Tesis sobre el tema "Vnf modeling"
Crea una cita precisa en los estilos APA, MLA, Chicago, Harvard y otros
Consulte los 41 mejores tesis para su investigación sobre el tema "Vnf modeling".
Junto a cada fuente en la lista de referencias hay un botón "Agregar a la bibliografía". Pulsa este botón, y generaremos automáticamente la referencia bibliográfica para la obra elegida en el estilo de cita que necesites: APA, MLA, Harvard, Vancouver, Chicago, etc.
También puede descargar el texto completo de la publicación académica en formato pdf y leer en línea su resumen siempre que esté disponible en los metadatos.
Explore tesis sobre una amplia variedad de disciplinas y organice su bibliografía correctamente.
Kline, Theodore S. "Broadband HF and VHF antenna design with terrain modeling". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA305429.
Texto completoThesis advisor(s): Rasler W. Smith, R.W. Adler. "December 1995." Includes bibliographical references. Also available online.
Overstreet, William Patton. "VHF bipolar transistor power amplifiers: measurement, modeling, and design". Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/71166.
Texto completoPh. D.
Najm, Riyadh K. "Wire-grid modelling of glass-mounted vehicular antennas at VHF". Thesis, University of Liverpool, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239950.
Texto completoMiller, Robert W. "Modeling methodology and data throughout analysis of a VHF land mobile radio network". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0002/MQ44853.pdf.
Texto completoZhang, Aibin. "CFD Modeling and Optimization of Primary sedimentation tank". Thesis, KTH, Vattendragsteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-217116.
Texto completoI detta projekt uppnåddes 2D modellering av avloppsflödesfältets karaktär hos en förenklade och rektangulär primära sedimenteringsbassäng, Syvab avloppsreningsverk, genom en transient-tvåfas-finita-volymmetoden med vatten och luft, som tillämpades med Volume-Of-Fluid (VOF) modellen. RNG k-ε turbulensmodellen användes även för att beräkna den kinetiska energin av turbulas och dess dissipationshastighet. Detta för att oönskade hydrauliska fenomen har uppmärksammats hos sedimenteringsbassängen hos avloppsreningsverket. För att minska flödeshastigheten och turbulens föreslås två optimeringsmetoder, vilket är att installera skärm och att ändra inloppets hastighet. Eeffekterna av de olika metoderna jämförs med hjälp av hastighets- och kinetisk energiprofiler. Det visar sig att båda metoderna kan ge gynsammare tillstånd för sedimentering av partikelar. Som avslutning ges prognos för den fortsatta forskningen och arbetsriktningen inom ämnet.
Thiele, Roman. "Modeling of Direct Contact Condensation With OpenFOAM". Thesis, KTH, Reaktorteknologi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-49825.
Texto completoAbtahi, Sayyed Mohammad. "Airborne Gravity Gradient, Magnetic and VLF datasets : Case studies of modelling, inversion and interpretation". Doctoral thesis, Uppsala universitet, Geofysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-300126.
Texto completoToninelli, Paolo. "Two-phase heat transfer in minichannels: modeling and heat pump applications". Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3425359.
Texto completoAttualmente vi è una crescente domanda di dispositivi compatti con prestazioni elevate in applicazioni di riscaldamento e raffreddamento; una geometria compatta consente di avere una carica ridotta di refrigerante rispetto agli scambiatori convenzionali. L'attività di ricerca è focalizzata sull'analisi del fenomeni di condensazione all'interno di un singolo minicanale e sull'applicazione della tecnologia a minicanali per condensatori ed evaporatori in sistemi di riscaldamento e raffreddamento. Quando il diametro interno diminuisce, nuovi parametri possono influenzare in modo significativo il trasferimento di calore in deflusso bifase. Oggigiorno potenti strumenti numerici permettono di ottenere un'analisi dettagliata dei meccanismi di trasferimento di calore in deflusso bifase all'interno di canali e di modellare l'interazione tra le fasi senza utilizzare alcuna legge empirica di chiusura. In questo modo è possibile avere un approccio puramente numerico che può essere applicato per diversi fluidi e diverse condizioni operative, risultando indipendente dalle correlazioni empiriche in letteratura. In particolare, il metodo VOF è stato utilizzato per studiare le caratteristiche principali dei fenomeni di condensazione all'interno di un singolo minicanale ed i risultati numerici sono stati poi convalidati con i dati sperimentali. Poiché le condizioni a bassa portata specifica sono le meno indagate a causa della elevata incertezza sperimentale quando il flusso termico è dell'ordine di pochi watt, simulazioni numeriche sono state effettuate allo scopo di ottenere una panoramica del processo di condensazione in tali condizioni operative, concentrando l'indagine sugli effetti della proprietà del fluido, la forma, le dimensioni e l'’inclinazione del canale. Le simulazioni VOF sono state poi estese allo studio delle instabilità all’interfaccia durante il processo di condensazione di R134a per un deflusso anulare-ondoso all'interno di un minicanale verticale con un diametro interno di 3.4 mm. I risultati numerici sull'evoluzione dell’interfaccia liquido-vapore nel tempo sono stati convalidati con visualizzazioni sperimentali e l'influenza delle onde sullo scambio termico è stata analizzata. Oltre all'analisi numerica del trasferimento di calore, l'applicazione della tecnologia a minicanali è stata anche investigata in sistemi di riscaldamento e raffreddamento. L'uso di minicanali negli scambiatori di calore permette di ridurre in modo significativo la carica di refrigerante rispetto ai tradizionali scambiatori di calore a batteria alettata. Questo è particolarmente utile in una pompa di calore reversibile quando lo stesso scambiatore di calore può funzionare come un condensatore o come evaporatore ed è particolarmente utile quando il refrigerante è infiammabile o mediamente infiammabile. Lo sviluppo di modelli fisici è necessario per la previsione delle prestazioni e per la progettazione di sistemi completamente innovativi. Procedure di calcolo sono state così implementate per valutare le prestazioni di una pompa di calore reversibile acqua-acqua e aria-acqua utilizzando i minicanali nel trasferimento di calore con l'aria, considerando sia l'aria che il terreno come possibili fonti di calore. Questo lavoro è stato possibile grazie al sostegno finanziario di Riello SpA .
Thunell, Rasmus. "Groundwater flow paths in fractured crystalline bedrock : Electromagnetic VLF measurements and modelling of a groundwater basin in Svanberga, Sweden". Thesis, KTH, Hållbar utveckling, miljövetenskap och teknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-231983.
Texto completoTestbädd dricksvatten är ett pågående projekt och testanläggning där tester och utveckling av filter och småskaliga tekniker för rening av dricksvatten samt kvalitetscertifiering för effektivitets och hållbarhetstester kommer utföras. Testanläggningen består av ett nedlagt grundvattenverk med tre tillhörande bergborrade brunnar i Svanberga utanför Norrtälje. Grundvattensystemet och flödesvägar för grundvattnet i området är relativt okända och bättre förståelse av hydrogeologin skulle kunna bidra till framtida arbete med att identifiera och bedöma risker för föroreningstransporter i området samt till grundvattenverkets brunnar. Detta examensarbete har genom beprövade metoder i form av sprick-kartering, geofysiska undersökningar (VLF) och grundvattenmodellering med COMSOL Multiphysics identifierat flera möjliga flödesvägar i berggrunden kopplade till grundvattenverket. Resultatet från studien visar att ett antal sprickzoner i öst-västlig riktning utgör en större risk för föroreningstransport av ämnen från trafik och jordbruk samt att en större del av det vatten som tillförs grundvattensystemet troligen har sitt ursprung från tjockare morän-lager i de norra delarna av området. Provpumpningar och verifiering av de identifierade sprick-zonerna genom spårämnestester och geofysiska undersökningar bör utföras för att stärka resultaten från detta arbete och möjligen utöka kunskapen om hydrogeologin i området kring Svanberga gamla grundvattenverk.
