To see the other types of publications on this topic, follow the link: BOUNDARY VERTICES.
Dissertations / Theses on the topic 'BOUNDARY VERTICES'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'BOUNDARY VERTICES.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
HANOT, RAHUL. "COMMUNITY DTECTION USING FIRE PROPAGATION AND BOUNDARY VERTICES ALGORITHMS." Thesis, DELHI TECHNOLOGICAL UNIVERSITY, 2020. http://dspace.dtu.ac.in:8080/jspui/handle/repository/18779.
Full textAbstract:
Community detection in complex networks deal with grouping related nodes together and
plays a vital role to understand the functioning of the system in real-life situations.
Community detection is classified as an NP-hard problem. Various algorithms are currently
available for it but the problem with these existing algorithms is either they have high in
time complexity or they have not able to partition the network perfectly. In this paper, we
propose a novel community detection algorithm that works in two phases. In the first phase,
we apply fire propagation technique in which choosing an arbitrary vertex as the core vertex
and connecting an adjacent vertex to it and shapes a community this is similar to how fire
spreads in real-life situations. In the second phase,we use the result of the first phase of an
overlapped community and detect all boundary vertices which are belongings to more than
one communities and assign them to the single community based on the weight that each
core vertex assign to that particular boundary vertex using Dijkstra distance and the count of
the adjacent vertex that belong that community. The proposed algorithm performs well as
compared to label propagation and walk-trap algorithm in terms of modularity score using
various synthetic and real-world datasets.
2
Parsadous, Ali. "Vertical sidewall boundary layers in combined waves and currents." Thesis, University College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339101.
Full text
3
Veitel, Hansjörg. "Vertical profiles of NO2 and HONO in the boundary layer." [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=964946211.
Full text
4
Siddons, J. T. "The vertical distribution of phytoplankton in a turbulent boundary layer." Thesis, University of Liverpool, 2018. http://livrepository.liverpool.ac.uk/3018308/.
Full text
5
Moresco, Pablo Diego. "Linear and weakly nonlinear stability of mixed convection boundary layers." Thesis, Keele University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325859.
Full text
6
Pufahl, Alexander G. "Vertical structure of the oceanic planetary boundary layer : a modelling approach." Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363992.
Full text
7
Grzeskowiak, Stephan. "An Empirical Examination of Boundary Conditions of Relational Exchange." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/26935.
Full textAbstract:
Current marketing channel literature overwhelmingly suggests that entering exchange relationships leads to positive outcomes for the exchange parties. Yet, not all exchanges employ relational exchange. Thus, research appears to lack an understanding of the boundary conditions of successful relational exchange.
This dissertation contributes to filling this gap by clarifying what is understood as relational exchange and differentiating it from vertical integration. Here, a two-dimensional perspective on exchange structure is offered that integrates our view of relational exchange and extends the conceptualization of vertical integration beyond sole ownership.
To derive boundary conditions of relational exchange the literature on interorganizational relationships is integrated into six determinants and two key outcomes of relational exchange. These boundary conditions thus represent the facilitating circumstances that make relational exchange viable and the outcomes of relational exchange that exchange partners seek to achieve.Ph. D.
8
Gumm, Zoe. "Thermal instabilities in an evolving boundary layer at a single vertical wall." Thesis, City University London, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.649372.
Full textAbstract:
In this research we look at the effects of heating a single vertical wall bounding a semi-infinite fluid. This investigation is based on a mathematical and numerical study of the equations that govern the fluid motion. Our main focus is on the study of thermal instabilities, the first stage in the breakdown of the smooth flow up the wall that may eventually lead to turbulence. In our research, a thermal instability is defined to be a growth in the disturbance energy by a set amount. Initially instabilities cannot develop and therefore the main aim of our research is to identify the time at which instabilities in our system begin to grow. This involves finding the most unstable initial conditions and looking at how the form of the instabilities change as the background flow evolves. By achieving this, we have obtained quantitative information regarding the onset of thermal instabilities which takes into account the time-dependent nature of the problem.
9
Nasiri, Farshad. "The Structure of Boundary Layer Along a Vertical, Surface-Piercing Flat Plate." Thesis, The George Washington University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10842581.
Full textAbstract:
The present work reports on Direct Numerical Simulations of a temporally developing, zero pressure gradient, turbulent boundary along a surface piercing flat plate and its interaction with the free surface. The simulations were driven by experiments of the same flow regime. Three separate Froude numbers were considered in increasing order. Consequently the interface progresses from a rigid and undisturbed surface to one with violent eruptions, breaking waves and air entrainment. At the lowest Froude number where the surface stays flat, the simulations agreed well with prior studies and captured the recirculation regions in the cross-stream plane which are shown to be due to Reynolds stress anisotropy. At intermediate Froude numbers it was found that the main source of vorticity beneath the surface is not the Reynolds stress anisotropy but rather the vorticity generated at the interface. This vorticity was found to affect turbulent statistics including distribution of friction velocity and the slope of the log-law layer. Moreover, the present work shows that the surface generated vorticity interacts mainly with eddies of small and intermediate wave numbers and the smaller scales with high wave numbers remain intact.
Air entrainment due to turbulence was also investigated. With the aid of a prototypical problem the parameters that play a role in entrainment are established. A novel approach to quantify the turbulent structures was defined. Using this method, turbulent structures were categorized into entraining and non-entraining vortices. A Linear Logistic Regression model was trained and validated to help predict future entrainment events. The model performs well and can accurately predict entrainment events for both the turbulent regime and the prototypical problem.
10
Veitel, Hansjörg. "Vertical Profiles of NO 2 and HONO in the Planetary Boundary Layer." [S.l. : s.n.], 2002. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB10047881.
Full text
11
Wu, Peng, Xiquan Dong, Baike Xi, Yangang Liu, Mandana Thieman, and Patrick Minnis. "Effects of environment forcing on marine boundary layer cloud-drizzle processes." AMER GEOPHYSICAL UNION, 2017. http://hdl.handle.net/10150/624343.
Full textAbstract:
Determining the factors affecting drizzle formation in marine boundary layer (MBL) clouds remains a challenge for both observation and modeling communities. To investigate the roles of vertical wind shear and buoyancy (static instability) in drizzle formation, ground-based observations from the Atmospheric Radiation Measurement Program at the Azores are analyzed for two types of conditions. The type I clouds should last for at least 5h and more than 90% time must be nondrizzling and then followed by at least 2h of drizzling periods, while the type II clouds are characterized by mesoscale convection cellular structures with drizzle occur every 2 to 4h. By analyzing the boundary layer wind profiles (direction and speed), it was found that either directional or speed shear is required to promote drizzle production in the type I clouds. Observations and a recent model study both suggest that vertical wind shear helps the production of turbulent kinetic energy (TKE), stimulates turbulence within cloud layer, and enhances drizzle formation near the cloud top. The type II clouds do not require strong wind shear to produce drizzle. The small values of lower tropospheric stability (LTS) and negative Richardson number (R-i) in the type II cases suggest that boundary layer instability plays an important role in TKE production and cloud-drizzle processes. By analyzing the relationships between LTS and wind shear for all cases and all time periods, a stronger connection was found between LTS and wind directional shear than that between LTS and wind speed shear.
12
Odudu, Okeoghene. "The boundary of Article 81 of the EC treaty 'vis-à-vis' vertical agreements." Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399414.
Full text
13
Miao, Qun. "Fine-scale vertical structure of clear-air echoes during the International H₂O Project as detected by an airborne Doppler radar." Laramie, Wyo. : University of Wyoming, 2006. http://proquest.umi.com/pqdweb?did=1296094731&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
Full text
14
Lawless, Mark R. "Scales of boundary resistance in gravel bed channels, vertical velocity profiles and 3-dimensional turbulence structure." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ59183.pdf.
Full text
15
Libicki, Charles M. "Acoustic sensing of the vertical and temporal structure of sediment transport in the benthic boundary layer /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487267024997702.
Full text
16
Artola, Such Francisco Javier. "Free-boundary simulations of MHD plasma instabilities in tokamaks." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0441/document.
Full textAbstract:
Un des dispositifs les plus prometteurs pour réaliser la fusion contrôlée est le réacteur de type tokamak. Dans ces réacteurs, un plasma chaud ionisé est confiné à l'aide d'un champ magnétique intense. Ce travail de thèse porte sur l'étude d'une classe particulière d'instabilités au sein d'un tokamak. Cette étude est menée par des simulations numériques magnétohydro-dynamiques (MHD). Le code JOREK-STARWALL est adapté et appliqué pour étudier les instabilités dites à frontière libre. Ce type d'instabilités nécessitent un traitement spécial concernant les conditions de bord du plasma, où l'interaction du plasma avec le vide et les structures conductrices environnantes doit être prise en compte. JOREK-STARWALL permet d'étudier la physique de deux instabilités particulières à frontière libre: les modes localisés au bord ("Edge Localized Modes", ELMs) déclenchés par des oscillations de la position verticale du plasma et les évènements de déplacement vertical (Vertical Displacement Events, VDEs). Deux résultats majeurs sont obtenus: 1. Le déclenchement des ELMs par des oscillations de la position verticale est pour la première fois reproduit avec des simulations auto-cohérentes. Celles-ci permettent d'étudier le mécanisme physique sous-jacent à ce phénomène. Les simulations révèlent que pour le projet international ITER, ces ELMs déclenchés sont principalement dus à une augmentation du courant au bord du plasma due au mouvement vertical. 2. Pour les VDEs, plusieurs comparaisons effectuées avec d'autres codes MHD existants montrent un bon accord avec JOREK-STARWALL et permettant ainsi de réaliser des simulations pour estimer la quantité attendue de courants de halo dans ITEROne of the most promising concepts for future fusion reactors is the tokamak. In these devices, a hot ionized plasma is confined with the use of large magnetic fields. The subject of this thesis is the study of a particular type of tokamak instabilities with MagnetoHydroDynamic (MHD) simulations. The code JOREK-STARWALL is adapted and applied to the simulation of the so-called free-boundary instabilities. The investigation of this type of instabilities requires a special treatment for the plasma boundary conditions, where the interaction of the plasma with the vacuum and the surrounding conducting structures needs to be taken into account. In this work, the modelling of the electromagnetic plasma-wall-vacuum interaction is reviewed and generalized for the so-called halo currents. The adapted JOREK-STARWALL code is applied in order to study the physics of two particular free-boundary instabilities: Edge Localized Modes (ELMs) triggered by vertical position oscillations and Vertical Displacement Events (VDEs). Two major results are obtained: 1. The triggering of ELMs during vertical position oscillations is for the first time reproduced with self-consistent simulations. These allow for the investigation of the physical mechanism underlying this phenomenon. The simulations reveal that for the international ITER project, a large-scale tokamak, these triggered ELMs are mainly due to an increase in the plasma edge current due to the vertical plasma motion. 2. For VDEs, several benchmarks are performed with other existing MHD codes showing a good agreement and therefore allowing the performance of ITER simulations to estimate the expected amount of halo currents in ITER
17
Holdaway, Daniel. "Coupling the planetary boundary layer to the large scale dynamics of the atmosphere : the impact of vertical discretisation." Thesis, University of Exeter, 2010. http://hdl.handle.net/10036/110413.
