scholarly journals Normal incidence sound insulation provided by Sonic Crystal Acoustic Screens made from rigid scatterers – assessment of different simulation methods

Acta Acustica ◽  
2021 ◽  
Vol 5 ◽  
pp. 28
Author(s):  
M.P. Peiró-Torres ◽  
M. Ferri ◽  
Luis M. Godinho ◽  
Paulo Amado-Mendes ◽  
Francisco Jose Vea Folch ◽  
...  
Keyword(s):  
Numerical Models ◽  
Traffic Noise ◽  
Normal Incidence ◽  
Alternative Methods ◽  
Propagation Path ◽  
Sound Insulation ◽  
Technical Solution ◽  
Simulation Methods ◽  
Interference Phenomenon ◽  
Sonic Crystal

Sonic crystal acoustic screens have been in progressive research and development in the last two decades as a technical solution for mitigating traffic noise. Their behaviour is quite different from that observed in classical barriers, with the latter being based on physically blocking the direct sound propagation path (only allowing diffracted noise to reach sensible receivers), and sonic crystals providing attenuation efficiency based on the creation of “band-gaps” at specific frequency ranges, due to the Bragg’s interference phenomenon. The distinct physical mechanisms of these two types of noise barriers complicates the use of classical simplified or even numerical models developed for traditional barriers to simulate and predict the attenuation performance of a sonic crystal, and alternative methods become thus required. In the acoustics scientific literature, several authors have proposed estimation and simulation methods based on different numerical tools to predict the sound insulation provided by these new noise abatement solutions. This paper presents a comparative evaluation of some of these methods, with emphasis on the assessment of their accuracy versus memory usage in order to determine which one is the most suitable for optimization methodologies in the design of new devices with improved acoustic performance.

scholarly journals Artificial Intelligence Application on Sediment Transport

2021 ◽  
Vol 9 (6) ◽  
pp. 600
Author(s):  
Hyun Dong Kim ◽  
Shin-ichi Aoki
Keyword(s):  
Sediment Transport ◽  
Numerical Models ◽  
Beach Nourishment ◽  
Hydraulic Model ◽  
Alternative Methods ◽  
Cross Sectional ◽  
Sand And Gravel ◽  
Incident Waves ◽  
Artificial Intelligence Application ◽  
Deep Learning Model

When erosion occurs, sand beaches cannot maintain sufficient sand width, foreshore slopes become steeper due to frequent erosion effects, and beaches are trapped in a vicious cycle of vulnerability due to incident waves. Accordingly, beach nourishment can be used as a countermeasure to simultaneously minimize environmental impacts. However, beach nourishment is not a permanent solution and requires periodic renourishment after several years. To address this problem, minimizing the period of renourishment is an economical alternative. In the present study, using the Tuvaluan coast with its cross-sectional gravel nourishment site, four different test cases were selected for the hydraulic model experiment aimed at discovering an effective nourishment strategy to determine effective alternative methods. Numerical simulations were performed to reproduce gravel nourishment; however, none of these models simultaneously simulated the sediment transport of gravel and sand. Thus, an artificial neural network, a deep learning model, was developed using hydraulic model experiments as training datasets to analyze the possibility of simultaneously accomplishing the sediment transport of sand and gravel and supplement the shortcomings of the numerical models.

Reducing Noise Polution Generated by the Gas Compresor Compressco Cj 360 in a Residential Area

2015 ◽  
Vol 801 ◽  
pp. 84-89
Author(s):  
Silviu Nicolae Platon ◽  
Adriana Tudor
Keyword(s):  
Risk Factor ◽  
Frequency Spectrum ◽  
Environmental Conditions ◽  
Noise Level ◽  
Work Capacity ◽  
Residential Area ◽  
Sound Insulation ◽  
Technical Solution ◽  
Legal Regulations ◽  
Health Work

Noise – as a risk factor in the environment – in case it exceeds the intensity limits it becomes a biological aggression factor, a medical and social contaminant with implications of prime importance in terms of health, work capacity and comfort.This research is an objective analysis of noise level and frequency spectrum emitted by gas compressor Compressco CJ 360 in order to identify and develop solutions for noise protection required for the establishment of the environmental conditions in accordance with legal regulations in the area desired by the beneficiary. The research proposes a technical solution for closing the compressor with sound insulation prior to placing it in the desired place, in suitable environmental conditions.

