9 results
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2. Acoustophoresis of disk-shaped microparticles: A numerical and experimental study of acoustic radiation forces and torques.
- Author
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Garbin, Alexander, Leibacher, Ivo, Hahn, Philipp, Le Ferrand, Hortense, Studart, André, and Dual, Jürg
- Subjects
ULTRASONIC waves ,ACOUSTIC radiation ,NUMERICAL analysis ,COMPUTER simulation ,STRUCTURAL plates - Abstract
Disk-shaped microparticles experience an acoustic radiation force and torque in an ultrasonic standing wave. Hence, they are translated by the acoustic field, an effect called acoustophoresis, and rotated. The torque effect is also known from the "Rayleigh disk" which is described in literature for sound intensity measurements. In this paper, inviscid numerical simulations of acoustic radiation forces and torques for disks with radius ≪ wavelength in water are developed in good agreement with former analytical solutions, and the dependence on disk geometry, density, and orientation is discussed. Experiments with alumina disks (diameter 7.5 µm), suspended in an aqueous liquid in a silicon microchannel, confirm the theoretical results qualitatively at the microscale and ultrasonic frequencies around 2 MHz. These results can potentially be applied for the synthesis of disk-reinforced composite materials. The insights are also relevant for the acoustic handling of various disk-shaped particles, such as red blood cells. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
3. On the stability of adaptation process in active noise control systems.
- Author
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Ardekani, Iman Tabatabaei and Abdulla, Waleed H.
- Subjects
NOISE control ,ELECTROACOUSTICS ,COMPUTER simulation ,SIMULATION methods & models ,NUMERICAL analysis ,LOCUS of control - Abstract
The stability analysis of the adaptation process, performed by the filtered-x least mean square algorithm on weights of active noise controllers, has not been fully investigated. The main contribution of this paper is conducting a theoretical stability analysis for this process without utilizing commonly used simplifying assumptions regarding the secondary electro-acoustic channel. The core of this analysis is based on the root locus theory. The general rules for constructing the root locus plot of the adaptation process are derived by obtaining root locus parameters, including start points, end points, asymptote lines, and breakaway points. The conducted analysis leads to the derivation of a general upper-bound for the adaptation step-size beyond which the mean weight vector of the active noise controller becomes unstable. Also, this analysis yields the optimum step-size for which the adaptive active noise controller has its fastest dynamic performance. The proposed upper-bound and optimum values apply to general secondary electro-acoustic channels, unlike the commonly used ones which apply to only pure delay channels. The results are found to agree very well with those obtained from numerical analyses and computer simulation experiments. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
4. Shear horizontal guided wave modes to infer the shear stiffness of adhesive bond layers.
- Author
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Le Crom, Bénédicte and Castaings, Michel
- Subjects
COMPUTER simulation ,ELECTROMECHANICAL analogies ,INVERSE problems ,NUMERICAL analysis ,SPEED - Abstract
This paper presents a non-destructive, ultrasonic technique to evaluate the quality of bonds between substrates. Shear-horizontally polarized (SH) wave modes are investigated to infer the shear stiffness of bonds, which is necessarily linked to the shear resistance that is a critical parameter for bonded structures. Numerical simulations are run for selecting the most appropriate SH wave modes, i.e., with higher sensitivity to the bond than to other components, and experiments are made for generating-detecting pre-selected SH wave modes and for measuring their phase velocities. An inverse problem is finally solved, consisting of the evaluation of the shear stiffness modulus of a bond layer at different curing times between a metallic plate and a composite patch, such assembly being investigated in the context of repair of aeronautical structures. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
5. Fast calculation system specialized for head-related transfer function based on boundary element method.
- Author
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Otani, Makoto and Ise, Shiro
- Subjects
- *
TRANSFER functions , *NUMERICAL analysis , *BOUNDARY element methods , *COMPUTER simulation , *ALGORITHMS - Abstract
Recently, development of a numerical calculation of the head-related transfer function (HRTF) has been conducted using a computer model of a human head and the boundary element method. The reciprocity theorem is incorporated into the computational process in order to shorten the computational time, which is otherwise very long. On the other hand, another fast HRTF calculation method for any source position, which is realized by calculating factors independent of the source position in advance, has been suggested by the authors. Using this algorithm, the HRTF for any source position can be obtained in a few seconds with a common PC. The resulting HRTFs are more precise and are calculated faster than those by using the reciprocity theorem. However, speeding the process up even further is required in order to respond to a head movement and rotation or to moving sources during binaural sound reproduction. In this paper, a faster calculation method by incorporating a time domain operation into the authors’ previous algorithm is proposed. Additionally, the new formulation, which eliminates the extra computational time in the preprocess, is proposed. This method is shown to be faster than the previous ones, but there are some discrepancies at higher frequencies. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
6. Extracting non-propagating oscillatory fields in concrete to detect distributed cracking.
- Author
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Song, Homin and Popovics, John S.
