Archive of

Advanced Engineering Science

Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-12-01-2022-103

Abstract :

China is one of the countries with the most serious disasters of dammed lakes, where the dammed lakes pose a great threat to the safety of people’s lives and properties among the upstream inundated area and the downstream outburst flood routing area. A deep understanding of the scouring and breaching processes of landslide dam can provide important scientific and technological basis for the design of emergency discharge channel and the formulation of downstream emergency measures. According to the event of 2018 Baige landslide-dammed lake in the Jinsha River, the scouring and breaching processes of landslide dam were systematically studied by conducting the laboratory physical modeling tests. Test results showed that the erosion and breaching processes of landslide dam could be divided into four stages, i.e., flow incubation stage, retrogressive scouring stage, dam break development stage, and riverbed rebalancing stage. When the retrogressive erosion scarp was traced back to the upstream slope top and the inlet section of the discharge channel was eroded, the discharge channel would connect to form a ramp with the bottom slope i>0. Then the flow velocity and flow rate increase suddenly, and the dam break developed rapidly. The results also showed that when the excavation width of the chute remained constant and the depth increased, the peak flow would decrease, the peak time would be delayed and the process of the burst flow became smoother; when the depth of the chute was fixed, the peak time would be delayed as the width increased. Finally, according to the testing results, some suggestions were put forward for the optimal design of the discharge channel: The location of the discharge channel should be arranged in the pass with the lowest crest elevation to reduce the peak flow and shorten the breaching time; when excavating the spillway, priority should be given to increasing its depth to minimize the water level of the dammed lake during dam breaching.

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-12-01-2022-102

Abstract :

Three kinds of magnesium-based foamed concrete with dry density grade A05 were prepared by chemical foaming with magnesium oxychloride cement, magnesium oxysulfide cement and magnesium phosphate cement as cementing materials respectively. By designing orthogonal tests, the influences of water/cement ratio, magnesium cement component ratio, retarder content, fly ash content and polypropylene fiber content on the compressive strength of three kinds of magnesia-based foamed concrete were determined, the action mechanisms of the important influencing factors were compared and analyzed, and the functional relationships between the specific strength of magnesium-based foamed concrete and the component ratio parameters of magnesium-based foamed concrete were established. The results showed that the primary and secondary factors affecting the compressive strength of magnesium oxychloride foamed concrete were the ratio of magnesium cement components>water/cement ratio>fly ash content>polypropylene fiber content>retarder content. The influence of various factors on compressive strength of magnesium oxysulfide foam concrete was the same as that of magnesium oxychloride foam concrete.The relationship between the factors influencing the compressive strength of magnesium phosphate foamed concrete was as follows: the ratio of magnesium cement components>retarder content>water/cement ratio>fly ash content>polypropylene fiber content. Different from magnesium oxychloride foam concrete and magnesium oxysulfide foam concrete, the content of retarder had a higher degree of influence. The component ratio of magnesium cement was an important index affecting the strength of magnesia-based foamed concrete. The compressive strength of magnesium oxychloride foamed concrete and magnesium sulfide foamed concrete had the same change trend with the increase of the component ratio of magnesium cement, both of which first decreased and then increased, while magnesium phosphate foamed concrete showed the trend of first increased and then decreased with the increase of the component ratio of magnesium cement. There was a power function relationship between the specific strength of three kinds of magnesium-based foamed concrete and the component ratio of magnesium-based foamed concrete.

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-12-01-2022-101

Abstract :

Frequency diverse array (FDA) radar applies a small frequency offset between the adjacent elements to synthesize a range-angle-dependent beampattern. It is difficult to control the beam steering for the coupled time-variant beampattern. For this problem, the time-variant characteristic and point beam forming of FDA radar were mainly studied in the paper. Firstly, the characteristic of transmit beampattern of FDA using linearly increasing frequency increment was analyzed. Secondly, two signal models of FDA using logarithmically frequency increments (log–FDA) and multicarrier frequency increments (multi-FDA) were constructed, where the multi-FDA transmit beampattern has lower sidelobes. Then, the relationship between the time variable of the frequency increase term and the time variable of the propagation term in the two time modulated signal models was studied in detail. If both of them are the same, the time-varying characteristics of the transmit beampattern can be eliminated by the two time variables offset. However, they have different physical meanings. When the electromagnetic signal is generated and propagated in space, the time variable in the frequency increase term will not change, whereas the time variable of the propagation term in the propagation process is related to the propagation characteristics of the electromagnetic wave, which is a variable quantity, so the two time variables cannot offset each other. Finally, the simulation results verify the correctness of the transmit beampattern analysis of time modulated FDA radar, and demonstrate that the spot transmit beampattern with dynamic forward propagation can be synthesized using log–FDA and multi-FDA, where the beampattern of the multi-FDA has lower sidelobes.

