Sonar array

Abstract

To provide a sonar array attached to a front part of a hull, which reduces a range behind the hull that cannot be probed, to enable detection in all directions.SOLUTION: A sonar array comprises multiple sets of transducers, which are arranged in a vertical direction on an outer peripheral surface of a housing, in a revolving direction of the outer peripheral surface, and is arranged at a front part of a hull, where a stern side of an outer periphery of a top surface of the housing has a curved shape that extends so that the stern side of an outer periphery of a bottom surface of the housing further protrudes in the stern direction, and the stern side of the outer peripheral surface has a shape that extends from a stern-side end part of the outer periphery of the bottom surface to a stern-side end part of the outer periphery of the top surface at a predetermined inclination angle.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to sonar arrays. [Background technology]

[0002] A three-dimensional sonar transmits sound waves underwater using a plurality of acoustic elements for transmission, receives the underwater sound waves using a plurality of acoustic elements for reception, and processes the received signals to display an underwater target in a three-dimensional image. For example, a sonar array is used as a three-dimensional sonar, in which a plurality of sets of acoustic elements arranged vertically are arranged in a circular direction on the outer periphery of a cylindrical housing (the outer periphery of the housing side wall connecting the outer peripheries of the bottom and top surfaces). For example, Patent Document 1 discloses a cylindrical housing as a three-dimensional sonar, as well as a housing with a cylindrical lower part formed in a hemispherical shape, a downward hemispherical housing, and a spherical housing, each of which is provided with a plurality of transducers (acoustic elements). Some sonar arrays for ships are arranged at the front of the hull (for example, the lower part of the bow or the bottom of the ship). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-200204 A Summary of the Invention [Problem to be solved by the invention]

[0004] A sonar array placed at the front of the hull is affected by, for example, the operating noise of the engine in the center of the hull and the propulsion noise caused by the rotation of the screw propeller at the rear of the hull. In addition, depending on the position of the sonar array, the hull itself may block underwater sound waves. For this reason, when exploring underwater sound waves by transmitting and receiving waves with a sonar array placed at the front of the hull, there are areas behind the hull that cannot be explored.

[0005] The present disclosure aims to provide a sonar array that is disposed at the front of a ship's hull, which reduces the area behind the ship's hull that cannot be explored, and enables exploration in all directions in the horizontal direction. [Means for solving the problem]

[0006] According to the present disclosure, a sonar array is disposed at the front of a hull and comprises multiple sets of transducers arranged vertically around the outer periphery of a housing, the sets comprising multiple sets of transducers arranged in the circumferential direction of the outer periphery, the stern side of the outer periphery of the top surface of the housing has a curved shape that extends so that the stern side of the outer periphery of the bottom surface of the housing protrudes further toward the stern, and the outer periphery has a shape that extends from the stern end of the outer periphery of the bottom surface to the stern end of the outer periphery of the top surface at a predetermined inclination angle. Effect of the Invention

[0007] According to the present disclosure, it is possible to provide a sonar array that reduces the unsearchable area behind the hull and enables detection in all directions. [Brief description of the drawings]

