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Post by mikegarrison on Apr 24, 2012 15:10:22 GMT -5
FYI taken right from your link. "The Magnus effect is a special case of Bernoulli's principle" So I would guess that Bernoulli is applicable but I could be misreading your link. I don't have any interest in getting into right now, but while the Bernoulli effect is very real (within certain constraints), by itself it would not explain any of this behavior. Please see the section in the Bernoulli article addressing lift. Aerodynamicists get awfully tired of trying address the misconceptions that people have on this subject. It's kind of like saying "gasoline burns, and that's why cars work." Well, yes, sort of, but burning gasoline by itself won't make your car go forward. There is a lot more involved. If you need to remember one name for explaining the aerodynamics of spinning balls, that name should be "Magnus," not "Bernoulli."
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Post by oldman on Apr 24, 2012 18:08:22 GMT -5
I have a complete understanding of the physic. If we were talking about a topspin then Magnus effect is the correct answer, however the question is about a floater hence non spinning ball which is best described by Bernoulli not Magnus.
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Post by mikegarrison on Apr 24, 2012 18:17:52 GMT -5
I have a complete understanding of the physic. If we were talking about a topspin then Magnus effect is the correct answer, however the question is about a floater hence non spinning ball which is best described by Bernoulli not Magnus. No, not really. That's why I included the link to the article on vortex shedding. The "float" has to do with differential separation of the boundary layer between one side of the ball and the other. This is a complex phenomenon of viscous flow and has nothing to do with Bernoulli, which is a principle of inviscid flow. (I'm not saying that a float serve sheds rhythmic vortices the way that is shown on that page. However, the idea is similar. The flow around the ball is different on one side than it is on the other, and that induces a difference in drag between one side and the other.)
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Post by BearClause on Apr 24, 2012 19:08:26 GMT -5
I'll do it for ten bucks less than whatever Garrison wants. Me and my trusty HP-45 scientific calculator can handle it. * * Actually, that's a bald faced lie. I hated tensor calculus. I learned just enough tensor calculus to create stress in my life. Now I know why I got into digital electronics. For me, life is a series of on and off switches.
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Post by Not Me on Apr 24, 2012 21:03:01 GMT -5
Now I remember one reason why I switched from engineering to business in college.
Too much thought and not enough girls.
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Post by Phaedrus on Apr 24, 2012 21:13:40 GMT -5
I learned just enough tensor calculus to create stress in my life. Now I know why I got into digital electronics. For me, life is a series of on and off switches. I can count from zero to one in integers too.
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Post by volleytragic on Apr 25, 2012 0:17:57 GMT -5
The magnus effect only relates to spinning object, so we are talking a topspin serve or hit. The effect is that the air that passes in the same direction as the ball is spinning travels faster and the air that passes across the top of the ball slows down or creates turbulence, causing the ball to dip. There was a study done quite awhile ago about the optimal speed of a ball with regards to a float and it was around 35mph. I would think, based on this that it would be more an advantage to serve in this range, than look at distance behind the base line.
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Post by BearClause on Apr 25, 2012 0:49:27 GMT -5
The magnus effect only relates to spinning object, so we are talking a topspin serve or hit. The effect is that the air that passes in the same direction as the ball is spinning travels faster and the air that passes across the top of the ball slows down or creates turbulence, causing the ball to dip. There was a study done quite awhile ago about the optimal speed of a ball with regards to a float and it was around 35mph. I would think, based on this that it would be more an advantage to serve in this range, than look at distance behind the base line. I think the distance behind the line as well as the height of the contact point make a difference on the vertical velocity. I'm pretty sure it's a parabolic flight to some degree, and a further distance has an effect. I remember seeing the typical flight path of a fly ball in baseball, and of course it wasn't a pure parabola. As anyone who has seen a game at Coors Field, the ball travels further in the thinner air. A volleyball traveling through the air will slow down and eventually drop. I've watched enough to see that a lot of the players who serve from way behind the service line tend to serve it rather flat, but are trying to get it to drop faster by the time it reaches the receiver.
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Post by lonewolf on Apr 25, 2012 1:53:21 GMT -5
The other issue is spin, and it is generally accepted that the maximum float will occur when the ball rotates about 1/4 to 1/2 of a rotation during its entire flight. (I'd like to see that verified, also.) This very small amount of spin will cause the ball to present differently shaped surfaces to the air flow and increase the random "float" movements. I've heard this often when commenting on a baseball. However (if the rotation is indeed needed for maximum float), I wonder if & how the different surface structures of a volleyball as compared to a baseball (or even among other volleyballs) would be affected, and what their optimum rotation (if any at all) would be.
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Post by Garand on Apr 25, 2012 19:43:59 GMT -5
A volleyball is about twice as heavy as a baseball, but because of its much larger size, it has about eight times the surface area of a baseball. Glossing over a few details, we can see that it will be subject to more movement in flight than a baseball. I think we would all agree that we can see this pretty easily when we watch these two sports.
Each ball has surface irregularities, both micro and macro. The micro, or general surface roughness, is roughly similar for each, and each ball has some macro irregularities: the seams. The effects of these surface qualities combine with other factors to produce movement in flight. Even without some of Phaedrus's fancy CFD modeling calcs, it is apparent that the volleyball can "dance around" more than a baseball.
I believe that someone mentioned earlier that they had seen some studies of the optimum floater rotation for a volleyball. Any links to that? I'm guessing the volleyball manufacturers have data like these.
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Post by hegotgame on Apr 25, 2012 21:03:12 GMT -5
For those of you nerds out there who get fired up about shear layers and sports ball aerodynamics, a few papers have come out recently on golf ball aerodynamics. These are the first direct numerical simulations at real golf ball velocities and they do a great job of showing how the dimples on the golf ball lead to the drag crisis for a non-rotating ball. In another paper that will be published soon they simulated a rotating golf ball and were able to reproduce the negative lift (down force) that can occur under the right conditions for a ball with backspin. I think that Thomas Cairns found a similar behavior in his studies of volleyball trajectories i.e. balls with topspin actually experienced a positive lift force under just the right conditions. Here are the references:
Smith, Beratlis, Balaras, Squires & Tsunoda, "Numerical investigation of the flow over a golf ball in the subcritical and supercritical regimes", International Journal of Heat and Fluid Flow Volume 31 (3) pp. 262-273. Beratlis, Squires & Balaras, "Numerical investigation of Magnus effect on dimpled spheres", Journal of Turbulence (to appear).
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Post by mikegarrison on Apr 25, 2012 21:28:36 GMT -5
I'm not sure the Reynolds numbers for golf balls and volleyballs are the same. I think a volleyball is about five times bigger than a golf ball, but is a golf ball drive five times faster than a volleyball serve? More? Less?
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Post by hegotgame on Apr 25, 2012 21:34:55 GMT -5
They're not that far off for a float serve at 30-40 mph and a golf ball at 130-150 mph (volleyball diameter is a little less than 5 golf ball diameters). If you look on YouTube for the long distance driving competition videos, the guys that win have club speeds around 150 mph and ball speeds over 200 mph.
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