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Vortex-induced vibrations of a pivoted circular cylinder and their control using a tuned-mass damperKheirkhah, Sina January 2011 (has links)
Vortex-induced vibrations of a pivoted circular cylinder and control of these vibrations were investigated experimentally. A novel experimental setup was employed to reproduce orbiting response observed in some engineering applications. An adaptive pendulum tuned-mass damper (TMD) was integrated with the cylindrical structure in order to control the vortex-induced vibrations. All experiments were performed at a constant Reynolds number of 2100 for a range of reduced velocities from 3.4 to 11.3
and damping ratios from 0.004 to 0.018. For the experiments involving TMD, the TMD mass ratio was 0.087 and the TMD damping ratios investigated were 0 and 0.24. The results of the experiments performed without the TMD show that, in the synchronization region, the frequencies of transverse and streamwise vibrations lock onto the natural frequency of the structure. The cylinder is observed to trace elliptic trajectories. A mathematical model is introduced to investigate the mechanism responsible for the occurrence of the observed elliptic trajectories and figure-8 type trajectories reported in previous laboratory investigations. The results show that the occurrence of
either elliptic trajectories or figure-8 type trajectories is governed primarily by structural coupling between vibrations in streamwise and transverse directions. Four types of elliptic trajectories were identified. The results show that the occurrence of the different types of elliptic trajectories is linked to phase angle between the streamwise and transverse vibrations of the structure, which depends on structural coupling.
The results of the experiments performed to investigate effectiveness of the TMD in controlling vortex-induced vibrations show that tuning the TMD natural frequency to the natural frequency of the structure decreases significantly the amplitudes of transverse and streamwise vibrations of the structure. Specifically, the transverse amplitudes of vibrations are decreased by a factor of ten and streamwise amplitudes of vibrations are decreased by a factor of three. The results show that, depending on the value of the TMD damping ratio, the frequency of transverse vibrations is either characterized by the natural frequency or by two frequencies: one higher and the other lower than the natural frequency of the structure, referred to as fundamental frequencies. Independent of TMD damping and tuning frequency ratios, the frequency of streamwise vibrations matches that of the transverse vibrations in the synchronization region, and the cylinder traces elliptic trajectories. The phase angle between the streamwise and transverse vibrations is nearly constant when the pendulum is restrained. However, with the TMD engaged and tuned to the natural frequency, the phase angle fluctuates significantly with time. A mathematical model was utilized to gain insight into the frequency response of the structure. The results of the modeling show that the frequency of transverse vibrations is characterized by the fundamental frequency or frequencies of the structure and the frequency of streamwise vibrations is characterized by
the fundamental frequency or frequencies as well as the first harmonic of the fundamental frequency or frequencies of the structure.
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Superharmonic nonlinear lateral vibrations of a segmented driveline incorporating a tuned damper excited by non-constant velocity jointsBrowne, Michael 2009 May 1900 (has links)
Linear vibration measurement and analysis techniques have appeared to be
sufficient with most vibration problems. This is partially due to the lack of proper
identification of physical nonlinear dynamic responses. Therefore, as an example, a
vehicle driveshaft exhibits a nonlinear super harmonic jump due to nonconstant velocity,
NCV, joint excitation. Previously documented measurements or analytical predictions
of vehicle driveshaft systems do not indicate nonlinear jump as a typical vibration mode.
The nonlinear jump was both measured on a driveshaft test rig and simulated with a
correlated model reproduced the jump. Subsequent development of the applied
moments and simplified equations of motion provided the basis for nonlinear analysis.
The nonlinear analyses included bifurcation, Poincare, Lyapunov Exponent, and
identification of multiple solutions.
Previous analytical models of driveshafts incorporating NCV joints are typically
simple lumped parameter models. Complexity of models produce significant
processing costs to completing significant analysis, and therefore large DOF systems incorporating significant flexibility are not analyzed. Therefore, a generalized method
for creating simplified equations of motion while retaining integrity of the base system
was developed. This method includes modal coupling, modal modification, and modal
truncation techniques applied with nonlinear constraint conditions. Correlation of
resonances and simulation results to operating results were accomplished.
