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Abrahamson, Scott. "Automated psycho-acoustic experimental station." Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/19566.
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Maier, Christian. "Experimental and theoretical aero-acoustics." Thesis, Glasgow Caledonian University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601630.
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Acoustic noise problems are encountered in many fields and are very often undesirable. The localisation of sound sources is the first step 10 reducing noise problems. In this thesis, the ability and feasibility of an acoustic camera in this regard is demonstrated The acoustic camera deals with the problem of sound sources coming from different directions by estimating the sound contributions incident to the acoustic camera. One example of an aero-acoustic noise problem is an air plane with its air foil. These cause unwanted noise due 10 the flowed air. Or another example is the current collector on trains which causes unwanted noise as well as affecting driving. Another problem, dealt with later in this thesis, is a cylinder flowed by air in a wind tunnel. A practical case 0/ this problem is a car antenna in the form of a cylinder; this causes noise due to the driving wind Fans can be optimised for aero-acoustics as well - an example is a cooling fan in a computer, or larger fans for air conditioners that can transport the noise over the whole tunnel in which they are built. Some processing techniques are used and implemented in the acoustic camera. The first technique is the "classical" Delay-and-Sum Beam/arming technique and the improved orthogonal beamforming, with the ability to separate non-correlated sound sources in a Single measurement. The second technique is based on the decomposition of the Eigenvalues of the cross spectral matrix. In addition to the experimental section of this thesis, the results are compared to a simulation, where a flowed object measured with the acoustic camera is compared to a suitable simulation with the same parameters like dimensions and velocity. Here f/owed means that a suitable object, a cylinder for example, is placed in the wind tunnel and flowed by air. The outcome of this thesis is the analysing of a flow induced problem, a fan for example. First steps were done with 2D flow simulations of a cylinder to become familiar with the topic program and implementing MATLAB® code to process the points of interest. This analysing could be done with a simulation or with the acoustic camera. The aim of this work is concerned with sound sources and the mechanism behind it. Suitable aero-acoustic experiments were chosen that can be analysed with the acoustic camera and with numerical simulation as well. With the acoustic camera, these sound sources can be visualised using the beamforming method A similar procedure should be done to the numerical simulations. These simulations are done and the sound sources are visualised there as well by rebuilt an array of microphones, which acts as acoustic camera, in the numerical simulations.
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Grothe, Timo. "Experimental Investigations of Bassoon Acoustics." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-150193.
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The bassoon is a conical woodwind instrument blown with a double-reed mouthpiece. The sound is generated by the periodic oscillation of the mouthpiece which excites the air column. The fundamental frequency of this oscillation is determined to a large extent by the resonances of the air column. These can be varied by opening or closing tone-holes. For any given tone hole setting a fine-tuning in pitch is necessary during playing. Musicians adjust the slit opening of the double-reed by pressing their lips against the opposing reed blades. These so-called embouchure corrections are required to tune the pitch, loudness and sound color of single notes. They may be tedious, especially if successive notes require inverse corrections. However, such corrections are essential: Due to the very high frequency sensitivity of the human ear playing in tune is the paramount requirement when playing music. This implies, that embouchure actions provide an important insight into a subjective quality assessment of reed wind instruments from the viewpoint of the musician: An instrument requiring only small corrections will be comfortable to play.
Theoretical investigations of the whole system of resonator, reed, and musician by use of a physical model nowadays still seem insufficient with respect to the required precision. Therefore the path of well-described artificial mouth measurements has been chosen here. For the separate treatment of the resonator and the double-reed, existing classical models have been used. Modifications to these models are suggested and verified experimentally. The influence of the musician is incorporated by the lip force-dependent initial reed slit height. For this investigation a measurement setup has been built that allows precise adjustment of lip force during playing. With measurements of the artificial mouth parameters blowing pressure, mouthpiece pressure, volume-flow rate and axial lip position on reed, the experiment is fully described for a given resonator setting represented by an input impedance curve. By use of the suggested empirical model the adjustment parameters can be turned into model parameters. A large data set from blowing experiments covering the full tonal and dynamical range on five modern German bassoons of different make is given and interpreted.
The experimental data presented with this work can be a basis for extending the knowledge and understanding of the interaction of instrument, mouthpiece and player. On the one hand, they provide an objective insight into tuning aspects of the studied bassoons. On the other hand the experiments define working points of the coupled system by means of quasi-static model parameters.
These may be useful to validate dynamical physical models in further studies. The experimental data provide an important prerequisite for scientific proposals of optimizations of the bassoon and other reed wind instruments. It can further serve as a fundament for the interdisciplinary communication between musicians, musical instrument makers and scientists.
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KULKARNI, PRASHANT M. "EXPERIMENTAL FORMULATION OF FOUR-POLE PARAMETERS FOR ANALYTICAL-EXPERIMENTAL HYBRID MODELING OF ACOUSTIC SYSTEMS." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1069348253.
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Pundarika, G. "Experimental And Theoretical Studies On Jet Acoustics." Thesis, Indian Institute of Science, 2001. http://hdl.handle.net/2005/250.
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A systematic research on aeroacoustics conducted around the world for the last few decades has revealed various inherent characteristics of the jet noise radiation. However, a lot more needs to be done for the theoretical as well as experimental predictions of various jet noise features based on actual flow details. The work reported in the present thesis is an attempt in this direction.
A critical study of existing literature on jet noise shows that none of the general wave equations lends itself easily for predictions of all the jet noise features. It is shown that while LighthilPs classical acoustic analogy approach, with some reasonable approximations, can be used to yield most of the information needed by the engineers, the convected wave equations of Phillips and Lilley are required to study the acoustic radiation in what has come to be known as "Refraction valley" or "Cone of relative silence".
The characteristics of the sound field of underexpanded cold jet impingement flows were studied by measuring the noise emanating from two convergent nozzles of throat diameter 2.5 mm and 5 mm each and a convergent - divergent nozzle of exit diameter of 6.49 mm, when the jet impinges on a flat plate kept perpendicular to the direction of the jet. The measurements were conducted upstream of the nozzle over an extensive envelope of jet operating conditions such as chamber stagnation pressure, mass flow rate through the nozzle and diameter of the nozzle.
The source strength at the jet boundary was obtained by measuring acoustic pressure amplitude close to the jet contour assuming it as locally cylindrical. Particular attention was focussed on backward projection of the sound field on to a cylindrical surface. This is the application of acoustic holography to study the sound radiation in the audio frequency region. With the help of FFT and software developed for this purpose, the theoretical predictions using data from several cylindrical surfaces were compared.
A detailed analysis of noise radiation from a cold sonic and supersonic free jet was also carried out. The experimental work involved the measurement of noise field from a 2.5 mm, 5 mm convergent and a convergent - divergent nozzle of exit diameter of 6.49 mm and area ratio 1.687 for designed Mach number of two.
The experimental setup consisted essentially of a pressure chamber made of mild steel, designed to withstand 50 bar pressure. This chamber is a cylinder with dia 0.421 m and length 0.85 m. The nozzles were made of mild steel. Compressed air approximately at room temperature is supplied to the nozzle via a control valve.
The measuring and recording instruments consists of B & K Microphones, Preamplifiers, Conditioning amplifier and a Mediator, which measure a Sound Pressure Level at a point. The nozzles were operated at pressure ratio upto 25 bar. The noise signal was processed through 12 channel data acquisition system. Acoustic pressure and SPL were" calculated using theoretical relations and software developed. Using this software Fast Fourier Transformations of raw signal was obtained from 20 Hz to 20 kHz. Also constant SPL contour graphs were obtained.
Source strength distribution at the jet boundary has been obtained by the principle of acoustic holography. Experimental values are closely matching with the results obtained by acoustic holography. The percentage error for acoustic pressure and SPL were less than 12%. The experimental results were used to obtain the source distribution in terms of gross jet parameters.
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Zhang, Wei. "Simulation and experimental study of room acoustics." Thesis, University of Ottawa (Canada), 2006. http://hdl.handle.net/10393/27311.
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Sound propagation is a complex subject, especially in an enclosure. The study of room acoustics involves not only a research into how sound is propagated in a room, but also a search into how to measure sound under different condition and how to control sound in the case of various wall materials.
