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Dissertations / Theses on the topic 'Parametric vibrations'
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Manzione, Piergiuseppe. "Nonlinear transverse vibrations of centrally clamped rotating circular disks." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/31524.
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A study is presented of the instability mechanisms of a damped axisymmetric circular disk of uniform thickness rotating about its axis with constant angular velocity and subjected to various transverse space-fixed loading systems.
The natural frequencies of spinning floppy disks are obtained for various nodal diameters and nodal circles with a numerical and an approximate method.
Exploiting the fact that in most physical applications the thickness of the disk is small compared with its outer radius, we use their ratio to define a small parameter.
Because the nonlinearities appearing in the governing partial-differential equations are cubic, we use the Galerkin procedure to reduce the problem into a finite number of coupled weakly nonlinear second-order equations.
The coefficients of the nonlinear terms in the reduced equations are calculated for a wide range of the lowest modes and for different rotational speeds. We have studied the primary resonance of a pair of orthogonal modes under a space-fixed constant loading, the principal parametric resonance of a pair of orthogonal modes when the disk is subject to a massive loading system, and the combination parametric resonance of two pairs of orthogonal modes when the excitation is a linear spring.
Considering the case of a spring moving periodically along the radius of the disk, we show how its frequency can be coupled to the rotational speed of the disk and lead to a principal parametric resonance. In each of these cases, we have used the method of multiple scales to determine the equations governing the modulation of the amplitudes and phases of the interacting modes.
The equilibrium solutions of the modulation equations are determined and their stability is studied.Master of Science
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Sternchuss, Arnaud Balmès Etienne. "Multi-level parametric reduced models of rotating bladed disk assemblies." S. l. : Ecole centrale de Paris, 2009. http://theses.abes.fr/2009ECAP0001.
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Megnounif, Abdellatif. "Parametric study on human response to vibrations of box girder bridges." Thesis, University of Ottawa (Canada), 1988. http://hdl.handle.net/10393/5339.
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Oueini, Shafic Sami. "Techniques for Controlling Structural Vibrations." Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/27176.
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We tackle the problem of suppressing high-amplitude vibrations of cantilever beams when subjected to either primary external or principal parametric resonances. Guided by results of previous investigations into the nonlinear dynamics of single- and multi-degree-of-freedom structures, we design mechatronic systems of sensors, actuators, and electronic devices and implement nonlinear active feedback control.
In the case of external excitation, we devise two vibration absorbers based on either quadratic or cubic feedback. We conduct theoretical analyses and demonstrate that when a two-to-one (one-to-one) internal resonance condition is imposed between the plant and the quadratic (cubic) absorber, there exists a saturation phenomenon. When the plant is forced near its resonant frequency and the forcing amplitude exceeds a certain small threshold, the nonlinear coupling creates an energy-transfer mechanism that limits (saturates) the response of the plant.
Our theoretical studies reveal that the cubic absorber creates regimes of high-amplitude quasiperiodic and chaotic responses, thereby limiting its utility. However, we show that superior results can be achieved when the natural frequency of the quadratic absorber is set equal to one-half the excitation frequency. Consequently, we apply the quadratic technique through a variety of linear and nonlinear actuators, sensors, and electronic devices.
We design and build second-order analog circuits that emulate the quadratic absorber. Using a DC motor, piezoelectric ceramics, and Terfenol-D struts as actuators and potentiometers, strain gages, and accelerometers as sensors, we demonstrate successful single- and multi-mode vibration control.
In order to realize a more versatile implementation of the control strategy, we resort to a digital signal processing (DSP) board. We compose a code in C and design a digital absorber by developing algorithms that, in addition to replacing the analog circuit, automatically detect the amplitude and frequency of oscillation of the plant and fine-tune the absorber parameters.
We take advantage of the digital realization, implement a linear absorber, and compare the performance of the quadratic absorber with that of its linear counterpart.
In the case of parametric excitation, we investigate two techniques. First, we explore application of the quadratic absorber. We prove theoretically and demonstrate experimentally that this control scheme is not reliable. Then, we propose an alternate approach. We devise a control law based on cubic velocity feedback. We conduct theoretical and experimental investigations and show that the latter strategy leads to effective vibration suppression and bifurcation control.Ph. D.
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Winnard, Thomas Johan. "Theoretical Parametric Study of Through-Wall Acoustic Energy Transfer Systems." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/103387.
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Technological advances require novel solutions for contactless energy transfer. Many engineering applications require unique approaches to power electrical components without using physical wires. In the past decade, awareness of the need to wirelessly power electrical components spawned many forays into the field of wireless power transfer (WPT). WPT techniques include capacitive energy transfer, electromagnetic inductive power transfer, electromagnetic radiative power transfer, electrostatic induction, and acoustic energy transfer. Acoustic energy transfer (AET) has many advantages over other methods. These advantages include lower operating frequency, shorter wavelengths enabling the use of smaller sized receiver and transmitter, extended transmitter-to-receiver distance therefore more manageable design constraints, achieving lower attenuation, higher penetration depth, and no electromagnetic losses. Most AET systems operate in the ultrasonic frequency range and are more commonly referred to as ultrasonic acoustic energy transfer (UAET) systems.
Through-wall UAET systems are constructed of a transmitter bonded to a transmission elastic layer, which in turn is bonded to a receiver. The transmitter and receiver layers are constructed of a piezoelectric material. Piezoelectric materials behave according to the piezoelectric effect, which is when a material generates an electric charge in response to mechanical strain. The transmitter utilizes the reverse of the piezoelectric effect. A sinusoidal input voltage is applied to the transmitter, inducing vibrations in the transmitter. The vibration-induced acoustic waves emanating from the transmitter travel through the initial bonding layer, the transmission layer, and the final bonding layer to the receiver. In turn, the acoustic waves cause the receiver to deform and undergo strain. This induces a flow of charge in the receiver, which is an electric current. The receiver feeds current to a resistive load. In this manner, energy is acoustically transferred between two transducers without wires. The performance of UAET systems can be evaluated based on power transfer efficiency, voltage magnification, and input admittance.
UAET systems require extensive modeling before experimental assembly can be attempted. The analytical models of UAET are either based on the mechanics of the constitutive relations of piezoelectricity and solid mechanics or using equivalent circuit methods. The equivalent circuit method approximates the physics of the UAET system with electrical assumptions. The mechanics-based method is the most comprehensive description of the physics of all the intermediate layers in a UAET system.
The mechanics-based method has been based on the assumption that the UAET system is operated in the thickness mode of vibration, i.e., piston-like vibration mode where the transmitter and receiver disks vibrate only in the thickness direction. This poses an issue for disks with aspect ratios between 0.1 and 20 because the piezoelectric transducers vibrate in both the radial and thickness modes.
In addition to this assumption, most of the works on UAET models only have accounted for the piezoelectric and transmission layers. The effects of the bonding layers were not considered. Bonding the piezoelectric layers to the transmission layer introduces epoxy material with mechanical properties that are not accounted for. The epoxy layers are extra barriers to the transmission that introduce attenuation and alter the vibrational and acoustical behaviors of the UAET system.
Investigations into UAET commonly focus on metal through-wall applications. Alternate transmission layer materials are not investigated and the impact of varying mechanical properties on the performance of a through-wall UAET system has not been comprehensively studied. Even with the metal transmission layers, the impact of the metal thickness has not been extensively investigated thoroughly.
This work addresses the issues of the thickness-mode assumption in UAET modeling, the effects of epoxy layers, the impacts of the metal layer geometry, and the performance of UAET systems with alternate transmission layer materials. Particularly, (1) we showed that the thickness-mode assumption, that has been used in the UAET modeling leads to inaccurate results. (2) We modified the available acoustic electro- elastic theoretical modeling to include the effects of radial modes as well as the epoxy bonding layers. (3) We showed that the geometry of the elastic/metal layer requires optimization for peak system efficiency. (4) The results show that using alternate transmission layer materials impacts the performance of UAET systems. The results of this work were investigated using an improved 5-layer analytical model and finite element modeling in COMSOL Multiphysics.Master of Science
Wireless power transfer (WPT) is an innovative solution to the problem of powering sophisticated technological applications. Such instances include the powering of implanted medical devices, recharging inaccessible sensor networks, and wireless powering of components in sealed containers. Acoustic energy transfer (AET) is a feasible WPT method that addresses these needs. AET is based on the propagation of acoustic waves to a piezoelectric receiver which converts the vibrations caused by incident acoustic waves into electrical energy. Most AET systems operate in the ultrasonic frequency range, and so AET can also be referred to as ultrasonic acoustic energy transfer (UAET). Through-wall UAET systems are constructed from a transmitter that is bonded to a transmission elastic layer. The transmission layer is bonded to a receiver. The transmitter and receiver are made of a piezoelectric material. This thesis addresses the modeling process of through-wall UAET systems. In previous works, the fundamental assumption has been that such systems vibrate purely in the thickness mode. Additionally, other investigations did not comprehensively analyze the effects of the bonding layers, ascertain the performance of non-metal transmission layers, or provide practical insight on the effect of the resistive loading on such systems. This work addresses all these issues with a mathematical framework and finite element modeling results.
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Kurpa, Lidiya, Olga Mazur, and Igor Tsukanov. "Application of R-Functions Theory to Study Parametric Vibrations and Dynamical Stability of Laminated Plates." Thesis, Точка, 2013. http://repository.kpi.kharkov.ua/handle/KhPI-Press/37087.