[0008] [Figure 1] 1A is a schematic diagram showing an example of a comparative example sonar array installed on the bow of a ship. FIG. 1B is an enlarged schematic diagram of the bow of the comparative example. FIG. 1C is a schematic diagram of an example sonar dome of the comparative example. FIG. 1D is a schematic perspective view of a comparative example cylindrical sonar array. [Diagram 2] 1A is a schematic plan view of a sonar array of a comparative example, FIG. 1B is a schematic front view of a sonar array of a comparative example, and FIG. 1C is a schematic side view of a sonar array of a comparative example. [Diagram 3] FIG. 2 is a diagram illustrating the horizontal search range of a sonar array according to a comparative example. [Figure 4] 1A is a schematic diagram showing an example of a sonar array of the present disclosure mounted on the bow of a ship, FIG. 1B is an enlarged schematic diagram of the bow of the present disclosure, and FIG. 1C is a schematic diagram of the sonar array of the present disclosure. [Diagram 5]1A is a schematic plan view of a sonar array of the present disclosure, (B) is a schematic front view of a sonar array of the present disclosure, and (C) is a schematic side view of a sonar array of the present disclosure. [Figure 6] 1 is a graph showing an example of vertical directivity of a sonar array of a comparative example. [Figure 7] 1 is a graph illustrating an example of vertical directivity of a sonar array of the present disclosure. [Figure 8] FIG. 2 is a diagram illustrating the horizontal search range of the sonar array of the present disclosure. [Figure 9] 1A is a diagram for explaining an example of an underwater sound wave propagation path in front of a hull in the present disclosure, and FIG. 1B is a diagram for explaining an example of an underwater sound wave propagation path in front of a hull in the present disclosure. [Figure 10] 1A is a diagram for explaining an example of an underwater sound wave propagation path behind a hull in the present disclosure, and FIG. 1B is a diagram for explaining an example of an underwater sound wave propagation path behind a hull in the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An embodiment of the present disclosure will be described. Below, a comparative example will be described first. FIG. 1(A) is a diagram showing a typical example of a comparative example in which a sonar array for a ship is fixed to the lower part of a bow. In FIG. 1(A), a sonar array 2 is a sonar array fixed to the lower part of the bow of a ship 1. In this comparative example, the sonar array 2 is cylindrical (cylindrical). An engine 4 mounted in the center of the hull of the ship 1 may be a diesel engine, a gas turbine engine, or the like. A screw propeller 5 is mounted on the rear part of the hull. There is no limit to the number of rudders 6 mounted on the ship 1. When the ship 1 is sailing, the engine 4 and the screw propeller 5 become noise sources for the sonar array 2. The bow (draft part) 7 cuts through the waves on the sea surface 3 when the ship 1 moves forward, generating wave-breaking sounds. This wave-breaking sound becomes a noise source for the sonar array 2. In FIG. 1(A), an escort ship equipped with a machine gun on the bow side is shown as a model of the ship 1, but the ship 1 is of course not limited to an escort ship or the like. In the drawings, an XYZ coordinate system is appropriately shown to make the directions easier to understand. The XYZ coordinate system is a left-handed system, and for example, with the center of the sonar array 2 as the origin, the positive direction of the Y axis is the traveling direction of the ship 1 (toward the bow), the negative direction is the rear of the ship 1 (toward the stern), the positive direction of the X axis is the port side of the ship 1, the negative direction is the starboard side of the ship 1, the positive direction of the Z axis is the upward direction, and the negative direction is the downward direction.

[0010] Fig. 1(B) is a partially enlarged schematic view of the vicinity of sonar dome 8 on the bow of Fig. 1(A). Sonar array 2 is housed in a hollow portion 71 under the bow of the hull of ship 1, and sonar dome 8 is attached to the hull so that hollow portion 71 is filled with seawater or the like. Sonar dome 8 is formed in a streamlined shape to reduce the resistance of water currents in the ocean generated by the navigation of ship 1, and is configured to reduce frictional noise generated by direct contact with the seawater current.

[0011] Sonar dome body 81 is a large structure made of materials that transmit sound waves, such as natural rubber, synthetic rubber, glass fiber, fiber reinforced plastics (FRP), etc. Figure 1(C) shows a schematic view of an example of a rubber window of sonar dome body 81 (supporting members such as a frame are not shown).

