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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
61

Aproximace prostorově distribuovaných hierarchicky strukturovaných dat / Approximation of spatially-distributed hierarchically organized data

Smejkalová, Veronika January 2018 (has links)
The forecast of the waste production is an important information for planning in waste management. The historical data often consists of short time series, therefore traditional prognostic approaches fail. The mathematical model for forecasting of future waste production based on spatially distributed data with hierarchically structure is suggested in this thesis. The approach is based on principles of regression analysis with final balance to ensure the compliance of aggregated data values. The selection of the regression function is a part of mathematical model for high-quality description of data trend. In addition, outlier values are cleared, which occur abundantly in the database. The emphasis is on decomposition of extensive model into subtasks, which lead to a simpler implementation. The output of this thesis is tool tested within case study on municipal waste production data in the Czech Republic.
62

Návrh konstrukce rychlého elektromagnetického ventilu semiaktivního tlumiče / The design of fast electromagnetic valve for semiactive damper

Žižlavský, Vít January 2021 (has links)
This diploma thesis’s focuses on the mechanical design of fast solenoid throttle valve for DCC semiactive damper. Current DCC dampers work with a time response of over 10 ms, which is not suitable for fast semiactive control of vehicle chassis. The time response needs to be shortened, to improve quality of regulation. The required time response is archived by new fast electromagnetic actuator for original CES valve. The actuator has been accelerated by reducing induction of eddy currents and by reducing weight of moving parts. New valve helped to reduce the time response of damper by 28 % to 8,1 ms. The results proved, that the time response is affected more by speed of the servo effect, which is closing main orifice, than by electromagnetic actuator. There is no more potential in accelerating CES valve by actuator.
63

Analýza signálů akustické a elektromagnetické emise / Analysis of acoustic and electromagnetic emission signals

Boudný, Petr January 2009 (has links)
Master´s thesis is focused to analyse the acoustic and electomagnetic emission signals. These signals generate external power applied on the material. This power put there plastic deformation and create cracks. Spectral analyse show that signals are non-stationary. Wavelet transformation was used to spectral analyse which informate about time-frequence vaules of the signal.
64

Dočasné zesilování silničních mostů / Temporary strengthening of road bridges

Suza, Dominik January 2018 (has links)
Bridge strengthening is frequently associated with costly, long-term reconstruction. In some cases the bridge load capacity is sufficient for standard traffic, but requirements for an extremely heavy vehicle can exceed the maximal bridge load capacity. These vehicles normally weigh hundreds of tons. Moreover, well-known bridge strengthening technologies are not efficient and economical for this special load case. This doctoral thesis presents a short-term bridge strengthening method using a temporary support structure for the assistance of the existing bridge carrying structure. Although this strengthening method is rather old, it is rarely known. Approaches from 1980, are still often used, rely on simplified principles and approximation models. This approximation causes restricted efficiency of the strengthening system and creates a mathematical model that is not necessarily safe. The introduced new short-term bridge strengthening theory is based on monitoring of real bridge structures and temporary support structures during the crossing of extremely heavy vehicles. A mathematical model, which represents behaviour of real structures suitable, is introduced. The major effects, which have the greatest influence on this strengthening method are discussed. Further more a safety hydraulic element invented at Brno University of Technology, which can be used with the strengthening system is shown. The application of this system ensures required boundary conditions and therefore it guarantees the proper usage of the strengthening system.
65

Diagnóstico de fallos electromecánicos en motores eléctricos mediante el análisis avanzado del flujo magnético y su implementación en hardware