Jiang, Wenbiao. "Simulation du bullage dans un photobioréacteur". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLC086/document.
Texto completoThe working principle of a typical photobioreactor is to inject gas bubbles into the culture medium, providing CO2 to the cells and also stirring the liquid. Subsequently, the cells convert inorganic carbon into organic carbon through photosynthesis under illumination. Therefore, physical phenomena, e.g. bubbly flow, mass transfer, radiative transfer, and biological phenomena, e.g. photosynthesis, cell growth and death, coexist in a photobioreactor. More importantly, all the basic phenomena are not completely independent to each other. For example, bubble volume and bubble shape can influence gas-liquid mass transfer according to Young-Laplace equation and Henry's law. Moreover, some recent research revealed that bubble behaviors also directly affect the biological process. In view of the important impact of bubble behaviors on productivity of a phototbioreactor, the bubbly flow was investigated in this thesis by both experimental and numerical methods.In the experimental study, we first manufactured a new photobioreactor in order to study the bubbles and other phenomena. Subsequently, the bubbles were captured by high speed camera by virtue of a shadowgraphy technique and bubble behaviors were obtained by processing and analyzing the images. From the experimental results, we found that both averaged bubble volume and bubbling frequency increased with gas flow rate. Furthermore, we also discovered that the distribution of bubble volume was almost monodisperse at low flow rate, and it became more and more polydisperse with increasing flow rate. Regarding bubble shape evolution, we used two shape factors, viz. aspect ration and circularity, to quantitatively study it. We found that both shape factors dropped rapidly during bubble rising (within the limit of the field of view of our video camera), which implied that bubbles were flattened in the course of rising. Nonetheless, bubbles became more vertically elongated at higher flow rate, partially due to the more frequent bubble coalescence at higher flow rate.In the numerical study, we adopted VOF method and OpenFOAM, an open source CFD library, as our numerical tool to represent bubbly flow. First of all, the robustness of OpenFOAM in simulating two-phase flow was validated by literature survey. Subsequently, 2D simulations were carried out for seeking the appropriate and not very time-consuming numerical parameters, i.e. maximum Courant number and mesh size. We found that mesh size should somehow be smaller than the nozzle diameter to have meaningful results. On the other hand, maximum Courant number had no particular importance in the simulations (as long as between 0 and 1). Furthermore, 3D simulations were in good agreement with the experiments in terms of bubble volume and bubble shape evolution. However, 3D simulations were not able to represent the polydispersity of bubble volume due to the limited computing power. In addition, several hydrodynamic characteristics were also explored by the proposed numerical tool, which gave reasonable results.To conclude, bubble behaviors were successfully captured by experimental methods and represented by numerical methods in this thesis, which will help us go further in understanding the complicated physical-biological phenomena of a photobioreactor
SORIA, MIJAIL FEBRES. "THREE DIMENSIONAL MODELING OF A SINGLE UNIT SLUG IN A HORIZONTAL PIPELINE WITH THE VOF MODEL". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=15125@1.
Texto completoO constante crescimento na demanda de combustíveis fósseis e as últimas descobertas de petróleo no Brasil têm tornado a modelagem de escoamentos multifásicos em tubulações e equipamentos na indústria do Petróleo numa tarefa crucial. Dentro as configurações possíveis que o escoamento multifásico pode adotar, o regime das golfadas possui uma enorme relevância devido às suas características intermitentes e seus fortes gradientes de pressão produzidos nas tubulações por onde escoa. Neste trabalho, estuda-se numericamente, com o método de volumes finitos, o regime das golfadas, determinando-se o campo de velocidade e pressão, assim como a forma do nariz da bolha de Taylor e a velocidade de translação de uma unidade básica de golfada tridimensional em uma tubulação horizontal. Considerou-se o escoamento isotérmico, e utilizouse o referencial coincidente com a bolha de Taylor. Para modelar o escoamento turbulento utilizou-se o modelo K−E RNG. A interface foi determinada com o modelo VOF (Volume of Fluid). Os resultados das simulações foram comparados com dados experimentais disponíveis, apresentando uma boa concordância.
Pipeline and equipment multiphase flow modeling in oil industry has become a crucial task due to the constant increasing fossil fuel demand and latest oil discovers in Brazil. Among all possible flow configurations that multiphase flow can take, the slug flow regime plays an important role due to its intermittent characteristics and its strong pressure gradients in pipelines, where this flow regime can be found. In the present work, a numerical study of a slug flow is performed, with the finite volume method. The flow and pressure field are determined, as well as, the Taylor bubble nose shape and the translational velocity of a three dimensional single unit slug in a horizontal pipeline. The flow field was considered isothermal and it was employed a coordinate system coincident with the Taylor bubble. To model the turbulent flow, the RNG K−E model was selected. The interface was determined with the Volume of Fluid models (VOF). The results from the simulations were compared with available experimental data, presenting good agreement.
Guo, Dongzhi. "Design, Analysis, Modeling and Testing of a Micro-scale Refrigeration System". Research Showcase @ CMU, 2014. http://repository.cmu.edu/dissertations/450.
Texto completoTeng, Penghua. "CFD MODELLING OF TWO-PHASE FLOWS AT SPILLWAY AERATORS". Licentiate thesis, KTH, Vattendragsteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-202392.
Texto completoQC 20170224
Pabon, Sanclemente Miguel Alejandro. "A Comparative Study of the Structural Features and Kinetic Properties of the MoFe and VFe Proteins from Azotobacter Vinelandii". DigitalCommons@USU, 2009. https://digitalcommons.usu.edu/etd/233.
Texto completoAxelsson, Johan y Roger Knutsson. "Numerical modeling of a slotted flip bucket spillway system – The Shibuya Hydropower Project". Thesis, KTH, Vattendragsteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-96227.
Texto completoRamasetti, E. K. (Eshwar Kumar). "Modelling of open-eye formation and mixing phenomena in a gas-stirred ladle for different operating parameters". Doctoral thesis, Oulun yliopisto, 2019. http://urn.fi/urn:isbn:9789526223568.
Texto completoTiivistelmä Senkkametallurgiassa kaasuhuuhtelu ja kuonakerroksen käyttäytyminen ovat tärkeitä teräksen seostamisen ja homogenisoinnin näkökulmasta. Senkan pohjalla sijaitsevasta suuttimesta puhallettava kaasu hajoaa kupliksi, jotka rikkovat kuonakerroksen ja muodostavat avoimen silmäkkeen. Avoimen silmäkkeen koko on yhteydessä voimakkaampaan kuonan emulgoitumiseen, joka tehostaa metallisulan ja kuonan välisiä reaktioita. Tietoa avoimen silmäkkeen paikasta ja koosta tarvitaan myös tehokkaaseen seostuspraktiikkaan. Avoin silmäke vaikuttaa lisäksi prosessin energiataseeseen lisäten sen lämpöhäviöitä. Tässä tutkimuksessa tutkittiin kokeellisesti ja laskennallisesti erilaisten operointiparametrien vaikutusta avoimen silmäkkeen muodostumiseen vesimallissa ja terässenkassateollisessa senkassa. Kokeellisia mittauksia tehtiin kaasuhuuhtelun, kuonakerroksen paksuuden, ja suuttimien määrän vaikutuksen tutkimiseksi 1/5-mittakaavan vesimallissa ja 150 tonnin terässenkassa. Numeerisessa mallinnuksessa systeemin ja siihen lukeutuvan kuonakerroksen käyttäytymisen simuloimiseen käytettiin volume of fluid (VOF) –monifaasimenetelmää. Avoimen silmäkkeen kokoon ja sekoittumisaikaan liittyvien numeeristen simulointien havaittiin vastaavan hyvin vesimallista ja teollisista mittauksista saatua kokeellista aineistoa
Wallin, Adéle. "Structural intrusion, flow disturbance and spillway capacity : CFD modeling of the Torpshammar dam". Thesis, Uppsala universitet, Elektricitetslära, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-369319.