- Subjects
CRACKING of concrete ,NUMERICAL analysis ,COMPUTER simulation ,CONCRETE - Abstract
Work to detect and locate distributed subsurface cracks in concrete by extracting non-propagating oscillatory fields is presented. The medium of interest is concrete, but the approach also applies to other types of inhomogeneous media. The theoretical basis of the work is first presented through a one-dimensional point-scatterer model that considers the wavefield set up by multiple distinct scatterers. More complex scattering scenarios are then investigated using numerical simulation. The numerical models consider two types of scatterers: elliptic large-scale particles distributed throughout a medium, and small-sized cracks localized within a damage zone. The theoretical and numerical analyses show that forward propagating waves undergo distinct scattering behavior within the crack damaged zone: non-propagating resonance-like oscillatory fields are set up within the cracked zone, and are distinct from the scatter caused by the large-scale particles. Frequency-wavenumber (f-k) domain analyses to extract the energy of non-propagating oscillatory fields and thus to detect and locate zones of distributed cracking are employed. The proposed approach is evaluated using numerical simulation and experimental data collected from concrete specimens that contain simulated distributed cracks. The results demonstrate that the location of distributed crack zones in discrete random media, such as concrete, can be successfully detected. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
7. Numerical analysis of three-dimensional acoustic propagation in the Catoche Tongue.
- Author
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Ballard, Megan S. and Sagers, Jason D.
- Subjects
NUMERICAL analysis ,ACOUSTIC wave propagation ,THREE-dimensional sound ,TIME series analysis ,DATA analysis ,BATHYMETRY ,COMPUTER simulation - Abstract
Analysis of modeled time series data is presented to provide insight into propagation physics of horizontally refracted sound in the Catoche Tongue region of the Gulf of Mexico. The analysis is motivated by the observation of out-of-plane arrivals in measured time series data. In particular, the extended duration of the refracted arrivals is shown to be caused by interaction with multiple locations along the steep sides of the Tongue. Comparison of the modeled time series is made to previous work by Sturm [J. Acoust. Soc. Am. 117(3), 1058-1079 (2005)], who examined the frequency dependence of out-of-plane modal arrivals for the wedge-shaped ocean. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
8. Subject-specific computational modeling of human phonation.
- Author
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Qian Xue, Xudong Zhenga, Mittal, Rajat, and Bielamowicz, Steven
- Subjects
HUMAN voice ,VOCAL cords ,COMPUTER simulation ,AIRWAY (Anatomy) ,NUMERICAL analysis ,MATHEMATICAL models ,PHYSIOLOGY - Abstract
A direct numerical simulation of flow-structure interaction is carried out in a subject-specific larynx model to study human phonation under physiological conditions. The simulation results compare well to the established human data. The resulting glottal flow and waveform are found to be within the normal physiological ranges. The effects of realistic geometry on the vocal fold dynamics and the glottal flow are extensively examined. It is found that the asymmetric anterior-posterior laryngeal configuration produces strong anterior-posterior asymmetries in both vocal fold vibration and glottal flow which has not been captured in the simplified models. It needs to be pointed out that the observations from the current numerical simulation are only valid for the flow conditions investigated. The limitations of the study are also discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
9. Multiple acoustic diffraction around rigid parallel wide barriers.
- Author
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Hequn Min and Xiaojun Qiu
- Subjects
GEOMETRICAL diffraction ,BOUNDARY element methods ,NUMERICAL analysis ,COMPUTER simulation ,ARBITRARY constants - Abstract
A ray-based method is presented for evaluating multiple acoustic diffraction by separate rigid and parallel wide barriers, where two or more neighboring ones are of equal height. Based on the geometrical theory of diffraction and extended from the exact boundary solution for a rigid wedge, the proposed method is able to determine the multiple diffraction along arbitrary directions or at arbitrary receiver locations around the diffracting edges, including the positions along the shadow or reflection boundaries or very close to the edges. Comparisons between the results of the numerical simulations and the boundary element method show validity of the proposed method. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
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