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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.
31

Medição de vibrações estruturais e de sistemas rotativos utilizando imagens fotográficas subamostradas / Measurement of vibration in structural and rotating systems using sub-sampled photographic images

Marcos Tan Endo 29 November 2013 (has links)
A análise de vibrações nos sistemas estruturais e rotativos permite detectar problemas indesejáveis, como a fadiga estrutural e o desgaste excessivo, que contribuem para a redução da vida útil do sistema e seus componentes. Tradicionalmente, a medição das vibrações é realizada por sensores de contato (acelerômetros e extensômetros), que possuem como inconveniente a adição de sua massa no sistema. Como alternativa, existem os sensores de não contato (LVD e ESPI), que são equipamentos de custo elevado. Este trabalho visa o desenvolvimento de um equipamento de baixo custo que realize medições multi-pontos sem contato do comportamento vibratório de estruturas e eixos rotativos. O método proposto utiliza como base os princípios da fotogrametria em conjunto com técnicas de subamostragem, que são utilizadas em estruturas ou máquinas com frequências de vibração conhecidas (e.g máquinas rotativas). A metodologia foi inicialmente aplicada em uma viga engastada-livre, excitada periodicamente por um shaker eletrodinâmico e posteriormente em um sistema rotativo montado em um bancada de testes. A viabilidade em se utilizar o método foi verificada comparando os resultados obtidos com as medições realizadas por um vibrômetro laser Doppler, no caso do sistema estrutural, e por sensores de proximidade indutivo nas vibrações do eixo rotativo. Com base nos comparativos, conclui-se que este método, mesmo apresentando limitações de resolução, pode ser perfeitamente empregado em medições de sistemas estruturais e rotativos assim como na análise modal operacional de estruturas. / The analysis of vibrations in structural and rotating systems allows the detection of undesirable problems, such as the structural fatigue and excessive wear, which contribute to the reduction of the useful life of the systems and their components. Traditionally, the measurement of vibrations is carried out by contacting sensors (accelerometers and strain gauges), which have the inconvenience of adding mass into the system. Alternativelly, there are the non-contacting sensors (LVD and ESPI), which are high cost equipments. This work aims at developing a low cost equipment that carry out multi-point non-contact measurements of the vibratory behavior of structures and rotating shafts. The proposed method uses as a basis the principles of photogrammetry together with sub-sampling techniques, which are used in structure or machines with known vibration frequencies (e.g rotating machines). The methodology was initially applied on a cantilever beam, periodically excited by an electrodynamic shaker and later in a rotating system mounted on a test bench. The feasibility of using the method was verified comparing the results obtained with measurements from a laser Doppler vibrometer, in the case of the structural system, and with inductive proximity sensors in the rotating shaft vibration. Based on the comparison analysis, one observes that this method can be perfectly used in vibration measurements in structural and rotating systems even with limitations in resolution as well as in operational modal analysis of structures.
32

Operational Modal Analysis of the Stockholm Waterfront Congress Centre

Grundström, Ulrika January 2010 (has links)
No description available.
33

Méthode de diagnostic à grande échelle de la vulnérabilité sismique des Monuments Historiques : Chapelles et églises baroques des hautes vallées de Savoie / Large-scale seismic vulnerability assesment method for the masonry architectural heritage : baroque chapels and churches of the French Savoye