For an acoustical environment, there are three separated parts: sound sources, room acoustics, and the listens. These three items form a source-medium-receiver chain, which is typical for most of communication models. In this thesis, the image method is applied to predict the acoustical quality of a real room, and the experiment for room acoustic measurement is set up. The simulation model using image method proved the design of the measurement system is efficient for room acoustics.
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Blandin, Rémi. "Theoretical and experimental study of vocal tract acoustics." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAT102/document.
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L'acoustique du conduit vocal est souvent décrite avec de simples modèles ondes planes à une dimension. Cependant, cela n'est pas satisfaisant quand à haute fréquence (à partir d'environ 5 kHz) des variations tridimensionnelles du champ acoustique sont présentes. La théorie acoustique multimodale a été implémentée pour prendre en compte les aspects tridimensionnels de l'acoustique du conduit vocal.Un système expérimental a été conçu pour mesurer avec précision des fonctions de transfert, des champs de pression et des diagrammes de directivité sur des maquettes de conduits vocaux. Les données expérimentales obtenues ont été comparées avec les simulations réalisées avec la théorie implémentée et avec la méthode des éléments finis. Le champ acoustique tridimensionnel et les diagrammes de directivité ont été prédit avec succès par les deux méthodes de simulation. Il a été observé que la propagation de mode acoustique d'ordre supérieur induit des variations tridimensionnelles du champ acoustique, génère des antirésonances et des résonances additionnelles et affecte la directivité du son rayonné de façon significative. L'excentricité de la forme du conduit vocal apparaît comme critique pour l'excitation et la propagation des modes d'ordre supérieur.Il est conclu qu'à haute fréquence (au-delà de 5 kHz), la fonction de transfert du conduit vocal peut avoir des variations significatives dans des intervalles de fréquences petit (de l'ordre de 100 Hz) et dans des régions angulaires restreintes (de l'ordre de 30°) qui nécessitent d'être prise en compte dans les études de la parole qui se focalisent sur les hautes fréquencesThe vocal tract acoustics is often described witha simple one dimensional plane wave approach.However, this is not satisfying when at high frequency(from about 5 kHz) three dimensional variations ofthe acoustic fieldare present. The multimodal acoustic theory has beenimplemented in order to account for the threedimensional aspects ofthe vocal tract acoustics.An experimental setup has been designed to measure accuratelytransfer functions, pressure field maps and directivitypatterns of vocal tract replicas.The experimental data obtained have been compared withsimulations performed with the implemented theory andwith a finite element method.The three dimensional acoustic fields and the directivitypatterns were successfully predicted by both simulationmethods.It has been observed that the propagation of higher orderacoustical modes, induces three dimensional variations ofthe acoustic field, generates anti-resonances andadditional resonances, and significantly affects the directivityof the radiated sound.The eccentricity of thevocal tract shape appears as critical for the excitation and thepropagation of the higher order acoustical modes.It is concluded thatat high frequency (above 5 kHz), the transfer functionof the vocal tract can have significant variationswithin short frequency intervals (of the order of 100Hz) and within small angular regions (of the order of30°) which need to be taken into account inthe studies of speech which focus on high frequencies
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Grialou, Matthieu. "Vibro-acoustics substructuring : Combining simulations and experimental identification of subdomains for low frequency vehicle acoustics." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI109/document.
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La sonorité de l’échappement joue un rôle significatif sur le confort acoustique des occupants, ainsi que sur le caractère du véhicule. L’étude proposée porte sur la problématique industrielle suivante : « Description et quantification de la transmission du son entre la bouche d’échappement et l’intérieur du véhicule ». Physiquement la transmission sonore entre l’échappement et l’intérieur du véhicule s’effectue en trois étapes : Propagation des ondes sonores de la canule à la surface extérieure du véhicule et conversion en énergie vibratoire (1) ; Le bruit structurel se propage de la peau extérieure du véhicule à l’habillage intérieur (2) ; La surface intérieure du véhicule rayonne de l’énergie dans l’air à l’intérieur (3). Dans l’état de l’art proposé, la méthode de sous-structuration vibro-acoustique Patch Transfer Functions (PTF) est considérée comme une alternative viable à la problématique proposée. Cependant, avant d’appliquer la méthode sur un véhicule complet, la problématique suivante devait être résolue : « Caractérisation expérimentale d’un sous-système par des mesures sur un système couplé ». Ce manuscrit propose une méthode originale pour mesurer des fonctions de transfert d’un système découplé, sur la base de la réponse d’un système couplé. En raison de la nature mal posée du problème inverse, une méthode originale de régularisation a été proposée. La méthode a été validée pas des essais numériques, puis par un test physiqueExhaust noise has a significant impact on acoustic comfort and the sound identity of a vehicle brand. The present study focuses on the: “Description and quantification of the sound transmission from the exhaust outlet into the interior of a vehicle”. Physically the noise propagation from the exhaust pipe to the cabin consists of three steps: The sound waves propagate through the air from the exhaust outlet to the external skin of the vehicle (1); the external skin vibrates and transmits its vibration to the internal skin (2); the internal skin radiates sound in the passengers’ cabin (3). The Patch Transfer Functions method, which is based on the framework of dynamic substructuring, allows for the consideration of this complex problem as simpler subproblems that consist of subsystem interactions. Yet the application of the method to a full vehicle requires addressing the problem: “Characterization of Patch Transfer Functions of a subsystem by means of measurement on a coupled system”. This dissertation presents an original inverse method for the measurement of Patch Transfer Functions. In industrial structures, this in-situ characterization is generally the only possible measurement method. Yet, due to the ill posed nature of the problem, the inversion process is difficult. An original regularization method is proposed. The method is tested through numerical simulations, and is validated with an experimental setup
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Sack, Stefan. "Experimental and Numerical Multi-port Eduction for Duct Acoustics." Doctoral thesis, KTH, Linné Flow Center, FLOW, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-207475.
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Sound generation and propagation in circular ducts for frequencies beyond the cut-on frequencies of several higher order acoustic modes is investigated. To achieve this, experimental and numerical set-ups are designed and used to research aeroacoustic interactions between in-duct components and to conceive noise mitigation strategies. Describing in-duct sound for frequencies with a moderate number of propagating modes is important, for example, for improving the noise emission from mid-size ventilation systems. Challenges that are largely unacknowledged in the literature involve efficient test rig design, quantification of limits in the methods, numerical modelling, and development of effective noise mitigation strategies for higher order modes. In this thesis, in-duct sound is mapped on a set of propagating pressure eigenmodes to describe aeroacoustic components as multi-ports with sound scattering (passive properties) and a source strength (active properties). The presented analysis includes genetic algorithms and Monte Carlo Methods for test rig enhancement and evaluation, multi-port network predictions to identify model limitations, and scale resolving (IDDES) and Linearized Navier Stokes computations for numerical multi-port eduction and the silencer design. It is first shown that test rig optimization improves the quality of multi-port data significantly. Subsequently, measurements on orifice plates are used to test the network prediction model. The model works with high accuracy for two components that are sufficiently separated. For small separations, strong coupling effects are observed for the source strength but not for the scattering of sound. The measurements are used for numerical validation, which gives reliable results for coupled and uncoupled systems. The total acoustic power of tandem orifices is predicted with less than 2 dB deviation and the passive properties for most frequencies with less than 5 % difference from the measurement. The numerical (FEM) models are also used to design a completely integrated silencer for spinning modes that is based on micro-perforated plates and gives broadband attenuation of 3-6 dB per duct diameter silencer length. The multi-port method is a powerful tool when describing aerodynamically decoupled in-duct components in the low- to mid-frequency range. Due to a robust passive network prediction, multi-port methods are particular interesting for the design of silencer stages. Furthermore, the demonstrated applicability to numerical data opens novel application areas.QC 20170522
IdealVent
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Ingemanson, Megan Lynn. "Experimental Characterization of Wind Turbine Blade Aerodynamic Noise." Thesis, University of California, Davis, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1539643.
