The spacing of spur dikes is an important consideration for the layout of spur dike channels. This study focuses on the local scour morphology and flow field characteristics of spur dikes with different spacings. The results show that the maximum scour depth is generally found in the vicinity of the first spur dike head. With the increase of the spacing of spur dikes, the shielding effect of the first spur dike is weakened. The maximum velocity in the main flow zone is twice that of the approach flow velocity in the fixed bed. But it is approximately the same as the incoming velocity in equilibrium scouring. The maximum turbulent energy appears to be mainly located in the backflow area of the fourth spur dike in the fixed bed, while the maximum value appears at the second spur dike head in the movable bed. Further, the shear stress decreases as scouring develops. Pearson correlation analysis was carried out between scour depth and shear stress. The analysis results are significantly correlated, indicating that the bed shear stress plays a prominent role in the scouring process. These discoveries can serve as a guide to determine the most reasonable spacing of spur dikes.

A piano key weir (PKW) is a solution for improving the efficiency and safety of reservoirs and simplifying their management. To investigate the influence of the inlet/outlet width ratio $W_i/W_o$ on the discharge efficiency of PKWs, a three-dimensional numerical model based on a standard $k-\epsilon$ turbulence model and volume-of-fluid (VOF) method is employed, and the flow characteristics of nine laboratory-scale PKWs with different $W_i/W_o$ ratios are studied numerically. The results confirm that PKW configurations with $W_i/W_o>1$ are generally superior to those with $W_i/W_o<1$ in terms of discharge capacity. However, as the water head rises, the discharge efficiency of the PKW with a greater $W_i/W_o$ decreases more rapidly. By decomposing the total discharge into inlet, lateral and outlet components, according to the flow features of each overflow crest and their contributions to the total discharge, the intrinsic influencing mechanism of $W_i/W_o$ on the discharge performance of PKWs is revealed.

Computing speed is a significant issue of large-scale flood simulations for real-time response to disaster prevention and mitigation. Even today, most of the large-scale flood simulations are generally run on supercomputers due to the massive amounts of data and computations necessary. In this work, a two-dimensional shallow water model based on an unstructured Godunov-type finite volume scheme was proposed for flood simulation. To realize a fast simulation of large-scale floods on a personal computer, a Graphics Processing Unit (GPU)-based, high-performance computing method using the OpenACC application was adopted to parallelize the shallow water model. An unstructured data management method was presented to control the data transportation between the GPU and CPU (Central Processing Unit) with minimum overhead, and then both computation and data were offloaded from the CPU to the GPU, which exploited the computational capability of the GPU as much as possible. The parallel model was validated using various benchmarks and real-world case studies. The results demonstrate that speed-ups of up to one order of magnitude can be achieved in comparison with the serial model. The proposed parallel model provides a fast and reliable tool with which to quickly assess flood hazards in large-scale areas and, thus, has a bright application prospect for dynamic inundation risk identification and disaster assessment.

High-speed and accurate simulations of landslide-generated tsunamis are of great importance for the understanding of generation and propagation of water waves and for prediction of these natural disasters. A three-dimensional numerical model, based on Reynolds-averaged Navier–Stokes equations, is developed to simulate the landslide-generated tsunami. Available experiment data is used to validate the numerical model and to investigate the scale effect of numerical model according to the Froude similarity criterion. Based on grid convergence index (GCI) analysis, fourteen cases are arranged to study the sensitivity of numerical results to mesh resolution. Results show that numerical results are more sensitive to mesh resolution in near field than that in the propagation field. Nonuniform meshes can be used to balance the computational efficiency and accuracy. A mesh generation strategy is proposed and validated, achieving an accurate prediction and nearly 22 times reduction of computational cost. Further, this strategy of mesh generation is applied to simulate the Laxiwa Reservoir landslide tsunami. The results of this study provide an important guide for the establishment of a numerical model of the real-world problem of landslide tsunami.

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 paper, an improved third-order finite difference weighted essentially non-oscillatory scheme is presented for achieving the optimal order near critical points. A new global smoothness indicator is obtained with the way of Taylor expansion for the local smoothness indicator. In the framework of the conventional WENO-Z scheme, we present an improved third-order finite difference WENO scheme. The proposed scheme is verified to achieve third-order accuracy by several benchmarks and the behaviour of the present scheme is proved on a variety of one- and two- dimensional standard numerical examples. Numerical results demonstrate that the proposed scheme gives better performance in comparison with the other third-order WENO schemes.