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1
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Accuracy Issues of Discrete Hilbert Transform in Identification of Instantaneous Parameters of Vibration Signals

100%
Meissner M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 1A
A-164-A-167
EN
In the paper, an accuracy of the discrete Hilbert transform method in a detection of amplitude and frequency of vibration signals has been examined. This issue was studied for sinusoidal damped vibrations often encountered in practical applications. It has been shown that an inexactness of the Hilbert transform generates fictitious oscillations of amplitude and frequency. For small damping of vibrations these oscillations were significant only at both ends of a discrete signal. An error induced by a numerical algorithm was especially severe for strongly damped vibrations because it manifested itself by a large overestimation of amplitude and erroneous jumps of frequency. To reduce the error generated by the Hilbert transform method, the appropriate modification of discrete signal was proposed.
2
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Structural Noise Reduction and Its Effects on Plate Vibrations

100%
Trojanowski R., Wiciak J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 1A
A-148-A-151
EN
The aim of this work is reduction of structural noise generated by plate and its impact on plates vibrations. For this purpose a one-side clamped aluminum plate with 5 piezo elements attached is used. One of the elements is used for plate excitation, two as vibration sensors, and two as actuators. Structural noise is measured by a microphone connected with SVAN 912 E. Study was divided into three parts: measurements of vibrations and noise generated by excited plate, active vibration control, and structural noise reduction. A significant noise local noise reduction is obtained, although with increase in plate vibrations.
3
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Comparison of Efficiency of Different Shapes of Homogeneous and Two-Part Piezo Elements on Vibration Reduction

100%
Trojanowski R., Wiciak J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 5
905-907
EN
The subject of this work is a numerical analysis of efficiency of different piezo element shapes and types used for vibration (and later structural sound) reduction. The shapes of both types of piezo elements used are as follows: square, right-angled triangle, and parallelogram. There are 2 types of piezo elements used in this study: homogeneous elements and elements consisting of 2 parts (inner and outer) of different composition. These are attached to steel plate clamped on all sides. For every simulation 5 elements are used as actuators, with 1 as disturbance source, and other 4 as active dampers. On the other side of a plate 4 elements are placed acting as vibration sensors. The actuator used as a disturbance source as well as sensors are always in the shape of a square. 4 modes were taken into account (analyzed each one singular and all together). Analyses were made with the use of ANSYS software.
4
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The Effect of Material Composition of Piezoelectric Elements with Chosen Shapes on Plate Vibration Reduction

100%
Wiciak J., Trojanowski R.
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vol. 125
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issue 4A
A-179-A-182
EN
This paper presents numerical analysis of efficiency of different shapes and material composition of piezoelectric actuators used for vibration reduction. Four numerical models representing a plate clamped on all sides with two attached piezoelectric elements were created. For each model, one element had the same shape and composition and was used for plate excitation, and the other one, used for vibration reduction, had different shape and possibly material composition and could be of square or circular shape with either homogeneous or two-part material composition. Two modes were taken into account: the first mode and the fifth mode. Analysis of results was performed with ANSYS software.
5
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Comparison of Vibration and Acoustic Pressure Reduction Using Different Types of Piezo actuators

100%
Wiciak J., Trojanowski R.
Acta Physica Polonica A
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2015
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vol. 128
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issue 1A
A-62-A-66
EN
This paper presents results of numerical simulations on reduction of sound pressure radiated from a square plate using different types of piezo actuators. For this purpose a FEM model was developed using ANSYS software with said steel plate with a hemisphere of air on one side of the plate. There are two criteria by which the reduction is measured: minimising vibrations of plate area and minimising sound pressure on a half sphere surrounding the plate. Changes in the results for both the radiated sound pressure and plate vibration are discussed.
6
Content available remote

Diagnostic Inferring on the Bases of Nonlinear Models

100%
Dąbrowski Z.
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issue 1
45-48
EN
Physical phenomena accompanying destruction processes of technical systems are nonlinear and "low-energetic" by nature, while during wearing out mainly a nonlinear disturbance changes. Out of many inference techniques - on the observation basis of the state of the system - the best one is undoubtedly the well-defined mathematical model, allowing inferring `backwards' and `forward', which means finding the genesis and prognosis of the phenomenon. However, such model should be nonlinear. Problems related to the identification of nonlinear dynamic models in a frequency domain and a proposition of solving this problem for the needs of technical diagnostics, i.e. in situations when the observed wear out effects are significantly smaller than the dynamic effects - are discussed in the hereby paper. The bases of the proposed method constitute the discussion of possible solutions of a certain class of nonlinear differential equations and resulting from that statements on the possibility of nonlinear disturbance approximations by a series of the selected harmonic frequencies.
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