Thèses : « Acoustic wave control in water »

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Kourchi, Hasna. « Μétaréseaux pοur la réflexiοn et la transmissiοn anοrmales de frοnts d’οnde acοustique dans l’eau ». Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMLH36.

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Un métaréseau est un assemblage périodique de diffuseurs conçu pour réfléchir ou réfracter une onde vers une direction anormale, non prévue par les lois de Snell-Descartes. Dans ce travail, nous avons conçu, fabriqué et caractérisé expérimentalement de tels métaréseaux pour le contrôle des ondes ultrasonores dans l’eau, en utilisant des tubes et des cylindres en laiton ainsi que des supports plastiques imprimés en 3D. Ces métaréseaux permettent de rediriger un front d'onde incident vers une direction arbitraire souhaitée, avec une efficacité élevée (proche de 100 %), aussi bien en réflexion sur une surface (comme l’interface eau/air) qu'en transmission. L’approche théorique repose sur les principes de la diffraction de Bragg et sur les interactions constructives et destructives des ondes. Les résultats de cette thèse démontrent l'efficacité des métaréseaux à induire des phénomènes acoustiques tels que la rétro-réflexion et la réponse asymétrique, grâce à l’utilisation de structures résonantes et non résonantes, validées par des simulations par éléments finis et des expérimentations. Cette recherche ouvre de nouvelles perspectives pour la manipulation des ondes acoustiques sous-marines, avec des applications potentielles dans les domaines de la détection, de l'absorption et de la réflexion des ondes en milieu marin
A metagrating is a periodic assembly of scatterers designed to reflect or refract a wave toward an anomalous direction, not predicted by Snell's law. In this work, we designed, fabricated, and experimentally characterized such metagratings for the control of ultrasonic waves in water, using brass tubes and cylinders as well as 3D-printed plastic supports. These metagratings enable the redirection of an incident wavefront to an arbitrarily desired direction with high efficiency (close to 100%), both in reflection on a surface (e.g., the water/air interface) and in transmission. The theoretical approach is based on the principles of Bragg diffraction and constructive and destructive wave interactions. The results of this thesis demonstrate the efficiency of metagratings in inducing acoustic phenomena such as retroreflection and asymmetric wave response, achieved through the use of resonant and non-resonant structures, validated by finite element simulations and experiments. This research opens new perspectives for the manipulation of underwater acoustic waves, with potential applications in the fields of wave detection, absorption, and reflection in marine environments

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Awodele, M. Kofoworola. « Control of charge transports in semiconductor superlattices using an acoustic wave ». Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/16738.

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In this work, we describe the electron dynamics in semiconductor superlattices (SLs) when driven by an acoustic wave. First, we discuss the physical features and structure of SLs. Then we describe semiclassical transport in periodic potential driven by a plane wave, and the dynamics of ultracold atoms in the periodic potentials. Secondly, we explore single electron dynamics in superlattices driven by an acoustic wave, then present and analyse the types of electron trajectories according to the strength of the acoustic wave amplitude. The two dynamical regimes obtained depend on the wave amplitude strength and the initial position of electrons in the acoustic wave. The frequency range of the oscillation produced can be as large as terahertz. Lastly, we discuss the effect of applying a static electric field to the acoustically driven SLs. When the acoustic wave and electric fields were applied together along the axis of SLs, we obtained a higher peak drift velocity than when the acoustic wave or electric fields were applied alone. We use the phase portrait to explain the electron trajectory and the path of the electrons. The global state associated with the drastic change in the drift velocity of the electrons depends on the varied parameters in the dynamical systems. We numerically calculate the electron trajectories while we varied the strength of electric field and wave amplitude to investigate the role of interactions in the system. When very high electric field and very high wave amplitude are applied together along the axis of SL, global catastrophe occurs. This is the discontinuous bifurcation in dynamical system.

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Turnbull, Katharine Frances Vogan. « A surface acoustic wave frost point hygrometer for measurements of atmospheric water vapour ». Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619580.

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葉子良 et Tsz-leung Yip. « Active water-wave control by a submerged pitching plate ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31237976.

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Yip, Tsz-leung. « Active water-wave control by a submerged pitching plate / ». Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19003067.

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Eden, L. « Measurements of atmospheric water vapour using a balloon-borne surface acoustic wave frost point hygrometer ». Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598746.

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A frost point hygrometer is described in this thesis which uses surface acoustic waves (SAWs) to detect water vapour condensation. The SAW device crystal is cooled by a thermoelectric cooler until condensation occurs, at which point, water vapour loading onto the SAW device causes changes in the SAW velocity and amplitude. Two methods of determining the frost point temperature are outlined in this thesis. The first uses a feedback loop algorithm to maintain a constant amount of water vapour on the SAW device and hence keep the temperature of the device at the frost point. The second uses heating and cooling cycles to oscillate the SAW device temperature above and below the frost paint. Changes in the SAW properties are then used to detect the condensation-evaporation equilibrium point which is equal to the frost point. The use of SAWs rather than a conventional optical detection system in this hygrometer allows a faster response time, increased sensitivity, and decreased risk of contamination. Between September 2001 and February 2004, the SAW hygrometer was flown on 28 balloon flights, in various configurations. All of these flight data sets show agreement with radiosonde relative humidity measurements to within 1%, using given criteria for extraction of reliable SAW hygrometer measurements. Accurate lower and mid tropospheric measurements have been made on each flight and four flights show accurate upper tropospheric and lower stratospheric measurements with water vapour mixing ratio values of less than 5 ppmv. The Hibiscus campaign flights in Bauru, Brazil, show excellent agreement between the different instruments measuring water vapour on the flight train and the SAW hygrometer. These data are discussed in conjunction with auxiliary data and model backward trajectories. Two different backward trajectory models have been used to assess the possible mechanisms of transport of water vapour above Bauru, one of which is a large scale model and the other is a meso-scale model. A sharp contrast in the air parcel transport above and below the tropical tropopause layer (TTL) is seen, with large scale convection or descent controlling the water vapour mixing ratios below the TTL, and a combination of large and small scale fields controlling the water vapour in and above the TTL.

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Chen, Feng. « Effect of mesoscale variability of water masses on acoustic wave propagation in a shallow sea ». Thesis, University of Plymouth, 2015. http://hdl.handle.net/10026.1/3219.

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Anthropogenic noise in the sea is now classed as a pollutant alongside chemical pollution and marine litter in accordance with the Marine Strategy Framework Directive. Noise from shipping is a major contributor to the ambient noise levels in the ocean, particularly at low (<300Hz) frequencies. The properties of sound propagation in shallow waters are highly influenced by the marine physical environment. Ocean modelling plays an important role in underwater noise studies since it can provide high resolution water column parameters over large geographic areas. This study investigates the noise patterns and their temporal variations in the Celtic Sea by using a coupled ocean model (POLCOMS) and an acoustic model (HARCAM). A method to predict noise exposure experienced by marine animals is then developed, following an application for diving seals. The ocean model is applied in the Celtic Sea to provide high-resolution 3D hourly temperature and salinity fields for the acoustic model. The model is validated against in-situ and satellite observations, giving high skills to simulate the water column structures. Sensitivity studies of modelled results to different atmospheric forcing are carried out in order to improve the accuracy of the model. The results show that the modelled sea surface temperature, stratification and water column structures are highly sensitive to the choice of surface forcing, especially in the summer time. The increase in resolution of surface forcing does not necessarily lead to more accurate results. The tidally frontal position is, however, insensitive to the forcing. The variability of noise propagation is studied using the coupled model, demonstrating high dependence on oceanographic conditions, geographic location of sound source and its depth. In summer, when the source of sound is on the inshore side of the bottom front, the sound energy is mostly concentrated in the near-bottom layer. In winter, the sound from the same source is distributed more evenly in the vertical. When the source is on the seaward side of the front, the sound level from a shallow source is nearly uniform in the vertical and the transmission loss is significantly greater (~16dB at 40km distance) in summer than in winter. In contrast, sound energy from a deep source is trapped in the bottom cold water, leading to a much lower transmission loss (~20dB) in summer than in winter. Note that ~10dB fluctuation of sound energy is found during the deterioration of the thermocline in late autumn. Shallow sources (e.g. ships) are sensitive to the surface heat flux as it changes significantly the vertical temperature gradient, while tides play an important role in determining the TL variability of deeper sources (e.g. pile driving) since they cause adjustments of positions of subsurface fronts. The seasonal noise patterns radiated by a large cargo ship are modelled by relating the AIS ship track data and the coupled model, showing a clear influence of the seasonal thermocline and associated bottom fronts on shipping noise distribution. The noise propagates much further (tens of kilometres) in winter than in summer. The predicted shipping noise exposure perceived by grey seals shows strong step changes in the sound level during their descent/ascent through the water column. Since grey seals tend to be benthic foragers, a hypothesis that the step change in sound exposure may have negative impacts on their foraging behaviour is proposed for biological specialists.

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Buck, John R. (John Richard). « Single mode excitation in the shallow water acoustic channel using feedback control ». Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/40604.

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López, Ríos Juan Carlos. « Water-wave equations and free boundary problems : inverse problems and control ». Tesis, Universidad de Chile, 2015. http://repositorio.uchile.cl/handle/2250/135179.

