SUBSIM Radio Room Forums - View Single Post - Sonar experts: How much sound crosses a layer?

OKO · 11-27-05, 12:14 AM

nothing better than some links =>

http://www.npmoc.navy.mil/KBay/backgroundnoise.htm

HYDRODYNAMIC NOISE

Self noise resulting from the flow of water past the hydrophones of the hull-borne sonar, its supports, and the hull structure of the platform is hydrodynamic noise. In submarines, this type of noise also includes the noise generated by turbulent pressures upon the hydrophones from flow eddies, as well as vibrations from the submarine's plating and sonar gear. In addition, the water flow around the sonar dome sometimes creates the major portion of self noise. This noise is known as flow induced resonance, or FIR.

http://en.wikipedia.org/wiki/Turbulence

Consider the flow of water over a simple smooth object, such as a sphere. At very low speeds the flow is laminar; i.e., the flow is smooth (though it may involve vortices on a large scale). As the speed increases, at some point the transition is made to turbulent ("chaotic") flow. In turbulent flow, unsteady vortices appear on many scales and interact with each other. Drag due to boundary layer skin friction increases. The structure and location of boundary layer separation often changes, sometimes resulting in a reduction of overall drag. Because laminar-turbulent transition is governed by Reynolds number, the same transition occurs if the size of the object is gradually increased, or the viscosity of the fluid is decreased, or if the density of the fluid is increased.

http://www.cora.nwra.com/~werne/eos/...urbulence.html

and the last (i won't spend all my time to prove you my assertions ...)

http://kr.cs.ait.ac.th/~radok/physics/f2.htm

Turbulent flow

At a critical velocity, a laminar flow becomes turbulent. If for a tube with a circular cross-section the the expression vd/n (v average velocity, d tube diameter) serves as critical number R, the validity of Poiseuille's Law ends at R = 2000, when turbulence begins. In a tube with a diameter of 1 cm, through passes water at 10ºC, R = 2000 yields a mean velocity of about 26 cm/sec. Through this tube, a slower flow, as every flow with a smaller value of R will be laminar (layered). If the velocity increases to this value of if you obtain it by enlargement of the tube diameter or heating of the water (decrease of m), there will occur the change over. The amount of fluid for a given pressure drop will then be smaller than the value, given by Poiseuille's formula, that is, the resistance experienced by the flow increases. The causes of turbulence were not yet known in 1935.

Now we need to determine the critical point for all subs
it's not so difficult to evaluate, as I said before.
And, more difficult, we need to evaluate what happen at the critical point, how much is the gap.
We could talk about that if you have finished to contest physical law :hmm:

11-27-05, 12:14 AM	#9
OKO Commander Join Date: Jan 2002 Location: Solar system, mainly on earth Posts: 476 Downloads: 62 Uploads: 0	nothing better than some links => http://www.npmoc.navy.mil/KBay/backgroundnoise.htm HYDRODYNAMIC NOISE Self noise resulting from the flow of water past the hydrophones of the hull-borne sonar, its supports, and the hull structure of the platform is hydrodynamic noise. In submarines, this type of noise also includes the noise generated by turbulent pressures upon the hydrophones from flow eddies, as well as vibrations from the submarine's plating and sonar gear. In addition, the water flow around the sonar dome sometimes creates the major portion of self noise. This noise is known as flow induced resonance, or FIR. http://en.wikipedia.org/wiki/Turbulence Consider the flow of water over a simple smooth object, such as a sphere. At very low speeds the flow is laminar; i.e., the flow is smooth (though it may involve vortices on a large scale). As the speed increases, at some point the transition is made to turbulent ("chaotic") flow. In turbulent flow, unsteady vortices appear on many scales and interact with each other. Drag due to boundary layer skin friction increases. The structure and location of boundary layer separation often changes, sometimes resulting in a reduction of overall drag. Because laminar-turbulent transition is governed by Reynolds number, the same transition occurs if the size of the object is gradually increased, or the viscosity of the fluid is decreased, or if the density of the fluid is increased. http://www.cora.nwra.com/~werne/eos/...urbulence.html and the last (i won't spend all my time to prove you my assertions ...) http://kr.cs.ait.ac.th/~radok/physics/f2.htm Turbulent flow At a critical velocity, a laminar flow becomes turbulent. If for a tube with a circular cross-section the the expression vd/n (v average velocity, d tube diameter) serves as critical number R, the validity of Poiseuille's Law ends at R = 2000, when turbulence begins. In a tube with a diameter of 1 cm, through passes water at 10ºC, R = 2000 yields a mean velocity of about 26 cm/sec. Through this tube, a slower flow, as every flow with a smaller value of R will be laminar (layered). If the velocity increases to this value of if you obtain it by enlargement of the tube diameter or heating of the water (decrease of m), there will occur the change over. The amount of fluid for a given pressure drop will then be smaller than the value, given by Poiseuille's formula, that is, the resistance experienced by the flow increases. The causes of turbulence were not yet known in 1935. Now we need to determine the critical point for all subs it's not so difficult to evaluate, as I said before. And, more difficult, we need to evaluate what happen at the critical point, how much is the gap. We could talk about that if you have finished to contest physical law :hmm: