade vertical do vento, apresentando e discutindo os resultados dessa aplicação, nas estimativas dos fluxos turbulentos de calor sensível através do método de Covariância dos Vórtices (MCV), e também das densidades espectrais de temperatura e velocidade vertical. Um dos grandes benefícios do estudo feito nessa dissertação, foi identificar que a correção do atraso de fase, que não era levada em consideração nos modelos de filtros digitais anteriores (FDR proposto por McMillen 1988) e, presente no modelo (FFDR Franceschi e Zardi 2003) conduz à estimativas satisfatórias, principalmente para espectros de temperatura turbulenta, que são os mais difíceis de se minimizar os efeitos de não estacionariedade. Ficou claro, observando nos resultados gráficos dos espectros, que a remoção de baixas freqüências nos espectros de temperatura, os deixou com o perfil típico de especros clássicamente esperados.
10
Polito, Martina. "Mean flow and turbulent exchange characteristics in real urban street canyons: the Lazzaretto case study." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Анотація:
In the context of the European iSCAPE project (Improving the Smart Control of Air
Pollution in Europe) an experiment was set up in order to test photocatalytic coatings
effectiveness in reducing the concentration of pollutants. Further analysis on various aspects of the urban environment have been possible thanks to the experiment.
The measurements collected during the experimental field campaign have been used to
study the differences in the atmospheric phenomena due to the different morphology of
two street canyons. Data in time periods characterized by non-synoptic conditions have
been selected and then compared. The first part of the study is dedicated to the characterization of the mean flow. Subsequently, turbulent fluxes have been studied for both
canyons with the Eddy Covariance method, in order to appreciate the different behaviour
of the two canyons. In the end, the data collected have been elaborated with the Quadrant Analysis. This latest study has made possible to compare the results obtained by
the measurements in a real urban canopy layer with the results obtained in a controlled
environment and in a vegetated canopy layer.
The study has examined the intensity of sweep and ejection effects in an urban canopy
layer. The results show that in both canyons sweep effects prevail for the downwind case.
Instead, for an upwind flow the dominant effects are those of ejection. For parallel wind
directions the two canyons behave differently, due to their different morphology. Furthermore, the intensity of both effects is not as strong as in the perpendicular cases. The
behaviour of the fluctuations of CO2 and H2O concentration with respect to the temperature fluctuations has been compared to the results obtained in a vegetated canopy
layer. The analysis has shown that in the downwind and parallel cases the trends are
in agreement with the ones obtained in the vegetated environment. For an upwind flow,
however, the expected trends are not found.
Книги з теми "Covariance turbulente":
1
Institute for Computer Applications in Science and Engineering., ed. A pseudo-sound constitutive relationship for the dilatational covariances in compressible turbulence: An analytical theory. Hampton, VA: Institute for Computer Applications in Science and Engineering, NASA Langley Research Center, 1995.
2
Institute for Computer Applications in Science and Engineering., ed. A pseudo-sound constitutive relationship for the dilatational covariances in compressible turbulence: An analytical theory. Hampton, VA: Institute for Computer Applications in Science and Engineering, NASA Langley Research Center, 1995.
3
United States. National Aeronautics and Space Administration., ed. Coherent Doppler Lidar signal covariance including wind shear and wind turbulence. [Washington, DC: National Aeronautics and Space Administration, 1993.
4
Ristorcelli, J. R. A pseudo-sound constitutive relationship for the dilatational covariances in compressible turbulence: an analytical theory. Hampton, Va: Institute for Computer Applications in Science and Engineering, 1995.
5
Khavaran, Abbas. A parametric study of fine-scale turbulence mixing noise. [Cleveland, Ohio]: National Aeronautics and Space Administration, Glenn Research Center, 2002.
6
James, Bridges, Freund Jonathan B, and NASA Glenn Research Center, eds. A parametric study of fine-scale turbulence mixing noise. [Cleveland, Ohio]: National Aeronautics and Space Administration, Glenn Research Center, 2002.
7
Stevens, Kurt Benedict. Remote measurement of the atmospheric isoplanatic angle and determination of refractive turbulence profiles by direct inversion of the scintillation amplitude covariance function with Tikhonov regularization. Monterey, Calif: Naval Postgraduate School, 1985.
