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1
Liddy, David W. Holmes John F. « Acoustic room de-reverberation using time-reversal acoustics / ». Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA374579.
Texte intégralRésumé :
Thesis (M.S. in Applied Physics) Naval Postgraduate School, September 1999."September 1999". Thesis advisor(s):, Andrés Larraza, Bruce C. Denardo. Includes bibliographical references (p. 49). Also available online.
2
Liddy, David W., et John F. Holmes. « Acoustic room de-reverberation using time-reversal acoustics ». Thesis, Monterey, California : Naval Postgraduate School, 1999. http://hdl.handle.net/10945/13698.
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This thesis probes the performance of one-channel time-reversal acoustics in a chamber in terms of the geometry of the cavity. In particular, a rectangular chamber is compared to an enclosure that has a stadium shape. The mode structure in the rectangular cavity is highly symmetric, while it is highly irregular in the stadium-shaped cavity. Time- reversal acoustic techniques produce an improved focus in the latter. The focusing quality is determined as a function of frequency, time-reversal window size, and spatial extent. A scheme for encrypted acoustic communication, both in air and underwater, that uses multiple broadband signals with identical bandwidth, Hanning window source spectra, and center frequencies separated by half the bandwidth, allowing for null detection between adjacent signals, is successfully investigated.
3
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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Fabre, Josette. « Representative Environments for Reduced Estimation Time of Wide Area Acoustic Performance ». ScholarWorks@UNO, 2010. http://scholarworks.uno.edu/td/1156.
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Advances in ocean modeling (Barron et al., 2006) have improved such that ocean forecasts and even ensembles (e.g., Coelho et al., 2009) representing ocean uncertainty are becoming more widely available. This facilitates nowcasts (current time ocean fields / analyses) and forecasts (predicted ocean fields) of acoustic propagation conditions in the ocean which can greatly improve the planning of acoustic experiments. Modeling of acoustic transmission loss (TL) provides information about how the environment impacts acoustic performance for various systems and system configurations of interest. It is, however, very time consuming to compute acoustic propagation to and from many potential source and receiver locations for multiple locations on an area-wide grid for multiple analysis / forecast times, ensembles and scenarios of interest. Currently, to make such wide area predictions, an area is gridded and acoustic predictions for multiple directions (or radials) at each grid point for a single time period or ensemble, are computed to estimate performance on the grid. This grid generally does not consider the environment and can neglect important environmental acoustic features or can overcompute in areas of environmental acoustic isotropy. This effort develops two methods to pre-examine the area and time frame in terms of the environmental acoustics in order to prescribe an environmentally optimized computational grid that takes advantage of environmental-acoustic similarities and differences to characterize an area, time frame and ensemble with fewer acoustic model predictions and thus less computation time. Such improvement allows for a more thorough characterization of the time frame and area of interest. The first method is based on critical factors in the environment that typically indicate acoustic response, and the second method is based on a more robust full waveguide mode-based description of the environment. Results are shown for the critical factors method and show that this proves to be a viable solution for most cases studied. Limitations are at areas of high loss, which may not be of concern for exercise planning. The mode-based method is developed for range independent environments and shows significant promise for future development.
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Root, Joseph Andrew. « Capabilities of an underwater acoustic volumetric array using time-reversal ». Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/18944.
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Anderson, Shaun David. « Time-frequency methods for the analysis of multistatic acoustic scattering of elastic shells in shallow water ». Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39640.
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The development of low-frequency sonar systems, using for instance a network of autonomous systems in unmanned vehicles, provides a practical means for bistatic measurements (i.e. when the source and receiver are widely separated) allowing for multiple viewpoints of the target of interest. Time-frequency analysis, in particular Wigner-Ville analysis, takes advantage of the evolution time dependent aspect of the echo spectrum to differentiate a man-made target (e.g. elastic spherical shell) from a natural one of the similar shape (e.g. solid). A key energetic feature of fluid loaded and thin spherical shell is the coincidence pattern, or mid-frequency enhancement echoes (MFE), that result from antisymmetric Lamb-waves propagating around the circumference of the shell. This thesis investigates numerically the bistatic variations of the MFE (with respect to the monostatic configuration) using the Wigner-Ville analysis. The observed time-frequency shifts of the MFE are modeled using a previously derived quantitative ray theory for spherical shell's scattering. Additionally, the advantage of an optimal array beamformer, based on joint time delays and frequency shifts (over a conventional time-delay beamformer) is illustrated for enhancing the detection of the MFE recorded across a bistatic receiver array.
7
Bajer, Tomáš. « Problematika využití surovin na bázi skelných recyklátů ». Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2018. http://www.nusl.cz/ntk/nusl-371894.
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Presented work deals with the problem of solar glass waste recycling. In theoretical part recent EU regulation regarding waste management is presented. Different ways of PV panels recycling are explained as well as raw materials for glass production are listed. Differences between regular and solar glass is explained. In experimental part different recipes using solar glass waste and polymer binders are presented. Grindability was tested on specimen tiles. Potential of solar glass waste for manufacturing products with acoustic properties was examined.
8
Kokolia, Jakub. « Senior park ». Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-226408.
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The master’s thesis project is developed for the implementation of a new building for the elderly and persons with reduced mobility - Senior Park. The building is divided into several parts: the main building with facilities and separate wooden houses for the accommodation. The main building is a single-storey structure with a vegetative roof. The houses are designed with gable roof, without a basement. There is an emphasis on utmost privacy of individuals along with the care and closeness to nature. I embedded the main building partially into the ground so as to offset the difference in land and thus facilitate the movement after the plot and also served as a park for the inhabitants.
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Anderson, Shaun David. « Space-time-frequency processing from the analysis of bistatic scattering for simple underwater targets ». Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45771.
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The development of low-frequency SONAR systems, using a network of autonomous systems in unmanned vehicles, provides a practical means for bistatic measurements (i.e. when the source and receiver are widely separated, thus allowing multiple viewpoints of a target). Furthermore, time-frequency analysis, in particular Wigner-Ville analysis, takes advantage of the evolution of the time dependent echo spectrum to differentiate a man-made target (e.g. an elastic spherical shell, or cylinder) from a natural one of the similar shape (e.g. a rock). Indeed, key energetic features of man-made objects can aid in identification and classification in the presence of clutter and noise. For example, in a fluid-loaded thin spherical shell, an energetic feature is the mid-frequency enhancement echoes (MFE) that result from antisymmetric Lamb waves propagating around the circumference of the shell, which have been shown to be an acoustic feature useful in this pursuit. This research investigates the enhancement and benefits of bistatic measurements using the Wigner-Ville analysis along with acoustic imaging methods. Additionally, the advantage of joint space-time-frequency coherent processing is investigated for optimal array processing to enhance the detection of non-stationary signals across an array. The proposed methodology is tested using both numerical simulations and experimental data for spherical shells and solid cylinders. This research was conducted as part of the Shallow Water Autonomous Mine Sensing Initiative (SWAMSI) sponsored by ONR.
10
Edelmann, Geoffrey F. « Underwater acoustic communications using time reversal / ». Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2003. http://wwwlib.umi.com/cr/ucsd/fullcit?p3099539.