Zamudio Ramírez, Israel 10 October 2023 (has links)
[ES] Los motores eléctricos son máquinas eléctricas rotatorias que permiten realizar la conversión de energía eléctrica en energía mecánica, misma que resulta de gran utilidad en diversos procesos industriales, principalmente para accionar mecanismos y cadenas cinemáticas complejas que ejecutan alguna tarea en específico. Dentro de los distintos tipos de motores eléctricos, las máquinas de inducción se han utilizado ampliamente en una gran variedad de procesos industriales. Esto se debe principalmente a sus excelentes características y prestaciones, como lo son: robustez, fácil control, simplicidad, confiabilidad, y fácil mantenimiento. Sin embargo, a pesar de su elevada robustez, este tipo de máquinas se encuentran sujetas a esfuerzos mecánicos, térmicos, eléctricos y ambientales bajo diversas condiciones de operación durante su vida útil, lo que de forma inevitable conduce a fallos. Los principales fallos que suelen presentarse en los motores eléctricos de inducción son aquellos relacionados a sus componentes internos como lo son barras de rotor rotas, desgaste en las pistas exterior e interior en los rodamientos, desgaste en la jaula del rodamiento, fallas en el estator (por ejemplo, cortocircuito entre espiras adyacentes), entre otros. Cuando un motor eléctrico se encuentra operando bajo alguna condición de falla su rendimiento puede verse afectado, lo que se traduce en consumos de energía más elevados, causando a su vez costos extras al momento de facturar. En este trabajo de investigación se presenta el desarrollo de una metodología innovadora, capaz de generar un diagnóstico adecuado y de forma automática de la ocurrencia de las fallas más comunes que pueden desarrollarse en los motores eléctricos de inducción bajo diversas condiciones de operación mediante el análisis del flujo magnético de dispersión (que puede ser capturado en la periferia del marco del motor) empleando herramientas de descomposición en tiempo-frecuencia, herramientas de clasificación de datos y parámetros de caracterización de señales. Así entonces, se prueba la validez de técnicas basadas en el análisis del flujo magnético de dispersión para el diagnóstico de distintas fallas electromecánicas en motores de inducción. Los resultados demuestran el excelente desempeño de la metodología de diagnóstico automático propuesta, al ser evaluada en una gran variedad de motores con diversas características constructivas. / [CA] Els motors elèctrics són màquines elèctriques rotatòries que permeten realitzar la conversió d'energia elèctrica en energia mecànica, la qual cosa resulta de gran utilitat en diversos processos industrials, principalment per a accionar mecanismes i cadenes cinemàtiques complexes que executen alguna tasca en específic. Dins dels diferents tipus de motors elèctrics, les màquines d'inducció s'han utilitzat àmpliament en una gran varietat de processos industrials. Això es deu principalment a les seues excel·lents característiques i prestacions, com ara robustesa, fàcil control, simplicitat, fiabilitat i fàcil manteniment. No obstant això, malgrat la seua elevada robustesa, aquest tipus de màquines estan sotmeses a esforços mecànics, tèrmics, elèctrics i ambientals en diverses condicions d'operació durant la seua vida útil, la qual cosa inevitablement condueix a fallades. Les principals fallades que solen presentar-se en els motors elèctrics d'inducció són aquelles relacionades amb els seus components interns, com ara barres de rotor trencades, desgast en les pistes exterior i interior dels rodaments, desgast en la gàbia del rodaments, fallades en l'estator (per exemple, curtcircuit entre espires adjacents), entre altres. Quan un motor elèctric està funcionant sota alguna condició de fallada, el seu rendiment pot veure's afectat, la qual cosa es tradueix en consums d'energia més elevats, causant al seu torn costos addicionals en el moment de facturar. En aquest treball d'investigació es presenta el desenvolupament d'una metodologia innovadora, capaç de generar un diagnòstic adequat i de forma automàtica de l'ocurrència de les fallades més comunes que poden desenvolupar-se en els motors elèctrics d'inducció sota diverses condicions d'operació mitjançant l'anàlisi del flux magnètic de dispersió (que pot ser capturat en la perifèria del marc del motor) emprant eines de descomposició en temps-freqüència, eines de classificació de dades i paràmetres de caracterització de senyals. Així doncs, es prova la validesa de tècniques basades en l'anàlisi del flux magnètic de dispersió per al diagnòstic de diferents fallades electromecàniques en motors d'inducció. Els resultats demostren l'excellent rendiment de la metodologia de diagnòstic automàtic proposada, en ser avaluada en una gran varietat de motors amb diverses característiques constructives. / [EN] Electric motors are rotating electrical machines that allow the conversion of electrical energy into mechanical energy, which is very useful in various industrial processes, mainly to drive mechanisms and complex kinematic chains that perform a specific task. Within the different types of electric motors, induction machines have been widely used in a wide variety of industrial processes. This is mainly due to its excellent features and benefits, such as robustness, easy control, simplicity, reliability, and easy maintenance. However, despite its high robustness, this type of machine is subject to mechanical, thermal, electrical, and environmental stress under various operating conditions during its useful life, which inevitably leads to failures. The main failures that usually occur in electric induction motors are those related to their internal components, such as broken rotor bars, wear on the outer and inner races of the bearings, wear on the bearing cage, stator failures ( for example, short circuit between adjacent turns), among others. When an electric motor is operating under some fault condition, its performance may be affected, which translates into higher energy consumption, causing extra costs at the time of billing. This research thesis presents the development of an innovative methodology capable of automatically generating an adequate diagnosis of the occurrence of the most common failures that can develop in electric induction motors under various operating conditions through the analysis of the stray magnetic flux (which can be captured at the periphery of the motor frame). This is performed by using time-frequency decomposition tools, data classification tools, and signal characterization parameters. Thus, the validity of techniques based on the analysis of the stray magnetic flux for the diagnosis of different electromechanical failures in induction motors is tested. The results demonstrate the excellent performance of the proposed automatic diagnosis methodology when evaluated in a wide variety of engines with different construction characteristics. / Zamudio Ramírez, I. (2023). Diagnóstico de fallos electromecánicos en motores eléctricos mediante el análisis avanzado del flujo magnético y su implementación en hardware [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/197989
66

