Sound Waves and Water Current

Yes. By whatever the velocity of the water is. Which will be negligible considering the speed of the waves in water is about 1,500 meters/second.

So for practical purposes, nothing to really consider when using gear that deploys at 10-15 knots?

I've never actually seen a difference in fish behavior up current or down but just thought I'd check. I always assumed the down current side was faster but once again, thinking back , I never really saw any difference in catch rates.

A big ol' project is coming up in two weeks and some government folk WILL surely ask this to be figured in the calculations for setting the prototype gears. I want some back up before I make a statement around these folks.

Thank you.

I should have mentioned the Doppler effect. It works in all mediums, not just air.

Lyn is correct. I was a sonar technician in the US Navy and studied the science of sound in water quite extensively. The speed of sound in water is approximately 4800 feet per second, and varies slightly with temperature and salinity. Water current will affect the "apparent" speed with respect to a stationary object (a fish). The Doppler effect lyn refers to is seen when a person near a train track hears an approaching, then departing train pass by. In water, this phenomenon allows one to determine an objects speed. Most commercially available fathometers do not take into account salinity or temperature. Therefore the given depth is only an approximation.

A fixed observer will experience the same Doppler effect as standing beside a highway as a truck passes.

To a similar degree, you will 'hear' it better if you are 'down-wind'.

But these are frequency compression and 'carry', characteristics of propagation, not speed.

As Lyn points out, the speed of the current is negligible in this.

Thank you all again.

Is this part of the deployment of your Asian Crap Project?

Did you really mean Crap? Perhaps Carp?

^{Typos can be hilarious!}

Yes. I am referring to the field trials of our Asian Carp project.

1. Spook Seine
2. Paupier Nets

* The Pound Net is a static capture device and field trials come after November as does the Twin Trawl testing which is a known high end acoustical gear that hopefully uses noise to panic fish into the capture zone.

We are even going to use low pulse electrical waves to stun and/or nudge fish , en masse, into a set of capture nets.

Its one of the most intricate projets I have ever been involved with. Those guys are dead serious about finding new ways to get rid of the 'jumping' fish menace!

You'll have to keep us updated with the results of those _{^{crappy Asian Carp}}

The sound probably travels faster but the observed frequency of the sound waves will be lower downstream. This is similar to listening to a train that just passed you.

That is an excellent analogy.

I am very interested in sound/vibration as a means of moving fish. My expertise is NOT in fish behavior per se. So I am not sure as to what wave lengths of noise 'nudge' and which wave lengths 'panic' specific species.

Except for these Asian Carp, the bulk of my customers are all looking for Y.O.Y ( Young of the Year) so that they can gauge recruitment for each species, each year.

I have always thought that accoustics could be used to nudge fish from their hide-aways and produce results quicker and with less mortality than just brute trawl-force or electro-fishing.

A combination of a hyper net coupled with a 'pinger' type gadget would be a serious improvement in this field.

....well I guess that will be another thread.

Thank you.

nm

You may find that sound in the water has a bigger impact on marine mammals than on fish - because it interferes with their mode of communication.

Fish do have otoliths which are delicate bones that would be sensitive to sound vibrations. I guess the only way to get any data on moving fish with sound would be by working with fish in a tank.

Sound and/or vibration ( lateral lines as well as otoliths) is a huge factor in behavior of all marine critters. I firmly believe that a sonar type pinger and/or some type of 'thumper' device may be the ticket.

Trouble is someone in the guv'ment has to think of it first so they can apply for sea trial funding..... that could be awhile. Suggestions from small fry guys like me are mostly shredder fodder.

Thank you again.

nm

Hey there netmaker, have you looked into Federal Grants? I have heard of some pretty ludicrous grants awarded for some off the wall researches, like reinventing the wheel.

I don't know about this. Many are stating doppler effect. Doppler effect deals with the pitch or frequency of the sound wave, not velocity. Red Shift is a doppler effect astronomers use to determine distances and rates of retraction. Light, for the most part has a constant velocity. The question is there an "absolute velocity" for sound. In a liquid or solid, I would think there is. Sound is a mechanical transmission from molecule to molecule. The only way to speed this, is to make the molecules closer together. e.g. the difference in transmission speeds between salt and freshwater as WJM described.

I agree with your first sentence, "I don't know about this."

The exact velocity of the propagation speed of sound in a given medium can be found as;

Velocity = k ( sqrt [elasticity of the medium / density of the medium]).

Refer to the following for the speed of sound in various media;

Air (0 deg C) = 331, Air (20 deg. C) = 343, Helium = 965,

Water (0 deg. C)= 1402, Water (20 deg. C) = 1482, Sea Water = 1522,

Steel = 5941, Granite = 6000.

Referring to the above formula, the propeller does not changes either elasticity or the density similarly any increase in temperature is not noticeable.

I assume that the figures given are for density of the material. Do you have elasticity figures as well?

denser water [upstream] will transmit signals faster.

From that ol' For-What-Its-Worth department, my father passed-along a number of handbooks from his (PE) days, including one from Bruel & Kjaer (http://www.bksv.com/), which divulged the equation below ... also found at http://www.bksv.com/library/dictionary.aspx?key=u&st=u

[sorry, browser isn't permitting me to insert hyperlinks appropriately...box is popping-up offscreen where I can't access it!]