8
Eddy Covariance A Practical Guide To Measurement And Data Analysis. Springer, 2012.
9
A pseudo-sound constitutive relationship for the dilatational covariances in compressible turbulence: An analytical theory. Hampton, VA: Institute for Computer Applications in Science and Engineering, NASA Langley Research Center, 1995.
Частини книг з теми "Covariance turbulente":
1
Pocheau, Alain. "Scale Covariance and Geometry in Turbulent Combustion." In Mixing, 187–204. Boston, MA: Springer US, 1999. http://dx.doi.org/10.1007/978-1-4615-4697-9_7.
2
Fischer, Frank Victor, and Wolfgang Polifke. "Modelling and Validation of Covariance Transport Equations for Large-Eddy-Simulation of Ternary, Turbulent Mixing." In Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 27–34. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-14243-7_4.
3
McComb, W. David. "The Kraichnan–Wyld–Edwards covariance equations." In Homogeneous, Isotropic Turbulence, 273–98. Oxford University Press, 2014. http://dx.doi.org/10.1093/acprof:oso/9780199689385.003.0009.
4
Susai, Masayuki. "Volatility Spillover Structure of Stock and Foreign Exchange Market between Korea, Japan, and Hong Kong." In Global Information Technology and Competitive Financial Alliances, 162–82. IGI Global, 2006. http://dx.doi.org/10.4018/978-1-59140-881-9.ch009.
Анотація:
Highly developed IT technology can be the source of volatility spillover between markets located in other countries. In this chapter, we investigate the interrelationship between stock returns in North East Asian countries and the effect of foreign exchange rate volatility on the interrelationship between stock returns. We bring out clear simultaneous interrelationship between stock return and foreign exchange volatility. Focusing on covariance of each asset returns, if we do not take foreign exchange rate volatility into account when we evaluate our international portfolio, the portfolio risk might be underevaluated. The analysis shows that foreign exchange market turbulence might be accompanied by increase in covariance between stock returns. Just after the Asian currency crisis, the relationship between stock returns and foreign exchange turbulence might have changed. For managing international portfolio risk, we should be aware of foreign exchange risk and structural change in covariance between stock returns.
5
Pocheau, A. "Scale Covariance and Scale-ratio Covariance in Turbulent Front Propagation." In Relaxation Dynamics in Laboratory and Astrophysical Plasmas, 219–52. WORLD SCIENTIFIC, 2009. http://dx.doi.org/10.1142/9789814291552_0007.
Тези доповідей конференцій з теми "Covariance turbulente":
1
Moulden, T. H. "Turbulence: the covariant structure." In AFM2014. Southampton, UK: WIT Press, 2014. http://dx.doi.org/10.2495/afm140151.
2
Churnside, James H., and Noaa Erl. "Joint PDF of optical scintillation." In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1988. http://dx.doi.org/10.1364/oam.1988.wp3.
Анотація:
We developed a model for the two-point joint probability density function for irradiance fluctuations in the atmosphere. Light was assumed to propagate some distance through refractive turbulence to two points located in a plane perpendicular to the propagation direction. Scattered light from turbulent eddies smaller than the Fresnel zone size is diffracted and assumed to produce a complex field whose real and imaginary parts are jointly Gaussian. This field adds coherently to the unscattered field to produce jointly Rician irradiance fluctuations. The light is also refracted by the larger eddies to produce an additional random modulation factor. The logarithm of this modulation factor was assumed to be jointly Gaussian. In weak turbulence, the result is nearly lognormal and has a single scale size. In strong turbulence, the scattered field has a jointly exponential density function with a small-scale size. The lognormal modulation has a larger scale size, which gives rise to the two-scale covariance function observed in strong turbulence. This model for the probability density function agrees well with recent experimental data.
3
Ochs, Gerard R., S. F. Clifford, and R. B. Fritz. "Observations of spherical-wave covariance in strong refractive-index turbulence." In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1986. http://dx.doi.org/10.1364/oam.1986.fa8.