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Wind turbine noise at low frequencies less than 300Hz is not only annoying to humans but has been proven to cause serious health issues. Additionally, animals are severely affected by wind turbines because a small increase in ambient noise (as is produced by wind turbines) significantly reduces their listening ability. In an attempt to better understand and characterize the aerodynamic noise of wind turbine blades, experimental testing was completed on PowerWorks 100kW and GudCraft WG700 blade specimens in the University of California, Davis Transportation Noise Control Center's anechoic chamber. Experimental testing and data analysis proved approximately 4.0dB to 6.0dB was produced due to the blades' geometric design for both blade specimens at low frequencies. This noise was maximized at the blades' leading edge along the central portion of the blades' radius. Theoretical prediction models have been used to determine that, for typical wind speeds and low frequencies, noise generated due to the tip passing frequency is clearly predominant.
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Ehrlich, Christian. "Experimental characterization of creep damage using the nonlinearity ultrasonic technique." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42752.
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Welded steel pipes are an essential structural part of any power plant. Longer lifetimes and higher pressures in the pipes cause an increased probability of failure due to creep damage. To maintain safe operation, nondestructive evaluation techniques to detect creep damage are needed. Nonlinear acoustic techniques employing longitudinal waves have been proven to be sensitive to creep damage. The objective of this research is to develop a robust experimental procedure to reliably measure the acoustic nonlinearity parameter using longitudinal waves, and then to validate the procedure on samples of different materials and sizes. Finally the technique is applied to characterize creep damage levels around the weld of a welded steel pipe. While the experimental technique presented can only measure the relative nonlinearity, it is accurate enough to detect changes in nonlinearity due to creep damage. Measurements show an increase in nonlinearity in the heat affected zone (HAZ). Experiments after annealing the creep damaged specimen show a decrease in nonlinearity in accordance with a decrease in dislocation density. Measurements on an undamaged welded A36 steel component suggest that the heat itself is not responsible for the increase in nonlinearity.
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Andrade, C. A. R. "Experimental methods in building acoustics for evaluating the flanking transmission." Master's thesis, Universidade de Valladolid, 2003. http://hdl.handle.net/10198/1845.
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Trabajo TuteladoAll the scientific work must have at the beginning presupposes and assumptions clarified, that could lead to an objective more easily to accomplish. In this line of thought, the present work is to achieve and clarify those presupposes and assumptions. The design of building and his constructions techniques must be built in such a way that the noise perceived by the occupants is kept down to a level that will not threaten their health and satisfactory living conditions. The acoustical comfort is nowadays one of the main issues for the satisfaction and integration on the society. This has more relevance in developed countries. There are many places where the normal human living is developed: home, work, leaser places, etc, has there are many forms of sound power that disturb those places. However, where the sound perturbation must not reach intolerable levels (acoustical comfort) are in buildings, especially in living buildings. Nowadays is known that sound could be transmitted by structural vibration or by other paths than the separating element of the dwellings. These paths could increase the sound levels of the adjoining rooms with a bigger importance than the supposed a few years ago. The present and future works are more a contribution to obtain better acoustical conditions in buildings and put to the scientific community more knowledge and “savoir faire”. Firstly a search was made in reviews, books and papers specialized in the areas of knowledge of building acoustics and flanking transmission. The information recovered was treated to clarify all the present work done till the moment and to put us in the center of the issue. Secondly several measurements were performed in an old building of the university (in situ measures), by pressure method and intensity method. Those measures were then treated, processed, compared and finally discussed to accomplish the main objective of this work, which is getting an objective theme to the future doctoral thesis.
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Su, Daoning. "Theoretical and experimental studies of the acoustic directional sensor." Thesis, Heriot-Watt University, 1988. http://hdl.handle.net/10399/985.
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He, Xiaoyin. "CHARACTERIZATION OF CORNEAL BIOMECHANICAL PROPERTIES USING EXPERIMENTAL AND COMPUTATIONAL METHODS." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1280178567.
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Tashmukhambetov, Arslan. "Experimental Design, Data Analysis, and Modeling for Characterizing the Three-Dimensional Acoustic Field of a Seismic Airgun Array." ScholarWorks@UNO, 2009. http://scholarworks.uno.edu/td/1084.
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In June 2003, the Littoral Acoustic Demonstration Center conducted an acoustic characterization experiment for a standard seismic exploration array. Two moorings with Environmental Acoustic Recording Systems (EARS) were deployed in the northern part of the Gulf of Mexico to measure ambient noise and collect shot information. A 21-element seismic airgun array was towed along five parallel linear tracks with horizontal closest approach points to the EARS buoy position of 63, 500, 1000, 2000, and 5000 m. Calibrated acoustic pressure measurements collected during the experiment were analyzed to obtain zero-to-peak sound pressures, sound exposure levels, and pressure levels in 1/3-octave frequency bands. In addition, the experimental data were modeled by using a modified underwater acoustic propagation model to fill in missing data measurements. The resulting modeling procedure showed good agreement between measured and modeled data in absolute pressure amplitudes and frequency interference patterns for frequencies up to 1000 Hz. The analysis is important for investigating the potential impact on marine mammals and fish and predicting the exposure levels for newly planned seismic surveys in other geographic areas. Based on results of the experiment conducted and data analysis performed, a new experimental design was proposed to maximize the amount of collected data using the available equipment while minimizing the time needed for the source ship. The design used three patches, one with 3º angular spacing between the lines at a reference depth. Embedded is a smaller patch with 1º spacing and within that a still smaller patch with one half degree spacing. This arrangement gives a reasonably uniform distribution of shots versus solid angle with a large variety of emission and azimuthal angles for different ranges. Due to the uncertainty of positioning systems, the angular space is divided into solid angle bins. Simulations predicted more than 200 shots per bin for emission angles greater than 13 degrees. Statistical analysis of collected data will be performed on the proposed bin basis. An experiment based on the proposed design was conducted in Fall 2007. The data measurements collected during the experiment are currently being analyzed and will be reported in the near future.
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Harris, Christopher A. "Acoustics and Fluid Dynamics Studies of High Speed Jet Noise Reduction Devices." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1218687698.
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Balugani, Sofia. "Experimental protocol for the determination of elastic properties at ambient and high pressure by picosecond acoustics technique." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/22350/.
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This thesis work focused on establishing an experimental protocol for the determination of the materials’ elastic constants at ambient pressure and at high pressure by picosecond acoustics. Picosecond acoustics is a pump-probe experimental technique that allows to measure the travel times of the acoustic waves that propagate across the sample. The acoustic waves’ velocities are derived from the travel times and from the sample thickness. An inversion program developed within the research group allows to extract the elastic constants from the measured sound velocities by inverting the Christoffel equation that relates them to the elastic tensor. The high pressure is generated by the diamond anvil cell (DAC) technology.
The investigated samples are magnesium oxide (MgO), a transparent insulator, oriented along the [001] direction, and ruthenium (Ru), an opaque metal, oriented along the [0001] direction. The first was studied at ambient pressure, while the second was studied at both ambient and high pressure. The elastic constants of MgO were extracted with the inversion program and the results obtained agree with the values found in the literature. The values obtained are: C11= (296.96± 0.19) GPa, C44= (153.60 ± 0.10) GPa, C12= (98.78 ± 0.11) Gpa.
The elastic constants at ambient pressure of Ru agree with the data in the literature and are: C11= (564± 6) GPa, C33= (626 ± 8) GPa, C44= (182.2 ± 0.5) GPa and C12= (175 ±7) Gpa.
The measurements at high pressure on ruthenium did not allow to derive the elastic constants as from the data analysis it emerged that the sample had been damaged during the pressure increase. Probably this was due to the selected pressure transmitting medium of the DAC, that did not guarantee completely the pressure hydrostaticity.
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López-Carromero, Amaya. "Experimental investigation of acoustic characteristics of radiation and playing gestures for lip-excited musical instruments." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/33207.
