Search

Evaluating capacities of quantum channels is the first purpose of quantum Shannon theory, but in most cases the task proves to be very hard. Here, we introduce the set of Multi-level Amplitude Damping quantum channels as a generalization of the standard qubit Amplitude Damping Channel to quantum systems of finite dimension d. In the special case of d = 3, by exploiting degradability, data-processing inequalities, and channel isomorphism, we compute the associated quantum and private classical capacities for a rather wide class of maps, extending the set of models whose capacity can be computed known so far. We proceed then to the evaluation of the entanglement assisted quantum and classical capacities. Estimating the capacity of quantum channels is relevant to understand at which rate quantum information can be exchanged. Here, the authors introduce multi-level amplitude damping channels that generalize the qubit amplitude damping noise model, analyse their quantum and private capacities, and exactly derive the capacities of quantum channels that are not anti-degradable. [ABSTRACT FROM AUTHOR]

The idea of localized resonance in phononic crystals is introduced to improve the low-frequency acoustic absorption of viscoelastic materials, which are widely used underwater to absorb the unwanted noise and meet a difficult challenge to enhance low-frequency absorption. Experimental measurements for acoustic absorptances of various viscoelastic polymer slabs embedded with locally resonant scatterers, i.e., heavy spheres coated by soft silicon rubber, are reported. Theoretical investigations using a layer-multiple-scattering method show good agreement with the experiment results, which supports unambiguously the observed low-frequency absorption phenomenon. The physical mechanism for the low-frequency absorption is also investigated by referring the elements of the Mie scattering matrix. The observations suggest that the scattered energy tends to remain in transverse waves, which enhance the multiple scattering, damp rapidly in viscoelastic polymer and dominate the acoustic absorption. [ABSTRACT FROM AUTHOR]

By applying a new two-step line-shape analysis to inelastic neutron and x-ray scattering spectra of glassy systems, we were able to resolve the acoustic excitations from the low-frequency excess modes and to accurately estimate the damping of sound waves in the terahertz frequency range. Using this approach, we estimated the damping parameter for terahertz acoustic waves in a wide class of chemically different glasses and did a quantitative comparison of the results with prediction of theoretical models. By comparing the estimates of the mean-free path of the acoustic modes in different glasses and the corresponding boson peak strengths, we show the existence of a simple correlation between these two quantities. The relationship between attenuation of the terahertz acoustic modes, strength of the boson peak, and fragility is discussed. [ABSTRACT FROM AUTHOR]

The vibration response of microcantilevers to simple harmonic base motion is formulated in terms of base motion plus modal responses relative to the moving base frame. Environmental damping is evaluated. The analysis gives the frequency responses of the first four modes and shows that the phase angle of each mode relative to the moving base frame is constant but that the phase angle of the absolute motion varies along the length of cantilevers. This finding is verified with experimental data. Phase changes along cantilevers depend on frequency ratios and the magnitude of environmental damping. Experimental data are used to establish damping factors, and phase angles are measured experimentally and compared with theoretical predictions. [ABSTRACT FROM AUTHOR]

Abstract The modal summation approach is extended to the prediction of the sound transmission loss for a finite plate with constrained viscoelastic layer. The predicted transmission loss for a single leaf plate is compared with the results given by commercial FEM code and the reasons for the discrepancies are discussed. Then the predicted transmission loss for a damped sandwich plate is presented and the laboratory measurements is also provided for a comparison. Furthermore, the predicted transmission loss is compared with that of an equivalent fourth order equation in which the damping influence due to constrained viscoelastic layer is taken into account. The influence of plate parameters on the sound transmission of the plates in the low frequency range is discussed, and the methods is able to be used for optimizing damped sandwich plates. [ABSTRACT FROM AUTHOR]

Abstract Helmholtz resonators (HRs) are widely used to damp acoustic oscillations, including in the combustors of aero-engines and power gas turbines where they damp thermoacoustic oscillations. The geometries of such combustors are often annular in shape, which means that low frequency acoustic modes exhibit both longitudinal and circumferential modeshapes, the latter across different circumferential wave numbers. For linear acoustic disturbances downstream of the flame, the presence of HRs leads to modal coupling and mode shape shifts, which makes design and placement of multiple HRs very complicated. A procedure which ensures that the design and placement of the HRs can be optimised for good acoustic damping performance would be very valuable, and such a procedure is presented in this work. A simplified linear, low-dimensional model for the acoustic behaviour in a hot annular duct sustaining a mean flow is extended to account for the attachment of multiple HRs. The HRs are assumed to sustain a cooling mean bias flow through them, towards the combustor, such that they can be modelled using linear, lumped element Rayleigh conductivity models. An optimisation method based on the gradient derived from adjoint sensitivity analysis is then applied to the low order network acoustic modelling framework for hot annular ducts incorporating HR models, for the first time. It is used to optimise over multiple HR geometry and placement parameters, to obtain optimum acoustic damping over all acoustic modes in a given frequency range. These optimisation procedures are validated via multi-dimensional parameter sweep results. Thus a novel and efficient tool for HR optimisation for thin annular ducts is presented. [ABSTRACT FROM AUTHOR]

Highlights • Semi-analytical model of Acoustic Black Hole (ABH) with constrained layer damping is firstly built. • Gaussian Expansion Method is proposed to improve numerical precision and treatment complexity. • PCVL treatment enhances ABH effect in low frequencies. Abstract Power-law profiles at the edges of beams and plates have proved to be a very efficient way to attenuate vibrations. In an ideal scenario, for a profile with zero end thickness, the energy of flexural vibrations would never reflect from the boundaries, giving place to the Acoustic Black Hole (ABH) phenomenon. In practice, however, the edge must be truncated which results in a non-zero reflection coefficient. To partially mitigate this problem, a viscoelastic layer (VL) is typically placed at the tip of the ABH termination to compensate for the effects of truncation. Instead, in this work it will be shown that one can achieve better results by resorting to passive constrained viscoelastic layer (PCVL). The latter consists of a sandwich made of a viscoelastic layer (VL) plus a constrained layer (CL). An analytical model is developed to describe the performance of a truncated ABH beam with PCVL, where the displacement fields are expanded by means of Gaussian functions. The model is validated through finite element (FEM) simulations and experiments. It is observed that a truncated ABH beam with PCVL at the tip performs better than an ABH beam with an unconstrained VL, even if they add equal mass to the system. [ABSTRACT FROM AUTHOR]

Abstract In this study, the phase–averaged wave action equation (WAE) is extended to incorporate the effect of submerged porous media with high permeability. The wave dissipation coefficient for submerged porous media is incorporated into the WAE of the wind wave model. The coefficient of turbulent flow resistance is obtained from the work by taking the imaginary part of a mathematical model of wave transformation over a submerged porous medium under the mild–slope assumption. A method to estimate the characteristic parameter of turbulent frictional resistance in porous media is proposed in this study. Comparisons with experiments and other numerical results showed that the proposed model could be applied to waves propagating over porous beds and reefs. Practical simulations were used to investigate wave damping due to porous seabeds in nearshore areas. Highlights • A study for adding the effect of submerged porous media to the wind wave model. • Consideration to high permeable porous media. • A method to estimate the parameter of turbulent frictional resistance. • The model can be applied to waves passing over porous beds and reefs. [ABSTRACT FROM AUTHOR]

Spurious numerical damping in the collocation boundary element method is considered for plane sound waves in two-dimensional ducts subjected to rigid and absorbing boundary conditions. Its extent is quantified in both conditions based on a damping model with exponential decay, and meshes of linear and quadratic continuous elements are studied. An exponential increase of numerical damping with respect to frequency is found and the results suggest an upper bound for given element-to-wavelength ratios. The quantification of numerical damping is required for evaluation of meshes covering a large number of waves, and real damping phenomena can be prevented from overestimation. [ABSTRACT FROM AUTHOR]

A novel approach to investigate and evaluate the damping loss factor of a planar multilayered structure is presented. A statistical analysis reveals the connection between the damping properties of the structure and the transmission of sound through the thickness of its laterally infinite counterpart. The obtained expression for the panel loss factor involves all the derivatives of the transmission and reflection coefficients of the layered structure with respect each layer damping. The properties of the fluid for which the sound transmission is evaluated are chosen to fulfil the hypotheses on the basis of the statistical formulation. A transfer matrix approach is used to compute the required transmission and reflection coefficients, making it possible to deal with structures having arbitrary stratifications of different layers and also granting high efficiency in a wide frequency range. Comparison with alternative formulations and measurements demonstrates the effectiveness of the proposed methodology. [ABSTRACT FROM AUTHOR]

Wolf notes are generally undesirable sounds that occur in string instruments, particularly in cellos. State-of-the-art passive wolf note eliminators affect the whole cello sound and can become ineffective when environmental conditions and, therefore, the cello's structural properties change. In this paper, an approach is presented that uses smart materials to eliminate the wolf note with little effects to the cello's sound. Based on preliminary measurements, a mathematical model of the cello for generating the wolf note and for developing a wolf note elimination controller is set up. The controller consists of a wolf detection criterion that triggers a velocity feedback controller to actively induce damping into the cello's body whenever a wolf note is detected. The controller setup is experimentally validated by an implementation on a test cello. The velocity feedback to induce the active damping is implemented by means of a piezoelectric patch actuator attached to the cello's body. Both the results of the mathematical model and the results of the experimental investigation show a good performance in eliminating the wolf note on a cello. [ABSTRACT FROM AUTHOR]

An acoustic radiation model of a cavity with a flexible plate treated with constrained layer damping (CLD) is developed by a combination of finite element method (FEM) and boundary element method (BEM). An acoustic topology optimization model is established with the objective of minimizing sound radiation power at specific modal frequency and design variables defined as locations of CLD treatments. The evolutionary structural optimization (ESO) method and genetic algorithm (GA) are employed to search optimal CLD configurations. Sound power sensitivity for CLD/plate is derived to determine search direction in ESO optimization procedure. The optimal CLD layouts for the flexible plate with two different boundary conditions are obtained and analyzed. Computational time, optimal layouts, and minimum sound power obtained using ESO and GA are compared. The results demonstrate effectiveness of the two methods, and ESO is more efficient to obtain deterministic and more practical optimal CLD material layouts for minimizing sound radiation power. The influences of CLD materials thickness and exciting force locations on optimal results obtained using ESO are discussed in detail. It is shown that the optimal rejection ratio varies with thicknesses of CLD materials and distribution of normal velocity of the flexible plate. Variation trend of the optimal rejection ratio is opposite for the two boundary conditions. [ABSTRACT FROM AUTHOR]

