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1

Noise Control Transmission Methods of the Combustion Engine by Means of Reduction of the Vibration

Žiaran S., Chlebo O.

Archives of Acoustics

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2016

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Vol. 41, No. 2

277--284

EN

Transmission of vibroacoustic energy from an internal combustion engine (ICE) to its surroundings largely depends on how it is mounted, on available transmission paths and on the construction of the vehicle body and/or its surrounding structures. This is especially true in low speed engines in enclosed areas which generate perceptually weak noise, but strong low-frequency waves which energy has a negative impact on human health, comfort and driving safety especially in prolonged exposure to the source. The primary aim of the article was to analyse components of the ICE unit which had a determining impact on the reduction of low-frequency waves. Thus, the structurally transmitted noise from the ICE to its surrounding structure (body of the passenger vehicle) was analysed. The results of the vibroacoustic measurements were compared to modal analysis in order to determine possible resonance sources in the vehicle body and/or for assessing the influence of the vehicles safety gear on the generated vibroacoustic energy transfer into the cabin area of the passenger vehicle. Measurements were made for a passenger vehicle at rest and operating in its most common operational speed as well as for the stationary ICE of a cogenerate unit (CGU). Measurements and FFT analysis were used for the detection of the vibroacoustic energy sound pressure level (noise) and mechanical vibration. Firstly, the low-frequency noise sources were determined and their direct effects on the human body were investigated. Finally, this paper suggests some measures which may contribute to the reduction of undesirable vibroacoustic energy in enclosed areas.

2

Effects of warmness and spatial nonuniformity of plasma waveguide on periodic absolute parametric instability

Zaki N. G., Bekheit A. H.

Nukleonika

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2011

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Vol. 56, No. 4

305-309

EN

The periodic absolute parametric instability (API) of the low-frequency oscillations excited by a monochromatic pumping field of an arbitrary amplitude in a warm 1-D (one-dimensional) nonuniform magnetoactive plasma is investigated. The separation method can be used for solving the two-fluid plasma equations describing the system. By applying this method we were able to determine the frequencies and growth rates of unstable modes and the self-consistent electric field. Plasma electrons are considered to have a thermal velocity. Different solutions for the spatial equation can be obtained the following cases: A) API in a uniform plasma, B) API in a nonuniform plasma. The latter has been studied here for two cases: B.1) the exact harmonic oscillator and B.2) the bounded harmonic oscillator (a bounded plasma). An increment has been found in the build-up of the oscillations, and it has been shown that the spatial nonuniformity of the plasma exerts the stabilizing effect on the parametric instability. A reduced growth rate of API in the warm plasma, in comparison to the cold plasma, is reported. It has also been found that the warmness of the plasma has no effect on the solution of the space part of the problem (only through the separation constant).

3

Badania i ocena uciążliwości hałasu niskoczęstotliwościowego w czterokondygnacyjnym budynku mieszkalnym

Wiciak J.

Diagnostyka

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2005

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Vol. 36

109--116

PL

W pracy przedstawiono badania i ocenę hałasu niskoczęstotliwościowego występującego w wybranym czterokondygnacyjnym budynku mieszkalnym. Ocenę warunków akustycznych występujących w badanym budynku przeprowadzono w oparciu o Instrukcję ITB 358/98.

EN

The paper presents results and analysis of investigations of low frequency noise sources, existing in living houses. The results of noise measurements in building were carried out according to instruction ITB 358/98.