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The Global ETD Search service is a free service for researchers
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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.
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Showing 31 to 40 of 46 (0.017 seconds)Spelling suggestions: "subject:"hertz"" "subject:"gertz""
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Développement d'un outil de pré dimensionnement de structures sandwich soumises à des impacts à vitesse intermédiaireMavel, Sébastien 04 October 2012 (has links) (PDF)
Dans le cadre du développement d'un outil semi-analytique de pré-dimensionnement de structures sandwich soumises à des impacts à vitesse intermédiaire (<20m.s-1), nous proposons la détermination d'une solution efficace, basée sur les séries de Fourier avec des conditions aux limites générales. Les équations gouvernantes qui permettent de décrire la réponse transitoire élastique de plaques stratifiées orthotropes avec prise en compte d'une loi non linéaire de contact hertzien sont développées en utilisant un schéma de discrétisation temporelle explicite. Pour les conditions aux limites générales, la solution en séries de Fourier est complétée par une série mixte de polynômes-cosinus, qui permet d'aboutir à la solution, tout en permettant à la série de satisfaire les équations d'équilibres ainsi que les conditions limites, de façon exacte en augmentant le nombre de termes de la série. Afin de tenir compte des phénomènes physiques locaux lors de l'impact de structure sandwich, la plasticité et la rupture locale de la plaque anti-perforation sont introduites dans une formulation modifiée du contact de Hertz et l'écrasement de l'âme du sandwich est ajouté dans l'équation d'équilibre du projectile. Les solutions obtenues par cette méthode sont en accord avec les résultats par modélisation éléments finis de plaques composites multicouches impactées par un projectile. Une campagne expérimentale d'impact de type " box corner " sur des plaques sandwich de 1m², a servi de référence expérimentale et permis la validation de ce modèle complet. Finalement, le couplage de ce modèle à un optimiseur basé sur les techniques de plans d'expériences et de surfaces de réponses (métamodèles), nous a permis de choisir la meilleure structure d'absorption d'énergie (matériaux et géométrie) pour des structures plaques soumises à des impacts de 7kJ. Un test sur un véhicule réel avec la configuration structurelle choisie, nous a permis de valider l'outil final de pré-dimensionnement et de confirmer la qualité des résultats numériques obtenus par ce modèle semi-analytique.
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Implementation and evaluation of V/f and vector control in high–speed PMSM drives / Kruger G.L.Kruger, Gert Lodewikus. January 2011 (has links)
The McTronX research group, at the Potchefstroom campus of the North–West University, has
been researching Active Magnetic Bearings (AMBs). A fully suspended, flywheel energy storage
system (FESS) has been developed. Due to excessive unbalance on the rotor, the motor drive
could not be tested up to its rated speed. In the interim, until the rotor can be balanced and
other rotor dynamic effects have been investigated, the group decided that the existing drive
control should be improved and tested on a high–speed permanent magnet synchronous motor
(PMSM), using normal roller element bearings.
In order to test the motor control a second (identical) PMSM, mechanically coupled to the
former, operates in generator mode which serves as the torque load. Two different control algorithms,
namely V/f and vector control, are designed and implemented on a rapid control
prototyping system, i.e. dSPACE®. The V/f control is an open–loop, position sensorless technique,
whilst the vector controller makes use of a position sensor.
From the design and implementation it became clear that the vector control is more robust,
in the sense that it is less sensitive on parameter variations and disturbances. It can start up
reliably even under full load conditions.
The V/f control is an attractive alternative to the vector control, especially in AMB systems,
where it may be difficult to mount the position sensor, has to operate in a hazardous environment
not suited to the sensor or could degrade the reliability of the AMB system. The cost of the
position sensor is not really a concern compared to the cost of an AMB system. The V/f control
is more suited to fan and pump applications, which has a low dynamic requirement. The V/f
control has high startup currents and is not recommended for applications requiring a high
starting torque or fast acceleration during operation.
The inverter, which drives the PMSM, also had to be developed. With regard to the motor
control, the effects of inverter non–idealities had to be accounted, especially for the V/f control.
The implemented control algorithms were tested up to 20 krpm. Discrepancies between the expected
and actual results are discussed. Overall, the controllers performed as desired. Generally,
the project goals have been reached satisfactorily. / Thesis (M.Ing. (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2011.