Limoge, Claire 01 April 2016 (has links)
L’objectif de ce travail est de proposer une méthode d’analyse de vulnérabilité sismique adaptée à l’étude d’un patrimoine historique complet très étendu, indépendamment de la renommée de chaque bâtiment. En effet la grande vulnérabilité sismique du patrimoine ancien, très souvent en maçonnerie, impose, afin d’éviter tout dommage irréparable, de se donner les moyens d’intervenir en amont. Notre démarche doit donc répondre à trois impératifs principaux: développer des outils de choix à grande échelle afin de hiérarchiser les besoins, offrir une analyse pertinente du comportement sous séisme d'une structure historique maçonnée même en première approche, et trouver des méthodes pour gérer le nombre important d’incertitudes qui caractérise le diagnostic des édifices anciens. Pour ce faire, nous étudions les églises et chapelles baroques des hautes vallées de la Savoie française, témoignages d'une période particulièrement prospère dans l'histoire de la Savoie et d'un mouvement artistique unique dans un environnement hostile. Dans ce contexte nous avons donc développé ou adapté différents outils afin de pouvoir traiter les particularités des édifices anciens et utiliser pour des édifices anciens en maçonnerie rustique les potentialités des techniques proposées pour les édifices modernes : modélisations numériques non-linéaires dynamiques temporelles, mesures vibratoires in-situ, analyse multi modale non-linéaire. / The aim of this thesis is to propose a seismic vulnerability assessment method well suited to the study of a complete historical heritage, regardless of the prestige of each building. Indeed the great seismic vulnerability of the historical heritage, often in masonry, requires to act preventively in order to avoid irreparable damage. Our approach must tackle three main requirements: to develop large-scale tools of choice to prioritize the needs, to provide relevant analysis of seismic behavior on the structural scale even in the first study, and to manage the large number of uncertainties characterizing the old buildings structural assessment. To this aim, we study the baroque churches and chapels in the high valleys of the French Savoie. They witness to a particularly prosperous period in the history of Savoy and a unique artistic movement adapted to a harsh environment. In this context we have therefore developed or adapted different tools in order to handle the peculiarities of the old buildings. This way we can use the today proposed techniques for modern buildings to study these ancient buildings in rustic masonry: non-linear temporal dynamics numerical modeling, vibratory in situ measurements, non-linear multi modal analysis.
34

Identification modale opérationnelle des robots d'usinage en service / Operational modal identification of machining robots in service

Maamar, Asia 25 March 2019 (has links)
L’identification des paramètres modaux des machines-outils et des robots d’usinage, en service, constitue un levier d’optimisation des performances de coupe. En effet, la connaissance en continue du comportement dynamique d’une machine permet une prédiction fine des conditions de stabilité, bases d’un pilotage intelligent des paramètres du procédé. Cependant, la présence de fortes excitations harmoniques, dues à la rotation de la broche et de l’outil coupant, rend les techniques classiques d’Analyse Modale Opérationnelle (AMO) inapplicables. Le premier objectif de cette thèse consiste à déterminer une méthode d’AMO adéquate pour une application en présence des harmoniques. Une étude comparative des méthodes existantes est conduite, à savoir : la méthode de décomposition dans le domaine fréquentiel (EFDD), la méthode d’identification dans le sous-espace stochastique (SSI), la méthode PolyMAX et la méthode basée sur la fonction de transmissibilité (TFB). La méthode TFB est choisie afin de réaliser une identification modale opérationnelle des robots d’usinage. Cette technique est tout d’abord investiguée sur une machine-outil cartésienne. Cette étape est justifiée par le fait qu’une machine-outil est une structure plus rigide qui présente moins de variations des propriétés dynamiques par rapport à un robot d’usinage. Les résultats montrent la pertinence de la méthode TFB pour identifier les paramètres modaux de la machine-outil en usinage, même en présence des composantes harmoniques fortement dominantes. Ensuite, l’identification modale opérationnelle du robot d’usinage ABB IRB 6660, qui présente une structure moins rigide par rapport à une machine-outil, est menée sur une trajectoire d’usinage. Les résultats obtenus permettent d’établir une base modale du robot montrant l’évolution de son comportement modal en service. L’originalité des travaux présentés réside dans le développement d’une procédure robuste d’identification modale opérationnelle qui permet de suivre l’évolution du comportement modal du robot en cours d’usinage dans son espace de travail. / The identification of the modal parameters of machining robots in service has a significant adverse influence on machining stability, which will, therefore, decrease the quality of the workpiece and reduce the tool life. However, in presence of strong harmonic excitation, the application of Operational Modal Analysis (OMA) is not straightforward. Firstly, the issue of choosing the most appropiate OMA method for an application in presence of harmonic components, is handled. For a comparison purpose, the modified Enhanced Frequency Domain Decomposition (EFDD) method, the Stochastic Subspace Identification (SSI) method, the PolyMAX method and the Transmissibility Function Based (TFB) method are investigated. The obtained results lead to the adoption of the Transmissibility Function Based (TFB) method for an OMA of machining robots. For an accurate modal identification procedure, the OMA of a machine tool is, initially, conducted. It is a preparation step in order to verify the performance of the chosen method under machining conditions as well as a machine tool is a rigid structure, thus, it has less variation in its dynamic behavior compared to a machining robot. Results demonstrate the efficiency of the TFB method to identify the machine tool modal parameters even in the presence of preponderant harmonic components. Finally, the OMA of the machining robot ABB IRB 6660, which has a flexible structure compared to a machine tool, is carried out for a machining trajectory. The obtained results allow the identification of a modal basis of the machining robot illustrating the evolution of its modal behavior, in service. The main novelty of this thesis lies in the development of a robust procedure for an operational modal identification of machining robots, in service, which makes it possible to continuously follow the variations in the modal parameters of machining robots.
35

