7,628 reputation
1628
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 3 years, 2 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.


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
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.
Jul
11
comment Computing the force generated by a sail on a boat
@T.Kiley: I'm afraid you need to know how the sail functions as an airfoil - namely what is its chord, its angle of attack, and its coefficients of lift and drag as a function of those.
Jul
11
comment How effective is speeding?
It's more important to minimize time spent going slow than to go fast.
Jul
9
comment Problem understanding basic sail mechanics
+1 @T.Kiley: Don't confuse yourself with the Bernoulli kerfuffle. Just consider the centerboard of the boat as if it were a skate. Consider the sail as if it were a knife blade, and the air were jello. Then satisfy yourself that no matter how fast the boat is sailing downwind, there is a sail angle that can give it forward thrust. A simple physical analogy is a wet watermellon seed squeezed between thumb and forefinger. Here's a similar question.
Jul
3
comment Do airlocks in space decompress violently as they do in movies?
For the airlock, it depends how suddenly the air is released. People consist of lots of muscle, fat, bones, etc. plus liquid plasma in fairly strong tubes, plus air in lungs. If they don't try to hold their breath, there's not much to decompress.
Jul
3
comment How should I throttle my rocket to reach highest altitude?
Here is a *very worthwhile read: *
Jul
2
comment Paper airplane physics
@J...: The OP had some basic misconceptions that needed to be corrected. When that is done, the equations just fall out. I was trying to correct the misconceptions.
Jun
30
comment What does a wing do that an engine can't?
There are misconceptions in some of the answers here. Lift/Drag ratio is beside the point. Angle of the engine axis is beside the point. Gliders vs. rockets are beside the point. Falling plates are beside the point. The answers that are on point are the ones that talk about momentum vs. energy of the downwash.
Jun
22
comment Prerequisites for Halliday Resnick Walker
Khan Academy is hard to beat. Just be sure, when you take calculus in school, that you are humble, and take the material at the rate it is taught, even if you know it already.
Jun
12
comment Why air above airplane's wing moves faster?
It is a recurring, and absolutely wrong, conception that the air has to rejoin itself at the trailing edge. In fact, wings could not work if it did, because lift requires circulation. Check this very good explanation.
Jun
4
comment Why is the application of probability in QM fundamentally different from application of probability in other areas?
@TwoBs has it right. In QM, probabilities don't add, they interfere, because their amplitudes add. And if you're concerned about independence, just break down the cross-product, and consider each possibility independently.
Jun
3
comment What's the advantage of NASA's flying saucer over traditional aerodynamic models?
Currently they go from 1) a small aeroshell to 2) a large parachute. They want something in between, a 1.5
Jun
3
comment Does gravity cause Archimedes' principle and how?
@mpv has the right answer. Flotation has nothing to do with gravity gradient. It has everything to do with pressure gradient, which is simply the weight of liquid above. The deeper you go, the more water you are holding up, so the higher the pressure. If you are a cylinder of air, then the weight above your lower surface is less than it would be if you were full of water. That difference in weight is the buoyancy force pushing you up.
Jun
2
comment Are there any substances that allow sound to travel better then air?
A lot depends on dimensions. If the medium is fully 3d over long distances, energy falls off as $1/r^2$. If it's 2d, like a temperature layer in air or water, it is $1/r$, so sound can carry a lot farther. If it's 1d, like a tin-can string, pipe, or iron rail, the sound can go very far without dissipating.
Jun
2
comment Are there any substances that allow sound to travel better then air?
+ Air isn't so bad either, at low frequencies.
Jun
2
comment Quick question on parallax and parsec
There is a background of relatively fixed stars. You see a pair of stars 3" apart. Six months later they are still 3" apart, but the pair of them together appear to have moved 1" against the background. The movement against the background is the parallax.
May
30
comment Does the lift created by a wing change when the slats are deployed?
What slats and flaps do is increase the effective camber, or curve angle of the wing. Then the definition of AoA gets a bit fuzzy. What is a chord line that everyone could agree on?
May
30
comment Why do clouds fly?
@user2820052: NP. The air has a temperature, which is just the air molecules moving around excitedly, bumping into themselves and everything else. That bumping is what pressure is. If you're teeny-tiny and weigh nothing (or practically nothing) you will just bump around in the general chaos. Now, take a cubic liter of water - it has 100 square cm area on a side, and weighs 1kg. Now take a cubic cc of water, it has 1 square cm area on a side, and weighs 1 gram. 100 times less area, 1000 times less weight. Keep going. That's why dust motes fly and mountains don't.
May
29
comment Why do clouds fly?
@user2820052: forget the density and temperature. What matters is the ratio of volume to area. If a droplet has a diameter of 10^-4 cm, then its ratio of volume to surface area is 10^-4 that of a cc of water. In other words, its weight becomes insignificant compared to its area, so gravity has no more effect on it than a hair on your head.