Анотація:
A reasonably complete understanding of the phenomenon of the saturation of the scintillation of a lightwave propagated through strong atmospheric turbulence now exists. Some questions remain, however, about the nature of very small details in the scintillation pattern, that is, those around the inner scale and smaller. We present some observations of the fine structure of intensity scintillation, with concurrent independent measurements of refractive-index turbulence and inner scale made over a 1-km path. Quantitative measurements of the spatial covariance were made by continuously cycling the spacing of two 1-mm diam detectors, by operating continuously at fixed spacings, and by converting the temporal frequency observed by a small-diameter detector, moving at high speed in a circular pattern, to spatial wavelength. Qualitative information was also obtained through high-speed photographs. Details much smaller than the inner scale, which did not arise from the last few meters of the path, were observed by all techniques.
4
Gerolymos, G. A., та I. Vallet. "The Destruction-of-Dissipation Tensor εεij in Wall Turbulence". У ASME 2017 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/fedsm2017-69316.
Анотація:
The paper investigates the destruction-of-dissipation tensor εεij in low-Reynolds number turbulent plane channel flow. This tensor, which represents the destruction of the dissipation tensor εij (appearing in the budgets of the covariances of fluctuating velocities rij) by molecular viscosity, exhibits specific near-wall anisotropy and is not 2-C at the wall. The budgets of εεij (turbulent and viscous diffusion, pressure-term, various production mechanisms, and destruction by molecular viscosity εεεij) are studied and various scaling relations are examined.
5
Frehlich, R. G. "Intensity covariance of waves propagating in a random medium with a Kolmogorov spectrum and an Inner scale of turbulence." In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1986. http://dx.doi.org/10.1364/oam.1986.fs5.
Анотація:
The intensity covariance of a point source of waves propagating in a random medium is calculated using the asymptotic theory and a Kolmogorov refractive-index spectrum with an innerscale cutoff. In strong scattering, the variance is only a function of one parameter. The variance and small correlation scale are both larger than predicted for zero-inner scale. The small-scale structure is controlled by irregularities near the receiver while the large-scale structure is controlled by irregularities near the transmitter. The theoretical predictions are compared to experiment. Higher terms in the asymptotic theory are required in order to adequately predict intensity covariance. Full saturation of intensity fluctuations (variance of unity) is unlikely for laser propagation in reasonable atmospheric conditions. A similar analysis can be applied to the case of a Gaussian beam. The variance of intensity from a Gaussian beam is equal to the point source case when the transmitter aperture is smaller than the Fresnel distance and the beam diameter at the receiver plane is larger than the effective scattering region. The plane wave case is approximated when the transmitter aperture is larger than the scattering region and the radius of curvature is larger than the propagation distance. When the laser beam is focused onto the receiver plane, there is a regime where the variance is independent of the incident beam dimensions.
6
Conan, Rodolphe. "Fast iterative optimal estimation of turbulence wavefronts with recursive block Toeplitz covariance matrix." In SPIE Astronomical Telescopes + Instrumentation, edited by Enrico Marchetti, Laird M. Close, and Jean-Pierre Véran. SPIE, 2014. http://dx.doi.org/10.1117/12.2054472.
7
Tahtali, Murat, and Andrew Lambert. "Statistical Turbulence Approach to the Covariance Matrices in the Shiftmap Prediction Using Kalman Filter." In Signal Recovery and Synthesis. Washington, D.C.: OSA, 2009. http://dx.doi.org/10.1364/srs.2009.stuc2.
8
Milton, N. Mark, Michael Lloyd-Hart, Jessica A. Bernier, and Christoph Baranec. "Real-time atmospheric turbulence profile estimation using modal covariance measurements from multiple guide stars." In Optical Engineering + Applications, edited by Robert K. Tyson and Michael Lloyd-Hart. SPIE, 2007. http://dx.doi.org/10.1117/12.734377.
9
Su, Moming, Chuan-gang Gu, and Yong-miao Miao. "Study of Three-Dimensional Viscous Flow Field in Axial-Flow Fan." In ASME 1996 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1996. http://dx.doi.org/10.1115/96-gt-420.