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Doctor en Ciencias de la Ingeniería, Mención Modelación Matemática
En este trabajo se aborda el problema de existencia de algunos tipos de soluciones para las ecuaciones de ondas en el agua así como la relación que existe entre estas soluciones y la forma de un fondo impermeable sobre la que se desliza el fluido. Empezamos por describir las ecuaciones que modelan el fenómeno físico a partir de las leyes de conservación; el modelo general de las ecuaciones de ondas en el agua, escrito para la restricción de la velocidad potencial a la superficie libre, es \begin{equation*} \left\{ \begin{aligned} &\partial_t\zeta-G(\zeta,b)\psi=0, \\ &\partial_t\psi+g\zeta+\frac{1}{2}|\nabla_X\psi|^2-\frac{1}{2(1+|\nabla_X\zeta|^2)}(G(\zeta,b)\psi+\nabla_X\zeta\cdot\nabla_X\psi)^2=0, \end{aligned} \right. \end{equation*} donde $G=G(\zeta,b)\psi$ es el operador Dirichlet-Neumann, el cual contiene la información del fondo $b$, \begin{equation*} G(\zeta,b)\psi:=-\sqrt{1+|\nabla_X\zeta|^2}\partial_n\phi|_{y=\zeta(t,X)}, \end{equation*} y \begin{equation*} \left\{ \begin{array}{rl} & \Delta\phi=0, \quad \R\times(b,\zeta), \\ & \phi|_{y=\zeta}=\psi, \quad \partial_n \phi|_{y=b(X)}=0. \end{array} \right. \end{equation*} Después de describir las condiciones para un teorema de existencia y unicidad de soluciones de las ecuaciones de ondas en el agua, en espacios de Sobolev, nos preguntamos sobre el mínimo de datos necesarios, sobre la superficie libre, para identificar el fondo de manera única. Por la relación que existe entre el operador Dirichlet-Neumann y la velocidad dentro del fluido y utilizando la propiedad de continuación única de las funciones armónicas hemos probado que basta conocer el perfil, la velocidad potencial y la velocidad normal en un instante de tiempo dado y un abierto de $\R$, aún cuando nuestro sistema es de evolución. En la segunda parte se estudia la existencia de soluciones en forma de salto hidráulico para las ecuaciones estacionarias de ondas en el agua, en dimensión dos y su relación con la velocidad aguas arriba, caracterizada por un parámetro adimensional, llamado el número de Froude, $F$, como consecuencia de la existencia de ramas de bifurcación de la solución trivial para el problema \begin{equation*} \mathcal{F}(\eta,F)=\eta+F\widetilde{\psi}_{y^{\prime }}+\frac{\epsilon}{2}(% \widetilde{\psi}_{x^{\prime }}^2+\widetilde{\psi}_{y^{\prime }}^2)-\epsilon^2\eta_x\widetilde{\psi}_{x^{\prime }}\widetilde{\psi}% _{y^{\prime }}+\frac{\epsilon^3}{2}\eta_x^2\widetilde{\psi}_{y^{\prime }}^2; \end{equation*} donde \begin{equation*} \left\{ \begin{aligned} &\Delta\widetilde{\psi}=\epsilon G, && (-L,L)\times(0,1), \\ &\widetilde{\psi}_{x'}=0, && x'=-L,L, \\ &\widetilde{\psi}=0, && y'=0, \\ &\widetilde{\psi}=-F\eta, && y'=1. \end{aligned} \right. \end{equation*}

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Dungan, Mary Elizabeth. « Development of a compact sound source for the active control of turbofan inlet noise / ». This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-03302010-020615/.

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Alamri, Sagr Mubarak. « SHOCK MITIGATION AND WAVE CONTROL USING ELASTIC METAMATERIAL STRUCTURES ». University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron154177943169993.

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Fernyhough, Mark. « Applications of the residue and Modified Residue Calculus Method in linear acoustic and water wave theory ». Thesis, University of Bristol, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238886.

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Chiu, Ching-Sang Denner Warren W. « Report on the Office of Naval Research USA-China Conference on Shallow Water Acoustics, December 18-21, 1995 ». Monterey, CA : Naval Postgraduate School, 1997. http://catalog.hathitrust.org/api/volumes/oclc/37486128.html.

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Freeman, Kate. « Numerical modelling and control of an oscillating water column wave energy converter ». Thesis, University of Plymouth, 2015. http://hdl.handle.net/10026.1/3290.

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An oscillating water column (OWC) wave energy converter (WEC) is a device designed to extract energy from waves at sea by using the water to move trapped air and thus drive an air turbine. Because the incident waves and the force caused by the power take-off (PTO) interact, control of the power take off (PTO) system can increase the total energy converted. A numerical model was developed to study the interaction of an OWC with the water and other structures around it. ANSYS AQWA is used here to find the effects on the water surface in and around the central column of a five-column, breakwater-mounted OWC. For open OWC structures, coupled modes were seen which lead to sensitivity to incident wave period and direction. The frequency-domain displacements of the internal water surface of the central column were turned into a force-displacement, time-domain model in MATLAB Simulink using a state space approximation. The model of the hydrodynamics was then combined with the thermodynamic and turbine equations for a Wells turbine. A baseline situation was tested for fixed turbine speed operation using a wave climate for a region off the north coast of Devon. A linear feedforward controller and a controller based on maximising turbine efficiency were tested for the system. The linear controller was optimised to find the combination of turbine speed offset and proportional constant that gave maximum energy in the most energy abundant sea state. This increased the converted energy by 31% in comparison to the fixed speed case. For the turbine efficiency control method, the increase was 36%. Energy conversion increases are therefore clearly possible using simple controllers. If increased converted energy is the only criterion for controller choice, then the turbine efficiency control is the best method, however the control action involves using very slow turbine speeds which may not be physically desirable.

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Rosette, Keith Andrew. « Investigation of a compact acoustic source array for the active control of aircraft engine fan noise ». Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-12302008-063020/.

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Johnson, William Richard. « Active Structural Acoustic Control of Clamped and Ribbed Plates ». BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4011.

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A control metric, the weighted sum of spatial gradients (WSSG), has been developed for use in active structural acoustic control (ASAC). Previous development of WSSG [1] showed that it was an effective control metric on simply supported plates, while being simpler to measure than other control metrics, such as volume velocity. The purpose of the current work is to demonstrate that the previous research can be generalized to plates with a wider variety of boundary conditions and on less ideal plates. Two classes of plates have been considered: clamped flat plates, and ribbed plates. On clamped flat plates an analytical model has been developed for use in WSSG that assumes the mode shapes are the product of clamped-clamped beam mode shapes. The boundary condition specific weights for use in WSSG have been derived from this formulation and provide a relatively uniform measurement field, as in the case of the simply supported plate. Using this control metric, control of radiated sound power has been simulated. The results show that WSSG provides comparable control to volume velocity on the clamped plate. Results also show, through random placement of the sensors on the plate, that similar control can be achieved regardless of sensor location. This demonstrates that WSSG is an effective control metric on a variety of boundary conditions. Ribbed plates were considered because of their wide use in aircraft and ships. In this case, a finite-element model of the plate has been used to obtain the displacement field on the plate under a variety of boundary conditions. Due to the discretized model involved, a numerical, as opposed to analytical, formulation for WSSG has been developed. Simulations using this model show that ASAC can be performed effectively on ribbed plates. In particular WSSG was found to perform comparable to or better than volume velocity on all boundary conditions examined. The sensor insensitivity property was found to hold within each section (divided by the ribs) of the plate, a slightly modified form of the flat plate insensitivity property where the plates have been shown to be relatively insensitive to sensor location over the entire surface of the plate. Improved control at natural frequencies can be achieved by applying a second control force. This confirms that ASAC is a viable option for the control of radiated sound power on non-ideal physical systems similar to ribbed plates.

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Meyer, Matthias. « The adjoint method of optimal control for the acoustic monitoring of a shallow water environment ». Doctoral thesis, Universite Libre de Bruxelles, 2007. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210610.

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Originally developed in the 1970s for the optimal control of systems governed by partial differential equations, the adjoint method has found several successful applications, e.g. in meteorology with large-scale 3D or 4D atmospheric data assimilation schemes, for carbon cycle data assimilation in biogeochemistry and climate research, or in oceanographic modelling with efficient adjoint codes of ocean general circulation models.

Despite the variety of applications in these research fields, adjoint methods have only very recently drawn attention from the ocean acoustics community. In ocean acoustic tomography and geoacoustic inversion, where the inverse problem is to recover unknown acoustic properties of the water column and the seabed from acoustic transmission data, the solution approaches are typically based on travel time inversion or standard matched-field processing in combination with metaheuristics for global optimization.

In order to complement the adjoint schemes already in use in meteorology and oceanography with an ocean acoustic component, this thesis is concerned with the development of the adjoint of a full-field acoustic propagation model for shallow water environments.

In view of the increasing importance of global ocean observing systems such as the European Seas Observatory Network, the Arctic Ocean Observing System and Maritime Rapid Environmental Assessment (MREA) systems for defence and security applications, the adjoint of an ocean acoustic propagation model can become an integral part of a coupled oceanographic and acoustic data assimilation scheme in the future.

Given the acoustic pressure field measured on a vertical hydrophone array and a modelled replica field that is calculated for a specific parametrization of the environment, the developed adjoint model backpropagates the mismatch (residual) between the measured and predicted field from the receiver array towards the source.

The backpropagated error field is then converted into an estimate of the exact gradient of the objective function with respect to any of the relevant physical parameters of the environment including the sound speed structure in the water column and densities, compressional/shear sound speeds, and attenuations of the sediment layers and the sub-bottom halfspace. The resulting environmental gradients can be used in combination with gradient descent methods such as conjugate gradient, or Newton-type optimization methods tolocate the error surface minimum via a series of iterations. This is particularly attractive for monitoring slowly varying environments, where the gradient information can be used to track the environmental parameters continuously over time and space.

In shallow water environments, where an accurate treatment of the acoustic interaction with the bottom is of outmost importance for a correct prediction of the sound field, and field data are often recorded on non-fully populated arrays, there is an inherent need for observation over a broad range of frequencies. For this purpose, the adjoint-based approach is generalized for a joint optimization across multiple frequencies and special attention is devoted to regularization methods that incorporate additional information about the desired solution in order to stabilize the optimization process.

Starting with an analytical formulation of the multiple-frequency adjoint approach for parabolic-type approximations, the adjoint method is progressively tailored in the course of the thesis towards a realistic wide-angle parabolic equation propagation model and the treatment of fully nonlocal impedance boundary conditions. A semi-automatic adjoint generation via modular graph approach enables the direct inversion of both the geoacoustic parameters embedded in the discrete nonlocal boundary condition and the acoustic properties of the water column. Several case studies based on environmental data obtained in Mediterranean shallow waters are used in the thesis to assess the capabilities of adjoint-based acoustic inversion for different experimental configurations, particularly taking into account sparse array geometries and partial depth coverage of the water column. The numerical implementation of the approach is found to be robust, provided that the initial guesses are not too far from the desired solution, and accurate, and converges in a small number of iterations. During the multi-frequency optimization process, the evolution of the control parameters displays a parameter hierarchy which clearly relates to the relative sensitivity of the acoustic pressure field to the physical parameters.

The actual validation of the adjoint-generated environmental gradients for acoustic monitoring of a shallow water environment is based on acoustic and oceanographic data from the Yellow Shark '94 and the MREA '07 sea trials, conducted in the Tyrrhenian Sea, south of the island of Elba.