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The geometrical characteristics of acoustical radiation are of great importance in instrument design and synthesis, and multiple simplified models have been developed in the past to describe them. In this work two experimental methodologies are proposed and carried out, studying the frequency-dependent radiation in a collection of popular brass instruments with different grades of flaring, and making use of the axis-symmetry of these instruments. The first method uses a scanning linear array and is carefully designed to extract the linear properties of the radiation field. The results of this experimental method are a database of impulse responses distributed in space, and effectively covering a bidimensional on-axis section of the radiation field approximately 0.6 m by 0.9 m. These data can then be used for the validation of a number of simplified physical models used to describe the radiation of these types of instruments. The second method aims at visualising radiation for high amplitude excitation, where shock waves are generated inside the instrument due to non-linear propagation of the plane wave. In this case, the experimental methodology used, taking advantage of the strong density and temperature gradients generated in the air, is an on-axis schlieren optical system. General results of this visualisation show a strong increase in focused directivity at high frequencies and loud playing dynamics, due to the spectral enrichment typical of this family of instruments. The second section of this thesis focuses on the study of playing gestures in the trombone, and could also be applicable to other slide instruments. During glissando playing in the trombone the length of the cylindrical slide section within the bore is altered while waves are propagating. Slide velocities of 2 metres per second are not unusual and result in a (small but measurable) Doppler shift in the wave coming from the mouthpiece before it arrives at the bell. An additional effect is observed in terms of the volume of air within the instrument changing telescopically, leading to a localised change in DC pressure and a resulting flow, which generates infrasound components within the bore. The effects of these playing gestures are investigated in two different setups; one with a high frequency sinusoidal excitation generated by a compression driver, and another one using an artificial mouth to play the instrument. In both experiments the pressures at the mouth or mouthpiece, water key and bell were tracked using microphones and the position of the slide was tracked using a laser distance sensor. Both Doppler shifting and infrasound components were detected for both experimental setups, although the effect on a soft termination such as the artificial lips requires further examination.
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McCall, George Samuel II. "An experimental apparatus for measuring underwater acoustic scattering from complex finite cylindrical shells." Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/17667.
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Wibron, Emelie. "A Numerical and Experimental Study of Airflow in Data Centers." Licentiate thesis, Luleå tekniska universitet, Strömningslära och experimentell mekanik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-67781.
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Airflow management is crucial for the performance of cooling systems in data centers. The amount of energy consumed by data centers is huge and a large amount is related to the cooling. In attempts to develop energy efficient data centers, numerical methods are important for several reasons. Experimental procedures are more expensive and time consuming but when done carefully, experiments provide trustful results that can be used to validate simulations and give additional insights. Numerical methods in their turn have the advantage that they can be applied to proposed designs of data centers before they are built and not only to already existing data centers. In this study, Computational Fluid Dynamics (CFD) is used to study the airflow in data centers. The aim is to use an experimentally validated CFD model to investigate the effects of using different designs in data centers with respect to the performance of the cooling systems. Important parameters such as quality of the computational grid, boundary conditions and choice of turbulence model must be carefully considered in order for the results from simulations to be reliable. In Paper A, a hard floor configuration where the cold air is supplied directly into the data center is compared to a raised floor configuration where the cold air is supplied into an under-floor space instead and enters the data center through perforated tiles in the floor. In Paper B, the performance of different turbulence models are investigated and velocity measurements are used to validate the CFD model. In Paper C, the performance of different cooling systems is further investigated by using an experimentally validated CFD model. The effects of using partial aisle containment in the design of data centers are evaluated for both hard and raised floor configurations. Results show that the flow fields in data centers are very complex with large velocity gradients. The k − ε model fails to predict low velocity regions. Reynolds Stress Model (RSM) and Detached Eddy Simulation (DES) produce very similar results and based on solution times, it is recommended to use RSM to model the turbulent airflow in data centers. Based on a combination of performance metrics where both intake temperatures for the server racks and airflow patterns are considered, the airflow management is significantly improved in raised floor configurations. Using side covers to partially enclose the aisles performs better than using top covers or open aisles.
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Steel, Robin. "An experimental and theoretical investigation of the wall-effect in doppler ultrasound flow phantoms." Thesis, Bangor University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263969.
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Heinemann, Michael Gerhard. "Experimental studies of applications of time-reversal acoustics to non-coherent underwater communications." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2000. http://handle.dtic.mil/100.2/.
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Thesis (M.S. in Engineering Acoustics and M.S. in Applied Physics) Naval Postgraduate School, March 2000.Thesis advisor(s): Larraza, Andrès ; Smith, Kevin B. "March 2000." Includes bibliographical references (p. 59-60). Also available online.
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Johansson, Örjan. "Experimental and multivariate analysis methods for sound quality evaluation of diesel engines." Doctoral thesis, Luleå tekniska universitet, Drift, underhåll och akustik, 1996. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18176.
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Noise control and sound quality analysis are important, since noise has been registered to be a predominant factor in stress and a source of great annoyance. Traffic noise is a problem and a major part of this noise comes from heavy vehicles. The only legislative requirement for heavy-duty trucks regarding noise emissions, is that the noise level does not exceed an Aweighted sound pressure level of 80 dB. The specification of an A-weighted sound pressure level is, however, not an adequate description of psychoacoustic annoyance and therefore work towards defining a better description of loudness is one of the principal fields of acoustics today. Sound radiation from trucks is speed-related. At medium and high speeds, the overall noise level is comprised mainly of the tyre noise, whereas at low speed and during acceleration, exhaust noise and noise from the engine and transmission structure are predominant. In front of the truck, the noise from the engine and especially that from the timing transmission cover, the torsional damper and the oil sump, comprises a greater proportion of the total noise. The aim of sound quality analysis of diesel engines is to find cost-efficient methods of reducing sound radiation and of changing the character of the sound in order to minimise annoyance. This thesis concerns the development of experimental methods for analysing the sound quality of diesel engines, and focuses on measurement of acoustic intensity, multivariate data analysis, structural modification and subjective assessment of engine noise. The applicability of the FFT-based sound intensity method is evaluated. It is found that the intensity measurements may be influenced by high reactivity, interference due to partlycoherent sources, difficulties in performing the spatial average, real-time limitations and engine speed variations. Scanning the intensity probe, preferably by a robot, is necessary when measuring within narrow bands to avoid interference problems. Scanning achieves more reliable estimates of sound power and intensity vectors. Experimental design and the multivariate techniques, principal components analysis (PCA) and partial least squares (PLS) were utilised to facilitate interpretation of intensity measurements. The results show that PCA and PLS enable independent phenomena in the sound field to be extracted and which can thereby be visualised by principal spectra and principal radiating patterns. The characteristics of sound radiation are determined by designed experiments, sound intensity measurements and operational deflection shape estimations. These methods enable the effects on sound radiation of structure modifications to be predicted. An annoyance index for in-line 6-cylinder diesel engines in stationary running conditions was developed using multivariate statistics. The index is based on engine sounds resulting from structure modifications and changes in fuel. The annoyance level was measured during listening tests of sound stimuli recorded in stereo and reproduced by loudspeakers under anechoic conditions. The different sound stimuli were ranked using paired comparisons or the method of successive intervals. It was found that 94% of the variance of annoyance can be explained by a model based on loudness (Sone), sharpness (Acum) and harmonic ratio (rumble). Impulsiveness, roughness and tonality were other important criteria used in the study and which were found to have a relationship with specific speed ranges. The annoyance was minimised by an increase in stiffness in the lower part of the engine achieved by using a ladder frame in combination with a bearing beam.Godkänd; 1996; 20061214 (biem)
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Quan, Ke Ming. "An experimental and theoretical study of ultrasound fields with reference to their use in physiotherapy and hyperthermia." Thesis, University of Aberdeen, 1991. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602294.
