7,000 reputation
1524
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 2 years, 11 months
seen 4 hours ago

BS Mechanical Engr.
PhD CS(AI)
CS Prof (4yr)
Numerous consulting jobs.
15 yr at http://www.pharsight.com
Published book on CS & several articles
4 kids, 2 grand
Pilot(student)

P.S. The picture is a Beta-prime distribution. It shows the program speedup factors you can get if you see a problem twice in 2, 3, 4, and 5 samples.


Aug
5
comment What does centre of lift depend on?
@Jan: The part of your question I'm not sure I can answer is - what produces the upwash? Could it be the lower pressure above the wing drawing the leading air up?
Aug
5
comment What does centre of lift depend on?
It's a good question. I like this source. The program he uses to calculate flow about an airfoil should give the answer.
Jul
31
comment Airplane on a treadmill
@MarkBiwojno: John is right. What matters to an airplane is air, not ground. A Cessna 172 requires air to be traveling past the wing at about 55 nautical miles per hour. The wing deflects the air downward, creating more lift than the plane weighs, so it takes off. The ground can be going forward, backward, sideways, whatever. What matters is the motion of air over the wing. The propeller creates thrust against air, to accelerate the aircraft. The wheels, skids, floats, are only there to hold it up when it's not supported by the air.
Jul
29
comment From where comes the raindrop
The cloud and the raindrop are carried by the mass of air, except that the raindrops fall because they are bigger and heavier than cloud droplets. They just do what the air tells them to do.
Jul
29
comment Erosion effect from Coriolis force in a South-to-North water channel?
I agree with your instinct that those sides would experience wear, and of course the flow rate would matter. I would expect the effect to be least at the equator, and greatest near the poles.
Jul
22
comment Is a falling, perfect sheet of fluid possible to create?
This would be a good experiment to try in micro-gravity. I think the only significant force would be surface tension, which you could minimize by a) making it large, or b) making it soapy :), or c) putting a solid ring around it.
Jul
18
comment Another layman blackhole question, pulling one end of a string out from behind the event horizon
You could just have a stationary scaffold around the entire black hole, and stand on that.
Jul
17
comment Add weight in front or behind the moving wheel?
@user55493: I see kids do it all the time. They go up-hill on their skateboards in a series of S-turns. Each curve of the S-turn, they are pushing sideways. It doesn't matter how many wheels they do it on, or whether their weight is forward or back. What matters is the sideways push.
Jul
16
revised Add weight in front or behind the moving wheel?
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Jul
16
answered Add weight in front or behind the moving wheel?
Jul
16
revised Add weight in front or behind the moving wheel?
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Jul
14
comment Does the Higgs boson give mass to ALL other particles?
Is it possible that the mass of nucleons is mostly the energy (over $c^2$) of the binding of their components, and not really anything to do with the Higgs field?
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS: It's a great question you asked. In my pilot training, I was taught to be very aware of "wake turbulence" - those invisible vortices coming off heavy-plane wingtips.
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS: I just googled "vortex merging" and a ton of high-quality stuff turned up!
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS: Now I'm the one who's skeptical :) Any vortex has to have a central region of low pressure, so that the pressure gradient provides the radial acceleration keeping it circular, so when the vortices come close together, the pressure gradients have to superimpose, affecting the paths of particles. But the trouble is, if that were the only effect, then counterrotating vortices would also merge. Hmmm...
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS: Well, as I said, when they come close together there will be counter-rotation between them. This will divert flow from each vortex to the other. If you're after a mathematical description of this process, maybe you should research it or better yet, construct it. For the other case, counter-rotating vortices, they don't merge because the physics are obvious, as Floris pointed out.
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS. Then check Floris' answer. It's a simple matter of conservation of vorticity (i.e. angular momentum), and kinetic energy.
Jul
14
revised Why do co-rotating vortices coalesce, but not counter-rotating ones?
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Jul
14
revised Why do co-rotating vortices coalesce, but not counter-rotating ones?
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Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS. Forget subsumption. They simply merge, because each little parcel of air follows a path.