Identification et modélisation du comportement dynamique des robots d'usinage / Identification and modeling of machining robots' dynamic behavior

Mejri, Seifeddine 08 April 2016 (has links)
La robotisation des procédés d’usinage suscite l’intérêt des industriels en raison du grand espace de travail et le faible coût des robots par rapport aux machines-outils conventionnelles et la possibilité d’usiner des pièces de formes complexes. Cependant, la faible rigidité de la structure robotique favorise le déclenchement de phénomènes dynamiques liés à l’usinage sollicitant le robot en bout de l’outil qui dégradent la qualité de surface de la pièce usinée. L’objectif de ces travaux de thèse est de caractériser le comportement dynamique des robots en usinage. Ces travaux ont suivi une démarche en trois étapes : La modélisation d’un premier modèle considéré de référence où le robot est au repos. Ensuite l’identification du comportement dynamique du robot en service. Enfin, l’exploitation des modèles dynamiques du robot en vue de prédire la stabilité de coupe. L’originalité de ces travaux porte sur le développement des méthodes d’identification modale opérationnelles. Elles permettent d’intégrer les conditions réelles d’usinage et d’élaborer des modèles plus précis que le premier modèle de connaissance sans être biaisés par l’effet des harmoniques de rotation de l’outil. Enfin, des préconisations sur le choix de configurations du robot et sur la direction des forces d’excitation sont proposées pour assurer la stabilité de la coupe lors de l’usinage robotisé. / Machining robots have major advantages over cartesian machine tools because of their flexibility, their ability to reach inaccessible areas on a complex part, and their important workspace. However, their lack of rigidity and precision is still a limit for precision tasks. The stresses generated by the cutting forces and inertia are important and cause static and dynamic deformations of the structure which result in problems of workpiece surface. The aim of the thesis work is to characterize the dynamic behavior of robots during machining operation. This work followed a three-step approach : Modeling a first model considered as a reference where the robot is at rest. Then the identification of the dynamic behavior in service. Finally, the prediction of the cutting stability using the robot dynamic model. The originality of this work is the development of new operational modal identification methods. They integrate the machining conditions and result into a more accurate model than the first model of reference without being biased by harmonics. Finally, guidlines of robot’s configurations and excitation forces’ direction are proposed to ensure the robotic machining stability.
36

Ověřování věrohodnosti měřicí metody z oblasti modální analýzy / Modal analysis experimental method verification

Pop, Miroslav January 2019 (has links)
This diploma thesis deals with the issue of operational modal analysis, which is one of the newer areas of structural dynamics that makes it possible to estimate modal properties of structures directly during their operation. The aim of this work is to create theoretical basis of operational modal analysis, more specifically of Frequeny Domain Decomposition method. Furthermore, apply this method to a selected structure and verify the achieved results using computational modelling and experimental modal analysis. The technique of dividing the experiment to separate measurements using reference sensor was used. Evaluation of the operational modal analysis was performed using self-created function for the MATLAB software and using the commercial PULSE Operational Modal Analysis software. Obtained results were verified by computational modelling and experimental modal analysis.
37

Analýza modálního tlumení strojní součásti pomocí metody OMA / The modal damping ratio analysis of the mechanical part using the OMA method

Sodomka, Tomáš January 2021 (has links)
In one of the first hours of study at the Institute of Mechanics of Bodies, Mechatronics and Biomechanics, the author of this work received three basic recommendations regarding measurement: 1) Do not measure! 2) If you measure, do not repeat the measurement!! 3) If you repeat the measurement, do not compare the measurements!!! However, this thesis boldly violates all three recommendations. In the introductory theoretical part, it briefly introduces the vibration of multi-degree of freedom damped systems and describes experimental ways of determining the modal damping. It also summarizes the Operational Modal Analysis (OMA) approach, explains the principle of the FDD method, and introduces EFDD (Enhanced Frequency Domain Decomposition) method which allows to determine not only natural frequencies and shapes as FDD does, but also modal damping of the shapes. A script in Matlab environment for processing vibrations using EFDD method is one of the thesis outputs. The script is first tested by computational model, where a model system with known damping is tested and damping is determined by the script. Subsequently, the work moves to the actual measurement of the real system - a bonded bar which is analysed by Experimental Modal Analysis and OMA, while the second variant uses commercial EFDD method (Brüel a Kjr company) and programmed script. In the conclusion of the thesis the damping results are compared to each other. The diploma thesis continues in Ing. M. Pop’s thesis – Modal Analysis Experimental Method Verification. From this work a part of measured data is taken. Specific cases of data use are always listed in the appropriate section of the text.
38