Full textAbstract:
Accurate coupling between the resolved scale dynamics and sub-grid scale physics is essential for accurate modelling of the atmosphere. Previous emphasis has been towards the temporal aspects of this so called physics-dynamics coupling problem, with little attention towards the spatial aspects. When designing a model for numerical weather prediction there is a choice for how to vertically arrange the required variables, namely the Lorenz and Charney-Phillips grids, and there is ongoing debate as to which is the optimal. The Charney-Phillips grid is considered good for capturing the large scale dynamics and wave propagation whereas the Lorenz grid is more suitable for conservation. However the Lorenz grid supports a computational mode. In the first half of this thesis it is argued that the Lorenz grid is preferred for modelling the stably stratified boundary layer. This presents the question: which grid will produce most accurate results when coupling the large scale dynamics to the stably stratified planetary boundary layer? The second half of this thesis addresses this question. The normal mode analysis approach, as used in previous work of a similar nature, is employed. This is an attractive methodology since it allows one to pin down exactly why a particular configuration performs well. In order to apply this method a one dimensional column model is set up, where horizontally wavelike solutions with a given wavenumber are assumed. Applying this method encounters issues when the problem is non normal, as it will be when including boundary layer terms. It is shown that when addressing the coupled problem the lack of orthogonality between eigenvectors can cause mode analysis to break down. Dynamical modes could still be interpreted and compared using the eigenvectors but boundary layer modes could not. It is argued that one can recover some of the usefulness of the methodology by examining singular vectors and singular values; these retain the appropriate physical interpretation and allow for valid comparison due to orthogonality between singular vectors. Despite the problems in using the desirable methodology some interesting results have been gained. It is shown that the Lorenz grid is favoured when the boundary layer is considered on its own; it captures the structures of the steady states and transient singular vectors more accurately than the Charney-Phillips grid. For the coupled boundary layer and dynamics the Charney-Phillips grid is found to be most accurate in terms of capturing the steady state. Dispersion properties of dynamical modes in the coupled problem depend on the choice of horizontal wavenumber. For smaller horizontal wavenumber there is little to distinguish between Lorenz and Charney-Phillips grids, both the frequency and structure of dynamical modes is captured accurately. Dynamical mode structures are found to be harder to interpret when using larger horizontal wavenumbers; for those that are examined the Charney-Phillips grid produces the most sensible and accurate results. It is found that boundary layer modes in the coupled problem cannot be concisely compared between the Lorenz and Charney-Phillips grids due to the issues that arise with the methodology. The Lorenz grid computational mode is found to be suppressed by the boundary layer, but only in the boundary layer region.
18
Lizotte, Pierre-Luc. "A portable profiling system for determining horizontal and vertical carbon dioxide advection /." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101865.
Full textAbstract:
In order to better quantify the continuous net ecosystem exchange (NEE) at the farm scale, a 24 m high transportable tower-based eddy covariance and profiling system was tested during three field campaigns during the summer and autumn of 2006. The profile measurement system, equipped with a low-cost closed-path infrared gas analyser (LI-840) was designed to measure the carbon dioxide (CO2) storage especially during weak mixing periods under stable conditions. A tethered blimp-based measurement system for the nocturnal boundary layer (NBL) budget technique was deployed on several calm nights to compare with the concentrations and fluxes determined with the profiling system. The profiling system was also installed to determine horizontal and vertical advection. The two-dimensional horizontal positioning of the profile inlets allowed an examination of the CO2 advective gradient in relation to the wind direction. A near-source advection analysis provided parameters for further adjustments of the NEE at the actual farmland.
19
Pryce, David. "Receptivity of a boundary-layer subject to vertical vibrations and the secondary instability of spanwise modulated shear flows." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/24907.
Full textAbstract:
The viscous drag of a passenger aircraft is influenced significantly by the laminar-turbulent transition in the boundary-layer. Classically the transition process occurs when the turbulence develops as a result of the amplification of instability modes. In the flow past a unswept wing one such mode of instability is observed, Tollmien-Schlichting waves. We deal with the Tollmien-Schlichting waves or, more specifically, with the receptivity of the boundary layer with respect to them. If the surface becomes curved a different instability mode is created: Gortler vortices, which we will investigate as an inviscid secondary instability. Many disturbances can aid the generation of these instabilities but we concentrate on the vibrations of the wing caused by engine noise and the elasticity of the wing itself. This thesis is separated into these two problems of boundary-layer flow over the vibrating wing surface. Firstly we focus on the generation of Tollmien-Schlichting waves due to wing surface vibrations and surface roughness. Piston theory is used to describe the response of the flow outside the boundary layer to wing surface vibrations. Then the perturbations in the Stokes' layer are analysed. The Stokes' layer itself cannot produce a Tollmien-Schlichting wave. Therefore, we will assume that there is a wall roughness. The analysis of the interaction of the Stokes' layer with a wall roughness can be analysed with the help of the Triple deck theory. This allows us to consider the downstream effects of our disturbances and under our flow regime, dependent on the size of wavelength of vibrations, we can Fourier transform and solve our problem for the disturbance pressure. Once we have inverted our solution back into real space with the use of Residue theory we are then able to calculate receptivity coefficients which can be compared to those of previous studies. In the second problem we concentrate on the curved part of the wing where the flow is assumed to be slowly varying in the y direction. This generates Gortler vortices and we expect a sheared base flow with periodicity in the spanwise direction. Using a WKBJ approximation we can derive a multi-scale system of equations, which at leading order can be solved numerically to give eigenvalues and eigenfunctions representing pressure within the boundary-layer. We can only do so with the aid of a two-dimensional problem from which we fix an effective streamwise wavenumber, and an effective maximum growth rate. We use this to create an initial value for our WKBJ eigenvalue. This restricts the values of the streamwise wavenumber that we can calculate solutions for. This also means that when the streamwise wavenumber approaches the effective streamwise wavenumber we get a turning point and hence a breakdown of our WKBJ solutions. We derive and calculate solutions for streamwise wavenumbers away from this limit and discuss the breakdown of these solutions.
20
Yoerger, Edward J. Jr. "Vertical Acoustic Propagation in the Non-Homogeneous Layered Atmosphere for a Time-Harmonic, Compact Source." ScholarWorks@UNO, 2019. https://scholarworks.uno.edu/td/2709.
Full textAbstract:
In this work we study vertical, acoustic propagation in a non-homogeneous media for a spatially-compact, time-harmonic source. An analytical, 2-layer model is developed representing the acoustic pressure disturbance propagating in the atmosphere. The validity of the model spans the distance from the Earth's surface to 30,000 meters. This includes the troposphere (adiabatic), ozone layer (isothermal), and part of the stratosphere (isothermal). The results of the model derivation in the adiabatic region yield pressure solutions as Bessel functions of the First (J) and Second (Y) Kind of order $-\frac{7}{2}$ with an argument of $2 \Omega \tau$ (where $\Omega$ represents a dimensionless frequency and $\tau$ is a dimensionless vertical height in z (vertical coordinate)). For an added second layer (isothermal region), the pressure solution is a decaying sinusoidal, exponential function above the first layer.
In particular, the vertical, acoustic propagation is examined for various configurations. These are divided into 2 basic classes. The first class consists of examining the pressure response function when the source is located on boundary interfaces, while the second class consists of situations where the source is arbitrarily located within a finite layer. In all instances, a time-harmonic, compact source is implicitly understood. However, each class requires a different method of solution. The first class conforms to a general boundary value problem, while the second requires the use of Green's functions method.
In investigating problems of the first class, 3 different scenarios are examined. In the first case, we apply our model to a semi-infinite medium with a time-harmonic source ($e^{-i \omega t}$) located on the ground. In the next 2 cases, a semi-infinite medium is overlain on the previous medium at a height of z=13,000 meters. Thus, there exist two boundaries: the ground and the layer interface between the 2 media. Sources placed at these interfaces represent the 2nd and 3rd scenarios, respectively. The solutions to all 3 cases are of the form $A \frac{J_{-\frac{7}{2}}(2 \Omega \tau)}{{\tau}^{-\frac{7}{2}}} + B \frac{Y_{-\frac{7}{2}}(2 \Omega \tau)}{{\tau}^{-\frac{7}{2}}}$, where \textit{A} and \textit{B} are constants determined by the boundary conditions.
