Coupling characteristics between bubble and free surface in a shallow water environment

Abstract

The bubble motion in the shallow water environment has significant applications in underwater explosion and seabed exploration, where the bubble characteristics are mainly associated with the two types of stand-off distance parameters γf and γs (the parameters are defined in Section 2.3). Based on the assumption that the liquid is inviscid and incompressible, the influences of γf and γs on the coupling characteristics between the bubble and the free surface in the shallow water environment are solved by the Euler equations with the finite volume method, and the bubble surface and the free surface are tracked by the front tracking method. For the case γs = 0.8, (i) the water spike always keeps rising during the bubble expansion and contraction when γf<1.25, (ii) the water spike velocity increases with the decrease of γf, and the maximum bubble jet velocity is generated when γf = 0.8, (iii) the bubble top elongated is no longer obvious when γf>1.5. For the case γf = 0.6, (i) the toroidal bubble is split into two sub-toroidal bubbles when γs≤ 0.6 and γs≥1.1, (ii) the water spike velocity and the step pressure decrease with the increase of γs.