Hysteretic wave drag in shallow water

General linear stability properties of monoclinal shallow waves

We analyze the linear stability of monoclinal traveling waves on a constant incline, which connect uniform flowing regions of differing depths. The classical shallow-water equations are employed, subject to a general resistive drag term. This approach incorporates many flow rheologies into a single setting and enables us to investigate the features that set different systems apart. We derive simple formulae for the onset of linear instability, the corresponding linear growth rates and related properties including the existence of monoclinal waves, development of shocks and whether instability …

用于气动表面减阻凹坑的贝叶斯优化与地形探索

Bayesian optimization and topographic exploration of drag-reducing dimples for aerodynamic surfaces

本研究采用MixMOBO贝叶斯优化器结合大涡模拟，优化气动表面减阻凹坑的四个设计变量，得到13.2%减阻率的最优菱形凹坑，明确了凹坑拓扑等关键设计因素及流动机制。

Tropical Vorticity Forcing and Superrotation in the Spherical Shallow Water Equations

The response of the nonlinear shallow water equations (SWE) on a sphere to tropical vorticity forcing is examined with an emphasis on momentum fluxes and the emergence of a superrotating (SR) state. Fixing the radiative damping and momentum drag timescales to be of the order of a few days, a state of SR is shown to emerge under steady large-scale and random small-scale vorticity forcing. In the first example, the stationary response to a pair of equal and oppositely signed vortices placed on the equator is considered. Here, the equatorial flux budget is dominated by the eddy fluxes and these d…

Surrogate Model for Shallow Water Equations Solvers with Deep Learning

Shallow water equations are the foundation of most models for flooding and river hydraulics analysis. These physics-based models are usually expensive and slow to run, thus not suitable for real-time prediction or parameter inversion. An attractive alternative is surrogate model. This work introduces an efficient, accurate, and flexible surrogate model, NN-p2p, based on deep learning and it can make point-to-point predictions on unstructured or irregular meshes. The new method was evaluated and compared against existing methods based on convolutional neural networks (CNNs), which can only make…

Orbiting of bacteria around micrometer-sized particles entrapping shallow tents of fluids

Hydrodynamics and confinement dominate bacterial mobility near solid or air-water boundaries, causing flagellated bacteria to move in circular trajectories. This phenomenon results from the counter-rotation between the bacterial body and flagella and lateral drags on them in opposite directions due to their proximity to the boundaries. Numerous experimental techniques have been developed to confine and maneuver motile bacteria. Here, we report observations on Escherichia coli and Enterobacter sp. when they are confined within a thin layer of water around dispersed micrometer-sized particles sp…

Boussinesq modeling of surface waves due to underwater landslides

Consideration is given to the influence of an underwater landslide on waves at the surface of a shallow body of fluid. The equations of motion which govern the evolution of the barycenter of the landslide mass include various dissipative effects due to bottom friction, internal energy dissipation, and viscous drag. The surface waves are studied in the Boussinesq scaling, with time-dependent bathymetry. A numerical model for the Boussinesq equations is introduced which is able to handle time-dependent bottom topography, and the equations of motion for the landslide and surface waves are solved …