Acoustic black holes (ABHs) have been explored and demonstrated to be effective passive treatments for broadband noise and vibration control. Performance metrics for assessing damping concepts are often focused on maximizing structural damping loss factors. Optimally performing damping treatments can reduce the resonant response of a driven system well below the direct field response. This results in a finite structure whose vibration input–output response follows that of an infinite structure. The vibration mobility transfer functions between locations on a structure can be used to assess the structure's vibration response phase, and compare its phase response characteristics to those of idealized systems. This work experimentally explores the phase accumulation in finite plates, with and without embedded grids of ABHs. The measured results are compared and contrasted with theoretical results for finite and infinite uniform plates. Accumulated phase characteristics, their spatial dependence and limits, are examined for the plates and compared to theoretical estimates. The phase accumulation results show that the embedded acoustic black hole treatments can significantly enhance the damping of the plates to the point that their phase accumulation follows that of an infinite plate. [ABSTRACT FROM AUTHOR]

The influence on the acoustics of the violin of the bridge and the island area between the f-holes is demonstrated by treating the body as a thin-walled shell structure. COMSOL finite element software is used as a quasi-experimental tool to identify and understand the coupling of the bridge, island area, offset soundpost, and bassbar to the radiating surfaces of the body shell by varying their properties, often over a wide range. The frequency dependence of the resulting input filter between the vibrating strings and body shell modes is derived using a quasi-statistical averaging approach involving the strong damping of the body shell modes. The bridge-island filter response over the whole playing range of the violin is shown to be strongly dependent on the properties of the bridge, island area, soundpost, and bassbar. Their properties influence both the intensity and tonal balance of the radiated sound and the broad Bridge-Hill feature in the vibro-acoustic response of many fine instruments. [ABSTRACT FROM AUTHOR]

Measurements of basilar-membrane (BM) motion show that the compressive nonlinearity of cochlear mechanical responses is not an instantaneous phenomenon. For this reason, the cochlear amplifier has been thought to incorporate an automatic gain control (AGC) mechanism characterized by a finite reaction time. This paper studies the effect of instantaneous nonlinear damping on the responses of oscillatory systems. The principal results are that (i) instantaneous nonlinear damping produces a noninstantaneous gain control that differs markedly from typical AGC strategies; (ii) the kinetics of compressive nonlinearity implied by the finite reaction time of an AGC system appear inconsistent with the nonlinear dynamics measured on the gerbil basilar membrane; and (iii) conversely, those nonlinear dynamics can be reproduced using an harmonic oscillator with instantaneous nonlinear damping. Furthermore, existing cochlear models that include instantaneous gaincontrol mechanisms capture the principal kinetics of BM nonlinearity. Thus, an AGC system with finite reaction time appears neither necessary nor sufficient to explain nonlinear gain control in the cochlea. [ABSTRACT FROM AUTHOR]

Vocal folds show a damped oscillatory movement while abducting at the end of a vocal emission. The phenomenon can be observed with high-speed videoendoscopy and with different glottographic methods. It reflects important mechanical properties of the vocal oscillator, and cannot be voluntarily controlled. It could become a valuable clinical parameter, particularly in a medicolegal context, but its large variability in a same subject limits its use. First, possibilities and limitations of each recording method are reviewed. Second, the three main physiological factors accounting for the variability are analysed: (1) the timing dynamics of the expiratory pressure with respect to the opening of the glottis; (2) the speed at which vocal fold edges are abducted and glottal resistance drops, the combined effect of (1) and (2) determining the persisting transglottal flow, hence a persisting driving force; (3) the morphological change of the oscillator, whose lip-like shape becomes flattened depending on the degree of abduction. For clinical/medicolegal applications, additional research is required as to the recording protocol. A possible solution could be an entire recording with high speed transnasal videokymography of a standardised passage read by the subject, with a posteriori automatic extraction, by dedicated software, of all damping phases and computation of the average damping coefficient. [ABSTRACT FROM AUTHOR]

Among vocal fold diseases, the presence of a surface growth is often encountered and can be considered a public health issue. While more energy is required to achieve phonation than in healthy cases, this situation can lead to a wide range of voice perturbations, from a change of voice quality to aphonia. The present study aims at providing finer comprehension of the physical phenomena underlying this type of pathological phonation process. A vocal fold replica is used to perform measurements of mechanical responses of each vocal fold as well as of the subglottal pressure in both healthy and pathological configurations. Besides these physical measurements, a theoretical model is derived, using the one-mass-delayed model involving asymmetry of mass and geometry in order to simulate pressure signals. The theoretical model parameters are determined according to mechanical measurements on the replica. Results from measurements and simulations show that this unique vocal fold replica behaves in a manner comparable to clinical observations. The energy required to produce sound increases in the presence of a growth as well as with the size of the growth. Further investigation tends to show that the contact of the growth on the opposite vocal fold, considered as additional damping, plays a critical role. [ABSTRACT FROM AUTHOR]