Variabilidade de alta frequência temporal da clorofila-a e sua relação com o campo de ventos e marés no canal de São Sebastião/SP / High-frequency temporal variability of chlorophyll-a and its relationship to the wind fields and tides at the São Sebastião Channel/SP

Bellini, Camilla Bonatto 30 September 2016 (has links)
Em ambientes costeiros, a variabilidade da biomassa de fitoplâncton é dirigida por forçantes físicas locais que apresentam distintas escalas temporais em ocorrência, intensidade e durabilidade. No canal de São Sebastião, ambiente advectivo, parte-se do pressuposto de que qualquer adição da biomassa de fitoplâncton não se deve ao crescimento local, mas ao transporte de células fitoplanctônicas movidas pelas correntes guiadas a ventos e marés. Dessa maneira, o objetivo central deste trabalho é analisar a variabilidade em alta frequência das variações da biomassa fitoplanctônica e investigar suas relações temporais com a intensidade e direção dos ventos e a amplitude das marés. Em média, o acúmulo de clorofila é estável no tempo, com curtos episódios de lento aumento e diminuições bruscas da biomassa fitoplanctônica, sendo os valores encontrados relativamente baixos, característicos de ambientes oligomesotróficos. Análises espectrais da série temporal da concentração de clorofila-a e da altura da maré revelaram alta correlação entre as duas séries durante as marés de sizígia, com periodicidades de aproximadamente 12 e 24 horas. Em relação à direção e intensidade do vento, o espectro cruzado de ondaletas apresentou áreas de forte correlação com a clorofila-a e periodicidades dominantes de três dias. Além disso, observou-se que ventos vindos do quadrante norte/nordeste carregam águas com maiores concentrações de materiais particulados ou detritos. / In coastal environments, the dynamics of phytoplankton biomass is driven by local physical forcings that have different time scales in occurrence, intensity and durability. For being an advective environment, it is normally assumed that any positive change in phytoplankton biomass in the São Sebastião Channel is not due to local growth, but to the transport of phytoplankton cells moved by currents associated with winds and tides. Thus, the main objective of this project is to analyze the variability in high-frequency variations of the phytoplankton biomass and investigate their temporal relationships with intensity and direction of winds and high tides. On average, the chlorophyll accumulation is stable over time, with short episodes of slow rise and sudden decreases of phytoplankton biomass and relatively low values, characteristic of oligo-mesotrophic environments. Spectral analysis of the time series of chlorophyll a concentration and tide height showed a high correlation between the two series during the spring tides, and dominant periodicities of about 12 to 24 hours. Regarding direction and intensity of the wind, the cross wavelet spectrum presented strong correlation areas with chlorophyll a and dominant periodicities of 3 days. In addition, it was observed that winds from the north/northeast quadrant carry water with higher concentrations of particulate matter or debris.
67

