How have mountains, hills, deserts, rivers and marshes gradually evolved over eons? Why is Pluto, marked by an extremely low air density, dotted with an abundance of dunes? Will there be sandstorms on Mars which is known as a desert planet?
It is these enigmas in nature that geophysicists have been endeavoring to unravel. Previous studies indicate that sediment transport is a universal phenomenon in aeolian and fluvial environments and is one of the most fundamental natural processes that shape of land forms. At the core of this issue is how to understand and describe the initiation, transport and deposition of sediments on the Earth’s surface. Measurements have revealed that the transport rate (Q) scales approximately linearly with fluid shear stress (τ)in aeolian (air-driven) transport, but scales nonlinearly with τ in fluvial (liquid-driven) transport. However, the physical origin of this distinction remains controversial and a general scaling law for Q elusive.
Recently, Dr. Thomas Pähtz from the Zhejiang University Ocean College derived a scaling law in simultaneous agreement measures in water and air streams. The finding was published in the journal of Physical Review Letters on April 20.
Using discrete element method-based sediment transport simulations, Dr. Thomas Pähtz discovered that the linear-to-nonlinear transition in the scaling of Q with τ is caused by a regime shift in the manner in which kinetic fluctuation energy of transported particles is dissipated. Via parametrizing this shift, he derived a general scaling law, valid for continuous (not intermittent) turbulent transport of nearly monodisperse sediment, in simultaneous agreement with measurements in water and air streams. In combination with a previous unification of the aeolian and fluvial transport threshold, researchers are now able to estimate planetary sediment transport and the evolution of planetary sediment surfaces much more reliably than before.
“The hard nut to crack in this study is to offer a physical explanation and a mathematical depiction of the simulated results. In the past 7 years, I have made numerous trials. I have spent of my waking hours pondering over this question in the first 4 years,” said Dr. Thomas Pähtz.