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A qualitative analysis of the model of the impact support mechanism, assuming two models of impact forces and a non-linear characteristic of the air pressure force has been presented in this paper. The ranges of parameters in which the system operates regularly have been estimated. It has also been found that in the case of parameter values outside the designated ranges, the movement may be chaotic. During such movement, undesirable collisions of certain structure elements often occur, which may lead to the destruction of some elements of the system. [ABSTRACT FROM AUTHOR]

Summary: We investigate the behavior of different shape functions for the discretization of hyperbolic problems. In particular, we consider classical Lagrange polynomials and B‐splines. The studies focus on the performance of the these functions as a spatial discretization approach combined with an explicit time marching scheme. In this regard, a major concern is the maximum eigenvalue that imposes restrictions on the critical time step size and suitable lumping techniques that yield a diagonal mass matrix. The accuracy of the discretization methods is assessed in an asymptotic manner in terms of the convergence of eigenvalues and eigenvectors. Further, the global accuracy is investigated in terms of the full spectrum. The results show that B‐spline discretization with a consistent mass matrix are more accurate than those based on Lagrange shape functions, which holds true in the boundary‐fitted as well as in the immersed setting. On the other hand, Lagrange shape functions are more robust with respect to standard lumping techniques, which cannot be directly applied for B‐splines without loss of accuracy. In general, we observe that none of the standard lumping schemes yields optimal results for B‐splines, even in the boundary‐fitted setting. For the immersed setting, also Lagrange shape functions show a drop in accuracy which depends on the position of the boundary that cuts the element. Several remedies are considered in order to overcome these issues, including interpolatory B‐spline bases as well as eigenvalue stabilization methods. While accuracy and stability can be improved using these remedies, we conclude from our study that it is still an open question, how to design a discretization method that achieves large critical time step sizes in combination with a diagonal mass matrix and high accuracy in the immersed setting. We note that these considerations primarily relate to linear structural dynamics applications, such as for example, structural acoustics. In nonlinear problems, such as automotive crash dynamics, other considerations predominate. An example of a one‐dimensional elastic‐plastic bar impacting a rigid wall is illustrative. [ABSTRACT FROM AUTHOR]

We consider a coupled hybrid system whose main application is the problem of the active control of noise. The model describes the interaction of acoustic vibrations in the interior of a given two-dimensional cavity with the mechanical vibrations of two damped strings located in a part of the boundary of the cavity, in which suitable feedbacks are acting. Our main result is that the total energy associated to this model decays exponentially as time goes to infinity. [ABSTRACT FROM AUTHOR]

Tautosyllabic segment sequences exhibit greater gestural overlap than heterosyllabic ones. In Spanish, it is presumed that word-final consonants followed by a word-initial vowel undergo resyllabification, and generative phonology assumes that canonical CV.CV# and derived CV.C#V onsets are structurally identical. However, recent studies have not found evidence of this structural similarity in the acoustics. The current goal is to investigate anticipatory and carryover vowel nasalization patterns in tautosyllabic, heterosyllabic, and resyllabified segment sequences in Spanish. Nine native speakers of Peninsular Spanish participated in a read-aloud task. Nasal airflow data were extracted using pressure transducers connected to a vented mask. Each participant produced forty target tokens with CV.CV# (control), CVN# (tautosyllabic), CV.NV# (heterosyllabic), and CV.N#V (resyllabification) structures. Forty timepoints were obtained from each vowel to observe airflow dynamics, resulting in a total of 25,200 datapoints analyzed. Regarding anticipatory vowel nasalization, the CVN# sequence shows an earlier onset of nasalization, while CV.NV# and CV.N#V sequences illustrate parallel patterns among them. Carryover vowel nasalization exhibited greater nasal spreading than anticipatory nasalization, and vowels in CV.NV# and CV.N#V structures showed symmetrical nasalization patterns. These results imply that syllable structure affects nasal gestural overlap and that aerodynamic characteristics of vowels are unaffected across word boundaries. [ABSTRACT FROM AUTHOR]

