Device for attenuating underwater sound pressure and the use of such a device
A device for reducing underwater sound energy and propagation, whereby the device includes at least one bubble generation unit and an air conduit for supplying pressurized air to the bubble generation unit, whereby the bubble generation unit has a fluidic oscillator for generating one or more pulsating air flows from a constant air flow, and whereby preferably the fluidic oscillator has an adjustable oscillation frequency, and a method for using such a device for reducing underwater sound propagation, whereby the air conduit and the bubble generation unit are placed underwater, whereby pressurized air is supplied to the air conduit and whereby air bubbles are generated by the bubble generation unit.
1. A device attenuating underwater sound pressure, comprising:
at least one bubble generator; and
an air conduit configured for supplying pressurized air to the bubble generation unit,
wherein the at least one bubble generator comprises a fluidic oscillator for generating one or more pulsating air flows from a constant air flow,
wherein the fluidic oscillator is a fluidic oscillator with an adjustable oscillation frequency, wherein the oscillation frequency of the fluidic oscillator is adjustable independently of the air pressure in the air conduit, and
wherein the device comprises a hydrophone and a controller, the controller being arranged to receive an input signal from the hydrophone and to send to the fluidic oscillator a control signal for controlling the oscillation frequency, wherein the controller is arranged to calculate the control signal using the input signal.
2. The device according to claim 1 , wherein the controller is arranged to calculate a sound frequency distribution from the input signal, and wherein the controller is arranged to calculate the control signal from the sound frequency distribution.
3. The device according to claim 1 , wherein the device comprises a first type of said fluidic oscillator and a second type of said fluidic oscillator, and wherein the first type of said fluidic oscillator and the second type of said fluidic oscillator are designed to operate at different oscillation frequencies if they are supplied with air at the same pressure.
4. The device according to claim 1 , wherein the air conduit is a flexible air hose, and wherein the device comprises a plurality of said at least one bubble generator arranged along at least a part of a length of the air hose.
5. The device according to claim 1 , wherein the at least one bubble generator comprises a bubble generation unit body having a bubble outlet channel open at a top end and a bottom end thereof, and wherein the fluidic oscillator comprises an air outlet which debouches in the bubble outlet channel.
6. The device according to claim 1 , wherein the fluidic oscillator comprises at least two separate air outlets operating at the same frequency but phase-shifted by half a wave period.
7. A method of using the device according to claim 1 for attenuating the sound energy of underwater sound, comprising the steps of:
placing the air conduit and the at least one bubble generation unit underwater;
supplying pressurized air to the air conduit; and
generating air bubbles by the at least one bubble generation unit.
8. The method of using according to claim 7 , wherein there is one or more of said device, wherein the air conduit or air conduits of the one or more of said device encircle a source of underwater sound, and wherein the one or more of said device comprises at least four bubble generators placed underwater.
9. The method of using according to claim 7 , wherein the hydrophone is placed underwater, and wherein the air conduit is placed between the hydrophone and a source of underwater sound.
10. The method of using according to claim 9 , wherein the controller controls the oscillation frequency of the fluidic oscillator depending on the frequency distribution of the sound captured by the hydrophone.
11. The method of using according to claim 7 , wherein the device comprises at least two fluidic oscillators, each of the at least two fluidic oscillators having an adjustable oscillation frequency, wherein the at least two fluidic oscillators are supplied with air from the same air conduit, wherein a first fluidic oscillator of said at least two fluidic oscillators is controlled to operate at a first oscillation frequency, and wherein a second fluidic oscillator of said at least two fluidic oscillators is controlled to operate at a second oscillation frequency.
12. The method of using according to claim 7 , wherein said device is a first device and a second device, wherein the air conduit of the first device forms at least part of an encirclement of a source of underwater sound, and wherein the air conduit of the second device forms at least part of an encirclement of the air conduit of the first device.
13. The method of using according to claim 12 , wherein the bubble generator of the first device generates bubbles of a different size than the bubble generator of the second device.