Previous NCV joint analyses address only the torsional degree of freedom.
Limited background on lateral excitations and vibrations exist, and primarily focus on
friction in the NCV joint or significant applied load. Therefore, the secondary moment
was developed from the NCV joint excitation for application to the driveshaft system.
This derivation provides detailed understanding of the vibration harmonic excitations
due to NCV joints operating at misalignment angles.
The model provides a basis for completing nonlinear analysis studying the
system in more detail. Bifurcation analysis identified ranges of misalignment angles and
speeds that produced nonlinear responses. Lyapunov Exponent analysis identified that
these ranges were chaotic in nature. In addition, these analyses isolated the nonlinear
response to the addition of the ITD nonlinear stiffness.
In summary, the system and analysis show how an ITD installed to attenuate
unwanted vibrations can cause other objectionable nonlinear response characteristics.
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Vibrations of plates with massesSolov'ëv, Sergey I. 31 August 2006 (has links) (PDF)
This paper presents the investigation of the
nonlinear eigenvalue problem describing free
vibrations of plates with elastically attached
masses. We study properties of eigenvalues and
eigenfunctions and prove the existence theorem.
Theoretical results are illustrated by numerical
experiments.
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Modélisation du frottement en pied d'aube par une approche fréquentielleNacivet, Samuel Jézéquel, Louis January 2002 (has links) (PDF)
Thèse de doctorat : sciences. Mécanique : Ecully, Ecole centrale de Lyon : 2002. / 103 réf.
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Extension et reformulation du modèle SEA par la prise en compte de la répartition des énergies modalesMaxit, Laurent Guyader, Jean-Louis. January 2001 (has links)
Thèse doctorat : Acoustique : Villeurbanne, INSA : 2000. / Titre provenant de l'écran-titre. Bibliogr. p. 213-223.
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Modélisation numérique de matériaux poreux hétérogènes application à l'absorption basse fréquence /Castel, Franck Atalla, Noureddine. Sgard, Franck. January 2006 (has links)
Thèse doctorat : Acoustique : Villeurbanne, INSA : 2005. Thèse doctorat : Acoustique : Université de Sherbrooke (Canada) : 2005. / Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre. Bibliogr. p. 197-202.
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Dissipation de l'énergie en mécanique vibratoire opérateur d'hystérésis, phénomène métrique /Al Majid, Ahmad Dufour, Regis. January 2004 (has links)
Thèse de doctorat : Génie mécanique : Villeurbanne, INSA : 2002. / Titre provenant de l'écran-titre. Bibliogr. p.138-149.
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Contribution au diagnostic industriel de défauts de roulement et de balourd par techniques neuronales application à la machine asynchrone à cage /Diouf, Saliou Madani, Kurosh. January 2007 (has links) (PDF)
Thèse de doctorat : Sciences de l'ingénieur. Génie informatique, automatique et traitement du signal : Paris 12 : 2007. / Titre provenant de l'écran-titre. 188 p. Bibliogr. : 36 réf.
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Localisation et quantification des sources vibratoires dans le cadre d'une maintenance préventive conditionnelle en vue de fiabiliser le diagnostic et le suivi de l'endommagement des composants mécaniques tournants : application aux roulements à billesChiementin, Xavier Dron, Jean-Paul January 2007 (has links) (PDF)
Reproduction de : Thèse doctorat : Mécanique : Reims : 2007. / Titre provenant de l'écran titre. Bibliogr. f. 153-159.
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Modélisation du frottement en pied d'aube par une approche fréquentielleNacivet, Samuel Jézéquel, Louis January 2002 (has links) (PDF)
Thèse de doctorat : sciences. Mécanique : Ecully, Ecole centrale de Lyon : 2002. / Titre provenant de l'écran-titre. 103 réf.
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