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Ribichini, Remo. "Modelling of electromagnetic acoustic transducers." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/9010.
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At present, the dominant technology for transducers in the field of Ultrasonic Non-Destructive Testing is piezoelectric. However, some industrially important applications, like the inspection of components operating at high temperature or while in motion, are difficult tasks for standard piezoelectric probes since mechanical contact is required. In these cases, contactless NDT techniques can be an attractive alternative. Among the available options, Electromagnetic Acoustic Transducers (EMATs) can generate and detect ultrasonic waves without the need for a physical contact between the probe and the test object, as their operation relies on electromagnetic, rather than mechanical coupling. Since EMATs do not require any coupling liquid, the experimental procedures for inspection set-up are simplified and a source of uncertainty is eliminated, yielding highly reproducible tests that make EMATs suitable to be used as calibration probes for other ultrasonic tests. A further advantage of EMATs is the possibility of exciting several wave-modes by appropriate design of the transducer. Unfortunately, EMATs are also characterized by a relatively low signal-to-noise ratio and by a complex operation relying on different transduction mechanisms that make their performance dependent on the material properties of the testpiece. The present work aims to develop a numerical model including the main transduction mechanisms, the Lorentz force and magnetostriction, that can be employed as a prediction tool to improve the understanding of EMAT operation. Following an overview on the historical development of EMATs and their models, the theory describing EMAT operation is presented. The governing equations are implemented into a commercial Finite Element package. The multi physics model includes the simulation of the static and dynamic magnetic fields coupled to the elastic fields through custom constitutive equations to include magnetostriction effects. The model is used to quantitatively predict the performance of a magnetostrictive EMAT configuration for guided waves without employing arbitrary parameters. The results are compared to experimental data providing a validation of the model and insight on the transduction process. The validated model, together with experimental tests, is exploited to investigate the performance of different EMAT designs for Shear Horizontal waves in plates. The sensitivities of each configuration are compared and the effect of key design parameters is analyzed. Finally, the model is used in the evaluation of the performance of bulk wave EMATs on a wide range of steel grades. Experimental data interpreted via numerical simulations are employed to investigate the relative weight of the transduction mechanisms, with implications on the applicability of EMATs on the range of steels usually encountered in inspections.
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Ramanathan, Sathish Kumar. "Linear Acoustic Modelling and Testing of Exhaust Mufflers." Thesis, KTH, Aeronautical and Vehicle Engineering, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4340.
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Intake and Exhaust system noise makes a huge contribution to the interior and exterior noise of automobiles. There are a number of linear acoustic tools developed by institutions and industries to predict the acoustic properties of intake and exhaust systems. The present project discusses and validates, through measurements, the proper modelling of these systems using BOOST-SID and discusses the ideas to properly convert a geometrical model of an exhaust muffler to an acoustic model. The various elements and their properties are also discussed.
When it comes to Acoustic properties there are several parameters that describe the performance of a muffler, the Transmission Loss (TL) can be useful to check the validity of a mathematical model but when we want to predict the actual acoustic behavior of a component after it is installed in a system and subjected to operating conditions then we have to determine other properties like Attenuation, Insertion loss etc,.
Zero flow and Mean flow (M=0.12) measurements of these properties were carried out for mufflers ranging from simple expansion chambers to complex geometry using two approaches 1) Two Load technique 2) Two Source location technique. For both these cases, the measured transmission losses were compared to those obtained from BOOST-SID models.
The measured acoustic properties compared well with the simulated model for almost all the cases.
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Hurrell, Andrew M. "Finite difference modelling of acoustic propagation and its applications in underwater acoustics." Thesis, University of Bath, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250842.
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Ajaz, Mahnoor. "Finite Difference Time Domain Modelling of Ultrasonic Parametric Arrays in Two-Dimensional Spaces." The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1619109761801613.
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Laurinčiukaitė, Sigita. "Acoustic modelling of Lithuanian speech recognition." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2008. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2008~D_20080626_121551-77545.
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This paper is devoted to an acoustic modelling of Lithuanian speech recognition. Word-, syllable-, contextual syllable-, phoneme- and contextual phoneme-based speech recognition was investigated. Investigations were performed for isolated words and continuous speech. The most popular sub-word units in Lithuanian speech recognition are phonemes and contextual phonemes, and research on other sub-word units is omitted. This paper aims to compare capacity of linguistic sub-word units to model speech and to demonstrate that investigation of sub-word units suggest using alternative sub-word units to phoneme and contextual phoneme.
The dissertation proposes a new methodology for acoustic modelling of syllables and phonemes, new sub-word unit – pseudo-syllable; technologies for acoustic modelling of separate sub-word units, including developed schemes, tools and recommendations. Speech corpus of isolated words was prepared and two versions of corpus of continuous speech LRN were developed for experimental research.
Investigation of recognition of isolated words and construction of acoustic models for words showed that a size of training set of acoustic models, a content of training set in regard to number of speakers have an influence on speech recognition accuracy. The recommendations for word-based acoustic modelling are given.
Investigation of recognition of isolated words and construction of acoustic models for words, syllables and phonemes showed that the best recognition... [to full text]Darbas „Lietuvių šnekos atpažinimo akustinis modeliavimas“ yra skirtas lietuvių šnekos atpažinimo akustiniam modeliavimui. Darbe buvo tirtas žodžiais, skiemenimis, kontekstiniais skiemenimis, fonemomis ir kontekstinėmis fonemomis grįstas šnekos atpažinimas. Tyrimai atlikti izoliuotiems žodžiams ir ištisinei šnekai. Iki šiol lietuvių šnekos atpažinime populiariausi kalbos vienetai buvo fonema ir kontekstinė fonema, o kitų kalbos vienetų analizė nebuvo atliekama. Šiame darbe siekiama palyginti lingvistinio tipo kalbos vienetų gebėjimą modeliuoti šneką ir parodyti, kad kalbos vienetų analizė siūlo alternatyvius fonemai ir kontekstinei fonemai kalbos vienetus. Darbe pasiūlyta metodika mišriam skiemenų ir fonemų akustiniam modeliavimui, naujas kalbos vienetas – pseudo-skiemuo; technologijos atskirų kalbos vienetų akustiniam modeliavimui (schemos, įrankiai, rekomendacijos). Eksperimentiniams tyrimams atlikti paruoštas izoliuotų žodžių garsynas ir sukurtos dvi ištisinės šnekos garsyno LRN versijos. Ištyrus izoliuotų žodžių atpažinimą, akustinius modelius konstruojant žodžiams, nustatyta, kad modelių mokymo aibės dydis, akustinių modelių mokymo aibės turinys daro įtaką šnekos atpažinimo tikslumui. Pateikiamos rekomendacijos akustiniam modeliavimui žodžių pagrindu. Ištyrus izoliuotų žodžių atpažinimą, akustinius modelius konstruojant žodžiams, skiemenims ir fonemoms, gauti rezultatai 98 ±1,8 % tikslumu siejami su skiemens tipo kalbos vienetais. Dėl skiemenų akustinio modeliavimo... [toliau žr. visą tekstą]
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Wong, Lawdy Siu Shan. "Auditorium acoustic modelling on chaotic realisation." Thesis, Oxford Brookes University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394625.
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Oxnard, Stephen. "Efficient hybrid virtual room acoustic modelling." Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/17459/.
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This thesis investigates approaches to virtual room acoustic modelling and auralisation in order to a develop hybrid modelling solution that is capable of efficient and accurate simulation of enclosed sound propagation. Emphasis is placed on the advantages and disadvantages of state of the art numerical and geometric acoustic modelling methods. Numerical methods have been shown to preserve important sound wave characteristics such as diffraction and room modes, and are considered more accurate for low frequency acoustic modelling than geometric techniques which fail to preserve such wave effects. However, the implementation of numerical acoustic models inherently requires large computational effort compared to more efficient geometric techniques such as ray-tracing. This is particularly problematic for simulations of large-scale 3D acoustic environments and for high spatio-temporal sampling rates. A novel acoustic modelling solution is presented, which seeks to circumvent the disadvantageous computational requirements of 3D numerical models while producing a suitable approximation to low frequency sound behaviour. This modelling technique incorporates multiple planar cross-sectional 2D Finite Difference schemes that are utilised in combination to synthesise low frequency wave propagation throughout the target acoustic field. In this way a subset of prominent low frequency sound wave characteristics may be emulated with low computational cost compared to 3D numerical schemes. These low-frequency results can then be combined with the high-frequency output from efficient geometric simulations to create a hybrid model providing accurate broadband results at a relatively low computational cost. Investigation of room impulse response rendering for a series of theoretic and real spaces demonstrates advantages of this new hybrid acoustic modelling technique over purely ray-based methods in terms of low frequency accuracy, and over 3D numerical methods in terms of computational efficiency. Conclusions are drawn from objective measurements obtained from simulation results of the virtual models produced. Results demonstrate the applicability of the novel hybrid approach to the enhancement of purely ray-based room impulse response rendering by which a more realistic representation of low frequency wave phenomena may be simulated in an efficient manner, improving the theoretical accuracy of objective and audible results. This study contributes towards research and design of high-speed, interactive virtual acoustic simulations appropriate for industrial and creative virtual reality applications.
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Hunter, Alan Joseph. "Underwater Acoustic Modelling for Synthetic Aperture Sonar." Thesis, University of Canterbury. Electrical and Computer Engineering, 2006. http://hdl.handle.net/10092/1117.
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Underwater acoustic modelling is an important aspect of Synthetic Aperture Sonar (SAS) system design and algorithm development. Sea-trials are an expensive and time-consuming exercise and simulations provide an efficient and economic alternative. However, there are few simulators (in the open literature) that can efficiently provide realistic SAS data for large, complicated scenes. Conventional side-scan sonar simulators are not suitable for SAS data simulation. These simulators utilise narrow-beam and narrow-band approximations; typical SAS systems are wide-beam and wide-band and these approximations are invalid. Moreover, conventional side-scan sonar is a non-coherent imaging technique and SAS processing relies on the phase. Existing SAS simulators are capable of modelling very simple scenes only. They utilise a decomposition of the scene into point or smooth facet primitives, which is very inefficient. Many primitives are required and this imposes a severe restriction on scene complexity and size. This thesis presents a rigorous mathematical framework for the modelling of SAS imagery. A novel acoustic scattering model is developed and its implementation in a wide-beam and wide-band, multiple-receiver Interferometric SAS (InSAS) simulator is detailed. The scattering model utilises a decomposition of the scene into rough (rather than smooth) facet primitives. The use of rough facet primitives provides a significant increase in computational efficiency since scenes are decomposed into fewer primitives. This facilitates the simulation of larger and more complicated scenes. Each rough facet is characterised by its far-field beampattern. The statistics of the beampattern are related to the facet shape and roughness statistics using the Kirchhoff approximation. The beampattern is realised from its first and second-order statistics. The SAS imagery is obtained using a coherent sum of the facet responses and occlusions and multiple-scattering are resolved by ray-tracing. The simulator is implemented for use on a parallel computing cluster. The simulator is shown to provide realistic SAS data that is qualitatively and quantitatively similar to real data. The simulated results are considered, in many ways, superior to the simulated results in the literature.
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Shannon, Sean Matthew. "Probabilistic acoustic modelling for parametric speech synthesis." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708415.
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Zhang, Ning. "The computational modelling of electromagnetic acoustic imaging." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:2c4c9946-b90c-43a3-9039-1c7df2dcd976.
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The Electromagnetic Acoustic (EMA) technique is a novel multi-modal technique for medical imaging. It is sensitive, in principle, to contrast in mechanical properties and electrical properties and has potential in a number of applications such as breast tumour detection where there will be contrast between diseased and healthy tissue and high intensity focused ultrasound monitoring, where there will be contrast when tissue is ablated. A complete computational model for the EMA imaging is developed. The model considers the linear or nonlinear propagation of ultrasound in soft tissue, the dynamic response of the viscoelastic soft tissue to acoustic radiation force (ARF) stimulation and scattering of electromagnetic waves with and without the Doppler effect. The suitability of the EMA imaging for breast tumour detection is evaluated, modelling a tumour as a spherical inclusion in an infinite homogeneous background tissue with clinically relevant material properties. The results show that variations of the mechanical properties of underlying healthy breast tissue and tumour tissue in clinically feasible range should result in a change in the amplitude of the first Doppler component (FDC) of up to 50%, and varying the electrical contrast leads to a change in the ratio of the FDC and unshifted component (UC) of less than 1 dB. The relative difference between the first Doppler component and the unshifted component is greater than 68 dB and therefore the frequency demodulation may pose a significant challenge if EMA imaging is used for breast tumour detection. The feasibility of using the EMA imaging for real-time monitoring of High Intensity Focused Ultrasound (HIFU) therapy is also investigated. Simulations conducted with realistic liver tissue properties show that the induced Doppler effect in the scattered EM wave is not well correlated with the growth of thermal lesion, therefore it is unlikely to be a good indicator of the lesion size. EMA imaging may not be appropriate for monitoring HIFU therapy.
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Jackson, Edward James. "Modelling and monitoring nonlinear acoustic phenomena in high-intensity focused ultrasound therapy." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:cea762cf-8a12-4265-b1b1-a15214c58ac3.
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High intensity focused ultrasound (HIFU) provides a wide range of noninvasive therapies ranging from drug delivery to the destruction of kidney stones. In particular, thermal ablation by HIFU presents an effective noninvasive method for the treatment of deep seated solid tumours. HIFUâs further uptake is limited by a need for improved treatment planning and monitoring. Two nonlinear acoustic phenomena that play key roles in HIFU treatment: finite amplitude effects that lead to the generation of harmonics and steepening of wavefronts, and acoustic cavitation. The former must be taken into careful consideration for treatment planning purposes, while the latter has the potential to provide fast, real-time, cost effective treatment monitoring. The first half of this thesis provides new measurements for the nonlinear acoustic properties of tissue, assesses the validity of two common modelling techniques for simulating HIFU fields. The second half develops a new method for combining passive acoustic mapping- an ultrasound monitoring technique- with MR thermometry, to assess estimates of cavitation enhanced heating derived from passive acoustic maps. In the first results chapter B/A was measured in ex-vivo bovine liver, over a heating/ cooling cycle replicating temperatures reached during HIFU ablation, adapting a finite amplitude insertion technique (FAIS), which also allowed for measurement of sound-speed and attenuation. The method measures the nonlinear progression of a plane-wave through liver and B/A was chosen so that numerical simulations matched measured waveforms. Results showed that attenuation initially decreased with heating then increased after denaturation, sound-speed initially increased with temperature and then decreased, and B/A showed an increase with temperature but no significant post-heating change. These data disagree with other reports that show a significant change and suggest that any nonlinear enhancement in the received ultrasound signal post-treatment is likely due to acoustic cavitation rather than changes in tissue nonlinearity. In the second results chapter two common methods of modelling HIFU fields were compared with hydrophone measurements of nonlinear HIFU fields at a range of frequencies and pressures. The two methods usedwere the KZK equation and the commercial package PZFlex. The KZK equation has become the standard method for modelling focused fields, while the validity of PZFlex for modelling these types of transducers is unclear. The results show that the KZK equation is able to match hydrophone measurements, but that PZFlex underestimates the magnitude of the harmonics. Higher order harmonics in PZFlex are not the correct shape, and do not peak around the focus. PZFlex performs worse at higher pressures and frequencies, and should be used with caution. In the final two chapters a system for estimating cavitation-enhanced heating from acoustic maps is developed and benchmarked against magnetic resonance thermometry methods. The first chapter shows that the ultrasound and MR monitoring systems are compatible, and registers the two imaging systems. The HIFUfocus is clearly visible in passive maps acquired in the absence of cavitation and these coincide with the centre of heating in MR temperature images. When cavitation occurs, it coincides spatially and temporally with the appearance of a clear spike in temperature, especially when the passive maps are processed using the Robust Capon Beamformer algorithm. The final chapter shows how passive maps can be converted into thermal heating inputs, and used to estimate cavitation-enhanced temperature increases. These estimates have the potential to closely match maximum temperature rise, and estimated thermal dose after the estimated temperature rise is spatially averaged. However, themethod is not always successful. This is partly due to uncertainties in MR thermometry estimates, partly due to uncertainties in the acoustic properties of tissue.
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Svensson, Elin. "Physical modelling of acoustic shallow-water communication channels." Doctoral thesis, Stockholm : Farkost och flyg, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4572.
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Thomas, Sadiq. "Comprehensive finite element modelling of electromagnetic acoustic transducers." Thesis, University of Leeds, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509874.
