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• A poro-visco-VIB is developed to simulate the time-dependent porous rock. • Porosity- and stress-dependent permeability of the porous rock and fracture are considered. • Stress reorientation near wellbore in production is studied. • Hydraulic refracture by plugging treatment is studied. The refracture is a promising restimulation technique in the unconventional reservoir during production. It can be realized due to the stress reorientation. To study the mechanism of stress reorientation and refracturing behaviors, a new poro-visco-VIB (virtual internal bond) method is developed in this paper. In the framework of Boit's theory, the visco-VIB is used to describe the skeleton instead of the conventional continuum constitutive model. Through this poro-visco-VIB, both the time- and stress-dependent behaviors of the porous rock can be well simulated. The simulation results of stress reorientation show that the smaller in-situ stress difference can result in a larger stress reorientation scope. To include the fractures into the numerical model, the element partition method (EPM) is adopted. By this VIB/EPM method, the refracture by plugging is studied. The results indicate the plugging position significantly impacts the reorientation distance of refracture. The reorientation distance by plugging fracture end is much larger than by plugging fracture mouth. Thus, it is critically important to control the plugging position in refracture treatment. These findings provide valuable references for the refracture design. It also provides an efficient approach to hydraulic fracture simulation with consideration of the porosity and the time-dependency effect. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates the fault detection problem for uncertain linear time invariant (LTI) systems subject to polytopic uncertainties, exploiting some properties provided by the observer-based robust fault detection filter (RFDF), which has possible applications in practical power systems. By means of parameter-dependent Lyapunov functions, the existence condition of RFDF is assessed through solving a group of linear matrix inequalities (LMIs). In order to further reduce the conservativeness, an efficient algorithm in terms of LMIs by generating homogeneous polynomial parameter-dependent Lyapunov functions of arbitrary degree on the uncertain parameters is presented, which includes as special case existing conditions for RFDF design. It can be established that as the degree of the polynomial increases, the number of LMIs and free variables increases and the test becomes less conservative. Moreover, the fault sensitivity index can be optimized via a convex optimization algorithm, leading to the optimal RFDF. The methodology proposed can also be applied to other relevant aspects such as determining the threshold. An uncertain LTI power system model is adopted as an illustrated example to demonstrate the efficacy of the proposed methods when compared to other methods from the literature. [Copyright &y& Elsevier]