What Term for the vacuum created by flat surface passing over hydraulic

planetrbm,

In aircraft, I believe this is called ground effect, as far as a formula, may try looking into bernoulli's equations for fluid flow.

phoenix911

Cavitation I beleive is the word your looking for.

Try looking at coeficient of drag

Resistance or drag. I believe Bernoulli's Equation is the way to calculate it.

http://en.wikipedia.org/wiki/Bernoulli%27s_theorem

So you're saying that Bernoulli's Equation explains why water is sucked out of a bilge?

Is this the same as a siphon?

A siphon works because of air pressure differential between the water surface and the discharge point, and gravity; that's why the discharge point of a siphon must always be lower than the water surface. And no, Bernoulli's equation doesn't explain this: it only calculates it. The explanation is called the Kutta Effect.

I'm trying to calculate how a sled, moving down a snow covered mountain, creates suction when the surface of the snow is wet. Is this calculated by bernoulli's equation?

Inuendo and out the other

Probably the best fit for what you are describing is the Coanda effect.

Ah, briliant! Answered by surface tension. Thank you Ken! Now: Is it posible to increase maximum fall rate velocity via the use of gravity driven or airodynamic propulsion like a turbo? i.e.: can you make a bowling ball fall faster to the earth by attaching anything (turbo jet?) Powered ONLY by the fall itself? My guess is a simple no..... really?

It seems apparent that if you have an object falling in a perpendicular line to earth because of the mutual attraction of the earth and the object, ie., gravity, and you add a force to push the object along that vertical fall line of attraction, then the rate of fall (Although no longer actually just a fall effectuated by gravity) will increase.

if you can't see that just draw a picture of the trajectory, which I have just done in my mind, and note the forces at work and sum them up.

j.

i.e.: can you make a bowling ball fall faster to the earth by attaching anything (turbo jet?)

actually,

a ramjet.

phoenix911

Ok.....

Who thinks Jack is smokin' the rope?

Anyhooooo...

v

Next question:

Can we increase terminal velocity using magnetic energy derived from friction durring the fall?

Sooooo restrictive. What happens during the other three Seasons?

Hi,

this suction can be changed to lift by only a little change of tilt backwards.

The pressure distribution between the two plates is generated by the fluid that undergoes compression or expansion (from inlet cross-section to outlet) by the velocity of the plate.

The sliders in the hard-disk-drives act similar on air, lifting the heads up on a very small gap: an airbearing.

To calculate you need to solve the simplified Reynolds equation: any inertia-terms neglected.

This was published in the 60ies and 70ies in the ASLE journal. I think, Vohr was one of the major contributors.

In reality it can be viewed as a specialised case of Sommerfeld's fluid bearing theory (Germany 1906?).

If you refrain to an elongated shape where pressure-driven fluid velocities will be only in one direction the solution is simple:

take an increment of the fluid between the two plates, let move one of the plates, this will compress or expand the volume, this will create pressure, this pressure will create flow. Continuity will give one equation, viscous flow (Hagen-Poiseuille) the other one.

There is an analytical solution if the gap is parallel and the velocity is perpendicular to the gap (external movement) : this is a squeeze-film-damper.

There is no analytical solution (?) if the gap is tilted, but the resulting differential equation is readily solvable by numerical calculation.

The "boat hull over water" is more difficult as there is no second plate and an in and out suction of water to create an inertia based cushion on which the pressure or suction is developing.

RHABE

Ya know . . .,

All this math is great (and really hurts my pointy lil head) but if you're trying to solve an ACTUAL problem, why not look to something already in practical use. A golf ball travels farther, faster and straighter because of the dimples in it's skin, trapping little pockets of air which become little ball bearings of air.

it may not be all that simple, your talk micro laminator air flow. and the ball would have somewhat equal forces (with the dimples).

The dimples are a good idea though.

planetrbm,

(two things i like to add)

15-20 years ago, I was working in the ship yard with development of special ops crafts for the navy seals, We hired a design tem from the UK to design it.

the hull surface was very flat (no curved lines) as well as the chines. I had asked tem about it, and there response was, you want flat surfaces and sharp edges on so the water flows off, the eddies behind the chines were nominal drag.

off on a tangent,

These guys knew what they we're talking about, they brought out a government auction book and showed me all their crafts that were confiscated from drug runners, and said they were the drug runners boat of choice.

Fools, I told them, the boats that were'nt in there are the one that got away. those were the fast boats, and the boats we should be building, they could'nt answer that.

One other point, we were developing a aircaft/boat, that skimmed just above the water....I just can't remember what it was called, it looked bat like. I knew the designer of it (not personally) , I think he was a descendant of Igor Sikorsky.

Man, I'll have to look in my files (if I still have them) to pull up the name. that could help you out.

phoenix911

Phoenix

What you are refering to is "ground effect" as you eluded to in your first response.

Ground effect enables turkeys to fly. It is the compresive factor of near ground or surface flight that enables heavier flying objects to float or hover, as in hover craft, or land, as in space shuttle. And, why hover crafts and turkeys can't just sail away.

My problem is I need to calculate drag/vacume/surface tension on a flat hard surface (plate) sliding on a semi hydrolic/semi hard surface. I believe I'm best to assume a smoothe flat surface with a hydrolic medium.

Does principles of viscocity answer any of this?

From your post 8 and what you saying, would require CFD software, I for one do not have that kind of background,

Hi phoenix911

• One other point, we were developing a aircaft/boat, that skimmed just above the water....I just can't remember what it was called, it looked bat like. I knew the designer of it (not personally) , I think he was a descendant of Igor Sikorsky.

I believe you are speaking of what is usually referred to as a wing in ground effect vehicle and they usually look something like the one in the image on the right.

You can read more about wing in ground effect by following the links.

The Russian Military also tried building some large ground effect vehicles but they technical problems associated with trying to operate what is fundamentally an aircraft flying at an altitude of a couple of metres killed off the concept. The biggest problem is corrosion and aluminium alloys usually react badly to being immersed in salt laden water making such craft extremely maintenance intensive. Jet engines also don't take kindly to ingesting salt laden water so the idea died a natural death.

On a trivial note back between WWI and WWII when Claudius Dornier was trying to build long range flying boats they flew Dornier Do-X across the Atlantic Ocean. The only problem was the range of the aircraft at that time was insufficient to guarantee a successful crossing so the pilots flew the monster in ground effect for as much of the crossing as possible. They had been experimenting with the technique for some time and found they could extend the range by between 5% and 10%. The ultimate idea was to operate airlines using flying boats as they could land anywhere there was a large enough area of sheltered water. Since most large population centers are near harbors or on rivers the lack of runways or landing fields was not a problem. The transatlantic flight by the Do-X was successful but the political and social environment of the time pretty much stymied Dornier's work and by the time things settled down after WWII the airfields and runways constructed during the war years meant there was no longer a need for aircraft that could land on water.

One thing you may also find interesting is the thread entitled Lies, More Lies, and Arithmetic that was started by Blink back in October 2006. Basically it looks at Bernoulli's principle as taught by science teachers and text books, to explain the lift created by a wing doesn't hold up in practice. Being a pilot of both light aircraft and gliders I found it somewhat surprising, but if you take Bernoulli's principle and apply it to real aircraft the wing can't supply anything like the lift that is required to get an aircraft off the ground.

masu,

bingo,

That one looks bigger than the one we were developing, I just recalled the name, it was called Flare Craft. If I recalled there were issues. one of which was getting a test pilot.