For the 2nd class, we examine the application to a time-harmonic, compact source placed arbitrarily within the 1st layer. The method of Green's functions is used to obtain a particular solution for the model equations. This result is compared with a Fast Field Program (FFP) which was developed to test these solutions. The results show that the response given by the Green's function compares favorably with that of the FFP.
Keywords: Linear Acoustics, Inhomogeneous Medium, Layered Atmosphere, Boundary Value Problem, Green's Function Method
21
Werner, Sandra R. (Sandra Regina). "The vertical structure of the bottom boundary layer on the southern flank of the George Bank during late winter." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/57662.
Full text
22
Bauduin, Sophie. "Remote sensing of atmospheric boundary layer composition using infrared satellite observations." Doctoral thesis, Universite Libre de Bruxelles, 2016. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/239053.
Full textAbstract:
Measuring the composition of the planetary boundary layer is essential for monitoring pollutants and for understanding their impact on environment and health. Nadir satellite remote sensing is particularly appealing to sound this part of the atmosphere, but is however challenging because pollutants concentrations are generally weak and confined in a small part of the atmospheric column. Among the sounders currently in orbit, those operating in the thermal infrared have usually their maximum sensitivity in the mid-troposphere, and are thought to be inadequate to measure the near-surface atmospheric composition. Their sensitivity to this part of the atmosphere is indeed generally limited by low temperature contrast (called thermal contrast) between the ground and the air above it. Shortly before the beginning of this PhD, this has however been challenged with different studies, which have shown the possibility to measure air pollution with thermal infrared sounders in case of high thermal contrast conditions. This was especially demonstrated with the measurement of ammonia global distribution using the Infrared Atmospheric Sounding Interferometer (IASI). This work aims at fully exploring the capabilities of thermal infrared sounders to sound the near-surface atmospheric composition. It mainly focuses on the observations of the IASI instrument, and addresses the following questions: where and when is IASI sensitive to the near-surface atmosphere? How large and how variable is the sensitivity to near-surface pollutants? What are the parameters that drive this variability? The answers to these questions are looked at for two pollutants: sulphur dioxide (SO2) and carbon monoxide (CO), and are obtained through a series of different analyses. SO2 is the first constituent on which this work focuses. The retrieval of its near-surface concentration is first of all attempted in an area surrounding the industrial area of Norilsk. This region, well-known for the extraction of heavy metals and its extremely high levels of pollution, encounters large temperature inversions in winter, which trap SO2 close to the ground. By exploiting these (corresponding to high negative thermal contrast), we show that it is possible to retrieve the surface SO2 concentrations in the region. This is done using a simplified version of the optimal estimation method, based on the use of a total measurement error covariance matrix. Further, we show that the surface SO2 concentration retrieval using the ν3 band is limited, in addition to thermal contrast, by the strong water (H2O) absorption, which renders the lowest atmosphere opaque in this spectral range in case of large humidity. Two conditions are therefore shown to be required to monitor near-surface SO2 in the ν3 band: large thermal contrast and low surface humidity. These findings are confirmed with the retrieval of SO2 at global scale, performed using a newly developed retrieval scheme based on the conversion of radiance indexes into SO2 columns using look-up-tables. It is composed of two successive steps: 1) the determination of the altitude of SO2 and the selection of low plumes (below 4 km), 2) for the selected observations, the conversion of radiance indexes into integrated SO2 0–4 km columns. The distributions and time series so obtained are used to better characterise the variability of IASI sensitivity to surface SO2 in the ν3 band at the global scale, and more particularly, in terms of thermal contrast strength and total column of H2O.The characterisation of IASI sensitivity to CO is realised in a second part of the work. Radiative transfer simulations are conducted first to determine the possibility to detect enhancement in CO near-surface concentrations with IASI. The framework of the optimal estimation is then used to investigate the capability of IASI to decorrelate, as a function of thermal contrast, the CO concentration in the low troposphere from that in the high troposphere. Finally, comparisons of IASI CO observations with co-located aircraft and ground-based measurements are shown to confirm with real data how IASI sensitivity to near-surface CO varies in terms of thermal contrast conditions, and to which extent it allows determining the CO abundance in case of high pollution.Mesurer la composition de la couche limite atmosphérique depuis les satellites est essentiel pour comprendre l’impact des polluants sur l’environnement global et sur la santé. Parmi les sondeurs actuellement en orbite, ceux opérant dans l’infrarouge thermique sont souvent considérés comme inadéquats pour cet objectif, leur sensibilité à l’atmosphère de surface étant généralement limitée par de faibles contrastes de température (appelés contrastes thermiques, TC) entre le sol et l’air au-dessus. Différentes études récentes ont cependant montré la possibilité de mesurer la pollution de l’air avec ce type de sondeur dans des conditions de TC élevé.Ce travail a pour objectif de redéfinir la capacité des sondeurs opérant dans l’infrarouge thermique à mesurer la composition de l’atmosphère de surface. Il se focalise sur les observations de l’instrument IASI (Interféromètre Atmosphérique de Sondage Infrarouge), et tente de répondre, pour les deux polluants que sont le dioxyde de soufre (SO2) et le monoxyde de carbone (CO), aux questions suivantes :Où et quand IASI est-il sensible à l’atmosphère de surface ?Quels sont les paramètres qui influencent cette sensibilité et dans quelle mesure?Dans une première partie, la thèse se focalise sur l’ajustement des concentrations de SO2 de surface pour la région industrielle de Norilsk, connue pour son niveau de pollution élevé. Nous montrons qu’il y est possible de restituer les concentrations de surface de SO2 en hiver, en exploitant les larges inversions de température (TC négatifs) qui s’y développent. Les restitutions reposent sur une version simplifiée de la méthode de l’estimation optimale, utilisant une matrice complète de l’erreur de mesure. En plus du TC, nous montrons que l’ajustement dans la bande ν3 du SO2 est également limité par la forte absorption de la vapeur d’eau (H2O), qui rend les basses couches de l’atmosphère opaques. La nécessité de combiner des TCs élevés et une faible humidité pour permettre la mesure du SO2 en surface est confirmée par une analyse à l’échelle globale, utilisant une méthode basée sur la mesure d’indices de radiance et leur conversion en colonnes de SO2 à l’aide de tables pré-calculées. Composée de 2 étapes, cette méthode identifie et sélectionne d’abord les panaches situés sous 4 km ;elle convertit ensuite les indices de radiance en colonnes de SO2 intégrées entre 0 et 4 km. Les distributions et séries temporelles obtenues sont utilisées pour caractériser, en termes de valeurs de TC et de colonnes totales d’H2O, la variabilité de la sensibilité de IASI au SO2 de surface dans la bande ν3.Dans la seconde partie du travail, des simulations de transfert radiatif sont entreprises pour déterminer la possibilité de détecter avec IASI des augmentations de la concentration de CO dans l’atmosphère de surface. Le formalisme de l’estimation optimale est aussi utilisé pour analyser l’influence du TC sur la capacité de IASI à décorreler les concentrations du CO dans la basse et la haute troposphère. Finalement, des comparaisons entre les concentrations de CO restituées des mesures IASI sous différentes conditions de TC et de pollution et celles mesurées par avions et par des stations au sol complètent la caractérisation.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
23
Rathmell, Katie. "The influence of the Loop Current on the diversity, abundance, and distribution of zooplankton in the Gulf of Mexico." [Tampa, Fla] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0001890.
Full text
24
Page, Jennifer Lynn. "The effects of plume property variation on odor plume navigation in turbulent boundary layer flows." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29752.
Full textAbstract:
Thesis (Ph.D)--Biology, Georgia Institute of Technology, 2009.Committee Chair: Weissburg, Marc; Committee Member: Hay, Mark; Committee Member: Kubanek, Julia; Committee Member: Webster, Donald; Committee Member: Yen, Jeannette. Part of the SMARTech Electronic Thesis and Dissertation Collection.
25
Dill, Thaís Freitas. "ANÁLISE DA ESTRUTURA VERTICAL DO ESCOAMENTO ATMOSFÉRICO DURANTE OCORRÊNCIA DE EVENTOS TURBULENTOS INTERMITENTES NA CAMADA LIMITE NOTURNA." Universidade Federal de Santa Maria, 2015. http://repositorio.ufsm.br/handle/1/10287.
Full textAbstract:
Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThe objective of this study is to analyze the vertical structure of the intermittent turbulent events in the very stable boundary layer, as well the analysis and characterization of events originated near the surface that propagate upward. Therefore, it was used observational data from the FLOSSII experiment, together with the results of simulations using a numerical model that is able to reproduce the occurrence of turbulence bursts in the very stable boundary layer. The data have a total of 108 nights, from 20th of November 2002 to 02nd of April 2003, held in North Park south of Walden in the state of Colorado, in the United States. The experimental analysis showed that most of the events generated in the surface are very weak, not being able to connect the surface with the highest levels of the tower. Consistent with other studies, it was observed that the occurrence of events that propagates downward cause an increase in temperature, while events which propagate upward cause a cooling of the air near the surface. Another important result is much of the observed events that propagate upward are generated by wind acceleration due to drainge. Finally, it is shown that the events reproduced by the numerical model are caused by the shear increased and they are transported vertically by turbulent transport of energy, as observed in real world.
