Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63G—OFFENSIVE OR DEFENSIVE ARRANGEMENTS ON VESSELS; MINE-LAYING; MINE-SWEEPING; SUBMARINES; AIRCRAFT CARRIERS
  • B63G7/00—Mine-sweeping; Vessels characterised thereby
  • B63G7/02—Mine-sweeping means, Means for destroying mines
  • B63G7/08—Mine-sweeping means, Means for destroying mines of acoustic type

Definitions

• Control equipment for a towed submarine acoustic wave transmitter in particular for dredging mines
• the present invention relates to equipment for controlling the emission parameters of an underwater acoustic wave transmitter towed by a ship.
• the invention applies mainly to the dredging of mines with acoustic influence, and will be described mainly in the case of this application; however, this application is in no way limiting, and the invention can be applied equally to other applications - in particular all underwater prospecting applications - in which the acoustic signal produced by one or more points is picked up a source of acoustic waves at a distance therefrom and, by bringing together (in particular by correlation) the signals transmitted and the signals received, certain information is derived, for example concerning the nature of the seabed.
• towing is carried out several hundred meters behind the towing vessel (the mine hunter), a dredge consisting of a broadband acoustic wave emitter that simulates the mechanical and hydrodynamic noise of 'a naval vessel.
• the aim is thus to cause the explosion of mines laid at the bottom of the sea or submerged at a certain level above the bottom of the sea; for this, the transmitter is towed with a constant ⁇ -immersion relative to the bottom, to maintain a constant emission level relative to the sea bottom.
• the emission is generally a directive emission, extending essentially in a plane perpendicular to the towing direction, obtained by transducers located on the side of the dredge so as to obtain a lateral and oblique sweep of the seabed.
• a zone of influence or "insonification zone” is thus determined for which the threshold of acoustic sensitivity of the mines is reached, this zone being very extended in the direction perpendicular to the towing direction, and relatively little extended in the direction of towing.
• the area still has a certain width, and it is obviously essential that the boat is outside this area so as not to trigger the explosion of mines located near or near it.
• acoustic levels depend on many parameters (variation in the immersion of the transmitter, acoustic propagation characteristics, nature of the seabed, etc.), so that the area of influence can present, in the direction of towing, a very variable width which is difficult to estimate in advance.
• the sound level should be measured directly above the ship, since this is where the ship is most vulnerable. But we then come up against a practical difficulty which is to tow a receiver located just under the boat, near the bottom.
• the invention proposes to overcome these difficulties with equipment having an original configuration and allowing a substantial improvement in the protection of the ship, without excessive increase in safety distances.
• the receiver is towed behind the transmitter and at a distance from the latter substantially equal to the distance separating the transmitter from a point located directly above the ship or other point. of reference for the control of said emission parameters.
• the signal received by the receiver is used to control the emission level of the transmitter, so that the acoustic level produced by the transmitter at the base of the ship or said reference point remains below a given threshold.
• the receiver is towed at the end of a cable connected to the ship.
• the receiver is towed at the end of a cable connected to the transmitter, itself towed at the end of a cable connected to the ship.
• the receiver comprises a flute formed of a plurality elementary receivers arranged in a linear network extending substantially in the direction of towing.
• the aforementioned equipment comprises a second receiver towed aft of the ship but in front of the transmitter, at a distance from the latter such that the transmitter is located substantially halfway of the two receivers.
• FIG. 2 is homologous with FIG. 1, for the configuration according to the present invention
• FIG. 3 is an alternative embodiment of FIG. 2, and
• FIG. 4 is an improved variant of FIG. 3.
• the invention consists in towing a receiver 40 Q behind the transmitter 10 (and no longer in front, as in the prior art), and at a horizontal distance D from the transmitter 10 substantially equal to that separating the transmitter 10 of the ship 20 (here and in the following, unless otherwise indicated, we will always consider distances projected on the horizontal plane).
• the acoustic level produced by the transmitter at the location of the receiver 40 will be substantially the same as that present at the point referenced 41, that is to say at a point located directly above the ship 20 0 and at the same level with respect to the sea bottom as the receiver 40 (if it is assumed that the bottom is substantially flat over the extent covered by the equipment, which is generally the case).
• This configuration has the advantage that the measurement can be made at a reference point as close as desired to the plumb line of the boat, or even possibly at a reference point located in front of it, without being encounter obvious practical difficulties in towing a receiver to locate it at this point.
• Another advantage is that, as the receiver is moved away from the towing vessel, the noise radiated by the latter is received with less intensity by the receiver, since advantage is taken of the propagation losses between the ship and the receiver. It is thus possible, for the control of the transmitter, to better separate the signal produced by the transmitter from the noise of the ship.
• the noise of the boat will be attenuated by approximately 15 dB compared to the signal from the transmitter (although understood, this theoretical figure is in reality very variable taking into account the conditions of propagation, in particular at the lowest frequencies, where the propagation is done by modes).
• This gain will allow the signal delivered by the receiver to be processed in better conditions, in particular by allowing better control of the transmitter's emission level.
• the receiver 40 is preferably made up of a plurality of hydrophones placed in a chain so as to form a linear network or flute; the detection thus covers an area having, in the direction of towing, a certain width.
• the emission level of the transmitter is then slaved to the maximum level detected, which avoids the effects of certain propagation singularities or interference phenomena which can locally produce attenuations in the level of the received signal.
• the receiver 40 is towed indirectly by the ship, by means of a connecting cable fixed to the transmitter 10, itself connected to the towing ship 20 by another cable.
• the receiver 40 is towed directly by a cable connected to the ship, the rest of the configuration being identical elsewhere.
• the weight of the cable is preferably calculated and adjusted so that, in a manner known per se, one is at the critical angle for the dredging speed, which avoids the use of a depressant.
• FIG. 4 a variant is shown in which a safety distance d is also provided, that is to say that the point 41 where the acoustic level is measured is no longer located directly above the ship as in Figures 2 and 3, but aft of it.
• a second receiver 30 has also been shown, which is of the same type as that of the prior art (FIG. 1), and which is towed aft of the ship at distance d; it is thus seen that the two systems, namely the system of the prior art and that of the present invention, can coexist so as to provide the most complete measurements possible.

Landscapes

• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Engineering & Computer Science (AREA)
• Aviation & Aerospace Engineering (AREA)
• Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=9368024

Family Applications (1)

Country Status (3)

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Family Cites Families (4)

• 1988
  • 1988-07-04 FR FR8808992A patent/FR2633584B1/fr not_active Expired - Fee Related
• 1989
  • 1989-06-27 EP EP19890908198 patent/EP0423203A1/de not_active Withdrawn
  • 1989-06-27 WO PCT/FR1989/000331 patent/WO1990000135A1/fr not_active Application Discontinuation

Non-Patent Citations (1)

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