The immersed boundary–lattice Boltzmann (IB-LB) coupling scheme is known as an efficient scheme for fluid–structure interactions (FSIs). However, the conventional IB-LB schemes suffer from instability because they involve a high-Reynolds-number flow or a larger stiffness structure. An averagely weighted iteration approach is presented to improve the stability restriction in this paper. This new approach, which improves the stability by mitigating the high-frequency fluctuations, is implemented by iteratively calculating the external force, and averagely weighting the force obtained at every iterative step. Five cases are simulated to verify the accuracy and effectiveness of the present approach. Under the premise of maintaining the accuracy of the conventional IB-LB method, the implementation of the present approach can significantly enhance the numerical stability. Compared with the conventional IB-LB method, the present approach can significantly expand the material parameter range for simulation; in particular, this approach qualitatively improves the upper limit of the bending rigidity coefficient by approximately 8000 times. To use the outstanding stability of the present approach, the IB inertia force can be directly incorporated into the simulation. In addition, under the low-viscosity condition, the present approach can effectively simulate the large-deformation FSI problem.

Bubble dissolution during the flood discharge creates high total dissolved gas (TDG) concentration zones downstream of the dams. The dissipation of supersaturated TDG is a very slow process. Thus, the elevated TDG may remain through the water body for hundreds of kilometers downstream and lead to gas bubble disease (GBD) and even mortality in fish. To improve the navigation conditions of waterways, dikes (i.e., a solid structure) of varied sizes and shapes are commonly constructed. However, this would affect the dissipation and transportation of the supersaturated TDG. It would significantly change the turbulence intensity and hydropressure of the flow, which dominates the dissipation of TDG. Therefore, TDG distribution in the waterway differs from that in the natural river. In this study, a numerical simulation of the TDG at the Yangtze River’s upper reaches (one of the inland waterways in China) was conducted with the establishment of a two‐dimensional TDG dissipation model. The effect of the dikes’ size and shape was analyzed to assess the influence of the regulation structures on the dissipation and transportation of the supersaturated TDG. Meanwhile, simulation in the study area with the natural topography was also set as blank control. Based on that, impact evaluation of TDG supersaturation on fish under different simulation scenarios was made. This study can provide a scientific basis for reducing the adverse effect of supersaturated TDG in fish and the construction of ecological waterway therefore.

The daily regulation and anti-regulation of upstream and downstream power stations, respectively, frequently alter the river flow regime, velocity, and surface gradient, thus resulting in unsteady flow characteristics of the river and hindering shipping, waterway maintenance, and wharf operations. This study investigated the influence of daily regulation on the navigation conditions in the deep reservoir by taking the rivers between the Three Gorges Dam and the Gezhouba Dam as the research object. Prototype observations and a depth-averaged 2-D model were used to determine the main factors affecting the propagation law of unsteady flow. The propagation pattern of unsteady flow and channel navigational conditions and measures of the power station were analyzed systematically. The results showed that the water level amplitude was affected primarily by the peak amplitude and duration of the peak shaving. Additionally, the base flow significantly influenced time spatial distributions of the water level amplitude. Impacted by the reservoir storage capacity, a threshold for the duration of peak shaving was noted; this may result in maximum water level variation. As the peak shaving duration increased, the amplitude of the water level decreased. The research results can provide theoretical support for the optimization of hub shipping.

To investigate the impact characteristics of oblique flow on dolphin-type pier structures in mountainous river confluence hubs, the Madao Hub of the Pinglu Canal—a pivotal component of China's Western Land-Sea New Corridor initiative—was examined in this study. Full-scale three-dimensional fluid–structure interaction (FSI) simulations were implemented, with validation against physical model experimental data. The flow characteristics and hydrodynamic pressure distributions around ship-berthing piers impacted by the tailwater flow from the Madao Hub were analyzed. Simulation results of the FSIs were benchmarked against standard empirical formulas. The results revealed that under the project's layout configuration, high-velocity flow propagated predominantly along the left bank, primarily impacting piers 8–10. The maximum positive pressure zone was located near the upstream corner of the most-affected berthing pier. As the flow traversed the pier’s leading edge and impinged upon the sidewalls, the hydrodynamic pressure progressively attenuated, transitioning to negative values at the downstream end of the front face and upstream end of the side face. Comparisons indicated that the predicted values matched well with AS500 and IRS standards, whereas IRC 6 standard underestimated the hydrodynamic forces by 85%–90%. Therefore, the IRC 6 standard requires calibration to enhance its safety factor. This study elucidated the pressure distributions around piers under oblique flow conditions, providing a scientific foundation for structural layout optimization, pier geometry selection, and force analysis of piers near mountain river confluences.

Landslide-induced waves are primarily controlled by granular dynamics during landslide–water impact. While particle size, velocity, and volume are recognized influences, the role of internal grain arrangement and segregation remains less clear. This study employs a coupled CFD-DEM model to investigate how vertical permutation of three fixed grain fractions and layered configurations affect surge generation and propagation. Simulations using three particle sizes (1, 3, and 5 mm) in six initial arrangements reveal that fine particles dominate leading wave formation through efficient momentum transfer, yielding an overall wave height growth of 5.22% and a maximum local growth rate of 2.42%. Grain size segregation governs deposit morphology, with larger particles migrating preferentially along the flow direction. Increasing still-water depth systematically shifts surge characteristics from strongly nonlinear, high-amplitude shallow-water waves to more linear, longer-wavelength, smaller-amplitude deep-water features. Energy dissipation, which is linked to reduced equivalent water depth, decreases wave celerity with propagation distance. The model reproduces granular collapse experiments with a relative error below 5%, confirming that granular segregation critically controls surge dynamics and providing a refined framework for simulating natural landslide-generated waves.