O objetivo deste trabalho é analisar a estrutura vertical de eventos de intermitência global na camada limite muito estável. A análise e caracterização feita foca, principalmente, nos eventos gerados em superfície que se propagam para cima. Para tanto, foram utilizados dados observacionais do experimento FLOSSII, juntamente com o resultado de simulações, utilizando um modelo numérico capaz de simular a ocorrência de intermitência na camada limite muito estável. Os dados possuem um total de 108 noites, no período de 20 de Novembro de 2002 a 02 de Abril de 2003, realizado em North Park ao sul de Walden, no estado do Colorado, nos Estados Unidos. As análises experimentais mostraram que a maior parte dos eventos gerados em superfície são muito fracos, não sendo capazes de conectar a superfície com os níveis mais altos da torre. Em concordância com outros trabalhos, foi observado que a ocorrência de eventos que se propagam para baixo causam aumento na temperatura, enquanto que eventos que se propagam para cima causam o resfriamento da atmosfera próxima à superfície. Outro resultado importante é que grande parte dos eventos observados, que se propagam para cima, são gerados pela aceleração do vento devido à presença de drenagem no escoamento. Finalmente, é mostrado que os eventos reproduzidos pelo modelo numérico são originados pelo aumento do cisalhamento e são transportados verticalmente pelo transporte turbulento de energia, assim como observado no mundo real.
26
Tizaoui, Abdelkhalek. "Etude théorique, numérique et expérimentale de l'échange de chaleur entre un fluide et le sol par un échangeur bitubulaire vertical." Valenciennes, 1989. https://ged.uphf.fr/nuxeo/site/esupversions/4e75693b-4fbb-4e3f-9f3d-b412562fb545.
Full textAbstract:
La thèse est consacrée à l’étude de l’échange de chaleur entre un fluide et un milieu solide tel que le sol par l’intermédiaire d’un échangeur bitubulaire vertical. Un modèle mathématique du comportement du système a été élaboré. Pour résoudre l’ensemble des équations, un algorithme de calcul numérique, basé sur l’utilisation des fonctions de Green afin de réduire le problème tridimensionnel à un problème bidimensionnel, a été mis au point. L’application du théorème de Duhamel a permis d’introduire la notion de réponse caractéristique de ce type d’échangeur. En vue de valider le modèle mathématique et numérique, une expérience a été réalisée en laboratoire. Les résultats des tests effectués avec des conditions aux limites différentes confirment avec une très bonne approximation les résultats théoriques. Ce modèle peut être alors utilisé comme un outil intéressant pour concevoir des échangeurs à puits multiples efficaces contribuant ainsi à l’élaboration de chaînes énergétiques rentables.
27
Kazanas, Konstantinos [Verfasser], Andreas [Gutachter] Wahner, and Thomas F. [Gutachter] Mentel. "Morning Aerosol vertical profiles in the Planetary Boundary Layer: Observations on a Zeppelin NT Airship and comparison with a Regional Model / Konstantinos Kazanas ; Gutachter: Andreas Wahner, Thomas F. Mentel." Köln : Universitäts- und Stadtbibliothek Köln, 2017. http://d-nb.info/1161531793/34.
Full text
28
Klein, Amélie. "Analyse du profil vertical de l'ozone dans la basse troposphère à Paris." Electronic Thesis or Diss., Sorbonne université, 2018. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2018SORUS192.pdf.
Full textAbstract:
Les mesures de l'ozone en surface ne sont pas suffisantes pour comprendre les mécanismes de formation de l'ozone dans la partie basse de la troposphère. Au cours de cette thèse, nous avons utilisé les instruments de la station QUALAIR, située à Paris, qui permettent d'obtenir des mesures de profils verticaux d'ozone ainsi que des mesures de dynamique atmosphérique et de colonnes intégrées de NO2 sur les premiers kilomètres de l'atmosphère. Une première approche statistique, à partir de quatre années de mesures consécutives de LIDAR ozone (2011-2014), a permis de comprendre les mécanismes responsables du gradient vertical et de la variabilité saisonnière de l'ozone à Paris. Afin de mieux évaluer l'influence du transport sur la variabilité spatio-temporelle de l'ozone, un deuxième travail a consisté à étudier les résultats d'une campagne instrumentale, organisée à Paris, et durant laquelle des mesures en continu d'ozone, de champs de vent et de turbulence dans la couche limite atmosphérique ont été réalisées. Ce travail a permis d'étudier l'impact de la réincorporation de la couche résiduelle sur l'évolution de l'ozone en surface à l'échelle locale. De plus, un modèle lagrangien de dispersion de particules (FLEXPART-WRF) a été utilisé afin d'évaluer l'impact du transport nocturne d'une couche appauvrie en ozone sur la variabilité de l'ozone en surface à l'échelle régionale. Enfin, le développement d'un modèle de chimie-transport à une dimension (PACT 1D) a permis de quantifier l'influence du transport vertical et de la chimie sur l'évolution de l'ozone dans la couche limite au cours de la journéeSurface ozone measurements are not sufficient to understand the mechanisms of ozone formation in the lower troposphere. In this study, we have used instruments from the QUALAIR station, located in Paris center, that can measure vertical profiles of ozone, atmospheric dynamics parameters, and integrated contents of NO2 in the lowermost troposphere. First, a statistical analysis, using four years of ground based ozone LIDAR measurements (2011-2014), is done to understand the mechanisms responsible for the vertical gradient and the seasonal cycle of ozone in Paris. Then, in order to better assess the influence of transport on the spatial and temporal evolution of ozone, we focus on the results obtained from an instrumental campaign, organized in Paris, and during which continuous measurements of ozone, wind and turbulence in the atmospheric boundary layer were performed. The results show the impact of the entrainment of the residual layer into the mixed layer on the surface ozone variability in the morning at the local scale. A Lagrangian particle dispersion model (FLEXPART-WRF) is used to better assess the impact of the nocturnal transport of a clean ozone layer via nocturnal low level jets from Paris on the surface ozone evolution at the regional scale. Finally, a one dimensional chemical transport model (PACT 1D) is used to quantify the influence of vertical transport versus photochemistry on the evolution of boundary layer ozone during daytime
29
Méndez, Margio González. "Simulations numériques de la transition de la couche limite sur une surface concave : application à la conception des éoliennes à axe vertical de type Savonius Heat-transfer analysis of a transitional boundary layer over a concave surface with Görtler vortices by means of direct numerical simulations Boundary layer transition over a concave surface caused by centrifugal instabilities." Thesis, Normandie, 2020. http://www.theses.fr/2020NORMIR05.
Full textAbstract:
Des simulations numériques directes (DNS) sont calculées afin d’étudier le processus complet de transition laminaire-turbulent d’une couche limite qui se développe sur une surface concave. On constate que l’écoulement traversant une telle géométrie est susceptible de développer des instabilités centrifuges sous forme de tourbillons de Görtler. La transition est déclenchée au moyen d’éléments de rugosité de paroi qui sont également utilisés pour prédéfinir la longueur d’onde transversale des tourbillons de Görtler. Les différentes régions rencontrées dans le processus de transition, c’est-à-dire linéaire, non-linéaire, transition et complètement turbulente, sont identifiées et caractérisées. Les instabilités primaires et secondaires (sinueux et variqueux) sont également identifiées et analysées. Des études paramétriques montrant l’effet de plusieurs paramètres physiques (le rayon de courbure, la longueur d’onde des tourbillons, l’amplitude et la localisation de la perturbation, et la géométrie des éléments de rugosité de paroi) sur le point de départ de la transition sont présentées. De plus, des analyses thermiques sont menées afin d’étudier la modification de la couche limite thermique produite par le mouvement rotatif des tourbillons de Görtler. L’évolution du transfert thermique de la surface est étudiée et on constate qu’il est considérablement augmenté dans la région non-linéaire dépassant les valeurs de la région turbulente. On constate également que l’analogie de Reynolds entre la quantité de mouvement dans le sens de l’écoulement et le transfert de chaleur est suivie tout au long du processus de transitionDirect numerical simulations (DNS) are computed in order to study the complete laminar-to-turbulent transition process of a boundary layer developing over a concave surface. It is found that the flow passing through such geometry is prone to develop centrifugal instabilities in the form of Görtler vortices. Transition is triggered by means of wall-roughness elements that are also utilized to preset the spanwise wavelength of the Görtler vortices. The different regions encountered in the transition process, i.e. linear, nonlinear, transition, and fully turbulent, are identified and characterized. Primary and secondary (varicose and sinuous) instabilities are identified and analyzed as well. Parametric studies showing the effect of several physical parameters (radius of curvature, the vortices wave-length, the perturbation amplitude and streamwise location, and the wall-roughness perturbation geometry) on the transition starting point are presented. Furthermore, thermal analyses are conducted in order to study the modification of the thermal boundary layer due to the Görtler vortices swirl motion. The streamwise evolution of the surface heat transfer is investigated finding that it is considerably enhanced in the non-linear region surpassing the turbulence-region values. It is also found that the Reynolds analogy between streamwise-momentum and heat transfer is followed throughout the whole transition process
30
Pegliasco, Cori. "Structure verticale des tourbillons de mésoéchelle dans les quatre grands systèmes d'upwelling de bord est." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30331/document.
