Calculation Of Transmission Loss Research Articles

Vibroacoustic characterization of small woven fabrics

This study is aimed to analyze the vibroacoustic behaviour of woven fabrics utilized in small acoustic devices for ingress protection. We first concentrate on predicting and describing the vibration behaviour of the woven fabric structure through flip around, since lumped modelling comes first. A vibration experiment is also conducted to measure the motion of the woven fabric structure under external excitation to validate the modelling. The numerical model is then employed to simulate the vibroacoustic behaviour of the woven fabric via transmission loss calculation; the simulation is then compared with transmission loss measurement based on the four-microphone method. This research demonstrates that despite some limitations, both the numerical and lumped models show a good degree of accuracy in predicting the vibration of the woven structure; the numerical model also performs well in vibroacoustic modelling.

A modular neural network to quickly approximate the modal dispersion in coastal waters

Low-frequency acoustic propagation modeling in coastal waters usually relies on numerical models based on modal theory such as Kraken and Orca. These models compute the modal parameters (e.g., modal wavenumbers and depth functions) that can be used in the calculation of the acoustic field. Their repeated use in broadband applications, or for inversion purposes, comes with a notable computational cost. To mitigate this, a modular neural network (NN) was trained to approximate modal parameters for varying modes and frequencies, across diverse environments, with variable water sound speed profile and variable seabed geoacoustic parameters. The training dataset is generated using Kraken and the NN is evaluated on many environments not seen during training. Once trained, the NN can make broadband predictions without prior knowledge on the number of modes, even when the number of modes changes over the frequency-band of interest. This approach reduces computation time compared to the original forward propagation model, while maintaining high precision. The effectiveness of our method is demonstrated through transmission loss calculations and a simulated geoacoustic inversion scenario.

Vibration reduction indices for junctions between cross-laminated timber floors and lightweight timber framed walls

Cross laminated timber elements are often used as the floors and the external walls in mass timber buildings in Canada, but the internal walls of these buildings are typically lightweight timber framed walls. The calculation of the flanking transmission loss and the apparent sound transmission class for the mix of lightweight and mass timber constructions requires the laboratory measured vibration reduction indices or flanking level differences of the different flanking paths. Junctions constructed in the new four room flanking facility at the National Research Council Canada have been used to evaluate both the vibration reduction indices and the flanking level differences of a cross laminated timber floor connected to lightweight timber walls.

3D Gaussian ray bundling to improve the speed and accuracy of transmission loss eigenrays and multi-static reverberation, in littoral environments

The wavefront queue 3D (WaveQ3D) model is a research effort to create fast and accurate acoustic transmission loss eigenrays and multi-static reverberation, in littoral environments, for real-time sonar simulation/stimulation systems that require simultaneous updates from hundreds of acoustic contacts. WaveQ3D is a Gaussian ray bundling model that improves computation speed of rapidly evolving scenarios by computing propagation results on a spherical earth. We will show that the added complexity of the spherical coordinate system has almost no impact on execution speed, and how it avoids the laborious task of transforming the 3D oceanographic data into Nx2D radials. WaveQ3D improves the accuracy of transmission loss and reverberation calculations in littoral environments by including 3D effects, such as horizontal refraction from the ocean bottom. This talk will focus on the design decisions that made during model development and their impact on the utility of WaveQ3D for a few different applications.

Sound transmission loss of a micro-perforated muffler with internal spiral structure

With sub-millimetre perforation, a micro-perforated muffler (MPM) has a high acoustic resistance and low mass reactance. It can provide considerable noise attenuation effect in low-frequency range. The wave propagation in a coaxial micro-perforated tube muffler is deduced based on the plane wave hypothesis, and the theoretical transmission loss calculation results are compared with finite element method simulation results. Then, a new type of micro-perforated tube muffler with internal spiral structure (MPMISS) is proposed, to improve the noise attenuation effect in middle and high frequency range. The effects of pitch, length, number of lines and micro-perforation of internal spiral structure on acoustic transmission loss is analysed. The CFD is used to calculate the influence of internal spiral structure on aerodynamic characteristics of tube muffler. Although the internal spiral structure slightly increases the pressure loss, it can prevent the direct transmission of middle and high frequency noise, so as to effectively improve the noise attenuation effect in middle and high frequency range.

