Experimental investigation of wave elevation and velocity evolution for a solitary wave passing a submerged spherical-cap topography

This study investigates the free-surface elevation and underlying velocity fields of a tsunami-like solitary wave propagating over a submerged spherical-cap topography, aiming to explore the physical connection between wave amplification and three-dimensional flow reorganization. An array of wave gauges is deployed to capture the spatiotemporal evolution of the free-surface elevation over a wide range of incident wave heights and submergence depths. A three-dimensional breaking criterion is established, indicating that the classical two-dimensional breaking condition cannot be directly applied because lateral energy redistribution alters the local wave-energy accumulation. The topography further induces pronounced lee-side wave focusing through the combined effects of shoaling, refraction, and diffraction. The maximum wave elevation at key measurement points is further described by an empirical power-law relationship involving the relative submergence depth and the wave-height-to-depth ratio, providing a quantitative characterization of topography-induced wave focusing. To resolve the flow mechanism beneath the free surface, a self-developed underwater two-dimensional three-component particle image velocimetry system is employed to measure the velocity fields at several characteristic cross sections. The measured velocity fields reveal the transition from front-side diffraction to lee-side spanwise convergence, together with vertical velocity reorganization near the topography. These results demonstrate that lee-side wave amplification is not governed by shoaling alone, but by the combined effects of shoaling, diffraction-induced convergence, vertical flow reorganization, and breaking-induced dissipation. The present measurements therefore provide direct experimental evidence linking free-surface amplification to three-dimensional flow structures over submerged topography, offering benchmark data and physical insight for modeling nonlinear wave-topography interactions.