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Willison, Peter A. "Transmission line matrix modelling of underwater acoustic propagation." Thesis, University of Essex, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334426.
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Leggetter, Christopher John. "Improved acoustic modelling for HMMs using linear transformations." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361709.
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Orme, E. A. "TLM applied to the modelling of underwater acoustic scattering." Thesis, University of Nottingham, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371287.
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Kirby, Raymond. "The acoustic modelling of dissipative elements in automotive exhausts." Thesis, Online version, 1996. http://ethos.bl.uk/OrderDetails.do?did=1&uin=uk.bl.ethos.361493.
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Hazzard, James F. "Numerical modelling of acoustic emissions and dynamic rock behaviour." Thesis, Keele University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265036.
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Simmons, Stephen Michael. "Non-linear modelling of the acoustic response of bubbles." Thesis, University of Newcastle Upon Tyne, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364761.
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Gonçalves, Da Silva Pinto Wagner José. "Modelling airframe noise : from aerodynamic topology to acoustic efficiency." Thesis, Poitiers, 2019. http://www.theses.fr/2019POIT2289.
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L’influence de la forme de cylindres longs sur leur rayonnement acoustique en écoulement est étudiée. Des simulations bidimensionnelles (2D) sont réalisées à bas nombre de Reynolds (Re=20-200), à l’aide du code de calcul direct (DNS) incompressible incompact3D au moyen d’une méthode de frontière immergée (IBM). Une formule dérivée de l’équation de Curle pour un cylindre compact permet la quantification de l’émission acoustique en 2D. En soufflerie anéchoïque, la signature acoustique d’une trentaine de géométries est mesurée, Re=4,000-53,000 ; l’anémométrie par fil chaud est utilisée pour la description des propriétés axiales de l’écoulement. L’avant corps et l’allongement (AR) sont les plus importantes propriétés géométriques tant pour l’écoulement que pour le rayonnement acoustique en 2D. Les géométries allongées sont généralement les plus silencieuses car les tourbillons sont moins intenses et repoussés vers l’aval et l’apparition de l’instationnarité est retardée. De leur côté, les résultats expérimentaux montrent que les géométries allongées sont les plus bruyantes, ce qui est à l’opposé des conclusions précédentes. Ceci est justifié par une augmentation significative de la cohérence de l’écoulement en envergure pour les AR les plus longs, presque complètement en phase, donc plus efficace acoustiquement. Globalement, cela implique que les géométries dont l’écoulement 2D est faiblement perturbé, marqué par un déclenchement plus tardif de l’instationnarité (Reynolds critique plus élevé), sont aussi plus organisées en 3D aux Re des mesures. La relation sous-jacente entre les transitions successives vers la turbulence nécessite une étude approfondieThe influence of the shape on the sound emission of cylindrical bluff-bodies is studied. Simulations are performed in two-dimensions (2D) at low-Reynolds number (Re=20-200), with the incompressible direct Navier-Stokes (DNS) solver incompact3D, using the Immersed Boundary Method (IBM) formalism; the acoustic emission is evaluated by a single formula derived from Curle’s equation for compact cylinders. In anechoic wind tunnel, the acoustic signature is measured for about 30 geometries, Re=4,000-53,000; hot-wire measurements of the spanwise flow characteristics are performed for a subset of the tested cylinders. The influence of both the shape of the upstream portion of the geometry and the breadth-to-height ratio (AR) are proved to be major features in terms of both the flow and its acoustic emission in 2D. By reducing the strength of the vortices and pushing them downstream and affecting the mechanics of the von Kármán instability (delaying the transition to unsteadiness), stretched shapes (with higher AR) are generally quieter. From the experiments, it is found that the geometries of biggest AR are the loudest, contraposing the results obtained in 2D. The disparity is justified by a significant increase of the spanwise coherence associated with the larger AR’s, practically fully-phased, thus more acoustically efficient. Globally, it is implied that geometries which have weakly perturbed flow in 2D, marked by a later transition to unsteadiness (larger critical Reynolds number), are also more organized in 3D, high-Reynolds number regimes. The underlying relationship between low and high-Reynolds number transitions must be further investigated
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Leonard, Gordon. "Acoustic modelling of bat pinnae utilising the TLM method." Thesis, Loughborough University, 2006. https://dspace.lboro.ac.uk/2134/20204.
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This thesis describes the numerical modelling of bioacoustic structures, the focus being the outer ear or pinnae of the Rufous Horseshoe bat (Rhinolophus rouxii). There have been several novel developments derived from this work including: • A method of calculating directionality based on the sphere with a distribution of measuring points such that each lies in an equal area segment. • Performance estimation of the pinna by considering the directionality of an equivalent radiating aperture. • A simple synthetic geometry that appears to give similar performance to a bat pinna. The outcome of applying the methods have yielded results that agree with measurements, indeed, this work is the first time TLM has been applied to a structure of this kind. It paves the way towards a greater understanding of bioacoustics and ultimately towards generating synthetic structures that can perform as well as those found in the natural world.
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Hörlin, Nils-Erik. "Hierarchical finite element modelling of Biot's equations for vibro-acoustic modelling of layered poroelastic media." Doctoral thesis, KTH, Farkost- och flygteknik, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95.
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This thesis concerns three-dimensional finite element modelling of Biot's equations for elasto-acoustic modelling of wave propagation in layered media including porous elastic materials. The concept of hierarchical (p-version) finite elements are combined with various weak forms of Biot's equations. Computationally efficient methods providing accurate solutions of sound propagation in layered porous media are discussed. The research falls within the areas linear acoustics and numerical acoustics. Important applications of the developed methods may be found within vehicle interior acoustics, e.g. engineering design of damping treatment based on multiple layers of porous materials.QC 20100618
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Hörlin, Nils-Erik. "Hierarchical finite element modelling of Biot's equations for vibro-acoustic modelling of layered poroelastic media /." Stockholm, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95.
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Campos, Antonio Guilherme Rocha. "Three-dimensional digital waveguide mesh modelling for room acoustic simulation." Thesis, University of York, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423754.
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Moss, Scott. "Modelling and experimental validation of the acoustic electric feedthrough technique." Fishermans Bend, Victoria : Defence Science and Technology Organisation, 2008. http://hdl.handle.net/1947/9738.
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Shen, Yijun. "Modelling the electro-acoustic characteristics of flow-through ultrasonic separators." Thesis, University of Southampton, 2003. https://eprints.soton.ac.uk/47551/.
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A flow-through ultrasonic separator is a novel type of separation device concentrating and separating suspended micro-particles from within a liquid in a standing ultrasonic field. It can accomplish a fast, sharp, efficient and controllable separation of micro-particles in a liquid suspension. The thesis focuses on modelling the electro-acoustic characteristics of flow-through ultrasonic separators with a special emphasis on analysing and designing the MEMS micromachined ultrasonic filter in an EPSRC and DSTL funded project. Based on the model results, a micromachined ultrasonic filter is designed and built using micromachining processes. The verification of the model against the fabricated device is made. A comparison of the predicted impedance results and the experimental measured results indicates a good match. It shows that the model can give high confidence in predicting the electro-acoustic characteristics and the filtration performance. The thesis uses an equivalent-circuit transducer model, coupled with acoustic impedance transfer relationships to analyse the transducer and cavity resonance model, and to investigate such ultrasonic separators with regards to the electro-acoustic characteristics of the resonator under different conditions. In particular, the influence of matching layer thickness and reflector thickness on the stored energy-frequency product of the layered resonator are examined in the cases of cells with a variety of transducer and cell characteristics. The thesis infers the acoustic force transfer equations and the acoustic pressure and velocity equations in the multi-layered resonator both with a rigid reflector and with an arbitrary termination. The stored energy-frequency product and the acoustic pressure distribution in the fluid chamber of the ultrasonic filters are investigated in detail. The modelled results regarding the electro-acoustic characteristics and the filtration performance of the resonator system in the ultrasonic separators have been satisfactorily validated by experimental measurement results in different ultrasonic separators. Research results show that the model can be used to tune the performance of flow-through ultrasonic separators by optimising the design of such efficient transducer resonators. Therefore, it can be widely used to predict the resonant behaviour as a result of modifications to a variety of multi-layered resonators of the ultrasonic separators.
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Wood, Michael Alan. "Modelling and prediction of acoustic disturbances from off-shore piling." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/412708/.