This article is concerned with the long term behavior of solutions to a structural acoustics model consisting of a semilinear wave equation defined on a bounded domain Ω ⊂ R 3 which is coupled with a Berger plate equation acting on a flat portion of the boundary of Ω. The system is influenced by several competing forces, in particular a source term acting on the wave equation which is allowed to have a supercritical exponent. Our results build upon those obtained by Becklin and Rammaha [8]. With some restrictions on the parameters in the system and with careful analysis involving the Nehari manifold we obtain global existence of potential well solutions and establish either exponential or algebraic decay rates of energy, dependent upon the behavior of the damping terms. The main novelty in this work lies in our stabilization estimate, which notably does not generate lower-order terms. Consequently, the proof of the main result is shorter and more concise. [ABSTRACT FROM AUTHOR]

Curved structures are used in many engineering applications. Temperature affects the performance of structural vibration and acoustics and can damage the equipment when its effects are severe. A theoretical model of the sound transmission loss (STL) of a simply supported curved plate considering the effect of temperature was established. Moreover, a numerical solution was obtained using the modal superposition method. The finite element results were compared to validate the theoretical model. The effects of temperature and acoustic loading on the modal frequency and STL were considered, and the variation laws of the radius of curvature, opening angle, and loss factor on the STL were analyzed. The results showed that the modal frequency increased with decreasing temperature, the frequency ratio of the same-order modal frequency varied approximately linearly with temperature, and the trough of the STL shifted toward high frequencies. The pitch angle substantially influenced the STL, whereas the azimuth angle was negligible. A larger radius increased the effect of temperature. In addition, an increase in the opening angle formed an aggregation of STL at (1, 1)-order modal frequencies. The loss factor affects only the amplitude of the trough position of the STL. Therefore, the proposed theoretical model can aid in the vibroacoustic design of curved plates in a thermal environment. [ABSTRACT FROM AUTHOR]

This study is the first to investigate the effect of chaotic vibration on the sound absorption of a curved perforated panel. Previous studies on the effect of nonlinear vibration on the sound absorption of a panel absorber have focused on periodic responses only. In this study, a sound absorption formula was derived by considering the panel impedance and perforation impedance. The numerical integration method was adopted to generate various chaotic vibrational responses, which were used to compute the corresponding sound absorptions. Several interesting findings that have never been observed in any previous studies on acoustic absorption were derived. First, in the chaotic and highly nonlinear cases, as the excitation frequency increased, the corresponding response frequencies decreased. This was opposite to the typical trend in linear cases, in which higher excitation frequencies corresponded to higher response frequencies. Second, in chaotic cases, absorption mainly occurred due to panel vibration effects. This is also in stark contrast to the findings of studies on perforated vibrating panels, in which the absorption effect mainly originates from perforations. Additionally, the absorption bandwidths are much wider and can shift to higher frequencies; however, the peak absorption coefficients were approximately 20% lower than in the case of the perforation effect only. Third, in the quasi-chaotic case, the absorption curve in the case of the perforation effect plus the vibration effect was between the absorption curves of the perforation effect only and the perforation effect plus the vibration effect. [ABSTRACT FROM AUTHOR]

The auxiliary superfield approach is proposed as a method to obtain statistical predictions of the acoustic response of complex elastic structures. The potential advantage of the method is the full retention of interference and resonance effects associated with the degrees of freedom being averaged over. It is not known whether this approach leads to tractable problems for structural acoustics systems, however. We have applied the method to the idealized case of an infinite, thin plate with attached oscillators to obtain the mean Green's function. The oscillators are assumed to have an uncorrelated, Gaussian distributed mass and stiffness distribution representing a simple form of complex internal structure. Using the auxiliary superfield approach, the mean Green's functions are expressed exactly as a functional integral. For relatively small disorder, the integral may be estimated by a saddle point approximation which leads to coupled integral equations for effective mass and stiffness matrices that can be solved numerically for a given spatial distribution of the disorder. With the solutions for these matrices, one obtains a self-consistently determined, generalized fuzzy structure model. We give analytical solutions for the simple case of a uniform spatial distribution. The results are promising for the application of the method to more challenging geometries. [ABSTRACT FROM AUTHOR]

We consider stability in an inverse problem of determining the material coefficient matrix for a coupled system that describes acoustic interactions, by the Riemannian geometrical approach. The stability is proved by the Carleman estimates and observability inequalities. [ABSTRACT FROM AUTHOR]

A city park is a place where, in an urbanized world, a person can experience nature. A park is the green lung of the city. The numerous trees and shrubs in parks improve the air condition, especially in densely populated agglomerations. It is a meeting place and allows you to spend time actively. The park allows recreation and relaxation for city residents. City parks are desirable, especially in city centres, densely populated and built-up places. Designing parks should meet people's needs. It is extremely important to properly select space elements that will positively affect the comfort of use. Apart from the obvious issue of taking care of the park's aesthetics, its flora and appropriate equipment, an important role is played by an appropriate acoustic climate. Hence, when designing open spaces such as city parks, the cooperation of specialists in many fields is important: landscape architects, town planners, people dealing with nature protection, artists, and finally, acousticians. This allows you to create a space that will meet the needs and expectations of residents. The paper shows the possibility of taking steps to correct the existing sound environment in selected places in the city park. [ABSTRACT FROM AUTHOR]

A numerical coupling approach is proposed to fast predict the acoustic radiation from a vibrating large-complicated underwater structure. In this study, the physical mechanism of sound radiation from underwater large target is used for the first time to improve the efficiency and keep the accuracy of the numerical algorithm. Although the traditional coupled finite element method/boundary element method (FEM-BEM) is accurate, it contains a large number of boundary elements and thus requires a long computation time for large-complicated structures. The research on the physical mechanism of structural acoustics shows that when BEM is applied on the near-field artificial boundary at a proper distance away from the wet structural surface, large-size boundary elements are acceptable and the number of boundary elements and computation time are remarkably reduced. Thus, the fluid outside the structure is divided into the interior domain and the exterior domain by the artificial boundary. Then, the numerical method is realized by coupling structural finite element modelling with interior fluid finite element modelling and with exterior fluid boundary element modelling. Compared with the theoretical value, the experimental value and the results of the traditional FEM-BEM, the correctness of the proposed algorithm and its advantage of computational efficiency are verified. The computation time of the proposed method is over 99% shorter than that of FEM-BEM in the calculation example of a large-complicated structure. The proposed method can be further applied to multidomain acoustic and multibody acoustic calculations. [ABSTRACT FROM AUTHOR]

A generalized modal radiation impulse response approach based on in vacuo eigenfunction expansions was recently developed to evaluate the space-time surface velocity vector field, instantaneous power, and energy transfer into a fluid resulting from the space-time force distribution of fluid loaded shell and panel structures. The impact excitation of a fluid loaded spherical shell is addressed in this paper to illustrate the generalized modal approach for an analytically tractable problem. In vacuo eigenfunctions of spherical shells are presented and a modal based pressure impulse response approach is developed to evaluate the associated transient pressure field. Coupled shell and acoustic field equations for the modal velocities in the time and frequency domains are developed to evaluate the modal velocities via the use of modal radiation impulse responses and impedances. The numerical results are presented to illustrate the characteristics of modal pressure impulse responses and modal radiation impulse responses, which couple the modal velocities, as well as the modal coupling effects of the fluid on the modal velocities, the energy transfer into a fluid, and the far field pressures for the breathing mode, rigid body mode, and higher order shell modes. [ABSTRACT FROM AUTHOR]

We present the detailed study of the spin kinetics of the nitrogen (N) donor electrons in 6H SiC wafers grown by the Lely method and by the sublimation "sandwich method" (SSM) with a donor concentration of about 1017cm-3 at T=10-40K. The donor electrons of the N donors substituting quasi-cubic "k1" and "k2" sites (Nk1,k2) in both types of the samples revealed the similar temperature dependence of the spin-lattice relaxation rate (T1-1), which was described by the direct one-phonon and two-phonon processes induced by the acoustic phonons proportional to T and to T9, respectively. The character of the temperature dependence of the T1 -1 for the donor electrons of N substituting hexagonal ("h") site (Nh) in both types of 6H SiC samples indicates that the donor electrons relax through the fast-relaxing centers by means of the cross-relaxation process. The observed enhancement of the phase memory relaxation rate (Tm -1) with the temperature increase for the Nh donors in both types of the samples, as well as for the Nk1,k2 donors in Lely grown 6H SiC, was explained by the growth of the free electron concentration with the temperature increase and their exchange scattering at the N donor centers. The observed significant shortening of the phase memory relaxation time Tm for the Nk1,k2 donors in the SSM grown sample with the temperature lowering is caused by hopping motion of the electrons between the occupied and unoccupied states of the N donors at Nh and Nk1,k2 sites. The impact of the N donor pairs, triads, distant donor pairs formed in n-type 6H SiC wafers on the spin relaxation times was discussed. [ABSTRACT FROM AUTHOR]

