Prediction Of Sound Pressure Level Research Articles

Steady state acoustic radiosity for the prediction of sound pressure levels in enclosures with diffuse surfaces

This paper presents a derivation for and shows practical application of the steady-state diffuse acoustic radiosity method to the prediction of steady state sound levels in rooms. The paper begins with a brief review of the general radiosity literature and a more thorough review of the radiosity method in acoustics and proceeds to derive the general steady state acoustic rendering integral equation applicable to radiative energy exchange enclosures with arbitrary surface reflection properties. The rendering equation is simplified assuming diffuse reflections and the enclosure surface is discretized to convert the integral equations into summations. A closed form matrix solution to the discrete equations and another matrix equation for computing mean square pressure at multiple locations from multiple sources are presented. The computer code used for further analysis is verified by comparison to a closed form solution for a special case. Convergence of the discretized solution is investigated and the method is shown to converge linearly as the patch size decreases. A practical implementation of the method for predicting of sound levels in a classroom is shown. Predictions using radiosity are compared with simple diffuse field theory and measurements of an actual room. The radiosity method is shown to match diffuse ray tracing to within a fraction of a dB and predictions with a discretization with patches as large as 2 m are shown to be within a fraction of a dB of the asymptotic values

Uncertainty analysis in acoustical modeling of room

For a long time there is a need in industry of acoustical modeling of rooms. It is necessary for new production room design, machine exchange, renovation or enlargement of production rooms, change in a production profile or acoustical room adaptation for acoustical work conditions improvement. In such cases modeling quality is essential and thanks to uncertainty analysis it is possible to quantitatively estimate the effect that input parameters value variation has on model behavior. The article presents general rules for sound pressure level prediction uncertainty calculation in a room. By partial uncertainty calculation analysis of input parameters influence on uncertainty prediction an effort was taken to find parameters with biggest influence on the prediction process. As an example an industrial production room is presented which was modeled to predict noise level on a work stands after it was expanded.

Simulation of Supersonic Jet Noise with Nonlinear CFD and Kirchhoff Surface Integral

An acoustic prediction capability for supersonic axisymmetric jets was developed on the basis of the OVERFLOW Navier-Stokes CFD (Computational Fluid Dynamics) code. Reynolds-averaged turbulent stresses in the flow field are modeled with the aid of Spalart-Allmaras one-equation turbulence model. Appropriate acoustic and outflow boundary conditions were implemented to compute time-dependent acoustic pressure in the nonlinear source-field. Based on the specification of acoustic pressure, its temporal and normal derivatives on the Kirchhoff surface, the near-field and the far-field sound pressure levels are computed via Kirchhoff surface integral, with the Kirchhoff surface chosen to enclose the nonlinear sound source region described by the CFD code. The method is validated by a comparison of the predictions of sound pressure levels with the available data for axisymmetric turbulent supersonic perfectly expanded jets.

Characterization of uncertainty in outdoor sound propagation predictions

Predictive skill for outdoor sound propagation is assessed using high-resolution atmospheric fields from large-eddy simulations (LES). Propagation calculations through the full LES fields are compared to calculations through subsets of the LES fields that have been processed in typical ways, such as mean vertical profiles and instantaneous vertical profiles synchronized to the sound propagation. It is found that mean sound pressure levels can be predicted with low errors from the mean profiles, except in refractive shadow regions. Prediction of sound pressure levels for short-duration events is much less accurate, with errors of 8 -10 dB for near-ground propagation being typical.

Influence of short-term variations of meteorological parameters on sound propagation outdoors

Predicting long-range sound propagation over a nonurban site with complex propagation media requires the knowledge of micrometeorological fields in the lower part of the atmospheric boundary layer. In the framework of road traffic noise characterization there is a need for reliable sound pressure level predictions for specific propagation conditions that must be representative of time and space (small scale and site effects) characteristics of the acoustic situation. Outdoor measurements involving roughly 100 meteorological and acoustic sensors have been carried out during 3 months in 2005 in the southwest of France. This large database enables us to study the variability of meteorological parameters (wind speed, temperature, etc.) on different time scales. Scaling parameters in the atmospheric surface layer (such as the friction velocity and the Monin-Obukhov length) are estimated every 15 min, which allows looking at relatively short-term variations. Some longer-term effects, from days to months, are studied too. These include occurrences of meteorological configurations and variation of ground parameters. The effect of meteorological variability on sound propagation is studied using parabolic equation simulations. Comparisons between numerical predictions and experimental data will be discussed.

Application of acoustic radiosity methods to noise propagation within buildings

The prediction of sound pressure levels in rooms from transmitted sound is a difficult problem. The sound energy in the source room incident on the common wall must be accurately predicted. In the receiving room, the propagation of sound from the planar wall source must also be accurately predicted. The radiosity method naturally computes the spatial distribution of sound energy incident on a wall and also naturally predicts the propagation of sound from a planar area source. In this paper, the application of the radiosity method to sound transmission problems is introduced and explained.

