scholarly journals Best-basis analysis of broadband tremor signals

1999 ◽  
Vol 42 (3) ◽  
Author(s):  
T. Bartosch ◽  
P. Steffen
Keyword(s):  
Fourier Transformation ◽  
Narrow Band ◽  
Near Field ◽  
Frequency Content ◽  
Standard Methods ◽  
Time Frequency ◽  
Short Time ◽  
Best Basis Algorithm ◽  
Short Time Fourier Transformation ◽  
Active Volcanoes

Active volcanoes usually generate highly non-stationary broadband tremor signals. Short-time shock events with a frequency content of several decades are superimposed on a stationary narrow band continuous tremor. Tremor signals of this type can be observed in the near field of many active volcanoes. In this paper we will demonstrate the analysis of such signals using a specific tremor signal of Mt. Stromboli (Sicily). We used the Best-Basis Algorithm (BBA) in order to compute a spectrogram which is adapted to signal properties on highly different scales. It turns out that the BBA can reveal better fitting properties of the tremor in the time-frequency plane compared to standard methods like Short-Time Fourier Transformation (STFT). Moreover, this very effective algorithm can be used for real time monitoring in the time-frequency plane, for data compression or for de-noising of the tremor signals.

scholarly journals Improving the Performance of Steel Machining Processes through Cutting by Vibration Control

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5712
Author(s):  
Mihaela Oleksik ◽  
Dan Dobrotă ◽  
Mădălin Tomescu ◽  
Valentin Petrescu
Keyword(s):  
Fourier Transformation ◽  
Vibration Analysis ◽  
Cutting Tool ◽  
Cutting Process ◽  
Manufacturing Processes ◽  
Machining Processes ◽  
Short Time ◽  
Short Time Fourier Transformation ◽  
Dynamic Phenomena

Machining processes through cutting are accompanied by dynamic phenomena that influence the quality of the processed surfaces. Thus, this research aimed to design, make, and use a tool with optimal functional geometry, which allowed a reduction of the dynamic phenomena that occur in the cutting process. In order to carry out the research, the process of cutting by front turning with transversal advance was taken into account. Additionally, semi-finished products with a diameter of Ø = 150 mm made of C45 steel were chosen for processing (1.0503). The manufacturing processes were performed with the help of two tools: a cutting tool, the classic construction version, and another that was the improved construction version. In the first stage of the research, an analysis was made of the vibrations that appear in the cutting process when using the two types of tools. Vibration analysis considered the following: use of the Fast Fourier Transform (FFT) method, application of the Short-Time Fourier-Transformation (STFT) method, and observation of the acceleration of vibrations recorded during processing. After the vibration analysis, the roughness of the surfaces was measured and the parameter Ra was taken into account, but a series of diagrams were also drawn regarding the curved profiles, filtered profiles, and Abbott–Firestone curve. The research showed that use of the tool that is the improved constructive variant allows accentuated reduction of vibrations correlated with an improvement of the quality of the processed surfaces.

scholarly journals Smart Cutting Tools Used in the Processing of Aluminum Alloys

Sensors ◽  
2021 ◽  
Vol 22 (1) ◽  
pp. 28
Author(s):  
Dan Dobrotă ◽  
Sever-Gabriel Racz ◽  
Mihaela Oleksik ◽  
Ionela Rotaru ◽  
Mădălin Tomescu ◽  
...  
Keyword(s):  
Aluminum Alloys ◽  
Fourier Transformation ◽  
Vibration Analysis ◽  
Cutting Tools ◽  
Optimal Conditions ◽  
The Finite Element Method ◽  
Intelligent Tools ◽  
Longitudinal Turning ◽  
Short Time ◽  
Short Time Fourier Transformation

The processing of aluminum alloys in optimal conditions is a problem that has not yet been fully resolved. The research carried out so far has proposed various intelligent tools, but which cannot be used in the presence of cooling-lubricating fluids. The objective of the research carried out in the paper was to design intelligent tools that would allow a control of the vibrations of the tool tip and to determine a better roughness of the processed surfaces. The designed intelligent tools can be used successfully in the processing of aluminum alloys, not being sensitive to coolants-lubricants. In the research, the processing by longitudinal turning of a semi-finished product with a diameter Ø = 55 mm of aluminum alloy A2024-T3510 was considered. Two constructive variants of smart tools were designed, realized, and used, and the obtained results were compared with those registered for the tools in the classic constructive variant. The analysis of vibrations that occur during the cutting process was performed using the following methods: Fast Fourier Transform (FFT); Short-Time Fourier-Transformation (STFT); the analysis of signal of vibrations. A vibration analysis was also performed by modeling using the Finite Element Method (FEM). In the last part of the research, an analysis of the roughness of the processed surfaces, was carried out and a series of diagrams were drawn regarding curved profiles; filtered profiles; Abbott–Firestone curve. Research has shown that the use of smart tools in the proposed construction variants is a solution that can be used in very good conditions for processing aluminum alloys, in the presence of cooling-lubrication fluids.

scholarly journals Joint Time-Frequency And Wavelet Analysis - An Introduction

2014 ◽  
Vol 21 (4) ◽  
pp. 741-758 ◽  
Author(s):  
Andrzej Majkowski ◽  
Marcin Kołodziej ◽  
Remigiusz J. Rak
Keyword(s):  
Wavelet Analysis ◽  
Frequency Analysis ◽  
Fourier Spectrum ◽  
Frequency Content ◽  
Short Time Fourier Transform ◽  
Time Frequency Analysis ◽  
Time Frequency ◽  
Stationary Signals ◽  
Frequency Window ◽  
Short Time

Abstract A traditional frequency analysis is not appropriate for observation of properties of non-stationary signals. This stems from the fact that the time resolution is not defined in the Fourier spectrum. Thus, there is a need for methods implementing joint time-frequency analysis (t/f) algorithms. Practical aspects of some representative methods of time-frequency analysis, including Short Time Fourier Transform, Gabor Transform, Wigner-Ville Transform and Cone-Shaped Transform are described in this paper. Unfortunately, there is no correlation between the width of the time-frequency window and its frequency content in the t/f analysis. This property is not valid in the case of a wavelet transform. A wavelet is a wave-like oscillation, which forms its own “wavelet window”. Compression of the wavelet narrows the window, and vice versa. Individual wavelet functions are well localized in time and simultaneously in scale (the equivalent of frequency). The wavelet analysis owes its effectiveness to the pyramid algorithm described by Mallat, which enables fast decomposition of a signal into wavelet components.

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