ABSTRACT The flow-induced vibrations of tubes in a rotated triangular array subject to cross flow are investigated numerically and experimentally. The parameters are inlet velocity of cross flow, number of tube, and tube natural frequency. In the study, the instantaneous fluid forces on tube surfaces are computed numerically, the instantaneous displacement of the tubes due to the fluid forces is calculated, and thus the motions of the tubes in cross flow are described. Experiments are also conducted to compare the numerical results. The tube vibrations in a water tunnel are measured by two accelerometers. The amplitudes, spectra, and trace of tube motion are presented. The critical velocities of tube vibrations are then determined. Experimental results show that some tubes vibrate seriously when the flow velocity increases up to a critical value, and hysteresis of the tube vibrations is observed. In case of the seven-tube array, the tubes in the fourth row exhibit the most serious vibration. When the flow velocity is above the critical value, only one dominant frequency of the tube vibrations is detected, comparing to multiple dominant frequencies in subcritical condition. Furthermore, the tube in supercritical condition behaves like a limit cycle, especially when the natural frequency is equal to or near the vortex shedding frequency from the upstream tubes. It is also shown that the critical velocity decreases with more surrounding tubes in the upstream and does not change as more adjacent tubes are added in the downstream. However, the tube number seems to have no effect on the critical velocity when the tube natural frequency is far from the vortex shedding frequency.

A low-order, dynamical systems approach is applied to the modeling of flow induced vibrations of flexible cables. By combining a coupled map lattice wake model with a linear wave equation cable model, both the free response of the cable as well as the resulting wake structures are examined. This represents an extension of earlier coupled map lattice models that only modeled the wake of forced cable vibration. The validity of the model is assessed through comparisons with both Computational Fluid Dynamics models (NEKTAR spectral element code) and wake experiments. The experimental wake data was collected through the use of hot-film anemometry techniques. Eight hot-film probes were placed along the span of a flexible cable mounted in the test section of a water tunnel. Through the use of frequency domain correlation algorithms, the phase of vortex shedding was calculated along the cable span from the hot-film velocity data. Results for an elastically mounted rigid cylinder showed that the freely vibrating CML model predicted behavior characteristic of a self-induced oscillator; the maximum amplitude of vibration was found to occur at a cylinder natural frequency that did not coincide identically with the natural shedding frequency of the cylinder. Furthermore, the variation of the frequency of cylinder vibration with its natural frequency was seen to be linear. For standing wave cable responses, the freely vibrating CML model predicted lace-like wake structures. This result is qualitatively consistent with both the NEKTAR simulations and experimental results. Little difference was found between the wakes of forced and freely vibrating cables at the Reynolds number of the study $Re=100$. Finally, it was found that the freely vibrating CML could match numerical predictions of cross-flow amplitude as the cable mass-damping parameter was varied over an order of magnitude (once the CML was tuned to match results at a specific mass-damping level). In addition to providing wake patterns for comparisons with the freely vibrating CML, experimental data was supplied to a self-learning CML scheme. This self-learning CML was able to estimate the experimental wake data with good accuracy. The self-learning CML is seen as the next extension of the freely-vibrating CML model, capable of estimating unmodeled wake dynamics through the use of experimental data.

Large structures exposed to the environment such as the collinear omni and large panel communication antennas in this research suffer damage from cyclic wind, rain, hail, ice load and impacts from birds and stones. Stresses from self-weight, ice loading and wind gusts will produce deformations of the structure that will lead to performance deterioration of the antenna. In order to avoid such a case, it is important to understand the static, dynamic and aerodynamic behavior of these structures and thus optimization can be achieved. In this research the current fluid-structure interaction methods are used to model, simulate and analyze these communication antennas in order to assess whether failure would occur under service loads. The FEA models developed are verified against analytical models and/or experiments. Different antenna configurations are compared based on their capacity to minimize vibration effects, stress-induced deformations and aerodynamic loading effects.

Large structures exposed to the environment such as the collinear omni and large panel communication antennas in this research suffer damage from cyclic wind, rain, hail, ice load and impacts from birds and stones. Stresses from self-weight, ice loading and wind gusts will produce deformations of the structure that will lead to performance deterioration of the antenna. In order to avoid such a case, it is important to understand the static, dynamic and aerodynamic behavior of these structures and thus optimization can be achieved. In this research the current fluid-structure interaction methods are used to model, simulate and analyze these communication antennas in order to assess whether failure would occur under service loads. The FEA models developed are verified against analytical models and/or experiments. Different antenna configurations are compared based on their capacity to minimize vibration effects, stress-induced deformations and aerodynamic loading effects.

