Particle Flow Characteristics and Transportation Optimization of Superfine Unclassified Backfilling

In order to investigate the high volume fraction problem of the solid phase in superfine unclassified backfilling pipeline transportation, characteristic parameters were obtained by fitting to test data with an R–R particle size distribution function; then, a Euler dense-phase DPM (Discrete phase model) model was established by applying solid–liquid two-phase flow theory and the kinetic theory of granular flow (KTGF). The collision and friction of particles were imported by the UDF (User-define function) function, and the pipeline fluidization system, dominated by interphase drag forces, was analyzed. The best concentration and flow rate were finally obtained by comparing the results of the stress conditions, flow field characteristics, and the discrete phase distributions. It is revealed that reducing the concentration and flow rate could control pressure loss and pipe damage to a certain degree, while lower parameters show negative effects on the transportation integrity and backfilling strength. Indoor tests and field industrial tests verify the reliability of the results of the numerical simulations. Research shows that the model optimization method is versatile and practical for other, similar, complex flow field working conditions

A Flexible Polynomial Expansion Method for Response Analysis with Random Parameters

The generalized Polynomial Chaos Expansion Method (gPCEM), which is a random uncertainty analysis method by employing the orthogonal polynomial bases from the Askey scheme to represent the random space, has been widely used in engineering applications due to its good performance in both computational efficiency and accuracy. But in gPCEM, a nonlinear transformation of random variables should always be used to adapt the generalized Polynomial Chaos theory for the analysis of random problems with complicated probability distributions, which may introduce nonlinearity in the procedure of random uncertainty propagation as well as leading to approximation errors on the probability distribution function (PDF) of random variables. This paper aims to develop a flexible polynomial expansion method for response analysis of the finite element system with bounded random variables following arbitrary probability distributions. Based on the large family of Jacobi polynomials, an Improved Jacobi Chaos Expansion Method (IJCEM) is proposed. In IJCEM, the response of random system is approximated by the Jacobi expansion with the Jacobi polynomial basis whose weight function is the closest to the probability density distribution (PDF) of the random variable. Subsequently, the moments of the response can be efficiently calculated though the Jacobi expansion. As the IJCEM avoids the necessity that the PDF should be represented in terms of the weight function of polynomial basis by using the variant transformation, neither the nonlinearity nor the errors on random models will be introduced in IJCEM. Numerical examples on two random problems show that compared with gPCEM, the IJCEM can achieve better efficiency and accuracy for random problems with complex probability distributions

Special Equipment Safety Supervision System Architecture Based on Blockchain Technology

With the use of the traditional safety supervision system of special equipment, the job burnout of supervision participants and other supervision problems emerge endlessly, which leads to the supervision for the prevention of safety accidents being greatly weakened. In recent years, the significance of introducing new technology to improve the original supervision system for safety accident prevention has been constantly growing. In this paper, based on the current situation of China’s special equipment safety supervision, we summarize several specific requirements for improving the supervision system, namely efficient accident responsibility tracing, more transparent, more efficient data sharing, and integrating more functions. On this basis, we have designed a new system architecture, by introducing the permissioned blockchain technology, which can meet all the improvement requirements and adapt to the technical features of safety supervision work. The extensibility design of the system architecture can meet the new requirements in future work. The design idea of the system architecture can not only be used in the field of special equipment, but can also be used for reference by other fields with safety supervision requirements

Research on the Pore Evolution of Sandstone in Cold Regions under Freeze-Thaw Weathering Cycles Based on NMR

The evolution of the rock pore structure is an important factor influencing rock mechanical properties in cold regions. To study the mesoscopic evolution law of the rock pore structure under freeze-thaw weathering cycles, a freeze-thaw weathering cycle experiment was performed on red sandstone from the cold region of western China with temperatures ranging from -20°C to +20°C. The porosity, T2 spectral distribution, and magnetic resonance imaging (MRI) characteristics of the red sandstone after 0, 20, 40, 60, 80, 100, and 120 freeze-thaw weathering cycles were measured by the nondestructive detection technique nuclear magnetic resonance (NMR). The results show that the porosity of sandstone decreases first and then increases with the increase of the freeze-thaw weathering cycles and reaches the minimum at 60 of freeze-thaw weathering cycles. The evolution characteristics of porosity can be divided into three stages, namely, the abrupt decrease in porosity, the slow decrease in porosity, and the steady increase in porosity. The evolution characteristics of the T2 spectrum distribution, movable fluid porosity (MFP), and MRI images in response to the freeze-thaw weathering process are positively correlated with the porosity. Analysis of the experimental data reveals that the decrease in the porosity of the red sandstone is mainly governed by mesopores, which is related to the water swelling phenomenon of montmorillonite. Hence, the pore connectivity decreases. As the number of freeze-thaw cycles increases, the effect of the hydrophysical reaction on the porosity gradually disappears, and the frost heaving effect caused by the water-ice phase transition gradually dominates the pore evolution law of red sandstone

Influence of Chemical Corrosion on Pore Structure and Mechanical Properties of Sandstone

Chemical corrosion plays a significant role in affecting the properties of rock materials. To understand the effects of chemical corrosion on the pore structure and mechanical properties of sandstones, porosity, T2 spectrum distribution, and NMR images of sandstone specimens were measured after every 10 days of immersion in chemical solutions using the nuclear magnetic resonance (NMR) technique. Static uniaxial compressive tests and dynamic compressive tests were conducted using a conventional servo-controlled testing machine and a split Hopkinson pressure bar (SHPB) system for specimens treated with chemical corrosion. The test results showed that after being treated with chemical corrosion, the porosity of a specimen increased, the T2 spectrum distribution would successively shift towards the right, and the distribution of pores tended to become more irregular. Additionally, all of the compressive strength and elastic modulus of sandstone treated with chemical corrosion under static and dynamic loads decreased, and the peak strain increased. The effect order of a chemical solution on the pore structure and mechanical properties of sandstone was H2SO4>NaOH>distilled water, which would be related to the different mechanisms of a water-rock reaction. According to the experimental results, the correlations between the mechanical properties and porosity were established. The results can serve as a reference for research in related fields

Strength Characteristics and the Reaction Mechanism of Stone Powder Cement Tailings Backfill

Stone powder cement (SPC) is widely used as a novel cement substitute material in concrete for its good gelling performance and low cost. In order to reduce the backfilling cost and assess the potential of SPC backfilling materials, a series of experiments were conducted to analyze the strength and hydration reaction mechanism of stone powder cement tailings backfill (SPCTB). The analysis was based on SPC and tailings, which were used as the gelling agent and the aggregate, respectively. The results showed that the strength of the backfill was greatly reduced at an early stage and slightly reduced in the final stages. The stone powder content was less than 15%, which met the requirement of mining procedure. The addition of stone powder reduced the content of adsorbed water and capillary water in the early stages, while it increased in the middle stages. The SiO2 contained in stone powder reacted with the hydration products at later stages, which is the reason why the growth of strength is rapid between the groups with the addition of stone powder. The addition of stone powder improved the microstructure of backfill and produced a denser three-dimensional (3D) network structure; however, the plane porosities of Groups A and B gradually increased with the increase in the content of stone powder. The cement powder mixed appropriately with the stone power could meet the strength requirement and reduce the cost of backfilling materials