Increase In Transmission Loss Research Articles

A multi-year study of acoustic propagation and ambient sound in a Thalassia testudinum seagrass meadow in a shallow sub-tropical lagoona).

Seagrasses provide a multitude of ecosystem services and act as important carbon sinks. However, seagrass habitats are declining globally, and they are among the most threatened ecosystems on earth. For these reasons, long-term and continuous measurements of seagrass parameters are of primary importance for ecosystem health assessment and sustainable management. This paper presents results from both active and passive acoustical methods for ecosystem monitoring in seagrass meadows. From a propagation perspective, gas bodies contained within the seagrass tissue as well as photosynthetic-driven bubble production result in attenuation, dispersion, and scattering of sound that produce increased transmission loss. For the passive approach, the detachment of gas bubbles from the plants is an important component of the ambient soundscape. Examples of both techniques will be presented based on data collected as part of a two-year continuous deployment of an acoustical measurement system operating in a moderately dense seagrass bed dominated by Thalassia testudinum (turtle grass) in Corpus Christi Bay, Texas. The data show annual trends related to the seasonal growth pattern of Thalassia as well as diurnal trends correlated with photosynthetically active radiation.

Model study on transmission loss of the split-stream rushing exhaust muffler for diesel engine

Numerical simulation was carried out on the transmission loss of the split-stream rushing exhaust muffler, and the accuracy of the simulation method was verified through experiments. Taking the transmission loss as the response value, the experiment was designed by using Box-Behnken module of Design Expert software. A mathematical regression model of transmission loss with experiment factors was established by using the Box-Behnken experimental design scheme, the experiment factors include the diameter of the interior pipe, the shape of the rushing hole, the center distance of the rushing hole, the cone angle of the interior pipe as well as the number of rushing holes, and the mathematical regression model's significance was tested. The response curvatures of second order interaction to the transmission loss by different variables were obtained and the interaction relationships among variables were analyzed. The results showed that the diameter of the interior pipe and the center distance of the rushing hole are the main factors that affect the transmission loss. The transmission loss increases with the increase of the diameter of the interior pipe. When the diameter of the interior pipe is between 70 mm and 80 mm, the transmission loss firstly increases and then decreases with the center distance of the rushing hole changes from Smin to Smax. When the diameter of the interior pipe is between 80 mm and 90 mm, the transmission loss decreases with the center distance of the rushing hole changes from Smin to Smax. The effect of the rushing hole shape on transmission loss is not significant. The transmission loss increases with the increase of the number of rushing holes, but the increase of transmission loss is not significant with the number of rushing holes changes from 4 to 6 groups. Taking the transmission loss as the optimization index, the better experimental condition was obtained. Compared to the not optimized muffler of the sample engine, the average transmission loss of the optimized muffler is increased by 48.70 % when the frequency is 0-1000 Hz, the average insertion loss of the optimized muffler is increased by 7.4 %. At inlet air velocity of 40 m/s, the pressure loss is reduced by 56.8 %.

Nonlinear vibro-acoustic analysis of an axially moving submerged circular cylindrical shell

In this study, the nonlinear vibro-acoustic dynamics and stability of doubly-clamped axially moving cylindrical shell are investigated. The exterior surface of the shell is in contact with fluid and subjected to oblique incident plane sound wave. Donnell’s nonlinear shallow shell theory is used to derive the nonlinear partial differential equation of the cylindrical shell for the radial motion. The Galerkin method is employed to discretize the equations of motion into the set of coupled nonlinear nonhomogeneous ordinary second order differential equations. Considering both driven and companion modes, Multiple Scales Method is used to obtain the response of the system. The effects of sound level, incident angle and axially velocity on the frequency response of the system are studied. The results show that, with increase in the shell velocity transmission loss of the circular shell increases. In addition, at low shell axial velocities simultaneous excitation of the driven and companion modes occurs.