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Thompson, Philip R. Z. (Philip Reed Zane). « Space, time and acoustics ». Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/78997.
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Thesis (M. Arch.)--Massachusetts Institute of Technology, Dept. of Architecture, 1988.Includes bibliographical references (leaves 156-159).
This thesis describes the development of new concepts in acoustical analysis from their inception to implementation as a computer design tool. Research is focused on a computer program which aids the designer to visually conceive the interactions of acoustics within a geometrical~y defined environment by synthesizing the propagation of sound in a three dimensional space over time. Information is communicated through a unique use of images that are better suited for interfacing with the design process. The first part of this thesis describes the concepts behind the development of a graphic acoustical rendering program to a working level. This involves the development of a computer ray tracing prototype that is sufficiently powerful to explore the issues facing this new design and analysis methodology. The second part uses this program to evaluate existing performance spaces in order to establish qualitative criteria in a new visual format. Representational issues relating to the visual perception of acoustic spaces are also explored. In the third part, the program is integrated into the design process. I apply this acoustical tool to an actual design situation by remodeling a large performance hall in Medford, Massachusetts. Chevalier Auditorium is a real project, commissioned by the city of Medford, whose program requirements closely match my intentions in scope, scale and nature of a design for exploring this new acoustical analysis and design methodology. Finally, I summarize this program's effectiveness and discuss its potential in more sophisticated future design environments.
by Philip R.Z. Thompson.
M.Arch.
12
Carocho, Antonio J. « Acoustic impedance of materials from reverberation time ». Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from the National Technical Information Service, 1991. http://edocs.nps.edu/npspubs/scholarly/theses/1991/Dec/91Dec_Carocho.pdf.
Texte intégralRésumé :
Thesis (M.S. in Engineering Acoustics) Naval Postgraduate School, December 1991.Thesis advisor(s) Coppens, Alan B. ; Sanders, James V. "December 1991." Includes bibliographical referenes. Also available online.
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Pallarés, Valls Oriol. « Time synchronization in underwater acoustic sensor networks ». Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/403876.
Texte intégralRésumé :
This thesis deals with the development of a time synchronization algorithm for underwater sensor networks. The ease of deployment and maintenance of wireless networks leaded this research to the use of an acoustic communication sensor network to share a common base time between all nodes.
Acoustic signals are well adapted to the underwater medium but experience very challenging impairments such as Doppler, extensive multi-paths and low transmission speed that can nevertheless be corrected at the reception side.
Several acoustic waveforms can be invoked to transmit digital data through the underwater medium, without loss of generality, in this study is considered Orthogonal Frequency- Division Multiplexing (OFDM) communication scheme to exchange data between wireless underwater nodes containing sensor time references. This communication link will be used among others to carry time stamp message required for network synchronization.
Time synchronization is a critical piece of infrastructure of any distributed system. UWSN make extensive use of synchronized time for many services provided by a distributed network. In UWSN, Global Positioning System (GPS) signals are not available and synchronization systems are mostly based on acoustic communication. Owing to high latency of the underwater acoustic transmission channel with respect to cabled or radio network makes the use of conventional synchronization protocols even more challenging underwater.
Many time synchronization algorithms for underwater wireless sensor networks (UWSN) can be found in literature, such as TSHL, D-SYNC, DA-Sync. but only a few of them take into account all the water channel challenges, such as low available bandwidth, long propagation delays and sensor node mobility.
To solve this problem, in this research a further development of the existing time synchronization protocols found in literature is driven. To perform time synchronization we apply Precision Time Protocol (PTP) std. IEEE 1588, which is capable to synchronize two clocks with a precision below hundreds of nanoseconds in a point to point cabled Ethernet Network, and DA-Sync protocol, which is a bidirectional message exchange based method between a master clock and an slave one, and refines its time synchronization parameters by using medium kinematic models.
In cabled synchronization systems, such as PTP, time stamps are acquired in physical layer (PHY) in order to achieve maximum precision, avoiding indeterministic time like Operating System (OS) time slots or medium access protocols. Analogously, it happens in acoustic communication, time stamps are extracted from a large acquisition window, and the improvement of these time stamps is treated in this thesis.
Contrary to cable networks, the low celerity of wave sound makes underwater acoustic communications system very sensitive to Doppler effect, yielding to non-uniform frequency scaling represented by compression or dilatation of the time axis. This frequency scaling can be induced by two factors: motion (sensor mobility, channel variation, etc...) and clock skew receiver between transmitter and receiver. Actually, in order to address this problem, some systems uses expensive inertial sensors for compensating Doppler scaling due to motion and temperature compensated low drift clocks. So in this thesis is evaluated the Doppler scaling caused by motion and skew in order to correct it.
Finally, several tests in the laboratory, test tank, and at sea are performed in order to check the performance of acoustic communication and time synchronization. Results show a correct behavior of hardware and software, and also validate the performance of the time synchronization applied to acoustic UWSN.La sincronización temporal es una pieza clave de cualquier sistema distribuido. Las redes de sensores submarinas hacen uso de los sistemas de sincronización entre nodos para diversos servicios disponibles en cualquier red distribuida. Cabe mencionar que en las redes submarinas, las señales GPS (Global Positioning System) no están disponibles para la referencia temporal, y los sistemas de sincronización se tienen que basar principalmente en comunicaciones acústicas. Además, debido a la alta latencia de dichas redes, la portabilidad de protocolos de sincronización cableados o terrestres, es prácticamente imposible debido a las grandes diferencias de velocidades de propagación de las ondas electromagnéticas frente a las acústicas en el medio marino. Las señales acústicas se adecúan bien al medio submarino, pero presentan una serie de inconvenientes como el efecto Doppler, largas trayectorias multi-camino, además de una velocidad de transmisión baja, que han de ser corregidos en el equipo receptor. Se ha elegido el uso de "Orhtogonal Frequency-Division Multiplexing" (OFDM) como esquema de comunicaciones para el intercambio de datos entre nodos inalámbricos que tienen las bases temporales de cada uno de sus sensores. Este link de comunicaciones será usado, entre otros, para propagar los marcajes de tiempos entre mensajes necesarios para la sincronización de la red. En la literatura se pueden encontrar varios sistemas de sincronización para redes de sensores submarinas basadas en comunicación acústica como TSHL, D-SYNC, DA-Sync, pero sólo unos pocos tienen en cuenta toda la problemática del medio marino, como el bajo ancho de banda, los largos tiempos de propagación, o la movilidad de los sensores. Para resolver esta problemática de la sincronización temporal se ha empleado como referencia "Precision Time Protocol" (PTP) std. IEEE 1588, el cual es capaz de sincronizar dos relojes en una red cableada punto a punto con una precisión por debajo de los centenares de nanosegundos. Además se han empleado sistemas de mejora de la precisión temporal basados en ecuaciones cinemáticas de los nodos, tal y como se presenta en el estudio DA-Sync. En el protocolo PTP, los marcajes de tiempo se realizan en la capa física con el propósito de lograr la mayor precisión posible, ya que de este modo se evitan incertidumbres debidas a las temporizaciones de los sistemas operativos, o los algoritmos de acceso al medio. Análogamente, en esta tesis se presenta un sistema de marcaje de tiempos que extrae mediante hardware el marcaje temporal del inicio de la adquisición de datos. Difiriendo de las redes cableadas, la baja velocidad de propagación de las ondas acústicas en el medio marino hace que la comunicación sea altamente sensible al efecto Doppler, resultando en escalados frecuenciales no uniformes, que afectan a la base temporal dilatándola o comprimiéndola. Este escalado de frecuencia puede deberse a dos factores: movimiento (movimiento de sensores, variaciones del canal, etc.) o derivas del reloj de un nodo frente a otro nodo. Actualmente, para resolver este problema, algunos sistemas utilizan sistemas inerciales muy costosos para estimar el movimiento del sensor y relojes compensados por temperatura. En esta tesis se ha utilizado la información del canal respecto al escalado Doppler, además de las ecuaciones cinemáticas de primer orden, para estimar la movilidad y la deriva de los relojes. Finalmente, varios tests en laboratorio, tanque de agua, y experimentación en el mar son presentados para verificar el correcto funcionamiento de ambos sistemas de comunicación y sincronización. Los resultados validan el funcionamiento de todos los algoritmos software y del hardware, además de verificar el funcionamiento del sistema de sincronización aplicado a redes de sensores submarinas con comunicación acústica.