Анотація:
The complex three-dimensional flow field in an axial-flow impeller incorporating high-Reynolds-number k-ε turbulence model is studied in this paper. The fully three-dimensional Reynolds averaged Navier-Stokes equations are solved. A computational procedure has been developed for predicting three-dimensional incompressible separated turbulent flows in the impeller. The SIMPLE-like algorithm is used. Convective terms are approximated with higher-order upstream-weighted approximations and a TVD-type MUSCL scheme. Physical covariant velocity components are selected as dependent solving variables. The non-orthogonal boundary-fitted coordinate system and collocated grid arrangement are also employed. Rhie and Chow’s momentum interpolation method is adopted to eliminate the non-physical pressure and velocity oscillations. Periodic boundary condition and moving wall boundary condition are considered to simulate truthfully the turbulent flow field in impeller. Two types of axial-flow impellers are computed. The first one is designed by ordinary method and the other is a improved design that has been considered with eliminating flow separation and viscous vortex in the first design. The computed results show that the fully tree-dimensional turbulent flows computation can efficiently predict three-dimensional separated flows and viscous vortex in axial-flow impeller and vaneless clearance. Using the program, a designer can improve passage geometric design to enhance the performance of the fan.
10
Khalitov, Daniel A., and Ellen K. Longmire. "Effect of Particle Size on Velocity Correlations in Turbulent Channel Flow." In ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45730.
Анотація:
The response of glass beads was examined in a fully developed turbulent channel flow of air with Reynolds number Reh = 4500 where h is the channel half width. Five sets of monodisperse particles were tested with integral Stokes numbers in the range 0.2–10 at the channel centerplane. Particle-to-air mass loadings were of order 10%. Laser sheets were aligned in streamwise-spanwise flow planes, and seeded, particle-laden flow was imaged with a dual-frame camera. A separation algorithm was used to obtain simultaneous gas and particle velocity measurements of homogeneous flow planes over a range of wall-normal distances. Profiles of single-point velocity statistics including mean and rms slip velocity, particle drift velocity, and gas-particle correlation were computed. In addition, two-point gas-particle and particle-particle velocity correlations were obtained. Near the wall, the gas-gas correlations yielded long, narrow patterns related to near-wall low-speed streaks. At the centerplane, the correlations were broader in the spanwise direction. Gas-particle and particle-particle correlations resembled the gas correlations in shape and size, but the values were smaller. The gas-particle covariance tended toward zero for St = 10. Particle-particle correlations were still significant for St = 4.
Звіти організацій з теми "Covariance turbulente":
1
Tanny, Josef, Gabriel Katul, Shabtai Cohen, and Meir Teitel. Application of Turbulent Transport Techniques for Quantifying Whole Canopy Evapotranspiration in Large Agricultural Structures: Measurement and Theory. United States Department of Agriculture, January 2011. http://dx.doi.org/10.32747/2011.7592121.bard.
Анотація:
Original objectives and revisions The original objectives of this research, as stated in the approved proposal were: 1. To establish guidelines for the use of turbulent transport techniques as accurate and reliable tool for continuous measurements of whole canopy ET and other scalar fluxes (e.g. heat and CO2) in large agricultural structures. 2. To conduct a detailed experimental study of flow patterns and turbulence characteristics in agricultural structures. 3. To derive theoretical models of air flow and scalar fluxes in agricultural structures that can guide the interpretation of TT measurements for a wide range of conditions. All the objectives have been successfully addressed within the project. The only modification was that the study focused on screenhouses only, while it was originally planned to study large greenhouses as well. This was decided due to the large amount of field and theoretical work required to meet the objectives within screenhouses. Background In agricultural structures such as screenhouses and greenhouses, evapotranspiration (ET) is currently measured using lysimeters or sap flow gauges. These measurements provide ET estimates at the single-plant scale that must then be extrapolated, often statistically or empirically, to the whole canopy for irrigation scheduling purposes. On the other hand, turbulent transport techniques, like the eddy covariance, have become the standard for measuring whole canopy evapotranspiration in the open, but their applicability to agricultural structures has not yet been established. The subject of this project is the application of turbulent transport techniques to estimate ET for irrigation scheduling within large agricultural structures. Major conclusions and achievements The major conclusions of this project are: (i) the eddy covariance technique is suitable for reliable measurements of scalar fluxes (e.g., evapotranspiration, sensible heat, CO2) in most types of large screenhouses under all climatic conditions tested. All studies resulted with fair energy balance closures; (ii) comparison between measurements and theory show that the model is capable in reliably predicting the turbulent flow characteristics and surface fluxes within screenhouses; (iii) flow characteristics within the screenhouse, like flux-variance similarity and turbulence intensity were valid for the application of the eddy covariance technique in screenhouses of relatively dilute screens used for moderate shading and wind breaking. In more dense screens, usually used for insect exclusions, development of turbulent conditions was marginal; (iv) installation of the sensors requires that the system’s footprint will be within the limits of the screenhouse under study, as is the case in the open. A footprint model available in the literature was found to be reliable in assessing the footprint under screenhouse conditions. Implications, both scientific and agricultural The study established for the first time, both experimentally and theoretically, the use of the eddy covariance technique for flux measurements within agricultural screenhouses. Such measurements, along with reliable theoretical models, will enable more accurate assessments of crop water use which may lead to improved crop water management and increased water use efficiency of screenhouse crops.
