ANALYSIS OF THE EFFICIENCY OF ACOUSTIC SCREENS OF DIFFERENT DESIGNS

Various sources of noise in cities and ways to combat them are considered. The effi ciency of two types of acoustic screens is analyzed: single-layer and two-and three-layer. The positive and negative characteristics of various designs of existing acoustic screens are listed. A fundamentally new design of the acoustic screen is described: the panels have a ridge profi le, they are located along the vertical axis of the frame with a step at which the panels above the located ridge cover the top of the lower ridge, the outer surfaces of the panels and their end parts are made of a material that has sound-refl ecting properties, and the inner surfaces of the panels are made of sound-absorbing material. Such an acoustic screen is devoid of the disadvantages inherent in acoustic screens of other structures and is more effi cient. The considered invention allows due to the use of the ridge shape of acoustic panels: prevent the refl ection of sound energy in the direction of noise sources (a small part will be directed upwards); provide almost complete absorption of sound energy as it passes through the channels formed by the ridge panels; provide the same effective protection against noise sources located on both sides of the screen; prevent the formation of snow and ice crust on sound-absorbing surfaces, which ensures the constant eff ectiveness of the screen in diff erent seasons of the year; reduce metal consumption, which will reduce the weight of the structure without reducing its effi ciency and reduce the cost of acoustic screens.

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Acoustics. Determination of sound power levels and sound energy levels of noise sources using sound pressure. Engineering methods for an essentially free field over a reflecting plane

10.3403/30094843 ◽

2011 ◽

Keyword(s):

Sound Pressure ◽

Energy Levels ◽

Free Field ◽

Sound Power ◽

Noise Sources ◽

Sound Energy

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The Simulation Design of Microwave Absorption Performance for the Multi-Layered Carbon-Based Nanocomposites Using Intelligent Optimization Algorithm

Nanomaterials ◽

10.3390/nano11081951 ◽

2021 ◽

Vol 11 (8) ◽

pp. 1951

Author(s):

Danfeng Zhang ◽

Congai Han ◽

Haiyan Zhang ◽

Bi Zeng ◽

Yun Zheng ◽

...

Keyword(s):

Layer Structure ◽

Optimal Solution ◽

Single Layer ◽

Simulation Design ◽

Wide Bandwidth ◽

Abc Algorithm ◽

Bee Colony ◽

Absorbing Material ◽

Important Means ◽

Carbon Based

The optimal design objectives of the microwave absorbing (MA) materials are high absorption, wide bandwidth, light weight and thin thickness. However, it is difficult for single-layer MA materials to meet all of these requirements. Constructing multi-layer structure absorbing coating is an important means to improve performance of MA materials. The carbon-based nanocomposites are excellent MA materials. In this paper, genetic algorithm (GA) and artificial bee colony algorithm (ABC) are used to optimize the design of multi-layer materials. We selected ten kinds of materials to construct the multi-layer absorbing material and optimize the performance. Two algorithms were applied to optimize the two-layer MA material with a total thickness of 3 mm, and it was found that the optimal bandwidth was 8.12 GHz and reflectivity was −53.4 dB. When three layers of MA material with the same thickness are optimized, the ultra-wide bandwidth was 10.6 GHz and ultra-high reflectivity was −84.86 dB. The bandwidth and reflectivity of the optimized material are better than the single-layer material without optimization. Comparing the GA and the ABC algorithm, the ABC algorithm can obtain the optimal solution in the shortest time and highest efficiency. At present, no such results have been reported.

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Propeller Cavitation Induced Hull Pressure Reduction by Air-Bubble Layer

10.5957/smc-2013-t31 ◽

2013 ◽

Author(s):

Jeung-Hoon Lee ◽

Hyoung-Gil Park ◽

Jin-Hak Kim ◽

Kyung-Jun Lee ◽

Jong-Soo Seo

Keyword(s):

Acoustic Scattering ◽

Destructive Interference ◽

Primary Concern ◽

Pressure Amplitude ◽

Pressure Reduction ◽

Noise Sources ◽

Air Bubble ◽

Excessive Consumption ◽

Bubble Layer ◽

The Cost

Cavitation generated by a marine propeller is a primary concern among the possible vibration- and noise- sources in commercial ships. By exploiting the compressibility of air, there have been many attempts to form an air-bubble layer underneath the stern-hull surface above the propeller, and consequently to isolate the cavity-induced pressure wave across the layer. However, it could not be popularly used because the cost was so expensive to deliver a huge amount of air for a sufficient isolation performance. In this work, full-scale ship measurements reveal that a significant reduction of pressure-amplitude is possible at the outside of an air-bubble layer, where the isolation effect is not involved. Moreover a hull-vibration reduction of approximately 75% was found to be achievable. Instead of excessive consumption of air, considerably small amount is necessary for a reduction of cavity-induced pressure amplitude, which can make the constitution of relevant system simple. Hence the purpose of this study is to provide a physical proof for such a beneficial phenomenon. By approximating the solution of acoustic scattering from a bubble, we find that phase-reversal reflection provoking a destructive interference is the main reason for a pressure reduction outside the layer.