This study starts with a simple question: can the vibration of plates or beams be efficiently reduced using a lightweight structure that occupies a small space? As an efficient technique to damp vibration, the concept of an acoustic black hole (ABH) is adopted with a simple modification of the geometry. The original shape of an ABH is a straight wedge-type profile with power-law thickness, with the reduction of vibration in beams or plates increasing as the length of the ABH increases. However, in real-world applications, there exists an upper bound of the length of an ABH due to space limitations. Therefore, in this study, the authors propose a curvilinear shaped ABH using the simple mathematical geometry of an Archimedean spiral, which allows a uniform gap distance between adjacent baselines of the spiral. In numerical simulations, the damping performance increases as the arc length of the Archimedean spiral increases, regardless of the curvature of the spiral in the mid- and high-frequency ranges. Adding damping material to an ABH can also strongly enhance the damping performance while not significantly increasing the weight. In addition, the radiated sound power of a spiral ABH is similar to that of a standard ABH. [ABSTRACT FROM AUTHOR]

This paper presents a damping loss factor estimation method for structures made of solid elastic and viscoelastic materials. Using an impulsive excitation signal, an acceleration impulse response of the panel in free edge boundary conditions is measured and the damping loss factor is determined at each frequency of interest, by applying an overlapped narrow band frequency decay method. This means that, for the duration of the impulse, the decay of each frequency band is measured in time domain and, using a backward integration approach, structural reverberation time is determined. Successively, the damping loss factor is calculated using a well-established relationship between measured quantities and frequencies. Firstly, several investigations related to the post-processing procedures for the determination of structural reverberation time will be analyzed in detail. Results will then be presented and discussed for different structures and compared with different available measurement techniques. [ABSTRACT FROM AUTHOR]

The study of vibration in uniform beams provides physics teachers with a platform by which a broad range of physics vibration-related topics can be explored without expensive and specialized equipment. This paper presents two laboratory exercises related to lateral beam vibrations. These exercises use beam theory coupled with free sound-analysis software (Raven Lite 2.0), and are appropriate for both high school and first-year college physics students. In this paper, the uniform beam is a slender tube with unsupported (or free) ends—such as a wind chime. [ABSTRACT FROM AUTHOR]

The flowability of the bulk materials was determined after development of yield locus, wall yield locus, and effect of time consolidation was measured. Data from the obtained curves were read and important parameters such as unconfined stress, major consolidation stress, angle of internal friction, angle of wall friction, and effective angle of internal friction were for further design of silo calculation made ready. Diagrams and relationships developed by Jenike were used to find important silo discharge opening parameters such as the angle of the conical or wedge shaped opening and critical silo opening diameter and width. The relative difference betweentefflour andtefseed was made in which the flour has a characteristics indicator of particle size distribution with lower dimension and the flour is cohesive and less flowable and accordingly needs more generous discharge parameters. The comparison between the flour and the seeds was shown in the measurement of flowability indexes and also reflected clearly on the designed silo discharge opening parameters. [ABSTRACT FROM AUTHOR]

To predict ultrasonic guided waves generated by a piezoelectric transducer (PZT) in a structure accurately, the dynamic coupling between the base structure and the surface-bonded PZT must be modeled accurately and analyzed in an efficient way. For so-called smart beams, which consist of a metallic base beam and a surface-bonded PZT layer, we propose a spectral element model that has the capability to accurately predict high frequency dynamic responses and guided waves. For the spectral element model, Timoshenko beam theory is applied to both the base beam and PZT layer, and Mindlin-Herrmann rod theory is adopted to account for the effects of lateral contraction in the thickness direction of the base beam. The high accuracy of the spectral element model is validated by comparing the results of the spectral element model with conventional finite element method (FEM) results and results from the commercial finite element analysis package ANSYS. The effects of PZT-induced axial-bending coupling and structural damping on the dynamics and guided waves are then investigated using numeral simulation. [ABSTRACT FROM AUTHOR]

We report the observation, by means of high-resolution inelastic x-ray scattering, of an unusually large temperature dependence of the sound attenuation of a network glass at terahertz frequency, an unprecedentedly observed phenomenon. The anharmonicity can be ascribed to the interaction between the propagating acoustic wave and the bath of thermal vibrations. At low temperatures the sound attenuation follows a Rayleigh-Gans scattering law. As the temperature is increased the anharmonic process sets in, resulting in an almost quadratic frequency dependence of the damping in the entire frequency range. We show that the temperature variation of the sound damping accounts quantitatively for the temperature dependence of the density of vibrational states. [ABSTRACT FROM AUTHOR]

Abstract: A study of the effects of damping on the low-frequency acoustics of listening rooms has been undertaken. The study was carried out using a new numerical implementation of an analytical solution based on a model developed by Bistafa and Morrissey. The model was designed to simulate the sound field in rectangular enclosures below the Schroeder cut-off frequency. Four hypothetical rooms were studied, a lightly damped room, a well damped room, a statistically compliant European Broadcast Union control room and a compliant European Broadcast Union control room. The most important result from the study using the proposed model was the influence of modes above the Schroeder cut-off frequency on reverberation time. This was caused by the variations in damping between mode types and variations in the modal coupling between the source and receiver. The research suggests that Schroeder's 1954 cut-off frequency for the influence of modes was more correct for highly damped rooms, in comparison with the Schroeder's 1964 relation. [Copyright &y& Elsevier]