Des données accélérométriques au comportement dynamique des bâtiments existants / From accelerometric records to the dynamic behavior of existing buildings

Fernández Lorenzo, Guillermo Wenceslao 17 October 2016 (has links)
L'objectif de cette thèse est de simuler l'histoire temporelle de la réponse d'un bâtiment de grande hauteur sous sollicitation sismique et de proposer des méthodologies simplifiées qui reproduisent correctement une telle réponse. Initialement, un modèle tridimensionnel par éléments finis est produit afin de valider sa fiabilité pour simuler le comportement réel du bâtiment pendant les mouvements du sol, enregistrés à l'aide d'accéléromètres. Il est proposé d'améliorer la précision du modèle numérique en imposant de multiples excitations, compte-tenu des effets de basculement et de la variabilité spatiale sur la sollicitation d'entrée. L'utilisation de fonctions de Green empiriques est proposée pour simuler la réponse sismique directement à partir d'enregistrements d'événements passés, sans avoir besoin de dessins de construction ni d'étalonnage des paramètres mécaniques. Une méthode de sommation stochastique, déjà utilisée pour prédire les mouvements du sol, est adoptée pour générer des signaux synthétiques à des hauteurs différentes du bâtiment, par extension du chemin de propagation des ondes du sol à la structure. Une représentation simplifiée du bâtiment comme une poutre homogène Timoshenko est proposée pour simuler la réponse sismique directement à partir des enregistrements des vibrations ambiantes. Des paramètres mécaniques équivalents sont identifiés à l'aide de l'interférométrie par déconvolution en termes de dispersion des ondes, de fréquences naturelles et de rapport de vitesse des ondes de cisaillement et de compression dans le milieu / The aim of this thesis is to simulate the time history response of a high rise building under seismic excitation and provide simplified methodologies that properly reproduce such response. Firstly, a detailed three-dimensional finite element model is produced to validate its reliability to simulate the real behavior of the building during ground motions, recorded using accelerometers. It is proposed to improve the accuracy of the numerical model by imposing multiple excitations, considering rocking effect and spatial variability on the input motion. The use of empirical Green's functions is proposed to simulate the seismic response directly from past event records, without the need of construction drawings and mechanical parameters calibration. A stochastic summation scheme, already used to predict ground motions, is adopted to generate synthetic signals at different heights of the building, extending the wave propagation path from the ground to the structure. A simplified representation of the building as a homogeneous Timoshenko beam is proposed to simulate the seismic response directly from ambient vibration records. Equivalent mechanical parameters are identified using deconvolution interferometry in terms of wave dispersion, natural frequencies and shear to compressional wave
39

Probing the cosmic-ray pressure in the Virgo Cluster and the origin of the very-high-energy gamma rays of M87 with H.E.S.S. and CTA