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The problem of nonlinear parametric vibrations and stability analysis of the symmetric laminated
plates is considered. The proposed method is based on multimode approximation of displacements
and solving series auxiliary linear tasks. The main feature of the work is the application of the R-functions
theory, which allows investigating parametric vibrations of plates with complex shape and
different boundary conditions.
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Grenat, Clément. "Nonlinear Normal Modes and multi-parametric continuation of bifurcations : Application to vibration absorbers and architectured MEMS sensors for mass detection." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI078/document.
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Un des buts de cette thèse est d’approfondir la compréhension de la dynamique non-linéaire, notamment celle des MEMS, en proposant de nouvelles méthodes d’analyse paramétrique et de calcul de modes normaux non-linéaires. Dans une première partie, les méthodes de détection, de localisation et de suivi de points de bifurcation selon un unique paramètre sont rappelées. Ensuite, une nouvelle méthode d’analyse multiparamétrique basée sur la continuation récursive d’extremums est présentée. Cette méthode est ensuite appliquée à un absorbeur de vibration non-linéaire afin de repousser l’apparition de solutions isolées. Deuxièmement, une méthode de calcul de modes normaux non-linéaires est présentée. Une condition de phase optimale et une régularisation de l’équation de mouvement sont proposées afin d’obtenir une méthode de continuation plus robuste au niveau des interactions modales. Ensuite, un problème quadratique aux valeurs propres modifié pour le calcul de stabilité et de points de bifurcation est présenté. Finalement, le calcul de modes normaux non-linéaires a été étendu aux systèmes non-conservatifs permettant la continuation des résonances d’énergie en déplacement et des résonances de phase. Troisièmement, la dynamique non-linéaire de réseaux de MEMS basé sur plusieurs micro-poutres résonantes est analysée à l’aide des méthodes proposées. Tout d'abord, un phénomène de synchronisation de points de bifurcations dû au couplage électrostatique dans les réseaux de MEMS est expliqué. Puis, la dynamique non-linéaire d'un réseau dissymétrisé par l'ajout d'une petite masse sur une micro-poutre est analysée. Enfin, des mécanismes de détection de masse exploitant ces phénomènes non-linéaires sont présentésOne of the goals of this thesis is to enhance the comprehension of nonlinear dynamics, especially MEMS nonlinear dynamics, by proposing new methods for parametric analysis and for nonlinear normal modes computation. In a first part, methods for the detection, the localization and the tracking of bifurcation points with respect to a single parameter are recalled. Then, a new method for parametric analysis, based on recursive continuation of extremum, is presented. This method is then applied to a Nonlinear Tuned Vibration Absorber in order to push isolated solutions at higher amplitude of forcing. Secondly, a method is presented for the computation of nonlinear normal modes. An optimal phase condition and a relaxation of the equation of motion are proposed to obtain a continuation method able to handle modal interactions. Then, a quadratic eigenvalue problem is shifted to compute the stability and bifurcation points. Finally, nonlinear normal modes are extended to non-conservatives systems permitting the continuation of phase and energy resonances. Thirdly, the nonlinear dynamics of MEMS array, based on multiple resonant micro-beams, is analyzed with the help of the proposed methods. A frequency synchronization of bifurcation points due to the electrostatic coupling is discovered. Then, the nonlinear dynamics of a MEMS array after symmetry breaking event induced by the addition of a small mass onto one of the beam of the array is analyzed. Finally, mass detection mechanisms exploiting the discovered phenomena are presented
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Schirén, Whokko, and Trixie Swahn. "Vibrations in residential timber floors : A comparison between the current and the revised Eurocode 5." Thesis, Linnéuniversitetet, Institutionen för byggteknik (BY), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-89293.
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The European standard Eurocode 5, a design method for timber structures,is currently under revision. In this study the draft for a reviseddesign method for vibrations in timber floors was compared to the currentmethod. The hypothesis of the thesis was that the revised designmethod might force some changes to the present construction practiceand that these changes may carry with them increased costs for the industry.Six common floor structures used in Sweden today were identifiedand for these floors design calculations were made according to the currentand the revised design method. It was checked whether the floorspassed the criteria in the two design methods and a comparison was madefor the only criterion which could be compared between the methods, thepoint load deflection. Floor structures could pass or fail the current designmethod based on two criteria, the point load deflection and the unitimpulse velocity response. All floors passed the current design methodexcept one which had a fundamental frequency below 8 Hz, because ofthe low frequency the current design method was not applicable to thefloor structure. In the revised design method the final result is a responsefactor and based on the response factor floors are given floor performancelevels. The seven step scale for the floor performance level go from I toVII where I is excellent and VII is unacceptable. All floor structures excepttwo achieved an acceptable floor performance level according to therevised design method. The two floors which failed were floors commonlyused in single family houses, they failed for a span length commonly usedtoday. A limited parametric study was performed where it was found thatthe modal mass used had a larger impact on the floor performance levelthan the mass per square meter included. For floors with a fundamentalfrequency above 8 Hz, including a higher mass per square meter resultedin a lower, i.e. better, response factor in all cases except one. For floorswith a fundamental frequency between 4.5 and 8 Hz, a higher mass resultedin a higher, i.e. worse, response factor. The study found that notall floor structures used in Sweden today are acceptable according to therevised design method therefore changes may have to be implemented andthese changes could result in an increased cost.
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Airimitoaie, Tudor-Bogdan. "Commande robuste et calibrage des systèmes de contrôle actif de vibrations." Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENT015/document.
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Dans cette thèse, nous présentons des solutions pour la conception des systèmes de contrôle actif de vibrations. Dans la première partie, des méthodes de contrôle par action anticipatrice (feedforward) sont développées. Celles-ci sont dédiées à la suppression des perturbations bande large en utilisant une image de la perturbation mesurée par un deuxième capteur, en amont de la variable de performance à minimiser. Les algorithmes présentés dans cette mémoire sont conçus pour réaliser de bonnes performances et maintenir la stabilité du système en présence du couplage positif interne qui apparaît entre le signal de commande et l'image de la perturbation. Les principales contributions de cette partie sont l'assouplissement de la condition de « Stricte Positivité Réelle » (SPR) par l'utilisation des algorithmes d'adaptation « Intégrale + Proportionnelle » et le développement de compensateurs à action anticipatrice (feedforward) sur la base de la paramétrisation Youla-Kučera. La deuxième partie de la thèse concerne le rejet des perturbations bande étroite par contre-réaction adaptative (feedback). Une méthode d'adaptation indirecte est proposée pour le rejet de plusieurs perturbations bande étroite en utilisant des filtres Stop-bande et la paramétrisation Youla-Kučera. Cette méthode utilise des Filtres Adaptatifs à Encoche en cascade pour estimer les fréquences de perturbations sinusoïdales puis des Filtres Stop-bande pour introduire des atténuations aux fréquences estimées. Les algorithmes sont vérifiés et validés sur un dispositif expérimental disponible au sein du département Automatique du laboratoire GIPSA-Lab de GrenobleIn this thesis, solutions for the design of robust Active Vibration Control (AVC) systems are presented. The thesis report is composed of two parts. In the first one, feedforward adaptive methods are developed. They are dedicated to the suppression of large band disturbances and use a measurement, correlated with the disturbance, obtained upstream from the performance variable by the use of a second transducer. The algorithms presented in this thesis are designed to achieve good performances and to maintain system stability in the presence of the internal feedback coupling which appears between the control signal and the image of the disturbance. The main contributions in this part are the relaxation of the Strictly Positive Real (SPR) condition appearing in the stability analysis of the algorithms by use of “Integral + Proportional” adaptation algorithms and the development of feedforward compensators for noise or vibration reduction based on the Youla-Kučera parameterization. The second part of this thesis is concerned with the negative feedback rejection of narrow band disturbances. An indirect adaptation method for the rejection of multiple narrow band disturbances using Band-Stop Filters (BSF) and the Youla-Kučera parameterization is presented. This method uses cascaded Adaptive Notch Filters (ANF) to estimate the frequencies of the disturbances' sinusoids and then, Band-stop Filters are used to shape the output sensitivity function independently, reducing the effect of each narrow band signal in the disturbance. The algorithms are verified and validated on an experimental setup available at the Control Systems Department of GIPSA-Lab, Grenoble, France
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Luboya, Silhady Tshitende. "Response of Footbridges equipped with TLD : A numerical and experimental assessment." Thesis, KTH, Bro- och stålbyggnad, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-278563.
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In recent years, an increase to design slender and aesthetically-pleasing structures have resulted in some structures having a low natural frequency. This is because the design calculation did not meet the requirement of serviceability performance. Structures can experience excessive vibrations when they are subjected to different types of dynamic loading. A device can be installed to prevent these vibrations.In this thesis, we study the response of buildings and lateral vibrations of footbridges equipped with Tuned Liquid Damper. The aim is to mitigate the first mode of vibration. Tuned Liquid Damper consists of a container in rectangular, cylindrical or arbitrary shape partially filled with shallow liquid, most often water is used as a regulating device system. The design properties of Tuned Liquid Damper is introduced and it is based on the analogyof the most popular damper, Tuned Mass Damper.An experimental study of a building frame model with four floors is conducted to validate the numerical results obtained from the simulation of the model in ANSYS. The linear and non-linear analysis are performed through a system coupling between Ansys mechanical and Fluent solver. The simulation results obtained are in good agreement with the experimental results.A parametric study is conducted with a simply supported steel footbridge. It is a 45 m long span with 3 m width and the flexural rigidity is modified to get the lateral vibration mode. The first lateral natural frequency obtained is 0.713 Hz. The load case for the study considered is according to Sétra guide. The variable parameters studied is the Tuned Liquid Damper water mass ratios: 0.7%, 1.0%, 2.0%, 3.0% and 4.0%. The results show a satisfactory performance of the footbridge model equipped with Tuned Liquid Damper. The accelerations are below 0.1 m/s2 which satisfied the requirement of 0.15 m/s2.
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Ghienne, Martin. "Conception et caractérisation de liaisons boulonnées pour la réduction robuste de vibrations de structures." Thesis, Paris, CNAM, 2017. http://www.theses.fr/2017CNAM1146/document.
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La conception des structures assemblées nécessite de disposer d'outils de simulation prédictifs permettant de minimiser les écarts entre les comportements réel et simulé de ces structures. Et ce, d'autant plus que les exigences en terme de performance du système sont élevées et qu'une conception optimale est recherchée. Lors du dimensionnement des structures assemblées, la pratique généralement adoptée en bureau d'étude consiste à définir un coefficient de sécurité permettant de tenir compte de la variabilité du comportement réel de ces structures. L'inconvénient est de conduire nécessairement à un surdimensionnement qui peut aller à l'encontre des objectifs de dimensionnement optimal de ces structures. Les liaisons sont le siège de phénomènes non-linéaires tels que le contact ou le frottement et différentes sources d'incertitude induisent une variabilité sur les caractéristiques dynamiques réelles des liaisons. Malgré les capacités des calculateurs actuels, la prise en compte conjointe des phénomènes non linéaires et des incertitudes lors de la simulation de structures assemblées complexes reste difficilement envisageable par une approche directe. L'objectif de ce travail est de proposer une approche pragmatique de caractérisation du comportement vibratoire des structures légères assemblées en tenant compte de la variabilité des paramètres des liaisons. L'intérêt de cette approche est de pouvoir être intégrée dans une phase de dimensionnement robuste. On peut ainsi envisager de dimensionner une solution d'amortissement des vibrations d'une structure assemblée en tenant compte de la variabilité du comportement réel des liaisons de cette structure. Ce travail étudie d'abord le comportement dynamique d'une structure légère réelle afin d'identifier un modèle nominal «juste suffisant» des liaisons considérées. Une approche non intrusive de caractérisation du comportement vibratoire d'une structure en présence de paramètres incertains est ensuite proposée. Cette approche, intitulée approche SMR (pour Stochastic Model Reduction), exploite le fait que la variabilité des vecteurs propres d'une structure est généralement d'un ordre de grandeur inférieur à la variabilité des fréquences propres associées ce qui permet de réduire considérablement le coût de calcul de l'approche tout en gardant une bonne précision sur l'estimation des fréquences propres aléatoires de la structure. Le principe de l'approche est alors d'adapter la modélisation stochastique à chaque fréquence propre aléatoire en fonction d'une exigence de précision globale sur l'ensemble des fréquences propres aléatoires recherchées. Le point clé de cette approche consiste à identifier le modèle stochastique adapté à chaque configuration de fréquence propre, pour cela un indicateur sans coût de calcul supplémentaire est proposé. Finalement, un modèle stochastique des liaisons de la structure considérée est proposé et l'approche SMR est utilisée dans un processus d'optimisation basé sur le principe du maximum de vraisemblance pour identifier les paramètres de ce modèle. Cette dernière étape de la démarche proposée permet alors de caractériser le comportement vibratoire de structures assemblées constituées de nombreuses liaisons en tenant compte de la variabilité du comportement de chacune des liaisons. La démarche mise en place dans le cadre de cette thèse est alors concrétisée par la proposition d'une stratégie originale de réduction robuste des vibrations d'une structure assemblée légèrePredictive models are needed to properly design assembled structures. The main issue with this kind of structure is to deal with non-linear phenomena as contact or friction while considering sources of uncertainties mainly responsible for the deviation between the effective behavior of the structure and results from deterministic simulations. This work aims to provide a pragmatic approach to characterize the vibrational behavior of light assembled structures considering the variability of parameters of the joints. This approach would be useful for robust design of solutions, such as solutions for damping vibrations, dedicated to assembled structures and taking into account the variability of the real behavior of each joint.In this work, the dynamical behavior of an actual light structure is studied in order to identify a "just sufficient" nominal model of the considered joints. A non intrusive approach is then proposed to reduce the vibrational stochastic model of a structure with random parameters is then proposed. This approach, referred as the SMR approach (for Stochastic Model Reduction approach), takes advantage of the order of variability of random eigenvectors which is usually lower than the variability of corresponding random eigenfrequencies. It then allows to significantly reduce the computational cost for a given accuracy to estimate the structure random eigenfrequencies. The cornerstone of this approach is to adapt the stochastic modeling to each random eigenfrequency depending on a global accuracy requirement on the whole set of sought random eigenfrequency. The key point is then to identify the stochastic model used for each configuration of random eigenfrequency. A computationally free indicator is then proposed. Finally, a stochastic mechanical model of the joints of the studied structure is proposed. The SMR approach is used in an optimization process based on the maximum likelihood principle to identify the parameters of this stochastic model. This last step allows to characterize the vibrational behavior of assembled structures involving many joints taking into account the variability of each joints. This work is then concluded by applying the proposed approach to the design of an original strategy for robust reduction of vibration of light structures
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Sternchüss, Arnaud. "Multi-level parametric reduced models of rotating bladed disk assemblies." Phd thesis, Ecole Centrale Paris, 2009. http://tel.archives-ouvertes.fr/tel-00366252.
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Les disques aubagés, que l'on trouve dans les turbomachines, sont des structures complexes dont le comportement vibratoire est généralement déterminé par l'exploitation de conditions de symétrie dans leur configuration nominale. Cette symétrie disparaît lorsque l'on assemble plusieurs de ces disques pour former un rotor ou que l'on introduit une variabilité spatiale des paramètres mécaniques (on parle de désaccordage intentionnel ou non). Le raffinement des maillages, nécessaire à une évaluation correcte de la répartition des contraintes, conduirait à des modèles de rotor complet de taille prohibitive (plusieurs dizaines de millions de degrés de liberté). L'objectif de cette thèse est donc l'introduction de méthodologies de réduction qui par combinaison de calculs acceptables permettent d'étudier de façon fine la dynamique d'ensemble sur des modèles 3D fins multi-étages et potentiellement désaccordés. L'étude des transformations de Fourier séparées des réponses de chaque étage permet, dans un premier temps, de bien comprendre les effets de couplage inter-harmonique liés au couplage inter-disque et au désaccordage. A partir de ce constat, une première méthode utilise les résultats de calculs en symétrie cyclique et à secteur encastré pour construire un modèle de secteur exact pour certains modes dits cibles et de très bonne qualité pour les autres modes. Cette méthode est ensuite étendue au cas multi-étage en construisant des bases de réduction de secteur par combinaison de solutions mono-harmoniques. Les illustrations montrent que la méthodologie proposée permet le traitement de modèles de très grande taille, tout en restant compatible avec une grande richesse de post-traitements (calculs de modes, calculs de réponses forcées, analyses de leur contenu harmonique spatial, répartition d'énergie et effets de localisation...). La méthodologie est enfin étendue à la gestion de modèles paramétrés en vitesse de rotation. L'enrichissement des ensembles de modes cibles par des calculs à trois vitesses permet ainsi une reconstruction rapide de l'évolution des fréquences pour l'ensemble d'un intervalle.
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Silva, Demian Gomes da. "Vibrações ressonantes não-lineares em estruturas tipo viga sob excitação paramétrica e combinada." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/18/18135/tde-06112006-091532/.
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Desenvolve uma pesquisa em dinâmica estrutural não-linear com enfoque teórico e experimental direcionada para uma importante classe de estruturas flexíveis. É motivada pelos novos requerimentos das indústrias em termos de inovações, das agências certificadoras em termos de segurança e conforto e, por restrições relativas ao meio ambiente cada vez mais severas. Como conseqüência, o cenário atual e os desafios da engenharia moderna são bem diferentes daqueles encontrados antigamente. Atualmente as estruturas são mais flexíveis e operam sob condições cada vez mais severas. O aumento da flexibilidade torna as não-linearidades mais ativas e, juntamente com a ação de diferentes formas de excitação, produzem um cenário dinâmico complexo. Neste cenário, diversos fenômenos dinâmicos intrinsicamente não-lineares podem se desenvolver e conseqüêntemente comprometer a integridade estrutural, prejudicar a operação e incrementar os problemas de ruído. Tais fenômenos são altamente perigosos, principalmente por não serem previstos e nem ao menos conhecidos pela teoria dinâmica linear. Dentre estes fenômenos, a pesquisa se propõe a abordar dois: vibrações ressonantes paramétricas e autoparamétricas. Especificamente, a pesquisa investiga a influência da viscosidade do meio de operação e da presença de excitações combinadas nos fenômenos de ressonância paramétrica. No caso das ressonâncias autoparamétricas o objetivo específico é avaliar técnicas experimentais na caracterização do fenômeno, assim como, promover entendimentos mais profundos sobre suas características. Para atingir os objetivos propostos, são construídas duas estruturas de laboratório com características aeronáuticas. A primeira faz alusão a um estabilizador vertical. Nesta estrutura foram desenvolvidos os trabalhos relativos à vibração ressonante paramétrica. A segunda é uma simplificação de um sistema estrutural asa-pilone-turbina. Nesta segunda estrutura foram avaliadas técnicas experimentais para a identificação, caracterização e análise da vibração ressonante autoparamétrica. Os resultados teóricos e experimentais demonstram que a viscosidade do meio de operação age positivamente na dinâmica da estrutura, reduzindo níveis máximos de vibração em regime permanente, simplificando a dinâmica em respostas transientes e facilitando as relações de estabilidade/instabilidade. Por fim, apresenta resultados experimentais demonstrando que a energia vibratória da asa pode ser transferida por intermédio de uma ressonância autoparamétrica principal para a sub-estrutura pilone-turbina resultando em níveis extremamente elevados de vibração.This document presents results of theoretical and experimental investigations on the non-linear vibration characteristics of an important class of flexible structures. The motivation for such a study arises mainly from the increasing need for lightweight structural members. The weight reduction associated to the use of novel materials contribute to the increase of flexibility what can cause the appearance of nonlinear effects not previously observed. These nonlinear phenomena associated to the fact that, in field conditions the structure is frequently subjected to complex dynamic loads of different nature, results in a complex dynamic environment when estimation of the structure's dynamic response is concerned. Moreover, these nonlinear effects potentially may cause undesired vibration level, in some cases causing bad function and failure of the entire structure. The research is focused on studying the effects of medium viscosity as well as combined excitations on parametrically resonant vibrating structures. It is speciffically aimed characterize the phenomenons either analytically and experimentally by constructing laboratory test specimens that resemble aircraft structures. For that purpose a vertical fin is built in order to conduct experiments on the principal parametric resonance phenomenon. An analytical single degree of freedom model of this structure including nonlinear terms is derived and the results of numerically simulated results through perturbation technique are compared to experimental results obtained in the laboratory. A second structure is built that resembles a typical wing-pylon-engine substructure and it is used to study autoparametric resonance vibrations. In this case the structure is considered with multiple degrees of freedom and the results of a finite element model is correlated with experimentally obtained results. Theoretical and experimental results show that the environment viscosity affects in a significant manner the dynamic response of the structures under test, decreasing the maximum vibration levels in steady-state regime, simplifying the dynamics in transient responses and facilitating the relationship between instability/stability. At the end, it is shown experimental results demonstrating that vibratory energy from the wing substructure can be transferred by an autoparametric resonance to the substructure pylon-engine. All the experimental results do not found linear theory counterparts.
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Castellanos, Silva Abraham. "Compensation adaptative par feedback pour le contrôle actif de vibrations en présence d’incertitudes sur les paramètres du procédé." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENT050/document.
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Dans cette thèse, nous proposons des solutions pour la conception de systèmes de contrôle actif de vibration robustes (AVC). Le manuscrit de thèse comporte deux grandes parties.Dans la première, les problèmes d'incertitude paramétrique dans les systèmes de contrôle actif de vibration sont étudiés. En plus des incertitudes sur la fréquence des perturbations, nous avons trouvé que la présence de zéros complexes peu amortis soulevait des problèmes de conception difficiles, même pour des systèmes et des modèles parfaitement connus. Dans ce contexte, nous avons proposé des solutions pour le problème linéaire. Une procédure améliorée d'identification en boucle fermée a été développée pour réduire les incertitudes dans l'identification de ces zéros. Pour traiter les incertitudes sur la perturbation, l'adaptation de la fréquence est de toute façon incontournable.La seconde partie est consacrée au développement et/ou à l'amélioration de deux algorithmes, désormais classiques, de compensation par feedback adaptatif direct, fondés sur la paramétrisation de Youla-Kučera. Le premier résulte de l'amélioration d'un précédent travail (Landau et al., 2005) ; les contributions concernent la synthèse du contrôleur central robuste et l'utilisation optionnelle de la surparamétrisation du filtre Q-FIR (réponse à temps fini) avec pour effet de minimiser l'effet « waterbed » sur la fonction de sensibilité de sortie. Le second algorithme présente une structure hybride directe/indirecte qui utilise un filtre Q-IIR (à temps de réponse infini). Les améliorations sont dues principalement au dénominateur du filtre, obtenu à partir d'une estimation de la perturbation. Cette solution permet également de simplifier la conception du contrôleur central.Les algorithmes ont été testés, comparés et validés sur un procédé réel du laboratoire Gipsa-lab, dans le cadre d'un benchmark internationalIn this thesis, solutions for the design of robust Active Vibration Control (AVC) systems are presented. The thesis report is composed of two main parts.In the first part of the thesis uncertainties issues in Active Vibration Control systems are examined. In addition of the uncertainties on the frequency of the disturbances it has been found that the presence of low damped complex zeros raise difficult design problems even if plant and models are perfectly known. Solutions for the linear control in this context have been proposed. In order to reduce the uncertainties in the identification of low complex zeros and improved closed loop identification procedure has been developed. To handle the uncertainties on the disturbance frequency adaptation has any way to be used.The second part is concerned with the further development and/or the improvement of the now classical direct adaptive feedback compensation algorithms using Youla Kucera controller parametrization. Two new solutions have been proposed in this context. The first one results from the improvement of a previous work (Landau et al., 2005). The contributions are a new robust central controller design to the optional use of over parameterization of the Q-FIR filter which aims to ensure a small waterbed effect for the output sensitivity function and therefore reducing the unwanted amplification. The second algorithm presents a mixed direct/indirect structure which uses a Q-IIR filter. The improvements are mainly the effect of the Q filter denominator, which is obtained from a disturbance identification. This solution in addition drastically simplifies the design of the central controller.The algorithms have been tested, compared and validated on an international benchmark setup available at the Control System Department of GIPSA-Lab, Grenoble, France
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Janssen, Michael T. "Investigations of parametric excitation in physical systems." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Jun%5FJanssen.pdf.
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Thufvesson, Eric, and Daniel Andersson. "Dynamic Analysis of the Skyway Bridge : Assessment and Application of Design Guidelines." Thesis, KTH, Bro- och stålbyggnad, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-208685.
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In recent years the design of pedestrian bridges has become more slender. As a result the bridges has lower natural frequencies and are more prone to excessive vibrations when subjected to dynamic loads induced by pedestrians. Akademiska Hus are building such a bridge at Nya Karolinska Solna where the bridge will span over Solnavägenconnecting the hospital building, U2, and the research facility BioMedicum. Due to practical reasons, it is not possible to connect one of the bridge ends mechanicallyto the building which increases the risk for lateral modes in the sensitivefrequency range of 0-2.5 Hz. The increased risk of lateral modes of vibrations within the sensitive frequency range as well uncertainties when determining the dynamic response led to this thesis. This thesis covers a frequency analysis of the previously mention bridge and an evaluation of the dynamic response under pedestrian loading by implementation of several design guidelines. A literature review was conducted with the aim of giving a deeper knowledge of human induced vibrations and the relevant guidelines for modelling of pedestrian loading. Furthermore, a parametric study was conducted for parameters which might be prone to uncertainties in data. The investigated parameters were the Young’s modulus for concrete and the surrounding fill materialas well as the stiffness of the connection to BioMedicum. The parametric study yielded a frequency range of 2.20-2.93 Hz for the first lateral mode and 5.96-6.67 Hz for the first vertical mode of vibration. By including nonstructural mass the lower limit for the frequencies were lowered to 2.05 and 5.59 Hzin the first lateral and vertical mode respectively. The parametric study also showed that the largest impact on the natural frequencies were obtained by manipulating the parameters for the supports, both for BioMedicum and the substructure. The implementation of the guidelines resulted in a lateral acceleration between 0.05 and0.599 m/s2. No evaluation was conducted for the dynamic response in the vertical direction due to a natural frequency of 5.59 Hz, which is higher than the evaluation criteria stated in Eurocode 0. The results showed that the design of the Skyway bridge is dynamically sound with regard to pedestrian loading and no remedial actions are necessary.
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Nguyen, Phillip Huu. "An exploration of parametric excitation as a tool for vibration control." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17509.
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Jia, Yu. "The convergence of parametric resonance and vibration energy harvesting." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648834.
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Wilson, Sean O. "Nonlinear oscillations of a triatomic molecule /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Jun%5FWilson%5FSean.pdf.
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Su, Xiangrong. "Parametric vibration of composite beams with integrated shape memory alloy elements." Thesis, University of Glasgow, 2009. http://theses.gla.ac.uk/1069/.
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This research is concerned with parametric vibration in composite beam structures with shape memory alloy elements. As a precursor to this investigation, a flexible steel beam of rectangular uniform cross-section is considered with a lumped end mass under a parametric excitation. A single frequency harmonic excitation in the vertical direction is applied to the system. As an extension of previsouly developed model by Cartmell (1990) and Forehand and Cartmell (2001), three nonlinear equations of motion, representing the first and second bending modes and the first torsion modes, are derived by recourse to the Lagrangian formulation. The variables in the equations of motions are , and respectively. They are coupled together and various nonlinearities appear in the equations. The three equations are used to predict different parametric resonances of the form , , by application of the perturbation method of multiple scales. Expressions for the transition curves for the three resonances have been derived which show the regions of stable and unstable solutions in a detuning parameter-excitation amplitude plane. Very close agreement is obtained between theoretical and experimental results for all the three resonance conditions. Laboratory tests confirm that these instabilities are bounded in practice by nonlinear effects. To investigate the effects of shape memory alloy on the dynamical properties of a composite material beam structure, two shape memory alloy strips are centrally-bonded to a glass epoxy beam with a lumped end mass. The two SMA strips are theoretically pre-strained and heated up to their full austenitic phase, and shown to generate large recovery forces due to this phase transformation. The forces are considered as compressive forces, and a theoretical model is introduced to evaluate the influences of the forces on the natural frequencies and the bending modes of the composite beam structure. The results show that the increase of the forces decrease the natural frequencies and reduce the excursion of the first and second bending modes. The beam system is then subjected to a vertical excitation. In order to utilize the Lagrangian formulation once again, the generalised forces corresponding to the generalised coordinates , and are derived in terms of the SMA recovery force. The three equations of motion of the free lateral vibration of the beam system are then derived. Three different parametric resonances are also predicted. Further study shows that the increase of the magnitude of the recovery force results in an increase of the instability region. An experimental investigation is conducted on two composite beam structures and each with an end mass, one with two centrally-bonded shape memory alloy (SMA) strips and the other with two diagonally-bonded SMA strips. The study suggests that when the strips are activated, the central-strip configuration can increase the natural frequencies of the bending modes noticeably more than the diagonal-strip one under certain circumstances, whilst the diagonal-strip configuration can easily be seen to change the frequencies of the torsion modes than the central-strip set-up.
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Limam, Wafa. "Nonlinear oscillations of self-excited systems under multifrequency parametric excitation." Thesis, Virginia Tech, 1989. http://hdl.handle.net/10919/43905.
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A self·excited system with weak nonlinearities and multifrequency parametric excitation is investigated in this study. The method of multiple scales is used to analyze the system under four different resonances relating parametric excitation frequencies with the natural frequencies. In the first case, the parametric excitation frequency is approximately equal to twice the natural frequency, λ≃2ω. In the second case, the parametric excitation frequency is approximately equal to the natural frequency, λ≃ω. The third case treats a system with two parametric excitation frequencies under the condition λ₁±λ₂≃2ω. In the last case, a two-degree-of-freedom system with natural frequencies ω, and ω, is considered and the resonance λ₁+ λ₂≃ωr- ωq , is analyzed. Different parameters (the 1' load amplitudes, a detuning parameter, and a system stiffness parameter) are varied in each case and the responses obtained are presented in plots. The stability of the solutions is affected by all the parameters mentioned, especially the load amplitudes and the detuning parameter.Master of Science
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Faghidi, Hamid. "Non-parametric and Non-filtering Methods for Rolling Element Bearing Condition Monitoring." Thèse, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/30689.
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Rolling element bearings are one of the most significant elements and frequently-used components in mechanical systems. Bearing fault detection and diagnosis is important for preventing productivity loss and averting catastrophic failures of mechanical systems. In industrial applications, bearing life is often difficult to predict due to different application conditions, load and speed variations, as well as maintenance practices. Therefore, reliable fault detection is necessary to ensure productive and safe operations.
Vibration analysis is the most widely used method for detection and diagnosis of bearing malfunctions. A measured vibration signal from a sensor is often contaminated by noise and vibration interference components. Over the years, many methods have been developed to reveal fault signatures, and remove noise and vibration interference components.
Though many vibration based methods have been proposed in the literature, the high frequency resonance (HFR) technique is one of a very few methods have received certain industrial acceptance. However, the effectiveness of the HFR methods depends, to a great extent, on some parameters such as bandwidth and centre frequency of the fault excited resonance, and window length. Proper selection these parameters is often a knowledge-demanding and time-consuming process. In particular, the filter designed based on the improperly selected bandwidth and center frequency of the fault excited resonance can filter out the true fault information and mislead the detection/diagnosis decisions. In addition, even if these parameters can be selected properly at beginning of each process, they may become invalid in a time-varying environment after a certain period of time. Hence, they may have to be re-calculated and updated, which is again a time-consuming and error-prone process. This undermines the practical significance of the above methods for online monitoring of bearing conditions.
To overcome the shortcomings of existing methods, the following four non-parametric and non-filtering methods are proposed:
1. An amplitude demodulation differentiation (ADD) method,
2. A calculus enhanced energy operator (CEEO) method,
3. A higher order analytic energy operator (HO_AEO) approach, and
4. A higher order energy operator fusion (HOEO_F) technique.
The proposed methods have been evaluated using both simulated and experimental data.
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Wu, Kai. "Vibration and Stability of Continuous Systems| New Parametric Instability Analysis and Spatial Discretization Method." Thesis, University of Maryland, Baltimore County, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10841201.
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Parametric instability in a system is caused by periodically varying coefficients in its governing differential equations. Parametric instability regions of a second-order non-dispersive distributed structural system in this work are obtained using the wave solution and the fixed point theory without spatially discretizing the governing partial differential equation. The parametric instability regions are classified as period-1 and period- i (i > 1) instability regions, where the former is analytically obtained, and the latter can be numerically calculated using bifurcation diagrams. The parametric instability phenomenon is characterized by a bounded displacement and an unbounded vibratory energy, due to formation of infinitely compressed shock-like waves. Parametric instability in a taut string with a periodically moving boundary is then investigated. The free linear vibration of the taut string is studied first, and three corresponding nonlinear models are introduced next. It is shown that the responses and vibratory energies of the nonlinear models are close to those of the linear model, which indicates that the parametric instability in the linear model can also exist in the nonlinear models.
A new global spatial discretization method for one- and two-dimensional continuous systems is investigated. General formulations for one- and two-dimensional systems that can achieve uniform convergence are established, whose displacements are divided into internal terms and boundary-induced terms. For one-dimensional systems, natural frequencies, mode shapes, harmonic steady-state responses, and transient responses of a rod and a tensioned Euler-Bernoulli beam are calculated using the new method and the assumed modes method, and results are compared with those from exact analyses. The new method gives better results than the assumed modes method in calculating eigensolutions and responses of a system, and it can use sinusoidal functions as trial functions for the internal term rather than possibly complicated eigenfunctions in exact analyses. For two-dimensional systems, natural frequencies and dynamic responses of a rectangular Kirchhoff plate that has three simply-supported boundaries and one free boundary with an attached Euler-Bernoulli beam are calculated using both the new method and the assumed modes method, and compared with results from the finite element method and the finite difference method, respectively. Advantages of the new method over local spatial discretization methods are fewer degrees of freedom and less computational effort, and those over the assumed modes method are better numerical property, a faster calculation speed, and much higher accuracy in calculation of high-order spatial derivatives of the displacement.
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石田, 幸男, Yukio ISHIDA, 剛志 井上, Tsuyoshi INOUE, 軍. 劉, Jun LIU, 昭宏 鈴木, and Akihiro SUZUKI. "重力と非線形ばね特性の作用を受ける偏平軸の振動 (調和型振動と超和差型振動）." 日本機械学会, 2001. http://hdl.handle.net/2237/9053.
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Wu, Xionghua. "Vibration of Planetary Gears Having an Elastic Continuum Ring Gear." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1276524893.
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Ganine, Vladislav. "Model order reduction for prediction of turbine engine rotor vibration response in presence of parametric uncertainties." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:8881/R/?func=dbin-jump-full&object_id=92182.
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Belák, Kristián. "Určení NVH parametrů skříně převodovky." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-378021.
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This master’s thesis deals with determination of NVH parameters of the gearbox housing. Introductory part is focused on the necessary theoretical knowledge. Subsequently, it contains the modal analysis with the computational and experimental approach, which are being compared to each other. In the case of the computational approach, analysis of the influence of bolt pretension on the modal properties is also involved. The thesis continues with the harmonic analysis with the computational and experimental approach, including their mutual comparison. Based on these analyses, design modifications for improvement of the NVH parameters are designed at the end of the thesis, which are being compared to each other and to the original geometry, using the computational approach.
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Bouchner, Michal. "Určení NVH parametrů rovinné desky." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-378142.
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The aim of this thesis is examination and verification of numeric model for solving acoustics and vibration problems. Specifically, we are speaking about cast iron plate machined from gearbox. Main objectives of this work is set of experimental and numerical analysis at this simplified part with follow-up numerical model, where same analyses examining not only structure, but especially acoustic space around were performed. Due to this we were able to compare data between experimental and numerical analyses and to be able to prove or disprove functionality and limitation of numerical model.
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Tonacio, Victor Coracini. "Avaliação de propulsores navais em relação a eficiência e excitação de vibração." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/3/3135/tde-21102014-112150/.