Contribution of the wave modes to the sound transmission loss of inhomogeneous periodic structures using a wave and finite element based approach

In recent years, a wide variety of inhomogeneous periodic structures including locally resonant metamaterials and phononic crystals have come to the fore in the search for innovative noise and vibration solutions which are lightweight and compact. With the often intricate design of these periodic cells, noise and vibration attenuation is achieved in targeted frequency ranges, called stopbands. The vibro-acoustic performance of these structures is mostly analyzed using unit cell modeling, by means of dispersion curves and/or sound transmission loss (STL) calculations. Although several techniques exist to compute the dispersion curves and/or STL, the link between these two performance indicators is often not straightforward, especially for increasingly complex unit cell designs, which can make their analysis and design cumbersome. To bridge this gap and come to a thorough understanding of these periodic structures, a method to rank the wave modes of the dispersion curves contributing to the sound transmission is required. Recently, a first step towards such an approach has been developed using a wave and finite element method (Yang et al., 2021). However, that technique is limited to in-plane homogeneous structures which can be represented by meshes with corner degrees-of-freedom only. To be able to investigate the relation between the STL and the dispersion curves of inhomogeneous (vibro-acoustic) periodic structures which require larger, and arbitrary complex meshes, this wave and finite element based methodology needs to be extended. Therefore, this work proposes a new methodology which addresses the current limitations. Several numerical case studies demonstrate the ability of the proposed methodology to bridge the gap between dispersion curves and STL calculations.

A New Model for Estimating Troposcatter Loss and Delays Based on Ray-Tracing and Beam Splitting With ERA5

The atmospheric environment is one of the critical factors affecting troposcatter transmission loss and propagation delay. This article proposes a new estimation model that can accurately calculate troposcatter transmission loss and propagation delay with a numerical weather model (NWM). The ERA5 reanalysis data as the NWM are applied to construct the new model. The 3-D ray-tracing and beam splitting are used to calculate propagation paths and delays. Compared with the existing methods, the new model thoroughly considered the bending and delaying effects of the atmospheric environment on electromagnetic waves, resulting in more accurate estimates. The transmission loss calculation capability of the new model is compared with the International Telecommunication Union (ITU) model and the terrestrial trans-horizon propagation loss data banks. The propagation delay calculation capability is compared with the Bello model. These comparison results show that the new model sufficiently reflects the meteorological environment’s influence on transmission loss and propagation delay. Finally, the daily variation characteristics of losses and delays are analyzed using the new model and further validate the model performance.

Transmission loss calculation of a pipe with dissipative silencer containing porous materials

Various types of silencers have been used to reduce noise transmitted through pipe system. In particular, a dissipative silencer containing absorbing materials inside has an ability of noise control by transferring acoustic/vibrational energy to thermal energy. In this study, the acoustic performance of a dissipative silencer lined with two-layer absorbing materials is investigated. Herein, the absorbing materials in the form of a polymer foam are considered as a porous medium composed of a solid polymer skeleton and internal pores. From the boundary conditions at the rigid wall and the interfaces between the porous materials, eigenvalues and eigenfunctions in the dissipative silencer are determined. Finally the transmission loss is obtained through the mode matching method. The effects of geometry and acoustic properties of the porous medium are also discussed.

Mixed layer acoustic propagation with small scale ocean dynamics

The effects of dynamic oceanographic processes in the upper ocean mixed layer on acoustic propagation are investigated using at-sea sound speed observations and acoustic transmission simulations. The sound speed environment is based on a 400 m deep and 1000 km long East-West salinity and temperature transect that was collected during April of 2005 in the North Pacific where there is a mixed layer acoustic duct with a mean depth of 89 m. The deterministic baseline of this sound speed measurement is first estimated from the observations using a spatial lowpass filter with a cut off length scale of 50-km. The remaining small length scale variations in sound speed are assumed to have two physically distinct contributions: one due to the vertical displacement of isopycnals caused by eddies and internal waves and another due to compensating temperature and salinity anomalies along isopycnals termed spice. These two contributions can be separated yielding three distinct sound speed fields: i(1) the deterministic background; (2) thedisplacement field; and (3) the spice field. Acoustic transmission loss calculations are carried out on these three fields for frequencies of 400 and 1000 Hz for sources both in and below the mixed layer duct. Statistical and deterministic results for acoustic normal modes and full field transmission loss are presented, which quantify the relative importance of displacement and spice for acoustic propagation in the upper ocean.

A time-domain simulation method to predict insertion loss of a dissipative muffler with exhaust flow

Insertion loss (IL) is a more useful acoustic index than noise reduction and transmission loss for muffler design, but it is harder to predict because the prediction of IL requires knowing the characteristics of the muffler itself and the acoustic source. A muffler with porous material and complex meanflow makes the prediction even more challenging. Although calculation of noise reduction and transmission loss with the transient computational fluid dynamics (CFD) can naturally solve the flow–acoustic interaction problem, the published CFD methods have not been adopted to evaluate the IL of the dissipative muffler with exhaust flow. In this paper, a time-domain simulation method is developed to predict the IL of a complex engine muffler with porous material. The noise reduction and load impedance of the muffler were first calculated using a three-dimensional CFD model, in which the porous material was simulated by the governing equations modified with the material porosity and flow resistivity. The IL was then predicted from the noise reduction, the load impedance, and the engine source extracted from the measured exhaust noise. This developed method explores the application of the three-dimensional CFD method in calculating noise reduction, load impedance, and insertion loss of complex dissipative mufflers with exhaust flow.