Full textAbstract:
Basé sur l'analyse conjointe et complémentaire de ~10 ans de données altimétriques et de profils verticaux de température et de salinité acquis par les profileurs Argo, l'objectif principal de cette thèse est d'étudier en détail les caractéristiques de surface et la structure verticale des tourbillons dans les 4 grands systèmes d'upwelling mondiaux (EBUS Pérou-Chili, Californie, Canaries et Benguela), qui partagent une dynamique à grande échelle relativement similaire. Les résultats principaux montrent que l'ensemble des tourbillons détectés sur les cartes altimétriques dans les 4 EBUS ont des propriétés physiques relativement proches, avec une forte proportion de tourbillons de faibles dimensions ayant une durée de vie relativement courte. Au contraire, la faible partie des tourbillons échantillonnés par les profileurs Argo montre des dimensions bien plus grandes pour des durées de vie plus longues. La sur-représentation de ces grandes échelles dans le jeu des tourbillons échantillonnés par les profileurs Argo est donc le biais majeur des résultats obtenus sur la structure verticale des tourbillons. L'analyse des profils moyens d'anomalies de température et de salinité acquis par les profileurs Argo dans les tourbillons révèle une forte hétérogénéité entre les 4 EBUS, mais également au sein de chacun de ces systèmes d'upwelling. Les structures verticales des tourbillons sont fortement liées à l'hydrologie et à la dynamique locale. Par exemple, les tourbillons de subsurface du PCUS occupent plutôt la partie Sud du système, alors que les tourbillons intensifiés en surface sont présents à la limite Nord de la gyre subtropicale. Dans le CALUS, la présence de Cuddies se devine à la côte, les autres sous-régions contenant des tourbillons dont les anomalies sont majoritairement intensifiées à la base de la pycnocline, avec comme particularité un changement de signe lié à la salinité des couches superficielles. Le CANUS est peuplé de tourbillons très différents en fonction de leur position par rapport à la zone frontale du Cap Vert : au Nord, des tourbillons intenses en subsurface, avec la présence de quelques Meddies ; au Sud, des tourbillons très superficiels. De même dans le BENUS, la partie au Nord de 15°S contient plutôt des tourbillons intensifiés dans les couches de surface, alors qu'au Sud du front d'Angola-Benguela, les tourbillons présentent des anomalies fortes sur une grande partie de la colonne d'eau. L'extrême Sud de cet EBUS est également le lieu de passage des Anneaux des Aiguilles. Les contributions de l'advection isopycnale et du déplacement de la colonne d'eau sur la verticale nous permettent d'affiner la description de ces différentes structures. La présence de grands types de tourbillons, à la morphologie bien distincte (cœur de surface, de subsurface, grande extension verticale, tourbillons fortement intensifiés, etc.), est confirmée par l'étude des tourbillons spécifiquement générés dans la bande côtière. L'analyse Lagrangienne de ces tourbillons nous permet également de décrire l'évolution temporelle de leur structure verticale, qui montre une homogénéité temporelle inattendue. Cette thèse présente donc plusieurs outils facilement applicables dans différentes régions océaniques pour caractériser la structure thermohaline des tourbillons et fournit pour la première fois une description des grands types de tourbillons peuplant les EBUS, soulignant la grande diversité de la mésoéchelleMerging ~10 years of altimetry maps and vertical profiles provided by Argo floats, we aim to study in details the eddy's surface characteristics and vertical structure in the 4 major Eastern Boundary Upwelling Systems (EBUS : Peru-Chile, California, Canaries and Benguela), sharing similar large-scale dynamics. Our main results show that the eddies detected on altimetry maps in the 4 EBUS have close physical properties, with a lot of small-scale structures (radius < 40km, amplitude < 1cm and lifetime < 30 days). In contrast, the few eddies sampled by Argo floats have larger dimensions (radius of ~90-140 km, amplitude of ~3-7 cm) and longer lifetimes (6-10 months). The major bias with the analyzed vertical structure is the over representation of these large-scale eddies. The temperature and salinity anomaly mean profiles acquired by Argo floats surfacing within eddies reveals a strong heterogeneity between each of the 4 EBUS, but also within them. The eddies' vertical structure is strongly influence by the local hydrology and dynamics. For example, the subsurface-intensified eddies of the PCUS tend to be located in the Southern part of this EBUS, while the surface-intensified eddies are preferentially located near the Northern boundary of the subtropical gyre. In the CALUS, we can identify Cuddies in some coastal sub-regions, but in this EBUS, most of the eddies are intensified at the base of the pycnocline, with a reversal of the salinity anomaly compared to the surface layers. In the CANUS, the Cape Verde frontal zone separates distinct subsurface-intensified eddies and some Meddies in the North, from the Southern part, where eddies are surface-intensified. In the same way, the Angola-Benguela Front of the BENUS separates the surface-intensified eddies in the North from strong, deep-reaching anomalies in the South. The Southern-most part of the BENUS is also a preferential pathway for the large Agulhas Rings and their associated cyclones. The respective contributions of isopycnal advection and vertical displacement improve the description of these very diverse structures. The presence of several eddy-types, with distinct thermohaline properties (surface or subsurface-intensified, deep vertical extend, intense or not, etc.) is confirmed by the study of eddies generated in the coastal area of each EBUS. Their Lagrangian analysis allows us to describe the temporal evolution of their vertical structure, which shows an unexpected temporal homogeneity. This manuscript presents different efficient tools used to analyze the surface characteristics, the thermohaline properties and the temporal evolution of mesoscale eddies in the 4 major EBUS, highlighting their diversity
31
Herman, Scott William. "A paleomagnetic investigation of vertical-axis rotations in coastal Sonora, Mexico| Evidence for distributed transtensional deformation during the Proto-Gulf shift from a subduction-dominated to transform-dominated plate boundary in the Gulf of California." Thesis, University of California, Santa Barbara, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1536547.
Full textAbstract:
The history of late Miocene (Proto-Gulf) deformation on the Sonoran margin of the Gulf of California is key to understanding how Baja California was captured by the Pacific plate and how strain was partitioned during the Proto-Gulf period (12.5-6 Ma). The Sierra el Aguaje and Sierra Tinajas del Carmen are located in southwestern coastal Sonora, Mexico, and represent the eastern rifted margin of the central Gulf of California. The ranges are composed of volcanic units and their corresponding volcaniclastic units which are the result of persistent magmatic activity between 20 and 8.8 Ma, including three packages of basalt and andesite that make excellent paleomagnetic recorders. Based on cross cutting relations and geochronologic data for pre-, syn-, and post-tectonic volcanic units, most of the faulting and tilting in the Sierra El Aguaje is bracketed between 11.9 and 9.0 Ma, thus falling entirely within Proto-Gulf time.
A paleomagnetic investigation into possible vertical axis rotations in the Sierra el Aguaje has uncovered evidence of clockwise rotations between ~13º and ~105º with possible translations. These results are consistent with existing field relations, which suggest the presence of large (>45°) vertical axis rotations in this region. This evidence includes: a) abrupt changes in the strike of tilted strata in different parts of the range, including large domains characterized by E-W strikes b) ubiquitous NE-SW striking faults with left lateral-normal oblique slip, that terminate against major NW-trending right lateral faults, and c) obliquity between the general strike of tilted strata and the strike of faults. These rotations occurred after 12 Ma and largely prior to 9 Ma, thus falling into the Proto-Gulf period. Such large-scale rotations lend credence to the theory that the area inboard of Baja California was experiencing transtension during the Proto-Gulf period, rather than the pure extension that would be the result of strain partitioning between Sonora and the Tosco-Abreojos fault offshore Baja California.
32
Brogno, Luigi. "Nocturnal low-level jets over complex terrain: driving mechanisms and analytical modeling." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20539/.
Full textAbstract:
Several studies in the Atmospheric Physics have focused on the analysis of the atmospheric circulation phenomena at the small scale and turbulent processes within the planetary boundary layer (PBL), whose formation and evolution is complicated by the topography.
The Low-Level Jet (LLJ) is one of the most studied phenomena and it is not yet completely understood. It consists in the occurrence of strong winds within a thin layer of the PBL.
A particular case is the formation of double-nose LLJs (or multiple LLJs), i.e. the simultaneous occurrence of two (or multiple) noses within the PBL.
Analysing data retrieved in complex terrain during the MATERHORN field campaigns, the objectives of this thesis are to understand the mechanisms which drive the formation of the double-nose LLJs identified using a newly-proposed criterion that upgrade the already existing ones.
The new identification criterion is used to analyse quiescent Intensive Observing Periods (IOPs), in which nocturnal stable boundary-layer conditions and local thermal circulation are not altered or driven by synoptic forcing.
During these IOPs, the formation of a LLJ due to inertial oscillations is typical few hours after the sunset.
However, the LLJ structure can be temporary perturbed generating a double-nose LLJ.
Two double-nose LLJ driving mechanisms are identified.
The wind-driven mechanism is when the two noses are associated with different air masses flowing one on top of the other.
The wave-driven mechanism is when a surface perturbation generates an inertial-gravity wave which transports momentum during its propagation.
Momentum is lost by the LLJ nose and transported upward where a second one is generated.
Furthermore, the evolution of the LLJs driven by the inertial oscillations is investigated by means of two models retrieved from the literature.
The models provides similar representation of the observed LLJs, concluding that the LLJs are well simulated when they are fully developed.
33
Vande, Hey Joshua D. "Design, implementation, and characterisation of a novel lidar ceilometer." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/11853.
Full textAbstract:
A novel lidar ceilometer prototype based on divided lens optics has been designed, built, characterised, and tested. The primary applications for this manufacturable ground-based sensor are the determination of cloud base height and the measurement of vertical visibility. First, the design, which was developed in order to achieve superior performance at a low cost, is described in detail, along with the process used to develop it. The primary design considerations of optical signal to noise ratio, range-dependent overlap of the transmitter and receiver channels, and manufacturability, were balanced to develop an instrument with good signal to noise ratio, fast turn-on of overlap for detection of close range returns, and a minimised number of optical components and simplicity of assembly for cost control purposes. Second, a novel imaging method for characterisation of transmitter-receiver overlap as a function of range is described and applied to the instrument. The method is validated by an alternative experimental method and a geometric calculation that is specific to the unique geometry of the instrument. These techniques allow the calibration of close range detection sensitivity in order to acquire information prior to full overlap. Finally, signal processing methods used to automate the detection process are described. A novel two-part cloud base detection algorithm has been developed which combines extinction-derived visibility thresholds in the inverted cloud return signal with feature detection on the raw signal. In addition, standard approaches for determination of visibility based on an iterative far boundary inversion method, and calibration of attenuated backscatter profile using returns from a fully-attenuating water cloud, have been applied to the prototype. The prototype design, characterisation, and signal processing have been shown to be appropriate for implementation into a commercial instrument. The work that has been carried out provides a platform upon which a wide range of further work can be built.
