Numerical Acoustic Model Research Articles

Modelling Newtonian noise of vibroacoustic origin in the Virgo gravitational wave detector

With ~100 detections by the LIGO-Virgo-KAGRA network, gravitational astronomy has definitely begun. The Virgo detector is a modified Michelson interferometer with two arms of 3km each, made of optical resonator housing ~100 kW laser beams. It can measure a gravitational strain (ΔL/L) of ~10^(-21). The detector is susceptible to various sources of noise within specific frequency bands. Among these, the "Newtonian" or "gravity-gradient" noise (seismic and atmospheric/acoustic) could limit the low-frequency sensitivity (below a few tens of Hz) of LIGO and Virgo as they reach their full sensitivity, as well as that of next-generation detectors such as the European Einstein Telescope and the US Cosmic Explorer. This paper focuses on modeling Newtonian noise of acoustic origin, which refers to the small fluctuations in the gravity field resulting from the acoustic field present in the experimental halls. The fluctuating gravitational field directly causes random forces on sensitive optical elements, such as the interferometer test masses. The induced noise is quantified using a numerical acoustic model of the experimental room when it is excited by the air conditioning system.

A novel transcranial MR Guided focused ultrasound method based on the ultrashort echo time skull acoustic model and phase retrieval techniques

Transcranial ultrasound stimulation (TUS) has been clinically applied as a neuromodulation tool. Particularly, the phase array ultrasound can be applied in TUS to non-invasively focus on the cortex or deep brain. However, the vital phase distortion of the ultrasound induced by the skull limits its clinical application. In the current study, we aimed to develop a hybrid method that combines the ultrashort echo time (UTE) magnetic resonance imaging (MRI) sequences with the prDeep technique to achieve focusing ventral intermediate thalamic nucleus (VIM). The time-reversal (TR) approach of the UTE numerical acoustic model of the skull combined with the prDeep algorithm was used to reduce the number of iterations. The skull acoustic model simulation therapy process was establish to valid this method’s prediction and focus performance, and the classical TR method were considered as the gold standard (GS). Our approach could restore 75% of the GS intensity in 25 iteration steps, with a superior the noise immunity. Our findings demonstrate that the phase aberration caused by the skull can be estimated using phase retrieval techniques to achieve a fast and accurate transcranial focus. The method has excellent adaptability and anti-noise capacity for satisfying complex and changeable scenarios.

Three-dimensional acoustic propagation of noise from impact pile driving in a complex costal environment and its effects on large yellow croaker (Pseudosciaena crocea)

The effects of high-intensity impulsive noise generated by pile driving on fish are a major concern in environmental impact assessments. Numerical acoustic models are essential for predicting underwater-acoustic-related problems in complex coastal environments prior to offshore construction. However, underwater noise modeling for impact pile driving has often been performed using simplistic propagation models that are inadequate for three-dimensional (3D) environments. A 3D parabolic equation method (PE) was established in this study to better predict broadband transmission loss (TL) from impact pile driving in complex coastal environments and its influence on the large yellow croaker (Pseudosciaena crocea). The effects of 3D propagation were investigated using two realistic scenarios with different bathymetric complexities. The values and attenuation rate of the broadband TL for the steeply sloped bottom were significantly greater than those for the flat and weakly varying bottoms over 3 km. At a water depth of 5 m, a difference of approximately 10 dB was observed between the two TL scenarios at a distance of 4.5 to 5 km. The simulation results are in reasonable agreement with the field measurement data, with a difference of less than 3 dB. The zones of behavioral response and injury in the large yellow croaker were estimated using the For3D model. The results showed that the effects of the noise generated by the impact pile driving on the large yellow croaker were evident and three-dimensional. Therefore, 3D propagation effects should be considered when analyzing the influence of underwater noise on marine animals.

Churches Acoustics as Intangible Cultural Heritage: Experimental and Numerical Characterization of the Temple of San Biagio

ABSTRACT The acoustic properties of churches are, to date, as much a cultural asset as their architectural features. The study, understanding and conservation of acoustic phenomena that characterize liturgical spaces, to date, make use of new technologies and methodologies that facilitate their practice. The study presented here analyzes the acoustic phenomena that characterize the Temple of San Biagio (Montepulciano, Tuscany, Italy). It makes use of experimental acoustic surveying and the aid of the laser scanning surveying technique for the creation of the geometry, subsequently adopted for numerical acoustic modeling of the church in Odeon Acoustics software, used for the study of its acoustic characteristics. The selected methodology allowed us to delve into dynamics often encountered in acoustic simulations, such as the calibration of numerical models and the influence of the mesh number of the generated geometric models, and to understand the acoustic characteristics of the church.

