TB23 vs TB16

[Deathblow]

Does anyone understand the reason that the TB23 washes out at lower speeds than the TB16? Isn't the TB23 the more advanced/sensitive array so shouldn't its washout speed be greater than the TB16?

Or the reason that the Hull Array wash out speed is lower than the spherical array. They are both seeing the same water flow speeds across the sensors...... actually the spherical array water flow is faster than the Hull Arrays so shouldn't it wash out sooner?

Can anyone rationalize the washout speeds as they are now? I'm not understanding the physics behind it.

[LuftWolf]

Because that's how I made it! :P

Seriously, the TB-23 and TB-29 are "Thin-Line Arrays" and the TB-16 is a "Thick-Line Array".

The same acoustic properties that give them greater sensitivity, also make them more suseptable to wash-out due to flow noise.

People who are actually schooled in sonar properties can probably give a better answer, but this is how I understand it.

[SeaQueen]

Originally Posted by Deathblow

Does anyone understand the reason that the TB23 washes out at lower speeds than the TB16? Isn't the TB23 the more advanced/sensitive array so shouldn't its washout speed be greater than the TB16?

Or the reason that the Hull Array wash out speed is lower than the spherical array. They are both seeing the same water flow speeds across the sensors...... actually the spherical array water flow is faster than the Hull Arrays so shouldn't it wash out sooner?

Can anyone rationalize the washout speeds as they are now? I'm not understanding the physics behind it.

The reason a hull array washes out at lower speeds than the spherical array is because the spherical array is closer to the "stagnation point" where the flow separates. At the stagnation point, there is no turbulent boundary layer, which is the origin of flow noise, therefore there is lower self noise. Additionally, the array is further away from the engine room, screws, etc. (the noise propagating surfaces of the boat) and has lower self noise.

Rationalizing why towed arrays have lower self noise than hull arrays is more complicated because in real life, towed arrays DO have flow noise problems, but it's frequency dependent.

Higher frequency self noise levels are typically less sensitive to speed. Lower frequency self noise is more sensitive. It has to do with the vibrational properties of the arrays as the water flows around them. While you can't look at the actual curves for a TB-16 or TB-23, you CAN look at curves for similar flexible towed arrays used for oil exploration. There's one in Principles of Underwater Sound by Urick. I'm sure if you poked around on the web you could find more. With some luck you might find one with comparable statistics and have a pretty reliable guestimate of a real towed array's performance. They're all pretty similar, honestly.

My guess is that they figured that since the problems are typically in the tens of Hertz range, and the curves for frequencies higher than that are pretty flat, the overall average broadband noise they generate is less.

[PeriscopeDepth]

Just curious, are passive or active arrays used for oil exploration? If they are passive, what are they trying to detect?

[SeaQueen]

Originally Posted by PeriscopeDepth

Just curious, are passive or active arrays used for oil exploration? If they are passive, what are they trying to detect?

Both, but in the case where they use passive arrays, they're listening for the echo from an explosion they set off, an air cannon blast, or some other powerful noise-making gizmo. Oil exploration is absolutely fascinating stuff.

The same idea is also used to find submarines today. EERs or "bangers" as P-3 people call them, are basically just a pair of SUS charges on a string. An EER sonobuoy field works by setting off an explosion underwater, then listening on other sonobuoys for the echo of that explosion. When the source and receiver are not co-located, the situation is referred to as "bistatic" or even "multistatic." One of the things on my wish list for the sim is for multistatic acoustics to be modeled.

Explosions are a good way to put a LOT of broadband acoustic energy in the water. That's another interesting topic Urick covers in glorious detail. Principles of Underwater Sound is really good reading if you want a good technical introduction to sonar and ocean acoustics. If your background isn't in physics or engineering, though it might be a little rough.