[0012] FIG. 1(D) shows a schematic diagram of an example of the cylindrical sonar array 2 of FIG. 1(A). On the outer circumferential surface (side surface) of the cylindrical housing (frame), a plurality of transducers 10 (acoustic elements) are regularly arranged at a predetermined interval in the vertical direction (up and down direction) and the circumferential direction. That is, a set of a plurality of transducers 10 arranged linearly at a predetermined interval in the vertical direction of the outer circumferential surface of the cylindrical housing is arranged at a predetermined interval in the circumferential direction of the cylindrical housing. The transducer 10 has a function of transmitting ultrasonic waves and a function of receiving ultrasonic waves, and is composed of an acoustic element (electrostrictive vibrator) capable of bidirectionally converting underwater sound waves (ultrasonic vibrations) and electric signals. The transducer 10 is electrically connected to a transmitting device and a receiving device (not shown) via a transmitting / receiving switch (not shown). During transmission, the connection is switched so that a transmission signal is sent from a transmitting device (not shown) (including a transmitting section and a transmission control section) to the transducer 10 of the sonar array 2, and during reception, the connection is switched so that an electrical signal converted from the ultrasonic signal by the transducer 10 is sent to a receiving device (not shown) (including a receiving section and a signal processing section).

[0013] The balloon in FIG. 1(D) is a diagram showing a schematic example of mounting of a transducer 10 of a cylindrical sonar array 2. In the cylindrical sonar array 2, the outer peripheral surface of a frame part 201, which is a metal housing, is provided with holes for transducers, each of which has a circular cross section and extends radially inward, and the transducer 10 is inserted radially into each hole and fixed. In the transducer 10, an electrostrictive transducer (piezoelectric element) 101 is provided between a front mass 102 and a rear mass 103, and a transmitting / receiving surface 104 on the front end surface of the front mass 102 is, for example, flat and provided so as to face forward. An electrically insulating and soundproofing member (not shown) is provided at the attachment portion of the electrostrictive transducer 101 to the frame part 201 (hole for transducer). For an example of how to attach the transducer 10 to the housing (frame) of the cylindrical sonar array 2, see, for example, Japanese Patent Application Laid-Open No. 2015-125110.

[0014] 1(D), for simplicity, a four-ring array configuration is shown as the transducer 10 in the vertical direction, but a ten-ring or more sonar array may be used. The sonar array 2 may be a cylinder with its upper surface covered with a lid or the like.

[0015] In Fig. 1(A), sonar vertical search ranges 9a and 9b show an example of the effective range of vertical directivity from the central axis of vertical directivity of the sonar array 2. The angles (spread angles) of the sonar vertical search ranges 9a and 9b are the same.

[0016] 2(A) to 2(C) are schematic diagrams for explaining the appearance of a cylindrical sonar array 2, and FIG. 2(A) is a schematic plan view of the sonar array 2 seen from below (or above). The radius of the top and bottom surfaces of the housing of the sonar array 2 is r. FIG. 2(B) is a schematic front view of the sonar array 2 seen from the bow side (similar when seen from the stern side). FIG. 2(C) is a schematic side view of the sonar array 2 seen from the starboard side (similar when seen from the port side). Although not particularly limited, the sonar array 2 in FIG. 2 has 10 rows of transducers 10 arranged at predetermined intervals in the vertical direction (z-axis direction) on the outer circumferential surface of a cylindrical housing (frame), and a total of 36 rows are arranged every 10 deg (degrees) in the circumferential direction, forming an array of 10 rings and 36 staves.

[0017] In the above-mentioned FIG. 1(A), the sonar vertical search range (rear) 9b is an area determined by the extensions of the two lines in FIG. 1(A) and includes the engine 4 and screw propeller 5 located behind the sonar array 2. For this reason, the sonar array 2 is affected by noise generated from the engine 4 in the center of the hull and the screw propeller 5 at the rear of the hull. As a result, as shown in FIG. 3, a sonar horizontal search impossible range (blind zone, undetectable area) 12 is created behind the hull.

[0018] In the cylindrical sonar array 2, for example, a transmission beam is transmitted from a plurality of transducers 10 (transmission line array) arranged vertically on the outer periphery of the housing, and during reception, the transducers 10 are switched to a receiving device (not shown), and a directional reception beam is formed from the signal received by the transducers 10 (reception line array) arranged in the circumferential direction (horizontal direction), and the target direction in the horizontal direction may be obtained. Also, the target direction in the vertical direction (up and down) may be obtained from the phase difference of multiple stages of transducers 10 in the vertical direction (four stages in FIG. 1(D)).