Intelligent calculation method of communication Transmission loss based on hybrid neural network

The traditional calculation method of communication transmission loss has the calculation error of communication loss, and the application scope of the calculation method is small. Therefore, this paper proposes an intelligent calculation method of communication transmission loss based on hybrid neural network. Based on the ideal free space transmission loss model, the transmission loss model of outdoor environment is established; the communication obstacles in the transmission process are determined; and the transmission loss calculation area is divided. The calculation of communication transmission loss is completed by using hybrid neural network combined with the specific parameters of the demarcated area. By comparing with the method based on neural network, it is verified that the method using hybrid neural network can improve the calculation accuracy by about 77.1%, and the method has a wider range of application.

A modified time domain approach for calculation of noise reduction and acoustic impedance of intake duct system

Calculation of noise reduction and acoustic impedance of the duct system is needed for the one-port source model, which is widely used in the field of duct acoustics for extracting the source characteristics and predicting the radiating noise at the open end. The flow field in the duct influences the acoustic characteristics when the flow velocity is relatively high. Recently, the time domain method has been adopted to study the flow effects on the acoustic response of the duct mufflers. However, the existing method only focuses on the calculation of transmission loss (TL) or transfer matrix. In this paper, a modified time domain approach is proposed for the first time to calculate the noise reduction and acoustic impedance of the intake duct system. In the proposed time domain model, the frequency dependent reflection at the intake port, rather the anechoic boundary used for TL calculation, is simulated by simply adding a correction pipe at the port. This approach has effectively simplified the implementation of the traditional time domain method in dealing with frequency dependent reflection at the open end. The porous sound-absorbing material commonly used in the intake system is modelled by modified equations with the material porosity and flow resistivity. The predicted time-domain sound pressure signals are then post-processed to obtain the noise reduction and the acoustic impedance in a different way from the traditional time domain TL calculation approach. The result of validation has shown that the noise reduction and acoustic impedance predicted with the modified time domain approach agree well with the measured results and the results calculated from frequency domain methods in the cases without and with meanflow.

Experimental Study of Orifice Shape Effect on Noise Reduction of Silencer

Abstract: Noise pollution is one of the most problems caused by internal combustion engines. In this study, the reduction of noise by changing the orifice shapes and inserting tape is experimentally investigation. The effect of orifice shape on noise reduction of silencer is presented. The calculation of transmission losses and transmission coefficient of noise for different shapes of orifice by using MATLAB program is obtained. In addition, the frequency for maximum and minimum losses is obtained. The results showed that the use of the square orifice and helical tape were better options to reduce the noise in the silencer.

Calculation of theoretical transmission loss in trunk gas pipeline

Owing to the limited accuracy and measurement uncertainty of the instruments installed in gas pipeline systems, it is impossible to completely avoid transmission loss during transportation of natural gas. This study established an uncertainty model for the measurement system determining the complex flow rates of trunk gas pipelines, analyzed the uncertainty calculation methods of different metering systems, and developed a calculation method for determining the theoretical transmission loss. Application showed that the theoretical transmission loss serves not only as an early warning regarding a transmission loss, but also as a guide to the pipeline enterprise for determining the transmission loss assessment index. If the actual transmission loss rate is smaller than the theoretical transmission loss rate during the calculation cycle, it means that the pipeline metering system is working normally. Otherwise, it is necessary to immediately investigate the reason behind the transmission loss and implement corresponding measures.

Analytical Model for Low-Frequency Transmission Loss Calculation of Zero-Prestressed Plates With Arbitrary Mass Loading

Abstract As the importance of sound attenuation through weight-critical structures has grown and mass law based strategies have proven impractical, engineers have pursued alternative approaches for sound attenuation. Membrane-type acoustic metamaterials have demonstrated sound attenuation significantly higher than mass law predictions for narrow, tunable bandwidths. Similar phenomena can be achieved with plate-like structures. This paper presents an analytical model for the prediction of transmission loss through rectangular plates arbitrarily loaded with rigid masses, accommodating any combination of clamped and simply supported boundary conditions. Equations of motion are solved using a modal expansion approach, incorporating admissible eigenfunctions given by the natural mode shapes of single-span beams. The effective surface mass density is calculated and used to predict the transmission loss of low-frequency sound through the plate–mass structure. To validate the model, finite element results are compared against analytical predictions of modal behavior and shown to achieve agreement. The model is then used to explore the influence of various combinations of boundary conditions on the transmission loss properties of the structure, revealing that the symmetry of plate mounting conditions strongly affects transmission loss behavior and is a critical design parameter.

