Subscribe to our free daily newsletters
. 24/7 Space News .




Subscribe to our free daily newsletters



TECH SPACE
Why buoyant spheres don't always leap out of the water
by Staff Writers
Logan UT (SPX) Nov 07, 2016


Researchers studied rising sphere pop-up height.

It's a common swimming pool game: Force a buoyant ball underwater and let it go. The ball springs to the surface and jumps into the air. But, submerge the ball deeper underwater and the effect is often disappointing. Contrary to our intuition, increasing the release depth often leads to a decreased pop-up height.

This simple fluid dynamics question has puzzled physicists for decades, but a new study published in Physical Review Fluids, offers new perspective into the phenomenon and may clarify topics related to water exit dynamics and ocean engineering.

A team of researchers from Utah State University, Dartmouth College and Brigham Young University used high-speed imaging and particle image velocimetry to describe why buoyant spheres ascending through a fluid don't always behave the way we expect them to.

"The pop-up height depends on the speed of the sphere at the point it breaches the free surface," said lead investigator and assistant professor of mechanical engineering at USU, Tadd Truscott. "It doesn't matter how deep the ball is when it's released. There are a number of factors that affect its speed and trajectory until it reaches the surface."

During ascent, wake and vortex structures often form around the sphere. Asymmetric vortex shedding and wake formations can alter a sphere's upward movement and result in a non-linear trajectory. The authors demonstrate that rising spheres usually fall under one of two acceleration categories: 1) a vertical regime, or 2) an oscillatory regime.

"The vertical regime exhibits a nearly vertical underwater trajectory and results in the largest pop-up heights," explains Brenden Epps, assistant professor of engineering at Dartmouth and co-author on the study. "The oscillatory regime exhibits a trajectory with periodic lateral motions and results in lower pop-up heights. Sometimes the ball may even breach the surface and skim across it rather than rising into the air."

To test rising sphere behavior, researchers submerged stainless steel balls into a test tank at various depths and held them in place using a suction cup connected to a vacuum release mechanism. After sufficient wait time to allow the water to become quiescent, the suction cup released the sphere while four synchronized high-speed cameras recorded its ascent.

In total, 664 tests were performed using four balls of varying diameters and release depths. As expected, the maximum pop-up heights occurred when spheres were released from shallow depths. The lowest pop-up heights occurred when spheres were released from greater depths.

But the conversation doesn't end there. Part of the pop-up height problem also depends on what happens to the sphere at the point of surface breach.

"Once the sphere clears the surface, the only force acting on it is gravity," Truscott added. "So the pop-up height is determined by a transfer of kinetic energy to potential energy of the sphere after clearing the surface. However, the speed (and thus kinetic energy) of the sphere after it has cleared the surface is dictated both by the speed at which it approaches the surface (set by the underwater dynamics) and the change in speed during breach."

The authors say their study has a broad range of applications. A better understanding of water exit dynamics, they explain, can be useful in maritime engineering and marine biology.

"Penguins exit the water after a hunt or to avoid predators," they write. "It has been hypothesized that emperor penguins use bubbles released from their feathers during ascent in order to reduce drag and increase exit velocity and pop-up height. ... Other important applications of the pop-up effect include underwater vehicle exit, floating sea structures and wave-energy converters."


Comment on this article using your Disqus, Facebook, Google or Twitter login.


Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once


credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly


paypal only

.


Related Links
Utah State University
Space Technology News - Applications and Research






Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Previous Report
TECH SPACE
Cal State LA partners with NASA to study how materials solidify in space
Los Angeles CA (SPX) Nov 04, 2016
NASA has awarded Cal State LA two grants to conduct materials science experiments with the International Space Station. The grants are made through NASA's Physical Sciences Research program and will provide a total of $840,000 in funding. Using simulation, the research will examine how materials solidify under different circumstances-in space, in the absence of gravity, and on earth where gravit ... read more


TECH SPACE
BRICS Space Agencies Sign Memorandum on Cooperation in Space Exploration

Clearing the Air in Space

Home is Where the Astronaut Is

Next stop Baikonur for ESA astronaut Thomas Pesquet

TECH SPACE
Aerojet Rocketdyne completes CST launch abort engine hot fire tests

NASA Uses Tunnel Approach to Study How Heat Affects SLS Rocket

SpaceX Aims to Resume Falcon 9 Flights in 2016, Blames Helium Tank for Explosion

Raytheon gets $174 million Hypersonic Air-Breathing Weapon contract

TECH SPACE
Unusual Martian region leaves clues to planet's past

A record of ancient tectonic stress on Mars

Curiosity Mars Rover Checks Odd-looking Iron Meteorite

New instrument could search for signatures of life on Mars

TECH SPACE
Nations ask to play part in space lab

China launches first heavy-lift rocket

China to launch Long March-5 carrier rocket in November

US, China hold second meeting on advancing space cooperation

TECH SPACE
ISRO's World record bid: Launching 83 satellites on single rocket

Shared vision and goals for the future of Europe in space

SSL delivers Sky Perfect JSAT satellite to Kourou

Dream coming true for ISS-bound rookie French astronaut

TECH SPACE
Establishing an advanced bonding technique for tungsten and copper alloys

Engineers develop new magnetic ink to print self-healing devices that heal in record time

Why buoyant spheres don't always leap out of the water

Cal State LA partners with NASA to study how materials solidify in space

TECH SPACE
What happens to a pathogenic fungus grown in space?

How Planets Like Jupiter Form

Giant Rings Around Exoplanet Turn in the Wrong Direction

Preferentially Earth-sized Planets with Lots of Water

TECH SPACE
Mystery solved behind birth of Saturn's rings

Last Bits of 2015 Pluto Flyby Data Received on Earth

Uranus may have two undiscovered moons

Possible Clouds on Pluto, Next Target is Reddish




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News






The content herein, unless otherwise known to be public domain, are Copyright 1995-2017 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement