Made available in DSpace on 2017-07-10T17:11:51Z (GMT). No. of bitstreams: 1 Giovano Mayer.pdf: 9964402 bytes, checksum: fa8e2023cd08bf7b10d7d806375b1277 (MD5) Previous issue date: 2012-12-10 / The use of alternative sources of energy requires electromechanical conversion equipments that exhibit low installation, operating and maintenance costs. In such way, small energy resources that are not connect to the power system (PS) can be benefited by the use of squirrel-cage induction generators (IG) which show such characteristics. When operating in an isolated mode, the IG is called SEIG - Self Excited Induction Generator, and in this configuration its self excitation is promoted through the connection of appropriate capacitors to the terminals of the machine stator. The existence of self-excitation in the IG depends on the value of the capacitor connected to the stator, the mechanical velocity and the load. This work aims to study the conditions of existence of self-excitation in induction generators having in mind applications in isolated generators systems. Towards this goal, initially the conditions for the existence of self-excitation are stated in terms of appropriate parameters, units and quantities, so as to highlight its relations with the operative characteristics of the machine. It is considered that the induction generator is connected to a load that contains both reactive and active components, parameterized in terms of its rated power. The self-excitation capacitors are represented by its reactive power, called self-excitation reactive power (PRAE). Self-excitation existence regions are defined which explicitate conditions for the existence and maintenance of self-excitation over, a region of operating conditions (OR) of the generator. Through the analysis of the existence of the self-excitation over the OR and the parameterization of the PRAE and the load in terms or rated power, procedures for SEIG design are established. With these procedures, the design of the SEIG is defined by the maximum load power, the worse load power factor condition, and the minimum self-excitation speed of the generator. The process of self-excitation of the generator and the design procedures are analyzed with the aid of dynamic simulations of the SEIG complete model, including the non linear model of the magnetizing inductance representing the magnetic saturation. A laboratorial bench was developed to allow studies with asynchronous generation, in particular with the SEIG. The parameters of the generator were identified experimentally and used all along the work, especially in the dynamic simulations showed. The results were also compared with experimental data collected from self-excitation tests performed with the developed laboratory bench. / A utilização de fontes alternativas de energia requer equipamentos de conversão eletromecânica que apresentem baixos custos de implantação, operação e manutenção. Desta forma, pequenos recursos energéticos não ligados ao sistema elétrico de potência (SEP) podem ser beneficiados pelo emprego do gerador de indução (GI) com rotor em gaiola, que apresenta tais características. Quando operado de forma isolada, o GI é denominado de SEIG Self Excited Induction Generator, e nesta configuração sua autoexcitação é promovida através do acoplamento de capacitores apropriados aos terminais do estator da máquina. A existência da autoexcitação no GI depende do valor do capacitor conectado ao estator, da velocidade mecânica e da carga. Este trabalho tem por objetivo estudar as condições de existência da autoexcitação em geradores de indução visando sua aplicação em sistemas isolados de geração. Neste sentido, inicialmente as condições de existência de autoexcitação são colocadas em termos de parâmetros, unidades e grandezas apropriadas, a fim de explicitar as relações com as características operativas da máquina. Também é considerado que o gerador de indução é acoplado a uma carga que contém componentes tanto ativos quanto reativos parametrizados em termos de potência. Os capacitores de autoexcitação são representados por sua potência reativa denominada de potência reativa de autoexcitação (PRAE). São definidas regiões de existência de autoexcitação explicitando condições para a existência e a manutenção da autoexcitação em torno de regiões operativas (RO) do gerador. Através da análise da existência da autoexcitação em torno da RO e da representação da PRAE e da carga em termos de potência, são estabelecidos procedimentos de projeto do SEIG. Com estes procedimentos, o dimensionamento do SEIG fica em função da carga máxima a ser acionada, da pior condição de fator de potência da mesma e da velocidade mínima de autoexcitação do gerador. O processo de autoexcitação do gerador e os procedimentos de projeto são analisados com o auxílio de simulações dinâmicas do modelo completo do SEIG, incluindo o modelo não linear da indutância de magnetização representando a saturação magnética. Uma bancada laboratorial foi desenvolvida para possibilitar estudos com geração assíncrona, em particular com o SEIG. Os parâmetros do gerador foram levantados experimentalmente e utilizados em todo o trabalho, inclusive nas simulações dinâmicas apresentadas. Os resultados foram confrontados também com dados experimentais de testes de autoexcitação obtidos com a bancada desenvolvida.

This thesis describes an experimental investigation of the response of lean turbulent swirling flames with different degrees of premixedness (i.e. different mixture patterns) to acoustic forcing using the same burner configuration and varying only the fuel injection strategy. Special emphasis was placed on the amplitude dependence of their response. Also, the behaviour of self-excited fully premixed flames was examined. kHz OH* chemiluminescence was used to study qualitatively the heat release response of the flames, while kHz OH Planar Laser Induced Fluorescence (PLIF) was employed to understand the response of the flame structure and the behaviour of the various parts of the flame. The Proper Orthogonal Decomposition (POD) method was used to extract the dominant structures of the flame and their periodicity. In the first part of the thesis, self-excited oscillations were induced by extending the length of the duct downstream of the bluff body. It was found that the longer the duct length and the higher the equivalence ratio, the stronger the self-excited oscillations were, with the effect of duct length being much stronger. The dominant frequencies of the system were found to increase with equivalence ratio and bulk velocity and decrease with duct length. For some conditions, three simultaneous periodic motions were observed, where the third motion oscillated at a frequency equal to the difference of the other two frequencies. A novel application of the POD method was proposed to estimate the convection velocity from the most dominant reaction zone structures detected by OH* chemiluminescence imaging. For a range of conditions, the convection velocity was found to be in the range of 1.4-1.7 bulk flow velocities at the inlet of the combustor. In the second part, the response of fully premixed, non-premixed with radial fuel injection (NPR) and axial fuel injection (NPA) flames was investigated and compared. All systems exhibited a nonlinear response to acoustic forcing. The highest response was observed by the NPR flame, followed by the fully premixed and the non-premixed with axial fuel injection flame. The proximity of forced flames to blow-off was found to be critical in their heat release response, as close to blow-off the flame response was significantly lower than that farther from blow-off. In the NPR and NPA systems, it was shown that the acoustic forcing reduced the stability of the flame and the stability decreased with the increase in forcing amplitude. In the fully premixed system, the flame area modulations constituted an important mechanism of the system, while in the NPR system both flame area and equivalence ratio modulations were important mechanisms of the heat release modulations. The quantification of the local response of the various parts of the flame at the forcing frequency showed that the ratio RL (OH fluctuation at 160 Hz to the total variance of OH) was greater in the inner shear layer region than in the other parts in the case of NPR and NPA flames. In fully premixed flames, greater RL values were observed in large regions on the downstream side of the flame than those in the ISL region close to the bluff body. The ratio of the convection velocity to the bulk velocity was estimated to be 0.54 for the NPR flame, while it was found to be unity for the respective fully premixed flame. In the last part of the thesis, the response of ethanol spray flames to acoustic oscillations was investigated. The nonlinear response was very low, which was reduced closer to blow-off. The ratio RL was the highest in the spray outer cone region, downstream of the annular air passage, while RL values were very low in the inner cone region, downstream of the bluff body. Unlike NPR and fully premixed flames, in case of spray and NPA systems, it was found that forcing did not affect greatly the flame structure. The understanding of the nonlinear response of flames with different degrees of premixedness in a configuration relevant to industrial systems contributes to the development of reliable flame response models and lean-burn devices, because the degree of premixedness affects greatly the flame response. Also, the understanding of the behaviour of forced spray flames is of great interest for industrial applications, contributing to the development of thermoacoustic models for liquid fuelled combustors. Finally, the estimation of the convection velocity is of importance in the modelling of self-excited flames and flame response models, since the convection velocity affects the flame response significantly.

Orientador: Prof. Dr. Jesus Franklin Andrade Romero. / Tese ( doutorado)- Universidade Federal do ABC. Programa de Pós-Graduação em Energia, 2016.

The presented thesis is involved in the biomechanics of phonation. The aim of the thesis is to set a fluid-structure interaction between the vocal folds and air flow when the pressure from lungs reaches the physiological values. In the expected outcome the self-oscillating vocal folds should be observable with characteristics shape-shift from convergent to divergent. In theory part of the thesis is described Anatomy of the vocal tract, physiology of the human phonation, research of computational simulations, experiments and visualisation methods are described in the theory part of the thesis. In the second part, setup of computational simulation with the finite element method is presented. Besides of the fluid-structure interaction the acoustical model is set. Achieved results are presented and compared to the results in literature. Displacements are evaluated from the structural model and pressures, velocities and flow velocities are evaluated from fluid model, so as acoustics results.

<p>Predmet istraživanja prikazanih u okviru doktorske diseracije su samopobudne vibracije pri obradi glodanjem. Na osnovu detaljne analize zakonitosti nastanka samopobudnih vibracija uspostavljena je određena paralela između glodanja i mikrogkodanja, za slučajeve kada je dubina rezanja veća od radijusa rezne ivice alata. Za tako usvojene pretpostavke, razvijeni su modeli unapređene numeričke simulacije procesa glodanja i mikroglodanja. Razvijeni modeli su svestrano verifikovani, s jedne strane, u segmentima gde postoje podaci u literaturi; poređenjem sa rezultatima drugih autora, a sa druge strane poređenjem sa sopstvenim eksperimentalnim ispitivanjima. Za eksperimentalno definisanje granične dubine rezanja pri glodanju predložena je inovativna metoda tangenti, a pri mikroglodanju, imajući u vidu raspoloživu mernu opremu, metoda hrapavosti obrađene površine. Matematički modeli i eksperimentalne metode su verifikovani pri obradi tri karakteristične vrste materijala i na dva obradna sistema pri glodanju, odnosno jednom materijalu i jednom obradnom sistemu pri mikroglodanju. Rezultati istraživanja su prezentovani kroz dvanaest poglavlja čiji sadržaj se navodi u nastavku.</p><p>U prvom, uvodnom poglavlju, ukazano je na značaj istraživanja samopobudnih vibracija pri makro i mikroglodanju. Prikazana je i aktuelnost istraživanja analizom broja naučnih radova koji se bave problematikom samopobudnih vibracija u periodu od poslednjih dvadeset pet godina.<br />Kroz drugo poglavlje detaljno su prikazana dosadašnja istraživanja samopobudnih vibracija pri makroglodanju, dok su u trećem poglavlju prikazana istraživanja samopobudnih vibracija pri mikroglodanju. Izvršena je analiza uticajnih parametri na graničnu dubinu rezanja, koja predstavlja osnovni pokazatelj dinamičke stabilnosti kako makro, tako i mikroobradnih sistema.<br />Na osnovu saznanja prikazanih u okviru drugog i trećeg poglavlja u četvrtom poglavlju su definisani ciljevi i hipoteze istraživanja.<br />Matematičke metode za definisanje karte stabilnosti obradnog sistema, prikazane su u petom poglavlju. Prikazana su dva matematička modela za definisanje karte stabilnosti pri makroglodanju, model srednjeg ugla kontakta alata u zahvatu i model Furijeovih redova. Prezentovana je numerička simulacija procesa obrade glodanjem, namenjena prvenstveno za simulaciju sila rezanja. Polazeći od prethodno prikazane ideje u okviru ovog poglavlja je razvijena nova matematička metoda predikcije granične dubine rezanja - unapređena numerička simulacija procesa glodanja.<br />U okviru šestog poglavlja prikazane su eksperimentalne metode identifikacije vibracija mašina alatki, odnosno eksperimentalno određivanje modalnih parametara obradnih sistema kao i metode detekcije samopobudnih vibracija pri glodanju. U cilju definisanja granične dubine rezanja, prikazana je metoda frekventne analize vibracija pri glodanju, kao metoda koja se često koristi u savremenim eksperimentalnim istraživanjima. Međutim, i matematičke i eksperimentalne metode analize vibracija pri glodanju imaju određena ograničenja. Polazeći od prethodnog, razvijena je inovativna metoda tangenti, bazirana na ranije korišćenoj metodi u okviru Laboratorije za mašine alatke Instituta za proizvodno mašinstvo FTN u Novom Sadu, i primeni savremenih mernih sistema. Pored toga, u ovom poglavlju je eksperimentalno potvrđen uticaj samopobudnih vibracija na kvalitet obrađene površine i geometrijsku tačnost obratka.<br />Metodologija sprezanja matematički i eksperimentalno definisanih funkcija frekventnog odziva elemenata mašine alatke prikazana je u sedmom poglavlju. Prezentovane su jednačine sprezanja pomerajnih odziva matematmički definisanih funkcija frekventnog odziva alata i držača alata, bazirane na Ojlerovoj teoriji grede, sa eksperimentalno definisanom funkcijom frekventnog odziva sklopa glavnog vretena mašine alatke.<br />U okviru osmog poglavlja razvijen je matematički model sila rezanja pri mikroglodanju. Predloženi model sila rezanja, koji uzima u obzir silu trenja između leđne površine alata i obrađene površine, implementiran je u unapređenu numeričku simulaciju glodanja čime je omogućena njena primena za definisanje graničnih dubina rezanja pri mikroglodanju.</p><p>Verifikacija razvijenih numeričkih i eksperimentalnih metoda za ispitivanje vibracija pri makroglodanju je prikazana u devetom poglavlju. Sproveden je niz eksperimentalnih ispitivanja, pri kojima su određivane granične dubine glodanja pri obradi tri različita materijala obratka (Al7075, 42CrMo4 i Ti-6Al-4V) na dva obradna sistema. Na osnovu ovih ispitivanjima izvršena je verifikacija unapređene numeričke simulacije glodanja i inovativne metode tangenti.<br />U desetom poglavlju prikazana je verifikacija metoda analize samopobudnih vibracija pri mikroglodanju. Primenom metodologije sprezanja pomerajnih odziva, definisani su modalni parametri obradnog sistema za mikroobradu, potrebni za definisanje graničnih dubina rezanja, tj. karte stabilnosti, unapređenom numeričkom simulacijom mikroglodanja. Karta stabilnosti definisana razvijenom unapređenom numeričkom simulacijom, verifikovana je eksperimentalno i poređenjem sa literaturnim izvorima.<br />U jedanaestom poglavlju data su zaključna razmatranja, kritički osvrt na ostvarene rezultate, i pravci budućih istraživanja.<br />Dvanaesto poglavlje prikazuje pregled korišćene literature, koju čini 218 referenci većim delom citirane u samom radu, a u zasebnom poglavlju dati su prilozi.</p> / <p>The subject of research presented in the doctoral dissertation are self-excited vibrations in milling. Based on a detailed analysis of the self-excited vibrations occurrence, a certain parallel has been established between macro and micromilling, for cases when the depth of cut is greater than the cutting edge radius of the tool. For such adopted assumptions, models of advanced numerical simulation of macro and micromilling processes were developed. The developed models were comprehensively verified, on the one hand, by comparison with the results of other authors, and on the other hand by comparison with own experimental results. An innovative tangent method has been proposed for the experimental definition of the cutting depth limit in milling, and the method of machined surface roughness has been proposed for micromilling, having in mind the available measuring equipment. Mathematical models and experimental methods were verified by machining three characteristic types of materials on two machining systems in macromilling, and one material on one machining system in micromilling. The results of the research are presented through twelve chapters, the content of which is listed below.</p><p>In the first, introductory chapter, the importance of the research of self - excited vibrations in macro and micromilling is pointed out. The topicality of the research is also presented by analyzing the number of scientific papers dealing with the issue of self - excited vibrations in the period of the last twenty - five years.<br />The second chapter presents in detail the previous research on self-excited vibrations during macromilling, while the third chapter presents research on self-excited vibrations during micromilling. An analysis of the influential parameters on the cutting depth limit was performed, which is a basic indicator of the dynamic stability of both macro and micromachining systems.<br />Based on the findings presented in the second and third chapters, the fourth chapter defines the goals and hypotheses of the research.<br />Mathematical methods for defining the stability lobe diagram of the machining system are presented in the fifth chapter. Two mathematical models for defining the stability lobe diagram for macromachining are presented, the model of the tool&rsquo;s mean contact angle and the model of Fourier series. Numerical simulation of the milling process is presented, intended primarily for the simulation of cutting forces. Starting from the previously presented idea, a new mathematical method for predicting the cutting depth limit has been developed within this chapter - an improved numerical simulation of the milling process.<br />In the sixth chapter, experimental methods of machine tools vibration identification are presented, ie experimental determination of machining systems modal parameters as well as methods of self - excited vibrations detection during milling. In order to define the cutting depth limit, the method of vibrations frequency analysis during milling is presented, as a method that is often used in modern experimental research. However, both mathematical and experimental methods of milling vibration analysis have certain limitations. Starting from the previous one, an innovative tangent method was developed, based on the previously developed method, used within the Laboratory for Machine Tools, Institute of Production Engineering Facultz of Technical Sciences in Novi Sad, and the application of modern measuring systems. In addition, in this chapter, the influence of self - excited vibrations on the machined surface quality and the geometric accuracy of the workpiece is experimentally confirmed.<br />The methodology of machine tool elements mathematically and experimentally defined frequency response functions coupling is presented in the seventh chapter. The displacement responses coupling equations of mathematically defined tools and tool holders FRF&#39;s (based on Euler &#39;s beam theory) with the experimentally defined FRF of the machine tool main spindle assembly are presented.