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Chapter 1, an introduction to the use of ultrasound in physiotherapy and in hyperthermia is given. Previous studies in ultrasound physiotherapy and hyperthermia are reviewed but the emphasis is given to those which investigated the mechanisms responsible for the beneficial effects of therapeutic ultrasound and for the efficacy of cell killing of ultrasound hyperthermia. A review of the studies of the non-thermal effects of ultrasound is the subject of Chapter 2. Some recent studies carried out in this field in our laboratory are included. Knowledge of acoustical power, spatial peak and spatial average intensities are central to useful studies of bioeffects and to patient safety in the cases of therapy and clinical hyperthermia. Some techniques for measurements of ultrasound dosimetry which have been employed (and studied) are outlined in Chapter 3. At present the total power output from a therapeutic transducer is often derived by measuring the radiation force of the ultrasonic beam exerting on either a total absorber or a total reflector suspended at 45 to vertical. In Chapter 4 and Chapter 5, I discuss some new problems of these techniques and the magnitude of errors which might be caused. Chapter 6 and Chapter 7 present the results of theoretical studies of the field distri-butions from a plane circular piston transducer under both progressive and standing wave conditions. The effect of wave diffraction on the field distribution, bulk streaming and mea-surement of radiation force using a plane reflector is discussed. The ratio of the spatial peak to spatial average intensity for plane circular transducers in a progressive field is theoretic-cally calculated and compared with experimental results. The question of how to define the standing wave ratio is considered by taking into account of the effect of wave diffraction. Chapter 8 and Chapter 9 concern the thermal distributions generated by ultrasound in tissues. An experimental study of the temperature distributions in tissue/bone phantoms induced by therapeutic ultrasound using infra-red technique is described in Chapter 8. In Chapter 9 the thermal patterns generated by a plane circular transducer in a 3-D tissue model were calculated and they were compared with the experimental results described in the previous chapter. The thermal distributions generated by an applicator consisting of five divergent transducers were simulated in the same tissue model. Possible advantages of using such an applicator for ultrasound therapy and for treating large superficial tumours are discussed.
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Karlsson, Linn. "A Numerical and Experimental Investigation of the Internal Flow of a Freezing Water Droplet." Licentiate thesis, Luleå tekniska universitet, Strömningslära och experimentell mekanik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17930.
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The overarching aim of this work is to study the freezing process of a single water droplet freezing on a cold surface, which is an interesting and important phenomenon with possible applications in many areas. Understanding the freezing process of a single water droplet is for example an important step when preventing unwanted icing, e.g. in the case of airplane wings and propellers, wind turbine rotor blades, and road surfaces.As a step in understanding the freezing process, the study specifically focuses on the internal flow in the droplet during the freezing process. To do this, the study combines the use of Computational Fluid Dynamics (CFD) to build a model of the freezing process and experimental methods, i.e. Particle Image Velocimetry (PIV) to validate the numerical results. Focus is to start with the heat- and mass transfer inside the droplet using simple geometries with a rigid boundary, not modelling the outside environment as the air and the cooling plate. These components will be incorporated in the model further on.Three papers will be included in the study. In Paper A the CFD model is created and tested on a simple 2D-geometry of a droplet. The numerical result is partially compared to experimental work found in literature. In Paper B the numerical model is developed even further and a more realistic geometry of a real droplet, although with rigid boundaries, is used. The numerical results are as for Paper A validated with experimental results found in literature. In Paper C the internal flow inside the droplet has been investigated experimentally to estimate the velocities in the water, so that in the future the results can be used to validate the numerical work.The results show that is possible to work with a very simple CFD model and still capture the main flow features and freezing characteristics in a freezing water droplet. In line with previous research, this study confirms that the natural convection induced by gravity is significant for the internal flow, as compared to conduction and effects of ice creation. If studying the freezing time the internal flow has little effect. However, when estimating the velocities in the water it is crucial. It can be seen that the gravity effects are most pronounced around the density maximum for water (at T = 4◦C). The experiments show that the method used to study the flow inside the droplet is a working method, and the velocities in the water has been estimated. The next step is to further develop the CFD model and validate the numerical work with the experimental results. An interesting next step is to incorporate a moving interface to capture the volume expansion during the phase change.Godkänd; 2015; 20151020 (kainlr); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Linn Karlsson Ämne: Strömningslära/Fluid Mechanics Uppsats: A Numerical and Experimental Investigation of the Internal Flow of a Freezing Water Droplet Examinator: Professor Staffan Lundström, Institutionen för teknikvetenskap och matematik, Avdelning: Strömningslära och experimentell mekanik Luleå tekniska universitet Diskutant: Professor Alexander Kaplan, Institutionen för teknikvetenskap och matematik, Avdelning: Produkt- och produktionsutveckling Tid: Fredag 18 december, 2015 kl 09.00 Plats: E231, Luleå tekniska universitet
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Rinehart, Aidan. "Numerical and experimental investigations of fluid-surface interaction." Licentiate thesis, KTH, Strömningsmekanik och Teknisk Akustik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-290658.
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Fluid-structure interactions play a central role in an overwhelming number of physical phenomena. All fluid dynamic students are familiar with the common assumption of a "smooth boundary". While this assumption often is enough to provide a high level understanding of the dynamics and physics at hand in practice this is not true. Much of the detail and the unique phenomena can be traced back to surface properties that deviate from this elementary assumption. In this work we investigate three problems all motivated by the existence of non-smooth surfaces. The first paper considers how inhomogeneous surfaces can generate a lift force for lubricated contacts. This work showcases how subtle changes to surface texture or chemistry modeled by a slip length can invoke non-trivial forces. These forces result in striking particle trajectories not possible in the presence of a smooth no-slip wall. The next work focuses on porous surfaces. Often the geometry of surfaces in nature and industry are complex covering a wide range of length scales. Resolving all the scales of motion arising from fluid interaction with such surfaces are computationally expensive. Effective equations are often applied to reduce the cost of such simulations. The Brinkman equation is one common model choice for free-fluid and porous surface interface. Despite the common application of the Brinkman equation, fundamental questions about what the effective viscosity should be remain open. We compare pore-scale Stokes flow solutions to the Brinkman model for several porous surfaces. This study provides a scaling for the effective viscosity as well as error quantification of the Brinkman model. Lastly, we investigate how porous surfaces modify a turbulent boundary layer. Streamwise preferential porous surfaces have recently been suggested as a surface modification that has the potential to reduce drag. We compare particle image velocimetry measurements with direct numerical simulations focusing on the near wall features that are modified from the canonical smooth wall case. We present some preliminary turbulent statistics and flow visualizations in the current report.
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Miller, Kyle Glen. "Theoretical and Experimental Investigation of a Quadspectral Nonlinearity Indicator." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/8710.
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Understanding the impact of jet noise and other high-amplitude sound sources can be improved by quantifying the nonlinearity in a signal with a single-microphone measurement. An ensemble-averaged, frequency-domain version of the generalized Burgers equation has been used to derive a quantitative expression for the change in spectral levels (in decibels) over distance due to geometric spreading, thermoviscous absorption, and nonlinearity, respectively. The nonlinearity indicator, called νN , is based on the quadspectral Morfey-Howell indicator, which has been used in the past to characterize nonlinearity in noise waveforms. Unlike the Morfey-Howell indicator, the νN indicator has direct physical significance, giving a change in decibels per meter of the sound pressure level spectrum specifically due to nonlinearity. However, a detailed characterization of the expected behavior and potential issues for the nonlinearity indicator has been lacking. The quadspectral nonlinearity indicator is first calculated for well-known solutions to several basic acoustical scenarios to determine its expected behavior in both the near field and far field. Next, the accuracy of νN is examined as a function of measurement parameters such as sampling frequency, signal bandwidth, scattering, and noise. Recommendations for conducting experiments are given based on the findings. Finally, the indicator is calculated for model-scale and military jet noise waveforms. These tests reveal the utility and accuracy of the νN indicator for characterizing broadband noise; the indicator gives frequency-dependent information about the waveform from a single-point measurement.
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Kapodistrias, Georgios. "A theoretical and experimental study on multiple scattering from bubbles, with emphasis on scattering from a bubble located close to the air-sea interface /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/7150.
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Monfort, Jeffrey Ross. "Experimental Investigation into Thermo-Acoustic Instability in Pre-Mixed, Pre-Vaporized Bluff-Body Stabilized Flames." University of Dayton / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1438202236.
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Bayraktar, Songul. "Theoretical And Experimental Investigation On Centrifugal Fan With A Special Interest On Fan Noise." Phd thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/3/12608097/index.pdf.
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In this study, the effects of design parameters on the fan noise level are investigated both theoretically and experimentally. For the theoretical study, a computational aero- acoustic method is used to predict the flow induced noise of a fan. This method involves the coupling of a flow solver and a wave equation solver. Unsteady flow analysis is performed with URANS using FLUENT. Then the time dependent data are processed with LMS Sysnoise to compute the acoustic radiation. Experimental studies are performed to verify the theoretical results and additionally to investigate the effects of different design alternatives on noise level of the fan. The sound pressure and intensity level measurements are performed in the full anechoic room of Arçelik A.S. Research and Development Laboratories. The validation experiments indicate that there is a good agreement between numerical and experimental results. The experimental study with different fan designs gives information about the noise reduction possibilities.