Starting from an initial guess of the environmental control parameters, either obtained through acoustic inversion with global search or supported by archival in-situ data, the adjoint method provides an efficient means to adjust local changes with a couple of iterations and monitor the environmental properties over a series of inversions.

In this thesis the adjoint-based approach is used, e.g. to fine-tune up to eight bottom geoacoustic parameters of a shallow-water environment and to track the time-varying sound speed profile in the water column.

In the same way the approach can be extended to track the spatial water column and bottom structure using a mobile network of sparse arrays.

Work is currently being focused on the inclusion of the adjoint approach into hybrid optimization schemes or ensemble predictions, as an essential building block in a combined ocean acoustic data assimilation framework and the subsequent validation of the acoustic monitoring capabilities with long-term experimental data in shallow water environments.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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Torrent, Martí Daniel. « Towards the full control of sound with sonic crystals and acoustic metamaterials ». Doctoral thesis, Universitat Politècnica de València, 2008. http://hdl.handle.net/10251/3061.

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El objetivo de este trabajo ha sido obtener expresiones matemáticas para los parámetros elásticos y acústicos efectivos de sistemas heterogéneos en el límite de homogeneización, lo que ha permitido el diseño de nuevos dispositivos acústicos y elásticos funcionales en un amplio rango de longitudes de onda. Los sistemas heterogéneos estudiados han sido, principalmente, estructuras de cilindros elásticos inmersos en un medio fluido no-viscoso, aunque otras geometrías han sido comentadas. La periodicidad de estas estructuras permite reducir el problema al estudio de la "celda unidad"; es decir, a la región del espacio que se repite. Sin embargo, el método desarrollado en el presente trabajo ha permitido analizar el comportamiento cuando la periodicidad se ve alterada por defectos estructurales. Matemáticamente este problema ha sido tratado mediante la teoría de dispersión múltiple, ya que las geometrías del problema son principalmente circulares y dicha teoría ha demostrado ser la más adecuada en ese caso. Se ha utilizado la citada teoría de dispersión múltiple para analizar el comportamiento de un sólo cilindro y de un conjunto de cilindros. Este conjunto de cilindros ha sido ordenado, por un lado, en filas infinitas, dando lugar a expresiones para la reflectancia y transmitancia. Por otro lado, la extensión a todo el plano de las redes de cilindros ha permitido obtener resultados para la estructura de bandas. Para obtener los parámetros efectivos se han desarrollado dos métodos de homogeneización que, si bien coinciden en resultados para los casos elementales, han demostrado ser complementarios para calcular situaciones más complejas. El primero se basa en la propagación de ondas elásticas a través de medios periódicos. Se ha demostrado que, en el límite de baja frecuencia, la propagación de estas ondas presenta una relación de dispersión lineal, de cuya pendiente se ha podido obtener la velocidad de propagación efectiva del medio uniforme asociado. El segundo
Torrent Martí, D. (2008). Towards the full control of sound with sonic crystals and acoustic metamaterials [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/3061
Palancia

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Lu, Donghang [Verfasser], Rolf [Akademischer Betreuer] Jakoby et Mario [Akademischer Betreuer] Kupnik. « Dual-load Hybrid Detection of Water Content Using Electromagnetic and Surface Acoustic Wave Sensors / Donghang Lu ; Rolf Jakoby, Mario Kupnik ». Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2016. http://d-nb.info/1121206972/34.

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Dungan, Mary E. « Development of a compact sound source for the active control of turbofan inlet noise ». Thesis, Virginia Tech, 1992. http://hdl.handle.net/10919/41872.

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The concept of a compact sound source driven by piezoactuators is experimentally investigated, and analytical design tools are developed. The sound source, consisting of a thin, cylindrically curved aluminum panel and a pair of collocated, surface-bonded piezoceramic actuators, was developed with the objective of employing it as a secondary sound source in the active control of turbofan bladeinteraction inlet noise. The sound source was fitted in an experimental duct representative of an aircraft engine inlet, and the interior and exterior sound pressure levels generated by the source were measured. The effects of excitation voltage, excitation frequency, duct length, and downstream termination of the duct were investigated. It was found that the source is capable of generating relatively high acoustic levels at its fundamental frequency (over 130 dB at maximum voltage input). Techniques for analytically predicting the acoustic levels are investigated. A commercial code for numerical modelling of structural - acoustic radiation was utilized. Results show generally good agreement with experimental measurements for the case of the short duct. It is believed that the model accuracy can be further improved through additional refinements in the modelling techniques.
Master of Science

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Moisel, Christoph, et Thomas Carolus. « A facility for testing the aerodynamic and acoustic performance of bidirectional air turbines for ocean wave energy conversion ». Elsevier, 2016. https://publish.fid-move.qucosa.de/id/qucosa%3A36338.

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Bidirectional air turbines are used in oscillating water column (OWC) power plants for harnessing ocean wave energy. This paper describes the bidirectional aerodynamic and aero-acoustic facility at the University of Siegen for model air turbines performance testing. At least nine test facilities are known worldwide, but their layout, the performance testing procedure and the presentation of performance data are not standardized to this day. The layout of the facility at the University of Siegen follows ideas in ISO 5801 for fan performance testing. The pressurized air supply is bidirectional but steady-state. Achievable values of Reynolds and Mach number of the test turbines are 1,000,000 and 0.5, respectively. In addition, the facility is equipped with acoustic attenuators in the air supply for allowing synchronous determination of aerodynamic and acoustic characteristics of a turbine. A good practice guideline for turbine performance testing and presentation is proposed by showing full sets of non-dimensional aerodynamic and acoustic performance characteristics from two sample model turbines. Eventually, a comparison of in situ data from a full-scale turbine in transient operation with scaled up steady-state model performance measurements underlines the usefulness of steady-state model performance testing.

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BONFANTI, MAURO. « Mixing the Power of Water and Oil : The Hydraulic PTO for Wave Energy Conversion ». Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2928620.

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Leng, Julien. « Controlling flexural waves using subwavelength perfect absorbers : application to Acoustic Black Holes ». Thesis, Le Mans, 2019. http://www.theses.fr/2019LEMA1027/document.

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Le contrôle des vibrations à basse fréquence adapté aux structures légères est un défi scientifique ettechnologique en raison de contraintes économiques et écologiques de plus en plus strictes. De récentes études enacoustique ont portées sur l’absorption totale d’ondes basses fréquences à l’aide d’absorbeurs parfaits sublongueursd’onde. Ces métamatériaux sont obtenus en exploitant la condition de couplage critique. Unegénéralisation de cette méthode pour le domaine élastodynamique serait d’un grand intérêt pour répondre auxexigences du contrôle des vibrations de structures légères à basse fréquence.Cette thèse vise à adapter le problème d’absorption parfaite des ondes de flexion dans des systèmes 1D et 2D avecdes résonateurs locaux en utilisant la condition de couplage critique. Une étude préliminaire sur des systèmes 1D àgéométries simples sont d’abord proposée. Celle-ci propose une méthode de conception de résonateurs simplespour une absorption efficace des ondes de flexion. Une complexification du système 1D est ensuite considérée avecl’étude du couplage critique de Trou Noir Acoustique (TNA) 1D. Ceci a motivé l’interprétation de l’effet TNA à l’aidedu concept de couplage critique afin de présenter des outils clés à de futures procédures d’optimisation pour ce typede terminaisons. La condition de couplage critique est ensuite étendue aux systèmes 2D. L’absorption parfaite parle premier mode axisymétrique d’un résonateur circulaire inséré dans une plaque mince infinie est analysée. Ladiffusion multiple par une ligne de résonateurs circulaires insérés dans une plaque mince 2D infinie ou semi-infinie,appelée métaplaque, est aussi considérée dans l’optique de se rapprocher d’une application industrielle. A traverscette thèse, des modèles analytiques, des simulations numériques et des expériences sont présentés pour valider lecomportement physique des systèmes présentés
The vibration control adapted to light structures is a scientific and technological challenge due toincreasingly stringent economic and ecological standards. Meanwhile, recent studies in audible acoustics havefocused on broadband wave absorption at low frequencies by means of subwavelength perfect absorbers. Suchmetamaterials can totally absorb the energy of an incident wave. The generalisation of this method for applicationsin elastodynamics could be of great interest for the vibration control of light structures.This thesis aims at adapting the perfect absorption problem for flexural waves in 1D and 2D systems with localresonators using the critical coupling condition. A study of 1D systems with simple geometries is first proposed. Thisprovides methods to design simple resonators for an effective absorption of flexural waves. The 1D systems thenbecome more complex by studying the critical coupling of 1D Acoustic Black Holes (ABH). The ABH effect is theninterpreted using the concept of critical coupling, and key features for future optimisation procedures of ABHs arepresented. The critical coupling condition is then extended to 2D systems. The perfect absorption by the firstaxisymmetric mode of a circular resonator inserted in a thin plate is analysed. Multiple scattering by an array ofcircular resonators inserted in an infinite or semi-infinite 2D thin plate, called metaplate, is also considered to getclose to practical applications. Through this thesis, analytical models, numerical simulations and experiments areshown to validate the physical behaviour of the systems presented

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He, Shujian. « A TRANSFER MATRIX APPROACH TO DETERMINE THE LOW FREQUENCY INSERTION LOSS OF ENCLOSURES INCLUDING APPLICATIONS ». UKnowledge, 2017. https://uknowledge.uky.edu/me_etds/104.

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Partial enclosures are commonly used to reduce machinery noise. However, it is well known in industry that enclosures sometimes amplify the sound at low frequencies due to strong acoustic resonances compromising the performance. These noise issues are preventable if predicted prior to prototyping and production. Though boundary and finite element approaches can be used to accurately predict partial enclosure insertion loss, modifications to the model require time for remeshing and solving. In this work, partial enclosure performance at low frequencies is simulated using a plane wave transfer matrix approach. Models can be constructed and the effect of design modifications can be predicted rapidly. Results are compared to finite element analysis and measurement with good agreement. The approach is then used to design and place resonators into a sample enclosure. Improvements in enclosure performance are predicted using plane wave simulation, compared with acoustic finite element analysis, and then validated via measurement.

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Десятниченко, Алексей Владимирович. « Электромагнитно-акустический толщиномер для контроля металлоизделий с диэлектрическими покрытиями ». Thesis, НТУ "ХПИ", 2015. http://repository.kpi.kharkov.ua/handle/KhPI-Press/17117.