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This work presents details of a number of approaches used to elucidate the noise generating mechanisms involved in pile-driving through multiple modelling techniques. Principally, the work is divided into four sections: fluid-sediment analysis, recording analysis, elastic-sediment analysis, and wave equation analysis of piles. In the fluid-sediment analysis section, finite-element models were used to investigate the effect of varying the hammer cushion compliance on the radiated noise of a pile in situ. The compliance of the cushion affected the frequency response of the forcing function with softer cushions having reduced energy at higher frequencies than harder cushions. Using these forcing functions as inputs to the finite-element model showed similar changes in the frequency domain of the radiated noise, illustrating the linear nature of the finite-element model. The results from a similar finite-element model were submitted for the COMPILE piling noise modelling benchmark meeting to be compared against others' contribution. In order to take into account damping in the sediment, the benchmark model description employed a loss factor in the embedded section of the pile. The results from all parties generated consistent results, with predicted SELs within 2 dB and Lp;0-p within 3 dB. Also considered in the section is a propagation model based on normal mode analysis. The radiated noise from piling propagates at predictable angles determined by the relative wave speeds in the pile and in the water. As normal mode decomposition reduces the field into individual modes propagating at distinct angles, great modelling efficiencies can be made by limiting analysis to a reduced number of modes near the expected angle of propagation particularly at higher frequencies. The recording of a large section of a piling sequence is analysed to provide a comparison against modelling techniques. The recordings showed that the rate of decay exhibited in the recording required a non-linear energy loss mechanism to be present in the system. Of the metrics recorded it was found that the pile set, the increased penetration per strike, had the greatest correlation to the radiated noise. On examination of the fluid-element models, the pile set was found to increase over time with no indication of settling. This led to investigations focussing on the effects of a non-fluid sediment both on the propagation of noise and the direct coupling with the pile itself. Finite-element models including an elastic sediment allows for the propagation of shear waves through the sediment. As the pile is directly coupled to the sediment, the shear waves are generated much more readily than for a source in the water column. Sediments often exhibit an increase in shear speed based on a power law. This causes refraction of shear waves towards the water-sediment; trapping the energy near the interface allows for efficient propagation of the shear waves. The finite-element models also show that the acoustic pressure near the interface can be comparable to the compressive waves from the pile through the water column. As the propagation of these waves is much slower than the compressive waves the acoustic pressure decays evanescently with increasing distance from the interface. Inspecting the effect of the non-fluid sediment on the pile motion led to an investigation into wave equation analysis of piles models. These are finite-difference models that are used in civil engineering to determine, among other things, the ultimate capacity of the pile. These are time-domain finite-difference models that model the pulse within the pile following impact. Using these results, the radial expansion of the pile can be determined from which, when coupled to an acoustic model, an acoustic output may be generated. The coupled models with non-linear sediment damping components demonstrated behaviour not realised in the finite-element models, and ultimately the influence the sediment can have on the pile motion and the radiated noise.
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Forsyth, Simon Andrew. "Modelling of ultrasonic transduction and measurement using finite elements." Thesis, Nottingham Trent University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312311.
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Ericsdotter, Christine. "Articulatory-Acoustic Relationships in Swedish Vowel Sounds." Doctoral thesis, Stockholm : Department of Linguistics, Stockholm University, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-699.
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Noreland, Daniel. "Numerical Techniques for Acoustic Modelling and Design of Brass Wind Instruments." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3507.
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Patterson, Richard Sven. "Acoustic modelling of near borehole anolmalies via the generalised radon transform." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/59049.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1992.Includes bibliographical references (leaves 89-91).
by Richard Sven Patterson.
M.S.
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van, Mourik J. "Higher-order finite difference time domain algorithms for room acoustic modelling." Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/15661/.
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The acoustic qualities of indoor spaces are fundamental to the intelligibility of speech, the quality of musical performances, and perceived noise levels. Computationally heavy wave-based acoustic modelling algorithms have gained momentum in the field of room acoustic modelling, as ever-increasing computational power makes their use more feasible. Most notably the Finite Difference Time Domain (FDTD) method is often employed for rendering the low- and mid-frequency part of room impulse responses (RIRs). However, this algorithm has known disadvantages, most prominently dispersion error, which renders a large part of the simulated RIR invalid. This thesis is concerned with the implementation and analysis of higher-order FDTD stencils as a means to improve the current state-of-art FDTD methods that solve the room acoustic wave equation. A detailed analysis of dispersive properties, stability, and required grid spacing of current and higher-order stencils is presented, and has been verified using a GPU implementation of the different algorithms. It is argued that the 4th-order stencil gives the best result in terms of output quality versus computational effort. In addition, this thesis focusses on the derivation of absorbing boundaries for the 4th-order scheme, its stability analysis, and detailed analysis of absorptive properties compared to established boundary models for 2nd-order schemes. The newly proposed 4th-order scheme and its boundaries are tested in two case studies: a large shoebox model, in order to test the validity against a common benchmark and a complex acoustic space. For the latter study, impulse responses were measured in the National Centre for Early Music in York, UK, and computationally generated using the current state-of-the-art as well as the proposed 4th-order FDTD algorithm and boundaries. It is shown that the 4th-order stencil gives at least as good as, or better results than those achieved using the 2nd-order stencil, at lower computational costs.
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Medeiros, Augusto Amador. "On the modelling and characterization of acoustic liners under grazing flow." reponame:Repositório Institucional da UFSC, 2015. https://repositorio.ufsc.br/xmlui/handle/123456789/136463.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2015.Made available in DSpace on 2015-11-17T03:06:05Z (GMT). No. of bitstreams: 1 335896.pdf: 3607600 bytes, checksum: eb35bf98ba72f6228bbd3656f6a1aacd (MD5) Previous issue date: 2015
A determinação da impedância acústica de liners utilizados em motores turbofan de aeronaves comerciais é um ponto de interesse da comunidade científica há várias décadas, especialmente na presença de escoamentos tangenciais, condição similar à de operação. Diferentes técnicas foram desenvolvidas para obtenção da impedância de liners. Atualmente, as mais comuns são as técnicas inversas, que consistem em duas etapas: (i) medição do campo acústico em um duto com escoamento e uma amostra de material, e (ii) simulação do campo acústico e aplicação de um processo de otimização para encontrar a impedância que minimiza a diferença entre resultados experimentais e analíticos. Neste trabalho, foram discutidos três métodos: dois métodos inversos, o Método da Matriz de Transferência e o Método do Acoplamento Modal, e um método direto, o Método Prony. Os três métodos foram implementados e validados através de resultados de simulação numérica em Método de Elementos Finitos. Foram avaliados também o custo computacional e a sensibilidade dos métodos à presença de modos de alta ordem no campo acústico medido. Além disso, amostras de materiais típicos foram caracterizadas em uma bancada de testes em velocidades até Mach 0.25 para comparar os resultados dos diferentes métodos. Modelos preditivos semi-empíricos, que utilizam parâmetros geométricos do material para determinar sua impedância, foram também abordados neste trabalho. Alguns destes modelos foram implementados, e seus resultados para amostras disponíveis comparados aos medidos com os métodos citados. Por fim, uma nova técnica de determinação de impedância foi proposta, incorporando um modelo matemático de impedância ao processo de otimização, de forma a reduzir significativamente o número de incógnitas do sistema, estabilizando assim a solução.
Abstract : The problem of determining the acoustic impedance of liners used in turbofan engines of commercial aircraft has been a point of interest for the scientific community for decades, especially in the presence of grazing flows, similar to operational conditions. Different techniques have been developed to determine liner acoustic impedance under grazing flow. The current trends are inverse methods, which consist of two steps: (i) measurement of the acoustic field in a duct with flow and a liner sample, and (ii) modeling of the acoustic field and application of an optimization procedure to find the impedance that minimize the difference between experimental and analytic results. In this work, three techniques were discussed: two indirect methods, the Two-Port Matrix Method and the Mode-Matching Method; and a direct technique, the Straight-Forward Method. The three methods were implemented and validated by means of Finite Element Method numerical simulation results. The computational cost and the sensibility to the presence of higher-order modes were also assessed for each method. Semi-empirical predictive models, which use the geometrical parameters of the materials to determine their impedance, were also discussed in this work. Some of these models were implemented, and their results for available liner samples were compared to those obtained by measurements with the previously cited methods. Lastly, a new technique for impedance determination was proposed, which incorporated a mathematical impedance model to the optimization process as a means to significantly reduce the number of unknowns, therefore stabilizing the solution.