Measurements of mid-frequency acoustic signal variability in the Western Barents Sea

Two Vertical Line Arrays (VLAs) and one source moorings were deployed to study along- and cross-shelf acoustic propagation in the Western Barents Sea during October 12–19, 2022. An ITC 2010 source was used to transmit Linear Frequency-Modulated (LFM) acoustic signals covering a frequency band of 0.7–4.2 kHz. Several oceanographic moorings were also deployed to measure time series of ocean currents and sound-speed profiles. Analysis of the acoustic data showed strong effects of tidal currents and surface roughness on mid-frequency acoustic propagation. Along- and cross-shelf acoustic propagation data showed semidiurnal travel-time fluctuations due to tidal currents. In addition, a 15 dB increase in Transmission Loss was observed during the storm events due to rough surface scattering. Finally, an assessment of the Polar Front and its effects on acoustic propagation (both travel-time and amplitude) are studied. Several data and simulated examples are provided to demonstrate the 3D effects of a Polar front and nonlinear internal waves on mid-frequency acoustic propagation. [Work supported by the ONR.]

On enhancing the noise-reduction performance of the acoustic lined duct utilizing the phase-modulating metasurface

This work proposes a noise-reduction structure that integrates phase-modulating metasurface (PMM) with acoustic liners (ALs) to enhance the narrow band absorption performance of a duct with relatively small length-diameter ratio. The PMM manipulates the wavefront by introducing different transmission phase shifts based on an array of Helmholtz resonators, so that the spinning wave within the duct can be generated. Compared with the plane wave, the generated spinning wave has a lower group velocity, which results in a greater traveling distance over the ALs in the duct. The optimization design is performed to determine the final structural parameters of the PMM, which is based on the predictions of the amplitude and phase shift of the acoustic wave at the outlet of the PMM using the theory of passive phased array. With the manipulation of the PMM, the incident plane wave is modulated into a spinning wave, and then enters into the acoustic liner duct (ALD), whose structural parameters are optimized by maximizing the transmission loss using the mode-matching technique. Finally, the noise-reduction performance of this combined structure is evaluated by numerical simulations in the presence of grazing flow. The results demonstrate that, compared with the traditional ALD, the proposed structure exhibits a significant increase in transmission loss within the considered frequency band, especially near the peak frequency of the narrow band noise.

ENVIRONMENTALLY FRIENDLY ACOUSTIC PANEL DESIGN FROM CURTAIN WASTE

Using leftover industrial curtain fabrics, this study aims to develop environmentally friendly acoustic panels. In this context, two forms of curtain fabric waste, blackout and dimout, which are segregated as waste from post-production process within Oba Perdesan, are transformed into fiber utilizing mini shredder. The hot press method is used to produce composite samples made of 100% blackout and 50% blackout/ 50% dimout fabric waste in two different thicknesses (0.5 and 1 cm). The thickness, density, basis weight, FTIR, sound absorption coefficient, and sound transmission loss of the manufactured panels are measured. The FTIR analysis reveals the distinctive peaks of the raw materials of the structures, while the acoustic test results show that the sound absorption coefficient and sound transmission loss increase along with the thickness and basis weight of the structures, respectively. While the 1 cm blackout/dimout blend sample has a superior sound absorption coefficient for 2000 Hz with 0.81, the 1 cm 100% blackout sample performs highest with 10dB sound transmission loss. The produced panels aid in solid waste management while consuming minimal raw materials, and an essential step is taken toward the development of sustainable, practical, and decorative panels.

Study of acoustic and aerodynamic performance of reactive silencer with different configurations: Theoretical, modeling and experimental

Periodic sound reduction at some frequencies and high pressure loss could be considered as the disadvantages of simple expansion silencers. Generally, reactive elements are applied in silencers to optimize their acoustic and aerodynamic performance. In this paper, we were going to investigate the combined and independent effects of reactive elements, baffle and extended tubes at the inlet and outlet of simple expansion silencer, on the acoustic performance and pressure loss of simple expansion silencer. Firstly, simple expansion silencer dimensions were determined based on theoretical calculations to attenuate the noise by 10 dB. Secondly, the simulation was performed using COMSOL acoustical module software based on finite element method to predict silencer sound transmission loss and pressure loss, respectively, before and after adding reactive elements. Then, according to ISO7235, ISO3744 and ISO3746 standards noise insertion loss of various silencers under study was measured in a free field and in the following that silencers pressure loss evaluated. Finally, the predicted results with the software were compared with the experimental ones. The addition of the extended tubes increased the transmission loss and insertion loss at low and medium frequencies and mitigated the pressure loss of the silencer compared to the simple expansion silencer. The baffle increased the transmission loss curve in the medium frequencies compared to the simple expansion silencer. The combination of baffle and extended tube elements caused an extraordinary increase in insertion loss and transmission loss at the medium frequencies and a decrease in pressure loss. It could be concluded from the present study that using extended tube might be probably the best choice to reduce pressure loss and increase the acoustic performance of simple expansion silencer at low and medium frequencies and what's more is that the best acoustic performance in medium frequencies can be achieved by using a combination of baffle and extended tube.

