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During urban flood events, the effect of urban rainwater pipeline siltation on overflow and stagflation intensifies the severity of flood disaster. However, the dynamic coupling mechanism of pipeline sedimentation and water flow is still unclear. To investigate the influence of two-phase flow on the hydraulic transport of siltation particles in rainwater pipelines, the numerical simulation model based on computational fluid dynamics (CFD) and discrete element method (DEM) is constructed. Then, the transient continuity governing equation and conservation equation of momentum are formulated to provide dynamic guidance and boundary constraint for CFD-DEM simulation. On this basis, the optimal drag force model and measurement method of equivalent siltation degree of pipeline are proposed and nested with CFD-DEM, and then, a high resolution numerical simulation model of pipeline sedimentation is formulated. The results show that the siltation degree affects the efficiency of drainage pipeline to a degree of 47%, which is much greater than the degree of influence of 33% for siltation length and 18% for slope. When the siltation degree is 0.1, the thickness of the silted bed surface under the influence of water flow scour is reduced by 33%. It revealed that the influence degree of siltation degree and flow rate was 168% and 20%, respectively, which was much larger than that of siltation length and slope. This study can provide technical support for subsequent pipeline cleaning and maintenance as well as flood prevention and mitigation. [ABSTRACT FROM AUTHOR]

With the increase in the length and age of urban sewer pipeline construction, black smelly water pollution caused by siltation and deposition has increased in sewer pipelines, affecting their flow capacity and increasing the risk of flooding. This presents a significant challenge to the water environment, urban environment, and human life and health. Hence, to investigate potential approaches for controlling pipeline siltation and deposition, governing equations and dynamic simulation model of fluid–structure coupling for silted pipeline are constructed by combining theory of fluid dynamics analysis, method of unit volume analysis, computational fluid dynamics (CFD), and discrete element method (DEM). Then, to predict sedimentation law of pipeline siltation particles with high accuracy, an adaptive punishment mechanism (APM) for intelligent prediction of particle settlement of pipeline sediment and hyperparameter optimization is adopted based on probability settlement function (PSF), non-dominated sorting genetic algorithm (NSGA) and multiscale bidirectional long short-term memory neural network (MBLSTM). By combining self-punishment mechanism based on PSF-NSGA-MBLSTM intelligent prediction of pipeline siltation particle settlement with CFD-DEM, a high-resolution numerical simulation method CFD-DEM-APM for hydraulic transport of siltation particles in sewer pipelines is proposed to describe the particle-phase and fluid-phase state transfer process. Experimental results show that the accuracy of CFD-DEM-APM is maintained within the 5%–11% range, which is far better than that of other algorithms. This study provides guidance on critical conditions for desilting and pipe inlet velocity/flow control to scour siltation and deposition of sewer pipelines for urban environment improvement and water pollution restriction. [ABSTRACT FROM AUTHOR]

Polyurethane grouting trenchless technology has been widely applied to the rehabilitation of concealed defects in engineering structures. The interfacial properties between polyurethane and engineering structures are key factors determining the stability of the composite structure. In practical applications, the interface shapes of different engineering structures vary significantly, and the influence of the interface shape on interfacial properties should not be overlooked. This study focuses on engineering structures with curved interfaces, such as pile foundations, pipelines, and tunnels. Direct shear tests were conducted on polyurethane and concrete composite specimens with curved interfaces. A comparative analysis of the shear behavior between curved and planar composite specimens was performed, and the influence of arc diameter and polyurethane density on the shear behavior of curved and planar composite specimens was investigated. Additionally, SEM (Scanning Electron Microscopy) was used to conduct a microscopic examination of the interfaces with different polyurethane densities after failure, and the microscopic shear mechanisms between polyurethane and concrete materials were explored. The results revealed that the shear behavior of curved specimens was significantly higher than that of planar specimens. The shear strengths of curved specimens with diameters of 400 mm, 500 mm, and 700 mm were approximately 1.50, 1.39, and 1.10 times those of planar specimens, respectively. With increasing polyurethane density, the variation trend of shear strength in curved specimens was similar to that of planar specimens. However, significant differences were observed in the shear modulus, peak displacement, and shear residual strength between curved and planar specimens as the polyurethane density varied. Different diameter curved interface specimens exhibited a similar trend of shear strength variation with polyurethane density, gradually decreasing as the curvature diameter increased, and ultimately approaching that of planar specimens. [ABSTRACT FROM AUTHOR]