Genguang Zhang

The morphology and depth of scour holes induced by ski-jump flows have long been central topics in hydraulic engineering research. Reliable prediction of essential for ensuring geometry and depth i...

In river ecological restoration projects within cold regions, in-stream structures are commonly implemented to enhance habitats, while seasonal ice covers significantly modify hydrodynamic and thermal conditions. Their complex effects on key processes in the hyporheic zone, such as hydraulic exchange and heat transport, require urgent clarification. Therefore, we propose a three-dimensional surface water and two-dimensional groundwater coupled numerical model, and systematically investigate the influence of in-stream structures combined with ice covers of varying roughness on the pressure distributions, thermal regimes, and hyporheic exchange processes in river systems. The results indicate that (i) the synergistic effect of ice cover roughness and in-stream structures significantly alters bed pressure distribution; the peak pressure difference across the log increases from 61.9 to 105.9 Pa with the increasing roughness, thereby enhancing the intensity of both downwelling and upwelling flows; (ii) with the effect of ice covers, a semi-elliptical relatively colder zone forms beneath the in-stream structures, with its area expanding by 20%–30% as ice roughness increases; however, the insulating effect of the ice layer reduces the overall thermal gradient; (iii) thermal heterogeneity in the hyporheic zone is markedly enhanced; under high-roughness ice cover, the peak Darcy velocity increases by approximately 68.6%, from 0.015 to 0.0253 m/s, accelerating heat exchange between surface water and the hyporheic zone; (iv) the sensitivity ranking of the factors influencing the hyporheic exchange process is as follows: inflow discharge > ice cover roughness > permeability > streambed length ≈ hyporheic zone depth. This research establishes a theoretical foundation for optimizing instream structure parameters in cold-region river restoration projects.

Hyporheic exchange is a fundamental process governing surface water–groundwater interactions, plays a critical role in regulating nutrient cycling, energy fluxes, and ecological dynamics. In this study, the impacts of log jams on riverbed deformation and the enhancement of hyporheic exchange were investigated using a proposed coupled model of surface water–groundwater interaction. Under log elevations ranging from 2 to 11 cm and flow discharges from 0.005 to 0.016 m3/s, the results revealed significant morphological and hydrodynamic changes. Lower log elevations intensified scouring, increasing scour pit depths from 1.29 to 3.19 cm and downstream deposition areas by 72%, while the hyporheic flux increased by 40%. At the highest flow discharge of 0.016 m3/s, the total hyporheic exchange flux reached 1.45 times that under 0.010 m3/s, driven by the enlargement of active exchange domains. Log-induced morphological forcing governed the spatial extent and transport efficiency of solute migration, with broader scour–deposition structures facilitating deeper and more distributed subsurface delivery. These hydrodynamic alterations enhanced oxygen availability and prolonged solute retention, thereby increasing physical and chemical gradient diversity that supports the formation of ecologically functional hyporheic habitats. The findings provide valuable insights and practical guidance for river ecological restoration and water resource management in alluvial channels, highlighting the importance of log jam-induced hydrodynamic processes in shaping aquatic ecosystems.

The drag and lift coefficients are important parameters that affect the particle motion in a viscous fluid. In the present study, the drag and lift coefficients of a spinning sphere in a water tank were studied experimentally using a high-speed camera. To this end, 22 cases were studied to cover a wide range of dimensionless angular speeds (0.149 < Rr < 3.471) and Reynolds numbers (610 < Re < 3472). Based on the present experimental data and the results obtained from the literature, expressions were developed to calculate the lift and drag coefficients. The performed analyses on lift coefficient show that there is a critical Reynolds number (Re_c) at each dimensionless angular speed. When 0 < Re < Re_c, the lift coefficient decreases with increasing the Reynolds number, while it is constant when Re_c < Re< 3500. The constant lift coefficient corresponding to different spin speeds was defined as the limit value of the lift coefficient. It is found that when 1 < Rr < 12, the limit value of the lift coefficient is 0.37, while the limit value of the lift coefficient increases with increasing dimensionless angular speed at 0 < Rr < 1. It is found that the spin increases the drag coefficient of a spinning sphere only when 0 < Rr < 10. Moreover, the performed analyses show that the drag coefficient of a spinning sphere is less than that of a non-spinning sphere when 10 < Rr < 25. Furthermore, the lift-to-drag ratio of a spinning sphere is discussed in this article.

How to optimize the spatial distribution of terraces in the watershed is an important scientific problem. It was researched through a watershed solid-scale physical model based on the 3D reappearance of a scene under the Cartesian coordinate system, with the lowest point of the watershed as the origin. The results showed that the change of the spatial pattern of terraced fields in the basin had an important impact on the production of runoff and sediment. There was an approximate quadratic-function relationship between the spatial location and the parameters of runoff and confluence. If R_t was terrace-erosion-reduction benefit, it could be defined as the reduction in the watershed-erosion modulus per unit of terrace area. The longitudinal distribution of R_t was upper and middle > lower parts, and the vertical distribution of R_t was high > low place. The erosion reduction was 77.67% of the terraces of the middle and upper, occupying 33% of the watershed area. The change of the R_t was logarithmically related to the relative distance (r) from the center of the terrace. When r was around 0.35, there was an inflection point in R_t growth. The results of this study have important practical significance for the planning and construction of terraces in the watershed.

Ships sailing in the area of a bridge are vulnerable to the influence of complex water flow, due to the complex flow pattern around the bridge pier. Ships often crash into bridge piers, leading to serious economic losses and threating personal safety. Based on the common forms of piers of skew bridges, the hydrodynamic problems encountered during ship–bridge interactions in the area of a skew bridge were studied using particle image velocimetry-based flume testing, physical model testing, and numerical simulation. The influence of the flow angle of attack of a round-ended pier on the force and center of gravity of a ship moving on both sides of a pier is discussed under various ship–bridge transverse spacings. The results show that as a ship passes through the bridge area, the bow roll moment exhibits three peak values: ‘positive’, ‘negative’, and ‘positive’, and the curve of the center of gravity position forms the shape of a ‘straw hat’. With an increase in the flow angle of attack of the pier, the negative peak value and the second positive peak value of the bow roll moment of the ship passing through the back flow side of the pier become greater than those on the upstream side. Moreover, the ship’s navigation attitude is more unstable compared to that upstream, and the ship is at risk of colliding with the pier and sweeping. The width of the restricted water area, determined by the hydrodynamic action between the ship and bridge in the skew bridge area, is the same as that determined by the critical lateral velocity. For the ship class referred to in this study, the current code can also be used in channel design, to safeguard ship and personal safety with piers with a large flow angle of attack.

Flocculation is a special phenomenon for fine sediment or silt in reservoirs and estuaries. Flocculation usually results in changes of size, morphology, and settling velocity of sediment particles and finally changes of bed topography of reservoirs and estuaries. The process of flocculation and sedimentation was simulated based on population balance modeling (PBM) and computational fluid dynamics (CFD); the changes of particle or floc size and their settling velocities over time were examined. The results showed that flocculation is a dynamic and nonlinear process containing aggregation, breakage, reaggregation, and rebreakage between particles, microflocs, and macroflocs. Furthermore, the visual process of flocculation and sedimentation was directly created by the simulation results and is in good agreement with the results of the previous experiments.