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Диссертация на соискание ученой степени кандидата технических наук по специальности 05.11.13 – приборы и методы контроля и определения состава веществ. – Национальный технический университет "Харьковский политехнический институт", Харьков, 2015. Диссертация посвящена решению важной научно-практической задачи обеспечения ультразвукового контроля толщины металлоизделий электромагнитно-акустическим методом при наличии диэлектрических покрытий (зазоров) толщиной до 10 мм. В работе выполнен анализ существующих акустических методов и устройств для измерения толщины, которые широко используются в отечественной и зарубежной промышленности, рассмотрены основные их преимущества и недостатки. Методы разделяются по типу контакта датчика с объектом контроля на два основные класса: контактные и бесконтактные. Бесконтактные на сегодняшний день являются наиболее перспективными. К ним относятся методы, основанные на: воздушно акустической связи, термо- и оптико-акустическом эффектах, а также на эффектах электрического и электромагнитного полей. По результатам анализа недостатков приведенных методов, выделен наиболее перспективный – ЭМА метод. Рассмотрены вопросы выбора оптимального сигнала для возбуждения акустических колебаний ЭМА методом. Приведены расчеты принимаемой энергии для общего случая при зеркальной схеме контроля, когда передающий и приемный датчики не располагаются соосно по высоте изделия. Рассмотрены модели расчетов для зеркально теневой схемы контроля, отдельно для режимов излучения ЭМАП в виде длинных и коротких импульсов. Дан анализ целесообразности использования вариантов зондирующего сигнала с различными соотношениями длины импульсов и расстояний между ними. Рассмотрена электрическая модель выходного каскада усилителя зондирующего сигнала и датчика, описаны особенности ее работы. Приведены результаты экспериментальных исследований и разработок, направленных на повышение качества и производительности контроля толщины с использованием ЭМА метод возбуждения и приема акустических колебаний. Представлена конструкция макета ЭМА преобразователя для контроля металлоизделий при наличии зазора между датчиком и изделием. Рассмотрены вопросы построения передающего и приемного аналоговых трактов, приведены схемотехнические и конструктивные решения. Приведены результаты исследований зависимости амплитуды сигнала на генерирующей обмотке ЭМАП от напряжения питания усилителя. Проведены исследования зависимости уровня полезного сигнала он напряжения на передающей обмотке датчика. Исследовано влияния зазора на уровень полезного сигнала. Приведены результаты зависимости длительности «мертвой» зоны от зазора и способы ее снижения. Определены факторы, влияющие на точность контроля. Разработан толщиномер основанный на электромагнитно акустическом методе возбуждения и приема акустических волн, приведены результаты этой разработки. Рассмотрены особенности построения его составных частей. Рассмотрены алгоритмы цифровой обработки принятого сигнала. Проведена оценка метрологических характеристик разработанного прибора, изготовлен контрольный образец для метрологического обеспечения толщиномера. Приведено сравнение нового прибора с существующими аналогами.
Thesis for granting the Degree of Candidate of Technical sciences in speciality 05.11.13 – Devices and methods of testing and materials structure determination. – National technical university "Kharkiv Politechnical Institute", Kharkiv, 2015. Thesis is devoted to solution of important theoretical and practical task to ensure ultrasound control of the metal products thickness by using electromagnetic-acoustical method in cases of dielectric coatings (gaps) with thickness up to 10 mm. Work includes analysis of existing acoustic methods and devices for thickness measurement, their main advantages and disadvantages are reviewed. Based on the results of analysis of the given disadvantages, the most advanced ways was set off - electromagnetic-acoustical (EMA) method. The problems of selection of the optimal signal agitate sonorous vibrations by EMA method were reviewed. Calculations of the taken energy are given for the analysis of the practicability to use variants of probing signal. Electric model of amplifier output stage of probing signal and sensor is reviewed, peculiarities of its operation are described. Results of researches and developments dedicated to increase thickness measurement quality and efficiency are given. Matters to build of the transmitting and receiving analog tracts are reviewed. The signal level dependence on voltage research on sensor's transmitting winding are conducted. Impact of a gap on the signal level was examined. Results of the dependence of dead spot length on a gap and methods to its reduction are given. Factors affecting accuracy of control are determined. EMA thickness gauge was designed. The main factors of design are examined. The digital processing algorithm of the received data was reviewed. Metrological characteristics of the developed device were made.

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Десятніченко, Олексій Володимирович. « Електромагнітно-акустичний товщиномір для контролю металовиробів з діелектричними покриттями ». Thesis, НТУ "ХПІ", 2015. http://repository.kpi.kharkov.ua/handle/KhPI-Press/17045.

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Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.11.13 – прилади і методи контролю та визначення складу речовин. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2015. Дисертація присвячена вирішенню важливої науково-практичної задачі, яка полягає у забезпеченні ультразвукового контролю товщини металовиробів електромагнітно-акустичним методом при наявності діелектричних покриттів (зазорів) товщиною до 10 мм. У роботі виконано аналіз існуючих акустичних методів і пристроїв для вимірювання товщини, розглянуті основні їх переваги та недоліки. За результатами аналізу недоліків наведених методів, виділений найбільш перспективний – ЕМА метод. Розглянуто питання вибору оптимального сигналу для збудження акустичних коливань ЕМА методом. Наведено розрахунки прийнятої енергії. Дано аналіз доцільності використання різних варіантів сигналу зондування. Розглянуто електричну модель вихідного каскаду підсилювача сигналу зондування і датчика, описано особливості її роботи. Наведено результати експериментальних досліджень і розробок спрямованих на підвищення якості та продуктивності контролю товщини. Представлена конструкція макета ЕМА перетворювача для контролю металовиробів при наявності зазору між датчиком і об'єктом. Розглянуто питання побудови передавального і приймального аналогових трактів, наведені конструктивні рішення. Досліджено залежність амплітуди сигналу на генеруючої обмотці ЕМАП від напруги живлення підсилювача. Проведено дослідження залежності рівня корисного сигналу він напруги на передавальній обмотці датчика. Досліджено впливу зазору на рівень корисного сигналу. Наведено результати залежності тривалості "мертвої" зони від зазору і способи її зниження. Визначено фактори, що впливають на точність контролю. Розроблено ЕМА товщиномір, розглянуті особливості побудови та питання схемотехніки його складових частин. Розглянуто алгоритми цифрової обробки прийнятого сигналу. Наведено опис виготовленого контрольного зразка для метрологічного забезпечення толщиномера.
Thesis for granting the Degree of Candidate of Technical sciences in speciality 05.11.13 – Devices and methods of testing and materials structure determination. – National technical university "Kharkiv Politechnical Institute", Kharkiv, 2015. Thesis is devoted to solution of important theoretical and practical task to ensure ultrasound control of the metal products thickness by using electromagnetic-acoustical method in cases of dielectric coatings (gaps) with thickness up to 10 mm. Work includes analysis of existing acoustic methods and devices for thickness measurement, their main advantages and disadvantages are reviewed. Based on the results of analysis of the given disadvantages, the most advanced ways was set off - electromagnetic-acoustical (EMA) method. The problems of selection of the optimal signal agitate sonorous vibrations by EMA method were reviewed. Calculations of the taken energy are given for the analysis of the practicability to use variants of probing signal. Electric model of amplifier output stage of probing signal and sensor is reviewed, peculiarities of its operation are described. Results of researches and developments dedicated to increase thickness measurement quality and efficiency are given. Matters to build of the transmitting and receiving analog tracts are reviewed. The signal level dependence on voltage research on sensor's transmitting winding are conducted. Impact of a gap on the signal level was examined. Results of the dependence of dead spot length on a gap and methods to its reduction are given. Factors affecting accuracy of control are determined. EMA thickness gauge was designed. The main factors of design are examined. The digital processing algorithm of the received data was reviewed. Metrological characteristics of the developed device were made.

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Ohlin, Mathias. « Ultrasonic Fluid and Cell Manipulation ». Doctoral thesis, KTH, Biomedicinsk fysik och röntgenfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-166779.