<br />Within the eighth chapter, a mathematical model of cutting forces in micromilling was developed. The proposed cutting forces model, which takes into account the friction force between the reliefe tool surface and the machined surface, is implemented in an advanced numerical micromilling simulation, which enables its application to define cutting depth limit in micromilling.</p><p>Verification of the developed numerical and experimental methods for vibrations analysis during macromachining is presented in the ninth chapter. A series of experimental tests were performed, during which the cutting depth limits were determined during the milling of three different workpiece materials (Al7075, 42CrMo4 and Ti-6Al-4V) on two machining systems.<br />In the tenth chapter, the verification of the methods of analysis of self-excited vibrations during micromilling is presented. Using the methodology of coupling displacement responses, the modal parameters of the machining system for micromachining are defined, needed to define the cutting depth limits, ie. stability lobe diagram, by advanced numerical micromilling simulation The stability lobe diagram, defined by the developed advanced numerical simulation, was verified experimentally and by comparison with literature sources.<br />The eleventh chapter provides concluding remarks, a critical review of the achieved results, and directions for future research.<br />The twelfth chapter presents an overview of the used literature, which consists of 218 references, mostly cited in the paper itself.</p>

<p>This thesis experimentally investigates the geometry of a high-speed subsonic planar jet impinging orthogonally on a large, rigid plate at some distance downstream. This geometry has been found to be liable to the production of intense narrowband acoustic tones produced by self-excited flow oscillations for a range of impingement ratio, Mach number and nozzle thickness. Self-excited flows and acoustic tones were found to be generated in two distinct flow regimes: a linear regime occurring at relatively low Mach number, and a fluid-resonant regime occurring at higher Mach numbers. The linear regime has been found to generate acoustic tones exhibiting relatively low pressure amplitudes with frequencies which scale approximately linearly with increasing Mach number, and is produced by a traditional feedback mechanism, whereas tones within the fluid-resonant regime are produced by coupling between the unstable hydrodynamic modes of the jet and trapped acoustic modes occurring between the nozzle and the plate, and produce tones at significantly larger amplitudes. Coupling with these trapped acoustic modes was found to dominate the self-excited response of the system in the fluid-resonant regime, with the frequencies of these acoustic modes determining the unstable mode of the jet being excited, and with the impingement ratio of the flow having only minor effects related to the convection speed. Phase-locked PIV measurements have revealed that self-excited flow oscillations in the fluid-resonant regime are produced by a series of five anti-symmetric modes of the jet, along with a single symmetric mode occurring for small impingement ratios. The behavior of large coherent flow structures forming in the flow has been investigated and quantified, and this information has been used to develop a new feedback model, which can be used to accurately predict the self-excited flow oscillation of the jet.</p> / Doctor of Philosophy (PhD)

<p>Theoretical studies of dusty plasmas have been performed by focusing attention principally on collective phenomena and on grain motion. This thesis consists of a collection of seven published papers that explore both the collective behavior of a complex plasma system as well as the dynamics of grains in plasmas. In paper 1, a mechanism that explains the energy gain which leads to the self excited grain oscillations is theoretically formulated. The newly developed mechanism explains the observed self excited oscillations through the coupling of plasma sheath fluctuations with the electrostatic force, which holds the dust grain. In paper 2, theoretical and simulation studies have been conducted to study the vertical oscillations of dust grains that are levitated in plasma sheaths, under low pressure conditions. The oscillations were driven either by an external force or by a plasma number density modulation. The proposed model gives a full picture of the dust grains dynamics and is capable of successfully explaining the experimental observations. Paper 3 explores both theoretically and numerically the origin of the nonlinearities that lead to the observed oscillation resonances. The feature of the confining potential