A large-eddy simulation of a three-dimensional numerical wave flume is used to study the forces on two tandem cylinders in a stratified strong shear internal wave (IW) environment. By analyzing the pressure distribution and the flow field around two cylinders compared with that of a single cylinder, the mechanism for the influence of the center-to-center (CTC) spacing (L), which is normalized by the cylinder diameter (D), i.e., (L/D), between the two tandem cylinders on the vortex disturbance intensity is explored, further revealing the mechanical response characteristics of the upstream (P₁) and downstream (P₂) cylinders. The results show that the vortex between two cylinders is the key factor affecting the pressure resistance of the cylinders in the IWs of the depression environment. The vortex disturbance intensity can be distinguished by a normalized critical CTC spacing (L_c/D): when L/D ≤ L_c/D = 2.5, the disturbance is strong, causing P₁ and P₂ to undergo large forces along and in the opposite direction of the waves, respectively. In addition, the vortex disturbance is more severe in the upper layer than in the lower layer. The correlation between the nondimensional force amplitude (C_Fn-max) and L/D and that between C_Fn-max and the nondimensional IW amplitude (η_o/H) is quantified. In the strong disturbance area (L/D ≤ L_c/D), C_Fn-max has an exponential relationship with (L/D)/(η_o/H) for P₁ and is a power function of (L/D)/(η_o/H) for P₂.

In this study, a three-dimensional internal wave (IW)—cylinder—terrain coupled numerical model is established. Based on the large-eddy simulation (LES) method, the IW mechanical characteristics of the cylinder and the flow field evolution around the cylinder over different types of terrains are explored. The similarities and differences in the mechanical characteristics of the cylinders in the environments with and without terrains are compared. The research results show that, when the IWs propagate over terrain, the waveform structures are prone to continuous changes. The intense reverse alternating flow of the upper and the lower water, bounded by the pycnocline, results in huge IWs forces differences between the case without terrains and the cases with terrains. In the case without terrains, the maximum horizontal resultant force on the cylinder is positive, while the resultant forces are negative in the cases with terrain. Compared with the case without terrain, the shallow-water effect caused by the combined action of the terrain and the IWs enhances the flow field strength, making the lower parts of the cylinder suffer larger horizontal forces in the opposite direction to the IW direction. Moreover, the additional vortices produced by the interaction between the IWs and the terrain causes a more complex flow field around the cylinder and the greater forces on the cylinder.

In this study, the evolution of transient pipe flow along the wet bed is numerically investigated. In the investigation, the shear stress transport k-ω model is used and the volume of fluid method is employed to track the surface of air and water. Two key parameters in the flow as upstream head H and initial water depth h in the pipe are examined. It is found that the bottom stress is significantly affected by the two parameters. The upstream head H determines the magnitude of the shear force, and the downstream water depth in the pipe affects the stability of the shear force. The boundary layer separation and flow pattern are the essential causes of shear instability. By analyzing the simulation results, an empirical equation with the average flow velocity is obtained to estimate the overflow capacity of the pipe by just the upstream water level and the depth of the wet bed.