34
Yamashita, Cintia. "Foraminíferos bentônicos vivos na margem sudoeste do Atlântico Sul, Bacia de Campos: processos oceanográficos condicionantes." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/21/21136/tde-23032016-110128/.
Full textAbstract:
O presente estudo compreende a análise de distribuição dos foraminíferos bentônicos vivos no talude continental da Bacia de Campos e Platô de São Paulo (entre 400 e 3000 m de profundidade), buscando entender os processos condicionantes dessa distribuição. Dados sedimentológicos, geoquímicos e microfaunísticos permitiram identificar três grupos na área de estudo. O grupo I inclui amostras do talude superior, médio e inferior (400-1300 m de profundidade), e é caracterizado por valores maiores de densidade de foraminíferos bentônicos, carbono orgânico total, concentração de fitopigmentos, biomassa de bactérias, menores valores de sortable silt e de conteúdo de carbonato de cálcio, e pela presença de espécies como Globocassidulina subglobosa, Reophax scorpiurus, Reophax subfusiformis, Reophax spiculotestus e Epistominella exigua. O grupo II, constituído de amostras do talude inferior e Platô de São Paulo (1900-3000 m de profundidade), é caracterizado por menores densidades de foraminíferos bentônicos, carbono orgânico total, concentração de fitopigmentos, biomassa de bactérias, maiores valores de sortable silt e de conteúdo de carbonato de cálcio, e pela presença de espécies como Saccorhiza ramosa, Rhizammina algaeformis, Karrerulina sp2. e Hyperammina rugosa. O grupo III (1900-3000 m de profundidade) diferencia-se do grupo II pela presença da Glomospira gordialis, Pyrgoella irregularis e Reophax helenae. Constatou-se que os processos hidrossedimentares (p.e. ação da Corrente do Brasil e Corrente de Contorno Intermediária junto ao fundo), o fluxo vertical de matéria orgânica particulada e concentração de fitopigmentos no sedimento são fatores controladores das condições tróficas no ambiente e estão relacionados às feições de mesoescala (meandros e vórtices de Cabo Frio, Cabo de São Tomé e Vitória), determinando, assim, variações na microfauna de foraminíferos bentônicos vivos na Bacia de Campos.The present study comprises the analysis of the distribution of living benthic foraminifera on the continental slope of Campos Basin and Plateau of São Paulo (400-3000 m water depth) in order to understand the environmental processes determining this distribution. Sedimentological, geochemical and microfaunal data indicated the existence of three groups in the study area. Group I includes samples from the upper and middle slope (400-1300 m water depth) and is characterized by high values of benthic foraminifera density, total organic carbon, phytopigment concentration, biomass of bacteria, lower values of sortable silt and calcium carbonate content, and the presence of species such as Globocassidulina subglobosa, Reophax scorpiurus, Reophax subfusiformis, Reophax spiculotestus and Epistominella exigua. Group II, consisting of samples of the lower slope and Plateau of São Paulo (1900-3000 m water depth), is characterized by lower densities of benthic foraminifera, total organic carbon, phytopigment concentration, biomass of bacteria, higher values of sortable silt and calcium carbonate content, and the presence of species such as Saccorhiza ramosa, Rhizammina algaeformis, Karrerulina sp2. and Hyperammina rugosa. Group III (1900-3000 m water depth) differs from group II due to the presence of Glomospira gordialis, Pyrgoella irregularis and Reophax helenae. Hydro-sedimentary processes (e.g. action of the Brazil Current and Intermediate Western Boundary Current), the particulate organic matter flux and phytopigment concentration in the sediment are factors controlling the trophic conditions in the environment, and are related to features of mesoscale (meanders and Cabo Frio, Cabo de São Tomé and Vitória eddies), thereby determining changes in living benthic foraminifera in Campos Basin.
35
Boillot, Benjamin. "Contribution à l'étude des écoulements turbulents en convection mixte." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10062.
Full textAbstract:
Ce travail porte sur l'etude des ecoulements turbulents en convection mixte. La premiere partie de ce travail fut consacree a la comparaison des couches limites de convection forcee et de convection naturelle. Nous avons pu montrer que ces deux ecoulements etaient fort differents, meme en proximite de paroi, tant sur les profils de grandeurs moyennes et les grandeurs fluctuantes que sur les transferts energetiques. Dans un deuxieme temps, nous avons calcule un ecoulement de convection mixte dans un canal vertical avec une paroi chaude et une froide. Pour cela, nous avons developpe un code unidimensionnel qui permet de calculer les profils etabli de cet ecoulement. Pour modeliser la turbulence, nous avons utilise un modele k- bas reynolds developpe par nagano et al. (celui-ci ayant donne les meilleurs resultats en convection forcee). Les resultats obtenus confirment ceux experimentaux de nakajima et al. . On observe une augmentation de l'intensite de la turbulence du cote de la paroi froide et inversement du cote de la paroi chaude. La principale conclusion porte sur les lois de paroi generalement utilisee en ecoulements turbulents. Ces lois de paroi de convection forcee paraissent inadequates pour resoudre des ecoulements avec forces de volume. En consequence, une etude experimentale sur l'etude de la turbulence en convection mixte semble necessaire afin d'obtenir une base de donnees detaillee pour developper des nouveaux modeles
36
Fantin-Cruz, Ibraim. "Efeitos da formação e operação de um reservatório de pequena regularização na alteração da qualidade da água e do regime hidrológico na planície de inundação do Pantanal." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/62108.
Full textAbstract:
Sabe-se que a formação de reservatórios altera a qualidade e a quantidade da água de montante e jusante e que a direção e a magnitude das alterações dependem de suas características construtivas, operacionais, morfométricas, bem como do regime hidrológico e climático da região. Porém, a maior parte deste conhecimento foi fundamentada em pesquisas de reservatórios com grande capacidade de regularização, que fazem parte da realidade do Pantanal, uma região que vem sendo impactada por um número cada vez maior de reservatórios com pequena capacidade de regularização, levantando questionamentos sobre seus possíveis efeitos no funcionamento da planície de inundação. Sendo assim, este trabalho procurou (i) identificar qual o fator chave determinante no processo de estratificação e mistura vertical do reservatório e se este pode influenciar na qualidade da água; (ii) avaliar os efeitos da formação e operação do reservatório na alteração da qualidade da água de montante e jusante e (iii) avaliar os efeitos da operação do reservatório na alteração do regime hidrológico de jusante, além de propor os limites preventivos para a sustentabilidade. O estudo foi desenvolvido no reservatório de Ponte de Pedra, localizado no rio Correntes, divisa dos estados de Mato Grasso e Mato Grosso do Sul (Centro Oeste do Brail), na fronteira entre o Pantanal e o Planalto. O reservatório apresentou prolongado período de estratificação vertical (mistura no inverno) dos parâmetros físicos e químicos da água nas partes médias e profundas, mantendo-se homogêneo na parte superior, onde se encontra a captação, não alterando as características da água de jusante. Entre os fatores analisados, o vento foi o único fator que influenciou significativamente a estrutura vertical da qualidade da água sendo beneficiada pelas características morfométricas e construtivas do reservatório. Longitudinalmente, a formação do reservatório alterou significativamente quatro dos dez parâmetros analisados, com redução média de 38% da turbidez, 28% do fósforo total, 23% dos sólidos totais e 14% do nitrato. Destes, apenas a turbidez e o nitrato foram afetados pelo controle operacional do tempo de retenção hidráulica. Em relação à alteração dos parâmetros do regime hidrológico anual, dos 31 analisados, os parâmetros de vazões mínimas de curta duração (1, 3 e 7 dias), vazões máximas de 90 dias e o número de pulsos baixos e altos foram significativamente alterados pela operação do reservatório. Destes, a vazão máxima de 90 dias e o número de pulsos altos resumem os impactos, e podem ser utilizados como parâmetros alvos para restauração e conservação do regime hidrológico. As vazões sazonais também foram significativamente alteradas, com maior impacto na estação seca (inverno). Com base na variabilidade natural do rio, foram propostos os limites preventivos para a sustentabilidade, com alterações diárias permitidas de ±18% no inverno, ±24% na primavera e ±22% no verão e outono, aplicados sobre a vazão natural. De maneira geral, as alterações na qualidade da água e no regime hidrológico provocado pela formação e operação do reservatório foram consideradas baixas, tanto em número de parâmetros alterados quanto nas magnitudes das alterações, e estas foram atribuídas às baixas concentrações de partículas e nutrientes na bacia, ao sistema de captação superficial, o curto tempo de retenção hidráulica, pequena capacidade de regularização associadas à sazonalidade no regime de chuvas e ventos na região, que limitam manobras operacionais para a maximização da eficiência energética.The formation of reservoirs changes the quality and quantity of water, both upstream and downstream, and the direction and magnitude of such changes depend on their characteristics of construction, operation, morphometry, as well as hydrological regime and climate of the region. However, much of this knowledge was based on large reservoirs, which is not the reality of the Pantanal, an area that is being impacted by a growing number of reservoirs with low capacity for regularization, raising questions about possible effects on the floodplain functioning. In this way, this study aimed (i) to identify the key factor in the process of stratification and vertical mixing of the reservoir, and whether this can influence the water quality, (ii) to evaluate the effects of the reservoir formation and operation on the quality of water upstream and downstream of the reservoir, and (iii) to examine the effects of the reservoir operation on the downstream hydrological regime, in addition to propose preventive limits for sustainability. The study was conducted at Ponte de Pedra Reservoir, located on the Correntes river, the motto between the states of Mato Grasso and Mato Grosso do Sul (Central West Brazil), on the border between the Plateau and the Pantanal. The reservoir had an extended period of vertical stratification (mixture in the winter) of physical and chemical water parameters in the medium and deep parts of the water column, being homogeneous in the upper part where the water is capitation, without changing the characteristics of the downstream water. Among the factors analyzed, the wind was the only factor that significantly influenced the vertical structure of the water quality, favored by morphometric and constructive characteristics of the reservoir. Along the longitudinal axis, the reservoir formation significantly altered the turbidity and concentrations of total phosphorus, total solids, and nitrate, with mean reduction of 38, 28, 23 and 14% of their values. Among these, only turbidity and nitrate were affected by the operational control of the hydraulic retention time. In relation to the change in parameters of the annual hydrological regime, parameters of short-term minimum flows (1, 3 and 7 days), maximum flows of 90 days and the number of low and high pulses were significantly modified by the reservoir operation. Of these, the maximum flow of 90 days and the number of high pulses have summarized the impacts, and can be used as target parameters for restoration and conservation of the hydrological regime. Seasonal flows were also significantly altered, with the greatest impact in the dry season (winter). Based on the natural variability of the river, it was proposed preventive limits for sustainability, with permitted daily changes of ±18% in winter, ±24% in spring and ±22% in summer and autumn applied on the natural flow. In general, changes in water quality and hydrological regime caused by the reservoir formation and operation were considered low, both in number of altered parameters as magnitudes of such changes, and these characteristics were ascribed to low concentrations of particles and nutrients in the basin, to the surface capitation system, short hydraulic retention time, low capacity of regularization associated with the seasonality of the regime of rainfall and wind in the region, limiting operational maneuvers for maximizing the energy efficiency.