<p> Two phase flow induced vibrations is a field that has many inherent modelling difficulties, making research in the area challenging. In order to study the problem more closely, a two phase flow loop using Freon 11 had been designed and commissioned at McMaster University. The initial design required some modifications to make the loop as "user friendly" as possible. The final result meets this desired capability. </p> <p> The loop was designed so that research into vibrations in tube bundles could be carried out. A test section had been designed to facilitate this task. However, this design also required modifications. Additionally, new vibration monitoring instrumentation making use of light was developed to avoid the detrimental effects of Freon 11. The introduction of these items has resulted in a complete facility for the purpose of studying two phase flow induced vibrations. Preliminary experiments revealed a problem relating to tube tuning. Generally, the results are promising and some interesting new phenomena were observed as well. </p> / Thesis / Master of Engineering (ME)

The goal of this project was to develop a wind generator that utilizes the collective oscillating motion of multiple piezoelectric devices. These devices would be an alternative to rotating turbine designs for low power generation, for use in applications such as remote power generation. A series of inexpensive devices were developed that harvested energy from vortex shedding, both as independent and cooperative devices. The behavior of single devices was studied, but more interestingly, the way that multiple devices arranged together can increase power output was studied. It was shown that individual devices could harvest more energy if they were placed as specific positions relative to the vortices shed by devices upstream. Through investigating the behavior of these devices, fundamental principles of the phenomenon of vortex induced vibrations were explored. Methods were developed to measure the amplitude and frequency of these vibrations in a wind tunnel, through high speed video and correlations that were found between oscillation and power output from the piezoelectric transducers. Similarly, vortex induced vibrations were explored in an approximation of a two dimensional system in a flowing soap film.

[ES] La Interacción Fluido Estructura consiste en un problema físico en el que dos materiales, gobernados por conjuntos de ecuaciones distintas, se acoplan de diferentes formas. La investigación en el campo de la Interacción Fluido Esructura experimentó un importante desarrollo desde principios del siglo XX, de la mano del campo de la aeroelasticdad. Durante el desarrollo de la industria aeroespacial en el contexto de las guerras mundiales, el uso de materiales más ligeros (y flexibles) comenzó a hacerse obligatorio para la obtención de aeronaves con un comportamiento (y costes) aceptable. A lo largo de los últimos años, el uso de materiales de construcción cada vez más ligeros, se ha extendido al resto de campos de la industria. A modo de ejemplo, podría servir el desarrollo de trackers en la producción de energia solar; la utilización de materiales ligeros en ingeniería civil o el desarrollo de elementos constructivos de plástico en la industria del automóvil. Como consecuencia, la predicción con exactitud de las deformaciones inducidas por un fluido y, si aplica, la influencia de estas deformaciones en el propio flujo, ha adquirido una importancia vital. Este documento intenta porporcionar, en primer lugar, una profunda revisión de los métodos experimentales y computacionales que se han utilizado en este contexto en la bibliografía, así como los análisis en problemas de este tipo realizados por otros investigadores de cara a presentar una primera aproximación a la Interacción Fluido Estructura. Se verá cómo existe una importante cantidad de herramientas y metodologías aplicables a cualquier tipo de problema y para cualquier combinación de flujos y estructuras. Sin embargo, no existe una aproximación general que, en función de valores de números adimensionales, permita establecer cuáles de ellos son los de mayor importancia en este tipo de problemas. En este sentido, se llevará a cabo un completo análisis paramétrico durante el desarrollo del Capítulo 2 para establecer cuáles de ellos son de mayor importancia. Una vez se establezca la importancia de estos parámetros, se analizará un caso que es de especial interés en la industria: la aerovibroacústica. Éste es un caso particular de Interacción Fluido Estructura en el que, debido a la combinación de parámetros adimensionales, la interacción se puede considerar como prácticamente unidireccional, permitiendo extender estudios mediante un conste computacional relativamente acotado. La Aerovibroacústica y la vibroacústica se analizarán mediante la presentación de dos casos de referencia, permitiendo proponer una metodología que se podrá extender a otros problemas similares. / [CAT] La Interacció Fluid Estructura consisteix en un problema físic en què dos materials, governats per conjunts d'equacions diferents, s'acoblen de diferents formes. La investigació en el camp de la Interacció Fluid Esructura va experimentar un important desenvolupament des de principis del segle XX, de la mà del camp de la aeroelasticdad. Durant el desenvolupament de la indústria aeroespacial en el context de les guerres mundials, l'ús de materials més lleugers (i flexibles) va començar a fer-se obligatori per a l'obtenció d'aeronaus amb un comportament (i costos) acceptable. Al llarg dels últims anys, l'ús de materials de construcció cada vegada més lleugers, s'ha estès a la resta de camps de la indústria. A tall d'exemple, podria servir el desenvolupament de textit trackers en la producció d'energia solar; la utilització de materials lleugers en enginyeria civil, el desenvolupament d'elements constructius de plàstic a la indústria de l'automòbil. Com a conseqüència, la predicció amb exactitud de les deformacions induïdes per un fluid i, si escau, la influència d'aquestes deformacions en el propi flux, ha adquirit una importància vital. Aquest document intenta porporcionar, en primer lloc, una profunda revisió dels mètodes experimentals i computacionals que s'han utilitzat en aquest context en la bibliografia, així com les anàlisis en problemes d'aquest tipus realitzats per altres investigadors de cara a presentar una primera aproximació a la Interacció Fluid Estructura. Es veurà com, encara que existeix una important quantitat d'eines i metodologies aplicables a qualsevol tipus de problema i per a qualsevol combinació de fluxos i estructures, no hi ha una aproximació general que, en funció de valors de nombres adimensionals, permeti establir quins d'ells són els de major importància en aquest tipus de problemes. En aquest sentit, es durà a terme una completa anàlisi paramètric durant el desenvolupament del Capítol 2 per a establir quins d'ells són de major importància. Un cop s'estableixi la importància d'aquests paràmetres, s'analitzarà un cas que és d'especial interès en la indústria: la aerovibroacústica. Això és un cas particular d'Interacció Fluid Estructura en què, a causa de la combinació de paràmetres adimensionals, la interacció es pot considerar com pràcticament unidireccional, permetent estendre estudis mitjançant un consti computacional relativament acotat. La Aerovibroacústica i la vibroacústica s'analitzaran mitjançant la presentació de dos casos de referència, permetent proposar una metodologia que es podrà estendre a altres problemes similars. / [EN] Fluid Structure Interaction is a physical problem where two different materials, governed by different set of fundamental equation, are coupled on different ways. The research on the field of Fluid Structure Interaction experienced a noticeable growth since the beginnings of the XXth century, by means of the field of aeroelasticity. During the development of the aerospace industry in the context of first and second Wolrd War, as the use of lighter (and softer) materials became mandatory for the correct behavior (and cost savings) of the produced aircrafts. During these past years, the use of use of increasingly lighter construction materials has extended to the rest of fields of the industry. As an example, it could be mentioned the use of solar trackers on the solar energy sector; the use of light materials on civil engineering or the use of plastic for some constructive elements in the context of the automotive field. As a consequence, the accurate prediction of the deformations induced to a fluid flow over a structure and, if needed, the influence of this deformation on the fluid flow itself is becoming of primal importance. This document intends to provide with a deep review of the computational and experimental reported methodologies already available on the literature and the previous works performed by other researches in order to infer a first approximation to the Fluid Structure Interaction Problem. It will be observed how an important amount of solving methodologies is available in order to face these problems regarding with the strength of the interaction. However, a general approximation allowing to predict this strength as a function of a set of dimensional number is rarely known. In this sense, a full parametric study will be performed during the development of Chapter 2 showing which of them are of higher importance. Once the influence of these parameters is determined, a case of special interest will be analyzed: aerovibroacoustics. This, is a particular case of Fluid Structure Interaction where, due to the combination of its nondimensional parameters, one directional coupling can be supposed for most of the cases. Aerovibroacoustics and vibroacoustics will be analyzed by means of two reference cases, allowing finally to propose a methodology which could be extended for other related problems. / Quintero Igeño, PM. (2019). Characterization of Fluid Structure Interaction mechanisms and its application to vibroacoustic phenomena [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/128412 / TESIS

