Archive for the ‘Fluid Dynamics’ Category

Cricket swing theory does not hold water: study

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The widely-held belief that moisture in the air during humid conditions helps make a cricket ball swing has been clean bowled in a scientific study.

Swing bowling — when a delivery curves sideways in mid-air — has long been regarded as one of the game’s dark arts, not only deceiving hapless batsmen but also puzzling cricket-loving scientists.
Researchers from Britain’s Sheffield Hallam University and the University of Auckland in New Zealand reviewed scientific literature on the subject and conducted their own tests to try to get to the bottom of the mystery.
From the earliest studies of the phenomenon in the 1950s to the “seminal review of sports ball dynamics” by NASA scientist Rabindra Mehta in 1985, they found humidity was consistently cited as a crucial factor in achieving swing.
The researchers tested the theory using 3D laser scanners in an atmospheric chamber to measure the effect different humidity levels had on deliveries using balls which had been “aged” to simulate match conditions.
While altitude and the age of the ball both increased swing, the scientists did not discover any link between moisture levels in the air and sideways movement of the ball.

While altitude and the age of the ball both increased swing during bowling, the scientists did not discover any link between moisture levels in the air and sideways movement of the cricket ball.

“This study shows that there is no direct or indirect manner in which humidity can significantly affect the ability of the bowler to make the ball swing,” they concluded in research published in the online journal Procedia Engineering this week.
“It is therefore logical to conclude that humidity may not have the significant influence on swing bowling that is widely assumed.”
Instead, the researchers put forward their own theory that cloud cover provided the ideal environment for swing bowling because it reduced turbulence in the air caused by heating from sunlight.
They said such still conditions meant the air surrounding the ball during the delivery was less likely to be disturbed, making it easier to produce the “asymmetrical” flight needed for swing bowling.
“What is clear is that the scientific community should turn their attention away from the question of humidity and focus their efforts to test the cloud cover hypothesis,” they said.
(c) 2012 AF
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Written by physicsgg

May 30, 2012 at 12:50 pm

Posted in Fluid Dynamics, PHYSICS

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Is this the most boring experiment ever?

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Scientists watch drops of pitch form – and there have been eight in 75 years

  • Experiment began in 1927 to prove pitch is a liquid
  • In 75 years, just EIGHT drops have fallen
  • The rate is slowing, and last drop fell 12 years ago
  • Current custodian has watched since 60s – but has missed all five drops that have fallen
  • Drop ‘could’ fall this year, but 2013 ‘is a better bet’

A lump of the black substance, which can be broken with a hammer, was put into a glass funnel – and the waiting began.The experiment has been running now for 85 years and it is estimated that it will last for another century

It’s the world’s longest-running experiment – and the very, very patient scientists in charge are waiting for a single drop of pitch to fall, 12 YEARS after the last one fell.
The ‘pitch drop’ experiment began in 1927 and was designed to show that solid-looking pitch was, in fact, a liquid.
The experiment has been running now for 85 years and it is estimated that it will last for another century…..