Variation in vibro-acoustic noise due to the defects in an automotive drum brake

Drum brakes are significant contributors to noise and vibration in automobiles causing discomfort to the passengers. The vibration and hence the resulting noise increase due to various inherent defects in the drum brake, such as asymmetry. This work aims to quantify the variation in the vibro-acoustic noise due to several common defects in the drum brake using an integrated non-linear vibration analytical model and a numerical acoustic model. The sources of vibro-acoustic noise sources such as contact and reaction forces are predicted using a four-degree-of-freedom non-linear contact mechanics based analytical model. A finite element based acoustic model of the drum brake is utilized to predict the force to the sound pressure transfer function in the drum brake. Product of the transfer functions and the forces gives the corresponding sound pressure level from which the overall sound pressure levels are estimated. The variation in the overall sound pressure levels due to different drum brake defects is evaluated by introducing defects to the analytical model. The results show that the overall sound pressure level is a strong function of the defects. It is envisioned that the current work will help in the development of effective health monitoring systems.

Comparison of noise generated from simplex and duplex configurations of drum brake using non-linear vibro-acoustic models

The drum brakes used on the rear wheels of automobiles have various configurations. These contribute to the differences in kinematic (geometry) and dynamic (contact, friction) aspects, eventually leading to significantly different vibration and acoustic response. This work attempts to estimate the difference in the vibro-acoustic noise generated by the drum brake's simplex and duplex variants using a combination of non-linear analytical vibration models and a numerical acoustic model. Four degrees-of-freedom lumped parameter models developed for the simplex and the duplex configurations with conformal contact predict the contact and reaction forces during braking. These forces act as the sources for the finite element based acoustic models developed for the two configurations to obtain the sound pressure to force transfer functions. The sound pressure levels are estimated by the product of the predicted forces with the respective transfer functions in the frequency domain. The sound pressure levels of the simplex and duplex drum brakes are quantitatively compared under different braking conditions, and the results are presented. It is expected that this vibro-acoustic analysis will help in designing quieter drum brakes.

Investigating the stability of frequency-dependent locally reacting surface boundary conditions in numerical acoustic models.

Numerical acoustic modeling enables simulation of sound propagation through bounded space. Recent research directed to refining Finite Difference Time Domain solutions for acoustic prediction has focused on emulating sound wave-surface interaction. Locally reacting surface properties are a popular choice for deriving boundary conditions that incorporate surface absorption properties. However, implementation of these boundary conditions, using the methods described in prevalent literature, is demonstrated here as unstable for complex room geometries. This work presents a reformulated implementation of frequency-dependent locally reacting surface boundary conditions for Finite Difference Time Domain simulations that is empirically demonstrated to be robust against simulation instabilities.

Sound transmission modeling and numerical analysis for automotive seal considering non-uniform compression

Automotive metal door panels and nonmetallic seals have complicated nonlinear interactions in their narrow mating sections, leading to non-uniform compression and complicating the sound transmission mechanism. Therefore, a new sound transmission modeling methodology and numerical analysis is developed for a refined sealing system by considering the geometrical boundaries and the non-uniform compression load. Nonlinear analysis is performed to obtain the geometrical parameters of the deformed seal, which are later input to the subsequent numerical acoustic model, by varying the compression ratios at different door locations under quantified nonlinear metal–seal interaction boundary conditions. A numerical prediction model of the sound transmission loss is constructed considering the deformed seal geometry using a double-wall-panel sound transmission model. Finite-element analysis and an infinite-element method are combined. Sound transmission loss experiments are conducted by varying the compression ratios of the seal. Experimental results are in good agreement with the numerical analysis. Furthermore, the sound transmission loss of the incident sound source with respect to a wide range of frequencies is numerically predicted for different compression magnitudes and directions using the verified methodology. This shows that the presented model and numerical methodology is valuable for optimizing the sound transmission loss performance of automotive door seals.

