Characteristics Evolution of Multiscale Structures in Deep Coal under Liquid Nitrogen Freeze-Thaw Cycles

Liquid nitrogen freeze-thaw fracturing has attracted more and more attention in improving the coal reservoir permeability. In order to reveal the impact of liquid nitrogen freeze-thaw on the multiscale structure of deep coal, the multiscale structure evolution law of deep and shallow coal samples from the same seam in the Qinshui coalfield during the liquid nitrogen freeze-thaw cycling was investigated using NMR T 2 spectrum, NMRI, and SEM. The connectivity between mesopores and macropores in deep and shallow coal is improved after liquid nitrogen freeze-thaw cycles. The influence of liquid nitrogen freeze-thaw cycles on the structure evolution of deep and shallow coal is the formation and expansion of microscopic fractures. The initial NMR porosity of deep coal is lower than that of shallow coal from the same coalfield and coal seam. The NMR porosity of both the deep and shallow coal samples increases with the increase of the number of freeze-thaw cycles, and the NMR porosity growth rate of the deep sample is lower than that of the shallow sample.

Towards resilient water supply in centralized control and decentralized execution mode

This paper shares a vision that sustainable water supply requires resilient water infrastructures which are presumably in the centralized control and decentralized execution (CCDE) mode with multiscale resilience. The CCDE should be planned based on the multiscale structure of water infrastructures, in which the systems are divided into a number of hierarchically organized subsystems. The CCDE allows independent execution of all subsystems under normal situations yet coordination of subsystems at different scales to mitigate any disturbances during failure events, i.e. the multiscale resilience. This vision is discussed in detail for water distribution systems (WDSs). Specifically, the conceptual design of the multiscale CCDE is described, and progress on understanding the multiscale structures in WDSs is summarized based on the literature review. Furthermore, a few theories consistent with the multiscale CCDE concept are discussed which include the decomposition theorems, fractal theory, control theories, and complex network theory. The next step in the vision will be to identify the optimal multiscale structure for the CCDE based on the best trade-off of different goals of WDS analysis and management. This process needs supports from not only innovative modelling tools and extensive datasets and theories but also inspiring exemplar systems, e.g. natural systems.