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Uhlenhake, Gregory David. "Characterization of Turbocharger Performance and Surge in a New Experimental Facility." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1287424192.
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Rejent, Andrew. "Experimental Study of the Flow and Acoustic Characteristics of a High-Bypass Coaxial Nozzle with Pylon Bifurcations." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1250272655.
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Li, Dongli. "Computational and experimental study of shock wave interactions with cells." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:38beffe8-06c9-4b49-89f8-f5318c527800.
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This thesis presents a combined numerical and experimental study on the response of kidney cells to shock waves. The motivation was to develop a mechanistic model of cell deformation in order to improve the clinical use of shock waves, by either enhancing their therapeutic action against target cells or minimising their impact on healthy cells. An ultra-high speed camera was used to visualise individual cells, embedded in tissue-mimicking gel, in order to measure their deformation when subject to a shock wave from a clinical shock wave source. Advanced image processing was employed to extract the contour of the cell from the images. The evolution of the observed cell contour revealed a relatively small deformation during the compressional phase and a much larger deformation during the tensile phases of a shock wave. The experimental observations were captured by a numerical model which describes the volumetric cell response with a bilinear Equation of State and the deviatoric cell response with a viscoelastic framework. Experiments using human kidney cancer cells (CAKI-2) and noncancerous kidney cells (HRE and HK-2) were compared to the model in order to determine their mechanical properties. The differences between cancerous and noncancerous cells were exploited to demonstrate a design process by which shock waves may be able to improve the specificity on targeted cancer cells while having minimal effect on normal cells. The cell response to shock waves was studied in a more biophysically realistic environment to include influence of cell size, shape and orientation, and the presence of neighbouring cells. The most significant difference was predicted when cells were in a cluster in which case the presence of neighbouring cells resulted in a four-fold increase on the von Mises stress and the membrane strain. Finally the numerical model was extended to capture the effect of cell damage using one of two paradigms. In the first paradigm the model captured microdamage during one shock wave but then assumed that the cell recovered by the time the next shock wave arrived. The second model allowed microdamage to accumulate with increasing number of shock waves. These models may be able to explain the strong effect that shock wave loading rate has on tissue damage. In conclusion a validated numerical model has been developed which provides a mechanistic understanding of how cells respond to shock waves. The model has application in suggesting improved strategies for current uses of shock waves, e.g., lithotripsy, as well as opening up new indications such as cancer treatment.
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Sahin, Fatma Ceyhun. "An Experimental Study On Off Design Performance And Noise In Small Pumps." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608418/index.pdf.
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This thesis study is focused on experimentally investigating pump noise at design and off-design operations and its relations with pressure fluctuations. Small size pumps are placed in a semi-anechoic chamber and operated at various system conditions and various rotational pump speeds. Pump operational data, noise data and time dependent pressure data are recorded. Fast Fourier Transform spectra of noise and pressure data are compared. Coherence spectrum between sound pressure level and hydraulic pressures are obtained. Data processing, Fast Fourier Transform and cross correlation are conducted with specific software Soundbook SAMURAI. The experiments have indicated that system characteristics or pump size do not have any influence on the noise of pump. On the other hand, pump characteristics are
found to be distinguishable by means of peak frequencies on the sound spectra which are proportional to blade passing frequency. Results of cross correlations also show that, pump outlet pressure is a more significant source of noise than pump inlet pressure.
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Holmberg, Andreas. "Experimental Determination of Aeracoustic Sources in Low Mach Number Internal Flows." Licentiate thesis, KTH, MWL Strömningsakustik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-26133.
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In this thesis, the in-duct experimental methods for determining aeroacoustic N-ports of in-duct elements are discussed and improved. The scattering matrix determination methods and the related wave decomposition methods are evaluated from measurements in an empty duct carrying a mean flow. The improvements of a new over-determination method for the source part of the N-port is studied using simulations and measurements; in quiescent air as well as measurements of the flow associated noise of a mixer plate, here a triangular plate inserted at an angle in a duct. The new method is shown to improve suppression of random errors while no improvement is achieved for bias errors. Further, the methods are applied in the study of two different aeroacoustic phenomena; one is the effect on the flow associated noise of the triangular plate achieved by varying the bending stiffness. For the most resilient plate tested, it is observed that when the Strouhal number of the flow noise coalesce with the Helmholtz number of a specific eigen-mode of the plate, the noise is drastically dampened. There is also a weaker broad band effect. The other phenomena studied is the amplification and attenuation obtained for sound waves propagating in a T-junction of rectangular ducts. It is found that by adding only 10% of inflow in the side branch relative to that in the main branch, the amplification is heavily increased. By adding another 10% the amplification is again similar to that of no side branch flow. Adding further flow lessens the effects still.QC 20101118
Experimental characterization of aero-acoustic sources
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ALLGOOD, DANIEL CLAY. "AN EXPERIMENTAL AND COMPUTATIONAL STUDY OF PULSE DETONATION ENGINES." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1095259010.
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Giraud, Jarom Henry. "Experimental Analysis of Energy-Based Acoustic Arrays for Measurement of Rocket Noise Fields." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3950.
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Microphone arrays are useful for measuring acoustic energy quantities (e.g. acoustic intensity) in the near-field of a full-scale solid rocket motor. Proper characterization of a rocket plume as a noise source will allow for more accurate predictions in engineering models that design for protection of structures, payloads and personnel near the rockets. Acoustic intensity and energy density quantities were measured in three rocket noise fields and have shown that the apparent source region of the rocket becomes smaller and moves upstream as frequency increases. Theoretical results accounting for some scattering and finite-difference errors arising in these types of energy-based measurements have been previously discussed by other authors. This thesis includes results from laboratory experiments which confirm some of this previous theoretical work as well as gives insight into the physical limitation of specific microphone array designs. Also, calibrations for both magnitude and directional response of the microphones are demonstrated. Of particular interest is the efficacy of phase calibration of array microphones for the low-frequency regime below 200 Hz.
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Chhabra, Manish. "Source Characterization using an Experimental Method and Prediction of Insertion of the Exhaust System." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin154399673454236.
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Friedman, Adam D. "Theoretical and experimental study of generation mechanisms for laser ultrasound in woven graphite /epoxy composites with translaminar stitching." W&M ScholarWorks, 2000. https://scholarworks.wm.edu/etd/1539623984.
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The aerospace industry is beginning to use advanced composite materials for primary load bearing structures and their failure mechanisms must be better understood to predict their behavior in service. The Combined Loads Tests (COLTS) facility is being constructed at the NASA Langley Research Center to characterize these failure mechanisms. Laser based ultrasonic NDE can monitor the samples during dynamic loading without interfering with the structural tests. However, the constraints of implementing laser ultrasound in a structures laboratory reduces the efficiency of the technique. The system has to be "eye-safe" because many people will be present during the structural tests. Consequently, laser light has to be delivered through fiber optics and a significant amount of light is lost. Also, the nature of the composite materials makes laser ultrasonic inspection difficult. The composites of interest are formed from woven layers that are stitched through the laminate thickness and bound in a resin matrix. These materials attenuate ultrasound strongly and exhibit a high degree of scattering.;Generation mechanisms in laser based ultrasound must be better understood to improve generation efficiency and consequently improve the signal-to-noise ratio. Although some experimental and theoretical studies have been conducted to characterize generation mechanisms, more extensive work is needed for composite materials. Specifically, we are concerned with generation mechanisms in thick, stitched composite structures. We describe a theoretical and experimental investigation of laser generated ultrasound in complex composite materials. We first develop a mathematical model describing the thermoelastic generation of ultrasound in a general anisotropic material. We then present a wide range of experimental data investigating the effects of laser and material parameters on the generated ultrasound. We specifically consider the relationship between laser pulse width, laser wavelength, and material composition. Finally, we compare this data to our mathematical model.
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Grothe, Timo [Verfasser], Roger [Akademischer Betreuer] Grundmann, Avraham [Akademischer Betreuer] Hirschberg, and Cornelis J. [Akademischer Betreuer] Nederveen. "Experimental Investigations of Bassoon Acoustics / Timo Grothe. Gutachter: Roger Grundmann ; Avraham Hirschberg ; Cornelis J. Nederveen. Betreuer: Roger Grundmann." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://d-nb.info/1068447982/34.