Texto completoMonaco, Marina. "Wave action on shallow water and applications to coastal hazard". Doctoral thesis, Universita degli studi di Salerno, 2010. http://hdl.handle.net/10556/127.
Texto completoThe mechanics of wave breaking in shallow water has been a major research field for many years, and a very large number of published results are available. No attempt is made here to review the whole literature. Some interesting – if somewhat outdated - descriptions of waves breaking on beaches are presented by Peregrine (1983), Battjes (1988) or Liberatore-Petti (1992). In fact, the most important process in the near coast zone of the shoreline motion is wave breaking. Some waves break in shallow water, some of them break at the water’s edge and in other circumstances waves do not break at all (with steep beach slopes, incident waves with low steepness - or long waves). In general, breaking in deep water is rarer than breaking in shallow water. The latter is triggered by the bottom and is more predictable, although the simple question ‘where breaking starts’ is far from having a unique answer, even in controlled physical experiments. The breaker types are, generally, classified as spilling (where the water spills down the front face), plunging (with a jet emanating from the front crest), surging (characterized by a rise in water surface before the breaking) and collapsing (between plunging and surging). The fluid dynamics of non-breaking waves can be described using potential theory in most of the flow field except near the bottom and near the free surface, where vorticity develops and is confined to a boundary layer. As long as the details near the free surface (e.g. necessary for wind–wave interaction) and/or near the bottom (e.g. necessary for sediment transport analysis) are not of interest, the potential theory approach is sufficient. After breaking, ‘waves’ and ‘eddies’, essentially a potential component and a rotational component of the flow field, are intimately mixed. The surf and swash zones are characterized by the complete transformation of the organized motion of the incident, sea-swell, waves into motions of different types and scales, including small-scale (less than a wave period) turbulence, and large-scale (much greater than the wave period) mean flows [Battjes, 1988]. It is obvious that [Stive and Wind, 1982; Lin and Liu, 1998a; Svendsen et al., 2000; Svendsen, 2005] contributions from terms which have traditionally been neglected in the traditional assumptions of hydrostatic pressure, depth uniform velocity profile, and negligible turbulence, are important and must be taken into full account in surf zone hydrodynamics. Non Linear Shallow Water equations (‘800) and Boussinesq models [Peregrine, 1967] have intrinsic limitations and can only simulate wave breaking and its evolution by assuming on semi-empirical ad hoc assumptions and threshold values to represent wave dissipation. Moreover, these models lack the capability to determine spatial distribution of the turbulent kinetic energy, which is of great importance for sediment transport studies [Lin and Liu, 1998b]. Given all this, it was only natural that the Navier-Stokes solvers now widely tested and developed in other fields of fluid mechanics, with less restricted assumptions involved, no wave theory assumed beforehand, and the capability to simulate complex turbulent processes, should soon become one of the main approaches to describe nearshore processes. Numerical modeling of three-dimensional breaking waves is extremely difficult. Several challenging tasks must be overcome. First of all, one must be able to track accurately the free surface location during the wave breaking process so that the near surface dynamics is captured. Secondly, one must properly model the physics of turbulence production, transport and dissipation throughout the entire wave breaking process. Thirdly, one needs to overcome the huge demand in computational resources. There have been some successful two-dimensional results. For instance, more recent is the treatment of the free surface within such an Eulerian framework with the marker and cell (MAC) method [e.g., Johnson et al.1994] and the volume of fluid method (VOF) [e.g., Ng and Kot 1992, Lin and Liu, 1998a]. The most common approach for simulating breaking waves is presently the application of 2D-Reynolds Averaged Navier-Stokes (RANS) equations with a Volume of Fluid (VOF) surface computation and a turbulence closure model. Such an approach, while being often tested for many years by many various Authors (see for instance Bovolin et al, 2004) only reached full maturity with a fundamental paper by Lin and Liu (1998a). This line of research has been going on successfully for many years to the point that reliable procedures now exist to simulate wave breaking, run up and interaction with structures. The next obvious step. i.e. the application of Large Eddy Simulation (LES) models has so far not been equally successful [Watanabe and Saeki, 1999; Christensen and Deigaard, 2001; Lubin et al, 2006; Christensen, 2006]. LES models necessarily require a fully three-dimensional solution and three-dimensional turbulence effects might be indeed important in the prediction of velocity within the surf zone, especially in the case of plunging breaker [Watanabe and Saeki, 1999]. Such models certainly are a promising tool in the study of surf zone hydrodynamics; however, the LES approach requires much finer grid resolution and a lager computational domain than the RANS approach, resulting in the very high demand on computational resource, at least for the time being. They are however a definite perspective for the future. Smoothed Particle Hydrodynamics (SPH) method, adapted from astrophysics into a number of fields, is a relatively new method for examining the propagation of highly nonlinear and breaking waves [Monaghan et al, 1977; Dalrymple et al, 2005; Viccione et al, 2007-2008]. SPH offers a variety of advantages for fluid modeling, particularly those with a free surface. The Lagrangian method is meshfree; the equivalents of mesh points are the fluid particles moving with the flow. The free surface requires no special approaches, such as the volume-of-fluid method or a Lagrangian surface tracking. Furthermore, the method can treat rotational flows with vorticity and turbulence. SPH is a technique based on computing the trajectories of particles of fluid, which interact according to the Navier–Stokes equations. Each of such particles carries scalar information, density, pressure, velocity components, etc. The work presented here is therefore mainly based on the application of the Eulerian 2-dimensional RANS/VOF equations to the study of surf zone processes on a beach. In particular the work is aimed at demonstrating the capability of RANS/VOF to improve the current modeling of surf zone hydrodynamics on sloping natural beach and in front of shallow water coastal structures , comparing its performance with laboratory observations and other theoretical and numerical results. [edited by author]
VIII n.s.
Da, Riva Enrico. "Two-phase Heat Transfer in Minichannel Heat Exchangers: Heat Pump Applications, Design, Modelling". Doctoral thesis, Università degli studi di Padova, 2009. http://hdl.handle.net/11577/3426130.
