Gongcheng Kexue Yu Jishu/Advanced Engineering Science

A segmentation network of Tiny cracks (TCS-Net) is proposed to solve the problems of small cracks with few pixels, low contrast between cracks and background, much interferences from similar textures, and uneven illumination. TCS-Net has a coding-decoding structure similar to that of U-Net network. The soft Pooling was used in down-sampling process to preserve the basic features of original images while maintaining the amplification of high-response features, thus reducing information loss and preserving the details and location of crack edges. In the up-sampling process, a semantic compensation module combining channel attention and spatial attention was added at the decoding end to fuse the features of each layer at the coding end, which could enhance the multi-scale details of cracks.In view of the classification problem of unbalanced data in crack segmentation task, in order to avoid the training process being dominated by most classes (background pixels), the binary cross entropy loss and Dice coefficient were combined by TCS-Net model as the objective loss function to solve the problem of training instability caused by attention tendency of single loss. It can also optimize performance indicators such as accuracy, crossover ratio and recall rate. Compared with the existing mainstream semantic segmentation models, TCS-Net fracture segmentation model improves the intersection over union ratio index by 5%~9% and recall ratio index by 9%~13%,which demonstrates that the model achieves higher detection rate and detection accuracy. The proposed TCS-Net can be effectively applied to the fine crack segmentation task under the conditions of serious imbalance between target and background, complex background with many disturbances

Deep geotechnical engineering often faces complex variable temperature environments. The thermal cycle effect of rock mechanical properties is important for the stability evaluation of reservoir and surrounding rock and the rational utilization of rock materials. For fine grained dense granite geothermal reservoir, its mechanical properties are related to energy-efficient exploitation and engineering safety. Therefore, thermal cycling experiment, uniaxial compression experiment, and optical microscope observation experiment were carried out to study the failure characteristics, the changes in mechanical parameters, and the influence mechanism of fine grained dense structure on the mechanical properties of granite. The results showed that the changing trend of rock failure characteristics and mechanical properties with the temperature and times of thermal cycle was closely related to the structure. For the fine grained dense granite, the uniaxial compressive strength and elastic modulus gradually decreased with the increase of upper limit temperature and times of thermal cycle, and the reduction rate of compressive strength became slow after more than 10 thermal cycles. The increase of the upper limit temperature of the thermal cycle can improve the sensitivity of the mechanical properties of granite to the deterioration of the thermal cycle. Internal thermal cycling at 300 ℃ would not change the brittle failure characteristics of fine grained dense granite. The microscopic observation and analysis show that the thermal cycle could significantly promote the crack propagation of granite. After 20 thermal cycles at 20～300 ℃, the linear crack density was 1.69 mm–1, which was 1.5 times that of one thermal cycle. Due to the fine and dense structure, the expansion and compaction effect of granite mineral particles was constrained, resulting in the predominance of crack initiation and propagation evolution induced by thermal stress, and then the macro mechanical parameters decreased nonlinearly with the corresponding linear crack density. This study had a certain reference value for the exploration of deep geotechnical engineering mechanics problems in variable temperature environments

As an efficient, accurate and convenient flow measurement instrument, electromagnetic flowmeter is widely used in the measurement of conductive fluids such as industrial fluid measurement, oilfield drilling fluid measurement and blood measurement. Due to the influence of external disturbance and flow velocity distribution, the electromagnetic flowmeter still has the problem of low measurement accuracy in the process of flow measurement. Improving the structure of the electromagnetic flowmeter excitation coil is one of the important means to improve accuracy. In this paper, based on a new type of positive eight sides, the accuracy of electromagnetic flow measurement was improved with magnetic field coil. Firstly, based on the study of the optimization principle of the weight function, the theoretical model of the magnetic field of the regular octagonal coil was analyzed to obtain the optimization idea of the electromagnetic flowmeter based on the uniform magnetic field theory. Secondly, based on the finite element analysis software, a simulation model of the regular octagonal excitation coil electromagnetic flowmeter was established, and the optimal structural parameters of the regular octagonal excitation coil magnetic field distribution were determined. By comparing the weight function distribution of the circular and square coils under the same conditions, the advantages of the uniformity of the weight function distribution of the regular octagonal coil were proved. Finally, an experimental platform was built to verify the magnetic field test experiment and the fluid test experiment. The magnetic field test results showed that the magnetic induction intensity of the regular octagonal coil electromagnetic flowmeter can be maintained at the central area of the pipeline. About 2.063 mT, the overall magnetic induction intensity fluctuation range is within 0.11 mT, indicating that the regular octagonal coil magnetic field has good uniformity. The fluid test result showed that when the flow rate is 0.743~2.582 m/s, the single-point relative indication value The maximum error is only 0.950%, and the system repeatability error is below 1.034%. The optimized system improves the measurement accuracy, which has guiding significance for the subsequent design of the excitation coil of the electromagnetic flow meter