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Christen, Jean-Loup. "Acoustic transmission through composite shells with noise treatment : Modelling and sensitivity." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEC028.
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La transmission acoustique de plaques et de coques est un problème présent dans de nombreuses industries, de l'automobile à l'aéronautique en passant par le génie civil. Il s'agit alors, en présence d'une source externe, de limiter le niveau de bruit à l'intérieur d'une cavité enclose par une structure vibrante, qu'il s'agisse d'une voiture, d'un avion ou d'un immeuble.Les matériaux composites sont de plus en plus largement utilisés par toutes les industries du transport, du fait de leur faible masse rapportée à leur grande rigidité. Ces caractéristiques, utiles pour réduire la consommation énergétique des véhicules, sont cependant un handicap lorsqu'il s'agit de limiter le niveau de bruit intérieur. Il est alors nécessaire d'ajouter des protections acoustiques. On s'intéresse dans ce travail à la transmission d'un bruit produit à l'extérieur de la cavité, et à des solutions antibruit passives, utilisant des matériaux poreux absorbants. Ceux-ci, mousses ou laines minérales, présentent en général de bonnes performances acoustiques pour des fréquences élevées, mais nettement mois intéressantes en basses fréquences. Ce travail s'inscrit dans le cadre d'un projet international ayant pour objectif d'étudier la réduction de bruit à travers des structures composites incluant des protections acoustiques passives. Deux axes y sont privilégiés, la modélisation et l'analyse de sensibilité. En effet, les matériaux poreux et composites présentent souvent de grandes incertitudes, dues au procédé de fabrication, à la difficulté de mesure, ou encore simplement à des choix de conception à faire. On cherche donc à s'assurer de la robustesse des solutions étudiées.Cette thèse est organisée en trois parties. La première traite de la modélisation des structures composites et des traitements poroélastiques. On s'intéresse surtout à deux types de structures, les plaques et les cylindres, pouvant dans les deux cas inclure un grand nombre de couches et de matériaux différents. La deuxième partie traite des méthodes d'analyse de sensibilité, et d'applications dans le cas de la transmission acoustique à travers des structures composites. On s'intéressera enfin dans la troisième partie à l'effet du traitement poroélastique, à travers des études numériques et expérimentalesAcoustic transmission through plates and shells is a problem that appear in many applications, for example in the automotive or aerospace industries, or in civil engineering. The idea is to reduce the noise level inside a caivty enclosed by a vibrating structure, which may be a car, a plane or a building. Composite materials are widely used in the transportation industries due to their light weight and high mechanic resistance, but these features tend to increase the acoustic transparency of the structures, thus making it necessary to add acoustic protections for reducing noise in the enclosed cavity. The most frequently used acoustic protections take the form of layers of poroelastic materials, which are very efficient noise absorbers in high frequencies, but perform less efficiently in lower frequency ranges.This thesis is part of an international project aimed at improving the noise reduction performance of composite structures through passive sound packages. This implies the development of reduced models of acoustic transmission through such structures, and optimization studies on these models. Besides, the robustness of a solution with respect to uncertainties in the model have to be ensured. This thesis is organised in three parts, dealing with numerical modelling, sensitivity analysis for acoustic transmission and the effect of a porous treatment on sound transmission
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Cettour-Janet, Raphael. "Modelling the vibrational response and acoustic radiation of the railway tracks." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLC040/document.
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Dans un contexte de densification des villes et de leurs réseaux de transport, les gens sont de plus en plus exposés au bruit. Ainsi, le résultat de l'étude d'impact vibro-acoustique joue un rôle primordial dans l'expansion du réseau ferroviaire. L'une des principales sources est le bruit de roulement : La rugosité de la surface de la roue et du rail produit un déplacement imposé sur ces derniers. Ce déplacement entraine une réponse vibratoire des roues et de la voie ferrée et leurs rayonnements acoustiques. Cette thèse propose une amélioration de la modélisation vibro-acoustique de la voie ferrée.Pour la réponse vibratoire, le coté infini de la voie et sa déformation dans les 3 dimensions rendent les modèles analytiques et les éléments finis non-optimales dans la gamme de fréquence de l’audible. La méthode élément fini semi-périodique (SAFEM) est utilisée dans cette thèse pour modéliser une voie à support continue. Elle est ensuite couplée au théorème de Floquet pour modéliser une voie à support périodique. Cependant, cette technique génère des problèmes numériques qui ont imposé un algorithme adapté. La méthode d'Arnoldi du second ordre (SOAR) est utilisée avant de résoudre l'équation SAFEM permet de résoudre ces problèmes ainsi qu’apporter la stabilité requise. Des comparaisons avec d’autres modèles et des données expérimentales permettent de valider la méthode.Pour le rayonnement acoustique, la simulation de grand domaine en haute fréquence rendent inadapté l'utilisation de techniques conventionnelles (FEM, BEM, ...). La méthode proposée ici : la théorie variationnelle du rayon complexe est particulièrement bien adaptée à ce cas. Les principales caractéristiques de l'approche VTCR sont l'utilisation d'une formulation faible du problème acoustique, qui permet de considérer automatiquement les conditions limites entre sous-domaines. Ensuite, l'utilisation d'une répartition intégrale des ondes planes dans toutes les directions permet de simuler le champ acoustique. Les inconnues du problème sont leurs amplitudes. Cette méthode qui a déjà montré son efficacité pour les domaines fermés a été étendue au domaine ouvert et couplée à la réponse vibratoire. Des comparaisons avec des solutions analytiques et des simulations FEM à basse fréquence permettent de valider la méthodeIn a context of urban and transport network densification, people are increasingly exposed to noise. Consequently, the result of vibro-acoustic impact assessment has a pivotal role in rail network expansion. One of the main sources is the rolling noise: Roughness on the wheel and rail surface produce an imposed displacement one the both. This last, generates vibrational response of wheels and the railway track and their acoustic radiation. This PhD thesis presents some improvements of the vibro-acoustic railway track modelling.Concerning vibrational response, the infinite dimension in the longitudinal direction of the track and its deformation in the 3 dimensions, make the analytical models and finite elements non-optimal. The Semi-analytical finite element method (SAFEM), used in this thesis, is particularly well adapted in this case. Firstly, it is used to model railway track on a continuous support. Then, it is coupled with Floquet theorem to model tracks with a periodic support. However, this technique suffers from numerical problems that imposed an adapted algorithm. The second-order Arnoldi method (SOAR) is used to tackle them. This reduction allows to eliminate critical values improving the robustness of the method. Comparison with existing techniques and experimental results validate this model.Concerning acoustic radiation, big domains simulations at high frequency are almost unfeasible when using conventional techniques (FEM, BEM,…). The method used in this thesis, the Variational theory of complex ray (VTCR) is particularly well adapted to these cases. The principal features of VTCR approach are the use of a weak formulation of the acoustic problem, which allows to consider automatically boundary conditions between sub-domains. Then, the use of an integral repartition of plane waves in all the direction allow to simulate the acoustic field. The unknowns of the problem are their amplitudes. This method well assessed for closed domain, has been extended to open domain and coupled to vibrational response of the rail. Comparison with analytic solution and FEM simulation at low frequency allow to validate the method.Coupling these both methods allowed to simulate complex real life vibro-acoustic scenarios. Result of different railway tracks are presented and validated
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Mosharrof, Mohammad Sazzad. "Study and modelling of lightweight floor structure regarding its acoustic properties." Licentiate thesis, Luleå tekniska universitet, Drift, underhåll och akustik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17520.
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Lightweight floor structure is widely used in building industries and to have better sound insulation builders come up with different ways of construction. Depending on the construction the floor structure could either be coupled (floor and ceiling coupled by beams) or decoupled (no mechanical connection between floor and ceiling). Although there are many models on coupled structure but for decoupled structure the number is not too many. Keeping that in mind the present thesis talks about lightweight floors: the construction, properties, behaviour etc with a focus on developing a model for decoupled floor structure where the core contribution being the decoupling and adding the moment effect at plate beam joints. The advantage of decoupled structure is that it disconnects the sound bridge through the beams. One consequence on the other hand is that cavity resonance dominates the low frequency region. A comparative analysis is also done with the coupled model. While developing the model this talks about different mathematical tools such as Fourier transform, Floquet principle, Poisson's sum formula etc This also gives an overview of different types of modelling technique available such as analytical, Numerical, energy based approach, empirical method etc. A parametric study is also done here to find out the relative influence of different elements on sound pressure level.Godkänd; 2010; 20100809 (sazmos); LICENTIATSEMINARIUM Ämnesområde: Teknisk akustik/Engineering Acoustics Examinator: Professor Anders Ågren, Luleå tekniska universitet Diskutant: Docent Jonas Brunskog, DTU, Department of Electrical Engineering, Denmark Tid: Tisdag den 7 september 2010 kl 14.00 Plats: F719 Taylor, Luleå tekniska universitet
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Kao, David. "The vibro-acoustic modelling and analysis of damage mechanisms in paper." Thesis, University of Greenwich, 2006. http://gala.gre.ac.uk/6205/.
