부산대학교 도서관

The stato-dynamic instability evolution is a process in which a system undergoes transition from a static (equilibrium) phase to dynamical state. The snow avalanche formation preceding release may pass through different phases of instabilities evolving within a snowpack on a slope from an initial static to dynamic phase of avalanche release. In this research work, the instability evolution within snow mass carried out under the laboratory conditions, monitored using Acoustic emission (AE), is presented to understand the mechanism of avalanche formation and release. For this purpose, the segregated (natural) snow particles were deposited in layers over a tilt-plane arrangement fixed at a particular angle using a remotely controlled mechanical system. Under the effect of gravitational pull on an inclined plane, the evolution of stato-dynamic instabilities prior to avalanche release (lab-scale) were monitored within the snow block using multi sensor AE network. Several resonant types AE sensors coupled to needle shaped waveguides were used to detect the AE activities within snow using broadband multichannel AE data acquisition system. In this work, a number of lab scale avalanche experiments were recorded in terms of the prominent AE parameters and voltage waveforms during the course of stato-dynamic instability evolution. The interpretation and analysis of AE voltage waveforms is carried out in terms of AE entropy (Hs), based on Shannon's information theory. The values of AE entropy are associated with the AE waveforms recorded at different stages of instability development which tend to follow an increasing trend until the failure. Further, a new parameter, Instability index (Iw) based on AE voltage waveforms, is formulated to measure the proportion of instability building up within a system prior to its failure. The rising trends of Instability index are consistent with the trends of AE entropy values during the stato-dynamic instability evolution within the snow block and the maximum values attributed to the lab scale avalanche. To predict the failure of snow mass, regression models are formulated based on the values of AE entropy and instability index. The results of experiments have verified that both the methods are efficient to elucidate the stato-dynamic instability development in the snowpack. The research work carried out is quite insightful to understand the instabilities evolving within an unstable snowpack on a slope during the avalanching process in terms of Acoustic emissions. [ABSTRACT FROM AUTHOR]