On using large-eddy simulation for the prediction of noise from cold and heated turbulent jets

The results of a series of large-eddy simulations of heated and unheated jets using approximately 106 grid points are presented. The computations were performed on jets at operating conditions originally investigated by Tanna in the late 1970s [H. K. Tanna, “An experimental study of jet noise Part I: Turbulent mixing noise,” J. Sound Vib., 50, 405 (1977)]. Three acoustic Mach numbers are investigated (Uj∕a∞=0.5, 0.9, and 1.5) at cold (constant stagnation temperature) and heated conditions (Tj∕T∞=1.8, 2.7, and 2.3, respectively). The jets’ initial annular shear layers are thick relative to experimental jets and are quasi-laminar with superimposed disturbances from linear instability theory. It is observed that qualitative changes in the jets’ mean- and turbulent field structure with Uj and Tj are consistent with previous experimental data. However, the jets exhibit a faster centerline mean velocity decay rate relative to the existing data, with a corresponding 3–4 % over-prediction of the peak root-mean-square level. The acoustic pressure fluctuations in the far field are analyzed in detail. The accuracy of the overall sound pressure level predictions is found to be a strong function of the jet Mach number, with the lowest speed jets being the least accurate. At all conditions the peak acoustic frequency occurs at approximately St=fDj∕Uj=0.25. The limited resolution of the computations is shown to impact the radiated sound by yielding effectively low-pass filtered versions of the experimental spectra, with a maximum frequency of St≈1.2.

원심압축기의 공력소음 저감에 관한 설계연구 Part I : 성능해석 및 소음예측

The objective of this research is to suggest anoise prediction method for a centrifugal compressor. It is focused on the Blade Passing Frequency component which is regarded as the main part of the rotating impeller noise. Navier-Stokes solver is used to simulate the flow-field of the centrifugal compressor, and the time-dependent pressure data are calculated to perform the near-field noise prediction by using Ffowcs Williams - Hawkings formulation. Indirect Boundary Element Method is applied to consider the noise propagation effect. Pressure fluctuations of the inlet and the outlet in the centrifugal compressor impeller are presented and the sound pressure level prediction results are compared with the experimental data.

Experiences with the application of a software for noise prediction in workrooms

For a couple of years, the BIA has been using a computer program for the calculation of room acoustic parameters and the prediction of sound pressure levels at the workplace. Experiences gathered with the program in connection with industrial consulting activities are presented and illustrated by examples. The software is based on a calculation method referred to in the German VDI guideline 3760 (image sound source method) requiring a mean degree of complexity in the description of the room. The software comprises a large library, indicating sound absorption coefficients for all tested materials. The program is mainly used for planning room acoustic improvements and new workrooms. Noise prediction in connection with production changes (replacement of machinery, new productions) is also possible. In some cases of hearing damage, the program was used for a retrospective determination of noise exposure at former workplace. A comparison of the calculated spatial sound decay curves and the thus-derived room acoustic parameters with the measurement readings showed good correspondence. The development of noise maps and the consequent presentation of the achievable noise reduction by means of concrete measures has become an important instrument for motivating and convincing companies.

Prediction of sound-pressure level in an occupied enclosure

In a room with inadequate sound absorption, occupants may suffer from low speech intelligibility due to the high noise level resulting from human activities. For effective communication, they tend to raise their voices. In the present study, a method which takes into account the effect of raising voices is derived to predict the variation of A-weighted sound level inside an enclosure in which the number of occupants changes with time. Site measurements are also performed in a canteen of capacity around 250. The model predicts the variations of A-weighted sound levels with a number of occupants with sufficient accuracy for engineering applications.

Improvement of sound quality through accurate acoustic diagnostic boundary element analysis

The boundary element method (BEM) has long been used effectively in the prediction of sound-pressure levels in acoustic cavities and surrounding vibrating bodies. While this is an important capability in the design of structures for noise constraints, it does not point the engineer to the appropriate remedial action if the noise is found to be excessive. This paper presents a discussion of ‘‘acoustic diagnostic analysis,’’ which is an analytical extension to the BEM which traces the source of any noise to its root cause. The impact of a design change can be seen immediately through the use of sensitivity computations, which clearly show the most effective modifications which can be made for noise reduction. The technique works by calculating the contributions made by each portion of the surface area to the sound-pressure level at an internal point. This allows an accurate evaluation of the contribution made from each part of the panel to the noise experienced at that point. The paper discusses some issues involved in performing the boundary element analysis for sound-pressure level prediction and calculating the panel contributions accurately. The paper also describes recent extensions to the method which allow acoustic diagnostic analysis of multidomain problems, and also how more accuracy can be obtained for problems including sound absorbing materials. Both of these developments have important consequences, in particular in automotive noise reduction. A test example shows how the technique locates the structural panels which are the major contributors to a noise problem, and which are therefore the panels which offer the most noise reduction effect for a given remedial action.