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Written by physicsgg

May 14, 2012 at 7:27 am

A tiny flame shines light on supernovae explosions

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This figure shows four snapshots in time as the flame propagates initially subsonically outward reaching a specified density (green) at which point the flame transitions to a detonation. Shown in color is a reaction progress variable describing the burning of nuclear statistical quasi-equilibrium (NSQE) products to nuclear statistical equilibrium (NSE) products. The blue contour marks the separation between the previously convective core and the isothermal outer layer. Note that the scale of the right-most figure is larger than the other three.
Starting from the behavior of small flames in the laboratory, a team of researchers has gained new insights into the titanic forces that drive Type Ia supernova explosions. These stellar explosions are important tools for studying the evolution of the universe, so a better understanding of how they behave would help answer some of the fundamental questions in astronomy.
Type Ia supernovae form when a white dwarf star – the left-over cinder of a star like our Sun – accumulates so much mass from a companion star that it reignites its collapsed stellar furnace and detonates, briefly outshining all other stars in its host galaxy. Because these stellar explosions have a characteristic brightness, astronomers use them to calculate cosmic distances. (It was by studying Type Ia supernovae that two independent research teams determined that the expansion of the Universe was accelerating, earning them the 2011 Nobel Prize in Physics).
To better understand the complex conditions driving this type of supernova, the researchers performed new 3-D calculations of the turbulence that is thought to push a slow-burning flame past its limits, causing a rapid detonation — the so-called deflagration-to-detonation transition (DDT). How this transition might occur is hotly debated, and these calculations provide insights into what is happening at the moment when the white dwarf star makes this spectacular transition to supernova. “Turbulence properties inferred from these simulations provides insight into the DDT process, if it occurs,” said Aaron Jackson, currently an NRC Research Associate working in the Laboratory for Computational Physics and Fluid Dynamics at the Naval Research Laboratory in Washington, D.C. At the time of this research, Jackson was a graduate student at Stony Brook University on Long Island, New York.
Jackson and his colleagues Dean Townsley from the University of Alabama at Tuscaloosa, and Alan Calder also of Stony Brook, will present their data at the American Physical Society’s (APS) Division of Fluid Dynamics (DFD) meeting in Baltimore, Nov. 20-22, 2011.
While the deflagration-detonation transition mechanism is still not well understood, a prevailing hypothesis in the astrophysics community is that if turbulence is intense enough, DDT will occur. Extreme turbulent intensities inferred in the white dwarf from the researchers’ simulations suggest DDT is likely, but the lack of knowledge about the process allows a large range of outcomes from the explosion. Matching simulations to observed supernovae can identify likely conditions for DDT.
“There are a few options for how to simulate how they [supernovae] might work, each of which has different advantages and disadvantages,” said Townsley. “Our goal is to provide a more realistic simulation of how a given supernova scenario will perform, but that is a long-term goal and involves many different improvements that are still in progress.”
The researchers speculate that this better understanding of the physical underpinnings of the explosion mechanism will give us more confidence in using Type Ia supernovae as standard candles, and may yield more precise distance estimates.
More information: The talk, “Turbulence and Combustion in Type Ia Supernovae,” is on Tuesday, Nov. 22, 2011. Abstract: http://absimage.ap … 1-001839.pdf
Provided by American Institute of Physics

Written by physicsgg

November 22, 2011 at 4:56 pm

Posted in ASTROPHYSICS, Fluid Dynamics

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The Physics of Guinness Beer

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Physics and beer… I know to some people (you know who you are, college kids!), that’s a definition of heaven. 🙂

This article, video, and paper should be up a lot of people’s alley. It discusses the physics of Guinness beer, and tries to tackle some very profound questions:

For example, look closely at a pint of Guinness and tell me: do the bubbles go up, or do the bubbles go down? Why is the head coloured the way it is? Is beer foam a gas, liquid or solid? I thought you might enjoy this little video as a follow up, where an Irish physicist discusses the “fizzics” of bubble formation in Guinness beer.

There is a video link to the article, which I will also link to here:

And the paper[1] that was published in Physics of Fluids (I kid you not) can be obtained from here as well.
[1] M. Robinson et al., Phys. Fluids v. 20, p.067101 (2008).

Written by physicsgg

August 4, 2011 at 3:10 pm

Posted in Fluid Dynamics, HUMOR

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Cloak could hide ships from flowing water

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A motorboat cuts a wake. Could vessels of the future evade detection using metamaterials?

Ships of the future may be able to move through the water without a creating a wake. That is according to a pair of physicists in the US, who have proposed a new type of material that lets water flow around an object as if it were not there at all. The design, which has yet to be built, could boost the energy efficiency of ships and submarines – and even prevent them from being detected. “The main function of [our] structure is to prevent fluid flowing around an object from ‘feeling’ that object,” says Yaroslav Urzhumov of Duke University.

The past five years have seen a flurry of research into invisibility cloaks. The first functioning cloak, which operated for electromagnetic waves in the microwave range, was demonstrated by a team led by David Smith at Duke University in 2006, and since then researchers have proposed and demonstrated cloaks that work for visible light, sound and even events in time….. Read the rest of this entry »

Written by physicsgg

July 21, 2011 at 2:20 pm

Posted in Fluid Dynamics, waves