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Chaotic behaviour of acoustic emission induced in hard coal by gas sorption-desorption

100%

Majewska Z. , Mortimer Z.

2006

tom Vol. 54, no. 1

50-59

This paper presents study of non-linear dynamics of acoustic emission (AE) generated in coal samples subjected to gas sorption-desorption. Carbondioxide and methane were used as sorbats. Experimental facilities used in high pressure sorption of CO2 and/or CH4 on coal comprised a pressure vessel and associated pressurisa-tion and monitoring systems. Tests were conducted on mediumrank coal obtained from the Upper Silesia Basin. Several approaches to the treatment of experimental results are proposed in order to detect and characterize deterministic chaos: (1) analysis of fractal/multi- fractal character of AE energy rate, using fractal generalised dimensions Dq(q); (2) analysis of temporal changes of AE energy rate and its fractal correlation di-mension D2; and (3) evaluation of attractor dimension within the reconstructed phase space from experimental time series. It was shown that AE generated during CO2 sorption on mediumrank coal is a more heterogeneous and lower dimensional process in comparison with AE induced by CO2 desorption. Yet, the AE associated with desorption of CO2 exhibits higher heterogeneity than the AE generated during desorption of CH4. There are certain similarities between changes of D2 during desorption of CO2 as well desorption of CH4. However, dynamics of these changes and character of time distributions of D2 differ, depending on a sorbate. We do not know the precise reason for observed differences, but we presume that the carbon-dioxide molecules dissimilarity to methane molecules can account for them.

Temporal variations of correlation dimensions of local mining seismicity with relation to the rockburst generating process

100%

Mortimer Z. , Luca L. D.

tom Vol. 47, nr 3

273-282

The studies concern variations in the spatial and temporal distribution of clusters of local mining induced seismic activity. As the descriptor of such clusters, the fractal correlation exponent dimension has been chosen. The results of testing on Monte Carlo simulated fractal sets show that a small size of temporal window allows us to get reliable estimates of correlation dimension and to study its variation as a short-time period precursor to rockbursts. The correlation between changes in time of spatial epicentre distribution D2 and temporal distribution Dt of epicentre and the occurrence of strong events was found, but not for the all data analysed. We cannot confirm the existence of some systematic evidence, but we found that an anomalous state of the fractal dimension could be observed prior to large events; however, there are no well determined features in its trend. Analysing the distribution of the intertime between the consecutive events, the dimension of its strange attractor has been calculated.

Badania dynamiki zdarzeń w przestrzeni fazowej procesu sejsmiczności indukowanej

80%

Laskownicka A. , Mortimer Z. , Korytowska B.

WUG : bezpieczeństwo pracy i ochrona środowiska w górnictwie

2006

tom nr 6

32-34

Prezentowane są badania wielowymiarowej przestrzeni fazowej strumienia sejsmiczności. Dynamika układu przejawia się przez zmiany zdarzeń sejsmicznych na trajektorii fazowej procesu. Wymiary przestrzeni fazowej i jej atraktor zostały oszacowane przy zastosowaniu szeregów czasowych uogólnionej odległości pomiędzy kolejnymi wstrząsami w przestrzeni energii i położenia zdarzeń.

Phenomena of mining induced seismicity are presented as nonlinear dynamics systems. The dynamics is characterized by changes of the seismic event position on the phase trajectory of the process. Embedded spaces constructed from the observations of individual variables were analysed. Dimensions of the phase space and its attractor were approximated based on the time series of the time distance and generalized distance between succeeding shocks, energy and the epicentre/hypocenter. Attention was chiefly concentrated on the generalized distances between succeeding shocks and their variations during high and low seismic activity.