Texto completoLa riduzione della carica di refrigerante nelle applicazioni di condizionamento e riscaldamento è uno dei vincoli di progetto principali quando vengono utilizzati, per motivi di carattere ambientale, refrigeranti naturali come idrocarburi ed ammoniaca. Alcune applicazioni dei minicanali per la minimizzazione della carica nelle pompe di calore vengono presentate e discusse nella presente tesi. Viene presentato il progetto di un condensatore, un evaporatore ed uno scambiatore di calore rigenerativo innovativi. Questi componenti sono degli scambiatori di calore a fascio tubiero utilizzanti minicali del diametro di 2 mm e progettati per l’uso con propano. Delle procedure di calcolo basate su di correlazioni disponibili in letteratura ed un modello semplificato del processo di scambio termico sono state utilizzate per il progetto. Le prestazioni sperimentali degli scambiatori con R22 e propano vengono riportate e confrontate con le stime fornite dalle procedure di calcolo. Gli scambiatori di calore sono stati installati in una pompa di calore della capacità termica di 100 kW utilizzante propano come fluido frigorigeno. Nell’impianto della pompa di calore, destinata a test di laboratorio, sono stati installati anche un condensatore ed un evaporatore a piastre convenzionali. In questo modo è stato possibile confrontare diverse configurazioni al fine di quantificare in via sperimentale i vantaggi apportati dall’utilizzo degli scambiatori a minicanali, in termini sia di prestazioni energetiche, sia di carica di propano richiesta. In particolare, le prestazioni delle configurazioni utilizzanti il condensatore a minicanali vengono confrontate con quelle delle configurazioni utilizzanti lo scambiatore a piastre, e l’influenza sulle prestazioni energetiche dello scambiatore rigenerativo viene misurata e discussa. Vengono inoltre riportati dati sperimentali relativi all’efficienza con propano del compressore semiermetico installato nella pompa di calore. Oltre a correlazioni empiriche in grado di stimare le prestazioni termiche globali, il progetto e l’ottimizzazione di scambiatori di calore richiede una più approfondita conoscenza del deflusso e dello scambio termico all’interno di minicanali. Vengono presentate in questa tesi delle simulazioni di termofluidodinamica computazionale tramite l’innovativo metodo VOF (Volume Of Fluid) in grado di simulare direttamente deflussi multifase senza la necessità di utilizzare correlazioni empiriche per la modellazione dell’interazione tra le fasi. Al fine di validare l’efficacia di questo metodo nel calcolare il moto dell’interfaccia gas-liquido, il quale è un aspetto cruciale nello scambio termico bifase, sono state in un primo momento eseguite delle simulazioni del regime di deflusso ”churn flow” per una miscela aria-acqua nel caso di un tubo liscio verticale adiabatico, a differenti valori di diametro del tubo e di velocità superficiale delle due fasi. I risultati sono stati confrontati con visualizzazioni sperimentali ed un modello teorico semplificato del processo di levitazione delle onde è stato sviluppato ed utilizzato per commentare i risultati numerici. Le simulazioni con il metodo VOF sono state in un secondo momento estese allo studio della condensazione di R134a all’interno di un minicanale del diametro di 1 mm. Vengono riportati risultati computazionali relativi all’evoluzione dell’interfaccia vapore-liquido e dei coefficienti di scambio termico lungo il minicanale.
Fenni, Ines. "Efficient domain decomposition methods for electromagnetic modeling of scattering from forest environments". Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066264/document.
Texto completoA 3-D full-wave model, based on the integral representation of the electric field and dedicatedto the analysis of bi-static scattering mechanisms by a forest in the VHF and UHF bands wasefficiently enhanced. In order to overcome the limitation of a previous 3D model to small simulationsscenes and low frequencies, we have developed, during this research work, a new model using basis functionsadapted to the problem of interest, in the context of the Characteristic Basis Function Method(CBFM) and we investigated the suitability of this direct method for computing the electromagneticfields inside and outside three-dimensional dielectric objects representing the tree trunks and branches.The CBFM has shown great performances, when applied to the forest scattering modeling, both interms of CPU time and memory resources needed. Once properly set, the CBFM-E is so efficient thatit is able to treat in few minutes electromagnetic problems totally intractable with the classical MoM.Consequently, we have developed a powerful 3D forest electromagnetic scattering tool which allows ustoday to compute large forest electromagnetic problems in few minutes without worrying about theaccuracy of the solution. On the other hand, we have demonstrated the efficiency and accuracy of theCBFM-E when applied to 3D dielectric objects in the context of the electric volumetric integral equation,and have consolidated thus its leading position in the computational electromagnetics, especiallyagainst the iterative solvers based numerical methods
Sebastia-Saez, J. Daniel. "CFD modelling of post-combustion carbon capture with amine solutions in structured packing columns". Thesis, Cranfield University, 2016. http://dspace.lib.cranfield.ac.uk/handle/1826/10024.
Texto completoHa, Oai The. "Modeling and Numerical Investigation of Hot Gas Defrost on a Finned Tube Evaporator Using Computational Fluid Dynamics". DigitalCommons@CalPoly, 2010. https://digitalcommons.calpoly.edu/theses/400.
Texto completoShao, Zhiyu S. "TWO-DIMENSIONAL HYDRODYNAMIC MODELING OF TWO-PHASE FLOW FOR UNDERSTANDING GEYSER PHENOMENA IN URBAN STORMWATER SYSTEM". UKnowledge, 2013. http://uknowledge.uky.edu/ce_etds/5.
Texto completoBrochier, Felipe Osmar Berwanger. "Otimização de um condicionador de ar do tipo split com vazão variável de refrigerante". Universidade do Vale do Rio dos Sinos, 2014. http://www.repositorio.jesuita.org.br/handle/UNISINOS/4619.
Texto completoMade available in DSpace on 2015-07-23T01:11:46Z (GMT). No. of bitstreams: 1 FelipeBrochier.pdf: 2248315 bytes, checksum: 51a12fbb2e530bf08f1847557932b381 (MD5) Previous issue date: 2014-02
Nenhuma
Este trabalho tem como objetivo otimizar o custo operacional dependente dos parâmetros de vazão de ar do condensador, número de aletas e de circuitos do condensador, frequência do compressor e parâmetros do dispositivo de expansão de um sistema de um condicionador de ar do tipo split hiwall unitário com vazão variável de refrigerante (VRV). Para a otimização foram consideradas as freqüências de ocorrência de quatro condições de temperatura do ambiente externo na cidade de Porto Alegre. O condicionador de ar abordado neste trabalho troca calor utilizando um ciclo de compressão de vapor de simples estágio, tendo como fluido de trabalho o refrigerante R-410A. O sistema completo, composto de um compressor, um condensador, um evaporador e tubo capilar, foi modelado analiticamente utilizando o software EES (Engineering Equation Solver) e ajustado de acordo com testes realizados em calorímetro. Para a otimização, um algoritmo genético foi programado no próprio EES. Após a otimização do custo operacional em função dos parâmetros físicos de projeto, o COP aumentou em até 12 % na condição de ar externo a 35 °C. A otimização em função dos parâmetros de controle mostrou aumento ainda mais significativo do COP do sistema. Também é feita uma comparação entre os valores de COP de um sistema de vazão constante de ar e refrigerante e um sistema com vazão variável de ar e refrigerante.
This work aims to optimize the operational cost of an air conditioning system with variable refrigerant flow (VRF). The cost is dependent of the following parameters: condenser air flow, number of condenser fins and circuits, compressor frequency and the expansion device. The optimization considered the frequencies of occurrence of four distinct ambient temperatures in the city of Porto Alegre. The air conditioner presented in this work exchange heat using a single stage vapor compression cycle, with the refrigerant R-410A as the working fluid. The complete system comprises a compressor, a condenser, an evaporator and a capillary tube and was analytically modeled using the EES (Engineering Equation Solver) software. The parameters were fitted according to results obtained in a calorimeter and for optimization, a genetic algorithm was programmed using the same software. After the optimization of the operational cost as a function of the project parameters, the COP was raised up to 12% in external ambient air at 35 °C. The optimization of the operational cost as a function of the control parameters showed even a more significant system COP raise. A comparison between the COP of a constant air and refrigerant flow system and a variable air and refrigerant flow system was also performed.
Akel, Junior Alberto Fares. "Modelagem de propagação subionosférica de ondas de frequência muito baixa". Universidade Presbiteriana Mackenzie, 2015. http://tede.mackenzie.br/jspui/handle/tede/1529.