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Frenne, Nicklas. « Acoustic time histories of vibrating partial sources / ». Luleå, 2004. http://epubl.luth.se/1402-1544/2004/24.
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Aydogmus, Murat. « Multireceiver acoustic communications in time-varying environments ». Thesis, Monterey, California : Naval Postgraduate School, 2014. http://hdl.handle.net/10945/42577.
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Approved for public release; distribution is unlimitedIn this thesis, we present a two-receiver underwater acoustic communications system. It is based on the Kalman filter for equalization and tracking of acoustic channels characterized by considerable multipath. To model this channel and its dependency on the ocean environment we use the Bellhop acoustic ray tracing model. Error-correction coding is applied to the source data. Recursively updated channel estimates are used to update the state filters and tracking of the channel. It is shown that, under moderate conditions of Doppler shift and signal-to-noise (SNR) ratio, this algorithm is effective in tracking the channel and reconstructing the transmitted data.
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Molisani, Leonardo Rafael. « A Coupled Tire Structure-Acoustic Cavity Model ». Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/11187.
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Recent experimental results have shown that the vibration induced by the tire air cavity resonance is transmitted into the vehicle cabin and may be responsible for significant interior noise. The tire acoustic cavity is excited by the road surface through the contact patch on the rotating tire. The effect of the cavity resonance is that results in significant forces developed at the vehicle's spindle, which in turn drives the vehicle's interior acoustic field. This tire-cavity interaction phenomenon is analytically investigated by modeling the fully coupled tire-cavity systems. The tire is modeled as an annular shell structure in contact with the road surface. The rotating contact patch is used as a forcing function in the coupled tire-cavity governing equation of motion. The contact patch is defined as a prescribed deformation that in turn is expanded in its Fourier components. The response of the tire is then separated into static (i.e. static deformation induced by the contact patch) and dynamic components due to inertial effects. The coupled system of equations is solved analytically in order to obtain the tire acoustic and structural responses. The model provides valuable physical insight into the patch-tire-acoustic interaction phenomenon. The influence of the acoustic cavity resonance on the spindles forces is shown to be very important. Therefore, the tire cavity resonance effect must be reduced in order to control the tire contribution to the vehicle interior. The analysis and modeling of two feasible approaches to control the tire acoustic cavity resonances are proposed and investigated. The first approach is the incorporation of secondary acoustic cavities to detune and damp out the main tire cavity resonance. The second approach is the addition of damping directly into the tire cavity. The techniques presented in this dissertation to suppress the adverse effects of the acoustic cavity in the tire response, i.e. forces at the spindle, show to be very effective and can be easily applied in practice.Ph. D.
17
Chaulk, Edwin K. « Arrival time tracking of partially resolved acoustic rays with application to ocean acoustic tomography ». Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/27999.
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Gagnon, Pascal. « Clock Synchronization Through Time-Variant Underwater Acoustic Channels ». Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/17368.
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Approved for public release; distribution is unlimitedThe goal of this work is to develop methodologies for synchronizing the clocks of neighboring nodes of an underwater acoustic network. Clock synchronization requires an estimate of the signaling time delay between the nodes, which is particularly challenging in the presence of multipath propagation through the acoustic communication channel. This thesis focuses on modeling the underwater acoustic communication channel, accounting for the multipath arrivals, and creating a set of signal processing algorithms for estimating the required delay times that enable clock synchronization protocols for the underwater acoustic network. The proposed method involves correlating the responses of the bidirectional channels to exploit the underlying reciprocity. Performed in two stages, a sequence of probe signals is first transmitted to create an ensemble, which contains information about the time-variability of the acoustic communication channel with multipath. From this ensemble, we determine its dominant time-invariant characteristic and use it as a reference datum for the time delay measurements. The second stage consists in performing time-delay estimation of two probe signals exchanged between nodes. The two stages are tested using simulated signal measurements, and actual signal measurements were performed in a fresh-water lake for the first phase only. Both computer simulations and experimental results show the effectiveness of the proposed techniques.
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Thottappilly, Arjun. « OFDM for Underwater Acoustic Communication ». Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/34873.
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Communicating wirelessly underwater has been an area of interest for researchers, engineers, and practitioners alike. One of the main reasons for the slow rate of progress in this area is that the underwater acoustic channel is in general much more hostile â in terms of multipath, frequency selectivity, noise, and the Doppler effect â than the over-the-air radio frequency channel. In this work a time warp based technique which can be used to model time-varying wideband Doppler shifts (as seen in an UWA channel) in MATLAB is proposed. A corresponding procedure to estimate the parameters from observed data, required for inverting the effect of the time warp, is also proposed. Two different Doppler correction methods are compared; both can be used to undo the Doppler effect in measured data from an experiment subject to the wideband Doppler effect.
The techniques presented correct for the wideband Doppler effect as if it changed the time scale of the received signal. The first resampling based technique corrects for the average expansion/contraction over a packet, inherently assuming the relative velocity to be constant over the duration of the packet. The second time warp based technique models time-varying Doppler shift. Sinusoids, added to the beginning and end of each packet, are used to estimate the parameters required to invert the effect of the warp.
The time warp based methods are demonstrated using Orthogonal Frequency Division Multiplexing (OFDM) signals, but will in principle work for other kinds of wideband signals also. The presented results â using MATLAB based simulations, and over-the-air experiments performed in such a way as to introduce the Doppler effect in the received signals â emphasize the improvements that can be attained by using the time warp based Doppler modeling and correction method. The thesis concludes with suggestions for future work.Master of Science
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Raikes, Geoff. « Temperature reconstruction and acoustic time of flight determination for boiler furnace exit temperature measurement ». Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29516.