[0019] In FIG. 3, the sonar horizontal search impossible range (blind zone) 12 is an area where underwater sound waves from the inner area between two line segments (dashed lines) La, La that spread out horizontally behind (stern side) the sonar array 2 cannot be detected by the sonar array 2 because the underwater sound waves from the inner area are affected by noise generated from the engine 4 in the center of the hull of the ship 1 and the screw propeller 5 at the rear of the hull. In addition, underwater sound waves from the area between the extensions of the two line segments (dashed lines) La, La cannot be detected. The sonar horizontal search range 11 represents a horizontal range where an echo signal can be detected by transmitting and receiving underwater sound waves from the sonar array 2. In the example of FIG. 3, the sonar horizontal search range 11 is shown as a range excluding the sonar horizontal search impossible range (blind zone) 12 surrounded by the two line segments (dashed lines) La, La from the circle Ra (radius La in the figure).

[0020] In FIG. 1(A), it can be seen that depending on the mounting position of the sonar array 2 on the ship 1, a sonar horizontal unsearchable range 12 in the stern direction will be created due to the sound wave shielding effect of the ship's hull itself.

[0021] In addition, in a structure in which the sonar array 2 and sonar dome 8 are attached to the bottom of the bow, the ship is subject to underwater noise generated by noise and vibrations from the ship itself, and the sonar array 2 and sonar dome 8 become a source of resistance to the water current, resulting in a decrease in the speed of the ship 1, etc.

[0022] If the sonar array 2 and sonar dome 8 are mounted at a position slightly higher than the bottom of the bow of the ship 1 in order to reduce the decrease in speed, as shown in FIG. 1(A), a sonar horizontal search-incapable range (blind zone) 12 will be created toward the stern, as shown in FIG. 3. As described above, since the sonar horizontal search-incapable range 12 will be created behind the ship's hull, it may be possible to use a towed sonar in combination with the sonar to detect an underwater vehicle approaching from behind the hull, for example. However, there is a risk that a towed sonar will come into contact with the seabed, floating objects on the sea surface such as driftwood, or underwater drifting objects such as marine organisms, and be damaged or lost.

[0023] The above problem is one example, but the sonar array of the present disclosure reduces or eliminates the range behind the hull that cannot be horizontally explored, making it possible to detect in all directions. In a sonar array that includes a plurality of sets of transducers (acoustic transducers) arranged in the vertical direction of the outer peripheral surface of a housing and in the circumferential direction of the outer peripheral surface and is arranged at the front of the hull, the bow side of the outer peripheral surface of the housing has a shape corresponding to the bow side of the outer peripheral surface of the bottom surface of the housing, and the stern side of the outer peripheral surface of the housing has a curved shape that expands so that the outer peripheral surface of the bottom surface of the housing further protrudes toward the stern side, and the outer peripheral surface has a shape that reaches the end of the outer peripheral surface of the top surface at a predetermined inclination angle from the end of the stern side of the bottom surface to the end of the stern side of the upper surface at a predetermined inclination angle. By providing a predetermined depression angle to the transducers (acoustic transducers) arranged on the stern side of the outer peripheral surface, the range behind the ship that cannot be horizontally explored (blind zone) is eliminated, making it possible to detect in all directions.