Acoustical methods for remote sensing in seagrass meadows

Seagrasses provide a multitude of ecosystem services and act as important carbon sinks. However, seagrass habitats are declining globally, and they are among the most threatened ecosystems on earth. For these reasons, long-term and continuous measurements of seagrass parameters are of primary importance for ecosystem health assessment and sustainable management. After a brief historical overview, this talk will present results from both active and passive acoustical methods for ecosystem monitoring in seagrass meadows. From a propagation perspective, gas bodies contained within the seagrass tissue as well as photosynthetic-driven bubble production results in attenuation and scattering of sound that produces increased transmission loss. For the passive approach, the detachment of gas bubbles from the plants is an important component of the ambient soundscape. Examples of both techniques will be presented based on data collected as part of an 18-month continuous deployment of an acoustical measurement system operating in a moderately dense seagrass bed dominated by Thalassia testudinum (turtle grass) in Corpus Christi Bay, Texas. The data show annual trends related to the seasonal growth pattern of Thalassia as well as diurnal trends correlated with photosynthetically active radiation. [Work supported by NSF.]

Evaluation of acoustic performance of cascaded cylindrical micro-perforated panel

A cylindrical micro-perforated panel (MPP) can be used to absorb the sound of a flow system in a circular duct of a vacuum cleaner. A cascaded cylindrical MPP is a special class type where two cylindrical MPPs are arranged in a series to improve sound attenuation. The manufacturing of MPP primarily involves the machining of micro-perforations, because small holes are not readily made using injection moulding due to the complexity of the die, flow control of the molten polymer through the small orifices and dimensional stability, making it unsuitable for mass production. This limitation can be overcome with the use of additive manufacturing (AM) technology, where the micro-perforations can be designed and manufactured, with relatively larger tolerances. Experimental validation ensures that the manufactured prototype in this study is performed according to design. Results show that the transmission loss of the model and the experimental outcomes agree. The cascaded arrangement of the cylindrical MPP results in a wider effective frequency range and an increased transmission loss. Parametric studies of the combined effects of the perforation diameter, perforation ratio and the depth of air cavity on the diameter of the duct and length ratio are conducted using a transfer matrix method. A case study is demonstrated here in the design. Moreover, an AM of cascaded cylindrical MPP is performed to attenuate peak noise at 1650 Hz, where the optimum parameters of the cascaded cylindrical MPP are obtained using a genetic algorithm. The manufactured cascaded cylindrical MPP is installed on a vacuum cleaner duct, and the measurement of sound power level shows a reduction of 4 dB(A).

Efficient Modelling of Acoustic Metamaterials for the Performance Enhancement of an Automotive Silencer

Significant potential for acoustic metamaterials to provide a breakthrough in sound attenuation has been unlocked in recent times due to advancements in additive manufacturing techniques. These materials allow the targeting of specific frequencies for sound attenuation. To date, acoustic metamaterials have not been demonstrated in a commercial automotive silencer for performance enhancement. A significant obstacle to the practical use of acoustic metamaterials is the need for low cost and efficient modelling strategies in the design phase. This study investigates the effect of acoustic metamaterials within a representative automotive silencer. The acoustic metamaterial design is achieved using a combination of analytical and finite element models, validated by experiment. The acoustic metamaterial is then compared with commonly used techniques in the silencer industry to gauge the effectiveness of the acoustic metamaterials. COMSOL simulations were used to validate the developed test rig and were compared to experimental results which were obtained using the two-load transmission loss test method. Through this testing method, the implementation of a labyrinthine metamaterial cylinder proved to be a significant improvement in transmission loss within the silencer, with an increase in transmission loss of 40 dB at 1500 Hz. The research has successfully shown that acoustic metamaterials can be used in practical settings, such as an automotive silencer, to improve the overall sound attenuating performance. The described analytical model demonstrates the potential for industrially relevant low cost design tools.

Transition of energy system by regulating of Power Quality for efficiency improvements

The supply of electrical energy is of importance for the value creation of most industrialized nations. Ultimately, electrical energy is able to provide the appropriate useful energy at the point of need with virtually no emissions. This aspect plays a greater role today than ever before. When using electrical energy as a clean and sustainable energy source, it is important to note that there can be significant losses in the transmission of electrical energy between the point of generation and the point of use. These transmission losses are caused, among other reasons, by line losses due to power quality deviating from the ideal value. In principle, any deviation from the nominal values of the supply voltage listed in EN 50160 (such as voltage level, frequency or harmonic distortion) leads to an increase in transmission losses. Thus, compliance with the power quality parameters is desirable from all perspectives of (economic, ecological, social) sustainability. Especially with reference to SDGs 7, 8 and 12, a supply voltage that complies with the specified parameters is important. Unfortunately, no incentives currently exist for minimizing deviations in power quality parameters and the transmission losses they cause. Goal should be to implement a transition of energy system that provides incentives to increase the transmission efficiency of electricity. One possibility for this is the unbundling of the guarantee of the power quality parameters on a separate market. Regulatory framework conditions must be adapted for sustainable improvements in energy transmission at all levels. Nevertheless, the economic viability of power quality based business models is difficult. A promising solution is to reintroduce a supplementary factor as an extension of the equation of the incentive based regulation. The vision of the business model explained in the paper is to contribute to the efficient operation of the power grid by avoiding the propagation of harmonics through the use of compensation equipment, this is a new approach that has not yet been investigated.

Development of combined resistance muffler for reduced noise of farm tractor

A farm tractor is the most important component of farm mechanization. Farm tractor noise, on the other hand, has a negative impact on human health. The exhaust system produces the most noise of all the noises produced by a tractor. A muffler is an acoustic filter that is used to reduce exhaust noise. Perforated ducts, baffles/perforated baffles, expansion chambers, and longer inlet/outlets are used to make mufflers. A person working in a workplace with a noise level of 90 dBA is limited to 8 h of work each day under the Occupational Safety and Health Act (OSHA, 1983). As a result, utilizing the finite element approach and acoustic theory, an existing muffler (Reactive type muffler) was optimized to a combined resistance muffler after installing in a 47.6 PS, 2200 rated RPM three-cylinder diesel engine. Except for the frequency range of 138–455 Hz, 515–851 Hz, and 1524 Hz, the optimized combined resistance muffler had a considerable increase in transmission loss in all other frequency ranges. The improved muffler's mean transmission loss was 3.77 dB higher than the original muffler's in the 0–2000 Hz range, which indicates notable improvement in the noise canceling effect. The noise reduction of this combined resistance muffler was tested at operator ear level (OEL). Near rated engine speed, the combined resistance muffler suggests a noise reduction of 1.2 dBA–1.9 dBA over the existing muffler. The upgraded muffler also served as a benchmark for similar muffler structural improvements.

ELECTRIC POWER DEFICIT AND ECONOMIC GROWTH IN NIGERIA: A SECTORAL ANALYSIS

In addition to capital and labour, electricity supply is another important factor that promotes economic growth in an economy. Often times, economic resources are used to generate electricity for domestic consumption by different sectors of an economy. In Nigeria however, the generated KWh is far higher than what eventually gets to the final consumers due to technical inefficiencies associated with electric power transmission and distribution in the supply chain resulting in huge losses. Thus, this study investigated the effect of electric power deficit proxied by electric power transmission and distribution losses on economic growth (disaggregated into agricultural and industrial RGDP) in Nigeria. This study employed the Autoregressive Distributed Lag (ARDL) model and time series data from 1981 to 2017. The hypotheses tested in this study were done at 5 and 10 percent levels of significance. The result obtain revealed that a 1 percent increase in electric power transmission and distribution losses will decrease agricultural output by 3 percent in the long run but insignificant in the short run. Similarly, electric power transmission and distribution losses do not have significant effect on industrial output. It was therefore recommended that the government should construct energy farms to muster and store the electricity that is produced before they are transmitted to the final consumers.Keywords: technical inefficiencies, electric power deficit, economic growth, energy farmsJEL Classifications: C12, C13, C30, F43, L70, Q19, Q43DOI: https://doi.org/10.32479/ijeep.11491