Texto completoFundação de Amparo a Pesquisa do Estado de São Paulo
We study the behavior of the Earth-ionosphere waveguide through the modeling of the propagation of very low frequency radio waves (VLF). We use the computational model LWPC (Long Wave Propagation Capability) to estimate changes in amplitude and phase of the VLF signals detected by the SAVNET network (South America VLF NETwork), and thus try to understand the behavior of the lower ionosphere under different ionization conditions. The research was divided into two parts. The first part investigates the behavior of the VLF signals in quiescent regimes of ionization. Amplitude and phase simulations for the were carried out, modifying adapting polynomials for the β and h parameters (or Wait s parameters) as a function of the zenithal angle. The second part of this research, uses these polynomials in the study of the lower ionosphere under transient ionization regimes in two distinct conditions: first during of solar flares and second during solar eclipse. For the simulations under solar flare conditions, we calculate the changes in β and ℎ′ parameters during the 25/03/2008 solar explosion. With these values, we calculate the electronic density profile through an exponential model and we find that the electronic density at 75 km is ∼ 104 cm−3, that is twenty times higher than during quiescent conditions. To evaluate our parameter estimates, we calculate the variation of the Wait s parameters for the case of twelve solar events of different classes. We note that the variations Δℎ′ found in this work are larger than that in Muraoka, Murata e Sato (1977) because they consider the variations in the conductivity gradient. For the solar eclipse simulations on 11/07/2011, we investigate its effect on the VLF phase. For this, we use the obscuration coefficient to estimate the guide height variation along the whole path during the eclipse. The simulations reproduce the phase behavior during the eclipse. However, a delay of about twenty four minutes was observed between the simulated and observed measurements. The observed delay is a direct consequence of own estimates of the perturbed ionospheric height and it causal relation with the obscuration during the eclipse. lower ionosphere, VLF, modeling, ionospheric disturbances, solar flares, solar eclipse.
Neste trabalho realizamos o estudo do comportamento do guia de ondas terra-ionosfera através da modelagem da propagação ondas de rádio de frequência muito baixa (VLF). Para isto, utilizamos o modelo computacional LWPC (Long Wave Propagation Capability) para estimar as variações de amplitude e fase de sinais de VLF detectados nos trajetos da rede SAVNET (South America VLF NETwork) e assim compreender o comportamento da baixa ionosfera em diferentes regimes de ionização. A pesquisa foi dividida em duas partes. A primeira parte, investigou o comportamento do sinal VLF em regimes quiescente de ionização, assim realizou-se simulações de amplitude e fase adaptando polinômios que definem os parâmetros β e ℎ′ (ou parâmetros de Wait) em função do ângulo zenital solar. Na segunda parte desta pesquisa, aplicou-se os polinômios no estudo da baixa ionosfera sob regimes transientes de ionização em duas condições distintas. A primeira para o caso de explosões solares e a segunda um para eclipse solar. Nas simulações relativas a explosões solares, calculamos as variações dos parâmetros β e ℎ′ durante o evento do dia 25/03/2008. Com esses valores, calculamos o perfil de densidade eletrônica, através de um modelo exponencial e observamos que a densidade eletrônica em 75 km é ∼ 104 cm−3, ou seja, vinte vezes maiores que antes da explosão. Para avaliar nossas estimativas, calculamos a variação dos parâmetros de Wait para doze eventos de diferentes classes. Observamos que as variações Δℎ′ neste trabalho são sempre maiores do que as descritas em Muraoka, Murata e Sato (1977), devido elas considerarem as variações no gradiente de condutividade. Nas simulações relativa ao eclipse solar do dia 11/07/2011, investigamos seu efeito na fase observada. Para esse estudo, utilizou-se o coeficiente de obscurecimento para realizar as simulações, desta forma foi possível estimar a variação da altura do guia ao longo de todo o trajeto durante o eclipse. As simulações reproduziram o comportamento da fase durante o eclipse. Entretanto, foi observado um atraso entre as medidas calculadas e observadas de aproximadamente ∼ vinte e quatro minutos. O atraso observado é diretamente decorrente da estimativa da altura de referência da ionosfera pertubada e de sua relação causal com o obscurecimento durante o eclipse.
Cuggia, Renaud. "MODÉLISATION D'ANTENNES TRÈS BASSES FRÉQUENCES (VLF/LF) : étude de l'influence de la structure, des composants associés et de l'environnement en vue de leur optimisation". Phd thesis, Université de Nice Sophia-Antipolis, 2010. http://tel.archives-ouvertes.fr/tel-00523630.
Texto completoGapillout, Damien. "Développement de bancs de tests dédiés à la modélisation comportementale d’amplificateurs de puissance RF et micro-ondes". Thesis, Limoges, 2017. http://www.theses.fr/2017LIMO0071/document.
Texto completoThe work presented in this manuscript is devoted to the study and development of a general characterization bench applied to the extraction of the TPM-NIM (Two-Path Memory Nonlinear Integral) amplifier behavioral model. This model, has one of the most advanced architectures at the XLIM laboratory. It requires a high-end microwave instrumentation, overpriced and beyond reach for most of the designers for its experimental implementation. The aim is to propose some original measurements principles allowing the TPM-NIM model’s identification with a standard instrumentation. Two benches are presented in these works : firstly, a characterization bench, developed using a high performance instrumentation with the best properties to extract the model. Then, a bench, built with a standard instrumentation but through innovative processing and measurement methods. These two benches have been used with several test vehicles and it appears that the second one decreases the noise of phase measurements while reducing the equipment’s total cost. Finally, a last part is dedicated to the comparison of the TPM-NIM model with two classic behavioral models by emphasizing its versatility
Khallahle, Jack Buckhill. "Numerical Simulation of Flow Parameters in Stratified Gas-Liquid Flow in a Horizontal Pipe". Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29931.
Texto completoPolitis, Konstantinos. "Développement de modèles numériques de tension superficielle pour la simulation d'écoulements avec interface à l'aide d'une formulation multi-fluides". Thesis, Ecole centrale de Nantes, 2016. http://www.theses.fr/2016ECDN0021.
Texto completoAir Lubrication methods are regarded by the scientific community as the next major technological breakthrough in Naval Engineering to achieve the reduction of drag in commercial vessels. The accurate modeling of the physical phenomena governing the drag reduction mechanisms of Air Lubrication methods, namely, the dynamics of surface tension, the instabilities of the air-water interfaces and air entrainment, are imperative for the design of air-lubricated hulls. To that end, we have implemented to ISIS-CFD several programming tools, interface reconstruction schemes and surface tension modeling. Two new surface tension methods were developed. Both use a global interface reconstruction scheme and are coupled with the compressive discretization volume fraction schemes for the unstructured finite volume formulation that the flow solver ISIS-CFD is based on. The results demonstrate that complicated dynamic interactions of either a single or multiple interfaces can be accurately captured. In the context of a future research study, the proposed approaches could lead to the further enhancement of the modeling capabilities of ISISCFD by introducing a macroscopic air entrainment model and eventually the assessment of different physical effects encountered in lubricated naval vessels using ISIS-CFD
Park, Jangho. "Efficient Global Optimization of Multidisciplinary System using Variable Fidelity Analysis and Dynamic Sampling Method". Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/91911.
Texto completoDoctor of Philosophy
In recent years, as the cost of aircraft design is growing rapidly, and aviation industry is interested in saving time and cost for the design, an accurate design result during the early design stages is particularly important to reduce overall life cycle cost. The purpose of the work to reducing the design cost at the early design stage with design accuracy as high as that of the detailed design. The method of an efficient global optimization (EGO) with variable-fidelity analysis and multidisciplinary design is proposed. Using the variable-fidelity analysis for the function evaluation, high fidelity function evaluations can be replaced by low-fidelity analyses of equivalent accuracy, which leads to considerable cost reduction. As the aircraft system has sub-disciplines coupled by multiple physics, including aerodynamics, structures, and thermodynamics, the accuracy of an individual discipline affects that of all others, and thus the design accuracy during in the early design states. Four distinctive design methods are developed and implemented into the standard Efficient Global Optimization (EGO) framework: 1) the variable-fidelity analysis based on error approximation and calibration of low-fidelity samples, 2) dynamic sampling criteria for both filtering and infilling samples, 3) a dynamic fidelity indicator (DFI) for the selection of analysis fidelity for infilled samples, and 4) Multi-response Kriging model with an iterative Maximum Likelihood estimation (iMLE). The methods are validated with analytic functions, and the improvement in cost efficiency through the overall design process is observed, while maintaining the design accuracy, by a comparison with existing design methods. For the practical applications, the methods are applied to the design optimization of airfoil and complete aircraft configuration, respectively. The design results are compared with those by existing methods, and it is found the method results design results of accuracies equivalent to or higher than high-fidelity analysis-alone design at cost reduced by orders of magnitude.