Exhaust System Muffler Volume Optimization of Light Commercial passenger Car Using Transfer Matrix Method

Nowadays, the automotive industry is focused on weight and size reduction. Main advantage of this weight and size reduction are improving the fuel economy. The specific fuel consumption of a vehicle can be improved through e.g. downsizing area of heat loss, if we focus on vehicle with weight reduction. Weight reduction can be done by replacing material or by changing the size (dimensions) of components. In the present work we have focused on Audi A6 muffler, troubleshooting and optimizing the muffler by changing pipe length of inlet and outlet, also by replacing the original mesh plate to porous pipe. Based on optimization, prototype has been built with the help of 3D design tool CATIA V5 and the calculations of transmission loss (TL) have been performed by MATLAB. Plane wave-based models such as the transfer matrix method (TMM) can offer fast initial prototype solutions for muffler designers. The principles of TMM for predicting the transmission loss of a muffler was used. Result of this present study of an existing muffler has been analysed and then compared with vehicle level test observation data. Noise level have been optimized for new muffler design. Other literatures were played significant rule for validate our results.

Underwater radiated noise from commercial ships in the Yellow Sea of China

During the past decades, ship-building and engine-manufacturing have developed very quickly. The source levels of modern ships may have changed. The underwater radiated noise from many commercial ships of opportunity was measured by bottom-mounted self-contained hydrophone near the shipping lanes in the yellow sea of China one day in each month from June. 2014 to Mar. 2016. Twenty seven ships among them are selected whose peak value of 20-1000Hz passing curve is 10dB higher than background noise level. A Gaussian source distribution in depth direction is supposed and source levels normalized at different ranges are averaged in source levels acquisition to reduce the error of transmission loss calculation. A key result was the estimated results of RANDI-3 are much greater than measured results universally for ships whose length are larger than 200 meters, however, the two are close for ships whose length are less than 150 meters. Furthermore, the samples were divided into two categories to analyze. The broad-band source levels of modern commercial ships are not highly correlated to ship length but closely related to ship speed. The decay slope is less than RANDI-3.

Theoretical calculation of transmission loss of noise panels

In the paper basic theoretical models of transmission loss calculation are described. Here only single homogeneous isotropic panels are analysed. Three impedance values of one rigid and two flexible body models of panel are described and analysed. As flexible models the thin plate (Kirchhoff-Love plate model) i thick (Mindlin – Reissner model) are analysed.

Broadband transmission losses and time dispersion maps from time-domain numerical simulations in ocean acoustics.

In this letter, a procedure for the calculation of transmission loss maps from numerical simulations in the time domain is presented. It can be generalized to arbitrary time sequences and to elastic media and provides an insight into how energy spreads into a complex configuration. In addition, time dispersion maps can be generated. These maps provide additional information on how energy is distributed over time. Transmission loss and time dispersion maps are generated at a negligible additional computational cost. To illustrate the type of transmission loss maps that can be produced by the time-domain method, the problem of the classical two-dimensional upslope wedge with a fluid bottom is addressed. The results obtained are compared to those obtained previously based on a parabolic equation. Then, for the same configuration, maps for an elastic bottom and maps for non-monochromatic signals are computed.

Derivation and Application of a New Transmission Loss Formula for Power System Economic Dispatch

The expression and calculation of transmission loss (TL) play key roles for solving the power system economic dispatch (ED) problem. ED including TL must compute the total TL and incremental transmission loss (ITL) by executing power flow equations. However, solving the power flow equations is time-consuming and may result in divergence by the iteration procedure. This approach is unsuitable for real-time ED in practical power systems. To avoid solving nonlinear power flow equations, most power companies continue to adopt the TL formula in ED. Traditional loss formulas are composed of network parameters and in terms of the generator’s real power outputs. These formulas are derived by several assumptions, but these basic assumptions sacrifice accuracy. In this study, a new expression for the loss formula is proposed to improve the shortcomings of traditional loss formulas. The coefficients in the new loss formula can be obtained by recording the power losses according to varying real and reactive power outputs without any assumptions. The simultaneous equations of the second-order expansion of the Taylor series are then established. Finally, the corresponding coefficients can be calculated by solving the simultaneous equations. These new coefficients can be used in optimal real and reactive power dispatch problems. The proposed approach is tested by IEEE 14-bus and 30-bus systems, and the results are compared with those obtained from the traditional B coefficient method and the load flow method. The numerical results show that the proposed new loss formula for ED can hold high accuracy for different loading conditions and is very suitable for real-time applications.