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During the last decade, ultrasonic manipulation has matured into an important tool with a wide range of applications, from fundamental cell biological research to clinical and industrial implementations. The contactless nature of ultrasound makes it possible to manipulate living cells in a gentle way, e.g., for positioning, sorting, and aggregation. However, when manipulating cells using ultrasound, especially using high acoustic amplitudes, a great deal of heat can be generated. This constitutes a challenge, since the viability of cells is dependent on a stable physiological temperature around 37°C. In this Thesis we present applications of ultrasonic manipulation of fluids, particles, and cells in temperature-controlled micrometer-sized devices fabricated using well established etching techniques, directly compatible with high-resolution fluorescence microscopy. Furthermore, we present ultrasonic manipulation in larger up to centimeter-sized devices optimized for fluid mixing and cell lysis. In the present work, two new ultrasonic manipulation platforms have been developed implementing temperature control. These platforms are much improved with increased performance and usability compared to previous platforms. Also, two new ultrasonic platforms utilizing low-frequency ultrasound for solubilization and cell lysis of microliter-volumed and milliliter-volumed samples have been designed and implemented. We have applied ultrasound to synchronize the interaction between large numbers of immune, natural killer cells, and cancer cells to study the cytotoxic response, on a single cell level. A heterogeneity was found among the natural killer cell population, i.e., some cells displayed high cytotoxic response while others were dormant. Furthermore, we have used temperature-controlled ultrasound to form up to 100, in parallel, solid cancer HepG2 tumors in a glass-silicon multi-well microplate. Next, we investigated the immune cells cytotoxic response against the solid tumors. We found a correlation between the number of immune cells compared to the size of the tumor and the cytotoxic outcome, i.e., if the tumor could be defeated. Finally, the effect of high acoustic pressure amplitudes in the MPa-range on cell viability has been studied in a newly developed platform optimized for long-term stable temperature control, independent on the applied ultrasound power. Lastly, we present two applications of ultrasonic fluid mixing and lysis of cells. One platform is optimized for small microliter-sized volumes in plastic disposable chips and another is optimized for large milliliter-sized volumes in plastic test tubes. The latter platform has been implemented for clinical sputum sample solubilization and cell lysis for genomic DNA extraction for subsequent pathogen detection
Ultraljudsmanipulering har under de senaste tio åren mognat och utvecklats till ett verktyg med ett brett användningsområde. Idag kan man finna applikationer inom allt från cellbiologisk grundforskning till industri samt sjukvård. Ultraljudsmanipuleringens kontaktlösa natur gör det till en varsam metod för att manipulera celler, till exempel inom positionering, sortering och aggregering. När ultraljud med hög amplitud används kan värmeutvecklingen, som är oundviklig, bli ett problem. För att kunna säkerställa hög cellviabilitet krävs temperaturkontroll som kan hålla en fysiologisk, stabil temperatur på 37°C. I denna avhandling presenterar vi tillämpningar av temperaturkontrollerad ultraljudsmanipulering i mikrometerstora anordningar fabricerade med väletablerade etsningstekniker. Dessa anordningar är optimerade för att vara fullt kompatibla med högupplöst fluorescensmikroskopi. Vi demonstrerar även ultraljudsmanipulering i centimeterstora anordningar optimerade för omrörning och blandning av vätskor samt lysering av celler. Två nya plattformar för ultraljudsmanipulering med inbyggd temperaturkontroll har utvecklats. Dessa två plattformar erbjuder ökad prestanda, flexibilitet samt även användarvänlighet. Utöver dessa plattformar har ytterligare två anordningar för lågfrekvent ultraljudssolubilisering och cellysering av mikroliter- och milliliterstora prover konstruerats. I denna avhandling har vi tillämpat ultraljud för att synkronisera interaktionen mellan populationer utav immunceller (natural killer-celler) och cancerceller för att på cellnivå studera det cytotoxiska gensvaret. Vi fann en heterogenitet hos immuncellspopulationen. Det manifesterade sig i en fördelning av immuncellerna, från celler med stort cytotoxiskt gensvar till inaktiva immunceller. Vi har dessutom använt temperaturkontrollerad ultrasljudsmanipulering för att skapa solida cancertumörer utav HepG2-cancerceller, upp till 100 stycken parallellt, i en multihåls-mikrotiterplatta bestående av glas och kisel. Med hjälp av dessa tumörer har vi studerat det cytotoxiska gensvaret från immuncellerna. Vi fann att förhållandet mellan antalet immunceller och storleken på tumören bestämde utfallet, det vill säga om tumören kunde bekämpas. Vi presenterar dessutom effekten utav högamplitudsultraljudsexponering av cancerceller i en plattform speciellt designad för höga tryckamplituder med implementerad ultraljudseffektsoberoende temperaturkontroll. Slutligen presenterar vi två tillämpningar av ultraljud för vätskeblandning och cellysering. Den första tillämpningen är anpassad för små volymer i plastchip för engångsbruk och den andra är optimerad för större volymer i plastprovrör. Den senare tillämpningen är speciellt framtagen för ultraljudssolubilisering och cellysering utav kliniska sputumprover för att möjliggöra DNA-extrahering för detektion av smittämnen.

QC 20150522

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Vaněk, Petr. « Posouzení vodního díla Těšetice za povodní ». Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2016. http://www.nusl.cz/ntk/nusl-240338.

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The Diploma Thesis focuses on the assessment of the current state of VD Tesetice to convert KPV parameters Q1000. Based on this evaluation, the thesis proposes corrective actions on waterwork constructions for the purpose of protection of their functioning during floods. Proposed corrective actions consist of designing new or additional safety features, mainly security spillway in abutment terrain.

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Guilloteau, Alexis. « Conception d'une clarinette logique ». Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4740.

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Le processus de conception des instruments à anche simple, élaboré au fil des siècles par les facteurs, est essentiellement basé sur des lois de comportement empiriques qui résultent de l’arbitrage des clarinettistes. Leurs critères subjectifs d’appréciation semblent être aussi bien alimentés par des descripteurs acoustiques (fréquence de jeu, spectre perçu, dynamique) que par l’aisance dans leur contrôle. Les connaissances actuelles en propagation guidée dans les réseaux de trous latéraux, offrent une base nécessaire à la prédiction du comportement acoustique linéaire du résonateur de l’instrument. Nous cherchons, à l’aide de ceux-ci, à proposer une méthode d’optimisation géométrique (positions et dimensions des trous latéraux) afin d’atteindre une retranscription objective, la plus proche possible, des critères d’appréciation du musicien. L’heuristique suivie au cours de cette étude vise à affiner les modèles de comportement ainsi que la construction des critères objectifs d’appréciation à l’issue de chaque réalisation d’un prototype de clarinette jusqu’à leur validation expérimentale. Avec l’aide d’un facteur d’instrument, deux prototypes ont été réalisés et nous exposerons les avantages et inconvénients des procédures d’optimisation appliquées à chacun d’eux
Single reed instruments conception process developed by instrument makers, is essentially based on empirical laws obtained from their interaction with musicians. Some of the subjectives criteria seems to be defined by both acoustic descriptors(like playing frequency, radiating spectrum and musical dynamics for exemple) and the ease of their control. Present knowledges in guided wave propagation in tone hole lattice are a necessary background to explain linear behavior of the clarinet. We aim to develop an optimisation method for clarinet geometrical variables in a way to reach the best objective translation of the clarinetists appraisal criteria. Then, the followed heuristic in this study consist in the enhancement of the acoustic behavior laws in parallel with the development of objective criteria after each logical clarinet making, until their experimental validation. The collaborative work with an instrument maker, helps us to make 2 prototypes with each specific procedure depicted in this document

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Feng, Shung-Hung, et 封昇宏. « Design of Voltage Control Surface Acoustic Wave Oscillator ». Thesis, 2004. http://ndltd.ncl.edu.tw/handle/33478459588110696203.

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碩士
義守大學
電機工程學系
92
Owing to the conveniences of wireless control and communication, the demands for various wireless circuits have been increased dramatically. In a modern wireless transceiver, the performance of the oscillator plays a major role in determine the thesis is to design a high frequency stability and low phase noise voltage controlled surface acoustic oscillator (VCSO). Surface acoustic wave resonator (SAWR) has advantages of high quality factor and low insertion loss over traditional lumped LC resonator. Fabricated on low temperature substrate, SAWR can be robust to the environment variation. In this thesis, a VCSO operated at 433MHz was designed and realized. A commercial one-port SAWR and a varactor diode were employed in resonant circuit. The theory of negative resistant was applied in designing the VCSO. The oscillation circuit was first simulated with high frequency circuit simulator (Ansoft Harmonica) and then it was realized on a print circuit board. The performances of the VCSO are: phase noise —97.58 dBc/Hz @10KHz and tuning range±480 ppm (0~ 8.8V).

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Sagers, Jason Derek. « Predicting acoustic intensity fluctuations induced by nonlinear internal waves in a shallow water waveguide ». Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-08-6025.

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Many problems in shallow water acoustics require accurate predictions of the acoustic field in space and time. The accuracy of the predicted acoustic field depends heavily on the accuracy of the inputs to the propagation model. Oceanographic internal waves are known to introduce considerable temporo-spatial variability to the water column, subsequently affecting the propagation of acoustic waves. As a result, when internal waves are present, errors in model inputs can significantly degrade the accuracy of the predicted acoustic field. Accurate temporo-spatial predictions of the acoustic field in the presence of internal waves therefore depend largely on one's ability to accurately prescribe the water column properties for the acoustic model. This work introduces a data-driven oceanographic model, named the evolutionary propagated thermistor string (EPTS) model, that captures the temporo-spatial evolution of the internal wave field along a fixed track, thereby permitting prediction of temporal fluctuations in the acoustic field. Simultaneously-measured oceanographic and acoustic data from the Office of Naval Research Shallow Water 2006 experiment are utilized in this work. Thermistor measurements, recorded on four oceanographic moorings spaced along the continental shelf, provide the data from which the EPTS model constructs the internal wave field over a 30 km track. The acoustic data were acquired from propagation measurements over a co-located path between a moored source and a vertical line array. Acoustic quantities computed in the model space, such as received level, depth-integrated intensity, and scintillation index are directly compared to measured acoustic quantities to evaluate the fidelity of the oceanographic model. In addition, a strong correlation is observed between the amplitude of the internal wave field and acoustic intensity statistics at a distant receiving array. It is found that the EPTS model possessed sufficient fidelity to permit the prediction of acoustic intensity distributions in the presence of nonlinear internal waves.
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Wen-JaiChen et 陳玟潔. « An Experimental Assessment of Acoustic Wave effect on Water Retention Curve ». Thesis, 2012. http://ndltd.ncl.edu.tw/handle/22331018831187389699.

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碩士
國立成功大學
水利及海洋工程學系碩博士班
100
Over the past decades, there have been growing research interests in studying the propagation and attenuation of elastic waves through a porous medium bearing two immiscible viscous compressible fluids because of its practical applications of engineering, such as the enhancement of both oil reservoir production and groundwater contaminant removal induced by low-frequency vibrations, and the detection of defects of bone and cartilage using high frequency (ultrasound) energy. Acoustic wave is one of elastic waves whose particle motion direction parallels to its propagation direction. Water retention curve has been long recognized as one of the important factors that give an influence on the propagation and attenuation of acoustic waves. In the past, variations in water content and soil volume caused by acoustic waves always were studied under the assumption that water retention curve remains unchanged. In this study, sandbox test is carried out to investigate if water retention curve varies due to acoustic effect. Ottawa sand (C109) is used in this study as an illustrative example. At first, soil properties are measured and then an experiment is conducted by recycling water level of sand box to simulate the imbibition and drainage processes of water retention curve based on the recorded tension head and volumetric water content. When water retention curve remains stable, six different excitation frequencies (100Hz, 150Hz, 200Hz, 250Hz, 300Hz and 350Hz) are selected to examine the effete of acoustic waves, in which the van Genuchten (1980) model is applied to fit experimental data for describing water retention curve. Our experiment result indicates that water retention curve is indeed affected by the introduction of acoustic waves. However, it is found that not all acoustic waves simultaneously offer an effect on the imbibition and drainage processes of water retention curve. It is revealed experimentally that acoustic wave with excitation frequency of 150Hz renders an impact on the imbibition process and drainage process, acoustic wave with excitation frequency of 200Hz has the most significant impact on the drainage process, and acoustic wave with excitation frequency of 250Hz has the most significant impact on the imbibition process. It is also shown that if water retention curve moves upward, the shape factor is observed to be smaller, while if water retention curve moves downward, we find that the shape factor would be greater.

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33

Horoshenkov, Kirill V., et Mostafa H. A. Mohamed. « Experimental Investigation of the effects of water saturation on the acoustic admittance of sandy soils ». 2006. http://hdl.handle.net/10454/3962.