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Implementation and evaluation of V/f and vector control in high–speed PMSM drives / Kruger G.L.Kruger, Gert Lodewikus. January 2011 (has links)
The McTronX research group, at the Potchefstroom campus of the North–West University, has
been researching Active Magnetic Bearings (AMBs). A fully suspended, flywheel energy storage
system (FESS) has been developed. Due to excessive unbalance on the rotor, the motor drive
could not be tested up to its rated speed. In the interim, until the rotor can be balanced and
other rotor dynamic effects have been investigated, the group decided that the existing drive
control should be improved and tested on a high–speed permanent magnet synchronous motor
(PMSM), using normal roller element bearings.
In order to test the motor control a second (identical) PMSM, mechanically coupled to the
former, operates in generator mode which serves as the torque load. Two different control algorithms,
namely V/f and vector control, are designed and implemented on a rapid control
prototyping system, i.e. dSPACE®. The V/f control is an open–loop, position sensorless technique,
whilst the vector controller makes use of a position sensor.
From the design and implementation it became clear that the vector control is more robust,
in the sense that it is less sensitive on parameter variations and disturbances. It can start up
reliably even under full load conditions.
The V/f control is an attractive alternative to the vector control, especially in AMB systems,
where it may be difficult to mount the position sensor, has to operate in a hazardous environment
not suited to the sensor or could degrade the reliability of the AMB system. The cost of the
position sensor is not really a concern compared to the cost of an AMB system. The V/f control
is more suited to fan and pump applications, which has a low dynamic requirement. The V/f
control has high startup currents and is not recommended for applications requiring a high
starting torque or fast acceleration during operation.
The inverter, which drives the PMSM, also had to be developed. With regard to the motor
control, the effects of inverter non–idealities had to be accounted, especially for the V/f control.
The implemented control algorithms were tested up to 20 krpm. Discrepancies between the expected
and actual results are discussed. Overall, the controllers performed as desired. Generally,
the project goals have been reached satisfactorily. / Thesis (M.Ing. (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2011.
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Caractérisation du comportement mécanique de la sous surface d'un polymère percé, sous une sollicitation de type hertzienne / Characterisation of mechanical behavior of a sub surface drilled polymer, under hertzian contact loadPalade, Adrian-Ciprian 20 September 2013 (has links)
Ce travail s'inscrit dans la compréhension du comportement de la sous-surface d'une pièce présentant des hétérogénéités contrôlées, soumise à un chargement de type hertzien sans affecter l'intégrité de sa surface initiale. Le but est de qualifier le champ de contraintes en sous couche. Pratiquement, des défauts de forme cylindrique sont positionnés là où le champ de contraintes est maximal. Le contact est dimensionné pour pouvoir observer, par photoélasticimétrie, les évolutions du champ de contraintes et développer une modélisation numérique pour étudier le comportement statique puis dynamique. Il ressort que la présence d'un trou sur l'axe de symétrie z (x = 0) est le facteur prépondérant. Les caractéristiques qui permettent de diminuer la contrainte de cisaillement sur l'axe de symétrie sont celles qui conduisent à un renforcement de la contrainte de cisaillement maximale dans le massif. Cette dualité nous conduit à proposer un indicateur qui prend en compte, à la fois, la contrainte de cisaillement, l'aplomb du contact et l"évolution de la contrainte maximale dans le massif. La méthodologie de travail a été mise en oeuvre et validée. Les approches analytiques et expérimentales ont permis de valider les modélisations numériques qui sont seules à même de permettre l'étude de nombreux cas. Les perspectives sont nombreuses, avec des incursions possibles en structuration de sous-surfaces, perçage simple, frittage sélectif par laser. Ce doctorat a permis de traiter le cas des défauts circulaires. Dans un autre domaine, le soudage est également un cas d'intérêt pour l'étude du comportement des cordons de soudure présentant des défauts de type porosités ou inclusions. / This research concerns the understanding of the sub-surface behaviour of a component presenting controlled heterogeneities and subjected to a Hertzian type load. The purpose is to qualify the stress field in the subsurface. Practically, defects of cylindrical shape are located where the stress field is maximal in sub surface. The contact is sized to be able to observe, by photoelasticity, the stress field and to develop a numerical model to simulate the behaviour (static and dynamic) of the friction area. It is highlighted that the presence of a hole on the z axis of symmetry (x = 0) is the dominating factor. The characteristics which allow decreasing the shearing stress on the symmetry axis are the ones which lead to a strengthening of the maximal shearing stress in the whole volume. This duality drives us to propose an indicator which takes into account, at the same time, the shearing stress below the contact and the evolution of the maximal stress in the whole volume. The working methodology was implemented and validated. The analytical and experimental approaches allow validating the numeric model which is the only one able to allow the study of numerous configurations. The perspectives are numerous, with possible incursions in structuring of sub-surfaces, simple drilling and selective laser sintering.... In another domain, the welding process is also a case of interest for the study of the behaviour of weld seam presenting defects of porosities or inclusions types