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Li, Wanlu. "EXPERIMENTAL STUDIES ON THE DETERMINATION OF ACOUSTIC BULK MATERIAL PROPERTIES AND TRANSFER IMPEDANCE." UKnowledge, 2014. http://uknowledge.uky.edu/me_etds/48.
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Soft trim absorbing parts (i.e., headliners, backwalls, side panels, etc.) are normally comprised of different layers including films, adhesives, foams and fibers. Several approaches to determine the complex wavenumber and characteristic impedance for porous sound absorbing materials are surveyed and the advantages and disadvantages of each approach are discussed. It is concluded that the recently documented three-point method produces the smoothest results. It is also shown that measurement of the flow resistance and the use of empirical equations is sufficient for many common materials. Following this, the transfer impedance of covers, adhesives, and densified layers are measured using an impedance difference approach. The transfer matrix method was then used to predict the sound absorption of a multi-layered materal which included a perforated cover, fiber layers, and an adhesive. The predicted results agree well with measurement.
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Kuoppala, Oskar. "Cavitation analysis on test rig. : An experimental and CFD study executed in collaboration with Epiroc AB." Thesis, Umeå universitet, Institutionen för tillämpad fysik och elektronik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-188337.
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This master thesis project was done in collaboration with Epiroc Group Ab. Epiroc supplies high-quality drills of various types that can be used both above and below ground. A major problem in their percussive rock drills is that that cavitation is formed. Cavitation is a phenomenon that occurs when a fluid is subject to a sudden pressure drop. This pressure drop causes the liquid to vaporize and create gas bubbles. These gas bubbles will cause erosion to the walls when imploded. These cavitation damages lead to drills breaking and parts having to be replaced preserved. An experimental rig was used to create cavitation. From the experimental rig, it was possible to measure the hydraulic transients that are created when the valve was closed. In this study, we examined whether one can visually see these damages occurring inside the pipe on valve parts that are subjected to these cavitation damages. CFD simulations were used to re-create the closing of the valve in the experimental rig. By exporting pressure data from the experiments one could compare the numerical result to the experimental data. It was also investigated if it is possible to see some connection between the gas formation and the damages seen visually from the experimental part. For the simulation the realizable k − ε methods were implemented with enhanced wall treatment. The mixture model was used since we have a multi-phase flow. Some visual damages were recognized during the experiments. However, no distinguished pattern or specific areas was established. From the simulations, it could be determined that they generated gas when the valve was closed. However, the pressure transients could not be replicated in the numerical result.
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Rosi, Giuseppe. "Control of sound radiation and transmission by means of passive piezoelectric networks : modelling, optimization and experimental implementation." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2010. http://tel.archives-ouvertes.fr/tel-00815038.
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Cette thèse a comme objet la réduction du rayonnement acoustique des structures minces par un réseau piézoélectrique passif. Une analyse détaillé des caractéristiques de rayonnement des structures minces est présenté, avec l'objectif d'utiliser ces caractéristiques pour l'optimisation de la structure intelligente. Deux stratégies de contrôle sont considérées: contrôle localisé et contrôle distribué. Le contrôle localisé utilise un réseau de actionneurs positionnés en des endroits optimisés, et le circuit est conçu pour concentré l'effort de contrôle dans la réduction de la puissance acoustique rayonnée. La modélisation, l'optimisation et l'étude expérimentale d'une structure intelligente localisée est ici présenté. Le contrôle distribué utilise un réseau uniforme de actionneurs piézoélectriques, connecté à un circuit optimisé pour profiter de cette distribution spatiale en termes de efficacité dans la réduction de la puissance acoustique rayonnée et transmise. Une nouvelle structure intelligente, la plaque avec un électrode résistif (PRE) est ici présenté.
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KADAM, PRASAD H. "DEVELOPMENT AND COMPARISON OF ANALYTIC, NUMERICAL AND EXPERIMENTAL TECHNIQUES TO FORMULATE FOUR-POLE MATRICES OF THREE-DIMENSIONAL ACOUSTIC SYSTEMS." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1145669967.
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Lindberg, Eskil. "A Vibro-Acoustic Study of Vehicle Suspension Systems : Experimental and Mathematical Component Approaches." Doctoral thesis, KTH, MWL Strukturakustik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-121575.
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The objective of the present work is to study the vehicle suspension as a vibro-acoustic system of high complexity, consisting of many sub-systems with fundamentally different acoustical properties. In a parallel numerical and experimental modelling effort, important contributions to the understanding of its behaviour have been achieved. These findings are based on a balance between component investigations and global modelling of the complete system; they have been formulated for the transmission of both tyre-road excitation and friction-induced vibrations in the brake system. Initially an experimental study was conducted on a full vehicle test rig studying the broadband interior brake noise problem of, here named, roughness noise. The purpose of the study was twofold: first, to determine if the transmission from the source to the interior of the vehicle was structure-borne; second, to study the complexity of the suspension as a vibro-acoustic system. Parameters a_ecting the vibro-acoustic source were varied to gain understanding of the source mechanisms. This experimental study laid the foundation of the first part of this thesis (paper A) and provided the directions for the second part, the development of a mathematical modelling approach (paper B and C). In these two papers, methods for analysing the complex vibro-acoustic transfer of structure-borne sound in a vehicle suspension system were developed. The last part was then focussed on the wheel rim influence on the vibro-acoustic behaviour (paper D) of the suspension system. As a whole, the work clearly demonstrates that it is possible to conduct component studies of subsystems in the vehicle suspension system; and from these component studies it is possible draw conclusions that very well may avoid severe degradations in the interior noise of future vehicle generations.QC 20130503
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Palathamveed, Naqash. "Acoustic behavior of intake manifolds under tip-in and steady flow conditions an experimental investigation /." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1199738161.
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Hedlund, Jakob. "Experimental Investigation of Hydrodynamic Effects on a Vibrating Kaplan Runner." Thesis, Luleå tekniska universitet, Strömningslära och experimentell mekanik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-62149.
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An experimental investigation of a vibrating Kaplan turbine runner was performed in order to understand the hydrodynamic effects and to obtain or confirm the mass and damping coefficients used for dimensioning at the design stage. Improved design can lead to increased efficiency and lifetime of hydropower stations. The method was based on the 90◦ phase shift between acceleration and velocity and their relationship with mass and damping respectively. The experiment examined frequencies between 1–9 Hz at displacements between 0.25–2.00 mm. Results showed a frequency dependent added mass which varied between 1.2 and 1.5 (neglecting the highest and lowest frequencies) and an added damping between 0.8 and 1.2 which became of importance at low frequencies. A mathematical interpretation of the fluid solid interactions (based on the constitutive equation for stresses in a Newtonian fluid) has been derived and connected to the obtained experimental data.
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Yelamanchi, Bharat. "Experimental Study of Disruption of Columnar Grain Growth during Rapid Solidification." Youngstown State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1442408459.
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Fattahi, Sadegh, and Philip Månsson. "Computational and experimental study of fuel leakage through a ventilation valve during various driving conditions." Thesis, Linköpings universitet, Mekanisk värmeteori och strömningslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-159194.
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Fuel leakage through a fill limit vent valve (FLVV) inside a fuel tank is an important factor to consider during the design of a new tank. The performance of the carbon canister which absorbs the hydrocarbon can be compromised if fuel manages to escape through the valve, so called Liquid Carry Over (LCO) and thus not fulfilling the fuel emission requirements. As of today this is not thoroughly investigated using experiments nor Computational Fluid Dynamics. The main focus of this study was to develop a method to simulate the behaviour of the FLVV during various driving conditions at an early design stage and if this gives rise to fuel escaping through the FLVV. This method was later to be validated with an experimental set-up and later used to perform some simulations to investigate LCO by varying different parameters such as fuel level and different types of driving. What happens when the canister is purging was also investigated to see if it has a pronounced effect on LCO. Purging is when hydrocarbons, absorbed by the canister, are sent to the engine and giving rise to an under pressure in the tank.The method was developed to run on a cluster utilizing 200 Central Processing Unit Cores where each simulated physical second required an average of 3 hours of simulation time.The flow inside the tank was simulated using a Volume Of Fluid (VOF) multiphase model and the dynamic behaviour of the floater inside the FLVV was simulated using an overset mesh with a Dynamic Fluid Body Interaction.The movement of the simulated dynamic floater was validated with an experimental set-up specifically developed for the overset mesh validation and the motion of the floater was captured at a fairly accurate level.A prototype for an experimental tank was also developed and produced to validate the VOF set-up used for sloshing inside the tank which was utilized on the real tank but due to time limitation the experiments were not performed. The results from the parameter investigation showed that LCO was present in cases with high fuel level inside the tank 95 % and that an aggressive driving gives rise to a higher level of LCO compared to normal driving. Simulations with a fuel level of 85 % and lower showed no evidence of LCO for this particular tank model. The purging of the tank induced a pumping effect giving rise to a higher level of LCO pumped through by the floater.
