Characteristics of Mach effect induced by oblique wave-wave interactions of internal solitary waves in ocean

Abstract

The Mach effect induced by the oblique wave-wave interactions of internal solitary waves is a special phenomenon of the ocean and is also the main reason of generating a large amplitude internal solitary wave, while they can cause it damage and even crash as the ocean engineering structures or underwater vehicles encounter the internal solitary wave with a large ampiltude in the ocean. In order to simulate the oblique interaction of internal solitary waves in the thermocline marine environment and control the Mach effect in the laboratory, two vertical bottomless barrels are placed in the fresh/saline water’s two-layer fluid. So the mixed fresh/saline water region is called the density thermocline of the marine. Keeping exchange of water under the barrel’s bottoms is to facilitate the formation of the mixed region height difference in the inner and outer parts of barrels. And then remove the two barrels smoothly and quickly, so that the mixed fresh/saline water region’s gravitational collapse motion can be made use of to generate two rows of internal solitary waves. They will occur the oblique wave-wave interaction in their propagating intersection area. The experimental results showed that two rows of solitary wave oblique interaction depends on the stratification environment, the distance between the two barrels and the amplitude and phase of two solitary waves. It has been vertfied that the above method can effectively control the generation of Mach effect in the stratified fluid tank. Further analysis showed that the Mach effect induced by the oblique interaction of internal solitary waves will lead to remarkably increasing amplitude in correspondence with its raising propagation velocity, whose direction is controlled by the amplitude difference between two internal solitary waves, and the greater amplitude difference will bring on the larger Mach effect’s critical angle. Through testing the theoretical models including KdV’, BO’ and MCC’s equations to compare with the experimental results , the adaptability of the Mach effect to the nonlinear theoretical models is verified by experiments.