37
Salmond, Jennifer Ann. "Vertical mixing of ozone in the very stable nocturnal boundary layer." Thesis, 2001. http://hdl.handle.net/2429/13889.
Full textAbstract:
Significant increases in nocturnal ozone concentration have been observed near the
surface in regions of complex terrain. These temporally isolated features are characterised by a
sudden increase ('spike') in ozone concentrations superimposed upon spatially uniform
background concentrations of near zero. They typically occur during the summer months when
synoptic conditions support the development of the very stable nocturnal boundary layer (NBL).
Although localised, these 'spikes' in ozone concentration may have environmental and health
consequences and play a significant role in determining diurnal pollutant budgets.
During the summer of 1998 a field experiment was conducted in the Lower Fraser
Valley, British Columbia, to investigate the relationship between near surface ozone
concentrations and the structure of the NBL. This thesis examines the hypothesis that nocturnal
spikes in surface ozone concentration result from vertical mixing processes which temporarily
couple the residual layer to the surface layer, facilitating the transport of ozone stored aloft to the
surface. The study uses a comparatively new quantitative analytical tool - wavelet analysis - to
objectively isolate periods of intermittent turbulence observed in the near surface layers through
the field campaign. A new technique is developed to isolate the flux associated with only the
turbulent ('burst') component of each time series, and to provide revised estimates of scalar
fluxes.
Despite the dominance of ozone sinks in the surface layer, localised spikes in ozone
concentration were observed throughout the Lower Fraser Valley during the field campaign. At
the field site these were well correlated with periods of increased turbulence associated with the
presence or rapid break-down of the nocturnal low-level jet and the development of down-valley
winds. However, spikes in surface concentration were also shown to be sensitive to surface
nitrogen monoxide concentrations and ozone concentration aloft. Ozone concentrations were
highly variable throughout the residual layer, and the largest spikes in surface concentration
coincided with periods when ozone concentrations in excess of 80 ppb were observed aloft.
Whilst the results demonstrate that vertical mixing processes can play a significant role in
determining local surface concentrations, in regions of complex coastal terrain the role of
advection in the NBL cannot be ignored.
38
Yao, Zun-Ren, and 姚尊仁. "Boundary Adjustment, Texture Balance Weighting and Sustain Detection in Vertical Mashups Generation." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/25136481453776207431.
Full textAbstract:
碩士國立臺灣大學
資訊工程學研究所
103
This paper, focus on solving problems in lead track’s boundary and sustain in music mashup systems and proposed improvement method to mashup. On the boundary problem side, ”End Point” is considered to adjust boundaries to make sure switching between two lead tracks is smoothly. On the sustain problem side, we proposed ”Texture Balance Weighting” to find suitable match. On the mashup improvement side, three mashup applications are considered. By taking the respectly method, the improvement in user satisfation is statistically significant.
39
van, den Berg Herman. "Knowledge-based Vertical Integration: The Nature of Knowledge and Economic Firm Boundary Location." Thesis, 2008. http://hdl.handle.net/1807/11271.
Full textAbstract:
This research extends the knowledge-based view of the firm as it relates to organizational structure. In particular, this research provides evidence that fundamental classifications of knowledge are measurable, in relative terms, as factors of production. It then relates differences in relative quantities of these classifications of knowledge to the presence or absence of inter-firm boundaries. Finally, this study provides evidence that financial performance may be related to the alignment of organizational structure with knowledge-based factors of production.
This study contributes to strategic management theory by offering a potential solution to the difficulties of measuring knowledge as a factor of production. The research was motivated by the belief that it is the cost and value of knowledge that determines economic efficiency (Simon, 1999). By surveying professionals in the mutual fund industry for their relative reliance on three classifications of knowledge, this study suggests a set of measures of knowledge-based factors of production. These measures in turn support the testing of hypotheses related to the vertical integration (or de-integration) of adjacent stages of production.
Researchers have typically categorized organizational knowledge as either tacit or explicit. This research develops the concept of encapsulated knowledge as a fundamental classification of knowledge. Encapsulated knowledge is neither tacit nor explicit, because it is externalized and implicit. Progress in measuring knowledge is made by distinguishing between knowledge that resides in human minds (tacit), knowledge that is codified as information (codified), and knowledge that is embodied in the design and functionality of physical artefacts (encapsulated).
Relative reliance on the fundamentally different knowledge-based factors of production was found to vary between adjacent stages of production, despite the essential overlap of jointly held substantive knowledge. Portfolio managers are generally less (more) reliant on tacit (encapsulated) knowledge than other investment management professionals in the mutual fund complex. In addition, portfolio managers whose firms are de-integrated from the mutual fund management firms were found to be more (less) reliant on tacit (encapsulated) knowledge than their integrated counterparts. Finally, alignment between mutual fund structure and reliance on knowledge-based factors of production was found to affect performance of mutual funds.
40
Veitel, Hansjörg [Verfasser]. "Vertical profiles of NO2 and HONO in the boundary layer / presented by Hansjörg Veitel." 2002. http://d-nb.info/964946211/34.
Full text
41
HAN, WEN-SHAN, and 韓文山. "Natural convection in vertical annular enclosures with mixed boundary condition on the outer wall." Thesis, 1987. http://ndltd.ncl.edu.tw/handle/23058513231121763284.
Full text
42
Lee, Hung-Chi, and 李弘祺. "A Study of Capacity Design for Vertical Boundary Elements in Steel Plate Shear Walls." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/37214486348783069891.
Full textAbstract:
碩士國立臺灣大學
土木工程學研究所
99
Steel Plate Shear Walls (SPSWs) have been recognized as a high lateral stiffness and ductility system for building structures. However, this system is still not commonly adopted in practice. It may be due to the following two reasons: 1) The capacity design of the boundary elements must be checked by using strips model, which may be complicated and time-consuming. 2) The column plastic hinge must be formed only at the 1st story column bottom end according to the AISC provisions. Therefore the flexural requirement for the 1st story column may be very large. For the purpose of developing a convenient capacity design method for the 1st story columns in the SPSWs, the equivalent brace model is considered in formulating the design procedures. Allowing the plastic zone to form approximately at 1/4-high of the first-story column, this study purposes a minimum column flexural capacity design requirement to prevent both the flexural and shear plastic hinges form at the top of the 1st story column. In order to verify the accuracy the proposed capacity design method, and to investigate the cyclic performance of the SPSWs with or without the plastic forming at the top of the 1st story column, three full-scale 3.42-meter wide and 3.82-meter high two-story SPSW specimens were tested in National Center for Research on Earthquake Engineering. The low yield strength steel plates of 2.7mm and the same boundary beams, but with the boundary columns designed according to three different flexural requirements, were adopted for three specimens. Results of the ABAQUS analyses and the cyclic tests up to a roof drift of 0.045 radians confirm that the proposed capacity design method is suitable for seismic design of 1st story column to achieve good performance and economy. The 1st story column with plastic deformations spreading over mid-high of the column still possesses rather good load-carrying capacity. However, the specimen with plastic hinges forming at the mid-high and the top of the 1st story column have seriously lateral torsional buckling. In addition, test results show the tension field angle changes from boundary elements elastic to plastic. For the 1st story, due to large plastic deformation in the mid-high of boundary columns, the tension field angle inclines to approximately 40 degree. For the 2nd story, however, the plastic deformation concentrates at on boundary beams, so the tension field angle inclines near 45 degree.
43
Wu, Cheng-Te, and 吳政特. "Study on Boundary-Layer Heat Transfer of Bio-magnetic Fluid along a Vertical Surface." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/gzmaef.
