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Featured Application: The XGBoost–GR–stacking gas outburst early warning model established in this article demonstrates high accuracy and practical performance, making it suitable for gas outburst risk warning in mining safety. To improve the accuracy of gas outburst early warning, this paper proposes a gas outburst risk warning model based on XGBoost–GR–stacking. The statistic is based on gas outburst data from 26 mines and establishes a data generation model based on XGBoost. The obtained virtual datasets are analyzed through visualization analysis and ROC curve analysis with respect to the original data. If the augmented data has an ROC area under the curve of 1, it indicates good predictive performance of the augmented data. Grey correlation analysis is used to calculate the grey correlation degrees between each indicator and the "gas emission". The indicator groups with correlation degrees greater than 0.670 are selected as the main control factor groups based on the sorting of correlation degrees. In this study, SVM, RF, XGBoost, and GBDT are selected as the original models for stacking. The original data and virtual data with correlation degrees greater than 0.670 are used as inputs for SVM, RF, XGBoost, GBDT, and stacking fusion models. The results show that the stacking fusion model has an MAE, MSE, and R2 of 0.031, 0.031, and 0.981. Comparing the actual and predicted values for each model, the stacking fusion model achieves the highest accuracy in gas outburst prediction and the best model fitting effect. [ABSTRACT FROM AUTHOR]

To improve the accuracy of gas outburst early warning, this paper proposes a gas outburst risk warning model based on XGBoost–GR–stacking. The statistic is based on gas outburst data from 26 mines and establishes a data generation model based on XGBoost. The obtained virtual datasets are analyzed through visualization analysis and ROC curve analysis with respect to the original data. If the augmented data has an ROC area under the curve of 1, it indicates good predictive performance of the augmented data. Grey correlation analysis is used to calculate the grey correlation degrees between each indicator and the “gas emission”. The indicator groups with correlation degrees greater than 0.670 are selected as the main control factor groups based on the sorting of correlation degrees. In this study, SVM, RF, XGBoost, and GBDT are selected as the original models for stacking. The original data and virtual data with correlation degrees greater than 0.670 are used as inputs for SVM, RF, XGBoost, GBDT, and stacking fusion models. The results show that the stacking fusion model has an MAE, MSE, and R2 of 0.031, 0.031, and 0.981. Comparing the actual and predicted values for each model, the stacking fusion model achieves the highest accuracy in gas outburst prediction and the best model fitting effect.

Featured Application: It solves the bottleneck problem of the low permeability of deep coal seams and the difficulty of coalbed methane mining, greatly improves the efficiency of coalbed methane mining, and reduces the risk of coal mining, which is of great significance to the project. To solve the bottleneck problem of low deep coal seam permeability and difficult coalbed methane (CBM) mining. Combining hydraulic splitting technology and directional drilling technology, a directional hydraulic splitting enhancement method of deep CBM mining was proposed. The selection equation for the directional hydraulic splitting of deep coalbed was constructed. The numerical simulation reveals the variation in coal fractures around different split angles. The split angle under the maximum coal damage effect was obtained. It was found that the combined effect of the double crack damage disturbance region led to reciprocal stress fluctuations during crack development and, eventually, the formation of a zigzag fracture. The larger the splitting angle, the larger the fissure development length and the larger the coal-damaged area. A double crack takes 25% less time to complete propagation than a single crack. When the splitting angle is 90°, the disturbed area occupies 2/3 of the area around the borehole, and the overall fracturing effect is the best. In the application process, the new directional hydraulic splitting technology can increase CBM mining by 5.08%, greatly improve CBM mining efficiency, and reduce the coal mining risk, which is of great significance to the project. [ABSTRACT FROM AUTHOR]

To solve the bottleneck problem of low deep coal seam permeability and difficult coalbed methane (CBM) mining. Combining hydraulic splitting technology and directional drilling technology, a directional hydraulic splitting enhancement method of deep CBM mining was proposed. The selection equation for the directional hydraulic splitting of deep coalbed was constructed. The numerical simulation reveals the variation in coal fractures around different split angles. The split angle under the maximum coal damage effect was obtained. It was found that the combined effect of the double crack damage disturbance region led to reciprocal stress fluctuations during crack development and, eventually, the formation of a zigzag fracture. The larger the splitting angle, the larger the fissure development length and the larger the coal-damaged area. A double crack takes 25% less time to complete propagation than a single crack. When the splitting angle is 90°, the disturbed area occupies 2/3 of the area around the borehole, and the overall fracturing effect is the best. In the application process, the new directional hydraulic splitting technology can increase CBM mining by 5.08%, greatly improve CBM mining efficiency, and reduce the coal mining risk, which is of great significance to the project.

