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1 Acta Geophysica

1 2006

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

Majewska Z., Mortimer Z.

Acta Geophysica

2006

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.