156,200 research outputs found

    Extraction of acoustic sources for multiple arrays based on the ray space transform

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    In this paper we present a source extraction technique for multiple uniform linear arrays distributed in space. The technique adopts the Ray Space Transform representation of the sound field, which is inherently based on the Plane Wave Decomposition. The Ray Space Transform gives us an intuitive representation of the acoustic field, thus enabling the adoption of geometrically-motivated constraints in the spatial filter design. The proposed approach is semi-blind since it needs as input an estimate of the source positions. We prove the effectiveness of the proposed solution through simulations using both white noise and speech signals

    Effects of internal waves on low frequency, long range, acoustic propagation in the deep ocean

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    Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2007This thesis covers a comprehensive analysis of long-range, deep-ocean, low-frequency, sound propagation experimental results obtained from the North Pacific Ocean. The statistics of acoustic fields after propagation through internal-wave-induced sound-speed fluctuations are explored experimentally and theoretically. The thesis starts with the investigation of the North Pacific Acoustic Laboratory 98-99 data by exploring the space-time scales of ocean sound speed variability and the contributions from different frequency bands. The validity of the Garret & Munk internal-wave model is checked in the upper ocean of the eastern North Pacific. All these results impose hard bounds on the strength and characteristic scales of sound speed fluctuations one might expect in this region of the North Pacific for both internal-wave band fluctuations and mesoscale band fluctuations. The thesis then presents a detailed analysis of the low frequency, broadband sound arrivals obtained in the North Pacific Ocean. The observed acoustic variability is compared with acoustic predictions based on the weak fluctuation theory of Rytov, and direct parabolic equation Monte Carlo simulations. The comparisons show that a resonance condition exists between the local acoustic ray and the internal wave field such that only the internal-waves whose crests are parallel to the local ray path will contribute to acoustic scattering: This effect leads to an important filtering of the acoustic spectra relative to the internal-wave spectra. We believe that this is the first observational evidence for the acoustic ray and internal wave resonance. Finally, the thesis examined the evolution with distance, of the acoustic arrival pattern of the off-axis sound source transmissions in the Long-range Ocean Acoustic Propagation EXperiment. The observations of mean intensity time-fronts are compared to the deterministic ray, parabolic equation (with/without internal waves) and (one-way coupled) normal mode calculations. It is found the diffraction effect is dominant in the shorter-range transmission. In the longer range, the (internal wave) scattering effect smears the energy in both the spatial and temporal scales and thus has a dominant role in the finale region.The funding that made this research possible came from the Office of Naval Research, and the WHOI Academic Programs Office

    Simulation of sound wave propagation in closed space, using tools of geometric acoustics

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    Tato bakalářská práce pojednává o simulaci šíření zvukové vlny v uzavřeném prostoru pomocí prostředků geometrické akustiky. Zejména se jedná o srovnání a použití Obrazové metody, metody Ray-Tracing a metody Beam-Tracing pro výpočet odrazů zvukových vln od stěn v uzavřeném prostředí bez překážek. Velká část bakalářské práce je zaměřena na algoritmy Obrazové metody a metody Ray-Tracing, které jsou zrealizovány v prostředí Matlab, a jejich výsledky jsou srovnány na základě provedených simulací.The bachelor thesis focuses on a simulation of sound wave spreading in closed space using tools of geometric acoustics. It mainly concerns on comparison and using of image source method, Ray-Tracing Method, and Beam-Tracing for counting of sound waves rebounds in close environment without obstacles. A big part of the thesis is measured by algorithms of image source method and Ray-Tracing Method. It´s realized in Matlab software. The results are compared on based of executed simulations.