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This thesis investigates the use of the acoustic emission (AE) monitoring technique for use in identifying the damage mechanisms present in paper associated with its production process. The microscopic structure of paper consists of a random mesh of paper fibres connected by hydrogen bonds. This implies the existence of the two damage mechanisms of interest, the failure of a fibre/fibre bond and the failure of a fibre. The majority of this work focuses on the development of a novel hybrid mathematical model which couples the mechanics of the mass/spring model to the acoustic wave propagation model for use in generating the acoustic signal emitted by complex structures of paper fibres under strain. A discussion of the coupling method is presented and the model is then analysed using a simple plucked fibre as a test case with a comparison between the numerical and experimental results. The hybrid mathematical model is then used to simulate small fibre networks aimed at providing information on the acoustic response of each damage mechanism. To do this the mass/spring model must successfully simulate the response of the fibre structure when undergoing a fibre/fibre bond failure or a fibre failure. This can be achieved by dynamically manipulating the mass and spring elements of the fibre structure. The simulated AEs from the two damage mechanisms are then analysed using a Continuous Wavelet Transform (CWT) to provide a two dimensional time/frequency representation of the signal. From the CWT certain features of the AEs can be attributed to each damage mechanism and as such a criteria for the time and frequency properties of each damage mechanism can be formulated. This criterion provides the basis for identifying the damage mechanisms present in the experimental data. The final contribution of this thesis is the investigation of training an intelligent classifier which can dynamically identify the AEs from the two damage mechanisms. This is achieved by converting the time and frequency criteria for each damage mechanisms into a set of features for the training of a Self-Organising Map (SOM). The significant step in this analysis is the method for the extraction of the features from the CWT of the AE. This work successfully combines four different scientific areas, paper physics, acoustic emission technology, data analysis and computational modelling to provide an insight into the micro-mechanics of paper. The most significant contribution of this work is the development of the hybrid model which has the ability to generate the acoustic response of a paper fibre structure undergoing two different damage processes. This alone has provided a significant insight into the micro-mechanics of paper to allow for the identification of the two damage mechanisms when the AEs are analysed with the CWT. Other contributions include the method used for the extraction of relevant features from the CWT to enable the training of a SOM for identifying the type of damage mechanism the AE originated from.
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Hjelmervik, Karl Thomas. "Sonar false alarm rate suppression using classification methods based on acoustic modelling." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14912.
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The use of high–resolution, active sonar systems in littoral environments often results in high false alarm rates. False alarm rate inflation (FARI) and non–Rayleigh reverberation (NRR) are two well–documented causes. FARI may occur when the reverberation in the normaliser window is non–stationary, while NRR may occur when the sonar footprint is too small for the central limit theorem to apply for the scatterer statistics. The main originator for false alarms in littoral environments are either the sea floor itself or objects located on the sea floor. Automatic classification methods may be used to reduce the false alarm rate. Conventionally, advanced sonar processing or image processing techniques have been used directly on received data. Increased availability of environmental information allows for more sophisticated algorithms that employ acoustic modelling to extract more information from recorded data. This thesis addresses two topics of interest. The first topic is on how acoustic modelling combined with environmental knowledge may be used to increase the ability of anti–submarine warfare sonars to classify a detected target. The second topic is on how environmental uncertainty may be reduced in order to improve the fidelity of the proposed classification algorithms
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Lippert, Stephan [Verfasser]. "Efficient vibro-acoustic modelling of aircraft components with parameter uncertainties / Stephan Lippert." Aachen : Shaker, 2010. http://d-nb.info/1081884940/34.
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Van, der Kelen Christophe. "Vibro-acoustic modelling of anisotropic poroelastic materials : characterisation of the anisotropic properties." Doctoral thesis, KTH, MWL Strukturakustik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-137809.
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The present-day challenges in the transport industry, steered by the increasing environmental awareness, necessitate manufacturers to take measures to reduce emissions related to the movements of goods and humans. In particular, the measures aiming at a reduced mass or higher load capacity to increase fuel efficiency, generally deteriorate the noise and vibration insulation properties of their products. In order to comply with the regulations and customer demands, modern vehicles increasingly move towards a multifunctional integrated design approach, if possible for all subcomponents involved. Such a multifunctional design approach is an iterative process, evaluating the proposed solutions in every stage, and is therefore best performed in a virtual testing environment. \\Poroelastic materials are interesting to include in a multifunctional design, offering reasonably good vibro-acoustic insulation properties at a low weight penalty. These materials can also be combined in multilayer arrangements to further enhance the overall performance. \\In order to achieve an accurate modelling of the vibro-acoustic behaviour of poroelastic materials, the input data describing the material properties should be of a high quality. Two characteristics inherent to these materials encumber a precise characterisation with traditional techniques. Poro-elastic aggregates are anelastic due to the constituent material used, and anisotropic as a consequence of the production process. Characterisation techniques allowing for an accurate determination of the material properties need to take these intrinsic characteristics into account.\\The objective in this thesis is to enable the characterisation of a constitutive material model for poroelastic materials which is as general as possible, and includes the inherent material anelasticity and anisotropy. For this purpose, a set of advanced characterisation techniques has been developed to characterise the anisotropic flow resistivity tensor and the anisotropic dynamic Hooke's tensor. \\These advanced characterisation techniques are based on an inverse estimation procedure, used consistently throughout the work, and includes both experiments and numerical predictions. The property to characterise is isolated in a specially designed set-up such that it can be modelled by physics solely involving this property. The obtained experimental and numerical data then serve as the input to an optimisation, which returns the material properties for which the difference between both is as small as possible. These methods have been successfully applied to melamine foam, which is found to be both anisotropic and anelastic, confirming the need for such advanced characterisation techniques.QC 20131219
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Allam, Sabry. "Acoustic modelling and testing of advanced exhaust system components for automotive engines." Doctoral thesis, KTH, Aeronautical and Vehicle Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-49.
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The increased use of the diesel engine in the passenger car, truck and bus market is due to high efficiency and lower fuel costs. This growing market share has brought with it several environmental issues for instance soot particle emission. Different technologies to remove the soot have been developed and are normally based on some kind of soot trap. In particular for automobiles the use of diesel particulate traps or filters (DPF:s) based on ceramic monolithic honeycombs are becoming a standard. This new exhaust system component will affect the acoustics and also work as a muffler. To properly design exhaust systems acoustic models for diesel particulate traps are needed. The first part of this thesis considers the modelling of sound transmission and attenuation for traps that consist of narrow channels separated by porous walls. This work has resulted in two new models an approximate 1-D model and a more complete model based on the governing equations for a visco-thermal fluid. Both models are expressed as acoustic 2-ports which makes them suitable for implementation in acoustic software for exhaust systems analysis. The models have been validated by experiments on clean filters at room temperature with flow and the agreement is good. In addition the developed filter models have been used to set up a model for a complete After Treatment Device (ATD) for a passenger car. The unit consisted of a chamber which contained both a diesel trap and a Catalytic Converter (CC). This complete model was also validated by experiments at room temperature. The second part of the thesis focuses on experimental techniques for plane wave decomposition in ducts with flow. Measurements in ducts with flow are difficult since flow noise (turbulence) can strongly influence the data. The difficulties are also evident from the lack of good published in-duct measurement data, e.g., muffler transmission loss data, for Mach-numbers above 0.1-0.2. The first paper in this part of the thesis investigates the effect of different microphone mountings and signal processing techniques for suppressing flow noise. The second paper investigates in particular flow noise suppression techniques in connection with the measurement of acoustic 2-ports. Finally, the third paper suggests a general wave decomposition procedure using microphone arrays and over-determination. This procedure can be used to determine the full plane wave data, e.g., the wave amplitudes and complex wave numbers k+ and k-. The new procedure has been applied to accurately measure the sound radiation from an unflanged pipe with flow. This problem is of interest for correctly determining the radiated power from an engine exhaust outlet. The measured data for the reflection coefficient and end correction have been compared with the theory of Munt [33] and the agreement is excellent. The measurements also produced data for the damping value (imaginary part of the wavenumber) which were compared to a model suggested by Howe [13]. The agreement is good for a normalized boundary layer thickness less than 30-40
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Di, Meglio Alberto. "Finite element-boundary elements modelling of acoustic scattering from viscoelastic anechoic structures." Thesis, University of Birmingham, 2000. http://etheses.bham.ac.uk//id/eprint/488/.