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The furnace exit gas temperature (FEGT) is one of the fundamental parameters necessary to determine the energy balance of the boiler in a coal-fired power plant, and is thus beneficial to the production of reliable thermo-fluid models of its operation and the operation of the systems down and upstream. The continuous measurement of the FEGT would also be a useful indicator to predict, prevent and diagnose faults, optimize boiler operation and aid the design of heat transfer surfaces. Acoustic pyrometry, a technique that measures temperature based on the travel time of an acoustic wave in a gas, is investigated as a viable solution for continuous direct measurement of the FEGT. This study focuses specifically on using acoustic pyrometry to reconstruct the temperature profile at the furnace exit including methods for accurately determining the time of flight (TOF) of acoustic waves. An improved reconstruction technique using radial basis functions (RBF) for interpolation and a least squares algorithm is simulated and its performance was compared to cubic spline interpolation, regression and Lagrange interpolation by evaluating its reconstruction accuracy in terms of mean and root-mean-squared (RMS) error when reconstructing set temperature profiles. Various parameters including transceiver positions, grid divisions and time of flight error, are investigated in terms of how they inform acoustic pyrometry implementation. The improved RBF interpolation function managed to reconstruct complex temperature profiles and had a greater reconstruction accuracy than compared interpolation methods, improving on the accuracy of previous work done. Random acoustic path error was found to not be additive with reconstruction error however repeating acoustic TOF readings improved reconstruction accuracy to mitigate this effect. In general, it was also found that symmetrical transmitter/receiver positions produced more accurate reconstructions as well as positioning receivers/transceivers and grid lines closer to the furnace walls, where the greatest temperature change occurs. In addition to testing reconstruction methods, a low-cost experimental set-up was constructed to measure the time of flight. The focus of this study was on using various signal processing methods to determine the time of flight and evaluating their accuracy in the presence of noise. Methods such as threshold detection with bandpass filtering, cross correlation, generalized cross-correlation (GCC) and a new method developed employing variable notch filters with locations and widths based on repetitive frequencies identified in the noise with cross correlation. The performance of methods was experimentally tested under varying signal to noise ratios (SNR) and noise conditions. These SNR tests showed that cross-correlation methods produced more reliable TOF readings under lower SNRs than threshold detection methods. Under white noise the smooth coherent transform (SCOT) GCC variation proved to produce the most accurate results producing an average TOF error of 0.84 % up until a SNR of 1.4 before reducing in accuracy. In coloured noise (generated based on previous boiler recordings) the variable notch filter method with crosscorrelation was able to identify repetitive noise frequencies filter them out and ultimately produced results with an average TOF error of 1.99 % up until a SNR of 0.67, where the noise level exceeds that of the signal.
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Taleb, Nardine. « Assessing the intelligibility and acoustic changes of time-processed speech ». Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1586637814204979.
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Huang, Yiteng (Arden). « Real-time acoustic source localization with passive microphone arrays ». Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/15024.
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Wang, Daniel Y. « Spatiotemporal processing and time-reversal for underwater acoustic communications ». Thesis, Massachusetts Institute of Technology, 2005. http://handle.dtic.mil/100.2/ADA455115.
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Leong-Kon, Dany. « A software system for real-time cardiac acoustic mapping ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq29609.pdf.
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Hwang, Sukyeon. « Acoustic seismic modeling in the slowness-time intercept domain / ». Access abstract and link to full text, 1993. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/9318174.
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Jenkins, William F. « Time/frequency relationships for an FFT-based acoustic modem ». Thesis, Monterey, California. Naval Postgraduate School, 2010. http://hdl.handle.net/10945/5205.
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Approved for public release; distribution is unlimited5km) communications in the 9-14 kHz band. The proposed scheme exploits a higher carrier frequency at 45 kHz and increased spectral bandwidth compatible with the short-range link, thus achieving an increased channel capacity. Analytical expressions are provided for the scheme, which combines principles of M-ary frequency-shift keying (MFSK) and orthogonal frequencydivision multiplexing (OFDM) in a modulation referred to as multi-channel MFSK. The proposed scheme consists of 32 orthogonally spaced channels, each of which contains a 4-ary FSK pulse train. Existing medium-range modem algorithms are adapted for the higher carrier frequency and candidate variations are implemented with bandwidths of 10 and 20 kHz. The variations involve bandwidth scaling or multiplexing the original 5 kHz spectral bandwidth. Of concern for short-range links in shallow water is multipath interference, which causes time-spreading and significant intersymbol interference (ISI). Dominant eigenray paths are determined in order to estimate the amount of time-spread expected in various shallow water environments. These are analyzed with respect to the time/frequency relationships of multi-channel MFSK to comparatively evaluate the candidate variations in terms of protection against ISI. On this basis, we propose multiplexing the 5 kHz MFSK modulation across the larger operating band.
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Hosom, John-Paul. « Automatic time alignment of phonemes using acoustic-phonetic information / ». Full text open access at:, 2000. http://content.ohsu.edu/u?/etd,282.
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Brevis, Vergara Rodrigo Ignacio. « Source time reversal methods for acoustic and elastic waves ». Tesis, Universidad de Chile, 2018. http://repositorio.uchile.cl/handle/2250/152342.
Texte intégralRésumé :
Tesis para optar al grado de Doctor en Ciencias de la Ingeniería, Mención Modelación MatemáticaEsta tesis estudia la detección y reconstrucción del término espacial de una fuente de variables separables en problemas de onda acústica y elástica. Para esto, estudiamos el método time-reversal mirror, el cual explota una invariancia intrínseca de la física a nivel microscópico que se observa también a nivel macroscópico en las ecuaciones de ondas. Esto significa que es posible recuperar la condición inicial de una ecuación de ondas homogénea revirtiendo la onda a través del tiempo. Para localizar y reconstruir el término espacial de la fuente, desarrollamos un método llamado source time reversal. La aplicación subyacente aquí es la detección de fuentes sísmicas en la minería. Es sabido que la actividad minera induce temblores dentro de las minas [50]. Esto se vuelve bastante peligroso si no se toman las precauciones adecuadas. Conocer sobre el origen de las actividades sísmicas puede ser utilizado para reducir el peligro de derrumbes y mejorar la seguridad dentro de las minas. Este trabajo se divide en tres capítulos; cada uno de ellos constituye un documento autocontenido para ser presentado como artículo. El primer capítulo aborda el problema de reconstrucción de fuente para ondas acústicas. Para esto introducimos el método source time reversal, la cual reconstruye el término espacial de una fuente de la forma f(x)g(t), donde f(x) entrega la forma y g(t) representa la distribución en tiempo de la fuente. Además, presentamos una estimación del error de la reconstrucción para el caso cuando f es una función de cuadrado integrable. Aquí, proponemos un método de regularización para implementar la reconstrucción de la fuente numéricamente. Adicionalmente, analizamos las principales características y limitaciones del método propuesto cuando se aplica a ondas acústicas. El capítulo dos estudia el problema de reconstrucción de fuente para ondas elásticas. Extendemos el método source time reversal para problemas elásticos. Además, introducimos un nuevo método de regularización para implementar la reconstrucción del término espacial de la fuente numéricamente para grandes volúmenes de datos. El nuevo método de regularización elimina las altas frecuencias presentes en la señal procesada, lo que permite utilizar mallas numéricas más gruesas y reduce el costo computacional. Finalmente, este capítulo presenta diversos experimentos numéricos para probar que el método es válido en el caso elástico. El último capítulo analiza un problema de reconstrucción de fuente diferente. Aquí consideramos una fuente compuesta por una suma finita de funciones de variable separable, donde cada término temporal de la fuente es una función delta de Dirac actuando a un tiempo diferente. Basado en una propiedad de tiempo reverso, la fuente puede ser localizada observando el desplazamiento y la velocidad de desplazamiento en el problema reverso [31]. Nosotros extendemos esta idea a sistemas de ondas elásticas. Adicionalmente, proponemos un algoritmo para la implementación numérica.