This article presents a simulation study on two integrated tuned vibration absorbers (TVAs) designed to control the global flexural vibration of lightly damped thin structures subject to broad frequency band disturbances. The first one consists of a single axial switching TVA composed by a seismic mass mounted on variable axial spring and damper elements so that the characteristic damping and natural frequency of the absorber can be switched iteratively to control the resonant response of three flexural modes of the hosting structure. The second one consists of a single three-axes TVA composed by a seismic mass mounted on axial and rotational springs and dampers, which are arranged in such a way that the suspended mass is characterized by uncoupled heave and pitch-rolling vibrations. In this case the three damping and natural frequency parameters of the absorber are tuned separately to control three flexural modes of the hosting structure. The simulation study shows that the proposed single-unit absorbers produce, respectively, 5.3 and 8.7 dB reductions of the global flexural vibration of a rectangular plate between 20 and 120 Hz. [ABSTRACT FROM AUTHOR]

The theory of damping and nonlinear frequency shifts from particles resonant with ion-acoustic waves (IAWs) is presented for multi-ion species plasma and compared to driven wave Vlasov simulations. Two distinct IAW modes may be supported in multi-ion species plasmas, broadly classified as fast and slow by their phase velocity relative to the constituent ion thermal velocities. In current fusion-relevant long pulse experiments, the ion to electron temperature ratio, Ti/Te, is expected to reach a level such that the least damped and thus more readily driven mode is the slow mode, with both linear and nonlinear properties that are shown to differ significantly from the fast mode. The lighter ion species of the slow mode is found to make no significant contribution to the IAW frequency shift despite typically being the dominant contributor to the Landau damping. [ABSTRACT FROM AUTHOR]

Abstract: Recently, considerable attention has been paid on the utilization of natural materials in structures. Utilizing natural materials over traditional, synthetic structures results in a reduction of carbon emissions from material synthesis; such a source of materials could also be renewable and recyclable. Currently, few reports exist on sound and vibrational properties in sandwich composites with the use of natural materials. Sandwich composites are commonly used in structures for their superior strength and stiffness-to-weight ratios, but from these same properties, they radiate noise efficiently. Here, in this study, the sound and vibration damping properties of natural material based sandwich composites were explored and characterized. It was experimentally observed that utilizing a balsa wood core with a natural fiber based face sheet has a 100% improvement in coincidence frequency, a metric of acoustic performance, and the combination of a natural fiber based face sheet with a Rohacell 51 WF synthetic core exhibits a 233% increase over a fully synthetic sandwich composite. As these improvements in acoustic performance are achieved with only small sacrifices in bending stiffness, these results suggest that, if optimized, natural material based sandwich composites could be an environmentally friendly solution to the sandwich structure-noise radiation problem. [Copyright &y& Elsevier]

Complex Modes is one of those topics that every vibration practitioner understands - just not fully. We all "know" that complex modes exhibit two shape functions that vibrate at a single frequency in phase quadrature. Experimentalists recognize complex modes from the "galloping nodes" in an animated display. Analysts understand them as result of the "non-proportional" distribution of damping. Most of us have found some aspect of the complex mode phenomenon, its analysis or measurement just a little mysterious. [ABSTRACT FROM AUTHOR]

Combustion instabilities are caused by the interaction of unsteady heat releases and acoustic waves. To mitigate combustion instabilities, perforated liners, typically subjected to a low Mach number bias flow (a cooling flow through perforated holes), are fitted along the bounding walls of a combustor. They dissipate the acoustic waves by generating vorticity at the rims of perforated apertures. To investigate the absorption of plane waves by a perforated liner with bias flow, a time-domain numerical model of a cylindrical lined duct is developed. The liners' damping mechanism is characterized by using a time-domain 'compliance.' The development of such time-domain compliance is based on simplified or unsimplified Rayleigh conductivity. Numerical simulations of two different configurations of lined duct systems are performed by combining a 1D acoustic wave model with the compliance model. Comparison is then made between the results from the present models, and those from the experiment and the frequency-domain model of previous investigation [Eldredge and Dowling, J. Fluid Mech. 485, 307-335(2003)]. Good agreement is observed. This confirms that the present model can be used to simulate the propagation and dissipation of acoustic plane waves in a lined duct in real-time. [ABSTRACT FROM AUTHOR]

We present a description and the results of a laboratory experiment on observing amplitude modulation of a weak continuous high-frequency wave under the action of a sequence of strong low-frequency pulses in a statically loaded grainy medium-water-saturated river sand. We present characteristic oscillograms of the obtained acoustic signals, testifying to the manifestation of dissipative nonlinearity of river sand; as well, we observed both the effect of damping and gain of sound by sound. In the first case, this is connected with an increase in the dissipation of the medium under the action of a powerful low-frequency pulse, and in the second case, with its decrease. [ABSTRACT FROM AUTHOR]

Acoustic wave propagation in lattice Boltzmann Bhatnagar–Gross–Krook simulations may be analysed using a linearization method. This method has been used in the past to study the propagation of waves that are viscously damped in time, and is here extended to also study waves that are viscously damped in space. Its validity is verified against simulations, and the results are compared with theoretical expressions. It is found in the infinite resolution limit k→0 that the absorption coefficients and phase differences between density and velocity waves match theoretical expressions for small values of ωτν, the characteristic number for viscous acoustic damping. However, the phase velocities and amplitude ratios between the waves increase incorrectly with (ωτν)2, and agree with theory only in the inviscid limit k→0, ωτν→0. The actual behaviour of simulated plane waves in the infinite resolution limit is quantified. [ABSTRACT FROM AUTHOR]