Variabilidade de alta frequência temporal da clorofila-a e sua relação com o campo de ventos e marés no canal de São Sebastião/SP / High-frequency temporal variability of chlorophyll-a and its relationship to the wind fields and tides at the São Sebastião Channel/SP

Camilla Bonatto Bellini 30 September 2016 (has links)
Em ambientes costeiros, a variabilidade da biomassa de fitoplâncton é dirigida por forçantes físicas locais que apresentam distintas escalas temporais em ocorrência, intensidade e durabilidade. No canal de São Sebastião, ambiente advectivo, parte-se do pressuposto de que qualquer adição da biomassa de fitoplâncton não se deve ao crescimento local, mas ao transporte de células fitoplanctônicas movidas pelas correntes guiadas a ventos e marés. Dessa maneira, o objetivo central deste trabalho é analisar a variabilidade em alta frequência das variações da biomassa fitoplanctônica e investigar suas relações temporais com a intensidade e direção dos ventos e a amplitude das marés. Em média, o acúmulo de clorofila é estável no tempo, com curtos episódios de lento aumento e diminuições bruscas da biomassa fitoplanctônica, sendo os valores encontrados relativamente baixos, característicos de ambientes oligomesotróficos. Análises espectrais da série temporal da concentração de clorofila-a e da altura da maré revelaram alta correlação entre as duas séries durante as marés de sizígia, com periodicidades de aproximadamente 12 e 24 horas. Em relação à direção e intensidade do vento, o espectro cruzado de ondaletas apresentou áreas de forte correlação com a clorofila-a e periodicidades dominantes de três dias. Além disso, observou-se que ventos vindos do quadrante norte/nordeste carregam águas com maiores concentrações de materiais particulados ou detritos. / In coastal environments, the dynamics of phytoplankton biomass is driven by local physical forcings that have different time scales in occurrence, intensity and durability. For being an advective environment, it is normally assumed that any positive change in phytoplankton biomass in the São Sebastião Channel is not due to local growth, but to the transport of phytoplankton cells moved by currents associated with winds and tides. Thus, the main objective of this project is to analyze the variability in high-frequency variations of the phytoplankton biomass and investigate their temporal relationships with intensity and direction of winds and high tides. On average, the chlorophyll accumulation is stable over time, with short episodes of slow rise and sudden decreases of phytoplankton biomass and relatively low values, characteristic of oligo-mesotrophic environments. Spectral analysis of the time series of chlorophyll a concentration and tide height showed a high correlation between the two series during the spring tides, and dominant periodicities of about 12 to 24 hours. Regarding direction and intensity of the wind, the cross wavelet spectrum presented strong correlation areas with chlorophyll a and dominant periodicities of 3 days. In addition, it was observed that winds from the north/northeast quadrant carry water with higher concentrations of particulate matter or debris.
68

Elektrotechninių įrenginių elektrodinaminių bandymų metodikos ir priemonių tyrimas / The investigation of elektrotechnical equipment‘s electrodynamics tests methodology and devices

Macevičius, Rimvydas 29 September 2008 (has links)
Įmonėje UAB ELGA nuolatos tobulina vidutinės įtampos skirstymo ir valdymo elektros įrenginių konstrukciją, todėl iškyla poreikis atlikti trumpo jungimo srovės bandymus naujai sukomplektuotai įrangai. Magistriniame darbe analizuojama įmonėje surenkamų vidutinės įtampos uždarųjų skirstyklų skirstymo ir valdymo elektros įrenginių USN-10, USN-20, naudojamų 6 ÷ 10, 24 kV įtampos, 50 Hz dažnio elektros energijos paskirstymui, prijungtų linijų apsaugai nuo perkrovimų ir trumpų jungimų atsparumo trumpojo jungimo srovėms tyrimo laboratorija. Narveliuose, ant ištraukiamojo elemento (vežimėlio) instaliuoti įvairių firmų pvz.: „ABB“; „SIEMENS“; „VEI“ ir t.t. vakuuminiai jungtuvai. Darbe pateikiami normatyviniai dokumentai, kuriais remiantis atliekami bandymai, bandymo laboratoriją sudarančių elementų varžų, terminio bei dinaminio atsparumo skaičiavimai, bandymo schemos, bei bandymų sąlygos. / Stock company „ELGA“ is constantly developing an air insulated medium voltage semi-metalclad type switchgear systems construction, so it happens that we need to do short – time and withstand current tests for new complemented equipment. The Master thesis analyses short – time and withstand current tests laboratory for in company prefab medium voltage semi-metalclad type switchgear systems USN-10, USN-20 designed to be used for 6 ÷ 10, 24 kV voltage, and 50Hz frequency power distribution, connected feeder with over current and overload protection. Various companies' circuit breakers for example „ABB“; „SIEMENS“; „VEI“ etc are installed on extractive element (trolley) in cubicle. Normative standards sustaining how the tests should be made, test laboratory formative elements resistant’s, short – time and withstand current calculation, test scheme and test conditions are presented in the Master thesis.
69