Fundamental issues of accuracy in boundary element analysis of acoustic problems

The boundary element method (BEM) has become well established as a primary technique for the computer simulation of acoustic fields. Its ability to provide accurate predictions of sound-pressure levels in a variety of media, including those extending to ‘‘infinity,’’ has led to a growth in the popularity of the method. Further, recent advances in acoustic diagnostic analysis, which is an extension of the traditional BEM approach, have added to the capabilities of this type of software simulation. It is important when using numerical simulation methods not to forget the potential sources of error which may be caused by improper usage of software systems. This paper discusses some of the fundamental modeling requirements of a good boundary element model, showing how the results can degrade when these requirements are violated.

Prediction of Sound Pressure Level of Broadband Noise due to Periodic Velocity Fluctuation in the Near Wake of a Rotating Flat-Plate Blade.

Prediction of Sound Pressure Level of Broadband Noise due to Periodic Velocity Fluctuation in the Near Wake of a Rotating Flat-Plate Blade.

Scattering of sound by atmospheric turbulence: Predictions in a refractive shadow zone

According to ray theory, regions exist in an upward refracting atmosphere where no sound should be present. Experiments show, however, that appreciable sound levels penetrate these so-called shadow zones. Two mechanisms contribute to sound in the shadow zone: diffraction and turbulent scattering of sound. Diffractive effects can be pronounced at lower frequencies but are small at high frequencies. In the short wavelength limit then, scattering due to turbulence should be the predominant mechanism involved in producing the sound levels measured in shadow zones. No existing analytical method includes turbulence effects in the prediction of sound pressure levels in upward refractive shadow zones. In order to obtain quantitative average sound pressure level predictions, a numerical simulation of the effect of atmospheric turbulence on sound propagation is performed. The simulation is based on scattering from randomly distributed scattering centers (‘‘turbules’’). The scattering effect of each turbule is calculated with the help of the first Born approximation to scattering, using independently measured micrometeorological variables such as the variance 〈μ2〉 and correlation length L of the refractive index fluctuations. Sound pressure levels are computed for many realizations of a turbulent atmosphere. Predictions from the numerical simulation are compared with existing theories and experimental data.

Scattering of sound by atmospheric turbulence: Predictions in a refractive shadow zone

According to ray theory, regions exist in an upward refracting atmosphere where no sound should be present. Experiments show, however, that appreciable sound levels penetrate these so-called shadow zones. Two mechanisms contribute to sound in the shadow zone: diffraction and turbulent scattering of sound. Diffractive effects can be pronounced at lower frequencies but are small at high frequencies. In the short wavelength limit, then, scattering due to turbulence should be the predominant mechanism involved in producing the sound levels measured in shadow zones. No existing analytical method includes turbulence effects in the prediction of sound pressure levels in upward refractive shadow zones. In order to obtain quantitative average sound pressure level predictions, a numerical simulation of the effect of atmospheric turbulence on sound propagation is performed. The simulation is based on scattering from randomly distributed scattering centers ('turbules'). Sound pressure levels are computed for many realizations of a turbulent atmosphere. Predictions from the numerical simulation are compared with existing theories and experimental data.

Prediction of sound pressure level of noise generated from low pressure axial and diagonal flow fans.

Prediction of sound pressure level of noise generated from low pressure axial and diagonal flow fans.

Research on a noise control device. 3rd report The fundamental design (2) of the device.

The structural design method of the noise control device was described in the 2nd report and it is possible to design the structure of the device by this method. But it is necessary to design how to set the device to the noise source when it is applied. That is, the appropriate set position to the noise source is required in order to obtain more noise reduction effect. Therefore, the design method for setting the device was considered through some model experiments in the anechoic room and the field, and the sound pressure level prediction method for the device with a barrier was obtained. These results are described in this paper.

An investigation of sound pressure level predictions in large lecture halls

An investigation of sound pressure level predictions in large lecture halls

An investigation of sound pressure level predictions in large lecture halls

Measurements of steady‐state sound pressure levels above the audience in large lecture halls show that the classical equation for predicting the sound pressure level is not accurate. The direct field above the seats was studied on a 1:10 scale model of a large lecture hall using the removable audience from the scale model. It was found to be dependent on the incidence angle and direction of sound propagation across the audience. The reverberant field above the seats was studied by subtracting the direct field from the measured field in the model. It was found to be dependent on the magnitude and particularly on the placement of absorption in the room. The decrease of sound pressure level versus distance in the total field depends on the angle (controlled by absorption placement) at which the strong reflections are incident upon the audience area. Sound pressure level decreases at a fairly constant rate with distance from the sound source in both the direct and reverberant field, and the decrease rate strongly depends on the absorption placement. The lowest rate of decay occurs when the side walls are absorptive, and both the ceiling and rear wall are reflective. The consequences are discussed with respect to prediction of speech intelligibility, and modifications are suggested for three current speech intelligibility prediction schemes.

Sound transmission between absorbing parallel planes

Partially absorbing parallel surfaces can be the dominant acoustical feature of many rooms. The sound fields in such rooms are not diffuse, which causes difficulty in predicting sound pressure levels. A method is developed for predicting sound pressure levels in these rooms. It rests on the prediction of sound pressure levels caused by a nondirectional source of known sound power radiating between absorbing parallel planes. The development proceeds from a geometrical acoustics viewpoint. Good correlation has been found between predicted and measured levels in existing rooms having simple geometries.