Annerstål, Viktor y Peter Ottosson. "Modellering och simulering av Multiantennsystem avsett för litet fartyg". Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-205347.
Texto completoInom militären finns stort behov av pålitlig kommunikation mellan fordon. Vid konstruktion av ett småfartyg i militärtoch bevakningssyfte är det viktigt att designa ett välfungerande antennsystem som inte försämras utav störningar, det ska även ses till att antennernas utsända effekt inte fastnar i småfartyget. Vi har fått en ritning av hur antennplaceringen är planerad, denna rapport går ut på att verifiera dess funktionalitet samt hitta en mjukvara som kan användas för att verifiera olika antennsystem. För att bedöma antennsystemet kommer denna rapport att undersöka att dess elektriska fält samt reflektionsoch EMC egenskaper, en uppgift som kan lösas med programvaran EMPro (Keysight). I programvaran skapas en 3Dstruktur som innehåller småfartyget, dess 3 stycken antenner samt omfattande havsvatten. Här tas hänsyn till objektens materialegenskaper, antennernas jordning samt de frekvenser antennerna arbetar på, 1.6-30MHz, 30-88MHz samt 100-512MHz. Simulering av systemet gav positiva resultat kring antennsystemets elektromagnetiskafält, antennerna kommer inte heller att störa varandra. Antennerna som vi har modellerat reflekterar orimligt mycket effekt, detta bortser vi från då vi inte haft tillgång till exakt avbildning av antennerna. EMPro är ett verktyg som är lämpligt att använda i detta samt liknande projekt. Dock krävs det att en kraftig dator finns tillgänglig då simuleringar av stora antennsystem baseras på stora uträkningar, som generellt tar lång tid.
Peña, Monferrer Carlos. "Computational fluid dynamics multiscale modelling of bubbly flow. A critical study and new developments on volume of fluid, discrete element and two-fluid methods". Doctoral thesis, Universitat Politècnica de València, 2017. http://hdl.handle.net/10251/90493.
Texto completoEl estudio y modelado de flujos bifásicos, incluso los más simples como el bubbly flow, sigue siendo un reto que conlleva aproximarse a los fenómenos físicos que lo rigen desde diferentes niveles de resolución espacial y temporal. El uso de códigos CFD (Computational Fluid Dynamics) como herramienta de modelado está muy extendida y resulta prometedora, pero hoy por hoy, no existe una única aproximación o técnica de resolución que permita predecir la dinámica de estos sistemas en los diferentes niveles de resolución, y que ofrezca suficiente precisión en sus resultados. La dificultad intrínseca de los fenómenos que allí ocurren, sobre todo los ligados a la interfase entre ambas fases, hace que los códigos de bajo o medio nivel de resolución, como pueden ser los códigos de sistema (RELAP, TRACE, etc.) o los basados en aproximaciones 3D TFM (Two-Fluid Model) tengan serios problemas para ofrecer resultados aceptables, a no ser que se trate de escenarios muy conocidos y se busquen resultados globales. En cambio, códigos basados en alto nivel de resolución, como los que utilizan VOF (Volume Of Fluid), requirieren de un esfuerzo computacional tan elevado que no pueden ser aplicados a sistemas complejos. En esta tesis, mediante el uso de la librería OpenFOAM se ha creado un marco de simulación de código abierto para analizar los escenarios desde niveles de resolución de microescala a macroescala, analizando las diferentes aproximaciones, así como la información que es necesaria aportar en cada una de ellas, para el estudio del régimen de bubbly flow. En la primera parte se estudia la dinámica de burbujas individuales a un alto nivel de resolución mediante el uso del método VOF (Volume Of Fluid). Esta técnica ha permitido obtener resultados precisos como la formación de la burbuja, velocidad terminal, camino recorrido, estela producida por la burbuja e inestabilidades que produce en su camino. Pero esta aproximación resulta inviable para entornos reales con la participación de más de unas pocas decenas de burbujas. Como alternativa, se propone el uso de técnicas CFD-DEM (Discrete Element Methods) en la que se representa a las burbujas como partículas discretas. En esta tesis se ha desarrollado un nuevo solver para bubbly flow en el que se han añadido un gran número de nuevos modelos, como los necesarios para contemplar los choques entre burbujas o con las paredes, la turbulencia, la velocidad vista por las burbujas, la distribución del intercambio de momento y masas con el fluido en las diferentes celdas por cada una de las burbujas o la expansión de la fase gaseosa entre otros. Pero también se han tenido que incluir nuevos algoritmos como el necesario para inyectar de forma adecuada la fase gaseosa en el sistema. Este nuevo solver ofrece resultados con un nivel de resolución superior a los desarrollados hasta la fecha. Siguiendo con la reducción del nivel de resolución, y por tanto los recursos computacionales necesarios, se efectúa el desarrollo de un solver tridimensional de TFM en el que se ha implementado el método QMOM (Quadrature Method Of Moments) para resolver la ecuación de balance poblacional. El solver se desarrolla con los mismos modelos de cierre que el CFD-DEM para analizar los efectos relacionados con la pérdida de información debido al promediado de las ecuaciones instantáneas de Navier-Stokes. El análisis de resultados de CFD-DEM permite determinar las discrepancias encontradas por considerar los valores promediados y el flujo homogéneo de los modelos clásicos de TFM. Por último, como aproximación de nivel de resolución más bajo, se investiga el uso uso de códigos de sistema, utilizando el código RELAP5/MOD3 para analizar el modelado del flujo en condiciones de bubbly flow. El código es modificado para reproducir correctamente el flujo bifásico en tuberías verticales, comparando el comportamiento de aproximaciones para el cálculo del término d
L'estudi i modelatge de fluxos bifàsics, fins i tot els més simples com bubbly flow, segueix sent un repte que comporta aproximar-se als fenòmens físics que ho regeixen des de diferents nivells de resolució espacial i temporal. L'ús de codis CFD (Computational Fluid Dynamics) com a eina de modelatge està molt estesa i resulta prometedora, però ara per ara, no existeix una única aproximació o tècnica de resolució que permeta predir la dinàmica d'aquests sistemes en els diferents nivells de resolució, i que oferisca suficient precisió en els seus resultats. Les dificultat intrínseques dels fenòmens que allí ocorren, sobre tots els lligats a la interfase entre les dues fases, fa que els codis de baix o mig nivell de resolució, com poden ser els codis de sistema (RELAP,TRACE, etc.) o els basats en aproximacions 3D TFM (Two-Fluid Model) tinguen seriosos problemes per a oferir resultats acceptables , llevat que es tracte d'escenaris molt coneguts i se persegueixen resultats globals. En canvi, codis basats en alt nivell de resolució, com els que utilitzen VOF (Volume Of Fluid), requereixen d'un esforç computacional tan elevat que no poden ser aplicats a sistemes complexos. En aquesta tesi, mitjançant l'ús de la llibreria OpenFOAM s'ha creat un marc de simulació de codi obert per a analitzar els escenaris des de nivells de resolució de microescala a macroescala, analitzant les diferents aproximacions, així com la informació que és necessària aportar en cadascuna d'elles, per a l'estudi del règim de bubbly flow. En la primera part s'estudia la dinàmica de bambolles individuals a un alt nivell de resolució mitjançant l'ús del mètode VOF. Aquesta tècnica ha permès obtenir resultats precisos com la formació de la bambolla, velocitat terminal, camí recorregut, estela produida per la bambolla i