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Ferro, Marco. "Experimental study on turbulent boundary-layer flows with wall transpiration." Doctoral thesis, KTH, Mekanik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-217125.
Full textAbstract:
Wall transpiration, in the form of wall-normal suction or blowing through a permeable wall, is a relatively simple and effective technique to control the behaviour of a boundary layer. For its potential applications for laminar-turbulent transition and separation delay (suction) or for turbulent drag reduction and thermal protection (blowing), wall transpiration has over the past decades been the topic of a significant amount of studies. However, as far as the turbulent regime is concerned, fundamental understanding of the phenomena occurring in the boundary layer in presence of wall transpiration is limited and considerable disagreements persist even on the description of basic quantities, such as the mean streamwise velocity, for the rather simplified case of flat-plate boundary-layer flows without pressure gradients. In order to provide new experimental data on suction and blowing boundary layers, an experimental apparatus was designed and brought into operation. The perforated region spans the whole 1.2 m of the test-section width and with its streamwise extent of 6.5 m is significantly longer than previous studies, allowing for a better investigation of the spatial development of the boundary layer. The quality of the experimental setup and measurement procedures was verified with extensive testing, including benchmarking against previous results on a canonical zero-pressure-gradient turbulent boundary layer (ZPG TBL) and on a laminar asymptotic suction boundary layer. The present experimental results on ZPG turbulent suction boundary layers show that it is possible to experimentally realize a turbulent asymptotic suction boundary layer (TASBL) where the boundary layer mean-velocity profile becomes independent of the streamwise location, so that the suction rate constitutes the only control parameter. TASBLs show a mean-velocity profile with a large logarithmic region and without the existence of a clear wake region. If outer scaling is adopted, using the free-stream velocity and the boundary layer thickness (δ99) as characteristic velocity and length scale respectively, the logarithmic region is described by a slope Ao=0.064 and an intercept Bo=0.994, independently from the suction rate (Γ). Relaminarization of an initially turbulent boundary layer is observed for Γ>3.70×10−3. Wall suction is responsible for a strong damping of the velocity fluctuations, with a decrease of the near-wall peak of the velocity-variance profile ranging from 50% to 65% when compared to a canonical ZPG TBL at comparable Reτ. This decrease in the turbulent activity appears to be explained by an increased stability of the near-wall streaks. Measurements on ZPG blowing boundary layers were conducted for blowing rates ranging between 0.1% and 0.37% of the free-stream velocity and cover the range of momentum thickness Reynolds number 10000<Reθ<36000. Wall-normal blowing strongly modifies the shape of the boundary-layer mean-velocity profile. As the blowing rate is increased, the clear logarithmic region characterizing the canonical ZPG TBLs gradually disappears. A good overlap among the mean velocity-defect profiles of the canonical ZPG TBLs and of the blowing boundary layers for all the Re number and blowing rates considered is obtained when normalization with the Zagarola-Smits velocity scale is adopted. Wall blowing enhances the intensity of the velocity fluctuations, especially in the outer region. At sufficiently high blowing rates and Reynolds number, the outer peak in the streamwise-velocity fluctuations surpasses in magnitude the near-wall peak, which eventually disappears.Genom att använda sig av genomströmmande ytor, med sugning eller blåsning, kan man relativt enkelt och effektivt påverka ett gränsskikts tillstånd. Genom sin potential att påverka olika strömningsfysikaliska fenomen så som att senarelägga både avlösning och omslaget från laminär till turbulent strömning (genom sugning) eller som att exempelvis minska luftmotståndet i turbulenta gränsskikt och ge kyleffekt (genom blåsning), så har ett otaligt antal studier genomförts på området de senaste decennierna. Trots detta så är den grundläggande förståelsen bristfällig för de strömningsfenomen som inträffar i turbulenta gränsskikt över genomströmmande ytor. Det råder stora meningsskiljaktigheter om de mest elementära strömningskvantiteterna, såsom medelhastigheten, när sugning och blåsning tillämpas även i det mest förenklade gränsskiktsfallet nämligen det som utvecklar sig över en plan platta utan tryckgradient. För att ta fram nya experimentella data på gränsskikt med sugning och blåsning genom ytan så har vi designat en ny experimentell uppställning samt tagit den i bruk.Den genomströmmande ytan spänner över hela bredden av vindtunnelns mätsträcka (1.2 m) och är 6.5 m lång i strömningsriktningen och är därmed betydligt längre än vad som använts i tidigare studier. Detta gör det möjligt att bättre utforska gränsskiktet som utvecklas över ytan i strömningsriktningen. Kvaliteten på den experimentella uppställningen och valda mätprocedurerna har verifierats genom omfattande tester, som även inkluderar benchmarking mot tidigare resultat på turbulenta gränsskikt utan tryckgradient eller blåsning/sugning och på laminära asymptotiska sugningsgränsskikt. De experimentella resultaten på turbulenta gränsskikt med sugning bekräftar för första gången att det är möjligt att experimentellt sätta upp ett turbulent asymptotiskt sugningsgränsskikt där gränsskiktets medelhastighetsprofil blir oberoende av strömningsriktningen och där sugningshastigheten utgör den enda kontrollparametern. Det turbulenta asymptotiska sugningsgränsskiktet visar sig ha en medelhastighetsprofil normalt mot ytan med en lång logaritmisk region och utan förekomsten av en yttre vakregion. Om man använder yttre skalning av medelhastigheten, med friströmshastigheten och gränsskiktstjockleken som karaktäristisk hastighet respektive längdskala, så kan det logaritmiska området beskrivas med en lutning på Ao=0.064 och ett korsande värde med y-axeln på Bo=0.994, som är oberoende av sugningshastigheten. Om sugningshasigheten normaliserad med friströmshastigheten överskrider värdet 3.70x10^-3 så återgår det ursprungligen turbulenta gränsskiktet till att vara laminärt. Sugningen genom väggen dämpar hastighetsfluktuationerna i gränsskiktet med upp till 50-60% vid direkt jämförelse av det inre toppvärdet i ett turbulent gränsskikt utan sugning och vid jämförbart Reynolds tal. Denna minskning av turbulent aktivitet verkar härstamma från en ökad stabilitet av hastighetsstråken närmast ytan. Mätningar på turbulenta gränsskikt med blåsning har genomförts för blåsningshastigheter mellan 0.1 och 0.37% av friströmshastigheten och täcker Reynoldstalområdet (10-36)x10^3, med Reynolds tal baserat på rörelsemängds-tjockleken. Vid blåsning genom ytan får man en stark modifiering av formen på hastighetesfördelningen genom gränsskiktet. När blåsningshastigheten ökar så kommer till slut den logaritmiska regionen av medelhastigheten, karaktäristisk för turbulent gränsskikt utan blåsning, att gradvis försvinna. God överens-stämmelse av medelhastighetsprofiler mellan turbulenta gränsskikt med och utan blåsning erhålls för alla Reynoldstal och blåsningshastigheter när profilerna normaliseras med Zagarola-Smits hastighetsskala. Blåsning vid väggen ökar intensiteten av hastighetsfluktuationerna, speciellt i den yttre regionen av gränsskiktet. Vid riktigt höga blåsningshastigheter och Reynoldstal så kommer den yttre toppen av hastighetsfluktuationer i gränsskiktet att överskrida den inre toppen, som i sig gradvis försvinner.
QC 20171101