Numerical study for increasement of low frequency sound insulation of double-panel structure using sonic crystals with distributed Helmholtz resonators

2019 ◽  
Vol 33 (14) ◽  
pp. 1950138
Author(s):  
Myong-Jin Kim
Keyword(s):  
Free Space ◽  
Transmission Loss ◽  
Numerical Study ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Sound Insulation ◽  
The Finite Element Method ◽  
Helmholtz Resonators ◽  
Sonic Crystal ◽  
Sonic Crystals

Numerical simulations of the sound transmission loss (STL) of a double-panel structure (DPS) with sonic crystal (SC) comprised of distributed local resonators are presented. The Local Resonant Sonic Crystal (LRSC) consists of “C”-shaped Helmholtz resonator columns with different resonant frequencies. The finite element method is used to calculate the STL of such a DPS. First, the STLs of LRSC in free space and the DPS with LRSC are calculated and compared. It is shown that the sound insulations of the local resonators inserted in the double panel are higher than that in free space for the same size of the SCs and the same number of columns. Next, STL of the DPS in which the SC composed of three columns of local resonators having the same outer and inner diameters but different slot widths are calculated, and a reasonable arrangement order is determined. Finally, the soundproofing performances of DPS with distributed LRSC are compared with the case of insertion of general cylindrical SC for SC embedded in glass wool and not. The results show that the sound insulation of the DPS can be significantly improved in the low frequency range while reducing the total mass without increasing the thickness.

Oblique, Stratified Winds about a Shelter Fence. Part II: Comparison of Measurements with Numerical Models

2004 ◽  
Vol 43 (10) ◽  
pp. 1392-1409 ◽  
Author(s):  
John D. Wilson
Keyword(s):  
Numerical Models ◽  
Normal Incidence ◽  
Energy Dissipation Rate ◽  
Velocity Shear ◽  
Navier Stokes ◽  
Urban Dispersion ◽  
Mean Velocity ◽  
Mean Wind Speed ◽  
Wind Statistics ◽  
Relative Wind

Abstract To evaluate Reynolds-averaged Navier–Stokes (RANS) models of disturbed micrometeorological winds, steady-state computations using a second-order closure are compared with observations (see Part I) in which the surface layer wind was disturbed by a long, thin porous fence (height h = 1.25 m; thickness dx ≈ 1 mm). Starting with the case of neutral stratification and normal incidence, it is shown that low-resolution RANS simulations (streamwise grid interval Δx/h = 1) produce reasonably good transects of mean wind speed, though with an ambiguity (or nonuniqueness) of at least 10%–15% of the amplitude of the relative wind curve, mainly arising from sensitivity to the choice of the solution mesh. For nearly perpendicular flows, the measured influence of stratification (stable or unstable) is to diminish the amplitude of the relative wind curve (i.e., windbreak is less effective), an effect that is replicated very well by the simulations. Obliquity of the incident wind, like stratification, also correlates with poorer shelter, but the computed response of the relative wind curve to obliquity is excessive. As for higher-order wind statistics, computed transects of velocity standard deviations compare poorly to those observed. Therefore, if this disturbed flow may be taken as representative, then caution must be recommended should it be thought that RANS-type models might be suitable (i.e., accurate, as well as convenient) for computing the disturbed wind statistics (typically mean velocity, shear stress tensor, and turbulent kinetic energy dissipation rate) that are needed to “drive” modern dispersion models in the complex wind regimes that must be confronted in such contexts as urban dispersion, or the wind migration of pollen.

scholarly journals Revealing the effect of rounded noise protection screens with finite sound insulation on an acoustic field around linear sound sources