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No
A novel technique for the laboratory characterization of the frequency-dependent acoustic surface admittance of partly saturated samples of sands is presented. The technique is based on a standard laboratory de-watering apparatus coupled with a standard acoustic impedance tube. The dependence of the surface admittance on the degree of water saturation is investigated for two samples of sand with widely different flow resistivities. It is shown that a relatively small change (e.g., from 0% to 11% by volume) in the degree of water saturation can result in a much larger change (e.g., twofold) in the acoustic surface admittance. An empirical relationship is found between the peaks observed in the real part of admittance spectra for the low flow resistivity sand and the degree of water saturation. The data are compared with predictions of two widely used ground impedance models: a semiempirical single parameter model and a two parameter model. A modified two-parameter version of a single-parameter model is found to give comparable fit to the two-parameter model. However, neither model provides an accurate fit.

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34

Chen, Hsin-Yu, et 陳信瑜. « Acoustic Wave Propagation in a Very Shallow Water Environment:Instrumentation and Experimental Data Analysis ». Thesis, 2006. http://ndltd.ncl.edu.tw/handle/18870740830119753459.

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碩士
國立中山大學
海下技術研究所
94
Sound propagation in very shallow water is one of the issues of the ocean acoustic. Because of close distance to the shore and short range to the bottom, the building of sound propagation model in shallow water is much more difficult than in deep water. Even though, the increasing needs of upper-sea construction engineering and near-shore surveillance make this subject more and more important. This study is to build a high sensitive underwater recording system, use it to collect data and to find out which parameters affect the sound propagation in very shallow water most. The study contains underwater recording system construction, shallow water recording experiment and comparison of OASES simulation results and the collective data. The system is constructed with two ITC6050C hydrophones and data acquisition devices. After several tests of reliability, the system is put in the sea area about 10 m depth. And the two hydrophones were moored 1 m above the bottom and 2.5 m below sea surface separately. The experiment use a moving fishing boat motor noise as sound source and the experimental results are shown as the spectrogram of sound field. The computer simulation uses OASES modules to simulate the experimental area and Pekeris waveguide propagation as the theoretical environment of very shallow water. By comparing the simulation results and the collective data ,the study finds out that the major parameters of sound propagation in the experimental area are the pressure sound speed and the depth of the sound source.

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35

Al, Jahdali Rasha. « Analyzing and Manipulating Wave Propagation in Complex Structures ». Diss., 2019. http://hdl.handle.net/10754/656666.

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The focus of this dissertation is analyzing and manipulating acoustic wave propagation in metamaterials, which can be used to assist the design of acoustic devices. Metamaterials are artificial materials, which are arranged in certain patterns at a scale smaller than the wavelength and can exhibit properties beyond those naturally occurring materials. With metamaterials, novel phenomena, such as focusing, super absorption, cloaking and localization of ultrasound, are theoretically proposed and experimentally verified. In recent years, a planar version of metamaterials, often called meta-surfaces, has attracted a great deal of attention. Meta-surfaces can control and manipulate the amplitude, phase, and directions of waves. In this dissertation, we conducted a systematic study by deriving the effective medium theories (EMTs), and developing the theoretical and numerical models for our proposed designed metamaterial. Very recently, acoustic meta-surfaces have been used in the design of acoustic lenses, which can achieve various functionalities such as focusing and collimation. In the designs of acoustic lenses, impedance is an important issue because it is usually difficult to make the impedance of the lens equal to that of the environment, and mismatched impedance is detrimental to the performance of the acoustic lens. We developed an EMT based on a coupled-mode theory and transfer matrix method to characterize the propagation behavior and, based on these models, we report two designs of acoustic lenses in water and air, respectively. They are rigid thin plates decorated with periodically distributed sub-wavelength slits. The building block of the acoustic lens in water is constructed from coiling-up spaces, and that of the acoustic lens in air is made of layered structures. We demonstrate that the impedances of the lenses are indeed matched to those of the background media. With these impedance-matched acoustic lenses, we demonstrate acoustic focusing and collimation, and redirection of transmitted acoustic energy by finite-element simulations. In the framework of the hidden source of the volume principle, an EMT for a coupled resonator structure is derived, which shows that coupled resonators are characterized by a negative value of the effective bulk modulus near the resonance frequency and induce flat bands that give rise to the confinement of the incoming wave inside the resonators. The leakage of sound waves in a resonance-based rainbow trapping device prevents the sound wave from being trapped at a specific location. Based on our EMT, we report a sound trapping device design based on coupled Helmholtz resonators, loaded to an air waveguide, to effectively tackle the wave leakage issue. We show that a coupled resonators structure can generate dips in the transmission spectrum by an analytical model derived from Newton’s second law and a numerical analysis based on the finite-element method. We compute the transmission spectra and band diagram from the effective medium theory, which are consistent with the simulation results. Trapping and the high absorption of sound wave energy are demonstrated with our designed device.

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36

Lu, Donghang. « Dual-load Hybrid Detection of Water Content Using Electromagnetic and Surface Acoustic Wave Sensors ». Phd thesis, 2016. https://tuprints.ulb.tu-darmstadt.de/5830/1/main.pdf.

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This work focuses on water content detection both in materials and in gases, i.e., measurements of moisture and humidity. To detect the moisture, a cavity perturbation method (CPM) is introduced to extract the relationship between permittivity and water content in material under test (MUT), which, in this application is tobacco at a single frequency. The obtained information is used as pre-knowledge for a mass flow sensor design in tobacco production. The mass flow sensor is an open cylindrical resonator that consists of two circular waveguides with different diameters. An on-sight test of the mass flow sensor is performed, and the measured weights are within a 10% discrepancy compared to the supplied weights. For the humidity measurement, a material named polyvinyl alcohol (PVA) is employed as a sensitive layer. The PVA film involves two mechanisms for humidity sensing, which are variations of electrical loading and mechanical loading with relative humidity (RH). To apply the electrical loading property, the PVA film is characterized by an interdigital capacitor (IDC) in a wide frequency range at different RHs, and the results are used to create a comprehensive model of the PVA film for computer simulation tools to predict the performance of the sensor. A wireless humidity sensor is designed to verify the PVA film model, and a good agreement between the simulation and measurement results proves the accuracy of the model. To utilize the mechanical loading property, the PVA film is loaded on surface acoustic wave (SAW) resonators. A wet chemical method of patterning the PVA film is found, and the influence of the PVA film thickness is investigated. With different patterns and thicknesses of the PVA film, humidity sensors can achieve various performances in terms of operation range, sensitivity, and quality factor. To apply both, electrical and mechanical loading properties of the PVA film for humidity sensing at the same time, a novel dual-load SAW resonator is introduced by using additional IDCs as reflectors with the PVA film loaded on top. The humidity sensor based on this novel hybrid structure extends its operating range, and shows better sensitivity and quality factor with different sensing mechanisms within certain RH ranges. A figure of merit (FoM) is defined to evaluate the sensitivity and quality factor of the sensor at the same time, and the sensing mechanism with better FoM can be selected for humidity sensing in a defined RH range.

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37

Wang, Yu-Tai, et 王裕太. « Acoustic Guided Wave Inspection for Water Generated in Flow Field Plate of PEM Fuel Cells ». Thesis, 2011. http://ndltd.ncl.edu.tw/handle/02999054963356884687.

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碩士
國立交通大學
機械工程學系
100
The operating performance of proton exchange membrane fuel cells (PEMFC) depends on the water production inside the cells. In this study, array piezoelectric ceramic transducers were surface adhered to flow field plate mockups made of aluminum alloy and used to generate and detect guided acoustic waves propagating along the flow channels. In-situ inspection of water distribution in PEM fuel cells is feasible by the presented method. The phase velocities for guided acoustic waves and their corresponding mode shapes were determined using finite element analysis (FEA). Besides the A0 and S0 modes, several additional bending modes caused by transverse vibrations of the stiffeners in flow field plate were found in the lower frequency range. In experiment, the acoustic wave signals were detected by two piezoelectric array sensors and laser Doppler interferometer for various amounts of water production. The fact of directly propagating guided waves interfered with multiply reflected echoes results in deviation of both measured and numerically predicted phase velocities of guided acoustic waves. The insertion loss between transmitted and received piezoelectric arrays was measured as a function of the quantity of water production. The results indicate that the attenuation of guided acoustic wave increases as the water content increases. The insertion loss is a significant index for monitoring water production in the flow field plate of PEM fuel cells.

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38

Wu, Min-Hsiu, et 吳旻修. « Acoustic Wave Sensors for Detection of Water Transport through Membrane in a PEM Fuel Cell ». Thesis, 2012. http://ndltd.ncl.edu.tw/handle/51061471809098669138.

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Résumé :

碩士
國立交通大學
機械工程學系
101
Water transport rate in the proton exchange membrane fuel cell (PEMFC) should be in a specific range to keep a good electric conductivity in the membrane. This thesis develops an in-situ inspection method to detect water transport through the membrane into flow channels by use of a novel acoustic guided wave transducer. Two anti-symmetric interdigitated piezoelectric fiber composite (AE-PFC) transducers used as the guided wave transmitter and receiver were adhered to the back surface of flow field plate. Guided waves propagate over the flow channel area and carry water information from the transmitter to the receiver. The transducer comes with advantages of narrowband, small mass and high acoustic directivity. In experiment, a carbon paper used as the gas diffusion layer overlays the area of flow channels. The influence of wet carbon paper on the guided acoustic wave was investigated in accordance with changes of the waveform envelop and the peak value of the signal spectrum. The result indicates the water in the carbon paper reduces reflected echoes of the first guided mode and increases the peak amplitude. On the contrary, the amplitude of the second guided mode decreases as it propagates over the wet area of flow channels. Based on the decreasing of amplitude, the water quantity distributed throughout either the ribs or the flow channels can be determined. The sensitivity of detection is 0.03 and 0.3 mV/μl for water on the ribs and in the flow channels. The range of measuring is 20 to 220 μl. The detecting resolution is up to 5 μl. Furthermore, finite element analysis was used to explore the electric field of AE-PFC in the process of polarization and guided wave propagation in the flow field plate. The numerical results indicate the electric field is nearly parallel to the piezoelectric fibers. The transient analysis shows the forking phenomenon in the guided mode signal spectra might be caused by the varying adhesive thickness between AE-PFC and the host structure.

