Bridge piers on river channels can cause obstacles for flood flow by reducing the cross-sectional area and inducing local eddy currents and high flow velocities, which may destroy hydraulic structures. A two-dimensional numerical model was used to investigate the effects of bridge piers on river flood hazards in the Jialing River, China. For the modeling, Mike 21 FM was used, which is an unstructured mesh and finite volume model that solves the shallow water equations. The numerical model was validated with collected historical flood traces, and sensitivity analyses identified the effects of the Manning coefficient and the dependence on the grid size. The influence of backwater effects on the flow field was analyzed by comparing numerical results with and without piers. The results showed that the most significant impacts were caused by the Fengxian Bridge. The maximum water level rise was about 1 m and the maximum velocity near this bridge decreased by 22.77% for a 10-year flood. We found that the top elevations of planned levees near the bridges must be increased by 0.15–0.36 m. The influence of bridge piers on the flood velocity field is more complex. These findings will help flood hazard management in this river and provides a reference for similar projects.

Rapid global development has resulted in the widespread use of water pipelines in industrial and agricultural production and life. During water transportation and deployment, water pipes with different angles need to be positioned according to different geographical and topographical problems. Flowmaster simulation software was used to simulate the leakage process of pipelines with different angles. The transient characteristics of fluids in the pipeline were studied in detail. The influences of parameters, such as the bending coefficient R/D (R is the turning radius of pipe, D is the inner diameter of pipe), leakage position, and leakage aperture on the transient flow law of pipelines with and without leakage, were analyzed. The results show that the periodic decay of the upstream flow and pressure curve at the valve with and without leakage has an insignificant relationship with the bending coefficient R/D; however, the amplitude of the sudden position change is positively correlated with the magnitude of R/D. The leakage aperture is positively correlated with the leakage flow and negatively correlated with the pressure value at the leak location node. The farther the leak position is from the valve, the greater the amplitude of the valve end pressure and the upstream flow curve, and symmetric fluctuations occur.

In the hydraulically suspended passive shutdown assembly, in order to prevent the liquid suspension rod falling too fast and the outer tube from violent impact, it is necessary to study the way to increase flow resistance. This study added grooves to the wall of the narrow channel to increase its flow resistance. Using the RNG k-ε turbulence model in Fluent, the influence of the groove structure parameters and the Reynolds number on the flow resistance of the narrow channel was discussed to find the optimal groove structure parameters. The results showed that the flow resistance of the narrow channel increased with the increase in the concave–convex ratio, and when the concave–convex ratio was small, the flow resistance decreased with increased groove thickness, while when the concave–convex ratio exceeded a certain critical value, the flow resistance increased with increased groove thickness. Additionally, the growth rate slowed down when the concave–convex ratio was greater than 3:1. As the unit length decreased, the flow resistance first increased and then decreased. When the unit length was 6 mm, the flow resistance reached the maximum. With the increase in the Reynolds number, the intensity of the local high-turbulence kinetic energy clearly increased.

The gas-lift system has a lot of significant advantages in sewage treatment, deep well oil recovery, liquid metal cooled reactor and magnetohydrodynamic power converters. The densities of different liquid media and gas media have great influences on the performance of gas lift system. Therefore, based on Fluent simulation software, using Euler model and k-w SST (shear stress transport) turbulence model, the gas-liquid two-phase flow behaviors in nitrogen-water, nitrogen-kerosene, nitrogen-mercury and air-water, argon-water, nitrogen-water of gas lift system are studied. The rules of gas volume fraction and liquid flow rate at lifting pipe, liquid radial velocity at lifting pipe outlet, promoting efficiency are analyzed. The results are shown as follows. 1) In the nitrogen-water, nitrogen-kerosene and nitrogen-mercury system, the higher the density of liquid medium, the smaller the gas volume fraction in the lifting pipe is; the greater the flow rate of lifting liquid, the higher the promoting efficiency is. 2) In the air-water, argon-water and nitrogen-water systems, the higher the density of gas medium, the smaller the gas volume fraction in the lifting pipe is; the larger the flow rate of lifting liquid, the smaller the peak value of promoting efficiency is. 3) With the increase of gas flow rate, the liquid radial velocity at the lifting pipe outlet increases with overall fluctuation rising. Finally, the liquid velocity near the center of pipe axis is large, near the pipe wall is small. These research results provide the scientific theoretical basis for optimizing the gas lifting technology in applications such as sewage treatment, deep well oil recovery, liquid metal cooled reactor and magnetohydrodynamic power converters.