CONICYT, CMM - Conicyt PIA AFB170001 y el proyecto GEAGAM
29
Gunn, Kathryn Louise. « Time-lapse acoustic imaging of oceanic fronts and eddies ». Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/284560.
Texte intégralRésumé :
Seismic reflection surveying is used to generate acoustic images of the water column. This technique employs conventional multi-channel equipment which is used to image the solid Earth. In the water column, acoustic impedance contrasts are produced by variations in temperature and, to some extent, salinity. Acoustic impulses generated by an array of airguns suspended behind a vessel are reflected from these contrasts and recorded on long cables of hydrophones that are towed below the sea-surface. In this way, two- and three-dimensional images of thermohaline circulation can be generated. Critically, these images have equal vertical and horizontal resolutions of \textit{O}(10)~m. Here, I describe, process, and analyse a calibrated two-dimensional seismic survey from the Bellingshausen Sea of the Southern Ocean and a three-dimensional seismic survey from the Brazil-Falkland Confluence located offshore Uruguay. First, the Bellingshausen survey was designed to image the thermohaline structure across the west Antarctic shelf where warm-core eddies are reported. Processed and calibrated seismic images reveal the detailed thermohaline structure of Circumpolar Deep Water. Many warm-core eddies are observed, which have diameters of 1--12~km and thicknesses of 100--200~m. Pre-stack analysis demonstrates that this eddy field is being advected onto the shelf at speeds of \textit{O}(0.1)~m~s$^{-1}$. An iterative inverse modelling procedure is used to convert reflectivity into temperature and salinity, which confirms that the eddies have anomalously warm centres (i.e. $\sim$1$^{\circ}$C). These results have significant implications for ice shelf melting. Secondly, the Uruguay survey is used to investigate a large-scale frontal system. Although this system has been studied using hydrographic methods, these studies either have limited spatial resolution or have restricted depth penetration. The three-dimensional seismic survey, which was acquired in a `racetrack' pattern, permits the volume to be interrogated. Since the frontal system migrates southwestwards at a speed of \textit{O}(10)~km~day$^{-1}$, this survey is time-lapse in nature. Processed images reveal a band of dipping reflections that extend to depths of $\sim$2000~m. These reflections represent the frontal interface between the Brazil and Falkland currents. Physical oceanographic properties are calculated for images that cross this front. On the warm side of the front, the water mass is characterised by flat and continuous reflectivity. On the cold side of the front, the water mass is characterised by deformed reflectivity on all scales. Pre-stack analysis suggests that near-surface flow at the frontal interface is convergent. Between 0.5 and 1~km depth, a substantial eddy that is 30~km long and 250~m thick is visible on the cold side of the front. Detailed mapping suggests that this eddy grew and decayed over a period of 6~days. Its observed scale and duration are inconsistent with analytical and numerical studies of intra-thermocline eddies. Nevertheless, its duration is consistent with scaling arguments of frictional spin-down. Spatial and temporal distributions of mixing rates (i.e. diapycnal diffusivities) are estimated by spectrally analysing vertical displacements of automatically tracked reflections. Both internal wave and turbulent regimes are identifiable. Recovered diapycnal diffusivities are of \textit{O}($10^{-6}$--$10^{-2.2}$)~m$^{2}$~s$^{-1}$, consistent with hydrographically determined estimates. Mixing is suppressed and enhanced on the warm and cold sides of the front, respectively. Seismic Oceanography has considerable potential to quantify aspects of thermohaline circulation on multiple scales.
30
Maillard, Julien. « Advanced Time Domain Sensing For Active Structural Acoustic Control ». Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30335.
Texte intégralRésumé :
Active control of sound radiation from vibrating structures has been an area of much research in the past decade. In Active Structural Acoustic Control (ASAC), the minimization of sound radiation is achieved by modifying the response of the structure through structural inputs rather than by exciting the acoustic medium (Active Noise Control, ANC). The ASAC technique often produces global far-field sound attenuation with relatively few actuators as compared to ANC. The structural control inputs of ASAC systems are usually constructed adaptively in the time domain based on a number of error signals to be minimized. One of the primary concerns in active control of sound is then to provide the controller with appropriate ``error'' information. Early investigations have implemented far-field microphones, thereby providing the controller with actual radiated pressure information. Most structure-borne sound control approaches now tend to eliminate the use of microphones by developing sensors that are integrated in the structure. This study presents a new sensing technique implementing such an approach. A structural acoustic sensor is developed for estimating radiation information from vibrating structures. This technique referred to as Discrete Structural Acoustic Sensing (DSAS) provides time domain estimates of the radiated sound pressure at prescribed locations in the far field over a broad frequency range. The structural acoustic sensor consists of a set of accelerometers mounted on the radiating structure and arrays of digital filters that process the measured acceleration signals in real time. The impulse response of each filter is constructed from the appropriate radiation Green's function for the source area associated with each accelerometer.
Validation of the sensing technique is performed on two different systems: a baffled rectangular plate and a baffled finite cylinder. For both systems, the sensor is first analyzed in terms of prediction accuracy by comparing estimated and actual sound pressure radiated in the far field. The analysis is carried out on a numerical model of the plate and cylinder as well as on the real structures through experimental testing. The sensor is then implemented in a broadband radiation control system. The plate and cylinder are excited by broadband disturbance inputs over a frequency range encompassing several of the first flexural resonances of the structure. Single-sided piezo-electric actuators provide the structural control inputs while the sensor estimates are used as error signals. The controller is based on the filtered-x version of the adaptive LMS algorithm. Results from both analytical and experimental investigations are again presented for the two systems. Additional control results based on error microphones allow a comparison of the two sensing approaches in terms of control performance.
The major outcome of this study is the ability of the structural acoustic sensor to effectively replace error microphones in broadband radiation control systems. In particular, both analytical and experimental results show the level of sound attenuation achieved when implementing Discrete Structural Acoustic Sensing rivaled that achieved with far-field error microphones. Finally, the approach presents a significant alternative over other existing structural sensing techniques as it requires very little system modeling.Ph. D.
31
Escolano, Carrasco José. « Contributions to discrete-time methods for room acoustic simulation ». Doctoral thesis, Universitat Politècnica de València, 2010. http://hdl.handle.net/10251/8309.
Texte intégralRésumé :
The sound field distribution in a room is the consequence of the acoustic properties of radiating sources and the position, geometry and absorbing characteristics of the surrounding boundaries in an enclosure (boundary conditions). Despite there existing a consolidated acoustic wave theory, it is very difficult, nearly impossible, to find an analytical expression of the sound variables distribution in a real room, as a function of time and position. This scenario represents as an inhomogeneous boundary value problem, where the complexity of source properties and boundary conditions make that problem extremely hard to solve.