2
Tanny, Josef, Gabriel Katul, Shabtai Cohen, and Meir Teitel. Micrometeorological methods for inferring whole canopy evapotranspiration in large agricultural structures: measurements and modeling. United States Department of Agriculture, October 2015. http://dx.doi.org/10.32747/2015.7594402.bard.
Анотація:
Original objectives and revisions The original objectives as stated in the approved proposal were: (1) To establish guidelines for the use of micrometeorological techniques as accurate, reliable and low-cost tools for continuous monitoring of whole canopy ET of common crops grown in large agricultural structures. (2) To adapt existing methods for protected cultivation environments. (3) To combine previously derived theoretical models of air flow and scalar fluxes in large agricultural structures (an outcome of our previous BARD project) with ET data derived from application of turbulent transport techniques for different crops and structure types. All the objectives have been successfully addressed. The study was focused on both screenhouses and naturally ventilated greenhouses, and all proposed methods were examined. Background to the topic Our previous BARD project established that the eddy covariance (EC) technique is suitable for whole canopy evapotranspiration measurements in large agricultural screenhouses. Nevertheless, the eddy covariance technique remains difficult to apply in the farm due to costs, operational complexity, and post-processing of data – thereby inviting alternative techniques to be developed. The subject of this project was: 1) the evaluation of four turbulent transport (TT) techniques, namely, Surface Renewal (SR), Flux-Variance (FV), Half-order Time Derivative (HTD) and Bowen Ratio (BR), whose instrumentation needs and operational demands are not as elaborate as the EC, to estimate evapotranspiration within large agricultural structures; and 2) the development of mathematical models able to predict water savings and account for the external environmental conditions, physiological properties of the plant, and structure properties as well as to evaluate the necessary micrometeorological conditions for utilizing the above turbulent transfer methods in such protected environments. Major conclusions and achievements The major conclusions are: (i) the SR and FV techniques were suitable for reliable estimates of ET in shading and insect-proof screenhouses; (ii) The BR technique was reliable in shading screenhouses; (iii) HTD provided reasonable results in the shading and insect proof screenhouses; (iv) Quality control analysis of the EC method showed that conditions in the shading and insect proof screenhouses were reasonable for flux measurements. However, in the plastic covered greenhouse energy balance closure was poor. Therefore, the alternative methods could not be analyzed in the greenhouse; (v) A multi-layered flux footprint model was developed for a ‘generic’ crop canopy situated within a protected environment such as a large screenhouse. The new model accounts for the vertically distributed sources and sinks within the canopy volume as well as for modifications introduced by the screen on the flow field and microenvironment. The effect of the screen on fetch as a function of its relative height above the canopy is then studied for the first time and compared to the case where the screen is absent. The model calculations agreed with field experiments based on EC measurements from two screenhouse experiments. Implications, both scientific and agricultural The study established for the first time, both experimentally and theoretically, the use of four simple TT techniques for ET estimates within large agricultural screenhouses. Such measurements, along with reliable theoretical models, will enable the future development of lowcost ET monitoring system which will be attainable for day-to-day use by growers in improving irrigation management.