Speed of Sound in Water (The Leroy Equation)

c = 1492.9 + 3(T - 10) - 6 × 10^-3 (T - 10)² - 4 × 10^-2 (T - 18)² + 1.2 (S - 35) - 10^-2 (T - 18) (S - 35) + Z/61

where:

• c is the sound speed in m/s
• T is the temperature in °C
• S is the salinity in parts per thousand
• Z is the depth in metres

Accurate to 0.1 m/s for T less than 20°C and Z less than 8000 m.

I wonder whether this has been "improved on"...(?)

I reference to the speed of sound in water verses normally assumed in air. Does it also apply to the formula for "breaking the speed of sound" in water like it does in air?

Would we expect the terrific noise?

Is this a weapon technology yet to be explored?

You're confusing two different things. The speed of sound is, more or less, the fixed velocity of the energy wave, not affected by an object moving through the medium. When an airplane "breaks the sound barrier" the sound it makes still travels at the same speed.

My comment was to trigger thought on a similar event happing in water like the event that happens in the atmosphere when a plane or aircraft accelerates past the speed of sound. A large explosion type sound is heard. A shock wave approaching infinite pressure is produced as an aircraft approaches that speed..It has been blamed for breaking windows, etc.

So, could underwater movement of an object be accomplished where it is actually moving faster than the speed of sound in water? And do we expect that a similar shockwave would result? Then if we could manage or have any control of the shockwave, what would be the damaging effects created by the shockwave to objects underwater? I am thinking underwater ultra sonic cannon.

The Navy has already perfected ways to kill unprotected animals unwerwater, with SONAR. For all I know theymay be working on some type of shock wave generator, for all I know.

The fact that water is incompressible and much denser than air leads me to believe that propelling an object beyond the speed of propogation of the energy wave is impossible.

I'd like to hear from WJMFIRE on this one.

Yes, it would make one whale of a shock wave.

Lyn, Isn't sound actually transmitted by the medium by small compression/decompression of the medium? Part of the fact that the sound travels faster in the dense material is that the molecules are more plentiful to react to the pressure changes.

Our first time out with the brand new (at the time) ANSQS53A Sonar system, we blew out most of the fluorescent lights in the Chesapeake Bay Bridge Tunnel. Never were allowed to go active again until 100 fathoms; passive only. On bottom bounce track mode we funneled 245 db in Omni-Directional Transmission mode down to 8-1/2 degree beam. That kind of sound wave would crack the pressure hull on a submarine within 100 feet. In our lower equipment rooms, the sound wave was unbearable and without the impact concussion, felt like someone hit a sheet of 1/4" plate steel mounted one inch from your ear with a .308 round. One can only guess about the marine life.

So, could underwater movement of an object be accomplished where it is actually moving faster than the speed of sound in water?
We don't have data on that one yet, as yet released.
I can tell you that there are other things which are in practice that bend some of the rules. Can you come up with a scenario where the "non-compressibility" of a fluid might be "tested", even dispelled? Might the density of the water be changed on a local level? Imagine water that is compressed to the extent it turns black. Sci-Fi...unfortunately not.

I like to approach these types of questions from several different ways. A scientific approach using known facts and time tested practices. A "outside the box" approach brings imagination, stepping away from facts and theorem, and sometimes a little smart a$$ commentary to shake up the discussion. For the "non-compressibility" question my thoughts drifted to water expanding when frozen and therefore "compressing" when heated but then as changed to steam expanding again. So if that liquid can change volume why not others, not implying that heating is the only catalyst to be considered to help a volume change. Considering there is a tremendous amount of hydraulic equipment, controls, and transmission of power that entirely depends on "non-compressibility" of liquids we will be confronted by skeptics for even thinking it would change.

The transmission of sound through water and steel must pass some characteristic from molecule to molecule in order for the sound to travel, even if it is using energy at each step until it is diminished. If it is not an electron travel, or heat traveling across the molecules, I say it is a pressure compressing the space between the molecules. So if we provide many molecules along the edge of the liquid with a little sound pressure do we not effectively compress the liquid?

Not familiar with WJ's (post33) "ANSQS53A Sonar system", but subsea seismic surveys for oil and gas are now accomplished using powerful compressor-operated seismic guns to produce the interrogating acoustic waves. Obviously, traveling at sonic speed, NOT "supersonic".

However, as beenaround mentioned above, energy is lost in a liquid with each paperthin distance traveled. Can't help but wonder if a "blast" (be it air powered or 'depth-charge') doesn't actually BEGIN its initial propagation at supersonic speed...

Thus the question: how much energy would it take to maintain an object (or wave) traveling FASTER than sound in water?

Hmmm... What effects might have been experienced under the surface at the Bikini Atoll blasts? http://en.wikipedia.org/wiki/Operation_Crossroads

For the record, water is actually compressible - just not very much, see this excerpt from wikipedia:

The compressibility of water is a function of pressure and temperature. At 0 °C, at the limit of zero pressure, the compressibility is 5.1×10⁻¹⁰ Pa⁻¹.^[27] At the zero-pressure limit, the compressibility reaches a minimum of 4.4×10⁻¹⁰ Pa⁻¹ around 45 °C before increasing again with increasing temperature. As the pressure is increased, the compressibility decreases, being 3.9×10⁻¹⁰ Pa⁻¹ at 0 °C and 100 MPa.

The bulk modulus of water is 2.2 GPa.^[28] The low compressibility of non-gases, and of water in particular, leads to their often being assumed as incompressible. The low compressibility of water means that even in the deep oceans at 4 km depth, where pressures are 40 MPa, there is only a 1.8% decrease in volume.^[28]