Summary: This article is devoted to the linear dynamics of liquid‐structure interactions for an elastic structure filled with compressible liquid (acoustic liquid), with sloshing and with capillarity effects on the free surface in presence of a gravity field. The objective is to detail the formulation and to quantify the role played by the elasticity in the neighborhood of the triple contact line between the free surface of the compressible liquid and the elastic structure in presence of sloshing and capillarity effects. Most of the works consider that the structure is totally not deformable (rigid tank). Nevertheless, for taking into account the elasticity of the tank, some works have introduced an approximation, which consists in considering a locally undeformable structure in the neighborhood of the triple contact line. The theory presented requires the use of quadratic finite elements for discretizing a new introduced boundary condition. An application has specifically been constructed and presented for quantifying the role played by the elasticity of the structure in the neighborhood of the triple contact line. [ABSTRACT FROM AUTHOR]

Summary: We present an efficient adjoint‐based framework for computing sensitivities of quantities of interest with respect to material parameters for coupled fluid‐structural acoustic systems with explicit interface coupling. The fluid is modeled using the Helmholtz equation and the structure is modeled using the Navier‐Cauchy equations. Sensitivities are used to drive a gradient based optimization algorithm to solve important problems in structural acoustics, viz noise minimization and vibration isolation. For each problem, we consider two different priors: one where the optimal solution has a smooth variation and another with a bimaterial distribution. These priors are imposed with the help of suitable regularization terms. The effectiveness of this approach is demonstrated on both interior and exterior structural acoustic problems. [ABSTRACT FROM AUTHOR]

Structural finite element coupled with the conjugated infinite element method is an efficient numerical technique for solving the acoustic radiation problem due to the vibration of underwater objects. However, for large complex structures, the total acoustic mesh would become very large if the artificial boundary is too far away from the structural wetted surface. Thus, the calculation time can become too long to confine the application of the conjugated infinite element method. On the other hand, if the artificial boundary is close to the structural wetted surface, it will lead to computation accuracy losing due to the near-field effects. Consequently, it is essential to present some guidelines based on the physical mechanism of structural acoustics to choose a suitable artificial boundary that optimizes calculation accuracy and efficiency. In present work, the evanescent wave theory of an infinite length cylindrical shell is adopted to theoretically analyze the decay characteristic of evanescent waves in near field. Then, the effect of the position of artificial boundary on computation accuracy of conjugated infinite element for a finite length ring-stiffened cylindrical shell is numerically investigated. Results suggested that for the cylindrical shell mentioned in this study, the artificial boundary can be placed at least 0.4 times the acoustic wavelength away from the structural wetted surface. What's more, for high frequencies or large-scale structures, the required non-dimensional distance between the artificial boundary and the structural wetted surface increases. [ABSTRACT FROM AUTHOR]

Spectral methods have previously been applied to analyze a multitude of vibration and acoustic problems due to their high computational efficiency. However, their application to interior structural acoustics systems has been limited to the analysis of a single plate coupled to a fluid-filled cavity. In this work, a general multidomain spectral approach is proposed for the eigenvalue and steady-state vibroacoustic analyses of interior structural-acoustic problems with discontinuous boundaries. The unified formulation is derived by means of a generalized variational principle in conjunction with the spectral discretization procedure. The established framework enables one to easily accommodate complex systems consisting of both a structure assembly and a built-up cavity with moderate geometric complexities and to effectively analyze vibroacoustic behaviors with sufficient accuracy at relatively high frequencies. Two practical examples are chosen to demonstrate the flexibility and efficiency of the proposed formulation: a built-up cavity backed by an assembly of multiple connected plates with arbitrary orientations and a thick irregular elastic solid coupled with a heavy acoustic medium. Comparison to finite element simulations and convergence studies for these two examples illustrate the considerable computational advantage of the method as compared to finite element procedures. [ABSTRACT FROM AUTHOR]

This paper presents an approach to noise, vibration and harshness (NVH) analysis suitable for electro-mechanical rotating systems, whereby both the electrical and mechanical sources of excitation are included and the response of the system is calculated. Focus is placed on modelling methods for the stator structure. The stator is considered to be a transversely isotropic structure and the effect that material properties can have on dynamic response is presented for a stator, both in isolation and in the full drivetrain model. NVH predictions are shown for a full drivetrain model of a prototype EV city car and compared to test data, demonstrating good correlation between test results and simulation with the described method.