The paper describes the results of experimental measurements of point mobility carried out on circular plates containing tapered holes of quadratic power-law profile with attached damping layers. The obtained results are compared to the developed numerical model, as a means of validation. The profiles of the tapered hole in the plates are designed to replicate near zero reflection of quasi-plane waves from a tapered hole in geometrical acoustics approximation, also known as acoustic black hole effect. The driving point mobility measurements are provided, showing a comparison of the results for a constant thickness circular plate, a constant thickness plate with a layer of damping film applied and a plate with a quadratic power-law profile machined into the center, which is tested with a thin layer of elastic damping material attached. The results indicate a substantial suppression of resonant peaks, agreeing with a numerical model, which is based on the analytical solution available for the vibration of a plate with a central quadratic power-law profile. The paper contains results for the case of free boundary conditions on all edges of the plates, with emphasis placed on the predictions of resonant frequencies and the amplitudes of vibration and loss factor. [ABSTRACT FROM AUTHOR]

This paper presents a novel technique for the determination of the material damping ratio in shallow soil layers. It is based on the spectral analysis of surface waves (SASW) test. The technique is an alternative to existing methods, where the damping ratio is determined from the spatial decay of the Rayleigh wave. These methods rely on the knowledge of the geometric damping, and may lead to incorrect results if the geometric damping is calculated based on an inaccurate shear wave velocity profile. The existing methods may also lead to incorrect results when higher modes contribute to the wavefield in the soil. In the proposed technique, the wavefield is transformed to the frequency–wavenumber domain. The resulting frequency–wavenumber spectrum exhibits a peak that corresponds to the fundamental Rayleigh wave. The dispersion curve is derived from the peak's position, whereas the attenuation curve is derived from its width, using the half-power bandwidth method. Due to the use of the appropriate wavenumber transformation, this method does not require the calculation of the geometric damping. In addition, the occurrence of higher Rayleigh modes does not affect the attenuation curve associated with the fundamental Rayleigh wave, as higher modes appear as separate peaks in the frequency–wavenumber spectrum that do not interfere with the peak corresponding to the fundamental Rayleigh wave (except at the osculation points). Three benchmark problems are considered to validate the outlined technique; the results are compared with those obtained using existing methods. All methods perform well when applied to a regular soil profile, where the stiffness of the soil increases with depth. For soil profiles with a soft layer trapped between two stiffer layers, or where the soil properties vary smoothly with depth, the proposed technique yields more accurate results than the existing methods. The practical applicability of the new method is finally illustrated using experimental data collected from a test site in Belgium. [ABSTRACT FROM AUTHOR]

Abstract: An acoustic impedance pump is comprised of a compressible section coupled at both ends to sections of different acoustic impedances. Liquid can be pumped from one end to another if the compressible section is actuated at certain locations. This paper presents an analytical model on the acoustic pumping effect in microchannels. A one-dimensional wave equation is developed for acoustic pressures in the compressible section, taking into account the actuations as acoustic source terms. The solution for the acoustic pressure is a set of standing waves established inside the compressible section, corresponding to the actuations. The pumping effect is attributed to the second-order terms of the acoustic pressures. Two control parameters are identified. One is the resonance frequency associated with the sound wave speed and length of the compressible section, and the other is the damping factor. The analytical results are compared with the experimental data, and a qualitative agreement is observed in terms of frequency characteristics of the pumping pressure. [Copyright &y& Elsevier]

The sound baffle is a useful component for the sonar design. According to the different requirement, it's the keyboard to optimize the physical and structural parameters of the baffle. A Genetic algorithm, as an efficient optimization method, is used widely in the engineering optimization. However, the composition of chromosome, the coding form and the definition of cost function would seriously influence the performance of genetic algorithm because its calculation doesn't depend on the external information. According to the aim at maintain the reflection coefficients minimized and uniformed in the scopes of both definite incident frequencies and angles, the optimization method of parameters of layered composite sound baffle based on the genetic algorithm will be presented. In this algorithm, the chromosome coding based on transfer matrix and the cost function based on the statistic principle are proposed. The dependability and validity of the algorithm are proved and the influence led by changing the cost function on the result from the optimum algorithm is analyzed with the simulation calculation. [ABSTRACT FROM AUTHOR]

Based on the periodicity of mechanical links, the sound transmission model is firstly established for double-plate structures coupled by mechanical links. The transmission loss and vibration energy formulations of the two plates are yielded by applying Fourier transform and inverse Fourier transform technique. Three zones are defined for the coupled double-plate structures. The respective sound insulation of the three zones is then studied. Obtained results show that the stiffness of mechanical links has a positive effect on the vibration transmission of the two plates. The response of the two plates equals to each other with strong coupling mechanical links. The sound insulation of the stiffness zone is subjected to co-effects of the stiffness of the mechanical links, air gap, and the plates. While in the damping zone, there are plenty of peaks and dips in the sound insulation curve. The increase of the value of damping loss factor results in the smooth of the curve. Numerical results also reveal that the wider spacing between the mechanical links results in changes of transmission loss in the three zones. The frequency ranges of stiffness-controlled and damping-controlled zone become narrower with a wider spacing, and the transmission loss moves to low frequency for the damping-controlled zone. The transmission loss increases by 5 dB per octave frequency band and by 5 dB with an increase of the mass. The sound insulation characteristics of double-plate structures with mechanical links are similar to that of single-wall structures. [ABSTRACT FROM AUTHOR]

A realistic model of the piano hammer-string interaction must treat the action mechanism and string as a single system. In this paper an elastic stiff string model is integrated with a dynamic model of a compliant action mechanism with flexible hammer shank. Action components represented as rotating bodies interact through felt-lined interfaces for which a specialized contact model with hysteretic damping and tangential friction was developed. The motion of the hammer during string contact is governed by the dynamics of the action mechanism, thereby providing a more sophisticated hammer-string interaction than a simple transverse impact hammer model with fixed contact location. Simulations have been used to compare mechanism response for impact on the elastic string as compared to a rigid stop. Hammer head scuffing along the string and time in contact were predicted to increase, while hammer shank vibration amplitude and peak contact force were decreased. Introducing hammer-string friction decreases the duration of contact and reduces the extent of scuffing. Finally, significant differences in hammer and string motion were predicted for a highly flexible hammer shank. Initial contact time and location, length of contact period and peak force, hammer vibration amplitude, scuffing extent, and string spectral content were all influenced. [ABSTRACT FROM AUTHOR]

Abstract: An efficient method is presented for implementing an acoustic echo canceller (AEC) that makes use of hybrid sub-band approach. The hybrid system is comprised of a fixed processor and an adaptive filter in each sub-band. The AEC aims at reducing the echo resulting from the acoustic feedback in loudspeaker-enclosure-microphone (LEM) systems such as teleconferencing and hands-free systems. In order to cancel the acoustical echo efficiently, various processing architectures including fixed filters, hybrid processors, and sub-band structure are investigated. A double-talk detector is incorporated into the proposed AEC to prevent the adaptive filter from diverging in double-talk situations. A de-correlation filter is also used alongside sub-band processing in order to enhance the performance and efficiency of AEC. All algorithms are implemented and verified on the platform of a fixed-point digital signal processor (DSP). The AECs are evaluated in terms of cancellation performance and computation complexity. In addition, listening tests are conducted to assess the subjective performance of the AECs. From the results, the proposed hybrid sub-band AEC was found to be the most effective among all methods in terms of echo reduction and timbral quality. [Copyright &y& Elsevier]

Abstract: In this paper, a novel single-chip MEMS capacitive microphone is presented. The novelties of the method relies on the moveable aluminum (Al) diaphragm positioned over the backplate electrode, where the diaphragm includes a plurality of holes to allow the air in the gap between the electrode and the diaphragm to escape and thus reducing acoustical damping in the microphone. Spin-on-glass (SOG) was used as a sacrificial and isolating layer. Backplate is monocrystalline silicon wafer, that it is more stiff. This work will focus on design, simulation, fabrication and characterization of the microphone. The structure has a diaphragm thickness of 3μm, a diaphragm size of 0.5mm×0.5mm, and an air gap of 1.0μm. The results show that the pull-in voltage is 105V, the initial stress of evaporated aluminum diaphragm is around 1500MPa and the zero bias capacitance of microphone is 2.12pF. Comparing with the previous works, this microphone has several advantages: the holes have been made on diaphragm, therefore no need of KOH etching to make back chamber, in this way the chip size of each microphone is reduced. The fabrication process uses minimal number of layers and masks to reduce the fabrication cost. [Copyright &y& Elsevier]

Abstract: This paper provides an overview of a number of nonlinear system identification methods as applied to the analysis of nonlinear automotive dampers. The motivation for illustrating a number of approaches is that each method provides different insights into the behavior of the systems and therefore the methods are complementary. The background for each of the methods is given and each is demonstrated through an experimental case study. [Copyright &y& Elsevier]

This paper discusses the various challenges faced in the acoustical remodel of a Burn Acute Care Unit. A specific focus is placed on the debridement treatment facility, where patients undergo daily removal of dead tissue. Debridement is extremely painful for patients and loud distress sounds are common. The existing facility consisted of institutional tiled walls, plaster ceiling, and ceramic tile floors. Privacy curtains provided the only separation between patient debridement stations and sound isolation between the debridement facility and the rest of the ward was inadequate. Patient distress sounds could clearly be heard throughout the ward, likely creating anxiety for the patients. The design philosophy for the remodeled facility was to create true treatment rooms, with "Spa-like" finishes. Details of the remodel are presented, including creation of sound locks for enhanced sound isolation and selection of absorptive treatment that met high sanitary standards. The L1 values for typical patient distress sounds as measured in adjacent spaces were reduced from 88 dBA before remodel to 55-58 dBA after the remodel. The result was enhanced privacy and acoustical comfort within the remodeled debridement treatment facility as well as to patient rooms throughout the ward. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new approach for harmonic disturbance rejection using semi-active vibration control. The approach is illustrated through application to the problem of maximizing the energy dissipated by a semi-active damper under harmonic excitation. In order to establish a baseline for the evaluation of the performance of the semi-active damper, the effectiveness of the optimal passive and active cases are first presented. The study then examines the ability of the clipped optimal control (or clipping control) approach to improve the energy dissipation capacity of the semi-active damper over the optimal passive damper. An approximate solution to the nonlinear dynamic problem, obtained using the method of averaging, and a time integration based numerical method indicate that this approach improves the energy dissipated by the semi-active damper over the optimal passive damper. The approach presented in this paper intends to further “improve”, or “fine tune”, the control parameters given by the clipped optimal control approach. This is done using an approximated solution of the problem and an appropriate optimization algorithm. Results clearly indicate that this new approach provides significant improvement on energy dissipation over the clipped optimal control approach for the semi-active damper. [Copyright &y& Elsevier]