We propose a second order exponential scheme suitable for two-component coupled systems of stiff evolutionary advection–diffusion–reaction equations in two and three space dimensions. It is based on a directional splitting of the involved matrix functions, which allows for a simple yet efficient implementation through the computation of small sized exponential-like functions and tensor-matrix products. The procedure straightforwardly extends to the case of an arbitrary number of components and to any space dimension. Several numerical examples in 2D and 3D with physically relevant (advective) Schnakenberg, FitzHugh–Nagumo, DIB, and advective Brusselator models clearly show the advantage of the approach against state-of-the-art techniques. • Efficiently solved multi component systems of 2D and 3D ADR equations. • Developed a second order direction split exponential integrator. • Solved important models, such as DIB, Schnakenberg, FitzHugh–Nagumo, and Brusselator. • Showed superiority in terms of achieved accuracy and wall-clock time with respect to established methods. [ABSTRACT FROM AUTHOR]

Transformation of a random variable is a common need in a design of many algorithms in signal processing, automatic control, and fault detection. Typically, the design is tied to an assumption on a probability density function of the random variable, often in the form of the Gaussian distribution. The assumption may be, however, difficult to be met in algorithms involving non‐linear transformation of the random variable. This paper focuses on techniques capable to ensure validity of the Gaussian assumption of the non‐linearly transformed Gaussian variable by approximating the to‐be‐transformed random variable distribution by a Gaussian mixture (GM) distribution. The stress is laid on an analysis and selection of design parameters of the approximate GM distribution to minimise the error imposed by the non‐linear transformation such as the location and number of the GM terms. A special attention is devoted to the definition of the novel GM splitting directions based on the measures of non‐Gaussianity. The proposed splitting directions are analysed and illustrated in numerical simulations. [ABSTRACT FROM AUTHOR]

• A visualized numerical model of polymer directional fracturing grouting considering the time-varying viscosity and swelling characteristics of slurry was established. • The diffusion mechanism of directional fracturing of polymer under the influence of grouting hole type, grouting amount, grouting rate, soil elastic modulus and cohesion was revealed. • A small fracturing pore-forming device was developed, and the polymer directional splitting grouting technology was applied to the practice of slope anti-seepage reinforcement engineering. • High density electrical method and DCP penetration test were used to evaluate the anti-seepage reinforcement effect. The split grouting method can play a very good anti-seepage and reinforcement effect for some soil dykes that are not compacted or have hidden dangers such as leakage channels, soft layers, cracks, biological caves and so on. The polymer oriented splitting grouting technology is a new measure with high efficiency, minimally invasive and no need for maintenance. The research literature on the application of polymer oriented splitting grouting technology in the field of seepage prevention and reinforcement of soil dyke is quite limited. In this paper, the law of directional splitting and diffusion of non-aqueous polymer grouting materials is studied. In view of the difficulty in simulating the dynamic process of directional splitting grouting of polymer by existing numerical methods, a visual model of directional splitting grouting process of polymer was established by using discrete element particle flow program (PFC2D) considering the influence of the expansion characteristics and viscosity of polymer materials with time, and the field test was carried out. The results show that the polymer directional splitting grouting process can be divided into four stages: filling, extrusion, split-extrusion cycle and final extrusion, and the final shape of slurry veins is "spindle". In addition, through the numerical simulation of PFC2D, it is found that the diffusion shape of polymer grouting materials is affected by the shape of grouting hole, the amount of grouting, the rate of grouting, the elastic modulus of soil and the cohesion of soil, and can play a role in filling and compacting soil to a certain extent. Finally, the application of polymer oriented splitting grouting is carried out for the leakage danger of a canal embankment project. Through the in-situ standard penetration test and high density electrical detection, it is proved that the polymer oriented splitting grouting technology can quickly stop the water and compacted the soil, and further improve the stability and integrity of the soil embankment. [ABSTRACT FROM AUTHOR]

ABSTRACT A compact representation is obtained for the separation of a scalar wavefield on a closed surface into parts due to internal and external sources. The formula assumes that the total field and its gradients are known on the surface, as is the exact Green function of the medium. The derivation involves four rather straightforward applications of Green's theorem or the representation theorem, though it is a remarkable result in that waves from either source that traverse the boundary many times are appropriately separated. The intermediate results at the four steps of the derivation also shed light on the possibility of acoustic shielding from unwanted sources without knowledge of the Green function for the medium. [ABSTRACT FROM AUTHOR]

Natural convection heat transfer in rectangular enclosures is an active research area, due to its significance for both fundamental interest and engineering applications such as thermal management of electronic components. In this present numerical study, combined conduction and natural convection have been analysed for one or two heat sources mounted on substrates in an enclosure. For one heat source, the substrate is mounted on a vertical wall, and for the case of two heat sources, the substrates are mounted vertically and horizontally. Buoyancy forces drive the fluid flow. The Picard method with a hybrid grid system is utilized to decouple between pressure and velocity components, resulting in componentwise splitting. Linear systems obtained via the Picard method have been solved by the ADI method, resulting in directional splitting. Effects of different parameters such as Prandtl number, Rayleigh number, and boundary conditions on the temperature and flow field have been analysed. [ABSTRACT FROM AUTHOR]

Abstract: We present a second-order γ-model BGK scheme for compressible multimaterial flows, which extends the authors'' earlier work on a first-order scheme [S. Jiang, G. Ni, A γ-model BGK scheme for compressible multifluids, Internat. J. Numer. Methods Fluids 46 (2004) 163–182]. The scheme is based on the incorporation of a conservative γ-model scheme given in [R. Abgrall, How to prevent pressure oscillations in multicomponent flow calculations: A quasi conservative approach, J. Comput. Phys. 125 (1996) 150–160] into the gas kinetic BGK scheme [K.H. Prendergast, K. Xu, Numerical hydrodynamics from gas-kinetic theory, J. Comput. Phys. 109 (1993) 53–66; K. Xu, K.H. Prendergast, Numerical Navier–Stokes solutions from gas kinetic theory, J. Comput. Phys. 114 (1994) 9–17]. Several numerical examples presented in this paper validate the scheme in numerical simulations of compressible multifluids. [Copyright &y& Elsevier]