[0024] 4(A) and 4(B) are diagrams for explaining an embodiment of the present disclosure, and correspond to the above-mentioned FIG. 1(A) and FIG. 1(B) (partially enlarged views). The same or equivalent elements as those in the comparative example of FIG. 1(A) are given the same reference numerals, and their description will be omitted unless necessary. Referring to FIG. 4(A) and FIG. 4(B), in the embodiment of the present disclosure, the sonar array 13 is housed in a sonar dome 8, similar to the sonar array 2 in the comparative example of FIG. 1(A), but the three-dimensional shape is different from the cylindrical type in FIG. 1. The stern side of the outer peripheral surface of the housing (frame) of the sonar array 13 has a shape that extends from the stern end of the bottom outer peripheral surface to the stern end of the top outer peripheral surface at a predetermined inclination angle, and a certain depression angle is given to a plurality of transducers (electrostrictive transducers) arranged vertically in the region of the stern end of the outer peripheral surface. That is, in the example of Fig. 4(A), the central axis of the vertical directivity of sonar vertical search range (forward) 14 is oriented horizontally like sonar vertical search range (forward) 9a in Fig. 1(A), but the central axis of the vertical directivity of sonar vertical search range (rear) 15 is oriented diagonally downward. Also, with reference to Fig. 4(B), the vicinity of the center of sonar array 13 in the up-down direction corresponds to the position of the bottom of the ship 72.

[0025] Fig. 4(C) is a schematic perspective view of the sonar array 13 of Fig. 4(A) and Fig. 4(B). The sonar array 13 includes a plurality of sets of transducers (electrostrictive transducers) 10 in the vertical direction of the outer peripheral surface 133 (connecting the outer peripheral surface of the bottom surface 132 and the outer peripheral surface of the top surface 131 with a surface), and a plurality of sets in the circumferential direction of the outer peripheral surface 133. The stern side of the outer peripheral surface 133 has a shape that reaches the stern side end of the bottom surface outer peripheral surface 131a at a predetermined inclination angle θ (acute angle). The sonar array 13 of the present disclosure may also be configured such that a transducer hole in the side wall (outer peripheral surface 133) of the frame portion 201 is accommodated in a direction perpendicular to the outer peripheral surface 133, as in Fig. 1(D) described above.

[0026] The sonar array 13 is mounted on the lower part of the bow of the ship 1 or on the bottom of the front part of the hull, and is configured so that the rear vertical directivity of the transducer 10 is directed downward at a depression angle of, for example, 45 degrees. This makes it possible to remove noise sources such as the engine 4 and screw propeller 5 of the hull, which are factors in the rear sonar unsearchable range (blind zone), from the sonar vertical search range (rear) 15 behind the sonar array 13. Therefore, the sonar array 13 enables omnidirectional detection (search).

[0027] 4(C), the bow side of the top outer periphery 131a of the housing of the sonar array 13 is shaped to correspond to the semicircle on the bow side of the bottom outer periphery 132a of the housing, and the stern side of the top outer periphery 131a is shaped to be a curved (bent) shape (e.g., a semi-ellipse) in which the semicircle on the stern side of the bottom outer periphery 132a extends so as to protrude further toward the stern. In the outer periphery 133 that connects the outer peripheries of the bottom and top surfaces 132 and 131 of the housing, the stern-side outer periphery 133 reaches the stern-side end of the top outer periphery 131a at a predetermined inclination angle from the stern-side end of the bottom outer periphery 132a to the stern-side end of the top outer periphery 131a.

[0028] As shown in FIG. 4(A), the central axis of the vertical directivity of the sonar vertical search range (rear) 15 is directed diagonally downward, so that no underwater acoustic waves are transmitted or received near the sea surface 3 rearward of the ship 1, resulting in a range where sonar horizontal search is not possible (blind zone) (17 in FIG. 8 described later).

[0029] Fig. 5(A) is a schematic plan view of the sonar array 13 in Fig. 4(C) seen from the bottom side, Fig. 5(B) is a schematic front view of the sonar array 13 in Fig. 4(C) seen from the bow side, and Fig. 5(C) is a schematic side view of the sonar array 13 in Fig. 4(C) seen from the port side. Here, the bottom surface 132 of the sonar array 13 is a circle. The radius of the bottom outer periphery 132a is r. Also, the height of the sonar array 13 is h.