inestabilitats que produeix en el seu camí. Però aquesta aproximació resulta inviable per a entorns reals amb la participació de més d'unes poques desenes de bambolles. Com a alternativa en aqueix cas es proposa l'ús de tècniques CFD-DEM (Discrete Element Methods) en la qual es representa a les bambolles com a partícules discretes. En aquesta tesi s'ha desenvolupat un nou solver per a bubbly flow en el qual s'han afegit un gran nombre de nous models, com els necessaris per a contemplar els xocs entre bambolles o amb les parets, la turbulència, la velocitat vista per les bambolles, la distribució de l'intercanvi de moment i masses amb el fluid en les diferents cel·les per cadascuna de les bambolles o els models d'expansió de la fase gasosa entre uns altres. Però també s'ha hagut d'incloure nous algoritmes com el necessari per a injectar de forma adequada la fase gasosa en el sistema. Aquest nou solver ofereix resultats amb un nivell de resolució superior als desenvolupat fins la data. Seguint amb la reducció del nivell de resolució, i per tant els recursos computacionals necessaris, s'efectua el desenvolupament d'un solver tridimensional de TFM en el qual s'ha implementat el mètode QMOM (Quadrature Method Of Moments) per a resoldre l'equació de balanç poblacional. El solver es desenvolupa amb els mateixos models de tancament que el CFD-DEM per a analitzar els efectes relacionats amb la pèrdua d'informació a causa del promitjat de les equacions instantànies de Navier-Stokes. L'anàlisi de resultats de CFD-DEM permet determinar les discrepàncies ocasionades per considerar els valors promitjats i el flux homogeni dels models clàssics de TFM. Finalment, com a aproximació de nivell de resolució més baix, s'analitza l'ús de codis de sistema, utilitzant el codi RELAP5/MOD3 per a analitzar el modelatge del fluxos en règim de bubbly flow. El codi és modificat per a reproduir correctament les característiques del flux bifàsic en canonades verticals, comparant el comportament d'aproximacions per al càlcul del terme de drag basades en velocitat de drift flux model i de les basades en coe
Peña Monferrer, C. (2017). Computational fluid dynamics multiscale modelling of bubbly flow. A critical study and new developments on volume of fluid, discrete element and two-fluid methods [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90493
TESIS
Dimou, Konstantinos. "Améliorations de l'accès paquet en sens montant du WCDMA". Phd thesis, Télécom ParisTech, 2003. http://pastel.archives-ouvertes.fr/pastel-00000671.
Texto completoΨαχούλιας, Γεώργιος. "Ηλεκτρομαγνητική μοντελοποίηση στις VHF και UHF περιοχές συχνοτήτων". Thesis, 2008. http://nemertes.lis.upatras.gr/jspui/handle/10889/846.
Texto completoThe aim of this master thesis is the RF modeling during rainfall for the VHF and UHF ranges. In order to infer conclusions for the quality of the supplied services (cellular and satellite telephony, transmission of television signals) the received power and a series of parameters are defined.
Tsai, Wang-Lin y 蔡旺霖. "Plasma Diagnostics and Kinetic Modeling on VHF PECVD of Microcrystalline Silicon". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/67898814650625917215.
Texto completo中原大學
化學工程研究所
99
In this study, the plasma diagnostics tools (including actinometrics OES and QMS) were used to investigate the influences of operating parameters on intrinsic layer deposition process of μc-Si:H thin film solar cell in parallel-plate PECVD system with an excitation frequency of 40.68 MHz (VHF). The diagnostics results were correlated to deposition rate and crystalline fraction of deposited silicon films. A combination of experimental diagnostics and computational modeling was utilized to understand the main reaction mechanism in the plasma. The plasma diagnostic results show that when plasma power is increased, both the silane dissociation efficiency and deposition rate are increased. Meanwhile, it also benefits to film’s crystallinity. Higher silane flow rate leads to a slightly decreased in silane dissociation efficiency, however there are much more dissociated radicals contributed to film growth. When operating pressure is increased, both the silane dissociation efficiency and deposition rate are decreased. Since higher pressure corresponds to higher species collision frequency, the H atoms get higher probability to etch silicon surface, resulting in better film’s crystallinity. By comparing OES and QMS results, quantitative analysis of the main species in the plasma can be achieved. On the basis of theoretical deposition model, we have proposed a flux ratio of H atom to SiHx radical as a new indicator of crystallinity during film growth of μc-Si:H. Finally, a global model of SiH4/H2 plasma is developed. Both gas phase plasma chemistry and silicon film deposition process are included in the model. The model is found to capture the trend in experiment results on the effect of operating parameters on film deposition rate and active species concentrations in the plasma.
Metello, Daniela Filipa Figueiredo Marques. "Modeling, Simulation and Experimental Validation of PVDF-based Electroactive Actuators". Master's thesis, 2020. http://hdl.handle.net/10316/93993.
Texto completoNos últimos 20 anos, os polímeros electroactivos (EAPs) têm recebido mais atenção no mundo dos mecanismos de actuação. O termo "electroactivo" significa que o polímero é electricamente activo ou reactivo, ou seja, que terá uma resposta mecânica a um estímulo eléctrico. Como qualquer polímero, este é conhecido por ser leve e fácil de processar. Para além disso, os EAPs são resistentes e capazes de produzir grandes tensões de actuação, quando comparados com actuadores convencionais. Portanto, a sua importância está a aumentar em várias aplicações, nomeadamente biomédicas, tais como instrumentos médicos, implantes biónicos, próteses e "músculos artificiais". Os EAPs dividem-se em iónicos e electrónicos, sendo a principal diferença o transporte físico: os EAPs iónicos utilizam cargas iónicas, enquanto os EAPs electrónicos utilizam cargas eléctricas. O P(VDF-TrFE-CTFE) é um polímero "ferrorelaxor" pertencente aos EAPs electrónicos e é considerado um material promissor pela sua elevada constante dieléctrica (~50), bem como pela elevada resposta electromecânica e densidade de energia elástica.Neste trabalho, três actuadores (cinco camadas) foram caracterizados electromecanicamente para estudar a influência de dois parâmetros geométricos: a espessura da camada do P(VDF-TrFE-CTFE), e a largura total do actuador. A defleção, a força de bloqueio e a rigidez à flexão de cada actuador foram obtidas através de testes mecânicos sob três valores de campo eléctrico. Subsequentemente, foi executada uma análise por MEF em COMSOL Multiphysics®. Realizou-se um estudo estacionário de cada actuador para avaliar o comportamento electromecânico sob três valores de campo eléctrico. A defleção em cada simulação foi comparada com os testes experimentais.A partir dos resultados dos testes, concluiu-se que a largura não influencia o desempenho do actuador. Além disso, um aumento da espessura do P(VDF-TrFE-CTFE) provocou um aumento da defleção, força de bloqueio e rigidez de flexão. Mais ainda, a simulação foi validada, pois o comportamento observado revelou-se semelhante nos testes experimentais, ou seja, a defleção aumentava linearmente com o aumento do campo eléctrico aplicado.Finalmente, comparando os três actuadores com outras tecnologias electroactivas, é possível afirmar que as defleções observadas são mais elevadas, mas a força de bloqueio exercida por estes actuadores é significativamente inferior a outras tecnologias de actuação já estabelecidas.
