Accurate streamflow modeling in data-scarce catchments remains a significant challenge due to the limited availability of historical records. Transfer Learning (TL), increasingly applied in hydrology, leverages knowledge from data-rich catchments (sources) to enhance predictions in data-scarce catchments (targets), providing new possibilities of hydrological predictions. Most existing TL approaches pre-train models on large-scale meteoro-hydrological datasets and show good generalizability across multiple target catchments. However, for a specific target catchment, it remains unclear which source catchments contribute most effectively to the accurate prediction. Including many irrelevant sources may even degrade model performance. In this study, we investigated how source catchment selection affects TL performance by employing similarity-guided strategies based on three key factors, i.e., spatial distance, physical attributes, and flow regime characteristics. Using the CAMELS-GB dataset, we conducted comparative experiments by pre-training the networks with different ranked groups of the source catchments and fine-tuning them on three target catchments representing distinct hydrological environments. The results showed that carefully selected small subsets (fewer than 40, or even as few as 10) of highly similar catchments can achieve comparable or better TL performance than using all 668 available source catchments. All three target catchments yielded better NSE results from source catchments with closer spatial proximity and more consistent flow regimes. The TL performance of physical attribute similarity-based selection varied depending on the attribute combinations, with those related to land cover, climate, and soil properties leading to superior performance. These findings highlight the importance of similarity-guided source selection in hydrological TL. In addition, they demonstrate ways to reduce computational costs while improving modeling accuracy in data-scarce regions.

The microfluidic technology based on surface acoustic waves (SAW) has been developing rapidly, as it can precisely manipulate fluid flow and particle motion at microscales. We hereby present a numerical study of the transient motion of suspended particles in a microchannel. In conventional studies, only the microchannel’s bottom surface generates SAW and only the final positions of the particles are analyzed. In our study, the microchannel is sandwiched by two identical SAW transducers at both the bottom and top surfaces while the channel’s sidewalls are made of poly-dimethylsiloxane (PDMS). Based on the perturbation theory, the suspended particles are subject to two types of forces, namely the Acoustic Radiation Force (ARF) and the Stokes Drag Force (SDF), which correspond to the first-order acoustic field and the second-order streaming field, respectively. We use the Finite Element Method (FEM) to compute the fluid responses and particle trajectories. Our numerical model is shown to be accurate by verifying against previous experimental and numerical results. We have determined the threshold particle size that divides the SDF-dominated regime and the ARF-dominated regime. By examining the time scale of the particle movement, we provide guidelines on the device design and operation.

In order to ascertain the combined effect of diameter ratio (d/D) and spacing ratio (L/D) on the flow around two tandem circular cylinders, a total of 43 research cases are numerically simulated using a large eddy simulation model in this study, including d/D = 0.2 (L/D = 0.80–6.00), d/D = 0.4 (L/D = 0.80–6.00), and d/D = 0.6 (L/D = 0.90–6.00) at Re = 3900. By systematically analyzing the instantaneous/time-averaged spanwise vorticity contours, the three-dimensional time-averaged Q-criterion iso-surfaces, the spanwise periodicity within the gap, and the Strouhal number (St), eight sub-flow regimes can be identified, namely, non-periodic reattachment-(1), small-scale periodic reattachment, large-scale periodic reattachment, non-periodic reattachment-(2), bi-stable flow, intermittent lock-in co-shedding, subharmonic lock-in co-shedding and no lock-in co-shedding. The occurrence of these sub-flow regimes depends on the combination of d/D and L/D. Besides, with regard to the larger downstream cylinder (DC), there are three possible dominant St values for the DC instantaneous drag coefficient (i.e. StCD-D1, StCD-D2, and StCD-D3). It is quite clear that StCD-D1 has almost the same value as StCL-D1, StCD-D2 is roughly equal to 2StCL-D1, and StCD-D3 is approximately the summation of StCL-D1 and StCL-D2, where StCL-D1 and StCL-D2 denote the primary and secondary dominant St values of the DC instantaneous lift coefficient, respectively. Additionally, various flow statistical parameters are obtained and compared for different combinations of d/D and L/D, such as the velocity, vorticity, St value, spanwise periodicity, force coefficient, base pressure coefficient, reattachment angle, and separation angle.

Leaky barriers mimic the natural accumulation of large wood in watercourses to effectively slow and store runoff and flow. Their role in flood management has attracted increasing attention due to their potential to reduce downstream risk. Numerous field studies have demonstrated the effectiveness of leaky barriers in retaining flood water in upstream catchment. However, their hydraulic behaviour remains poorly quantified due to limited empirical data and the modelling challenges. This review systematically investigates and synthesises research conducted over the past five years on the hydraulic behaviour and numerical representation of leaky barriers, while also drawing on earlier relevant studies to provide broader context. Additionally, it summarizes key hydraulic parameters, empirical equations, and modelling approaches that are used to characterise these structures. Furthermore, this review highlights the challenges of modelling individual leaky barriers in the field, which complicate their structural design and implementation. Future research should investigate the long-term performance of leaky barriers and explore optimal placement strategies to enhance flood mitigation within a catchment.

The dispersed nature of ocean wave energy distribution often leads to uneconomical wave energy exploitation when conversion devices are deployed only at certain locations. Inspired by the metamaterial concentrator for electromagnetic waves, an annular water wave manipulator has recently been proposed to amplify wave heights in a specific area. A computational fluid dynamics model is developed to investigate the wave evolution around this device, with the numerical predictions compared well with the experimental data. The wave energy concentration performance of the device is systematically analyzed, considering various structural designs, wave frequencies, water depths, and wave heights. The findings confirm the significant increase in wave heights within the concentrator, reaching up to two times the incident wave height in both baffled and unbaffled configurations, as a result of wave refraction and superposition. The effective channeling effect of the guiding baffles enables both the energy concentration within the concentrator and the invisibility downstream of the concentrator. The baffled design produces superior amplification as the nonlinearity of the incident wave increases.

The submerged floating tunnel (SFT) is a promising underwater transportation solution for deep-water crossings. Existing designs primarily address ordinary wave actions, while tsunami impacts on SFTs remain understudied despite the threat posed by tsunamis to nearshore infrastructure. This study employs a smoothed particle hydrodynamics (SPH) model to investigate the hydrodynamic characteristics of SFTs under a tsunami-like solitary wave impact. The SPH model is first validated against published experimental data. Parametric studies then examine the effects of cross-sectional shape (CSS), buoyancy-weight ratio (BWR), and mooring cable angle (MCA) on kinematic motions and mooring forces. Results show that the SFT exhibits coupled sway, heave, and roll motions. Compared with an elliptical CSS of equal area, a circular CSS reduces the maximum motion amplitudes by between 4.2% and 53.2% and the maximum mooring forces by 41.7% and 46.8%. Increasing the BWR from 1.2 to 1.4 reduces the maximum motion amplitudes by between 12.9% and 53.8% and the maximum mooring forces by 6.9% and 45.4%. Lowering the MCA from 60° to 45° reduces the maximum motion amplitudes by between 19.0% and 48.1% and the maximum mooring forces by 11.3% and 33.3%. These findings provide guidance for the design of SFTs subjected to tsunami impacts.