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A escolha do propulsor é uma etapa-chave no projeto de um navio. Muito do que se espera qualitativamente do desempenho de uma embarcação implica em economia de energia, em condições de operação e habitabilidade adequadas à tripulação, e em baixo custo de manutenção dos elementos estruturais e dos equipamentos. Essas questões estão diretamente relacionadas ao aproveitamento de combustível pelo sistema propulsivo e à propagação de vibração, cabendo ao propulsor um papel significativo para a performance do navio em ambos os aspectos. Por esta razão, a dissertação propõe a avaliação de propulsores navais com respeito à excitação de vibração e à eficiência, quando atuando em esteira não uniforme. A dissertação inicia-se com uma abordagem resumida especificamente sobre os estudos já realizados sobre indução de vibração pelo propulsor focados nas chamadas forças de mancal. Em seguida, revisam-se os assuntos pertinentes ao projeto de propulsor, isto é, definição de sua geometria, de seus coeficientes de operação, e dos métodos teóricos e computacionais utilizados para estudar seu comportamento hidrodinâmico. A metodologia do trabalho fundamenta-se no estudo paramétrico da geometria do hélice, objetivando identificar a influência de cada um dos parâmetros de projeto do propulsor nos dois aspectos destacados no início. As diversas configurações geométricas são submetidas a campos de velocidades advindos de diferentes navios, que representam três grupos de embarcações (navios série 60, porta-containers e navios-tanque), com o intuito de verificar as diferentes tendências de comportamento possíveis. Para a execução computacional, elabora-se uma rotina encarregada de sistematizar o processo de alterações geométricas, encaminhar os numerosos casos à análise hidrodinâmica, realizar o processo de integração casco-hélice e o pós-processamento dos resultados. A análise hidrodinâmica citada é feita através do uso de um software comercial, que, baseado na teoria do escoamento potencial, aplica o método dos painéis para a resolução do escoamento ao redor do propulsor. Os esforços excitados pelo hélice são traduzidos em critérios objetivos, baseados na transmissão de vibração através do eixo, que, associados ao critério de eficiência propulsora e à restrição relativa à ocorrência de cavitação, avaliam os casos e identificam-se o comportamento dos parâmetros de projeto. Obtém-se, como conclusão, uma metodologia de avaliação aplicável em outros casos de propulsores e navios.The propeller choice is a key-step of the ship design. The high quality of the vessel performance requires energy economy, appropriated operating and environmental conditions for the crew, and low maintenance costs of structural elements and equipment. These questions consider directly fuel consumption by the propulsion system and the transmitted vibration, regarding the propeller an important role in the ships performance about both attributes. For this reason, the evaluation of marine propellers, regarding the induced vibration and the propulsive efficiency under a non-uniform inflow, is proposed. The study begins with a briefly state of the art about the propeller induced vibration focused in bearing forces. Then, a propeller design overview is made about subjects such as geometry definition, operation coefficients, and theoretical and computed methods for studying its hydrodynamic behavior. The methodology is based on a parametric study of the propeller geometry, in order to identify the influence of each of the propeller design parameters in both aspects highlighted in beginning. The several geometric configurations are submitted to the wake fields from different ships, that represent three groups of vessels (60 series, containers and tankers), then different tendencies of behavior can be expected. For computational execution, a routine is in charge of systematizing the process of geometrical parameterization, send the cases to the hydrodynamic analysis, make the hull-propeller integration and post process the data. The hydrodynamic analysis is compelled by a HSVA® software, which applies the panel method in the propeller flow, based on potential flow theory. The propeller induced bearing forces are converted in objective criteria, based on vibration transmission through the shaft, which, combined with the propulsive efficiency criteria and the cavitation restriction, evaluate the propeller geometric configurations. As a conclusion, a propeller evaluation methodology applicable to another kind of propeller series and wake fields is obtained.
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Didoszak, Jarema M. "Parametric studies of DDG-81 ship shock trial simulations." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Mar%5FDidoszak.pdf.
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Podolník, Adam. "Experimentální analýza dynamických parametrů kolejového roštu." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2014. http://www.nusl.cz/ntk/nusl-226628.
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In terms of deciding on the appropriate use of the railway superstructure assemblies in both the recommendations arising from the theoretical analysis (modeling), as well as recommendations obtained under static and dynamic testing of the finished product play an important role. Such tests can then be applied in the laboratory or in the field. The thesis will be devoted to operational testing of selected track grid structures in situ. For measurement purposes an appropriate measuring point will be chosen and the methodology of measurement will be proposed. In terms of track geometry sections in curves will be selected. On the basis of tests carried out dynamic parameters of structures will be determined. To their evaluation suitable mathematical system will be chosen. It assumes the use of mathematical methods in time and frequency areas. In the thesis there will also be a comparison of the parameters of the tested structures. Based on the measurements it will be a source of recommendations for the practice.
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Ratislavová, Eva. "Analýza akusticko-vibračních parametrů kolejového roštu." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-226029.
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This diploma thesis is focused on experimental measurement and acoustic and dynamic behavior analysis of railway construction with the Y – steel sleepers and their comparison with concrete sleepers. The measurements were taken in situ, in suitable sections of a railway line. These sections meet the requirements of regional railway tracks in the Czech Republic. Monitored parameters were obtained by measuring a response of testing trains and were analyzed using frequency and time analysis. Based on these evaluations, comparisons of particular constructions and their recommendations for practice were made.
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Turčíková, Hana. "Analýza akustických a vibračních parametrů od železniční dopravy." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2014. http://www.nusl.cz/ntk/nusl-226623.
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This diploma thesis is focused on operational testing of selected railway lines with different structures of superstructure. For the measurement purposes suitable measuring sections in directional curves on the rail corridors were chosen and suitable measuring methodology was designed. Based on all the tests the dynamic and acoustic parameters of tested structures were determined. For the test evaluations suitable mathematic methods in both time and frequency zone was chosen. Part of my work is also to compare the parameters of the tested structures and to make recommendations for practise.
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Ubinha, Jose Alexandre. "Estudo de metodo de identificação dos parametros de desbalanceamento e de fundação de maquinas rotativas." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263789.
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Orientador: Milton Dias JuniorDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: A identificação de um modelo preciso de fundação flexível e dos parâmetros de desbalanceamento (amplitude e fase) de um sistema girante, através das medições de vibração da máquina, tem sido alvo de constantes pesquisas e desenvolvimento ao longo das últimas décadas. A utilização de programas computacionais, cujos recursos de processamento e visualização de dados são periodicamente atualizados, proporcionou um grande avanço na área de análise de vibrações em máquinas rotativas. Neste contexto, o presente trabalho tem como objetivo a implementação e aplicação de um método híbrido numérico - experimental de determinação dos parâmetros de desbalanceamento e de fundação, que utiliza a resposta ao desbalanço medida durante a partida ou parada da máquina e um modelo numérico preciso do sistema girante. O trabalho apresenta o desenvolvimento teórico da metodologia estudada e discute os aspectos computacionais da implementação numérica do mesmo. O desempenho do procedimento de identificação é verificado numericamente através da simulação de diversos sistemas rotativos e a influência dos diversos fatores que interferem na precisão dos resultados é discutida criteriosamente. Na maioria dos casos, a metodologia apresentou resultados muito bons e verificou-se que a experiência do analista na utilização do método é importante para a obtenção de resultados confiáveis
Abstract: The identification of an accurate model of a flexible foundation and unbalance parameters (amplitude and phase) for a rotating system, through the measurement of the vibration amplitude of the machine, has been subject of frequent researches and development along the last decades. The use of computational software, in which processing resources and data visualization are periodically updated, provided a great progress in the area of vibration analysis in rotating machines. In this context, the present work aims the implementation and application of a hybrid numerical and experimental identification method for the unbalance parameters and the foundation model, through the measurement of the unbalance response during start-up or run-down of the machine and an accurate numerical model of the rotating system This work presents the theoretical development of the this methodology and discusses the computational aspects of the numerical implementation. The performance of the identification procedure is numerically verified through the simulation of several rotating systems and the intluence of many conditions that can affect the accuracy of the method is discussed in detail. In the major part of the cases, the methodology presented very good results and it was observed that the analyst experience in the utilization of method is very important for the achievement of reliable results
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica
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Pavloň, Martin. "Analýza dynamických parametrů laserových vibrometrů." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2017. http://www.nusl.cz/ntk/nusl-316221.
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This diploma thesis deals with the theoretical description of interference methods used to measure vibrations, examines main parasitic effects and analyses its contribution to achievable the resolution. In the practical part, it uses several measurements to verify the effects of the level of reflected beam, stand-off distance and speckle noise. It also proposes a practical experiment for measuring dynamic parameters and signal-noise ratio. Results show that, the noise is exponentially dependent on the level of the reflected beam. The visible maximum of the vibrometer proved to be critical in terms of time stability of the measured signal level in two of the three measurements. Results of the dynamic measurement show that, the measured deviations were not degraded or significantly disturbed by the noise signal. From the measurement of the speckle noise, it emerged that the lowest level of noise is achieved with smooth and highly reflective materials.
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Awrejcewicz, Jan, Lidiya Kurpa, and Olga Mazur. "Investigation of the parametric vibration of the orthotropic plates subjected to periodic in plane forces by multi-modal approximation and R-functions method." Thesis, NTU "KhPI", 2010. http://repository.kpi.kharkov.ua/handle/KhPI-Press/37138.
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The original method of studying parametric vibrations of orthotropic plate with complex shape is proposed. Suggested approach is based on combined application of variational methods and the R-functions theory. Using the proposed method and developed software the regular and chaotic regimes of T-shaped plate are analyzed.
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Batista, Fabiano Bianchini. "Identificação de parametros elasticos em placas finas de materiais compositos." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265472.
