Surface & internal waves in two layered fluids

Abstract

In the paper we carried out two experiments: periodic linear waves and solitary waves. In part 1, a small scale experiment associated with the generation and propagation of linear sinusoidal waves in two-layered fluids was conducted. A ratio of amplitude of free-surface wave to interfacial-surface wave was measured by adjusting the frequency of wave maker and position of wave maker was changed from lower layer to upper layer. This ratio is compared to two analytic wave modes: barotropic mode and baroclinic mode which are induced by linear wave theory. In a perspective of wave mode, oscillating of wave maker generates two wave modes but the primary mode would be different according to variation of frequency. To confirm this phenomenon, two modes were decoupled by using two snapshots with different time. The results of observation are explained in terms of the amplitude of each mode, wave energy, wave energy flux and wave profile. In this experiments thickness ratio: "h" _"2" /"h" _"1" was 0.28 and frequency changed from 0.3 Hz to 1.2 Hz. In part 2, we present experimental results about the generation and propagation of solitary waves with free-surface in two-layered fluids. Two methods: dam breaking and pushing a panel are used to generate solitary waves. Before the experiments in two layer fluids, preliminary experiments in homogeneous fluids were carried out to make sure the result of two layer fluids. In two layer fluids, two modes are observed: baroclinic and barotropic modes. For small amplitude, wave experimental results well matched Peter and Stoker’s theory in both modes. However, for large amplitude, the interfacial surface waves are close to the Kdv-mKdv equation in baroclinic mode. Particular attention is paid to the measurement of the variation of wave heights according to their propagation speeds and this is compared to the existing analytical solitary wave solutions.