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A smart adaptive load for power-frequency support applicationsCarmona Sanchez, Jesus January 2016 (has links)
At present, one of the main issues in electric power networks is the reduction in conventional generation and its replacement by low inertia renewable energy generation. The balance between generation and demand has a direct impact on the system frequency and system inertia limits the frequency rate of change until compensation action can be undertaken. Traditionally generation managed frequency. In future, loads may be required to do more than just be able to be switched off during severe under frequency events. This thesis focuses on the development and practical implementation of the control structure of a smart adaptive load for network power-frequency support applications. The control structure developed makes use of advanced demand side management of fan loads (powered by AC drives) used in heating, ventilation, and air conditioning systems; where a change in power at rated load has little effect on their speed due to the cubic relationship between speed and power. The AC drive implemented in this thesis is based on an induction motor and a two level voltage source converter. To achieve the smart adaptive load functionality, first a power-frequency multi-slope droop control structure (feedforward control) is developed; relating the frequency limits imposed by the network supplier and the fan power-speed profile (Chapter 2, Fig 2.19). Secondly, this control structure is combined with the control developed, in Chapter 3, for the AC drive powering the fan load. The full development of the control structure of the AC drive, its tuning process and its practical implementation is given; an equation is developed to find suitable tuning parameters for the speed control of the nonlinear load (fan load), i.e. Eq. (3.59).The analysis and simulation results provided in Chapter 4 conclude that a fast control of the active power drawn by the AC drive is possible by controlling the electromagnetic torque (hence current) of the induction motor without disturbing the fan load overly. To achieve this, changes between closed loop speed control and open loop torque control (power control) are performed when needed. Two main issues were addressed before the hardware implementation of the smart adaptive load: the estimation of the network frequency under distorted voltage conditions, and the recovery period of the network frequency. In this thesis two slew rate limiters were implemented to deal with such situations. Other possible solutions are also outlined. Finally, experimental results in Chapter 5 support results given in Chapter 4. A full power-frequency response is achieved by the smart adaptive load within 3s.
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Studium přechodových jevů mezi zcela zaplaveným a hladovějícím elastohydrodynamicky mazaným kontaktem / The study of transition between fully flooded and starved regimes in EHL ContactPopelka, Michal January 2012 (has links)
The diploma thesis deals with The study of transition between fully flooded and starved regimes in EHL Contact. The work is focused on problems of starved contact and surface texturing of rubbing surfaces. Surface texturing of rubbing surfaces is one of the adjustments that cause in a sense improved lubricity and reduce friction and wear. The aim of this study is to compare numerical models with real experimental results measured on the Experimental apparatus.
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Koncepce řadového vstřikovacího čerpadla pro tlaky 120 MPa / The Concept of In-line Injection Pump for 120 MPa PressuresTichý, Ondřej January 2016 (has links)
This thesis provides an overall evaluation of the concept of inline injection pump for pressure 120 MPa. The name of this pump is "Mj" and it is a product of the Motorpal, a.s. company. This thesis also contains an analysis of the contact pressures between the cam lobe and the pumping element's roller tappet. This includes comparing three different shapes of the roller and their influence on the magnitude of contact pressures. Calculations of the plunger helix and of the fuel delivery's impact on the relative position of plunger are also present.
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On the radiation gauge for spin-1 perturbations in Kerr–Newman spacetimeHollands, Stefan, Toomani, Vahid 27 April 2023 (has links)
We extend previous work (2020Class. Quantum Grav. 37 075001)to the case of
Maxwell’s equations with a source. Our work shows how to construct a vector
potential for the Maxwell field on the Kerr–Newman background in a radiation
gauge. The vector potential has a ‘reconstructed’ term obtained from a Hertz
potential solving Teukolsky’s equation with a source, and a ‘correction’ term
which is obtainable by a simple integration along outgoing principal null rays.