Room acoustic simulation, as treated in this thesis, comprises the algebraical approach to solve the wave equation, and the way to define the boundary conditions and source modeling of the scenario under analysis.
Numerical methods provide accurate algorithms for this purpose and among the different possibilities, the use of discrete-time methods arises as a suitable solution for solving those partial differential equations, particularized by some specific constrains. Together with the constant growth of computer power, those methods are increasing their suitability for room acoustic simulation. However, there exists an important lack of accuracy in the definition of some of these conditions so far: current frequency-dependent boundary conditions do not comply with any physical model, and directive sources in discrete-time methods have been hardly treated.
This thesis discusses about the current state-of-the-art of the boundary conditions and source modeling in discrete-time methods for room acoustic simulation, and it contributes some algorithms to enhance boundary condition formulation, in a locally reacting impedance sense, and source modelling in terms of directive sources under a defined radiation pattern. These algorithms have been particularized to some discrete-time methods such as the Finite Difference Time Domain and the Digital Waveguide Mesh.Escolano Carrasco, J. (2008). Contributions to discrete-time methods for room acoustic simulation [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/8309
Palancia
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Schofield, James. « Real-time acoustic identification of invasive wood-boring beetles ». Thesis, University of York, 2011. http://etheses.whiterose.ac.uk/1978/.
Texte intégralRésumé :
Wood-boring beetles are a cause of significant economic and environmental cost across the world. A number of species which are not currently found in the United Kingdom are constantly at risk of being accidentally imported due to the volume of global trade in trees and timber. The species which are of particular concern are the Asian Longhorn (Anoplophora glabripennis), Citrus Longhorn (A. chinensis) and Emerald Ash Borer (Agrilus planipennis). The Food and Environment Research Agency's plant health inspectors currently manually inspect high risk material at the point of import. The development of methods which will enable them to increase the probability of detection of infestation in imported material are therefore highly sought after. This thesis describes research into improving acoustic larvae detection and species identification methods, and the development of a real-time system incorporating them. The detection algorithm is based upon fractal dimension analysis and has been shown to outperform previously used short-time energy based detection. This is the first time such a detection method has been applied to the analysis of insect sourced sounds. The species identification method combines a time domain feature extraction technique based upon the relational tree representation of discrete waveforms and classification using artificial neural networks. Classification between two species, A. glabripennis and H. bajulus, can be performed with 92% accuracy using Multilayer Perceptron and 96.5% accuracy using Linear Vector Quantisation networks. Classification between three species can be performed with 88.8% accuracy using LVQ. A real-time hand-held PC based system incorporating these methods has been developed and supplied to FERA for further testing. This system uses a combination of dual piezo-electric based USB connected sensors and custom written software which can be used to analyse live recordings of larvae in real-time or use previously recorded data.
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Suwal, Pasang Sherpa. « Passive Acoustic Vessel Localization ». PDXScholar, 2012. https://pdxscholar.library.pdx.edu/open_access_etds/757.
Texte intégralRésumé :
This thesis investigates the development of a low-cost passive acoustic system for localizing moving vessels to monitor areas where human activities such as fishing, snorkeling and poaching are restricted. The system uses several off-the-shelf sensors with unsynchronized clocks where the Time Difference of Arrival (TDOA) or time delay is extracted by cross-correlation of the signal between paired sensors. The cross-correlation function uses phase correlation or Phase Transform (PHAT) which whitens the cross-spectrum in order to de-emphasize dominant frequency components. Using the locations of pairs of sensors as foci, hyperbolic equations can be defined using the time delay between them. With three or more sensors, multiple hyperbolic functions can be calculated which intersect at a unique point: the boat's location. It is also found that increasing separation distances between sensors decreased the correlation between the signals. However larger separation distances have better localization capability than with small distances. Experimental results from the Columbia and Willamette Rivers are presented to demonstrate performance.
34
Pierson, David Michael. « Buried-Object Detection Using Time-Reversed Acoustics ». NCSU, 2004. http://www.lib.ncsu.edu/theses/available/etd-01122004-083659/.
Texte intégralRésumé :
The work presented here is a comprehensive study of using time reversal to detect objects located in an inhomogeneous environment using backscattered signals with an emphasis on littoral environments. Time reversal of acoustic signals in the ocean has been studied for more than two decades with the emphasis on the use of the forward scattered field. All studies share similar geometries where both the acoustical source and an adjacent array of transducers are placed in the water column. This configuration, known as a time-reversal mirror (TRM), is not practical when detecting an object that is located in a different environment than the TRM, such as beneath the ocean floor. Little work has been done to study the efficacy of a single transceiver performing the time-reversal operation on the backscattered signals from targets buried beneath the ocean floor. Here, I start by presenting the theory for such a system in both time and frequency domains for scattering by a sphere. Then by using simulations I show that time reversal of backscattered signals provides a robust method to detect targets buried in an acoustically inhomogeneous sediment using a point transceiver in the water column several meters above the sea floor. Effects of the time-reversal window (TRW) on the iterative time-reversal operation are also presented. I define a signal-to-noise ratio (SNR) that treats the return with the sphere as the signal and the return without the sphere as noise to quantify improvements to the sphere returns. I consider two different sediment models and angle of incidence to show that the TRO operates independently of the sediment type and transceiver orientation. Theoretical analysis reveals that the time-reversal of backscattered signals converges to a subset of waveforms defined by the target and time-reversal window, not the initial pulse. Analysis further reveals that the time-reversal operator detects the sphere after only two iterations of the TRO, with more iterations enhancing the sphere return through the non-linear filtering property of the TRO. Through this work, I demonstrate that time reversal is a robust method to detect objects.
35
Späth, Bastian, Matthias Philipp et Thomas Bartnitzki. « Machine performance and acoustic fingerprints of cutting and drilling ». Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2018. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-231193.
Texte intégralRésumé :
‘It is always dark ahead of the pick!’ This centuries-old miners’ expression still reveals the uncertainty about the upcoming rock properties during exploration and extraction processes. It is still tough to predict what a drill rig or a cutting machine will experience during operation. However, in terms of safety, energy consumption and the performance of the whole machine it would be beneficial to be able to monitor such an extraction process. Hence, different sensors or sensor combinations are tested during cutting and drilling processes within RealTime Mining project. First aim is to depict the machine performance of the machine at any time. In a second step sensor information is also used to conclude on mechanical rock properties during the process.
Measuring the machine performance for cutting and drilling is quite similar and has been condensed under the terms Monitoring-While-Cutting (MWC) respectively Monitoring-While-Drilling (MWD). Both monitoring systems contain a bundle of sensors to depict the whole process. As an example, the energy demand of such a machine can be determined by measuring the power consumption of the engines constantly. Furthermore, the process parameters like advance rates and drilling or cutting speed have to be evaluated as well to be able to depict the whole extraction machine.