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This research work focuses on the analysis of multi-layered, anechoic tiles for underwater applications, especially in the field of communications. It is firstly shown how the sound absorbing properties of viscoelastic materials can be modified and enhanced by the proper use of fillers, such as lead oxide and mica. Successively, a new method for identifying the viscoelastic frequency-dependent properties of such materials from experimental data is presented. The method is based on a variational method analogous to the Hamilton Principle. It allows calculating hard-to-find properties such as the complex viscoelastic response functions and the complex Poisson ratio. After the materials properties have been determined, it is shown how they can be incorporated into the combined finite-element-boundary element method to provide accurate numerical solutions to the acoustic scattering problem. A tile made of three layers, a reflecting aluminium layer, an absorbing butyl rubber layer and a matching layer made of a regular grid of polyurethane cones is finally analysed in several scattering and geometrical configurations. The scattering patterns produced by a plane wave incident on the tile are plotted, discussed and compared with experimental data obtained from in-tank scattering measurements of a model tile.
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Nyandeni, Zamashobane. "Computational aeroacoustic modelling using hybrid RANS/LES methods with modified acoustic analogies." Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/25388.
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This study considers a numerical approach to identifying noise mechanisms in tandem cylinders to understand aircraft landing gear as a primary contributor to airframe noise during approach and landing. Fluctuations in the flow properties induced by turbulence are computed as well as the corresponding propagations. A hybrid IDDES turbulence model is employed, to compute the boundary layer and fluctuations in the flow properties. Larsson et al. modified Curle's analogy leading to the derivation of a version of Curle's analogy that makes use of strictly time derivatives which has been proven to be less sensitive to numerical errors. Brentner and Farassat derived a formulation of the Ffowcs-Williams and Hawkings analogy for a permeable surface enclosing the acoustic sources which accounts for the quadrupole acoustic sources in the flow without the costly calculation of a volume integral. This study will consider the impact of neglecting the volume sources through a comparison of the two modified versions of Curle's and FWH analogies with the results of other CFD practitioners as well as experimental data.
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Hernández, Vera Ignacio. "Soot modelling in flames and Large-Eddy Simulation of thermo-acoustic instabilities." Thesis, Toulouse, INPT, 2011. http://www.theses.fr/2011INPT0134/document.
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Dans la première partie de cette thèse de doctorat une méthodologie est présentée qui permet de prédire les niveaux de suies produits dans des flammes laminaires monodimensionnelles, ou un modèle semi-empirique de suies est utilisé en combinaison avec une chimie complexe et un solveur radiatif détaillé. La méthodologie est appliquée au calcul de suies dans une série de flammes de diffusion à contre-courant d'éthylène/air. Plusieurs modèles d'oxydation de suies sont testés et les constantes du modèle sont ajustées afin de retrouver un meilleur accord avec les expériences. L'effet des pertes thermiques radiatives sur la formation de suies et la structure des flammes est évalué. Finalement, la performance du modèle de suies est évalué sur des flammes prémélangées monodimensionnelles, ou une expression alternative du terme de croissance de surface est proposée pour reproduire les résultats expérimentaux. Dans la deuxième partie de cette thèse, des outils de Simulation aux Grandes Échelles (SGE) et d'analyse acoustique sont appliqués à la prédiction des oscillations de cycle limite (OCL) d'une instabilité thermo-acoustique qui apparaît dans un brûleur académique partiellement prémélangé de méthane/air à pression atmosphérique. La SGE prédit bien l'apparition et le développement des OCL est un bon accord est trouvé entre simulations et expériences en termes d'amplitude et fréquence des OCL. La simulation permet de révéler certains aspects clés responsables du comportement instable de la flamme. Ensuite, une analyse préliminaire de la quantification des incertitudes est fait, ou l'effet des paramètres tels que l'impédance des entrées, le degré de raffinement du maillage ou les pertes thermiques sur les caractéristiques des OCL est évalué. Aussi, la SGE prédit bien la dépendance de la stabilité de la flamme du point d'opération et de la géométrie du brûleurIn the first part of the present PhD. thesis a methodology is presented that allows to predict the soot produced in one-dimensional academic flames, where a semi-empirical soot model is used in combination with a complex chemistry and a detailed radiation solver. The methodology is applied to the computation of soot in a set of ethylene/air counterflow diffusion flames. Several oxidation models are tested and the constants of the model were adjusted to retrieve the experimental results. Also, the effect of radiative losses on soot formation and the flame structure is evaluated. Finally, the performance of the soot model is evaluated on 1D premixed flames, where an alternative expression for the surface growth term is proposed to better reproduce the experimental findings. In the second part of the thesis, Large-Eddy Simulation (LES) and acoustic analysis tools are applied to the prediction of limit cycle oscillations (LCO) of a thermo-acoustic instability appearing in a partially premixed methane/air academic burner operating at atmospheric pressure. The LES captures well the appearance and development of the LCO and a good agreement is found between simulations and experiments in terms of amplitude and frequency of the LCO. Some light is shed on the mechanisms leading to the existence of such instability. Then, a preliminar uncertainty quantification (UQ) analysis is performed, where the effect on the features of the LCO of several computational parameters such as the inlets impedances, mesh refinement or heat losses is assessed. Also, the LES captures well the flame stability behaviour dependence on the operating point and the burner geometry
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Jackson, Philip J. B. "Characterisation of plosive, fricative and aspiration components in speech production." Thesis, University of Southampton, 2000. https://eprints.soton.ac.uk/254111/.
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This thesis is a study of the production of human speech sounds by acoustic modelling and signal analysis. It concentrates on sounds that are not produced by voicing (although that may be present), namely plosives, fricatives and aspiration, which all contain noise generated by flow turbulence. It combines the application of advanced speech analysis techniques with acoustic flow-duct modelling of the vocal tract, and draws on dynamic magnetic resonance image (dMRI) data of the pharyngeal and oral cavities, to relate the sounds to physical shapes. Having superimposed vocal-tract outlines on three sagittal dMRI slices of an adult male subject, a simple description of the vocal tract suitable for acoustic modelling was derived through a sequence of transformations. The vocal-tract acoustics program VOAC, which relaxes many of the assumptions of conventional plane-wave models, incorporates the effects of net flow into a one-dimensional model (viz., flow separation, increase of entropy, and changes to resonances), as well as wall vibration and cylindrical wavefronts. It was used for synthesis by computing transfer functions from sound sources specified within the tract to the far field. Being generated by a variety of aero-acoustic mechanisms, unvoiced sounds are somewhat varied in nature. Through analysis that was informed by acoustic modelling, resonance and anti-resonance frequencies of ensemble-averaged plosive spectra were examined for the same subject, and their trajectories observed during release. The anti-resonance frequencies were used to compute the place of occlusion. In vowels and voiced fricatives, voicing obscures the aspiration and frication components. So, a method was devised to separate the voiced and unvoiced parts of a speech signal, the pitch-scaled harmonic filter (PSHF), which was tested extensively on synthetic signals. Based on a harmonic model of voicing, it outputs harmonic and anharmonic signals appropriate for subsequent analysis as time series or as power spectra. By applying the PSHF to sustained voiced fricatives, we found that, not only does voicing modulate the production of frication noise, but that the timing of pulsation cannot be explained by acoustic propagation alone. In addition to classical investigation of voiceless speech sounds, VOAC and the PSHF demonstrated their practical value in helping further to characterise plosion, frication and aspiration noise. For the future, we discuss developing VOAC within an articulatory synthesiser, investigating the observed flow-acoustic mechanism in a dynamic physical model of voiced frication, and applying the PSHF more widely in the field of speech research.