Structural-acoustic optimization procedures can be used to find the optimal design for reduced noise or vibration in many real-world scenarios. However, the time required to compute the structural-acoustic quantity of interest often limits the size of the model. Additionally, structural-acoustic optimization using state-of-the-art evolutionary algorithms may require tens of thousands of system solutions, which add to the limitations for large full-scale systems. To reduce the time required for each function evaluation, parallel processing techniques are used to solve the system in a highly scalable fashion. The approach reduces the analysis time by solving the system using a frequency-domain formulation and distributing solution frequencies amongst processors to solve in parallel. To demonstrate, the sound radiated from a curved panel under the influence of a turbulent boundary layer is minimized in the presence of added point masses, which are varied during the optimization procedure. The total mass is also minimized and the Pareto front relating the trade-off between added mass and reduced noise is determined. Solver scaling information is provided that demonstrates the utility of the parallel processing approach. [ABSTRACT FROM AUTHOR]

The article discusses the Acoustics Week that was held from October 9–11, 2019 at the Sutton Place Hotel in Edmonton, Alberta. Topics discussed include perceptual and physiological Responses to Room Acoustics and Noise; documenting the phonetic structures of Canada's Indigenous languages; views of Hildegard Westerkamp on soundscape; and building and spaces of acoustic interest.

In this paper sound radiation of simply supported rectangular plate has been reported. The novelty in this research paper is a new method is prescribed for sound radiation calculation. The phenomenon of uncoupled structural acoustics have been followed such that structure is the critical part in structural vibration using modal analysis and harmonic response calculation for frequency range of interest 0 to 200 Hz, but in harmonic acoustic analysis the structure does not takes part in physics point of view but is used for only for transferring the normal velocity from wetted surface of the structure to the interface acoustic medium i.e. air. Sound Radiation parameters like Sound Pressure Level, Sound Power Level and Sound Radiation efficiency has been reported. Upon comparing the results with that from I. Zaman's literature, it is found that the results are quite varying due to the fact the speed of sound in air as taken in literature is unjustified. So true simulation using correct data has been carried out in this paper and sound radiation results has been reported for frequency range of interest 0 to 200 Hz. It is found that the maximum sound pressure level is 72 dB and maximum sound power level is 78 dB which is suitable for noiseless environment. [ABSTRACT FROM AUTHOR]

This paper presents an approach to noise, vibration and harshness (NVH) analysis suitable for electro-mechanical rotating systems, whereby both the electrical and mechanical sources of excitation are included and the response of the system is calculated. Focus is placed on modelling methods for the stator structure. The stator is considered to be a transversely isotropic structure and the effect that material properties can have on dynamic response is presented for a stator, both in isolation and in the full drivetrain model. NVH predictions are shown for a full drivetrain model of a prototype EV city car and compared to test data, demonstrating good correlation between test results and simulation with the described method. [ABSTRACT FROM AUTHOR]

For vibro-acoustic applications, a turbulent wall pressure (TWP) fluctuations model was derived. The model is based on the resolution of Poisson's equation. The pressure is characterized in time and space through its spectrum in the frequency wave-number domain. The developed model follows trends commonly observed using Corcos model in a large frequency range but also shows new behaviors for low and high frequencies. The radiated noise due to TWP fluctuations is then computed in accordance with the form of the TWP spectrum. A specific computational methodology is proposed to perform the calculation without introducing limiting hypothesis on the radiated impedance. [ABSTRACT FROM AUTHOR]

In this study we consider a coupled system of partial differential equations (PDE's) which describes a certain structural acoustics interaction. One component of this PDE system is a wave equation, which serves to model the interior acoustic wave medium within a given three dimensional chamber Ω. This acoustic wave equation is coupled on a boundary interface Γ0 to a two dimensional system of thermoelasticity: this thermoelastic PDE is composed in part of a structural beam or plate equation, which governs the vibrations of flexible wall portion Γ0 of the chamber Ω. Moreover, this elastic dynamics is coupled to a heat equation which also evolves on Γ0, and which imparts a thermal damping onto the entire structural acoustic system. As we said, the interaction between the wave and thermoelastic PDE components takes place on the boundary interface Γ0, and involves coupling boundary terms which are above the level of finite energy. We analyze the stability properties of this coupled structural acoustics PDE model, in the absence of any additive feedback dissipation on the hard walls Γ1 of the boundary ∂Ω=Γ0∪Γ1. Under a certain geometric assumption on Γ1, an assumption which has appeared in the literature in connection with structural acoustic flow, and which allows for the invocation of a recently derived microlocal boundary trace estimate, we show that classical solutions of this thermally damped structural acoustics PDE decay uniformly to zero, with a rational rate of decay. [ABSTRACT FROM AUTHOR]