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Reducing the harmful effects of noise on the human environment. Sound insulation of industrial skeleton enclosures in the 10–40 kHz frequency range

Journal of Environmental Health Science and Engineering ◽

10.1007/s40201-020-00560-2 ◽

2020 ◽

Vol 18 (2) ◽

pp. 1451-1463

Author(s):

Witold Mikulski

Keyword(s):

Sound Pressure Level ◽

Sound Pressure ◽

Sheet Steel ◽

Pressure Level ◽

Sound Insulation ◽

Frequency Range ◽

Noise Sources ◽

Human Environment ◽

Absorbing Material ◽

Acoustic Enclosures

Abstract Purpose The purpose of the research is to work out a method for determining the sound insulation of acoustic enclosures for industrial sources emitting noise in the frequency range of 10–40 kHz and apply the method to measure the sound insulation of acoustic enclosures build of different materials. Methods The method is developed by appropriate adaptation of techniques applicable currently for sound frequencies of up to 10 kHz. The sound insulation of example enclosures is determined with the use of this newly developed method. Results The research results indicate that enclosures (made of polycarbonate, plexiglass, sheet aluminium, sheet steel, plywood, and composite materials) enable reducing the sound pressure level in the environment for the frequency of 10 kHz by 19–25 dB with the reduction increasing to 40–48 dB for the frequency of 40 Hz. The sound insulation of acoustic enclosures with a sound-absorbing material inside reaches about 38 dB for the frequency of 10 kHz and about 63 dB for the frequency of 40 kHz. Conclusion Some pieces of equipment installed in the work environment are sources of noise emitted in the 10–40 kHz frequency range with the intensity which can be high enough to be harmful to humans. The most effective technical reduction of the associated risks are acoustic enclosures for such noise sources. The sound pressure level reduction obtained after provision of an enclosure depends on its design (shape, size, material, and thickness of walls) and the noise source frequency spectrum. Realistically available noise reduction values may exceed 60 dB.

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Characterization and Design of Honeycomb Absorbing Materials

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.294.51 ◽

2019 ◽

Vol 294 ◽

pp. 51-56

Author(s):

Hui Min Sun ◽

Le Chen ◽

Zhao Zhan Gu

Keyword(s):

Double Layer ◽

Low Frequency ◽

Single Layer ◽

Electromagnetic Parameters ◽

Honeycomb Sandwich ◽

Absorbing Materials ◽

Absorbing Material ◽

The Difference ◽

Free Space Method ◽

Honeycomb Sandwich Structure

Honeycomb absorbing materials are anisotropic structural materials. Depending on the size of honeycomb lattices, the absorbent content of the impregnated layer is different, the thickness of the impregnated layer is different, and the absorbing function of the impregnated honeycomb absorbing materials is also different. For the characterization of electromagnetic parameters of honeycomb absorbing materials, this paper adopts free space method for testing, uses CST software for modeling, and inverts the electromagnetic parameters of honeycomb absorbing structures. The absorbing performance of single-layer and double-layer honeycomb sandwich structures was simulated by RAM Optimizer software. The research shows that the height of the single-layer honeycomb absorbing material is 22mm. When the absorber content is 65%, 75% and 85% respectively, the harmonic peak moves slightly to the low frequency electromagnetic wave with the increase of the absorber content, but the absorbing strength decreases with the increase of the absorber content. For the double-layer honeycomb sandwich structure, the difference of absorber content in the upper and lower honeycomb absorbing materials is smaller, and the absorbing performance is stronger. When the thickness of the wave-transparent panel is thinner, the harmonic peak of the absorbing curve moves slightly to the high frequency.

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Pipe Supports and Skid Platforms: An Overlooked Noise Problem

Volume 2: Integrity and Corrosion; Offshore Issues; Pipeline Automation and Measurement; Rotating Equipment ◽

10.1115/ipc2000-269 ◽

2000 ◽

Author(s):

Richard G. Patching

Keyword(s):

Energy Source ◽

Turbulent Flow ◽

Energy Industry ◽

Structural Vibration ◽

Support Structures ◽

Noise Sources ◽

Sound Energy ◽

Transmission Path ◽

Noise Energy ◽

Acoustic Impact

When an energy industry facility must meet environmental noise regulations, the primary noise sources are the drivers (such as engines and motors), driven tools (such as compressors and pumps), air moving devices, and turbulent flow in valves and piping. The primary sound transmission path is the airborne radiation of noise, which is controlled by enclosures, lagging and silencers. The opportunity for sound energy to be transmitted through structural vibration and reradiated at another location is largely overlooked in typical acoustic impact analyses. Pipe support and skid structures often have large flat panels which are very efficient radiators of noise energy, where the sound energy generated by compressors can be emitted into the environment at some distance from the actual energy source. How a pipe is mounted on its supports, and the design of those supports, can have a significant effect on the noise emissions from its support structures.