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Bolmsvik, Åsa. "Structural-acoustic vibrations in wooden assemblies: : Experimental modal analysis and finite element modelling." Doctoral thesis, Linnéuniversitetet, Institutionen för bygg- och energiteknik (BE), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-24562.
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This doctoral thesis concerns flanking transmission in light weight, wooden multi-storey buildings within the low frequency, primarily 20-120 Hz. The overall aim is to investigate how the finite element method can contribute in the design phase to evaluate different junctions regarding flanking transmission. Two field measurements of accelerations in light weight wooden buildings have been evaluated. In these, two sources; a stepping machine, and an electrodynamic shaker, were used. The shaker was shown to give more detailed information. However, since a light weight structure in field exhibit energy losses to surrounding building parts, reliable damping estimates were difficult to obtain. In addition, two laboratory measurements were made. These were evaluated using experimental modal analysis, giving the eigenmodes and the damping of the structures. The damping for these particular structures varies significantly with frequency, especially when an elastomer is used in the floor-wall junction. The overall damping is also higher when elastomers are used in the floor-wall junction in comparison to a screwed junction. By analysing the eigenmodes, using the modal assurance criterion, of the same structure with two types of junctions it was concluded that the modes become significantly different. Thereby the overall behavior differs. Several finite element models representing both the field and laboratory test setups have been made. The junctions between the building blocks in the models have been modeled using tie or springs and dashpots. Visual observation and the modal assurance criterion show that there is more rotational stiffness in the test structures than in the models. The findings in this doctoral thesis add understanding to how modern joints in wooden constructions can be represented by FE modelling. They will contribute in developing FE models that can be used to see the acoustic effects prior to building an entire house. However, further research is still needed.Denna doktorsavhandling behandlar flanktransmission i flervåningshus med trästomme, inom det lågfrekventa området, främst 20-120 Hz. Det övergripande målet är att undersöka hur finita elementmetoden kan bidra i konstruktionsfasen för att utvärdera olika knutpunkters inverkan på flanktransmissionen. Två fältmätningar av accelerationer i trähus har utvärderats. I dessa har två olika lastkällor använts, i den första en stegljudsapparat och i den andra en elektrodynamisk vibrator (shaker). Det visades att shakern kan ge mer detaljerad information, men eftersom vibrationerna även sprider sig till omgivande byggnadsdelar vid fältmätningarna var det svårt att estimera tillförlitliga dämpningsdata även då shaker användes. Fältmätningarna följdes av två mätningar i laborationsmiljö. Dessa två experiment utvärderades med experimentell modalanalys, vilket ger egenmoder och dämpning hos strukturerna. Dämpningen för dessa trähuskonstruktioner varierar kraftigt med frekvens. Extra stora variationer registreras då en elastomer användes i knutpunkten mellan golv och vägg. Den totala dämpningen är generellt högre när elastomerer används i knutpunkten mellan golv och vägg i jämförelse med då knutpunkten är skruvad. Genom att analysera egenmoder och deras korrelationer (MAC), för samma trästruktur men med olika typer av knutpunkter, drogs slutsatsen att knutpunkten drastiskt förändrar strukturens dynamiska beteende. Flera finita elementmodeller av både fält- och laboratorieuppställningar har gjorts. I dessa har knutpunkterna mellan byggnadsdelar modellerats helt styvt eller med hjälp av fjädrar och dämpare. Visuella observationer av egenmoder och korrelationen dem emellan visar att det finns mer rotationsstyvhet i försöken än i finita elementmodellerna. Resultaten i denna doktorsavhandling har gett förståelse för hur knutpunkter i träkonstruktioner beter sig och kan simuleras med finit elementmodellering. Vidare kan resultaten bidra till utvecklingen av FE-modeller som kan användas för att kunna se de akustiska effekterna redan under konstruktionsstadiet. Dock behövs ytterligare forskning inom området.
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Falcetelli, Francesco. "Modelling of Pencil-Lead Break Acoustic Emission Sources using the Time Reversal Technique." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16554/.
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In Acoustic Emissions (AE), Hsu-Nielsen Pencil-Lead Breaks (PLB) are used to generate sound waves enabling the characterization of acoustic wave speed in complex structures. The broadband signal of a PLB represents a repeatable emission, which can be applied at different regions of the structure, and therefore can be used to calibrate the localization algorithms of the AE system. In recent years, the use of Finite Element Method (FEM) has flourished for modelling acoustic Lamb wave propagation, which is present in thin plate-like structures. The primary challenge faced by the AE community is the lack of a well-known mathematical function of a PLB signal that can be applied in numerical simulations. This study makes use of a Time Reversal (TR) approach to identify the emission source of the PLB on a 7075-T651 aluminum plate. An ABAQUS CAETM model with piezoelectric actuators and sensors was developed. In order to avoid edge reflections, absorbing boundaries based on the Stiffness Reduction Method (SRM) were considered. The captured PLB signals were used as input to the FEM and was time-reversed. Furthermore, a band-limited white noise signal was used to calibrate the contribution of the broadband frequencies found in the transmitted wave packet. Preliminary results indicate that the TR approach can be used to understand the shape and function of the original transmitted signal.
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Culf, Alistair David. "Acoustic sounding and numerical modelling of the atmospheric boundary layer at Halley, Antarctica." Thesis, Lancaster University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306457.
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Chappell, David James. "Modelling the transient interaction of an elastic structure within an exterior acoustic field." Thesis, University of Brighton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439215.
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Goussard, George Willem. "Unsupervised clustering of audio data for acoustic modelling in automatic speech recognition systems." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6686.
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Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011.ENGLISH ABSTRACT: This thesis presents a system that is designed to replace the manual process of generating a pronunciation dictionary for use in automatic speech recognition. The proposed system has several stages. The first stage segments the audio into what will be known as the subword units, using a frequency domain method. In the second stage, dynamic time warping is used to determine the similarity between the segments of each possible pair of these acoustic segments. These similarities are used to cluster similar acoustic segments into acoustic clusters. The final stage derives a pronunciation dictionary from the orthography of the training data and corresponding sequence of acoustic clusters. This process begins with an initial mapping between words and their sequence of clusters, established by Viterbi alignment with the orthographic transcription. The dictionary is refined iteratively by pruning redundant mappings, hidden Markov model estimation and Viterbi re-alignment in each iteration. This approach is evaluated experimentally by applying it to two subsets of the TIMIT corpus. It is found that, when test words are repeated often in the training material, the approach leads to a system whose accuracy is almost as good as one trained using the phonetic transcriptions. When test words are not repeated often in the training set, the proposed approach leads to better results than those achieved using the phonetic transcriptions, although the recognition is poor overall in this case.
AFRIKAANSE OPSOMMING: Die doelwit van die tesis is om ’n stelsel te beskryf wat ontwerp is om die handgedrewe proses in die samestelling van ’n woordeboek, vir die gebruik in outomatiese spraakherkenningsstelsels, te vervang. Die voorgestelde stelsel bestaan uit ’n aantal stappe. Die eerste stap is die segmentering van die oudio in sogenaamde sub-woord eenhede deur gebruik te maak van ’n frekwensie gebied tegniek. Met die tweede stap word die dinamiese tydverplasingsalgoritme ingespan om die ooreenkoms tussen die segmente van elkeen van die moontlike pare van die akoestiese segmente bepaal. Die ooreenkomste word dan gebruik om die akoestiese segmente te groepeer in akoestiese groepe. Die laaste stap stel die woordeboek saam deur gebruik te maak van die ortografiese transkripsie van afrigtingsdata en die ooreenstemmende reeks akoestiese groepe. Die finale stap begin met ’n aanvanklike afbeelding vanaf woorde tot hul reeks groep identifiseerders, bewerkstellig deur Viterbi belyning en die ortografiese transkripsie. Die woordeboek word iteratief verfyn deur oortollige afbeeldings te snoei, verskuilde Markov modelle af te rig en deur Viterbi belyning te gebruik in elke iterasie. Die benadering is getoets deur dit eksperimenteel te evalueer op twee subversamelings data vanuit die TIMIT korpus. Daar is bevind dat, wanneer woorde herhaal word in die afrigtingsdata, die stelsel se benadering die akkuraatheid ewenaar van ’n stelsel wat met die fonetiese transkripsie afgerig is. As die woorde nie herhaal word in die afrigtingsdata nie, is die akkuraatheid van die stelsel se benadering beter as wanneer die stelsel afgerig word met die fonetiese transkripsie, alhoewel die akkuraatheid in die algemeen swak is.