This article provides a contribution to the macrostructural study of Educational Inequality. It is based here, the empirical existence of a "differentiated rationality" between the Basic Cycle and the Oriented Cycle of the middle school both in its national and Buenos Aires jurisdiction, for the period 2001/2015. This differentiated behavior is evident from the analysis of indicators of enrollment and internal efficiency from continuous statistics of the national and provincial ministries, and the national population censuses of 2001 and 2010. This finding is interpreted from the critical theoretical-methodological contributions of the Sociology of Education. In this case, from the "structural - genetic" perspective (Bourdieu and Wacquant, 2005). From it, the historical-structural behavior of the middle school in the "meta-field" of the State is interpreted. It also incorporates the category of "hegemony" (Gramsci, 1967), thus complicating the study of the educational system - power relationship. [ABSTRACT FROM AUTHOR]

Highlights • Cross-frequency couplings produced by nonlinear acoustic oscillators were studied. • Causal, epiphenomenal and spurious cross-frequency couplings were identified. • Non spurious cross-frequency couplings are possible in non-sinusoidal dynamics. • Acoustic estimation of bubbles' radial position and spatial stability was performed. • Manipulation of harmonics of the acoustic field was implemented in real time. Abstract In this work, the analysis of cross-frequency couplings (CFC) is introduced in the context of nonlinear acoustics related to the dynamics of bubble(s)-resonator systems. The results obtained from experiments specifically designed to untangle the causal connection between the CFC patterns observed at the signal level and the underlying physical processes, are discussed. It was found that "causal" amplitude-to-amplitude (AAC) and amplitude-to-phase (APC) couplings emerge in the system dynamics as a consequence of the bubble(s)-resonator mechanistic interaction in the oscillatory steady-state. In these CFC patterns, the amplitude of the fundamental frequency component ( f 0 ) effectively modulates the amplitude and relative phase of the harmonic components ( Nf 0 ). Moreover, these AAC and APC couplings give rise to "epiphenomenal" phase-to-amplitude (PAC) and phase-to-phase (PPC) couplings, in which the link between modulating and modulated parameters represents a correlation rather than a causal connection. It is shown that these CFC patterns can be exploited to determine the presence, spatial stability and radial position of nonlinear oscillating bubble(s) trapped within the acoustic chamber. Potential applications of the proposed techniques are also discussed. Substantial evidence is presented showing that CFC patterns emerging from quasi-periodic non-sinusoidal waveforms are informative on the interaction between underlying oscillators. [ABSTRACT FROM AUTHOR]

Brick masonry is not only a question of building physics, building construction and durability, i.e. sustainability, but has much to do with aesthetics and making sense, which may have been forgotten in modern architecture with its absolute lack of décor. Masonry as an art form has been scarce since the era of brick expressionism. Recently, there have been some exceptions – and thoroughly welcome. The "Fjordenhus" in Vejle, Denmark, is an astonishing example. [ABSTRACT FROM AUTHOR]

For the response analysis of periodical composite structural–acoustic systems with multi-scale uncertain-but-bounded parameters, a bounded hybrid uncertain model is introduced, in which the interval variables and the bounded random variables exist simultaneously. In the periodical composite structural–acoustic system, the equivalent macro constitutive matrix and average mass density of the microstructure are calculated through the homogenization method. On the basis of the conventional first-order Taylor series expansion, a homogenization-based hybrid stochastic interval perturbation method (HHSIPM) is developed for the prediction of periodical composite structural–acoustic systems with multi-scale bounded hybrid uncertain parameters. By incorporating the Gegenbauer polynomial approximation theory into the homogenization-based finite element method, a homogenization-based Gegenbauer polynomial expansion method (HGPEM) is also proposed to calculate the bounds of expectation and variance of the sound pressure response. Numerical examples of a hexahedral box and an automobile passenger compartment are given to investigate the effectiveness of the HHSIPM and HGPEM for the prediction of periodical composite structural–acoustic systems with multi-scale bounded hybrid uncertain parameters. [ABSTRACT FROM AUTHOR]