Calibration, Optimality and Financial Mathematics

Lu, Bing January 2013 (has links)
This thesis consists of a summary and five papers, dealing with financial applications of optimal stopping, optimal control and volatility. In Paper I, we present a method to recover a time-independent piecewise constant volatility from a finite set of perpetual American put option prices. In Paper II, we study the optimal liquidation problem under the assumption that the asset price follows a geometric Brownian motion with unknown drift, which takes one of two given values. The optimal strategy is to liquidate the first time the asset price falls below a monotonically increasing, continuous time-dependent boundary. In Paper III, we investigate the optimal liquidation problem under the assumption that the asset price follows a jump-diffusion with unknown intensity, which takes one of two given values. The best liquidation strategy is to sell the asset the first time the jump process falls below or goes above a monotone time-dependent boundary. Paper IV treats the optimal dividend problem in a model allowing for positive jumps of the underlying firm value. The optimal dividend strategy is of barrier type, i.e. to pay out all surplus above a certain level as dividends, and then pay nothing as long as the firm value is below this level. Finally, in Paper V it is shown that a necessary and sufficient condition for the explosion of implied volatility near expiry in exponential Lévy models is the existence of jumps towards the strike price in the underlying process.
70

Microlocal Analysis of Tempered Distributions

Schulz, René M. 12 September 2014 (has links)
Diese Dissertation ist dem Studium temperierter Distributionen mittels mikrolokaler Methoden gewidmet. Die fundamentale Größe der mikrolokalen Analysis, die Wellenfrontmenge, wird durch zwei analoge Konzepte ersetzt, die den pseudo-differentiellen SG- und Shubin-Kalkülen zugeordnet sind. Die Eigenschaften dieser globalen Wellenfrontmengen werden studiert und ferner werden unterschiedliche Möglichkeiten, diese globalen Singularitäten zu charakterisieren, untersucht, insbesondere mittels der FBI-Transformation. Zahlreiche Konstruktionen, die den klassischen Wellenfrontmengenbegriff beinhalten, werden in den globalen Kontext übersetzt, insbesondere Rechenoperationen mit temperierten Distributionen wie etwa (getwistete) Produkte, Pull-backs und Paarungen, für die mikrolokale Existenzkriterien angegeben werden. Als eine Anwendung wird eine Klasse von temperierten Oszillatorintegralen eingeführt, welche durch inhomogene Phasenfunktionen und Amplituden aus SG-Symbolklassen parametrisiert werden. Die SG-Wellenfrontmengen dieser Distributionen werden untersucht und es stellt sich heraus, dass diese durch eine Verallgemeinerung der Menge stationärer Punkte der Phasenfunktionen beschränkt werden. In diesem Kontext wird eine Verallgemeinerung des klassischen Begriffs einer konischen Lagrange-Untermannifaltigkeit des T*R^d vorgenommen und diese Objekte werden auf ihre Parametrisierungseigenschaften untersucht. Es stellt sich heraus, dass jedes solche Objekt lokal als die Menge der stationären Punkte einer SG-Phasenfunktion realisiert werden kann. Als weitere Anwendung werden einige Konstruktionen der axiomatischen Quantenfeldtheorie, die Distributionen beinhalten, im temperierten Kontext realisiert.

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