Numerical modeling of dispersion phenomena in thick plate
This paper reports on a technique for the analysis of propagating multimode signals. The method involves a 2-D Fourier transformation of the time history of the waves received at a series of equally spaced positions along the propagation path. The output of the transform being presented using an isometric projection that gives a 3-D view of the wave number dispersion curves. The time history of the waves was obtained by the commercial finite element (FE) code, MARC. The results of numerical studies and the dispersion curves of Lamb waves propagating in the 2.0-mm-thick steel plate are presented. The results are in good agreement with analytical predictions and show the effectiveness of using the 2-D Fourier transform method to identify and measure the amplitudes of individual Lamb modes.
Šíření elastických vln v prizmatických tělesech se strmými změnami tvaru
Due to using non-destructive diagnostics method - the acoustic emission- the best knowledge of the rules of the elastic wave propagation in bodies are required. So this work treats the elastic wave propagation in the basic elements of structures. The samples with the most common shape transitions are used - here experimental bodies with the offsets (like a stair shape) at various sizes. The results of the analytical computations (generalized ray theory), numerical simulations (the finite element method implemented in software MARC/MENTAT) and experimental results (broadband piezoceramics transducers) are verified and compared mutually.
Dispersion mode separation in ultrasonic signal processing
This paper reports on a technique for the analysis of propagating multimode signals. The method involves a 2-D Fourier transformation of the time history of the waves received at a series of equally spaced positions along the propagation path. The output of the transform being presented using an isometric projection that gives a 3-D view of the wave number dispersion curves. The time history of the waves was obtained by the commercial finite element (FE) code, MARC. The results of numerical studies and the dispersion curves of Lamb waves propagating in the 2.0-mm-thick steel plate are presented. The results are in good agreement with analytical predictions and show the effectiveness of using the 2-D Fourier transform method to identify and measure the amplitudes of individual Lamb modes.
The elastic wave propagation over the shape transitions of bodies
Due to using non-destructive diagnostics method - the acoustic emission- there is required the best knowledge about the rules of the elastic wave propagation in bodies. So this work treats the elastic wave propagation in the basic construction elements of structures. The samples with the most common shape transitions are used - here some experimental bodies with the shoulders (like a stair shape) at various sizes. The results of the analytical computations, numerical simulations and experimental results are verified and compared mutually. The generalized ray theory - one from the analytical methods - is applied. For the extensive numerical simulations the finite element method (implemented in software MARC/MENTAT) is used. The transient piezoceramics transducers are employed for the experimental measuring.
Zpracování signálů akustické emise waveletovými balíčky
Metoda waveletových balíčků je zobecněním waveletového rozkladu, které nabízí bohatší analýzu signálů. Jednotlivé waveletové balíčky popisují tři přirozeně interpretované parametry: pozice a škála (jako u waveletového rozkladu) a frekvence. Pro danou ortogonální waveletovou funkci se generuje knihovna bází waveletových balíčků. Každá báze představuje určitý způsob kódování signálů, který zachovává celkovou energii a umožňuje přesnou rekonstrukci původního signálu. Dále zbývá určit nejvhodnější bázi vzhledem ke kritériu založeném na výpočtu entropie. V závěru článku jsou uvedeny zkušenosti získané při kompresi signálů akustické emise waveletovými balíčky.
Numerical modeling and experimental evaluation of geometrical dispersion effects
For precise acoustic emission (AE) source localization and quantitative AE signal processing it is necessary to analyze signal distortion caused by wave propagation from the source to receiving sensor. Dominant wave modes propagating in thin-walled structures are so called guided waves which exhibit strong dispersion. Experimental determination of the structural impulse response, based on a point source/receiver technique, is necessary to evaluate signal distortion in such structures.
Analýza disperzních napěťových vln spojitou waveletovou transformací
The time-frequency analysis of dispersive stress waves is reviewed. It is shown that the wavelet transform using the Morlet pseudowavelet effectively decomposes the strain response into its time-frequency components and that the wavelet transform enables us to identify the dispersion relation of the group velocity.
Použití spojité waveletové transformace pro časofrekvenční analýzu disperzních napěťových vln
The time-frequency analysis of dispersive stress waves is reviewed. It is shown that the wavelet transform using the Morlet pseudowavelet effectively decomposes the strain response into its time-frequency components and that the wavelet transform enables us to identify the dispersion relation of the group velocity.
Analýza waveletovými balíčky
The wavelet packet method is a generalization of wavelet decomposition that offers a richer signal analysis. Wavelet packet atoms are waveforms indexed by three naturally interpreted parameters: position and scale (as in wavelet decomposition) and frequency. For a given orthogonal wavelet function, we generate a library of wavelet packet bases. Each of these bases offers a particular way of coding signals, preserving global energy and reconstructing exact features. The wavelet packets can then be used for numerous expansions of a given signal. We then select the most suitable decomposition of a given signal with respect to an entropy-based criterion.
Waveletový přístup k násobení matic
In this paper is described the algorithm for the rapid numerical applying a dense matrix N x N to a vector. As is well known, applying directly a dense N x N - matrix to a vector requires roughly N^2 operations, and this simple fact is a cause of serious difficulties encountered in large-scale computations. The algorithm of this paper require order O(N logN) operations.