Low-frequency vibro-acoustic response of an optimized fiber-reinforced graphite truss sandwich panel filled with wood-based material

Conventional metallic sandwich panels are widely used for noise control owing to their good noise control capabilities and excellent mechanical strength-to-weight ratio property. Furthermore, sound-absorbing products consisting of glass or mineral fiber materials are generally filled into the sandwich structures to lower the vibration response in resonance frequency and to enhance the structural noise attenuation capacity. In the present study, a fiber-reinforced graphite material is used as an alternative to its metallic counterparts. Moreover, a wood-based renewable absorption material is used as the absorption material and is filled into the sandwich structural core. The vibro-acoustic characteristics of the panel with such a design are numerically investigated using Actran. The findings of the research indicate that the proposed sandwich structure achieves advanced low-frequency noise control performance in comparison with other conventional metallic sandwich panels. Approximately 7 dB increase in sound transmission loss in the audible-frequency range is achieved in addition to a reduced panel weight and more stable vibration with reduced amplitude. The existing data available in the literature are employed for validating and illustrating the accuracy and reliability of the proposed approach.

Performance enhancement of an automotive silencer using acoustic metamaterial baffles

The potential for acoustic metamaterials to provide a breakthrough in sound attenuation has been unlocked in recent times due to advancements in additive manufacturing techniques. These materials allow the targeting of specific frequencies for sound attenuation. To date acoustic metamaterials have not been experimentally tested in an automotive silencer for performance enhancement. This study investigates the effect of acoustic metamaterials within a representative automotive silencer. These results are then compared with commonly used techniques in the silencer industry to gauge the effectiveness of the acoustic metamaterials. COMSOL simulations were used to validate the developed test rig and were compared to experimental results which were obtained using the two-load transmission loss test method. Through this testing method, the implementation of the acoustic labyrinthine DENORMS cylinder proved to be the most significant improvement in transmission loss within the silencer, with an increase in transmission loss of 40 dB at 1500 Hz. It was also found that the traditional hard wall internal baffle silencer performance can be improved by replacing it with a DENORMS internal baffle. Acoustic metamaterials have potential as a novel method for automotive companies to attenuate sound of specific frequencies.

Tunable Elastic wave Bandgaps and Waveguides by Acoustic Metamaterials with Magnetorheological Elastomer

There is proposed a tunable acoustic metamaterials cell composed of a micro-electromagnetic coil as the mass element and a magnetorheological elastomer (MRE) as cladding layer. The cell resonance frequency is changed by changing the magnetic field generated by the micro-electromagnetic coil to control the shear modulus of the MRE cladding layer. The tunable bandgaps, transmission loss, and waveguides of the tunable acoustic metamaterials are investigated using the finite element method. The results show that the bandgap frequency and width, the maximum attenuation frequency and transmission loss increase with the increasing of applied magnetic field strength. Meanwhile, without changing the structure of the acoustic metamaterials, the localization, guidance, demultiplex and multiplex of elastic waves can be realized by changing the cell resonance frequency. These results will greatly contribute to the application of tunable acoustic metamaterials in vibration control, new waveguides, and filter components.

