Wyniki wyszukiwania - BazTech

1

Impulse Excitation in a Watertight Steel Circular Cylindrical Shell and Influence of Structural Configuration on Underwater Radiated Noise

Wu Chen-I, Too Gee-Pinn, Wu Bo-Hsien

Archives of Acoustics

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2023

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Vol. 48, No. 4

509--521

EN

This study used experimental measurements and the finite-element method (FEM) simulations to investigate transient underwater radiated noise induced by the impulse excitation of water surrounding a watertight steel-structured circular cylindrical shell submerged in the 176 × 8 × 4 m towing tank. The excitation was caused by dropping an iron block onto a structural bracket in the shell to generate structural vibration. The experimental results were found to be consistent with the FEM results, with the difference between the experimental and simulated sound pressure levels being less than 3 dB. Moreover, it was determined that the structural vibration also generated airborne noise in the cylindrical shell, but this contributed much less than the impulse excitation to the induction of underwater radiated noise. Finally, analysis of the sound field of the underwater noise radiation showed that it was influenced by the wall thickness of the watertight steel cylindrical shell and that of the reinforced bracket seat structure. In particular, the structural reinforcement position proved to be the diffusion breakpoint of the underwater sound radiation. This demonstrates that compared with the studied structure, a thicker and more complex reinforced structure will transmit less or incomplete sound radiation into water.

2

Possibility to apply unified methodology in vibration analysis for long lasting and impulse sources, in terms of influence on people in buildings

Józef Duda

Acta Geophysica

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2023

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Vol. 71, no. 2

813--821

EN

The present work addresses the problem of unified methodology use for vibration analysis caused by various anthropogenic sources. The experimental part of the paper contains analysis and results comparison of the vibration, induced by freight train passages and hammer percussion. Ground vibrations are important for the civil engineering objects condition since the vibration induced by train is transmitted through the ground to the foundation and structure. Ground vibration can also be a source of disturbance for the residents. However, various factors cause vibration that varies in both intensity and frequency measures. The analysis of vibration timelines, running RMS and Fourier spectra are applied. The major part of the dissertation is the analysis of RMS accelerations and velocities in one-third octave frequency bands in 1 to 80 Hz spectrum, and comparison to the background vibration noise, recorded in the same localization. The different values of time-window observation are applied to analyse the results. The results of long lasting cargo-induced vibrations are less dependent on time-window duration than the results of impulse-induced vibrations. The acceleration and velocity analysis results are compared to the literature data concerning the ground vibration caused by railway transport and mining activity. The paper indicates the possibility to apply unified methodology for vibration analysis caused by both long-lasting sources, as trains and short-lasting ones, as industrial blasts or mine tremors. The results indicate an optimal time window for vibration measurement that would enable to automate vibration monitoring.

3

Metoda wyznaczania dynamicznego modułu sprężystości betonu z wykorzystaniem impulsowego wzbudzenia drgań i analizy modalnej

Jurowski K., Kokot S., Bobra P., Grzeszczyk S.

Inżynieria i Budownictwo

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2016

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R. 72, nr 11

612--615

PL

Porównano normowe procedury wyznaczania dynamicznego modułu sprężystości betonu. W celu sprawdzenia poprawności proponowanych w normach procedur obliczeniowych dokonano analizy wyników badań próbek z różnego rodzaju betonów o różnych wymiarach gabarytowych.

EN

A comparison of standard procedures of dynamic elastic modulus testing is provided. In order to check the correctness of the calculation methods proposed by the standards an analysis of samples of different kinds of concrete of different sizes is presented.

4

A comparison of the human body-seat model responses to several types of impulse excitations

Książek M. A., Łacny Ł.

Journal of Theoretical and Applied Mechanics

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2014

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Vol. 52 nr 3

839--845

EN

The purpose of this paper is to present the response of a human body-seat model to the external disturbance in form of an impulse excitation. A 2-DOF Active Human Body Model with two distinct positions (“back-on” an “back-off”) is used in the simulations. Additionally, two different seat types are considered: rigid and passive. Several types of impulse excitations are used ranging in shape, amplitude and disturbance time. A comparison of the results is made: the first on the assumption of equal excitation energy, and the second one for impulses of equal amplitudes but different duration.