The singularity structure of our vector potential is discussed in the case of a
point particle source
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Utveckling av luftkompressormonterad ljuddämpare / Development of an air compressor mounted silencerMustafa, Kobin, Rozumberski, Kristian January 2018 (has links)
Ett ljudfenomen som uppstår i samband med luftkomprimeringen i den nya D7 motorn har uppmärksammats som ett problem av kunderna. Ljudfenomenet som resonerar i hytten bidrar till en obehaglig arbetsmiljö. Uppdraget har i sin tur varit att utveckla en luftkompressormonterad ljuddämpare mot en kravspecifikation som eliminerar detta fenomen. Med hjälp av diverse verktyg och en spiral produktutvecklingsprocess utfördes ett flertal iterationer av dem koncept som kan tänkas lösa problemet. Dessa iterationer konstruerades i mjukvaran CATIA V5 för att sedan beställas in som fysiska prototyper i materialet Pa12. För att bekräfta prototypernas funktionalitet utfördes simuleringar samt fysiska tester. Det resulterande arbetet blev ett konceptförslag till Scania CV AB som uppfyller kravspecifikationerna. Lösningens ljuddämpningsförmågan reducerade ljudfenomenet med 73% i genomsnitt. Med hjälp av observationer och analyser under de fysiska testgenomförandet uppmärksammades komplikationer som bör åtgärdas. Det mest kritiska med det nuvarande konceptet är dem vibrationer som uppstår. För att åtgärda detta problem kommer det krävas ytterligare infästningspunkter på motsvarande sida till de nuvarande. All mätdata i denna rapport är modifierat. Detta för att skydda känslig information. / A noise phenomenon that arises in connection with air compression in the new D7 engine has been noted as a problem by the customers. The sound phenomenon resonates in the cabin contributes to an unpleasant work environment. The mission, in turn, has been to develop an air compressor-mounted silencer against a requirement specification to eliminate this phenomenon. Using various tools and a spiral product development process, a number of iterations were made of those concepts that could solve the problem. These iterations were engineered in the CATIA V5 software, then ordered as physical prototypes in the material Pa12. To confirm the prototypes' functionality, simulations and physical tests were performed. The resulting work became a concept proposal for Scania CV AB that meets the requirements specifications. The solution managed to reduce the sound phenomenon by 73% on average. With the help of observations and analyzes during the physical test implementation, complications were noted that should be addressed. The most critical on the current concept is the vibration that occurs. To fix this problem additional attachment points will be required on the corresponding side to the current ones. All data in this report have been modified. This is to protect sensitive information.
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Contribution à la détermination de surfaces conjuguées pour la transmission de puissance.Guyonneau, David 16 July 2013 (has links)
Les travaux présentés à travers ce manuscrit s'inscrivent dans un contexte de recherches exploratoires sur l'optimisation des surfaces engrenantes. Après une étude approfondie de l'emploi des engrenages dans un environnement aéronautique, l'élaboration d'une nouvelle méthodologie de génération de profils de denture est proposée. Les travaux s'attachent à caractériser le comportement mécanique spécifique d'un montage d'engrenages dans les Boites de Transmission de Puissances (BTP) d'hélicoptère.Un outil informatique a été créé dans le module VBA (Visual Basic Application) d'Excel. Il permet de créer automatiquement des profils de denture conjugués et optimisés. Il a l'avantage de définir analytiquement plusieurs grandeurs physiques. L'outil a ainsi pour objectif de proposer des profils de denture optimisés selon plusieurs critères. Les « objectifs » retenus sont le rendement et la contrainte équivalente de Hertz au contact suivant le critère de Von Mises.Les travaux s'articulent autour de trois axes : - la reconstruction de profils conjugués de denture par une approche novatrice basée sur le « contact », - la construction de critères physiques (glissement, pression, contrainte, …), - la recherche de profils de denture optimaux en utilisant la simulation de Monte Carlo.Enfin, la perspective de rendre générique cette méthode afin qu'elle puisse générer n'importe quels types d'engrenage est envisagée en fin de manuscrit. / The work described in the present manuscript is part of exploratory researches dealing with gears meshing surfaces optimization. After a short study of gears used in an aeronautical environment, the development of an innovative tool for tooth profile design is defined. Then, the specific behavior of a gear mesh within a helicopter main gearbox (MGB) is evaluated.A VBA software has been coded under MS Excel to generate conjugated and optimized gear tooth profiles. It advantageously defines and uses several physical parameters with their analytical formulation. The software provides at the user optimized tooth profiles according to a couple of criteria. The two “objective” functions evaluated are the efficiency and the Hertz equivalent stress within the contact using the Von Mises criterion.The work has been focused on three aspects:- The design of conjugated tooth profiles by contact sharing,- The definition of the relevant physical parameters,- The optimization of tooth profiles using Monte Carlo SimulationEventually, a generic method to design gear profiles, taking into account any physical parameters related to a gear mesh, could be expected as a future of this thesis work.
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