Unstable cliffs frequently collapse when the foundation rock beneath them is crushed in numerous coastal zones and gorges. The safety of people can be threatened by large sea waves.
Chinese researchers describe the method by which these cliffs collapse as well as the process by which massive, tsunami-like waves, known as impulse waves, are produced in this week’s issue of Physics of Fluids from AIP Publishing.
Since there haven’t been many experimental studies of this phenomenon, this work adds important new information that can be used to prepare for the coming tragedy. In a rectangular, transparent container, the experiments were conducted.
The box had a vast pool of water at one end and a mound of granules at the other. A moveable gate keeps the pile away from the water. The pile crumbles and slips into the ocean when the gate is raised swiftly, creating waves.
The granular particles were designed to imitate samples from the Three Gorges Reservoir Region of China in shape. It was possible to see the water’s motion as well as the additional floating and suspended debris. A camera outside the box recording at 100 frames per second picked up the movement of this second collection of particles.
The scientists changed the granular pile’s width and height as well as the height of the body of water individually. It was discovered that the pile height-to-width ratio is crucial, affecting both how the pile collapses and the kinds of impulse waves that are generated.
These formulas are highly suitable for the collapse of partially submerged granular piles.
Huang Bolin
The pile eventually pushed the water away after collapsing in four phases. Under specific circumstances, the resulting water movements were returned to the pile and produced vortices. There were three different kinds of water waves produced: bores, solitary waves, and transition waves.
As they travel, transition waves eventually fade. However, solitary waves are made up of a single water crest that travels quickly without losing amplitude. The top of the wave breaks and flows forward in a bore.
The researchers created a method to forecast which kind of wave will be generated by fitting the observed experimental data to a formula.
“These formulas are highly suitable for the collapse of partially submerged granular piles,” said co-author Huang Bolin.