2021 ◽  
Vol 1 (5 (109)) ◽  
pp. 16-22
Author(s):  
Vitalii Didkovskyi ◽  
Vitaly Zaets ◽  
Svetlana Kotenko
Keyword(s):  
Acoustic Field ◽  
Traffic Noise ◽  
The Body ◽  
Sound Insulation ◽  
Physical Parameters ◽  
Algebraic Equations ◽  
Sound Sources ◽  
Study Results ◽  
Almost All ◽  
Screen Model

This paper reports studying the reduction of traffic noise by rounded noise protection screens with finite sound insulation, that is, those that can pass sound. Almost all models of acoustic screens, which are examined by analytical methods, are either direct or such that disregard the passage of sound through the screen, that is, it is assumed that the screen sound insulation is non-finite. This approach made it possible to solve the problem for a simplified model analytically but made it impossible to analyze the required sound insulation of noise protection screens. In the current paper, the problem of investigating an acoustic field around the screen whose sound insulation is finite has been stated, that is, it was taken into consideration that a sound wave propagates through the body of the screen. In addition, a given problem considers a rounded screen, rather than vertical, which is also used in different countries. Such a problem was solved by the method of partial domains. This method has made it possible to strictly analytically build a solution to the problem by simplifying it to solving an infinite system of algebraic equations, which was solved by the method of reduction. The screen model was set by the values of the density and speed of sound in the screen material. This approach has made it possible to change the acoustic impedance of the screen material and thereby change the sound insulation of the screen. That has made it possible to quantify the effect of screen sound insulation on its effectiveness. It has been shown that the efficiency of noise protection screens with finite sound insulation is approaching the efficiency of acoustically rigid screens, provided that the screen's natural sound insulation is 13–15 dB greater than the estimated efficiency of the rigid screen. The study results could make it possible to more accurately assess the effectiveness of noise protection screens. Determining the screen acoustic efficiency would make it possible to set requirements for its sound insulation characteristics. That could make it possible to select the designs of noise protection screens with minimal physical parameters, such as thickness, weight, etc.

scholarly journals Geomechanical key parameters of the process of hydraulic fracturing propagation in fractured medium

2019 ◽  
Vol 74 ◽  
pp. 58 ◽  
Author(s):  
Rouhollah Basirat ◽  
Kamran Goshtasbi ◽  
Morteza Ahmadi
Keyword(s):  
Hydraulic Fracturing ◽  
Numerical Models ◽  
Fractured Reservoirs ◽  
Natural Fracture ◽  
Propagation Path ◽  
Fracture Density ◽  
Strength Parameters ◽  
Propagation Process ◽  
Fractured Medium ◽  
Hf Propagation

Hydraulic Fracturing (HF) is a well-stimulation technique that creates fractures in rock formations through the injection of hydraulically pressurized fluid. Because of the interaction between HF and Natural Fractures (NFs), this process in fractured reservoirs is different from conventional reservoirs. This paper focuses mainly on three effects including anisotropy in the reservoir, strength parameters of discontinuities, and fracture density on HF propagation process using a numerical simulation of Discrete Element Method (DEM). To achieve this aim, a comprehensive study was performed with considering different situations of in situ stress, the presence of a joint set, and different fracture network density in numerical models. The analysis results showed that these factors play a crucial role in HF propagation process. It also was indicated that HF propagation path is not always along the maximum principal stress direction. The results of the numerical models displayed that the affected area under HF treatment is decreased with increasing the strength parameters of natural fracture and decreasing fracture intensity.