To conclude on mechanical rock properties several other sensor solutions have been tested and finally integrated into those monitoring systems. One of the most important rock properties for drilling and cutting is the rock strength. Increasing rock strength during an extraction process leads to increasing forces that are needed to break a certain amount of rock. Hence, e.g. measuring the torque of a drill string or the cutting forces can be an indicator on rock resistance or rock strength. Not minor important, is the characteristic rock breakage behavior which can be classified by the use of ‘acoustic’ sensors. Dependent on the rock properties that currently is drilled or cut through a characteristic fracture occurs in front of the tool. This results in audible and also inaudible characteristic acoustic waves that propagate through the machine body and can be gathered on the machine by piezo-electric sensors. The interpretation of these signals could lead to a material classification already during the extraction process.
Several tests of these sensor technologies have been conducted in laboratory environment as well in field tests. The most promising results are going to be presented.
36
McFadzean, Angus G. « An investigation of a real-time distributed problem-solving architecture applied to sonar interpretation ». Thesis, Heriot-Watt University, 1992. http://hdl.handle.net/10399/1483.
Texte intégral
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Tsang, Kwong Man. « A real-time acoustic imaging system using digital signal processor array ». HKBU Institutional Repository, 1995. http://repository.hkbu.edu.hk/etd_ra/49.
Texte intégral
38
Crocker, Steven Edward Miller James H. « Time domain modal beamforming for a near vertical acoustic array / ». Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from the National Technical Information Service, 1991. http://handle.dtic.mil/100.2/ADA245272.
Texte intégral
39
Crocker, Steven Edward. « Time domain modal beamforming for a near vertical acoustic array ». Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/24239.
Texte intégral
40
Dayal, Avik. « Nonlinear Doppler Warp Correction for Acoustic OFDM ». Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/78157.
Texte intégralRésumé :
The Underwater Acoustic (UWA) channel has been an area of interest for many researchers and engineers, but also a very challenging area. Compared to the over-the-air radio frequency (RF) channel, the underwater acoustic channel causes multiple distortions – due to multipath, frequency selectivity, noise, and Doppler – some of which are more severe. The increased distortion causes many techniques and assumptions made for typical RF communication systems to break down.
One of the assumptions that breaks down is that the Doppler effect that the signal undergoes can be modelled with a simple shift in frequency, since the signals used to communicate in a UWA channel are effectively wideband. In this work the Doppler Effect that a signal undergoes is modelled as a nonlinear time warp. A procedure is developed to estimate the parameters of the time warp from the observed signal. These time warp parameters are then used to reverse the effect of the time warp. Two different methods for estimating the time warp parameters and correcting the Doppler are compared.
The first technique uses sinusoids placed at the beginning and end of the signal to estimate the parameters of the warp that the signal undergoes. The second technique uses sinusoids that are present during the signal to estimate and correct for the warp. The frequencies of the sinusoids are outside of the frequency range used for the transmitted data signal, so there is no interference with the information that is being sent.
The transmitted data signal uses Orthogonal Frequency Division Multiplexing (OFDM) to encode the data symbols, but the Doppler Correction technique will in principle work for other kinds of wideband signals as well. The results, which include MATLAB based simulations and over-the-air experiments, show that performance improvements can be realized using the time warp correction model.Master of Science
41
Du, Xinpeng. « Laser-Ultrasonic Measurement of Single-Crystal Elastic Constants from Polycrystalline Samples by Measuring and Modeling Surface Acoustic Wave Velocities ». The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524177819455643.
Texte intégral
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Deane, Anne Margaret. « Time domain work on brass instruments ». Thesis, University of Surrey, 1986. http://epubs.surrey.ac.uk/847357/.
Texte intégralRésumé :
This work investigates brass instruments in the time domain, rather than the traditional frequency domain, and considers first, impulse measurements and secondly, their analysis. An existing apparatus for measuring the response to an acoustic impulse at the input of a brass instrument has been refined. Problems of impulse inconsistency, ambient temperature variation and source reflections have been resolved. Developments of the above equipment are used to test the quality of brass instruments on a factory production line. A prototype and a test instrument are compared by taking the arithmetical difference of their impulse responses. The equipment has detected small faults missed by normal inspection methods. The usefulness of this technique to brass instrument manufacturers is discussed. Links between the instrument's measured transient response and its bore geometry have been developed. The stages involved are deconvolution and bore reconstruction. Various deconvolution methods have been studied systematicaly by applying them to simulated noiseless and noisy data. Noise introduces errors, particularly at high frequencies, so deconvolution of real measured data is distorted. Techniques to reduce the effects of noise have been investigated. Attempts to employ the Gerchberg restoration algorithm 'to restore high frequency information proved unsuccessful. A new inverse method, based on an iterative z-transform procedure, of reconstructing an instrument's bore shape and damping profile from its transient response has been developed. It produces perfect results for noiseless model data, but even the smallest amount of noise renders the method unstable. Regularisation is therefore required. The corresponding direct process of predicting the transient response from bore and damping data is stable and produces results which compare well with measured responses. The work strengthens relationships between an instrument's shape and its musical quality, and will enhance the design of better instruments. Further research on the link between transient response and subjective quality is recommended.
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Späth, Bastian, Matthias Philipp et Thomas Bartnitzki. « Machine performance and acoustic fingerprints of cutting and drilling ». TU Bergakademie Freiberg, 2017. https://tubaf.qucosa.de/id/qucosa%3A23182.
Texte intégralRésumé :
‘It is always dark ahead of the pick!’ This centuries-old miners’ expression still reveals the uncertainty about the upcoming rock properties during exploration and extraction processes. It is still tough to predict what a drill rig or a cutting machine will experience during operation. However, in terms of safety, energy consumption and the performance of the whole machine it would be beneficial to be able to monitor such an extraction process. Hence, different sensors or sensor combinations are tested during cutting and drilling processes within RealTime Mining project. First aim is to depict the machine performance of the machine at any time. In a second step sensor information is also used to conclude on mechanical rock properties during the process.
Measuring the machine performance for cutting and drilling is quite similar and has been condensed under the terms Monitoring-While-Cutting (MWC) respectively Monitoring-While-Drilling (MWD). Both monitoring systems contain a bundle of sensors to depict the whole process. As an example, the energy demand of such a machine can be determined by measuring the power consumption of the engines constantly. Furthermore, the process parameters like advance rates and drilling or cutting speed have to be evaluated as well to be able to depict the whole extraction machine.
To conclude on mechanical rock properties several other sensor solutions have been tested and finally integrated into those monitoring systems. One of the most important rock properties for drilling and cutting is the rock strength. Increasing rock strength during an extraction process leads to increasing forces that are needed to break a certain amount of rock. Hence, e.g. measuring the torque of a drill string or the cutting forces can be an indicator on rock resistance or rock strength. Not minor important, is the characteristic rock breakage behavior which can be classified by the use of ‘acoustic’ sensors. Dependent on the rock properties that currently is drilled or cut through a characteristic fracture occurs in front of the tool. This results in audible and also inaudible characteristic acoustic waves that propagate through the machine body and can be gathered on the machine by piezo-electric sensors. The interpretation of these signals could lead to a material classification already during the extraction process.
