8,647 reputation
1730
bio website en.wikipedia.org/wiki/…
location United States
age 71
visits member for 3 years, 10 months
seen 46 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.


Jun
13
comment By what factor would you have to slow down time for water to feel like glass?
The idea that glass is a liquid is an urban legend.
Jun
12
comment Fluid Dynamics applied to Aircraft wings
Please check out the other answers on the site. The flat-bottom-curved-top business is a widely-taught absolutely wrong explanation, and totally fails to explain aerobatic airplanes, which have symmetric airfoils. They fly just as well upside-down as right-side up. Almost any shape can fly, as long as it pulls the air into a downwash.
Jun
11
comment If one object, moving at a constant speed collides with another object - which is at rest - how much force has been applied?
There is no answer, because it depends on how stiff they are. If they are tennis balls (springy) the force will be less than if they are steel (hard).
May
28
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.
May
28
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.
May
26
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
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
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
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
13
comment Numerical modelling of a step function in time in a hydrodynamic system. (Runge Kutta fourth order)
It's not a deep concept. It happens all the time in pharmacometric modeling, like here. Here's something that may be a bit much. Basically, any pharmacometric model expressed as a set of differential equations has to receive doses at points in time. So the ODE solver runs up to that time and stops. Then the dose is given which, for example, bumps the amount of drug in blood plasma. Then the ODE solver is started up again, up to the next event time, like an observation.
May
13
comment Why don't we build helicopter based space shuttles?
Can airplanes fly in no atmosphere? Of course not. There's nothing for the wing to react against. A helicopter rotor is just a wing that goes in a circle. (They are called "rotary wing aircraft".)
May
12
comment If atoms are mostly empty space, why doesn't light pass through everything?
True, if you keep in mind that where an electron "is" is uncertain - it is a wave function that is spread out. So is a photon.
May
11
comment Why is paper (or any tailless) airplane pitch stable?
If you see it nosing up and stalling, that means move the weight further toward the front. It needs to be forward of the center of lift, wherever that is (but not too far forward).
May
11
comment Why is paper (or any tailless) airplane pitch stable?
@Cleric: Actually you can choose any point you like as the fulcrum, it doesn't matter. If you choose the CG, the lift of the main wing produces an up torque, and the tail a down torque. (In a vacuum there is no lift.) Go back to the simple aircraft. Now lengthen the back of the main wing until it touches the horizontal stabilizer. Now you have a single-wing aircraft, but it still works, because at the back there is less lift than at the front (or negative lift). The differential lift between front and back produces the torque. A simple paper airplane can illustrate this perfectly.
May
11
comment Why is paper (or any tailless) airplane pitch stable?
@Cleric: The speed-dependent torque due to differential lift doesn't go to zero. The weight in the nose produces its own torque that counteracts the speed-dependent torque, so it's stable when the total torque is zero.