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Variable Size Twin-Rotor Wind Turbine

Energies ◽

10.3390/en12132543 ◽

2019 ◽

Vol 12 (13) ◽

pp. 2543 ◽

Cited By ~ 4

Author(s):

Piotr Doerffer ◽

Krzysztof Doerffer ◽

Tomasz Ochrymiuk ◽

Janusz Telega

Keyword(s):

Wind Turbine ◽

Vertical Axis ◽

Vertical Axis Wind Turbine ◽

Efficient Operation ◽

Turbine Efficiency ◽

Small Wind Turbines ◽

Strong Winds ◽

New Feature ◽

The Cost ◽

Twin Rotor

The paper presents a new concept of a vertical axis wind turbine. The idea is focused on small wind turbines, and therefore, the dominating quality is safety. Another important necessary feature is efficient operation at small winds. This implies an application of the drag driven solution such as the Savonius rotor. The presented concept is aimed at reducing the rotor size and the cost of implementation. A new wind turbine solution, its efficiency, and functionality are described. The results of numerical simulations being a proof of the concept are reported. The simulations were followed by wind tunnel tests. Finally several prototypes were built and investigated for a longer period of time. The new wind turbine concept has undergone various testing and implementation efforts, making this idea matured, well proven and documented. A new feature, namely, the wind turbine size reduction at strong winds, or in other words, an increase in the wind turbine size at low winds is the reason why it is difficult to compare this turbine with other turbines on the market. The power output depends not only on the turbine efficiency but also on its varying size.

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Wake of a Ducted Vertical Axis Tidal Turbine in Turbulent Flows, LBM Actuator-Line Approach

Energies ◽

10.3390/en12224273 ◽

2019 ◽

Vol 12 (22) ◽

pp. 4273 ◽

Cited By ~ 4

Author(s):

Mikaël Grondeau ◽

Sylvain Guillou ◽

Philippe Mercier ◽

Emmanuel Poizot

Keyword(s):

Turbulent Flows ◽

Vertical Axis ◽

Tidal Currents ◽

Eddy Simulation ◽

Tidal Turbines ◽

Tidal Turbine ◽

Vertical Axis Tidal Turbine ◽

Ambient Turbulence ◽

The Cost ◽

Boltzmann Method

Vertical axis tidal turbines are devices that extract the kinetic energy from tidal currents. Tidal currents can be highly turbulent. Since ambient turbulence affects the turbine hydrodynamic, it is critical to understand its influence in order to optimize tidal farms. Actuator Line Model (ALM) combined with Large Eddy Simulation (LES) is a promising way to comprehend this phenomenon. In this article, an ALM was implemented into a Lattice Boltzmann Method (LBM) LES solver. This implementation gives good results for predicting the wake of a vertical axis tidal turbine placed into a turbulent boundary layer. The validated numerical configuration was then used to compute the wake of a real size ducted vertical axis tidal turbine. Several upstream turbulence rates were simulated. It was found that the shape of the wake is strongly influenced by the ambient turbulence. The cost-to-precision ratio of ALM-LBM-LES compared to fully resolved LBM-LES makes it a promising way of modeling tidal farms.

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An analysis of the impact of draft tube modifications on the performance of a Kaplan turbine by means of computational fluid dynamics

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/0954406217713520 ◽

2017 ◽

Vol 232 (11) ◽

pp. 1937-1952

Author(s):

Juergen Schiffer ◽

Helmut Benigni ◽

Helmut Jaberg

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Draft Tube ◽

Vertical Axis ◽

Hydropower Plant ◽

Construction Costs ◽

Turbine Efficiency ◽

Kaplan Turbine ◽

The Cost ◽

The Impact

Due to the low electricity prices in central Europe, cost optimisations related to all parts of a new hydropower plant have become increasingly important. In case of a run-of-river hydropower plant using a vertical axis Kaplan turbine, one of the cost drivers are the excavation works. Thus, a decisive factor for the reduction of construction costs is the minimisation of the construction depth of the elbow-type draft tube. In course of the design phase of a new hydropower plant in Austria, an analysis of the impact of draft tube modifications on the performance of the Kaplan turbine was carried out by applying computational fluid dynamics. The net head of the turbine with a diameter of D = 3.15 m accounts for Hnet = 9.00 m and the maximum discharge per unit is Qmax = 57.5 m3/s. After it was proven that there is a good agreement of the numerically calculated and experimentally measured turbine efficiency for the original turbine configuration, various draft tube designs were tested in order to find out their impact on the turbine efficiency and to analyse the sources of draft tube losses in detail. Finally, it was possible to find a new draft tube design representing a compromise of reduced construction costs and acceptable turbine efficiency.

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