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39

Xu, Rui-Fu, et 許瑞福. « Broadband Polarization Control of Bulk Acoustic Wave-Mediated Multiferroic Antenna Based on Thickness Shear Modes ». Thesis, 2019. http://ndltd.ncl.edu.tw/handle/9kpxm5.

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碩士
國立臺灣大學
電信工程學研究所
107
Antenna miniaturization has been more and more important these days. Many applications like IOT, biomedical devices, wearable devices, and 5G demand higher performance with smaller feature size. Many works on antenna miniaturization have been done before, such as using substrate with high permittivity or permeability, diverse structure antenna design, etc. However, no matter in UHF or VLF band, as long as the electrical size of an antenna is much smaller than one, the radiation efficiency will be extremely low, making the antenna infeasible. In 2015, theoretical groundwork of using multiferroic material to achieve antenna miniaturization was firstly propose, named “bulk acoustic wave-mediated multiferroic antenna”. The core concept is that the wavelength of mechanical wave is five orders of magnitude smaller than electromagnetic wave under the same resonant frequency. As long as the loss can be further reduced, it owns great potential to approach Chu’s limit for electrically small antennas. In the above mentioned works, the radiation is mainly generated based on longitudinal acoustic wave. In this thesis, thickness shear mode is used instead of longitudinal one. By using the shear mode, two sets of symmetrical but orthogonal resonant modes can be manipulate by applying 90° phase difference to generate circularly polarized (CP) wave. In addition, the shear wave can excite in-plane magnetic current, which will double the radiation instead of cancelling out each other when the device is placed above a metallic ground plane according to the image theory. Such concept can also be used for tunable polarization control. The design concept is preliminarily investigated through FEM-based multi-physics solver, COMSOL, and post processing by an in-house MATLAB code. It is shown that under the ideal input RF signal pair of equal magnitude and with 90° phase difference, the proposed design can achieve very broadband CP with satisfactorily low in-band axial ratio. The design is fabricated by Dr. Sidhant Tiwari from UCLA. The test pieces were tested, and the results thus obtained are presented and discussed through a couple of comparisons. This work envisions the possibility of broadband polarization control and/or tunability of electrically small antennas.

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40

Lin, Yi-Jhou, et 林羿州. « Applications of the addition theorem and superposition technique for acoustic and water wave problems with circular boundaries ». Thesis, 2009. http://ndltd.ncl.edu.tw/handle/98487995120399917958.

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碩士
國立臺灣海洋大學
河海工程學系
97
Based on the null-field integral equation approach, we introduce the degenerate kernel, namely the addition theorem, Fourier series and adaptive observer system to construct the linear algebraic system for solving Helmholtz problems. After obtaining the unknown Fourier coefficient, a linear algebraic system in obtained, the interior potential can be calculated. By introducing the superposition technique, a problem can be decomposed into two parts. One is the fundamental solution of free field and the other is an infinite plane with circular boundaries subject to the specified boundary conditions derived from the addition theorem. After superposing the two solutions, the governing equation and boundary condition are both satisfied. Five advantages: (1) mesh-free generation (2) well-posed model, (3) principal value free (4) elimination of boundary-layer effect (5) exponential convergence, are achieved. Finally, a general-purpose program for deriving the Helmholtz problems with arbitrary number of circular boundaries and/or cylinders of arbitrary radii and various positions involving the Dirichlet or the Neumann boundary condition was developed. Two applications in acoustic problem with a point source and water wave problems, were done. Besides, the effect of porous parameter and disorder on the force in case of near-trapped modes was also examined.

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41

Mokhtari, Alireza. « The influence of flow, geometry, wall thickness and material on acoustic wave resonance in water-filled piping ». 2017. http://hdl.handle.net/1993/32119.

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The study of acoustic resonance in fluid-filled piping systems with and without mean flow is important for the nuclear industry. For this industry, it is vital to understand the acoustic resonance in their systems; however, no comprehensive experimental benchmark data or accurate modeling tool exists for predicting such a phenomenon. The main goals of the current research are to create a new experimental data bank for the conditions not tested earlier using the configurations of straight lines and branches, and to evaluate the applicability of the linear wave solution using different damping methods and a computational fluid dynamic (CFD) code to simulate the acoustic resonance in fluid-filled piping systems. In this experimental study, data on resonant frequencies and resonant amplitudes are collected and analyzed for a frequency range of 20–500 Hz for straight and branched tubes by varying their wall thicknesses, materials, and branch configurations at different flow rates and outlet boundary conditions. To be closer to the nuclear industry medium, water is employed in our experiments, contrasting to the fact that most of the available experiments reported were with air at a much lower sonic velocity. I consider here, in particular, measurements at the end of closed branches, upstream, downstream, and at different locations of the main line, as well as the interactions of different sonic velocities along the main pipes. A small diameter is chosen for the branched experiments since the decrease in the width of the main line and the branches has a pronounced effect on the resonant amplitudes due to an increased interaction among the unsteady shear layers forming across the side branches. The experimental results show that there is a strong effect of turbulent flow, wall material, and wall thickness on resonant amplitudes at frequencies above ∼250 Hz. Numerical investigations are performed solving the one-dimensional (1D) linear wave equation with constant and frequency-dependent damping terms and a CFD code. Employing frequency-dependent damping methodologies shows improvement in terms of resonant amplitude prediction over constant volumetric drag method. Comparing the 1D and CFD results shows that the CFD solution yields better predictions.
February 2017

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42

Benevides, Francis Leo. « Estimating ocean wave directional spectra from measurements of water particle motion by a surface buoy acoustic ranging system ». Thesis, 1990. http://hdl.handle.net/10125/10001.

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43

Ho, Ya-Lun, et 何亞倫. « Development of a Surface Acoustic Wave Based Micro-Droplet Control System and its Application of Nucleic Acid Amplification ». Thesis, 2010. http://ndltd.ncl.edu.tw/handle/43732841823831743871.

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碩士
國立臺灣大學
應用力學研究所
99
In this thesis, an automatic micro-droplet control system applied to amplification of nucleic acid is accomplished by the combination of a surface acoustic wave (SAW) device, micro-heaters, micro-sensors of temperature, and a PI controller. The SAW device constituted of slanted finger interdigital transducers (SFITs) is utilized to actuate the micro-droplet by the acoustic streaming and to detect the micro-droplet by the frequency responses of the SAWs. With the development of PI controller, the micro-droplet can be manipulated automatically. In order to reduce the driving power and manipulate the mineral oil which is necessary for the reaction of the nucleic acid amplification, a perﬂuoroalkylsilane (PFAS) and tetraethoxysilane (TEOS) hydrophobic film is utilized for surface modification. Furthermore, with the PFAS/TEOS hydrophobic film, the cross-contamination can be prevented, and the micro-droplet control system is reusable for different DNAs and reagents. Utilizing the developed micro-droplet control system, the amplification of nucleic acid can be successfully achieved. The consumption of the biomedical reagent and the production cost of devices can be reduced, and the efficiency of reaction can be improved. The developed micro-droplet control system is suitable for various types of lab-on-a-chip system in biomedical fields.

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44

Rajapakse, G. « Control and power management of grid connected vented oscillating water column wave energy converter arrays ». Thesis, 2021. https://eprints.utas.edu.au/37931/1/Rajapakse_whole_thesis.pdf.

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Wave energy is a vast, sustainable, and low environmental impact renewable energy source with a high degree of predictability and availability at large scale. Over the last six decades, numerous studies have been conducted, and various technologies have been developed to convert wave energy into electricity. Nevertheless, Wave Energy Conversion (WEC) is still not a widespread technology, compared to other dominant renewable energy technologies such as wind and solar. One of the contributing factors for this is the large and periodic fluctuations present in the extracted power in WEC systems. Even though intermittencies are present in the extracted power in the wind and solar generation systems, the level of fluctuations present in those systems are much smaller compared to that in wave energy. Therefore, the direct connection of a WEC system to a power grid without any power conditioning could lead to instabilities. The use of energy storage is a promising solution to absorb fluctuation and thereby ensure smooth power delivery to the grid. Battery energy storage is the most common solution recommended for similar issues in the wind and solar energy systems. Nevertheless, due to the short-term and periodic (10 -15 seconds) nature of the power pulses present in wave energy, a combination of battery and supercapacitor is recommended as the most suitable energy storage solution for WEC systems. Most studies reported in the literature on WEC systems with battery-supercapacitor hybrid energy storage have considered only a single WEC system. The effects of spatial and temporal averaging of extracted power in wave energy converter arrays on the sizing of energy storage systems have not been explored so far. Therefore, this study has attempted to fill this knowledge gap using vented oscillating water column (VOWC) wave energy converter arrays. VOWC is a novel WEC technology developed at the Australian Maritime College in collaboration with the Wave Swell Energy company in Australia. This technology produces energy only during the inhale stage resulting in large discrete power pulses. These characteristics of VOWC make control and power smoothing even more challenging compared to conventional bi-directional WEC technologies such as Wells turbines. As solutions, novel control and power management strategies have been developed to suit the characteristics of the VOWC. The efficacy of the developed control and power management solutions are validated through simulations carried out on the MATLAB/Simulink digital simulation platform. The results verify the efficacy of the proposed control strategy in tracking the setpoints efficiently with minimal overshoots and oscillations. Furthermore, the findings confirm that the proposed PMS can reduce the mismatch between supply and demand, while maintaining smooth delivery of power to the grid in single and array configurations of VOWC WECs. Moreover, further findings reveal that the required ESS capacity drops when WEC systems are placed correctly in array configurations.

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45

Panigrahi, Satyanarayan. « Analysis Of Multiply-Connected Acoustic Filters with Application To Design Of Combination Mufflers And Underwater Noise Control Linings ». Thesis, 2006. https://etd.iisc.ac.in/handle/2005/367.