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-12-01-2022-100

Abstract :

In order to alleviate the burden of continuous increasing energy consumption falling on the power system and solve the complex calculation problem in the joint dispatching of large-scale electrical equipment, a hybrid decentralized optimization of dispatching the large-scale controllable appliances and energy storage equipment considering demand side response was proposed in this paper. Firstly, two mathematical models of controllable electrical equipment load and energy storage equipment were established. On this basis, a mixed integer non-linear centralized optimization model was mathematically formulated under the constraints of the operation characteristics of the system and equipment, with the objective of minimizing the sum of electricity purchase cost, users’ dissatisfaction cost and energy storage equipment loss cost. Secondly, for tackling the difficult nonlinear centralized optimization problems of high dimensionality, multi objectives and multiple constraints, the Lagrange relaxation method was used to decompose the problem into two sub-problems, namely, optimally scheduling the controllable electrical equipment load and optimizing the dispatch of the energy storage equipment. Then, the former was further decomposed into optimizing dispatch of each controllable electrical equipment and solved by the interior point method, while the latter was decomposed into a set of mixed integer linear optimization sub-problems of scheduling each energy storage equipment and solved in parallel by the Benders decomposition method. Thirdly, a series of numerical simulations together with comparison analysis were performed to verify the effectiveness and superiority of the proposed dispatch optimization method. For example, the optimization objective value and the optimal dispatch solution corresponding to the proposed method were illustrated and compared with those of the centralized method to demonstrate the effectiveness of the hybrid decentralized optimization method. And the influence of different numbers of dispatching equipment on the computation efficiency was investigated on the centralized and decentralized optimization method to show the superiority of the proposed hybrid decentralized optimization method. According to the numerical simulation results, the optimization objective value of the proposed method is basically consistent with that of the centralized. Moreover, the identified dispatch solution enables to efficiently respond to the time-of-use and results in good effect of peak-shaving and valley-filly. Besides, the calculation efficiency of the proposed hybrid decentralized optimization method is of high computation efficiency and not affected by the increasing number of the schedulable electrical equipments.

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-12-01-2022-99

Abstract :

Exploring the fluid flow mechanism in rock masses is of great significance for preventing water inrush during excavation of underground constructions such as tunnels. Quantitative descriptions of the hydraulic properties of single rock fracture subject to normal stresses and shear displacement are the basis for understanding the coupled hydro-mechanical processes in fractured rock masses; however, the quantitative relationships among stress, deformation, aperture, inertial coefficients have not been developed in previous works. Granite specimens with single fracture were prepared and flow tests with variable water heads were carried out, in which incremental normal stresses were applied at each fixed shear displacement to characterize the evolution of permeability. The surface morphology of fractures was digitalized using a three-dimensional high-resolution scanning system. A self-designed numerical code was employed to calculate the deformation of fractures under normal stresses based on the framework of variational principles in contact mechanics. The fracture deformation and void space variation under different shear displacements and normal stresses were investigated. By extracting the aperture data and solving Navier–Stokes equations using COMSOL software, a series of numerical simulations were performed to investigate the nonlinear flow behavior of fluids within fractures under different shear displacements and normal stresses. The relationships among shear displacement, normal stress, void space distributions and parameters describing the nonlinear flow were quantitatively analyzed. The results showed that the fracture surface damage areas obtained from the experiment agreed well with the numerical simulation results, which verified the reliability of the deformation calculation code. The normal stress and the shear displacement exhibited a decreasing power function and an increasing exponential function with the fracture aperture, respectively. The increase in the shear displacement resulted in the concentration of contact areas. The inertia coefficient B in the Forchheimer equation and the critical hydraulic gradient Jc could quantitatively characterize the nonlinear flow behavior. B and Jc exhibited decreasing power functions with the shear displacement. The increasing rates and ranges of Jc and B decreased gradually as shear advances. When the shear displacement increased from 2 to 8 mm, the range of Jc decreased from 6.10×10–3 to 1.20×10–3 by a rate of 80.32%. The range of B decreased sharply from 2.97×1014 Pa·s2·m–7 to 2.43×1013 Pa·s2·m–7 by a rate of 91.28%. A similar power function relationship existed between RSD~B and between RSD~Jc. Finally, a predictive function was proposed to quantify the onset of nonlinear fluid flow through fractures.

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