Post-processing speech recordings during MRI

We discuss post-processing of speech samples that have been recorded simultaneously during Magnetic Resonance Imaging (MRI) of the upper airways. Speech recordings contain acoustic noise from the MRI scanner. The required noise reduction is based on adaptive comb filtering designed for accurate formant extraction. Two kinds of speech materials were used to validate the post-processing algorithm. The primary material consists of samples of prolonged vowel productions during MRI. The comparison data was obtained from the same test subject, and it was recorded in anechoic chamber in a similar configuration as used during the MRI. Spectral envelopes and vowel formants were computed from the post-processed speech and from the comparison data. Vowel samples (with a known formant structure) were artificially contaminated using MRI scanner noise to determine performance of the post-processing algorithm. Resonances computed from a numerical acoustic model and spectra measured from 3D printed vocal tract physical models were used as comparison data. The properties of the recording instrumentation or the post-processing algorithm do not explain the observed frequency dependent discrepancy between the vowel formant data from two kinds of experiments: recordings during MRI and comparison data. It is shown that the discrepancy is statistically significant, in particular, where it is largest at ca. 1 kHz and 2 kHz. Numerical and experimental evidence suggests that the surfaces of the MRI head coil change the acoustics of speech which results in “exterior formants” at these frequencies. The discrepancy is too large to be neglected if the recordings during MRI are to be used for parameter estimation or validation of a numerical speech model, based on the MR images. However, the role of test subject adaptation to noise and constrained space acoustics during an MRI examination cannot be ruled out.

Operational wind farm noise and shipping noise compared with estimated zones of audibility for four species of fish.

A comparison between different underwater sound sources such as ships and operational wind farms are not straightforward to perform due to their qualitative difference in signal properties. However, in order to study possible effects of noise on fish, this comparison has to be made, and possible cumulative effects investigated. This study shows that a wind farm located in a shallow area in the Baltic Sea will add significant noise levels to the region even though intense shipping activities occur. This is due to the fact that the wind farm produces a strong tonal component at 127 Hz, a frequency otherwise relatively unaffected by shipping noise. The results were obtained by developing a numerical acoustic model of the wind farm taking account of their integrated effect. The model was evaluated against measurements performed at several distances from the wind farm during various weather conditions. Additionally, zones of audibility for cod, herring, salmon, and European eel were estimated.

Numerical acoustic modeling code applied to sonar transducers and arrays: review and perspectives

In this paper a review based on several examples of Thales Underwater Systems (TUS) design and modeling of transducers will be presented: several examples like wide band free flooded ring flextensional and bender transducers, high frequency transducers with thermal analysis modeling included, will be discussed. An approach of the problem of the mutual impedance computation appearing in array modeling will be also presented. Tus used since several decades FEM ‐ BEM codes to design acoustic transducers and arrays. The perspectives in transducer and array modeling will be indicated like the possibility to take into account the non‐linearities in the material, the time dependent problem and the use of new kind of piezoelectric material will be also discussed. Specific aspect of single crystal transducers modeling will be presented. The increase of the computing power will also permit to take into account the complex problem of the interaction between transducers in an array (mutual impedances). We will conclude on complex ultra wide band antenna (based on strong transducers interactions) optimization and the associated modeling architecture issues.

MODE AND PE PREDICTIONS OF PROPAGATION IN RANGE-DEPENDENT ENVIRONMENTS: SWAM'99 WORKSHOP RESULTS

Three numerical acoustic models, a coupled normal-mode model (C-SNAP), an adiabatic normal-mode model (PROSIM), and a parabolic equation model (RAM), are applied to test cases defined for the SWAM'99 workshop. The test cases consist of three shallow water (flat bottom) scenarios with range-dependent sound-speed profiles imitating internal wave fields and a shelf-break case, with range-dependent sound-speed profiles and bathymetry. The bottom properties in all the cases are range-independent and modeled as a homogeneous fluid half-space. The results from the modeling are presented as transmission loss for selected acoustic frequencies and source-receiver geometries, and as received time series. The results are compared in order to evaluate the effect of applying different propagation models to the same range-dependent underwater environment. It should be emphasized that the propagation analysis is not an attempt to benchmark the selected propagation models, but to demonstrate the performance of practical, range-dependent models based on different approximations in particular underwater scenarios.