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This thesis endeavors towards developing various concepts employed in analysis and design of acoustic ﬁlters for varied applications ranging from combination mufflers for automobiles to complex networks of gas carrying ducts to multiply connected complex automotive silencing devices to the noise control coatings for underwater applications. A two-dimensional wave modeling approach has been proposed to evaluate sound attenuation characteristics of dissipative mufflers of ﬁnite length with/without extended inlet and outlet tubes including very large mufflers. The correctness of the method has been validated through comparison with experimental results from literature. Two other frequently used approximate schemes have been discussed brieﬂy with reference to the available literature. These three approaches have then been weighed against each other to show the effectiveness and limitations of each one. A thorough comparison study has been performed to investigate each one’s extent of applicability. A parametric study with different parameters suggests some useful design guidelines that can be put to use while designing such mufflers. Beneﬁts and drawbacks of reactive and dissipative mufflers have been discussed with an intention of striking a compromise between them to achieve a better transmission quality over a broad frequency range. This has been accomplished by combining these two types of mufflers/ﬁlters explicitly. These combination mufflers are analyzed using a transfer matrix based approach by extending the aforesaid concept of two-dimensional wave modeling for ﬁnite dissipative ducts. The present approach has been used to analyze axi-symmetric circular lined plenum chambers also. The effectiveness of the bulk reaction assumption to model absorptive lining is illustrated. A parametric study has been carried out to investigate the effects of different thicknesses and placements of the absorptive lining. The contributions of reﬂective and absorptive portion of the combination mufflerto overall attenuation performance have been investigated from the designer’s point of view A generalized algorithm has been developed for studying the plane sound wave propa- gation in a system of interconnected rigid-walled acoustic ﬁlter elements. Interconnection between various elements is represented by a connectivity matrix. Equations of volume velocity continuity and pressure equilibrium at the interconnections are generated using this connectivity matrix and are solved using the Gauss-Jordan elimination scheme to get the overall transfer matrix of the system. The algorithm used for generalized labeling of the network and computation of Transmission Loss has also been discussed. The algorithm has been applied to investigate a multiply connected automobile mufflers as a network of acoustic elements which guides the way to a specialized application discussed next. Results for some conﬁgurations have been compared with those from the FEM analysis and experiments. A parametric study with respect to some geometric variables is carried out. The acoustical similarity between apparently different networks is discussed. The approach is ﬂexible to incorporate any other acoustic elements, provided the acoustic variables at the junctions of the element can be related by a transfer matrix a priori. Commercial automotive mufflers are often too complex to be broken into a cascade of one dimensional elements with predetermined transfer matrices. The one dimensional (1-D) scheme presented here is based on an algorithm that uses user friendly visual volume elements to generate the system equations which are then solved using a Gauss-Jordan elimination scheme to derive the overall transfer matrix of the muffler. This work attempts and succeeds to a great extent in exploiting the speed of the one dimensional analysis with the ﬂexibility, generality and user friendliness of three dimensional analysis using geometric modeling. A code based on the developed algorithm has been employed to demonstrate the generality of the proposed method in analyzing commercial muffers by considering three very diverse classes of mufflers with diﬀerent kinds of combinations of reactive, perforated and absorptive elements. Though the examples presented in the thesis are not very complex for they are meant to be just representative cases of certain classes of mufflers, yet the algorithm can handle a large domain of commercial mufflers of high degree of complexity. Results from the present algorithm have been validated through comparisons with both the analytical and the more general, three-dimensional FEM based results. The forte of the proposed method is its power to construct the system matrix consistent with the boundary conditions from the geometrical model to evaluate the four pole parameters of the entire muffer and thence its transmission loss,etc. Thus, the algorithm can be used in conjunction with the transfer matrix based muffler programs to analyze the entire exhaust system of an automobile. A different kind of acoustic ﬁlter than the above mentioned cases is then taken up for investigation. These refer to the specialized underwater acoustic ﬁlters laid as linings on submerged bodies. These kind of underwater noise control linings have three different types of objectives, namely, Echo Reduction, Transmission Reduction (TL maximization) and a combination thereof. These coatings have been shown to be behaving very differently with different shape, size and number of air channels present in the layer. In this regard, a ﬁnite element model based methodology has been followed. An hybrid type ﬁnite element based on the Pian and Tong formulation has been modiﬁed and used so as to make the computational efforts less demanding as compared to the original one. The developed ﬁnite element has been shown to be immune to the difficulties that arise due to the near incompressible characteristics of the viscoelastic materials used and the high distortion of the elements of the FE mesh. The adequacy of this formulation has been shown by comparing its results with the analytical, FE based, and experimental results. Then, this methodology has been used to analyze and generate design curves to control various geometrical parameters for proper designing of these linings. Different unit cell representations for different types of distributions of air cavities on the linings have been discussed. Four different types of layers have been introduced and analyzed to address different objectives mentioned above. They have been termed as the Anechoic layer, Insulation layer and Combination Layer of coupled and decoupled type in this thesis. The ﬁrst two layers have been designed to achieve very dissimilar characteristics and the next two layers have been designed to balance their disparities. A thorough parametric study has been carried out on the geometrical parameters of all the layers to come up with the design guidelines. For anechoic and the insulation layers, different distributions have been analyzed with different unit cell geometries and their usability in speciﬁc situations has been outlined. Effect of static pressure has also been studied by using an approximate ﬁnite element method. This method can be used to simulate deep-sea testing environment.

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46

Panigrahi, Satyanarayan. « Analysis Of Multiply-Connected Acoustic Filters with Application To Design Of Combination Mufflers And Underwater Noise Control Linings ». Thesis, 2006. http://hdl.handle.net/2005/367.

Texte intégral

Résumé :

This thesis endeavors towards developing various concepts employed in analysis and design of acoustic ﬁlters for varied applications ranging from combination mufflers for automobiles to complex networks of gas carrying ducts to multiply connected complex automotive silencing devices to the noise control coatings for underwater applications. A two-dimensional wave modeling approach has been proposed to evaluate sound attenuation characteristics of dissipative mufflers of ﬁnite length with/without extended inlet and outlet tubes including very large mufflers. The correctness of the method has been validated through comparison with experimental results from literature. Two other frequently used approximate schemes have been discussed brieﬂy with reference to the available literature. These three approaches have then been weighed against each other to show the effectiveness and limitations of each one. A thorough comparison study has been performed to investigate each one’s extent of applicability. A parametric study with different parameters suggests some useful design guidelines that can be put to use while designing such mufflers. Beneﬁts and drawbacks of reactive and dissipative mufflers have been discussed with an intention of striking a compromise between them to achieve a better transmission quality over a broad frequency range. This has been accomplished by combining these two types of mufflers/ﬁlters explicitly. These combination mufflers are analyzed using a transfer matrix based approach by extending the aforesaid concept of two-dimensional wave modeling for ﬁnite dissipative ducts. The present approach has been used to analyze axi-symmetric circular lined plenum chambers also. The effectiveness of the bulk reaction assumption to model absorptive lining is illustrated. A parametric study has been carried out to investigate the effects of different thicknesses and placements of the absorptive lining. The contributions of reﬂective and absorptive portion of the combination mufflerto overall attenuation performance have been investigated from the designer’s point of view A generalized algorithm has been developed for studying the plane sound wave propa- gation in a system of interconnected rigid-walled acoustic ﬁlter elements. Interconnection between various elements is represented by a connectivity matrix. Equations of volume velocity continuity and pressure equilibrium at the interconnections are generated using this connectivity matrix and are solved using the Gauss-Jordan elimination scheme to get the overall transfer matrix of the system. The algorithm used for generalized labeling of the network and computation of Transmission Loss has also been discussed. The algorithm has been applied to investigate a multiply connected automobile mufflers as a network of acoustic elements which guides the way to a specialized application discussed next. Results for some conﬁgurations have been compared with those from the FEM analysis and experiments. A parametric study with respect to some geometric variables is carried out. The acoustical similarity between apparently different networks is discussed. The approach is ﬂexible to incorporate any other acoustic elements, provided the acoustic variables at the junctions of the element can be related by a transfer matrix a priori. Commercial automotive mufflers are often too complex to be broken into a cascade of one dimensional elements with predetermined transfer matrices. The one dimensional (1-D) scheme presented here is based on an algorithm that uses user friendly visual volume elements to generate the system equations which are then solved using a Gauss-Jordan elimination scheme to derive the overall transfer matrix of the muffler. This work attempts and succeeds to a great extent in exploiting the speed of the one dimensional analysis with the ﬂexibility, generality and user friendliness of three dimensional analysis using geometric modeling. A code based on the developed algorithm has been employed to demonstrate the generality of the proposed method in analyzing commercial muffers by considering three very diverse classes of mufflers with diﬀerent kinds of combinations of reactive, perforated and absorptive elements. Though the examples presented in the thesis are not very complex for they are meant to be just representative cases of certain classes of mufflers, yet the algorithm can handle a large domain of commercial mufflers of high degree of complexity. Results from the present algorithm have been validated through comparisons with both the analytical and the more general, three-dimensional FEM based results. The forte of the proposed method is its power to construct the system matrix consistent with the boundary conditions from the geometrical model to evaluate the four pole parameters of the entire muffer and thence its transmission loss,etc. Thus, the algorithm can be used in conjunction with the transfer matrix based muffler programs to analyze the entire exhaust system of an automobile. A different kind of acoustic ﬁlter than the above mentioned cases is then taken up for investigation. These refer to the specialized underwater acoustic ﬁlters laid as linings on submerged bodies. These kind of underwater noise control linings have three different types of objectives, namely, Echo Reduction, Transmission Reduction (TL maximization) and a combination thereof. These coatings have been shown to be behaving very differently with different shape, size and number of air channels present in the layer. In this regard, a ﬁnite element model based methodology has been followed. An hybrid type ﬁnite element based on the Pian and Tong formulation has been modiﬁed and used so as to make the computational efforts less demanding as compared to the original one. The developed ﬁnite element has been shown to be immune to the difficulties that arise due to the near incompressible characteristics of the viscoelastic materials used and the high distortion of the elements of the FE mesh. The adequacy of this formulation has been shown by comparing its results with the analytical, FE based, and experimental results. Then, this methodology has been used to analyze and generate design curves to control various geometrical parameters for proper designing of these linings. Different unit cell representations for different types of distributions of air cavities on the linings have been discussed. Four different types of layers have been introduced and analyzed to address different objectives mentioned above. They have been termed as the Anechoic layer, Insulation layer and Combination Layer of coupled and decoupled type in this thesis. The ﬁrst two layers have been designed to achieve very dissimilar characteristics and the next two layers have been designed to balance their disparities. A thorough parametric study has been carried out on the geometrical parameters of all the layers to come up with the design guidelines. For anechoic and the insulation layers, different distributions have been analyzed with different unit cell geometries and their usability in speciﬁc situations has been outlined. Effect of static pressure has also been studied by using an approximate ﬁnite element method. This method can be used to simulate deep-sea testing environment.

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Thèses sur le sujet « Acoustic wave control in water »

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