Multi cases optimal reactive power dispatch using evolutionary programming

<span>Evolutionary Programming (EP) is one of many types in Evolutionary Computation (EC) that used for optimization process. EP technique is used to find the optimal reactive power dispatch (ORPD) since it is one of the accessible options schemes that can be used on the system as a reactive power support. Sometimes, it is not necessary to operate all generators in order to perform ORPD to in achieve the objectives. Also, increment of reactive power load to the system will cause voltage decomposes with the increase in transmission loss in the system. Therefore, the proposed method decides the best grouping of generators that should be operated in system by bearing in mind the transmission loss reduction. ORPD will be used to minimize the transmission loss as well the increasing reactive power loading. This method conducted on IEEE 30-bus Test System with multi cases scenario. The best combination of operating generators determined and the transmission loss after optimization is smaller compared to the transmission loss before optimization resulted.</span>

Feasibility of Plasmonic Circuits in Nanophotonics

The configuration of plasmonic circuits comprising SiO2-load waveguides and their characteristics within the nanophotonic range are presented and compared with electronic and lightwave circuits in 1300 and 1550 nm wavelength bands. In the nanophotonic range of less than $1~\mu \text{m}$ , plasmonic signals propagate in narrow waveguides with cross-sections less than a few hundred square nanometers, while lightwaves exhibit only slight propagation in high-refractive-index (i.e., Si) waveguides owing to the transmission loss increase via the cut-off wavelength of the waveguide. Additionally, the plasmonic signal transmission loss is lower than that of electric signals for transmission lengths less than a few hundred micrometers. During signal transmission, a narrow spectral width of the plasmonic signals is needed to suppress any signal shape deformation induced by the frequency dependence of the collective oscillation of electrons in plasmonic signals. In the nanophotonic range, the degree of integration for plasmonic circuits is not governed by the transmission loss but by the leak distance of the plasmonic signal optical field from the side-walls of the waveguides and components. Employing a metal/insulator/metal structure in plasmonic circuits is a valid way to heighten the integration density, and its effectiveness is numerically and experimentally confirmed in a plasmonic multiplexer less than $1~\mu \text{m}$ in length. On the basis of these results, the feasibility of plasmonic circuits is discussed and it can be said that plasmonic circuits including waveguides and components are promising photonic techniques for signal transmission in the nanophotonic range

МЕТОДИКА ОЦЕНКИ ФИНАНСОВОГО СОСТОЯНИЯ ЭЛЕКТРОСЕТЕВЫХ ОРГАНИЗАЦИЙ: СУЩНОСТЬ И РЕЗУЛЬТАТЫ АПРОБАЦИИ

The article describes the economic principles of the work of power supply organizations in terms of government regulating of tariffs (prices) for their services. The influence of restraining prices in the electricity market on the financial condition of power supply companies has been shown as following: slowdown in profitability, lack of funds for the renewal and modernization of production assets, increase in transmission losses, malfunctions and reduced quality of the provided services. It has been stated that using the data of the objective assessment of financial state, it is possible to achieve an increase in the efficiency of the power supply organizations and to ensure their stable financial condition. The need to develop methods for assessing the financial status of power grid organizations, taking into account their industry characteristics has been substantiated. The method proposed in the research, which is based on using a point-rating system, involves the classification of organizations according to the type of their financial condition, according to the actual level and rating of each of the selected financial indicators in points. Approbation of the developed methods (as an example are taken the power supply organizations of the Primorsky Territory: Far Eastern Distribution Grid Company JSC, Mikhailovskagropromenergo JSC, Transfiguration Energy Networks LLC) shows their reliability. The methods provide a comprehensive and objective assessment of the financial status of power supply organizations and allow not only to identify specific shortcomings in the activities of a particular organization, but also to provide conditions for their elimination in order to sustainably develop the enterprises of the electric power industry and increase the efficiency of their operation.

Power Quality in Energy Efficient Buildings – a Case Study

Energy-efficient buildings are increasingly equipped with modern automation and control systems that enable significant energy savings by providing energy in the exact place and time of the demand. Moreover, high-performance LED light sources are used as interior lighting. Since the computers, automation system controllers and LED light sources require a lower voltage than the mains voltage, the buildings use a large number of power electronic converters adjusting the power supply conditions for the devices being serviced. Operation of this type of strongly non-linear receivers leads to an increase in transmission losses of electrical energy related to reactive power flow and generation of higher harmonics. Striving to reduce energy consumption in buildings leads to increasing use of these devices, which in consequence will aggravate the problem of insufficient quality of electricity. The paper discusses the provisions of standards for the quality of electricity. The paper presents the results of research on the quality of electricity in the Malopolska Laboratory of Energy Efficient Building – an experimental building equipped with a building automation and control system.