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.

Rivers in the northwestern region of China have a high sediment content, and the construction of reservoirs on these rivers must address the problem of sedimentation that results in a loss of reservoir capacity. In this study, the YZD (Yazidang) reservoir was considered as a typical case, to address the problem of sedimentation in injection-type water supply reservoirs in Northwest China. The temporal and spatial characteristics of the sediment in this water diversion project were analyzed based on available 46-year water and sediment data. The concept of 'sediment avoidance diversion' was proposed, which reduces the entry of sediment into the reservoir. A one-dimensional numerical model for water-sediment coupling was established, and the characteristics of water-sediment erosion and deposition for different operational modes were analyzed. The results show that during a period of high sediment content, large-scale siltation occurs in a water diversion channel. To alleviate sediment deposition in a diversion channel, two control strategies for mitigating siltation were formulated. Considering the pros and cons of these control strategies, a reasonable water-sediment joint operation plan has been proposed to extend the service life of the YZD reservoir. This research provides a theoretical basis for sedimentation treatment and control of similar reservoirs.

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Accurate prediction of water waves generated by landslides is of significant importance in the early warning and risk assessment of landslide disasters. And previous studies shown that landslide-induced waves are of various types, which indicates that there are different generation regimes for landslide induced waves. In the present study, the generation of water waves by a rigid landslide is studied numerically and theoretically. According to the motion characteristics of a landslide, three types of landslide motions, including piston-like, plunger-like, and transition landslide motions are detected. The performed analyses demonstrate that the solitary-like wave and dissipative transient bore are generated by piston-like landslides. Moreover, nonlinear oscillatory and transition waves are generated by plunger-like and transition landslides, respectively. It is also found that the wave height generated by piston-like landslide depends on the effective velocity of fluid translated by the landslide. For piston-like landslide motion, the correlation between the wave height, wavelength, and the effective velocity of a rigid landslide are established theoretically, and then it is verified using numerical results. The present study is expected to provide a reference to investigate early warning of landslide-induced waves.

In this study, friction factor of a fully developed laminar flow in a noncircular duct, which is used in an automotive cooler system, is investigated. The Poisson equation of velocity with homogeneous boundary conditions is solved by using the method of separation of variables and analytical solutions of velocity, wall shear stress and friction factor for arbitrary symmetric noncircular ducts are obtained. The analytical solutions are validated by comparing against analytical and experimental data available for rectangular and triangular ducts. Cross-sectional distribution of velocity, wall shear stress along the duct boundary and friction factor are analysed in depth. It is obtained that the friction factor for this specific duct is λ=95Re, with Re defined with equivalent diameter as length scale. Moreover, the applicability of a general equation of friction factor proposed by Duan et al. is validated for this specific duct by comparing with the analytical solution. The result shows that the general equation is accurate enough and can be used for the evaluation of flow resistance in design of the cooler system.