Computational models of the flow-induced vibrations of the vocal folds are powerful tools that can be used in conjunction with physical experiments to better understand voice production. This thesis research has been performed to contribute to the understanding of vocal fold dynamics as well as several aspects of computational modeling of the vocal folds. In particular, the effects of supraglottal geometry have been analyzed using a computational model of the vocal folds and laryngeal airway. In addition, three important computational modeling parameters (contact line location, Poisson's ratio, and symmetry assumptions) have been systematically varied to determine their influence on model output. Variations in model response were quantified by comparing glottal width, frequency, flow rate, open quotient, pressures, and wave velocity measures. In addition, the glottal jet was qualitatively analyzed. It was found that for various supraglottal geometries (either symmetrically or asymmetrically positioned), there was little asymmetry of the vocal fold motion despite significant asymmetry in the glottal jet. In addition, the vocal fold motion was most symmetric when consistent jet deflection was present (even if asymmetric). Inconsistent deflection of the glottal jet led to slightly larger asymmetries in vocal fold motion. The contact line location was found to have minimal impact on glottal width, frequency, and flow rate. The largest influence of the contact line location was seen in predicted velocity fields during the closed phase and in the pressure profiles along the vocal fold surfaces. Variations in Poisson's ratio strongly affected vocal fold motion, with lower Poisson's ratios resulting in larger amplitudes. The model did not vibrate when a Poisson's ratio of 0.49999 was used. The response of a full model (with two vocal folds) was shown to vary slightly from that of a half model (one vocal fold and a symmetry boundary condition), the greatest difference being in the deflection and dissipation of the glottal jet. It was concluded that for many scenarios the half model will be sufficient for modeling vocal fold motion; however, a full model is suggested for studies of material asymmetry or glottal jet dynamics. Application of these results to computational models of the vocal folds will lead to improved modeling and understanding of vocal fold dynamics.

No description available.

Cette thèse s’intéresse à la faisabilité de la mise en place de modèles d’ordre réduit pour l’étude des vibrations sous écoulement au sein de faisceaux tubulaires d’échangeurs de chaleur. Ces problématiques sont cruciales car les systèmes étudiés sont des éléments majeurs des centrales nucléaires civiles et des chaufferies embarquées dans les sous-marins.Après avoir rappelé le fonctionnement et les risques vibratoires existants au sein des échangeurs de chaleur, des calculs complets d’écoulement et de vibrations sous écoulement ont été effectués, d’abord pour un tube seul en milieu infini, puis pour un faisceau de tubes. Ces calculs ont été menés avec l’outil CFD Code_Saturne. La méthode de réduction de modèle POD (Proper Orthogonal De-composition) a été appliquée au cas des écoulements avec la structure laissée fixe.Les résultats obtenus montrent l’efficacité de la méthode pour ces configurations, moyennant l’introduction de méthodes de stabilisation pour l’écoulement au sein du faisceau. La méthode POD-multiphasique, permettant d’adapter la méthode POD à l’interaction fluide-structure, a ensuite été appliquée. Les grands déplacements d’un cylindre seul dans la zone d’accrochage (lock-in) ont été correctement reproduits par cette méthode de réduction de modèle. De même, on montre que les grands déplacements d’un cylindre en milieu confiné dans un faisceau de tubes sont fidèlement reconstruits.Enfin, l’extension de l’utilisation de la réduction de modèle aux études d’évolution paramétrique a été testée. Nous avons d’abord utilisé la technique considérant une base POD unique pour reproduire des écoulements à divers nombres de Reynolds autour d’un cylindre seul. Les résultats confirment la prédictivité bornée à une gamme de paramètres de cette méthode. Enfin, l’interpolation de bases POD pré-calculées pour une famille de paramètres donnés, utilisant les variétés de Grassmann et permettant de générer de nouvelles bases POD, a été testée sur des cas modèles. / The objective of this thesis is to study the ability of model reduction for investigations of flow-induced vibrations in heat exchangers tube bundle systems.These mechanisms are a cause of major concern because heat exchangers are key elements of nuclear power plants and on-board stoke-holds.In a first part, we give a recall on heat exchangers functioning and on vi-bratory problems to which they are prone. Then, complete calculations leaded with the CFD numerical code Code_Saturne are carried out, first for the flow around a single circular cylinder (fixed then elastically mounted) and then for the case of a tube bundle system submitted to cross-flow. Reduced-order method POD is ap-plied to the flow resolution with fixed structures. The obtained results show the efficiency of this technique for such configurations, using stabilization methods for the dynamical system resolution in the tube-bundle case.Multiphase-POD, which is a method enabling the adaptation of POD to fluid-structure interactions, is applied. Large displacements of a single cylinder elastically mounted under cross-flow, corresponding to the lock-in phenomenon,are well reproduced with this reduction technique. In the same way, large displace-ments of a confined moving tube in a bundle are shown to be faithfully recon-structed.Finally, the use of model reduction is extended to parametric studies. First,we propose to use the method which consists in projecting Navier-Stokes equations for several values of the Reynolds number on to a unique POD basis. The resultsobtained confirm the fact that POD predictability is limited to a range of parameter values. Then, a basis interpolation method, constructed using Grassmann mani-folds and allowing the construction of a POD basis from other pre-calculated basis,is applied to basic cases.