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Orientadores: Eder Lima de Albuquerque, Milton Dias JuniorDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Neste trabalho são abordados dois métodos para identificar constantes elásticas em materiais compósitos de aplicações estruturais. São métodos que apresentam características não destrutivas, envolvem testes simples e não requerem grandes esforços computacionais. Podem ser aplicados a materiais anisotrópicos e, conseqüentemente,a materiais isotrópicos e ortotrópicos, o que os tomam ferramentas optativas de grande auxílio ao estudo dos materiais compósitos. No primeiro método, as freqüências naturais e os modos próprios adequados, obtidos da análise moda!, serão os dados de entrada para a solução de um sistema linear de equações oriundas da equação diferencial que representa a vibração transversal de placas finas anisotrópicas sob a condição de todos os bordos livres. As constantes elásticas desta equação são os parâmetros desconhecidos e estão associadas aos devidos modos próprios de vibrar. A verificação da precisão deste método é feita baseada em simulações numéricas realizadas em um software de Elementos Finitos, Ansys 7.0, e testado experimentalmente em uma placa isotrópica de aço. O segundo método trata-se de um problema de projeto ótimo cuja solução é feita através da combinação do método dos Elementos Finitos e um método de otimização, ambos executados em um único software comercial, Ansys 7.0. A análise moda! é requerida para obtenção somente das freqüências naturais, que são variáveis utilizadas na função objetivo. A verificação do método é feita em simulações numéricas e testada experimentalmentecom a mesma placa isotrópica de aço utilizada no método anterior. Para esta placa de aço, os resultados obtidos através dos dois métodos foram muitos satisfatórios. Entretanto, com relação à placa anisotrópica utilizada, os resultados obtidos pelo segundo método não foram satisfatórios
Abstract: In this work two methods are analyzed to identify elastic constants in composite materiais of structural application. They are methods that have nondestructive eharacteristie, comprised of simple tests and don't require high computational efforts. They can be employed to anisotropic materials as well as isotropic or ortotropic materials, making them useful alternative tools to composite materiais studies. In the first method, both natural frequencies and suitable mode shapes are input data for the solution of a linear system that come from differential equation that governs the transverse vibration of a free-free thin plate. Elastic constants of this equation are unknown parameters and are associated with vibration mode shape. Numerical simulations of Finite Element software, Ansys 7.0, and experimental modal analysis indicate the accuracy of this method. The second method refers to an optimum design problem and its solution is obtained by combining both Finite Elements and optimization methods in a single eommercial software, Ansys 7.O. The modal analysis is required to obtain only the natural frequencies that are the variables used in the objective function. The second method is verified using numerical simulations and tested experimentally with the same isotropic steel plate used in the first method. Results obtained for this steel plate from both methods were highly satisfactory. In relation to the anisotropic plate, results obtained ftom the second method weren't satisfactory
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica
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Holemý, Ondřej. "Analýza dynamických parametrů železničního svršku." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2014. http://www.nusl.cz/ntk/nusl-226636.
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The masters thesis is about operational testing on selected constructions of a railway track „in situ“. There were selected two sections with and without under sleeper pads on a railway track for measurement. These measurements were evaluated then. The result is an assessment of the suitability or unsuitability for under sleeper pads for a rail transport.
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Guo, Yichao. "Analytical Study On Compound Planetary Gear Dynamics." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1312289370.
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Isaienko, Oleksandr. "Development of ultra-broadband ultrafast infrared sources and applications to nonlinear vibrational spectroscopy of interfaces." Diss., Temple University Libraries, 2011. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/141408.
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ChemistryPh.D.
Interfaces play a crucial role in the exchange of energy and matter in various physical, chemical and biological systems. A particular interest has been to study interfaces between aqueous phases and various minerals because of their importance in understanding geochemical phenomena as well as for applications such as enhanced oil recovery. The nonlinear optical technique of vibrational sum-frequency generation (SFG) spectroscopy, introduced over 20 years ago, has become a powerful tool to investigate various surfaces, in particular, mineral-water interfaces. One of the challenges of the SFG spectroscopy of aqueous surfaces is the need to tune the central frequency of relatively narrowband IR lasers through the broad range of the OH-stretch frequencies of water molecules (3000 - 4000 cm-1). We have developed a novel ultrabroadband IR laser source that generates infrared pulses in the ~2800-6000 cm-1 range (lambda~3300-1800 nm) with bandwidths Delta(nu)>1000 cm-1, and bandwidths >2000 cm-1 in the near-IR range (lambda~1000-2000 nm). Pulse front tilt of signal pulse has been corrected allowing for compression of signal pulses down to 25 fsec. Such ultrabroadband IR pulses allow us to perform SFG spectroscopy of aqueous surfaces over the entire frequency range of water molecule spectrum (extending from ~2900 cm -1 to ~3800 cm -1) simultaneously, without tuning the laser ("in one shot"). We have used this novel ultrabroadband IR source to investigate the vibrational SFG spectra of silica/water interfaces. The high signal-to-noise ratio of our spectroscopic setup has allowed us to study low-intensity features that were not studied in detail, or recognized previously in the SFG-spectroscopy investigations, including: 1) non-hydrogen bonded OH vibrations at hydrophilic silica/water interfaces; 2) combination [stretch+bend] bands of water at the silica surface appearing at ~5000-5200 cm -1. 3) Overtones of water stretching modes at silica/water interfaces. The most important conclusions from these studies are outlined below. 1. Non-hydrogen bonded hydroxyls at silica/water interface. Typically SFG-studies of mineral/water interfaces (in particular, silica/water) have focused on the most pronounced features - peaks of H-bonded hydroxyls at ~3150 and ~3450 cm -1. We have been able to systematically observe and study a weaker peak at ~3670 - 3700 cm -1. This peak becomes more pronounced as the pH of aqueous phase decreases, as well as the ionic strength increases, indicating that the hydroxyls corresponding to this spectral feature are situated in a very close proximity to the surface. Isotopic dilution experiments indicate that the 3700 cm -1 feature is not due to asymmetric OH stretches as was suggested before. Based on our results, we suggest that this spectral feature corresponds to hydroxyls of water molecules at the silica surface that cannot hydrogen bond with silanol groups because of the lower density of silanols compared to H2O. We believe this to be the first surface-specific study of non-hydrogen bonded hydroxyls at silica, a surface widely accepted as hydrophilic. 2. SFG spectroscopy of [ν(OH)+δ(HOH)] combination bands of water at silica surface. We have extended SFG spectroscopy of the interfacial hydroxyls at mineral/water surfaces into the near-IR frequency range. The studies of overtones of interfacial OH(OD) groups will provide information on the anharmonicity of such species, and thus on the energy of dissociation. In addition, the positions of the overtone frequencies of the hydroxyls are more sensitive to interactions with the environment than the fundamental stretch frequencies. Our particular focus has been to study the stretch+bend combination band nu comb nu;(OH)+delta;(HOH) of liquid water which occurs in the near-IR spectral range at ~5000-5200 cm -1. It is typically much weaker in the FTIR absorption spectra than the fundamental transitions of the OH stretches or HOH bending, similar to overtones of these modes. We have performed, what we believe to be, the first surface-specific vibrational SFG spectroscopic measurements of combination bands of water molecules at silica surfaces. SFG spectroscopy of water combination band allows access to the water bending mode (delta~1600 cm -1), which still has not been observed in sum-frequency.
Temple University--Theses
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Máca, Jiří. "Konstrukční návrh zkušebního stavu s otevřenou smyčkou toku momentu pro experimentální ověření parametrů převodových ústrojí." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-378390.
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This final diploma thesis deals with the issue of vibration and noise measurement of transmission devices. The research part describes the basic issues of noise and vibration generation, their measurement, as well as sources of vibrations in gear units. The practical part deals with the design proposal of the attachment of the experimental single-stage gearbox and the load dynamometer to the anechoic chamber including the drawings. Further, by checking the modal properties of the proposed test stand, using the finite element method, the analytical and numerical control of the torsional vibrations of the rotating parts with respect to the expected frequency ranges of use.
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Bartošová, Daniela. "Chyba převodu u čelního ozubení s přímými zuby." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-378019.
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This master’s thesis is deal with the area of determining the static transmission error in spur gears. Nowadays, around vibration and noise formation, the issue of transmission error is being discussed quite often. In the first part of this master’s thesis, there is a description of the theoretical requirements concerning the above stated issue. These theoretical requirements are further applied in parametric planning of the spur gears as well as in measuring the transmission error itself. In this master’s thesis, both the detailed description of planning the parametric model of spur gears and the strain-stress analysis may be found. These requirements are needed for calculating the transmission error. In conclusion of this master’s thesis, specific results of the static transmission error in spur gears achieved at diversifying load torque, center distance modifications as well as tip relief modifications of spur gears are being presented. The issue was solved by computation approach with the help of CAD software called Creo Parametric and FEM software called Ansys Workbench and Ansys Mechanical APDL.
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Ameyaw, Daniel Adofo [Verfasser], and Dirk [Akademischer Betreuer] Söffker. "New parametric evaluation and fusion strategy for vibration diagnosis systems and classification approaches applied to machine learning and computer vision systems / Daniel Adofo Ameyaw ; Betreuer: Dirk Söffker." Duisburg, 2020. http://d-nb.info/1218465220/34.
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Otipka, Václav. "Konstrukční návrh zkušebního stavu s uzavřenou smyčkou toku momentu pro experimentální ověření parametrů převodových ústrojí." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-378013.