Structural intensity on plates or shells can provide insights on how the vibrational energy is transmitted throughout a sample. Its assessment via experimental deflections are widely documented in the case of plates, which just requires the computation of spatial derivatives of out-of-plane displacements or velocities and a knowledge of the sample's material properties. However, if the structural intensity is to be assessed on arbitrary shells, a more elaborate data processing is required. The in-plane displacements become relevant terms and the spatial derivatives along a predefined local coordinate system need to be computed. Here, a method from which experimental data is interpolated on a finite element mesh is proposed. First, the global displacements and shape of a sample's outer-surface are measured. These data are then projected on a quadratic mesh, where the Kirchhoff plate theory is invoked for the individual elements. The data differentiation is computed via quadratic shape functions, from which the strains and structural intensity are estimated. Through the obtained vibrational energy results on the basis of measured displacement and shape data and by validating the method via a numerical simulation, the proposed work has shown to be a reliable tool to assess energy transmission on irregular shells. [ABSTRACT FROM AUTHOR]

Abstract This paper is focused on the development a new metric that can provide information on similarity between a frequency response function (FRF) from a finite element (FE) model and from an experiment to determine a target level of FE model accuracy in a deterministic sense. Typically, this metric could be used in setting a target level of model updating of an FE model that predicts structural-acoustic responses in high modal density mid-frequency regimes. The FRF similarity metric (FRFSM) is based on the likelihood between two FRFs with an assumed normal distribution of structural-acoustic responses. A normalization process over the frequency range of concern provides a metric value between 0 and 1. A numerical model that consists of two substructures and joint bushings objectively examined the characteristics of the proposed FRFSM with known parameter errors. The numerical study showed that the proposed FRFSM well represented the overall difference between two FRFs over the whole frequency band. Next, subjective evaluations that consist of evaluating the similarity for two pairs of FRFs by an expert group within an automotive company were conducted to assess the performance of the proposed metric. Subjective evaluations were conducted for various FRF sets in automotive noise and vibration responses. After compensating the subjective test results in calculating the correlation with the proposed metric, the performance of the metric was investigated. Additionally, the capability of the proposed metric when it represents the amount of updating in the frequency domain was illustrated by comparing the degree of correlation with the subjective evaluations. Comparisons with the results of the subjective evaluations showed that the FRFSM well represented the experts' knowledge on the similarity of two FRFs, both in an absolute sense and in relative accuracies of the updated FE models. Graphical abstract Image 1 Highlights • A new similarity metric for two FRFs on a normalized scale [0, 1] was proposed. • FRFSM well represented the difference of FRFs over the whole frequency band. • FRFSM showed excellent correlation with that of expert evaluations. • FRFSM is appropriate in the model validation of large and complex FE models. [ABSTRACT FROM AUTHOR]

In the framework of the present project within the DFG priority program 1897 "Calm, Smooth and Smart," dissipation of kinetic energy of vibrating structures into the acoustic far field is studied. It can be understood as radiation damping and is particularly relevant for weakly damped lightweight structures, music instruments and underwater applications. In this paper, the coupled equations of time‐harmonic elastodynamics and acoustics are addressed respectively by means of finite and boundary element methods and solved monolithically. The loss factor, which quantifies the extent of radiation damping, is determined subsequent to a harmonic analysis by relating radiated sound power to structure‐inherent power. First steps towards more efficient numerical formulations, which enable the consideration of radiation damping in structural simulations, are outlined. They comprise forming the Schur complement and a polynomial approximation of the resulting acoustic impedance matrices. [ABSTRACT FROM AUTHOR]

Interior noise in vibro-acoustic cavities may be generated due to acoustic and structural disturbances. Earlier studies have shown that for global control, the maximum reduction in acoustic potential energy can be realised by using an optimum combination of acoustic and structural actuators. However, it is observed that this reduction in interior noise may also be accompanied with an increase in kinetic energy of the cavity structure. This paper presents the development of a feedforward technique for active noise control in vibro-acoustic cavities ensuring that the noise reduction does not lead to an increase in kinetic energy. The problem is formulated as a constrained minimisation problem to minimise the acoustic potential energy subject to a constraint that the kinetic energy does not increase. Through a numerical study, it is shown that the optimum solution of the above problem indeed is favourable in terms of reduction in acoustic potential energy in the cavity and kinetic energy of the structure. The paper further proposes a method for solution of this constrained minimisation problem using a penalty function method and solution of sequential unconstrained problems. The proposed method is validated through a numerical study on a car-like cavity for single- and multi-tonal noise. [ABSTRACT FROM AUTHOR]