Full textAbstract:
碩士國立虎尾科技大學
機械與機電工程研究所
100
In this paper we analyze the flow of bio-magnetic fluid along a vertical surface under the influence of a localized magnetic field, which is generated by an electric current going through a wire placed parallel to the plate. Numerical solutions are generated by the finite difference method to explore the influence of important parameters on the flow and heat transfer characteristics. The velocity and temperature profiles in the boundary layer for various values of magnetic induction are obtained. Also, the local friction coefficient and local Nusselt number are calculated. The influence of magnetic induction on the transport parameters are examined. Moreover, the impacts of change of the wire location on the flow and heat transfer are investigated. The results show that the velocity profiles are increased due to the influence of magnetic induction. When magnetic induction increases, the velocity profiles increase more apparently. The temperature profiles are decreased due to the influence of magnetic induction. When mangetic induction increases, the temperature profiles decrease more obiviosly. The local friction coefficient and local Nusselt number are affected by the magnetic induction in a similar way as that for the velocity profile. In addition, the change in the wire location has significant influence on the local friction coefficient, local Nusselt number, velocity and temperature profiles.
44
Jou, Eh-Down, and 周鄂東. "Dual Boundary Element Analysis of the Effect of Fixed Rigid, Vertical Thin Barriers on Waves." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/95326864518471905019.
Full text
45
"Effects of finitely-extensible polymers on heat transport in both horizontal and vertical boundary layer flows." 2014. http://repository.lib.cuhk.edu.hk/en/item/cuhk-1291638.
Full textAbstract:
Yu, Wilson = 有限伸展的聚合物對水平及垂直邊界層流中熱量傳輸的影響 / 余俊傑.Thesis M.Phil. Chinese University of Hong Kong 2014.
Includes bibliographical references (leaves 73-75).
Abstracts also in Chinese.
Title from PDF title page (viewed on 01, November, 2016).
Yu, Wilson = You xian shen zhan de ju he wu dui shui ping ji chui zhi bian jie ceng liu zhong re liang chuan shu de ying xiang / Yu Junjie.
46
XU, FANG-GUAN, and 許芳全. "The influence of inlet boundary conditions for two-dimensional laminar free convection between vertical parallel plates." Thesis, 1988. http://ndltd.ncl.edu.tw/handle/19670869512678638472.
Full text
47
Liao, Yu-Tseng, and 廖祐增. "Parametric Analyses for Vertical and Torsion Dynamic Responses of Circular Foundation and Semi-Infinite Structural Transmitting Boundary." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/89333758376065670529.
Full textAbstract:
碩士中華技術學院
土木防災工程研究所
96
The objective of this research is to identify the rigid disk foundation subjective to the vertical and twisting harmonic forces and to construct the nondimensional parametric relations of dynamic responses with SASSI 2007 software package. An infinite boundary element has been incorporated in the SASSI 2007 to enhance the capacity in simulating an infinite solid element and to reduce the computational effort. With the aid of the nondimensional parametric analysis, the limitations of material properties and size factors are completely removed. The ratios of reponses of the rigid disk foundation with the twisting harmonic forces are correlated to the functions of ratio between a nondimensional frequency and a nondimensional mass, accordingly. This can insight the correlations between the ratios of responses due to the twisting harmonic forces and nondimensional frequencies. The responses of the vertical harmonic loadings are achieved with Poisson’s ratios, nondimensional frequencies, and tributary masses in the vertical direction. Natural frequency proportionally increases with an increase of Poisson’s ratios. Verification is conducted with the rigid disk foundations either situating on the ground level or embedding in the ground, with the difference in the homogeneous or nonhomogeneous media, and with the far field responses in addition to the local dynamic responses. An agreement in responses of two approaches is achieved in comparison with Wass and SASSI 2007, the former using a 2D axisymmetric element and the latter adopting a 3D soil-structural element developing in SASSI 2007 recently. An infinite element incorporated in SASSI 2007 is implemented to simulate a pavement with a various soil log. To circumvent this infinite extension problem, a transmitted boundary is adopted to reduce the computational cost. A rigorous analysis with SASSI 2007 has further confirmed the accuracy of the validity of the transmitted boundary in the responses of the horizontal and the vertical directions.
48
Sharma, Deepan. "Steady Sedimentation of Particles in Long Vertical Tube and Effect of End Boundary Conditions on Convective Motion." Thesis, 2021. https://etd.iisc.ac.in/handle/2005/5637.
Full textAbstract:
Sedimentation – settling of particles in a fluid- is observed in nature like rain droplets and dust particles in the atmosphere, and in a variety of industrial processes, like to clarify liquid as well as separate particles of different size and density. The simplest system is the sedimentation of mono-disperse particles in a vast stationary fluid. The main parameters are Particle Reynolds Number (〖Re〗_p based on terminal velocity), ratio of particle density to fluid density (ρ_p/ρ_f ), particle volume fraction (φ), and container dimensions for experimental and numerical methods. Two main questions arise: what is the mean settling velocity (V_g), and nature and values of fluctuation in particle velocity (V^/), and how do they compare with the terminal velocity (V_t) of an isolated particle in an infinite fluid. At low particle Reynolds number, V_t is given by the Stokes law. Experiments have been typically performed in a tank containing the fluid with particles initially well mixed and tracking the motion of the particles or performing PIV to obtain mean settling velocity (V_g), fluctuating particle velocities (V^/) etc. The main focus of these studies has been to correlate different parameters like mean settling velocity, velocity fluctuation, correlation length with volume fraction, and dimension of the container. Though this apparently simple problem has been studied theoretically, experimentally, and numerically over many decades, there are several unanswered questions. For example, the experimental results for velocity fluctuations do not agree with the theoretical predictions. The origin of scalings for velocity fluctuations are unclear. In our study, we try to address some of these issues using a new type of experiment.
In our experiment, particles are fed at a constant rate at the top and allowed to settle in a long vertical tube containing quiescent fluid, closed at the bottom. The constant particle feed rate ensures mean steady particle settling in contrast to the standard experiments done previously where the settling process is transient. Also, the long vertical extent of the tube ensures Axial Homogeneity. We have done two types of experiments: water droplets (10 μm, 〖Re〗_p~〖10〗^(-3)) falling in the air, and spherical glass beads (110 μm, 〖Re〗_p~1 ) settling in water. The estimated volume fractions for the former is 〖10〗^(-7) and for the latter, it is〖 10〗^(-3). For the droplet-air system, the tube dimension is 5×5 〖cm〗^2 and for the particle-water system, three tube dimensions (4×4 〖cm〗^2 , 5×5 〖cm〗^2, 7×7 〖cm〗^2 ) have been used. Experiments have been done with different mass flux values. We have used high-speed imaging illuminated by a sheet of laser light to visualize the particle motion fields and Particle Image Velocimetry (PIV) to get the mean and fluctuating particle velocities and the spatial and temporal correlations. We have observed a variety of sedimentation-induced convective motions, including regions of particle patches moving upwards. The conditions at the tube end significantly alter the convective patterns and the fluctuating velocities. Convective motions, though hypothesized to exist, have not been observed in earlier experiments. We present results for the mean and fluctuating velocities and spatial and temporal correlations of the velocity fields for the range of mass fluxes and different tube dimensions. Besides the existence of convective motion, the main findings are: the mean settling velocity varies between 0.80-1.1 V_t. The fluctuating velocities are in the range 0.30-0.80 V_t and strongly depend on mass flux. Correlation lengths scale with tube width. We present these results in a non-dimensional form which suggest different scaling laws.
49
Liu, Mong-Lung, and 劉孟龍. "Liquid Motions in a Two-Dimensional Rectangular Tank Subjected to Forced Horizontal and Vertical Excitations by Boundary Element Methods." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/15750731365349126681.
Full textAbstract:
碩士國立臺灣大學
造船及海洋工程學研究所
90
This study emphasized on two-dimensional nonlinear liquid sloshing problems inside a rectangular tank that is subjected to horizontal and vertical forced oscillations. First of all, the liquid is assumed to satisfy the potential theory, and then the Boundary Element Method is applied to solve the potential and velocity distributions on the free surface. Next, the Taylor series expansion and the Lagrangian description are used to compute free-surface positions. Finally, some numerical examples are included in this study to demonstrate wave motions when the tank is subjected to horizontal or vertical excitations.
50
謝國發. "The Analysis of the Vertical Structure of the Boundary Layer and Determine its Effect on Ozone Concentration over Taichung Basin." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/43006722174788478053.
Full textAbstract:
碩士東海大學
環境科學系
87
Ozone concentrations were analyzed from the data collected by the nine air-quality monitoring stations in the central region of Taiwan during 1996-1998. It shows that ozone episodes (O3≧80 ppb) occured most often during Autumn with fewer in Spring. High ozone concentrations happened mostly during easterly winds which mainly happen under two conditions. It occurs when high pressure occupies mainland China and the East China Sea and when the tropical low pressure moves northwind and starts to influence the Taiwan region. To analyse the vertical structure of the boundary layer of various synoptic weather patterns and determine its effect on ozone concentration over Taichung Basin, two field campaigns had been performed at urban station (Chung-Hsing University ) and suburban station (Chieh-Lao elementary school), during Fall 1998 and Spring 1999, respectively. The vertical meteorological factor vitural potential temperature profiles and wind profiles were derived from tethersonde. The O3、NO、NO2、NOX and NMHC concentrations vertical profiles were collected at ground and height of 30、100、300、500 meters by black-covered Teflon sampling bag. These results showed that the atmospheric boundary layer was well mixed during daytime, and not during night time because of radiational inversion. During ozone episodes the mixed layer heights were low ( in the range 300-500 m) at 9 a.m. which favors the percursors of photochemical pollution such as Nitrogen Oxides and NMHC to accumulate and cause high ozone day. Measurements of pollutants showed that they well mixed at the higher portions of the mixed layer during the daytime. During nighttime, ozone concentration decreased near the ground and exponentially increased with altitude to a maximum near 500 m above ground level. The NO、NO2 and NMHC decreased with altitude, and are almost not detectable above 300 m.