    Virtual acoustic rendering by state wave synthesis

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    International audienceIn the context of the class of virtual acoustic simulation techniques that rely on traveling wave rendering as dictated by path-tracing methods (e.g, image-source, ray-tracing, beam-tracing) we introduce State Wave Synthesis (SWS), a novel framework for the efficient rendering of sound traveling waves as exchanged between multiple directional sound sources and multiple directional sound receivers in time-varying conditions.The proposed virtual acoustic rendering framework represents sound-emitting and sound-receiving objects as multiple-input, multiple-output dynamical systems. Each input or output corresponds to a sound traveling wave received or emitted by the object from/to different orientations or at/from different positions of the object. To allow for multiple arriving/departing waves from/to different orientations and/or positions of an object in dynamic conditions, we introduce a discrete-time state-space system formulation that allows the inputs or the outputs of a system to mutate dynamically. The SWS framework treats virtual source or receiver objects as time-varying dynamical systems in state-space modal form, each allowing for an unlimited number of sound traveling wave inputs and outputs.To model the sound emission and/or reception behavior of an object, data may be collected from measurements. These measurements, which may comprise real or virtual impulse or frequency responses from a real physical object or a numerical physical model of an object, are jointly processed to design a multiple-input, multiple-output state-space model with mutable inputs and/or outputs. This mutable state-space model enables the simulation of direction- and/or position-dependent, frequency-dependent sound wave emission or reception of the object. At run-time, each of the mutable state-space object models may present any number of inputs or outputs, with each input or output associated to a received/emitted sound traveling wave from/to specific arrival/departure position or orientation. In a first formulation, the sound wave form, the traveling of sound waves between object models is simulated by means of delay lines of time-varying length. In a second formulation, the state wave form, the traveling of sound waves between object models is simulated by way of propagating the state variables of source objects along delay lines of time-varying length. SWS allows the accurate simulation of frequency-dependent source directivity and receiver directivity in time-varying conditions without any time-domain or frequency-domain explicit convolution processing. In addition, the framework enables time-varying, obstacle-induced frequency-dependent attenuation of traveling waves without any dedicated digital filters. SWS facilitates the implementation of efficient virtual acoustic rendering engines either as software or in dedicated hardware, allowing realizations in which the number of delay lines is independent of the number of traveling wave paths being simulated. Moreover, the method enables a straightforward dynamic coupling between virtual acoustic objects and their physics-based simulation counterparts as performed by computer for animation, virtual reality, video-games, music synthesis, or other applications.In this presentation we will introduce the foundations of SWS and employ a real acoustic violin and a real human head as illustrative examples for a source object and a receiver object respectively. In light of available implementation possibilities, we will examine the basic memory requirements and computational cost of the rendering framework and suggest how to conveniently include minimum-phase diffusive elements to procure additional diffuse field contributions if necessary. Finally, we will expose limitations and discuss future opportunities for development

    Static structure factor of two-dimensional liquid 3He adsorbed on graphite

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    International audienceLiquid 3He is a model system for strongly correlated Fermi liquids. For this reason, many X-ray and neutron scattering experiments have been performed to understand the structure and dynamics of this quantum fluid. We have recently shown that two-dimensional liquid 3He sustains long-lived zero-sound excitations at large wave-vectors (Nature 483, 576, 2012). Here we show that its static structure factor can be obtained with reasonable accuracy by integrating the experimental S(Q,ω) over a suitable energy range. A good agreement is found between the static structure factor deduced from the experiment and theoretical models: Quantum Monte Carlo simulations and Dynamical Many Body Theory (DMBT). At high wave-vectors, the experimental values are underestimated because of the limited accessible phase space; nevertheless, even at atomic wave-vectors a semiquantitative agreement is observed with the theoretical predictions

    Travel time stability in weakly range-dependent sound channels

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    Travel time stability is investigated in environments consisting of a range-independent background sound-speed profile on which a highly structured range-dependent perturbation is superimposed. The stability of both unconstrained and constrained (eigenray) travel times are considered. Both general theoretical arguments and analytical estimates of time spreads suggest that travel time stability is largely controlled by a property ω\omega ^{\prime} of the background sound speed profile. Here, 2π/ω(I)2\pi/\omega (I) is the range of a ray double loop and II is the ray action variable. Numerical results for both volume scattering by internal waves in deep ocean environments and rough surface scattering in upward refracting environments are shown to confirm the expectation that travel time stability is largely controlled by ω\omega ^{\prime}.Comment: Submitted to J. Acoust. Soc. Am., 30 June 200
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