Abstract: Thermo-elastic damping is the dominant mode of energy loss due to the coupling of thermal and elastic fields in a body vibrating at or near resonant frequency. While the literature contains both exact and numerical schemes to quantify it, no technique is available yet to reduce thermo-elastic damping. We address this issue by introducing a secondary elastic field to derive an exact expression that predicts linear reduction in thermo-elastic damping with respect to frequency. Contrary to the current understanding, introduction of a static axial stress in addition to the flexural stresses is shown to increase quality factor and resonant frequency simultaneously. [Copyright &y& Elsevier]

The bender element test has shown to be a reliable tool to determine the shear wave velocity. This paper aims to extend the bender element technique to also measure the material damping ratio in a triaxial cell. Three different interpretation techniques are developed for this purpose. The first technique uses a modal test of a cylindrical soil specimen in a triaxial cell, the second approach uses multiple arrivals of a bender element signal, and third, a self-correcting method using different travel paths is presented. These methods are applied on test results on undisturbed samples of a silt and a heavily overconsolidated clay, and show promising results for the assessment of the material damping ratio. [ABSTRACT FROM AUTHOR]

Error correction procedures are considered which are designed specifically for the amplitude damping channel. Amplitude damping errors are analyzed in the stabilizer formalism. This analysis allows a generalization of the [4, 1] "approximate" amplitude damping code. This generalization is presented as a class of [2(M + 1), M] codes; quantum circuits for encoding and recovery operations are presented. A [7,3] amplitude damping code based on the classical Hamming code is presented. All of these are stabilizer codes whose encoding and recovery operations can be completely described with Clifford group operations. Finally, optimization options are described in which recovery operations may be further adapted according to the damping probability. [ABSTRACT FROM AUTHOR]

An analysis is made of the sound generated by the impingement of a high-speed ventilating gas jet on the gas–water interface of a ventilated supercavity. A precise analytical problem is formulated and solved in which the supercavity is modelled by a spherical cavity of equal interior volume and the jet consists of a planar, radially symmetric flow from the centre of the sphere. The gas content of the sphere is assumed to be maintained at a constant mean level by steady exhaust into the water from the ‘rear end’ of the cavity. It is estimated that the damping of jet-induced oscillations by this outflow is negligible compared with conventional losses produced by acoustic radiation and by viscous and thermal dissipation. The sound radiated into the water is omnidirectional at low frequencies, but with increasing frequency it progressively exhibits the directional characteristics of an acoustic dipole with axis centred on the radial axis of the gas jet. [Copyright &y& Elsevier]

The paper presents a model for the squeezed film damping, the resistance of the holes, and the corresponding spring forces for a periodic perforated microstructure including the effects of compressibility, inertia, and rarefied gas. The viscous damping and spring forces are obtained by using the continuity equation. The analytical formula for the squeezed film damping is applied to analyze the response of an ultrasonic transducer. The inclusion of these effects in a model significantly improves the agreement with measured results. Finally, it is shown that the frequency dependence of the total damping and total spring force for a cell are very similar to those corresponding to a rectangular open microstructure without holes. A separate analysis reveals the importance of each particular correction. The most important is the compressibility correction; the inertia has to be considered only for determining the spring force and the damping force for sufficiently high frequencies. [ABSTRACT FROM AUTHOR]

Feedforward control is a popular strategy of active noise/vibration control. In well-damped noise/vibration systems, path transfer functions from actuators to sensors can be modeled by finite impulse response (FIR) filters with negligible errors. It is possible to implement noninvasive model independent feedforward control by a recently proposed method called orthogonal adaptation. In lightly damped noise/vibration systems, however, path transfer functions have infinite impulse responses (IIRs) that cause difficulties in design and implementation of broadband feedforward controllers. A major source of difficulties is model error if IIR path transfer functions are approximated by FIR filters. In general, active control performance deteriorates as model error increases. In this study, a new method is proposed to design and implement model independent feedforward controllers for broadband in lightly damped noise/vibration systems. It is shown analytically that the proposed method is able to drive the convergence of a noninvasive model independent feedforward controller to improve broadband control in lightly damped noise/vibration systems. The controller is optimized in the minimum H2 norm sense. Experiment results are presented to verify the analytical results. [ABSTRACT FROM AUTHOR]

In order to attenuate structural waves in beams, a damped mass–spring absorber system is considered that is attached continuously along the beam length. Compared with other measures, such as impedance changes or tuned neutralisers applied at a single point, it is effective for excitation at any location along the beam. Although it is a tuned system, it can also be designed to be effective over a broad frequency range by the use of a high damping loss factor and multiple tuning frequencies. It has the advantage over constrained layer damping treatments that it can be effective even when the structural wavelength is long. The parameters controlling its behaviour are investigated and simple formulae developed, allowing optimisation of its performance. The effective frequency bandwidth increases as the mass ratio of the absorber and the beam is increased and, for moderate-to-high damping, it also increases as the damping loss factor is increased. The maximum decay rate is independent of mass and damping for light damping, but for higher damping it reduces as loss factor increases and increases as the mass ratio increase. A particular application is the reduction of noise from a railway track, which requires the attenuation of structural waves along the rail to be increased over a frequency band of two or more octaves. [Copyright &y& Elsevier]