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The thesis deals with the design of the experimental testing rig. Test rig is designed to measure NVH transmission parameters. First, basic knowledge of vibro-acoustic measurement is discussed. This is followed by an evaluation of the most commonly used power devices to derive real loads on measured gearboxes. In more detail, a back-to-back test rig is disassembled among other things. In the thesis are described two main components, which are composed of a connecting element and a test bench. Both components were optimized during the design due to their modal properties. Numerical modal analysis was performed in ANSYS Workbench software. The thesis also includes strength calculations performed using both numerical and analytical approaches. The indispensable result of the design work is the complete drawing documentation. Finally, measurements of vibrations and noise on the physically made connecting element assembly have been performed and subsequently evaluated.
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Czakó, Alexander. "Stanovení chyby převodu u čelního ozubení s šikmými zuby." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-433537.
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This diploma thesis primarily deals with the transmission error issue which is one of the dominant sources of vibration in gear pairs and transmission systems. The vibrations subsequently generate noise which is often subjected to increasingly stricter demands across the industry, including the automotive one. It turns out that reducing the peak-to-peak value of the transmission error has a beneficial effect on the vibro-acoustic properties of gears and gear pairs. This thesis aims to determine the transmission error under static conditions, since a gear pair with a low static transmission error is a good assumption for a low transmission error even under dynamic effects. The resulting values of the transmission error can be influenced already during the design of the gear macro-geometry. It is also suitable to apply micro-geometric adjustments – modifications to the gear teeth. For this reason, the search part of the thesis is dedicated to theoretical knowledge, especially concerning the geometry of gears, modifications of teeth and the overall transmission error and its determination. The transmission error can be determined in several ways, including a technical experiment. However, due to time and financial reasons, this is not always possible, and therefore, the possibility of using numerical simulations is offered. In this thesis, the approach using stress-strain quasi-static contact analysis using the finite element method in Ansys Workbench software is used. The advantage is, among other things, a good comparability of results. The input to the FEM analysis is 3D CAD geometry – in this case, it is specifically a helical gear pair with parallel axes. The model/assembly of this gear pair is created in PTC Creo software fully parametrically, so it is possible to generate arbitrary gear pair configurations by changing the input parameters, which significantly saves time. At the end of this diploma thesis, the stress-strain analysis of various gear configurations is evaluated, with respect to the equivalent stress and contact pressure. Furthermore, the static transmission error – its graphs and peak-to-peak values – is determined from FEM analyses for different gear geometry, including tooth modifications, and for various loading torques. Last but not least, the effects of contact/overlap ratio and centre distance are evaluated.
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Dahoo, Pierre Richard. "Sur l'intensite et l'elargissement par la pression des raies de vibration-rotation des bandes nu3, nu1 plus nu3 et nu1 plus nu3 moins 2nu2-o de 12c1602 et nu3 de 14n2160 : etude experimentale et interpretation des parametres d'elargissement au moyen." Paris 6, 1988. http://www.theses.fr/1988PA066175.
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Etude experimentale, a l'aide d'un spectrometre a reseau a haute resolution, des intensites et des parametres d'elargissement par o::(2) et n::(2), entre 296 et 198 k pour co::(2). Deduction des facteurs d'interaction rovibrationnelle de co::(2) a partir des intensites et du coefficient de variation thermique des parametres d'elargissement ( equiv. A 0,72). Calcul de l'elargissement par effet de pression, resultant des interactions collisionnelles entre molecules, a partir de modele semi-classiques pour tester les potentiels et les valeurs des parametres utilises pour les calculer: importance instable des forces a courte et moyenne portee dans l'elargissement des raies de co::(2) par o::(2) et n::(2) et des raies auto-perturbees de j eleve pour co::(2) et n::(2)o, au moyen des theories d'anderson-tsao-curnutte et de robert-bonamy; role de l'interaction entre translation et rotation, qui semblerait devoir etre prise en compte
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Widjaja, Matius Andy. "The Influence of the Recommended LRFD Guidelines for the Seismic Design of Highway Bridges on Virginia Bridges." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/31453.
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The influence of the recommended LRFD Guidelines for the seismic design of highway bridges in Virginia was investigated by analyzing two existing bridges. The first bridge has prestressed concrete girders and is located in the Richmond area. The second bridge has steel girders and is located in the Bristol area. The analysis procedure for both bridges is similar. First the material and section properties were calculated. Then the bridge was modeled in RISA 3D. Live and dead load were imposed on the bridge to calculate the cracked section properties of the bridge. The period of vibration of the bridge was also calculated. After the soil class of the bridge was determined, the design response spectrum curve of the bridge was drawn. The spectral acceleration obtained from the design spectrum curve was used to calculate the equivalent earthquake loads, which were applied to the superstructure of the bridge to obtain the earthquake load effects. Live and dead loads were also applied to get the live and dead load effects. The combined effects of the dead, live and earthquake loads were compared to the interaction diagram of the columns and moment strength of the columns. The details of the bridge design were also checked with the corresponding seismic design requirement.A parametric study was performed to explore the effects of different column heights and superstructure heights in different parts of Virginia. The column longitudinal reinforcing was increased to satisfy the bridge axial loads and moments that are not within the column interaction diagram.Master of Science
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Pan, Hong-Bin, and 潘弘斌. "Study on Cable Parametric Vibrations." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/36589153531211820928.
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碩士國立高雄大學
土木與環境工程學系碩士班
99
Cable-stayed bridges have become more and more popular in modern society due to their strong functionality and aesthetically appealing solution. In order to increase span, the addition of cable system makes the bridge more flexible and prone to vibrate under environmental and service loading such as wind, rain, traffic, and earthquake. The effects lead to significant new dynamic phenomena. In particular, high amplitude localized oscillations can arise in the stay cable. For cable stayed bridges, the global vibration amplitude of deck can be examined by wind tunnel testing. However, stay cables are very low-damped and flexible due to their length. Hence local vibrations of stay cables may be excited and are of critical importance from the safety point of view. In this paper, an analytic work is adopted to find out and to verify the mechanisms of local vibration of the stay cables subject to bridge deck excitations. A continuum model by using the analytical methods will be find out for the study of cables subjected to anchorage excitation. Finally, the effects of the non-linear planar dynamics on the stay cable are investigated by using Kao Ping Hsi cable-stayed bridge.
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Luo, Zhusan. "Parametric vibrations of traveling plates and the mechanics of washboarding in bandsaws." Thesis, 2001. http://hdl.handle.net/2429/13767.
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This thesis presents a study on the high frequency dynamic behavior of traveling plates subjected to in-plane stresses. The effects of damping, parametric and modulated excitations on the vibration characteristics of the plates are considered. The application of this work to the explanation of the mechanisms responsible for washboarding in bandsaws is presented. A high frequency mode of a traveling plate is defined using the envelope of its mode shapes. Modal analysis of a traveling plate is conducted theoretically and experimentally. The effects of the traveling speed, the in-plane stresses and the plate geometry on the natural frequencies are examined. The self-excited vibration of a smooth band subjected to lateral regenerative forces is studied and the instability regions are determined. In order to model the tooth profiles and the moving lateral cutting forces applied at the teeth of a bandsaw blade, a finite element model is built and three moving plate elements are developed. The stability of the blade is investigated based on this model. The analytical results based on the smooth band model and the finite element model are consistent with the experimental results from modal testing. The vibration responses and stability of a damped spring-mass system and a damped smooth band subjected to both parametric and modulated excitations are investigated. The maximum magnification factor corresponds to the excitation at the lowest exciting frequency due to the effect of regenerative forces. The instability regions of this system are reduced by increasing damping or decreasing regenerative forces. A kinematic model of washboarding is built based on the loci of teeth so that a washboarding pattern can be simulated and the washboarding mode can be determined by decoding the pattern. Two types of washboarding patterns are observed in the cutting tests. Type I washboarding is explained as the result caused by the modulated and forced vibration due to the displacement excitations from the guides. Type II washboarding is caused by the self-excited vibration due to the regenerative cutting forces.
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Rogers, Samuel. "Pedestrian-Induced Bridge Response: Using a modal response model to predict the vibrations of a bridge when subjected to periodic pedestrian loads." Thesis, 2010. http://hdl.handle.net/1974/5666.
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The availability and use of new materials and construction techniques are allowing bridges to be built that are longer and more slender to those that have been constructed in the past. This can cause bridges to have lower stiffness and damping, and thus be less able to resist dynamic effects. This is of special concern for pedestrian bridges, because the harmonic loads that pedestrians apply to the bridge have the potential to excite the bridge’s natural frequencies. In addition, pedestrians can be sensitive to these vibrations.
A model was developed in order to better understand the effects that a pedestrian can have on these vibration-prone bridges. The model consisted of two parts: a finite element model that used the structural data for the bridge in order to produce mass-normalized mode shapes, and a bridge-pedestrian interaction program that used the structural and modal data, along with pedestrian loading scenarios, to generate the bridge response.
A parametric study of two bridges was conducted. The bridges included: a short span bridge that would not be expected to respond excessively to pedestrian loads, and a long-span, lively bridge that had natural frequencies in the range of pedestrian loading. Many loading cases were examined by varying the following parameters: load case, number of pedestrians, damping, and pacing frequency.
The modal solution was an effective method of finding the bridge responses. It was determined that pedestrian loads can be represented by a simple constant plus sinusoidal load. The excessive vibrations of long and slender bridges could be addressed by increasing damping on susceptible modes.Thesis (Master, Civil Engineering) -- Queen's University, 2010-05-03 12:36:05.561