The coal dust disaster is serious in deep mining of coal mine. The use of nonionic surfactant can effectively improve the wettability of coal dust and inhibit the generation and diffusion of coal dust. In order to explore the wetting process and mechanism of different surfactants on coal dust surface, the effects of nonionic surfactants lauryl glucoside (APG) and Triton X–100 on the wettability of coal dust surface were studied by molecular dynamics simulation and experiment. Three coal–water interface adsorption system models were established based on benzene ring carbon skeleton structure. Analysis the adsorption equilibrium configurations and spatial distribution of the surfactant on surface of coal were calculated on the basis of the interaction energy between coal/surfactant/water and energy changes, looked at the two kinds of surfactants and the ability of water molecules to form hydrogen bond. The coal samples from three groups of coal seams in Pingdingshan mining area in Henan Province were tested, the experiments of sedimentation and contact angle were carried out, and the surface free energy composition of the coal samples was calculated. The simulation results were verified, the characteristics of aromatic hydrocarbon groups in the coal samples and the interaction mechanism between Triton X–100 and coal molecules were tested by Fourier infrared spectroscopy (FT–IR). The results showed that when the adsorption equilibrium state is reached, the non-ionic surfactant molecules are connected with each other through alkyl chains to form an aggregation state, which is distributed at the coal water interface and the water gas interface. Triton X–100 can promote the adsorption of water molecules on the coal surface by enhancing the interaction with water molecules, which has a great impact on the wettability of the coal surface. The indoor test results showed that the wetting effect of Triton X–100 on the coal surface is better than APG, and the effect is the best at the critical micelle concentration. The higher the content of aromatic hydrocarbons in coal dust, the better the adsorption of Triton X–100. The research results provided a theoretical support and guidance for scientific and efficient dust suppression in deep mining

Alkali-resistant glass fiber has good mechanical performance, economy and durability. By adding alkali-resistant glass fiber, cement-based composites can be well strengthened, which has a wide range of engineering application prospects. To study the compressive properties and the stress–strain relationship of alkali-resistant glass fiber engineered cementitious composites (ECC), 33 groups of high-performance cement-based material specimens were tested under axial load. The effects of fiber content, fiber length, and water-cement ratio on the compressive properties and stress–strain relationship of alkali-resistant glass fiber ECC were emphatically analyzed, and the calculation model for the stress–strain relationship of alkali-resistant glass fiber ECC was proposed. The results show that the crack resistance, mechanical property, and deformation capacity of cement-based materials can be significantly improved by adding alkali-resistant glass fiber under uniaxial compression. The improvement of compressive strength and deformation capacity of the alkali-resistant glass fiber ECC is related to the fiber content, fiber length, and water-cement ratio. The compressive strength and deformation capacity of alkali-resistant glass fiber ECC specimens roughly tend to increase with the increase of fiber content and length, but the compressive strength of specimens decreases due to the obvious “agglomeration” phenomenon when the fiber content is too much. The compressive strength of specimens is mainly affected by the water-cement ratio, and it exhibits smaller with a larger water-cement ratio. When the fiber mass content is 6.5%, the fiber length is 18 mm and the water-cement ratio is 0.32, the comprehensive mechanical properties of alkali-resistant glass fiber ECC are relatively better, and compared with the comparison specimens, the compressive strength and deformation capacity can be increased by 25.6% and 88.0%, respectively. The calculation results of the proposed stress–strain relationship model are in good agreement with the experimental values, which can be used to describe the whole process of compression failure of alkali-resistant glass fiber ECC.