Internal solitary waves (ISWs) typically manifest as soliton or wave trains in the ocean. Previous studies have extensively explored the dynamic properties of individual ISWs over topography. However, when the distance between successive ISWs in a wave train is less than a certain threshold, the interaction of multiple ISWs with the topography introduces mutual interference, leading to a more complex dynamical process. Therefore, this study established a numerical model based on OpenFOAM and analyzed the dynamical processes of two successive ISWs interacting with Gaussian ridges at different intervals. The findings reveal that the velocity field induced by the second wave (Wb) can transport and deform the vortex generated by the first wave (Wa) when Rab < 5 (Rab=Dab/Lw, where Dab is the distance between two ISWs, and Lw is the half-amplitude width). Additionally, the background field variation induced by Wa affects the shoaling and breaking of Wb. Particularly, when Rab < 3, the energy radiated to both sides of the ridge varies markedly with changes of Rab. The reflected leading wave of Wa is strengthened, while the transmitted leading wave of Wb is weakened, transferring energy to the transmitted trailing wave of Wa(the peak occurs at Rab=2.52). The interaction between the two waves not only modifies the energy structure but also distinguishes the variation in the dynamics of the bottom boundary layer from that of a single ISW. Notably, the negative bottom shear stress extremes induced by Wb are significantly enhanced, with the maximum value increasing by about 60%.

The breaking and energy distribution of mode-1 depression internal solitary wave interactions with Gaussian ridges are examined through laboratory experiments. A series of processes, such as shoaling, breaking, transmission and reflection, are captured completely by measuring the velocity field in a large region. It is found that the maximum interface descent ( $a_{max}$ ) during wave shoaling is an important parameter for diagnosing the type of wave–ridge interaction and energy distribution. The wave breaking on the ridge depends on the modified blockage parameter $\zeta _m$ , the ratio of the sum of the upper layer depth and $a_{max}$ to the water depth at the top of the ridge. As $\zeta _m$ increases, the interaction type transitions from no breaking to plunging and mixed plunging–collapsing breaking. Within the scope of this experiment, the energy distribution can be characterized solely by $\zeta _m$ . The transmission energy decreases monotonically with increasing $\zeta _m$ , and there is a linear relationship between $\zeta _m^2$ and the reflection coefficient. The value of $a_{max}$ can be determined from the basic initial parameters of the experiment. Based on the incident wave parameters, the depth of the upper and lower layers, and the topographic parameters, two new simple methods for predicting $a_{max}$ on the ridge are proposed.

Internal tides serve as essential intermediate steps in the cascading of oceanic energy, playing a crucial role in oceanic mixing. M2 internal tides are the dominant tidal constituent in many oceanic regions, significantly influencing ocean dynamics. The Madagascar–Mascarene Region has high-energy internal tides, but due to a lack of observational studies, their propagation remains underexplored and warrants further investigation. In this study, we used satellite altimetry data to capture the sea surface manifestation of the first-mode M2 internal tides in the region. The results show that the Mascarene Plateau plays a key role in shaping the region’s uneven internal tide distribution. The Mascarene Strait is the most intense generation area, with an east-west energy flux of 1.42 GW. Using the internal tidal energy concentration index, we decomposed the internal tidal beams, finding the primary beam oriented at 148°. These beams propagate outward for over 800 km, with a maximum distance exceeding 1000 km. Geostrophic currents intensify the northward refraction of westward-propagating internal tides in the Mascarene Basin, particularly between 15°S and 20°S.