well which traps the grain, the influence of an electrode voltage modulation on the trapping well, and hence on the grain dynamics, and the resulting nonlinear resonances are analyzed in detail. The numerical simulations presented successfully reproduce a broad range of dynamical phenomena, including the self excited oscillations, for a range of different parameters. Paper 4 is dedicated to the analysis of the propagation of Dust Acoustic Waves (DAW) in a medium with an equilibrium dust density distribution. It has been theoretically shown that only some harmonics of the dust density distribution will influence the propagation of the DAW, thus modifying its frequency. Paper 5 presents a theoretical and numerical analysis of the excitation of higher harmonics of electrostatic dust cyclotron waves. The instability is driven by the ion and electron currents flowing along the magnetic field. The dispersion relation and the wave instability conditions have been derived, and a detailed numerical analysis has been performed. In Paper 6, we explore theoretically some cross field instabilities of low frequency, long wavelength electrostatic modes in fully and weakly ionized plasmas. It is shown that in a magnetoplasma with a transverse equilibrium dc electric field, the energy associated with the cross field motion of the plasma particles can be coupled to low frequency electrostatic waves. Paper 7 explores the properties and instabilities of low frequency electrostatic waves propagating in a current carrying magnetoplasma with equilibrium density and field aligned ion flow with a transverse gradient. The paper contains previous results as limiting cases, together with additional instabilities related to the equilibrium plasma density distribution. </p>

Theoretical studies of dusty plasmas have been performed by focusing attention principally on collective phenomena and on grain motion. This thesis consists of a collection of seven published papers that explore both the collective behavior of a complex plasma system as well as the dynamics of grains in plasmas. In paper 1, a mechanism that explains the energy gain which leads to the self excited grain oscillations is theoretically formulated. The newly developed mechanism explains the observed self excited oscillations through the coupling of plasma sheath fluctuations with the electrostatic force, which holds the dust grain. In paper 2, theoretical and simulation studies have been conducted to study the vertical oscillations of dust grains that are levitated in plasma sheaths, under low pressure conditions. The oscillations were driven either by an external force or by a plasma number density modulation. The proposed model gives a full picture of the dust grains dynamics and is capable of successfully explaining the experimental observations. Paper 3 explores both theoretically and numerically the origin of the nonlinearities that lead to the observed oscillation resonances. The feature of the confining potential well which traps the grain, the influence of an electrode voltage modulation on the trapping well, and hence on the grain dynamics, and the resulting nonlinear resonances are analyzed in detail. The numerical simulations presented successfully reproduce a broad range of dynamical phenomena, including the self excited oscillations, for a range of different parameters. Paper 4 is dedicated to the analysis of the propagation of Dust Acoustic Waves (DAW) in a medium with an equilibrium dust density distribution. It has been theoretically shown that only some harmonics of the dust density distribution will influence the propagation of the DAW, thus modifying its frequency. Paper 5 presents a theoretical and numerical analysis of the excitation of higher harmonics of electrostatic dust cyclotron waves. The instability is driven by the ion and electron currents flowing along the magnetic field. The dispersion relation and the wave instability conditions have been derived, and a detailed numerical analysis has been performed. In Paper 6, we explore theoretically some cross field instabilities of low frequency, long wavelength electrostatic modes in fully and weakly ionized plasmas. It is shown that in a magnetoplasma with a transverse equilibrium dc electric field, the energy associated with the cross field motion of the plasma particles can be coupled to low frequency electrostatic waves. Paper 7 explores the properties and instabilities of low frequency electrostatic waves propagating in a current carrying magnetoplasma with equilibrium density and field aligned ion flow with a transverse gradient. The paper contains previous results as limiting cases, together with additional instabilities related to the equilibrium plasma density distribution.