Highlights • A measurement campaign on flanking transmission on CLT junctions is presented. • There is a strong dependence of the K ij of the connection system. • The use of resilient interlayers is effective starting from 400 Hz. • The formulae of ISO 12354 do not match with experimental data at low frequencies. • The damping of CLT is discussed in relation to the classification of the junctions. Abstract The acoustic modelling of timber constructions is a major concern since wood construction technology has started to tackle multi-storey buildings. The recent update of the EN ISO 12354:2017 package of standards introduced indications relative to lightweight timber structures and a distinction between CLT and frame buildings that is related to the different characterisation of flanking transmissions. Within this framework, this work presents the results of a measurement campaign conducted on CLT junctions to study the influence of the connection on the vibration reduction indices. The investigation regards the influence of the kind and number of connectors, the hierarchy of the transmission paths and the use of the resilient interlayers. The experimental data show that the transmission of vibrations between CLT panels is strongly related to the metallic connectors that characterise the junction. The analysis on the damping of CLT panels suggests that the reverberation time does not strictly depend on the adjacent elements; a comparison between the loss factor normalised data and the geometry normalised data is finally proposed. [ABSTRACT FROM AUTHOR]

At low frequencies the assessment of the sound reduction index of building elements in the laboratory according to the standard ISO 10140-2:2010 is burdened by a large variation in the measurement results. This is due to the fact that at low frequencies the acoustic field is not sufficiently diffuse. This paper discusses a measurement procedure in which a diffuse field is created in the source room by means of an array of loudspeakers positioned closely to the building insulation element under test. This procedure exploits the acoustic near field of the loudspeaker array. The problems related to the breakdown of the diffuse field assumption of the receiving room are eliminated by measuring the structural response of the building insulation element under test by means of laser Doppler vibrometry and the application of the Rayleigh integral to compute the radiated sound power. The sound reduction index is determined from the ratio of the incident sound power, created by the loudspeaker array, and the radiated sound power. The measurement approach is validated by means of a measurement of the sound reduction index of a single layer glazing. Comparisons are made with an analytical model and with a standardized ISO 10140-2:2010 measurement. Although the method offers clear, strong points in terms of removing room acoustic effects from the measurements in the lower frequency range, a point of concern is the measurement effort. [ABSTRACT FROM AUTHOR]

A numerical parametric analysis of a vibro-acoustic coupling method that considered the influence of vibro-acoustic coupling was carried out to investigate the casing vibrations and feathers of vibrational noise induced by unsteady flow of the centrifugal fan at the best-efficiency point (BEP). There are three important aspects of this method. First, an unsteady flow-field with a whole impeller-volute configuration was solved based on three-dimensional incompressible Navier-Stokes equations and a standard k - ε turbulence mode to obtain the source of the vibro-acoustics. Second, a one-way-flow structural acoustic coupling method was implemented to study the volute vibrations and behaviors of vibrational noise by adoption. The generation mechanism of vibrational noise of the volute casing was revealed. Third, the parametric analysis method was used to explore the parametric relationship between the panel thicknesses (such as front-panel thickness [FT], side-panel thickness [ST], and back-panel thickness [BT]) and the outlet acoustical power of the volute casing surface. The parametric analysis provides a reasonable range of values of three panel thicknesses that result in minimal vibrational sound radiation. [ABSTRACT FROM AUTHOR]

The panel acoustic contribution analysis is used to determine the contribution of vibrating panels to the noise level inside closed spaces like a car cabin. The use of numerical techniques makes it possible to rate the panels according to their contributions accounting for the interaction between the structural vibrations and the acoustic pressure at a listening point. We consider the application of the finite and boundary element methods and the numerical Green’s function approaches to the problem and discuss the pros and cons regarding their use. The results show that the numerical Green’s function approach coupled to structure can be effectively used for the panel contribution analysis in situations with multiple panels and few listening points. [ABSTRACT FROM AUTHOR]