8,422 reputation
1730
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 3 years, 8 months
seen 45 mins 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.


45m
revised Why is a beam reach the fastest point of sail on modern sailboats?
added 377 characters in body
1h
revised Why is a beam reach the fastest point of sail on modern sailboats?
added 11 characters in body
1h
answered Why is a beam reach the fastest point of sail on modern sailboats?
21h
comment Why is a beam reach the fastest point of sail on modern sailboats?
Have you ever taken a wet watermelon seed between your thumb and finger and squeezed it, to make it shoot out? That's a crude way to describe what's going on. The sail is one finger, and the centerboard is the other. If there were no water drag, there is really no limit to how fast the boat could go. It can really do this downwind or upwind as well, but the effect is strongest on a reach.
1d
comment Coriolis Effect vs airplane
@pittacus: If instead of an airplane, you launched a rocket above the atmosphere, yes it would be in a different place when it reached the equator. In the airplane, the air mass it is traveling in gradually picks up speed as the plane goes south, so it would experience this as a slight force from the right, just as in the car. Any plane is constantly adjusting for wind, so it would not be noticed.
2d
comment How do compressible fluids behave near a sink?
You have a spherical reservoir, in 0G, with a sink at the center. Velocity depends on the volume flow rate out of the sink, and you don't say anything about that. As long as the velocity is sufficiently below the speed of sound in the fluid, you can treat the fluid as incompressible. Keep in mind you're going to get a vortex around the sink, because the angular momentum of the fluid will almost certainly be > 0.
May
26
answered Are atoms compressible?
May
24
comment Balloon aerodynamics
You're basically saying the balloon is a bubble, and as it goes up, it expands (just as it would if it only contained air, not helium). That doesn't explain the extra tube hanging off the gas bag. I don't know its purpose either, though I can guess it's for filling, as @PeterKämpf said.
May
22
revised Determine travel for different rate springs in series
edited body
May
22
answered Determine travel for different rate springs in series
May
22
answered What is the curve described by the water of a wet spinning tennis ball?
May
21
comment Volumetric flow rate as a function of radius of pipe
@Floris: you put it better than I did.
May
21
comment Volumetric flow rate as a function of radius of pipe
Keep in mind that flow through an orifice and flow through a pipe are different. Flow through a pipe is viscosity-limited, so flow rate is proportional to pressure drop. Flow rate through an orifice is proportional to square root of pressure drop. It also depends strongly on the shape of the entrance to the orifice. Google "orifice flow".
May
19
comment How fast will 1 Liter of 65°C water get back to 20°C?
Not really. This is not a simple subject. Just google "boiler heat loss".
May
19
comment How fast will 1 Liter of 65°C water get back to 20°C?
You don't mention the insulation of the boiler.
May
17
comment Ocean surface mean current flow meaning
Excellent question, and there's also the issue of wind. Would it make sense to filter it, to smooth out local noise?
May
16
awarded  aerodynamics
May
15
comment Numerical modelling of a step function in time in a hydrodynamic system. (Runge Kutta fourth order)
@Floris: The models we make are always idealized at some level - we take that as a given. Since we're trying to fit a model to rather sparse data, we have to keep the model simple enough that the data can say something about it, so the exact mechanism for things that take almost no time is pedantic.
May
14
comment How do eagles fly slowly for a long time?
@Jubobs: It's not that soaring is different from flapping. All birds flap their wings to put energy into their flight, and all birds glide when they don't need any additional height or speed. All birds are able to soar, which is just gliding in updrafts. Some soar more than others, depending on what they need to do.
May
14
revised How do eagles fly slowly for a long time?
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