Jie Dai

1. Fish passes are used where dams, weirs, and other hydraulic structures barrier fish migration upstream, with the goal of alleviating habitat fragmentation and restoring ecological connectivity i...

River confluences are key nodes in river network systems and exhibit complex three-dimensional hydrodynamics strongly influenced by tributary topography. In this study, the effects of tributary floodplain side slope angles [(90° (C1), 45° (C2), 30° (C3), and 0° (C4, bed discordance)] on confluence flow structures and turbulence characteristics were investigated using large-eddy simulation. The numerical model was validated against laboratory measurements, showing good agreement in three-dimensional mean velocity and turbulent kinetic energy, as well as in the position and size of the separation zone and secondary circulation. As the tributary side slope angle decreases, the secondary circulation shifts toward the inner bank, and the near-bed separation zone is progressively disrupted by the secondary flow and eventually disappears in C4. The secondary circulation intensity near the tributary floodplain step remains similar among cases due to comparable tributary inflow momentum; however, in C4 it becomes significantly stronger downstream and then rapidly weakens after impinging on the inner bank wall. Elevated turbulent kinetic energy and coherent vortical structures are mainly concentrated in the shear layer, tributary floodplain step, and boundary of the separation zone. Q-criterion analysis shows that these structures remain stable in C1 and C2, are partially disrupted by secondary circulation in C3, and are substantially reduced in C4 due to the disappearance of the separation zone. These findings advance the understanding of confluence hydrodynamics under different tributary topographies and provide potential support for river network systems management.

Large-eddy simulations (LESs) were performed to investigate turbulent flow past a triangular baffle in a culvert at three orientations of 45°(C45), 90°(C90), and 135°(C135). The Reynolds and Froude numbers were fixed at Re=70 000 and Fr=0.376, respectively. The LES approach was first validated against laboratory measurements of mean velocity and turbulence intensity, showing good agreement. The time-averaged velocity fields indicate that the blockage effect decreases with the increasing baffle angle, with high-velocity regions concentrated near the baffle in C135. Flow separation produces recirculation zones upstream and downstream of the baffle; the upstream recirculation disappears in C135, while the downstream zone shortens and weakens with angle and elevation. Reynolds shear stress and turbulent kinetic energy contours confirm that turbulence is strongest in the shear layer and most intense in C135. Instantaneous flow structures identified by the Q-criterion highlight coherent vortices and strong vortex shedding, particularly at larger baffle angles. Quadrant analysis shows a transition from a balanced distribution of turbulent events in C45 to dominant ejection–sweep interactions in C90 and C135, accompanied by increased fluctuation intensity. Spectral analysis reveals vortex-shedding frequencies of 0.196–0.296 Hz, corresponding to Strouhal numbers of 0.055–0.083, which increase with baffle angle.

The arrangement of vegetation patches in rivers creates critical habitats, but the hydrodynamics of alternating patch-cavity systems are not fully understood. This study investigates the flow structure and turbulence in an open channel with one-sided rectangular vegetation patches of two densities (solid volume fraction ϕ = 0.10 and 0.05). Three-dimensional velocity data were collected using an acoustic Doppler velocimeter. We found that the downstream flow adjustment distance (Xeq) was negatively correlated with vegetation density ϕ. In the developed equilibrium region, the flow field consists of a low-velocity cavity and a high-velocity mainstream, separated by a turbulent mixing layer. Flow visualization revealed two distinct exchange mechanisms: weak internal circulation driven by shear-layer eddies in the dense case and suppressed eddy penetration due to strong “bleed flow” through the patch in the sparse case. At the cavity-mainstream interface, quadrant analysis showed that momentum exchange was dominated by ejection (Q2) and sweep (Q4) events with sweeps being the most intense contributors to Reynolds stress. These findings provide a quantitative basis for designing patch-cavity systems to create specific ecological functions, such as refugia or dispersal corridors, in river restoration projects.

Arrays of bank-attached rectangular vegetation patches, common in river ecosystems, exhibit complex hydrodynamics influenced by patch density (ϕ) and aspect ratio (l/B). Understanding these effects is crucial for river management but remains incomplete, particularly regarding the coupled influence of ϕ and l/B. This study employs numerical simulation, validated by physical experiments, to investigate flow structure, momentum exchange, and drag characteristics around such arrays along one channel bank. Results show the arrays induce an inner–outer double shear layer structure. Cavity vortex formation and position are significantly modulated by the coupled effects of ϕ and l/B. Lateral outflow proportion (Qm/Qc) increases markedly with ϕ. Notably, turbulent kinetic energy at the cavity–mainstream interface and mean streamwise drag per patch display non-monotonic dependence on ϕ, peaking at an intermediate density (ϕ = 0.098), suggesting an optimal density for maximizing turbulence and resistance. Quadrant analysis reveals momentum exchange is dominated by sweep (Q4) events, while ejection (Q2) contributions show complex trends with ϕ. The lateral-to-total drag ratio generally increases with ϕ but decreases for high-density, large-aspect-ratio cases. Drag fluctuations intensify at medium-to-high densities and large aspect ratios. This research quantitatively elucidates the complex, coupled mechanisms through which vegetation density and geometric morphology influence flow structure, turbulence characteristics, and hydraulic resistance within laterally arranged rectangular vegetation patch arrays. It enhances the understanding of hydrodynamics associated with spatially heterogeneous vegetation and provides valuable insights for ecological channel design, river restoration efforts, and aquatic habitat management strategies.

Consistent application of neurotropic factors is necessary in peripheral nerve regeneration, yet challenging to achieve. Here we used a novel neurotropic factor controlled release system consisted of fibrin, fibronectin and hydrogel to slowly release two neurotrophic factors. At the same time, physiological saline and reverse nerve suturing were used as negative and positive control. A year after surgery, animals which were treated by neurotrophic factor slow release system achieved far better neural regeneration and myelination, as well as superior recovery of hindfoot than the negative control group. In the meanwhile, the results in the experimental group are still inferior to the nerve allograft group. In can be concluded from those results that, consistent releasing of neurotrophic factors can significantly promote long peripheral nerve regeneration, but still short of achieving the results same as the gold standard of autologous nerve grafting.