The science behind skipping stones
Researchers uncover dynamics of buoyant spheres and the formation of horizontal air cavities at the air-water interface

Date:
July 11, 2023
Source:
American Institute of Physics
Summary:
An interdisciplinary team presents a study of the dynamics of
buoyant spheres at the air-water interface. Their work reveals
complex hydrodynamics involved in forming horizontal air cavities
and the transition between floating and skipping. One of the
team's key findings is that as the pulling force and speed of the
spheres increase, their behavior becomes more irregular. They also
discovered larger pulling angles result in different air-cavity
lengths, larger skipping distances, and earlier water exit behavior.


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FULL STORY ========================================================================== Inspired by the need to safeguard marine animals and promote sustainable solutions within marine environments, an interdisciplinary team of
researchers from King Abdullah University of Science and Technology
in Saudi Arabia and Sofia University in Bulgaria are delving into the hydrodynamics of buoyant objects at the air-water interface.

By studying these dynamics, their goal is to expand the understanding
of fluid hydrodynamics and complex surface interactions -- and advance
fields such as the design and performance of marine engineering systems,
buoy systems, and underwater vehicles.

In Physics of Fluids, from AIP Publishing, the team presents a study of
the dynamics of buoyant spheres (think skipping stones) at the air-water interface.

Their work revealed complex hydrodynamics involved in forming horizontal
air cavities and the transition between floating and skipping.

The study of fluidics and physics within the context of buoyancy involves several key principles: buoyancy, hydrodynamics, fluid resistance,
and a Reynolds number.

Buoyancy refers to the upward force exerted on an object immersed within
a fluid, while hydrodynamics focuses on the motion of the fluid and its interactions with solid objects.

Fluid resistance, or drag, occurs when an object moving through a fluid experiences resistance due to the friction between its surface and
the fluid.

This resistance depends on factors such as an object's shape, size,
speed, and fluid properties.

To further analyze fluid behavior, scientists use a dimensionless
parameter, a Reynolds number, to determine the type of flow around
an object.

One of the team's key findings is that as the pulling force and speed of
the spheres increase, their behavior becomes more irregular. "The spheres exhibit oscillatory motions, diving into the water, rising toward and
piercing the water surface, and attaching underwater air cavities in a horizontal direction," said co-author Farrukh Kamoliddinov of KAUST.

They also discovered larger pulling angles result in different air-cavity lengths, larger skipping distances, and earlier water exit behavior --
meaning that the pulling angle plays a significant role in shaping the hydrodynamics of the buoyant spheres.

And the cavity maintains a steady horizontal motion at a constant
velocity over a certain distance. The air cavity formation exhibits
distinct features, including an inverted wing shape and a turbulent
wake behind it. This steady and controlled horizontal motion of the
cavity provides insight into complex fluid dynamics and opens the door
to further exploration and applications.

"Understanding buoyant sphere dynamics and cavity formation can inspire
new designs and innovations in fields beyond marine engineering," said Kamoliddinov. "It can potentially lead to new novel propulsion systems,
drag reduction strategies, fluidic propulsion systems, and fluidic
devices that harness the characteristics of buoyant spheres."
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Content may be edited for style and length.


========================================================================== Journal Reference:
1. Farrukh Kamoliddinov, Ivan U. Vakarelski, Sigurdur T. Thoroddsen,
Tadd T.

Truscott. Skipping under water: Buoyant sphere hydrodynamics at
the air- water interface. Physics of Fluids, 2023; 35 (7) DOI:
10.1063/5.0153610 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/07/230711133104.htm

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