An improved approach for normal-incidence sound transmission loss measurement using a four-microphone impedance tube

2020 ◽  
pp. 107754632092690
Author(s):  
Zechao Li ◽  
Sizhong Chen ◽  
Zhicheng Wu ◽  
Lin Yang
Keyword(s):  
Transfer Matrix ◽  
Sound Absorption ◽  
Transmission Loss ◽  
Sound Transmission ◽  
Normal Incidence ◽  
Sound Insulation ◽  
Sound Transmission Loss ◽  
The Common ◽  
Wavefield Decomposition ◽  
Insulation Performance

The main aim of this study is to introduce an improved method for determining the sound properties of acoustic materials which is more precise than the common wavefield decomposition method and simpler than the common transfer matrix method. In the first part of the article, a group of formulae for calculating sound transmission loss is represented by combining the wavefield decomposition and transfer matrix methods. Subsequently, a formula for calculating sound absorption coefficients is derived from these formulae by definition. Furthermore, the present formulae are validated by comparing the experimental results achieved with the present formulae and those results obtained by other methods recorded in published articles. Eventually, it is demonstrated that the method can accurately measure the sound insulation performance of materials and the sound absorption properties of limp and lightweight materials.

Effect of centrifugal load on crack path in thin-rimmed and webbed gears

2015 ◽  
Author(s):  
F. Curà ◽  
A. Mura ◽  
C. Rosso
Keyword(s):  
Finite Element ◽  
Crack Propagation ◽  
Root Zone ◽  
Crack Nucleation ◽  
Numerical Models ◽  
Propagation Path ◽  
Initiation Point ◽  
Centrifugal Load ◽  
Bending Load ◽  
Uncertainty Zone

Thin rimmed and webbed gears are used in particular applications to reduce systems weight. This kind of gears need an accurate and fail safe design. As a matter of fact, a possible failure, due to bending fatigue, consists in crack nucleation and consequent growth, in particular in the tooth root zone. These cracks may propagate through the tooth or through the rim. Crack propagation direction is basically influenced by the wheel geometry parameters, above all the rim thickness. Studies available in literature emphasize three ranges for the backup ratio values, involving different behaviors. These ranges are related to the crack propagation paths; respectively through the tooth, through the rim and in an unforeseeable way. This last uncertainty zone depends on other parameters, related to both geometry and loading conditions. In this work the effect of wheel speed related to the bending load has been investigated. The investigation has been carried out by means of numerical models involving both 2D finite element and extended finite element models (XFEM). Results shows that both crack initiation point and crack propagation path are strongly influenced by centrifugal load; this effect is mainly evident in the uncertainty zone of the backup ratio.

Technical Notes: Practical Concerns Associated with Single-Number Ratings in Measuring Sound Transmission Loss Properties of Partition Panels

2013 ◽  
Vol 38 (1) ◽  
pp. 115-124 ◽  
Author(s):  
Naveen Garg ◽  
Anil Kumar ◽  
Sagar Maji
Keyword(s):  
Swot Analysis ◽  
Transmission Loss ◽  
Traffic Noise ◽  
Aircraft Noise ◽  
Sound Insulation ◽  
Noise Sources ◽  
Significant Dependence ◽  
Single Number ◽  
Spectrum Adaptation ◽  
Lower Frequencies

Abstract The paper presents an extensive review investigating the practical aspects related to the use of single- number ratings used in describing the sound insulation performance of partition wall panels and practical complications encountered in precise measurements in extensive frequency range from 50 Hz to 5 kHz. SWOT analysis of various single number ratings is described. A laboratory investigation on a double wall partition panel combination revealed the significant dependence of STC rating on transmission loss at 125 Hz attributed to 8 dB rule. An investigation conducted on devising alternative spectrums of aircraft noise, traffic noise, vehicular horn noise and elevated metro train noise as an extension to ISO 717-1 Ctr for ascertaining the sound insulation properties of materials exclusively towards these noise sources revealed that the single-number rating Rw + Ctr calculated using ISO 717-1 Ctr gives the minimum sound insulation, when compared with Rw + Cx calculated using the alternative spectrums of aircraft noise, traffic noise, etc., which means that material provides a higher sound insulation to the other noise sources. It is also observed that spectrum adaptation term Cx calculated using the spectrum of noise sources having high sound pressure levels in lower frequencies decreases as compared to ISO 717-1 Ctr owing to significant dependence of Ctr at lower frequencies.

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