Several tests of these sensor technologies have been conducted in laboratory environment as well in field tests. The most promising results are going to be presented.
44
Spa, Carvajal Carlos. « Time-domain numerical methods in room acoustics simulations ». Doctoral thesis, Universitat Pompeu Fabra, 2009. http://hdl.handle.net/10803/7565.
Texte intégralRésumé :
L'acústica de sales s'encarrega de l'estudi del comportament de les ones sonores en espais tancats.La informació acústica de qualsevol entorn, coneguda com la resposta impulsional, pot ser expressada en termes del camp acústic com una funció de l'espai i el temps. En general, és impossible obtenir solucions analítiques de funcions resposta en habitacions reals. Per tant, en aquests últims anys, l'ús d'ordinadors per resoldre aquest tipus de problemes ha emergit com una solució adecuada per calcular respostes impulsionals.En aquesta Tesi hem centrat el nostre anàlisis en els mètodes basats en el comportament ondulatori dins del domini temporal. Més concretament, estudiem en detall les formulacions més importants del mètode de Diferències Finites, el qual s'utilitza en moltes aplicacions d'acústica de sales, i el recentment proposat mètode PseudoEspectral de Fourier. Ambdós mètodes es basen en la formulació discreta de les equacions analítiques que descriuen els fenòmens acústics en espais tancats.
Aquesta obra contribueix en els aspectes més importants en el càlcul numèric de respostes impulsionals: la propagació del so, la generació de fonts i les condicions de contorn de reactància local.
Room acoustics is the science concerned to study the behavior of sound waves in enclosed rooms. The acoustic information of any room, the so called impulse response, is expressed in terms of the acoustic field as a function of space and time. In general terms, it is nearly impossible to find analytical impulse responses of real rooms. Therefore, in the recent years, the use of computers for solving this type of problems has emerged as a proper alternative to calculate the impulse responses.
In this Thesis we focus on the analysis of the wavebased methods in the timedomain. More concretely, we study in detail the main formulations of FiniteDifference methods, which have been used in many room acoustics applications, and the recently proposed Fourier PseudoSpectral methods. Both methods are based on the discrete formulations of the analytical equations that describe the sound phenomena in enclosed rooms.
This work contributes to the main aspects in the computation of impulse responses: the wave propagation, the source generation and the locallyreacting boundary conditions.
45
Raghukumar, Kaustubha. « Pressure sensitivity kernels applied to time-reversal acoustics ». Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3359854.
Texte intégralRésumé :
Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed July 23, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
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Hargreaves, J. A. « Time domain boundary element method for room acoustics ». Thesis, University of Salford, 2007. http://usir.salford.ac.uk/16604/.
Texte intégralRésumé :
This thesis is about improving the suitability of the time domain Boundary Element Method (BEM) for predicting the scattering from surface treatments used to improve the acoustics of rooms. The discretised integral equations are typically solved by marching on in time from initial silence; however, this being iterative has potential for divergence. Such instability and high computational cost have prohibited the time domain BEM from widespread use. The underlying integral equation is known to not possess unique solutions at certain frequencies, physically interpreted as cavity resonances, and these manifest as resonant poles, all excited and potentially divergent due to numerical error. This has been addressed by others using the combined field integral equation; an approach built upon in this thesis. Accuracy and stability may also be compromised by poor discretisation and integration accuracy. The latter is investigated on real-world surfaces, demonstrating that the popular Gaussian integration schemes are not suitable in some circumstances. Instead a contour integration scheme capable of resolving the integrands‟ singular nature is developed. Schroeder diffusers are Room Acoustic treatments which comprise wells separated by thin fins. The algorithm is extended to model such surfaces, applying the combined field integral equation to the body and an open surface model to the fins. It is shown that this improves stability over an all open surface model. A new model for compliant surfaces is developed, comparable to the surface impedance model used in the frequency domain. This is implemented for surfaces with welled and absorbing sections, permitting modelling of a Schroeder diffuser as a box with surface impedances that simulate the delayed reflections caused by the wells. A Binary Amplitude Diffuser - a partially absorbing diffuser - is also modelled. These new models achieve good accuracy but not universal stability and avenues of future research are proposed to address the latter issue.
47
Rossiter, David Paul. « Real-time visual displays for voice tuition ». Thesis, University of York, 1995. http://etheses.whiterose.ac.uk/10805/.
Texte intégral
48
Hallaj, Ibrahim M. « Nonlinear acoustics in underwater and biomedical applications : array performance degradation and time reversal invariance / ». Thesis, Connect to this title online ; UW restricted, 1999. http://hdl.handle.net/1773/5987.
Texte intégral
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Sinclair, Stephen. « Velocity-driven audio-haptic interaction with real-time digital acoustic models ». Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114232.
Texte intégralRésumé :
Acoustic models driven by real-time velocity signals can suffer unduly from quality issues due to sampling and differentiation, especially at high sampling rates. In audio-haptic friction interaction, as found in a bowed stringsimulation for example, this noise appears as a gritty or dry feel, and is audible in the sound.In this thesis, two approaches to this problem are proposed: firstly, reduction of the sensitivity of the model to velocity noise by the application of a position-dependent friction model; secondly, the improvement of velocity estimation by means of filtering and enhanced sensing.Several estimators are compared, by means of parameter optimisation, to direct velocity measurement in order to find a good trade-off between filter-imposed delay and noise rejection. Optimised estimators are then compared by subjects in an online scenario to test their respective effect on the impedance range and noise qualities of a bowed string friction display.Les modèles acoustiques commandés en temps réel par des signaux de vitesse peuvent souffrir indûment de problèmes de qualité dus à l'échantillonnage et à la différenciation de la position, en particulier à des taux d'échantillonnage élevé. Dans l'interaction audio-haptique basée sur la friction, que l'on trouve dans la simulation d'une corde frottée par exemple, ce bruit se présente comme une sensation granuleuse ou sèche, et est audible dans le son. Nous proposons dans cette thèse deux solutions à ce problème: d'une part, la réduction de la sensibilité au bruit du modèle de simulation par l'application d'un modèle de friction dépendant de la position; d'autre part, l'amélioration de l'estimation de la vitesse en utilisant différents filtres ainsi que des capteurs supplémentaires. Plusieurs estimateurs sont comparées entre eux et à la mesure directe de la vitesse, dans le but de trouver un compromis acceptable entre le retard imposé par le filtrage et la réduction du bruit.Ces estimateurs optimisés sont ensuite évalués par des participants afin de tester leurs effets sur la gamme d'impédance obtenue ainsi que sur la qualité du bruit dans la simulation de corde frottée.
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Li, Weichang. « Estimation and tracking of rapidly time-varying broadband acoustic communication channels / ». Cambridge, Mass. : Woods Hole, Mass. : Massachusetts Institute of Technology ; Woods Hole Oceanographic Institution, 2006. http://hdl.handle.net/1912/1509.
Texte intégralRésumé :
Originally issued as the author's thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2006."February 2006". "Doctoral dissertation." "Department of origin: Applied Ocean Physics and Engineering." "Joint Program in Oceanography/Applied Ocean Science and Engineering"--Cover. Bibliography: p. 197-206.