Mode and PE Predictions of Propagation in Range-Dependent Environments SWAM'99 Workshop Results

Three numerical acoustic models, a coupled normal-mode model (C-SNAP), an adiabatic normal-mode model (PROSIM), and a parabolic equation model (RAM), are applied to test cases defined for the SWAM'99 workshop. The test cases consist of three shallow water (flat bottom) scenarios with range-dependent sound-speed profiles imitating internal wave fields and a shelf-break case, with range-dependent sound-speed profiles and bathymetry. The bottom properties in all the cases are range-independent and modeled as a homogeneous fluid half-space. The results from the modeling are presented as transmission loss for selected acoustic frequencies and source-receiver geometries, and as received time series. The results are compared in order to evaluate the effect of applying different propagation models to the same range-dependent underwater environment. It should be emphasized that the propagation analysis is not an attempt to benchmark the selected propagation models, but to demonstrate the performance of practical, range-dependent models based on different approximations in particular underwater scenarios.

The use of acoustic streamlines and reciprocity methods in automotive design sensitivity studies

A wide variety of numerical acoustic modeling tools exist for forced response and eigenmode analysis of automobile enclosures. However, design tools based on these calculational procedures are not readily available. In this work, innovative analysis procedures have been developed to enable the designer to make intelligent design choices in geometry studies. Through the use of so-called acoustic streamline functions and reciprocity techniques, procedures have been developed which enable quick prediction of the effect of inserting barriers in an acoustic cavity and which areas of the boundary are most sensitive to external input. Numerical and experimental comparisons are given comparing acoustic eigenfrequencies, mode shapes and forced response spectra for a test cavity. Examples are also presented which demonstrate the new analysis techniques.

An investigation of the acoustic properties of vibrating finite cylinders

To aid in the preliminary design, or in the trouble-shooting of acoustically radiating cylindrical structures, there exist few analytical approximations for finite length cylinders, or exact solutions for infinite length cylinders. In this work a flexible acoustic radiator model is implemented that can encompass a wide range of finite cylinder geometries subject to various modes of vibration. The boundary element method is applied to an integral form of the Helmholtz equation. The efficiency and accuracy of the analysis is enhanced by employing a quadratic isoparameteric element discretization of the radiating surface. Velocity profile inputs to the acoustic model include profiles generated from both rigid body and flexural motion types. Results from all of the velocity profiles examined in this work indicate strong radiating abilities for frequencies of vibration where the acoustic wavelength is less than approximately one-sixth the cylinder radius. In the low-frequency region, the effectiveness of the radiator is found to be related to the complexity of the applied velocity profile. The trends observed in the present numerical solutions agree well with those of previous work. An experimental verification of the modelling procedure has been carried out. In accordance with the modal analysis testing technique, velocity profiles were experimentally determined and used as boundary conditions to the numerical acoustic model. Measurements of the actual far-field acoustic pressure compare well with the results predicted from the numerical modelling.

Environmental considerations applicable to numerical acoustic modeling studies across ocean fronts

A systematic approach towards an understanding of the basic acoustical effects of ocean fronts can be accomplished by the use of numerical acoustic models. A fundamental prerequisite for this approach is an understanding and precise definition of the ocean environment. Physical characteristics of ocean fronts that may be important to ocean acoustics are therefore discussed. Also, definitions, types, and the horizontal/vertical extent of various fronts are presented in the context of their possible acoustical impact. Special attention is devoted to the Labrador‐Gulf Stream and Sargasso Sea water mass provinces. [Work supported by CND/NORDA.]

Effect of ocean frontal extent on sound transmission

Oceanographic fronts associated with transitions between water masses such as the Labrador Shelf Water, the Gulf Stream, and the Sargasso Sea are experimentally not well defined, and their acoustical effects are not well understood. Numerical simulation of the acoustical effects employing simple environmental representations for such water masses and associated frontal regions may shed some light on the importance of frontal extent or frontal width. Sound transmission calculations employing a two‐dimensional parabolic equation (P.E.) approximation model have been made for two simple environmental representations of different tracks through the Labrador‐Gulf Stream‐Sargasso provinces (E. Hashimoto, Environmental Considerations Applicable to Numerical Acoustic Modeling Studies Across Ocean Fronts, this meeting). In particular, the acoustical significance of the fronts as a function of frontal width was investigated through numerical simulation. The results of this study along with the limitations imposed by the environmental representation and method of solution will be presented and discussed. [Work supported by CND/NORDA.]