In the last 20 years, electroactive polymers (EAPs) have gained attention in the world of actuation mechanisms. "Electroactive" means that the polymer is electrically active or responsive, i.e. that it will have a mechanical response to an electric stimulus. As any polymer, they are known for being lightweight and easy to process. Adding to this, EAPs are resilient and able to produce large actuation strains, when compared to conventional actuators. Therefore, their importance is increasing in several applications, namely biomedical applications such as surgery-assisting tools, bionic implants, prosthetics and "artificial muscles". EAPs are divided into ionic and electronic, with the major different being the physic transport: ionic EAPs use ionic charges, while electronic EAPs use electric charges. P(VDF-TrFE-CTFE) is a ferrorelaxor polymer that belongs to electronic EAPs and it is considered one of the most promising materials for its high dielectric constant (~50), as well as its high electromechanical response and elastic energy density.In this work, three cantilever-like multilayered actuators (five layers) were electromechanically characterized to study the influence of two geometry parameters: the thickness of the active layer, P(VDF-TrFE-CTFE), and the total width of the actuator. The tip displacement, blocking force and bending stiffness of each actuator were obtained through mechanical testing under three values of electric field. Subsequently, a FEM analysis was executed on COMSOL Multiphysics®. A stationary study was performed for each actuator, to evaluate the electromechanical behavior under the three values of electric field. The tip displacement in each simulation was also obtained and compared with the experimental tests.From the tests' results, it was concluded that the width of the actuator does not play a major influence in the performance of the actuator. Moreover, an increase in the thickness of the active layer translated in an increase of the tip displacement, blocking force and bending stiffness. On the other hand, the simulation was validated as the tip displacement increased linearly with the electric field, which was a behavior already observed in the experimental tests.Finally, comparing these three actuators with other electroactive technologies, it is possible to state the displacements observed are higher, but the blocking force exerted by these actuators is significantly lower than other existing actuation technologies.
"The geophysical very low frequency electromagnetic (VLF-EM) method: effects of topography and surface water investigated with simulations and field measurement". Thesis, 2015. http://hdl.handle.net/10388/ETD-2015-03-2020.
Texto completoTsai, I.-Long y 蔡逸龍. "Measurement and Modeling of TV-Band (VHF/UHF) Propagation in the middle region of Taiwan". Thesis, 1995. http://ndltd.ncl.edu.tw/handle/40094070068225775536.
Texto completo國立交通大學
電信研究所
83
In this report, field strength measurements of TV-Band (UHF/VHF) propagation in the middle region of Taiwan have been conducted. The measurement procedure follows FCC's regulations. Meanwhile, a theoretical model, based on geometric optics and knife-edge diffraction theory has been developed. By comparing the measured field strength with that precdicted by FCC's, CCIR's or the theorectical model, it shows that FCC and CCIR have better predicting accuracy in the VHF band and the theoretical model is more accurate in the UHF band.
Wang, Wei-Chao y 王威超. "A Study on the Analysis and Modeling of Maritime VHF Wave Propagation- Based on AIS Sea Trials in Coastal Waters of Taiwan". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/89366344995221730801.
Texto completo國立海洋大學
導航與通訊系碩士班
91
Automatic Identification System (AIS), which integrates the mobile communication and satellite positioning technologies, has great potential in contributing to navigation safety and maritime security. All vessels subject to the Safety of Life at Sea Convention(SOLAS)are required to be fitted with AIS within a very tight schedule. It is therefore of urgency needs of AIS researches to support the planning and implementations of shore-based AIS facilities and services. However, as compared with the situation on land, field measurements with sea trials are really costly, subject to weather/sea conditions and vessel motions, even restricted in route by the concern about navigation safety. Available database of the coastal land area such as the digital terrain model is also rather incomplete due to either the remoteness or confidential factors. This study focuses on making the most use of limited sea trial measurements and environmental database for the planning of AIS shore-based facilities. Matlab numerical methods and the Mapinfo geographical information system (GIS) are used for the simulation and analysis of AIS signal propagation in the maritime VHF band around 162MHz. Lee Model, which takes field measurement and terrain height data as important parameters, is adopted for the simulation. Research area mainly covers coastal waters of northern Taiwan and the Kaohsiung Harbor, where sea trials are performed by using an AIS base station and a class A AIS mobile station. Comparison between field measurements and simulations by linear regression analysis shows that the difference in path loss slope is about 1.3dB/dec, corresponding to a coverage range difference about 3.7km in the case of northern coastal waters. While the difference in path loss slope is only about 0.35dB/dec, corresponding to a coverage range difference about 0.2km in the case of Kaohsiung Harbor. Considering the fact that measurements were taken at a much worse sea state for the case of northern Taiwan than the case of Kaohsiung Harbor, the simulation fits well with the measurement, especially when in calm sea. Consequently, the mention presented should be applicable to large-scale predictions along the coast of Taiwan with reasonable results.
Tran, Nhi. "MONASH-VN: Development of a dynamic CGE model for the Vietnamese economy and analysis of structural changes during 1996-2003". Thesis, 2007. https://vuir.vu.edu.au/29422/.
Texto completoΓεωργόπουλος, Ιωάννης. "Ηλεκτρομαγνητική μοντελοποίηση στην VHF και UHF περιοχή ραδιοφάσματος για εφαρμογές στα σύγχρονα ασύρματα δίκτυα". Thesis, 2010. http://nemertes.lis.upatras.gr/jspui/handle/10889/4345.
Texto completoIn modern wireless communications, a wide range of RF models are used to provide the median (average) value of the signal strength at a given distance from the transmitter and for a given frequency spectrum. In this procedure, certain geographical (ground, humidity, terrain irregularities), topological (heavy or scattered population, type of obstacles, density of the buildings) characteristics of the area, as well as certain specifications of the transmitter and receiver antennas (most notably antenna height and antenna gain) have to be taken into consideration. In most cases, the mean value of the path loss is expressed in dB in dependence with the frequency of the operating system and the distance between the transmitter and the receiver (for given antenna characteristics and a certain type of environment where the system operates). Thus, a deterministic knowledge of the average path loss (which along with the average rain loss and diffraction loss provides the overall propagation loss in dB) is available. However, distance and frequency limitations have led research to a further study and expanding of the existing empirical and semi-empirical models , for both outdoor and indoor scenarios. A fundamental parameter-based study of the path loss models is based on the concept that the second power law that is predicted by the Friis equation does not apply in real-life scenarios except for standard LOS paths. The modified power law research allows engineers and scholars to calculate the mean received power of a signal transmitted over a wireless link in a more realistic approach. It has been suggested that the third-power law is more suitable for a plethora of applications based on wireless communications for an outdoor environment.The indoor propagation channel, in particular, demands a lot more than a deterministic formula of calculating the average signal strength as a function of distance and frequency. The increased impact of multipath and other propagation phenomena such as reflection and scattering, as well as the existence of many objects whose proportions are comparatively close to the wavelength of the operating wireless systems, render the propagation of a signal and its arrival at a receiver (mobile or fixed) a rather complex procedure. The precision of the path loss models depends heavily on their ability to demonstrate and reflect, in the calculations, these complex phenomena to the best possible way .The majority of these models have been developed and validated for mobile telephony systems in both outdoor and indoor schemes (GSM, PCS-1800, GPRS, UMTS). Certain extensions of many of these models were conducted in order to expand the frequency and distance limitation of the original formulas. New empirical models have also been suggested for these certain frequencies .Taking into account the very sensitive and subject to many different factors nature of the indoor propagation channel, it is easily concluded that both researchers in academia and engineers in industry need to have reliable models that will predict precisely the average path loss over the indoor 2.4 GHz channel which is of utter importance as the de facto frequency of Wi-Fi and WLAN systems. A gap in aforementioned research, however, is that it either concentrates on multipath parameters or does not feature a full comparative validation of most well-known indoor path loss models.The purpose of this work is to present, all the data collected through experiments in realistic conditions and real telecom systems, in order to validate and modify (where necessary) the existing RF models. Furthermore an empirical formula to measure attenuation due to shadowing is derived through these RF models.Measurements took part in five different topologies. In each of them the mean received power was recorded, for various distances between the transmitter and the receiver, in order for our endeavor to validate the RF models in question to be reliable. Through this procedure, RF models where examined towards each topology’s distinctive characteristics that reflect in quality and quantity all the attenuation mechanisms that affect the propagated signal.