Les bruits automobiles induits par le frottement sont à l’origine de nombreuses plaintes clients et occasionnent des coûts de garantie considérables pour les constructeurs automobiles. Les objectifs de la thèse consistent à comprendre la physique à l’origine de ces bruits et proposer des méthodologies de simulation afin de les éradiquer. Un système générique est tout d’abord étudié. Ce système discret met en jeu un contact entre deux masses et une loi de frottement de Coulomb présentant une discontinuité à vitesse relative nulle. Des calculs de valeurs propres complexes de ce système linéarisé autour de sa position d’équilibre glissant sont menés et montrent la présence d’instabilités par flottement voire par divergence. Les simulations temporelles montrent quant à elles que les non-linéarités de contact permettent de stabiliser les niveaux vibratoires en cas d’instabilité selon quatre régimes distincts. De plus, malgré ses trois degrés de liberté, ce système est capable de reproduire les mécanismes de stick-slip, sprag-slip et couplage modal ainsi que les bruits de crissement, grincement et craquement rencontrés sur les systèmes automobiles. Des études paramétriques sont également présentées et mettent en avant des bifurcations de Hopf ainsi que l’effet déstabilisant potentiellement induit par l’amortissement. Des méthodologies permettant de catégoriser les réponses en termes de bruit et de mécanisme sont par la suite proposées. Les occurrences et risques de ces derniers sont alors analysés et des tendances sont dégagées. Enfin, la relation entre les bruits et les mécanismes est établie. L’attention est ensuite portée sur un système automobile particulier. Afin d’étudier son comportement crissant, les analyses de stabilité et les simulations temporelles sont désormais menées sur des modèles éléments-finis. Les simulations temporelles permettent d’observer l’établissement de vibrations auto-entretenues et d’identifier, parmi tous les modes instables prédits lors des analyses de stabilité, celui qui est réellement à l’origine de l’instabilité. L’effet du coefficient de frottement sur les motifs de coalescence et les cycles limites est également investigué. Le risque de crissement est ensuite évalué pour des conditions d’utilisation variées du système. La méthodologie, basée sur des analyses de stabilité, permet de retrouver les principaux constats expérimentaux obtenus sur banc d’essai. Le rôle des géométries et des matériaux constituant le système est également discuté. Enfin, une solution permettant de réduire de façon significative le risque de crissement est proposée. / Automotive friction-induced noises are the source of many customer complaints and lead to hugewarranty costs for car manufacturers. The objectives of the thesis are to improve the understanding ofthe physics at the origin of these noises and to propose numerical methodologies to eradicate them.A generic system is first investigated. This discrete system includes a contact between two masses anda Coulomb friction law with a discontinuity at zero relative velocity. Calculations of complex eigenvaluesof the linearized system around its sliding equilibrium position are carried out and show the presence offlutter and even divergence instabilities. Time simulations show that contact non-linearities permit tostabilize the vibrational levels in case of instability according to four distinct behaviors. Furthermore,despite its three degrees of freedom, this system is able to reproduce the stick-slip, sprag-slip and modecouplingmechanisms as well as the squeal, squeak and creak noises encountered in automotive systems.Parametric studies are also presented and highlight Hopf bifurcations as well as the destabilizing effectpotentially induced by damping. Methodologies allowing the categorization of the responses in termsof noise and mechanism are then proposed. Occurrences and risks of these noises and mechanismsare thus analyzed and trends are highlighted. The relationship between noises and mechanisms is alsoestablished.A specific automotive system is then considered. In order to study its squeal behavior, stabilityanalysis and time simulations are now carried out on finite element models. Time simulations allowto observe the establishment of self-excited vibrations and to identify, among all the unstable modespredicted by the stability analysis, the one which is actually the source of the instability. The effectof friction on the coalescence patterns and limit cycles is also investigated. The risk of squeal is thenevaluated in different operating conditions. The methodology, based on stability analysis, leads toresults in good agreement with the experimental observations. The role of geometries and materialsconstituting the system is also discussed. Finally, a solution with significantly low risk of squeal isproposed.

This thesis deals with computational modeling of curve squeal noise phenomena which occurs during cornering tight curves by trams. Lateral creep between rail and wheel and slip-stick phenomena leads to self-excited vibrations of the wheel which, therefore, emits unpleasant high-pitched noise. Two FEM models in frequency domain are carried out. First model is based on prestressed modal analysis. Due to unsymmetric stiffness matrix, unstable eigenvalues can occur. It is assumed that self-excited vibrations occurs on frequencies corresponding to that eigenvalues. Second model uses harmonic response analysis. It examines vibrations of the wheel excited by lateral creep force acting in contact region. This force is obtained externally by simple time-domain model. Results from harmonic response are used consequently for noise radiation computation.