Barbosa Martins, Victor 22 July 2022 (has links)
Das High Energy Stereoscopic System (H.E.S.S.) ist ein System von fünf atmosphärischen Cherenkov-Teleskopen (IACT) in Namibia. Die H.E.S.S. Teleskope sind empfindlich für sehr energiereiche (VHE) Gammastrahlen zwischen ~30 TeV und 100 TeV. Mit einer Entfernung von 16,5 Mpc ist Messier 87 (M87) eine der nächsten Radiogalaxien und beherbergt eines der massereichsten supermassiven Schwarzen Löcher, das Materie in einen Plasmastrahl relativistischer Teilchen emittiert. Der Strahl wird im Bereich des gesamten elektromagnetischen Spektrums beobachtet und untersucht. M87 befindet sich im Zentrum des Virgo-Galaxienhaufens, eines kühlen Galaxienhaufens, der von Gas gefüllt ist, das in der Nähe des Zentrums kälter und in den Außenbereichen des Galaxienhaufens heißer ist. Gemäß der Cooling Flow (CF) Theorie kühlt das Plasma in Cool Core (CC) Haufen am Rand des Haufens ab und sinkt nach innen, wodurch die Sternentstehungsrate im Zentrum erhöht wird. Optische Messungen des Virgo Galaxienhaufens scheinen diesem Modell jedoch zu widersprechen. Als Heizmechanismus wird der aktive galaktische Kern Rückkopplungsmechanismus vorgeschlagen, der die Abkühlung des ICM ausgleicht und dessen CF vermeidet. Die kosmische Strahlung des Jets interagiert mit der ICM und erzeugt neutrale Pionen, die in Gammastrahlen zerfallen und ein nicht variables und ausgedehntes Gammastrahlensignal erzeugen. Allerdings konnten keine Gammastrahlen-Beobachtungen mit dem Pionenzerfall in dem Galaxienhaufen in Verbindung gebracht werden. In dieser Studie der H.E.S.S. Beobachtungen des niedrigen Strahl-Aktivitätszustands von M87 haben keine signifikante Ausdehnung der Emissionsregion gezeigt, woraus eine 3σ Obergrenze von 0.016° ≈ 4.6 kpc abgeleitet wurde. Das Verhältnis des Drucks in kosmischer Strahlung zur thermischen Strahlung ist auf <0.36 im Zentralregion beschränkt. Diese abgeleitete Obergrenze nimmt einen Gleichgewichtszustand zwischen den Erwärmungs und den Kühlprozessen an. Die neue Generation von IACTs, das Cherenkov Telescope Array Observatory (CTAO), wird eine unvergleichbare Empfindlichkeit und Winkelauflösung bieten. Um die langfristige Verfügbarkeit der Teleskope sicherzustellen, wurde ein auf Schwingungsmessungen basierendes Strukturüberwachungssystem entwickelt und zwischen 2019 und 2020 in Berlin am Prototyp des mittelgrossen Teleskopes erfolgreich getestet. CTAO wird in der Lage sein die Gammastrahlung des Virgo Haufens zu untersuchen und sie laut Simulationen und dem Steady-State-Modell innerhalb von ~210 h zu detektieren. / The High Energy Stereoscopic System (H.E.S.S.) is an array of five Imaging Atmospheric Cherenkov Telescopes (IACTs) located in Namibia. The H.E.S.S. telescopes are sensitive to Very-High-Energy (VHE) gamma rays between ~30 TeV and ~100 TeV. At a distance of 16.5 Mpc Messier 87 (M87) is one of the closest radio-galaxies, hosting one of the most massive Super-Massive Black Hole, which accretes matter and launches an inclined jet of relativistic particles. The jet is detected and studied by radiation emitted through the entire electromagnetic spectrum. M87 is located at the very center of the Virgo galaxy cluster, a Cool Core (CC) cluster, characterized by an Intra-cluster Medium (ICM) that is colder close to the center and hotter towards the outskirts of the galaxy cluster. According to the Cooling Flow (CF) theory, the plasma in CC clusters cools in the outskirts of the cluster and falls inwards, increasing the star formation ratio in the region. However, optical measurements of the Virgo Cluster seem to contradict this model. The Active Galactic Nucleus (AGN) feedback mechanism is proposed as a heating mechanism, which counterbalances the cooling of the ICM and avoids its CF. The cosmic rays from the jet interact with the ICM producing neutral pions, which decay to gamma rays, forming a non-variable and extended gamma-ray signal. However, no gamma-ray observations could be associated with pion decay in galaxy clusters. In this work, deep H.E.S.S. observations of M87's low state are analyzed, and the results have shown no significant gamma-ray extension leading to a 3σ upper limit of 0.016° ≈ 4.6 kpc. The ratio of cosmic-ray pressure to thermal pressure XCR is constrained to < 0.36 at its maximum position, assuming a steady-state between the heating and the cooling processes. The new generation of IACTs, the Cherenkov Telescope Array Observatory (CTAO) will offer unprecedented sensitivity and angular resolution. To assure the long-term availability of the telescopes, a structure monitoring system based on vibration measurements was developed and successfully tested at the Medium-sized Telescope (MST) prototype between 2019 and 2020 in Berlin. CTAO should be able to probe the gamma-ray emission from the Virgo Cluster, and, according to simulations and to the steady-state model, significantly detect it after ≈ 210 h.

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