[0030] Referring to FIG. 5(A), the first outer periphery 131a-1 on the bow side of the upper surface outer periphery 131a corresponds directly to the semicircle of the bottom surface outer periphery 132a on the bow side (the semicircle of the bottom surface outer periphery 132a on the bow side is translated in parallel). The second outer periphery 131a-2 on the stern side of the upper surface outer periphery 131a is curved (semi-elliptical) in which the semicircle of the bottom surface outer periphery 132a on the stern side is expanded so as to protrude further toward the stern side. Note that the first outer periphery 131a-1 and the second outer periphery 131a-2 are introduced to explain the shape of the upper surface outer periphery 131a, and do not mean that the upper surface 131 is made of two members. However, the outer periphery 133 of the housing does not have to be made of one surface, and may of course be made by assembling multiple members in the circumferential direction.

[0031] As shown in Figures 5(B) and 5(C), the sonar array 13 has an asymmetrical cylindrical housing with a larger top surface than the bottom surface, and has rows (sets) of, for example, 10 (stages) of transducers 10 arranged at equal intervals in the vertical direction (longitudinal direction, Z direction), and 36 rows (sets) of transducers 10 arranged at a predetermined angle (for example, 10 degrees) in the circumferential direction (horizontal direction: XY plane).

[0032] As shown in FIG. 5(C), the outer circumferential surface 133 of the housing of the sonar array 13 has the transducer 10 attached obliquely (facing downward) only on the stern side (rear). In the example of FIG. 5(C), the outer circumferential surface 133 of the sonar array 13 has a shape that extends from the stern end of the bottom outer circumferential surface 132a to the stern end of the second outer circumferential portion 131a-2 of the top outer circumferential surface 131a at an inclination angle of 45 deg. The depression angle of the transducer 10 disposed on the outer circumferential surface 133 including the area connecting the stern end area of ​​the second outer circumferential portion 131a-2 of the housing and the stern end area of ​​the bottom outer circumferential surface 132a is 45 deg (see the balloon in FIG. 5(C)). Here, the transducer 10 is disposed in a direction perpendicular to the outer circumferential surface 133 (frame portion 201 in FIG. 1(D)) as shown in FIG. 1(D).

[0033] In an embodiment in which the inclination angle of the stern end of the outer circumferential surface 133 of the sonar array 13 is 45 deg, as shown in Fig. 5(A), the first outer circumferential portion 131a-1 on the bow side of the upper surface outer circumferential surface 131a of the sonar array 13 is a semicircle with a radius of r. The second outer circumferential portion 131a-2 on the stern side of the upper surface outer circumferential surface 131a is a partial ellipse (semi-ellipse) with a semiminor axis of r and a semimajor axis of r+h (h is the height of the outer circumferential surface 133). The stern end of the first outer circumferential portion 131a-1 (semicircle) of the upper surface outer circumferential surface 131a and the bow end of the second outer circumferential portion 131a-2 (semi-ellipse) of the upper surface outer circumferential surface 131a are continuously connected. The shape of the second outer periphery 131a-2 of the upper surface outer periphery 131a is not limited to a semi-ellipse, and may be a shape having vertices smoothly connected by curves, such as a partial polygon, such as a trapezoid convex toward the stern or part of a hexagon, depending on the application.

[0034] The inclination angle of the aft end of the outer circumferential surface 133 of the sonar array 13 is set to an angle (45 deg in FIG. 5(C)) at which the engine 4 and screw propeller 5 on the aft side of the sonar array 13 are out of the sonar vertical search range (rear) 15. The inclination angle of the aft end of the outer circumferential surface 133 may be determined based on the position (height) of the sonar array 13 on the hull, the relationship between the sonar vertical search range (rear) 15 and the positions (heights) of the engine 4 and screw propeller 5, etc.

[0035] 6 and 7 are graphs showing an example of the vertical directivity of the sonar array 2 of the comparative example described above and the sonar array 13 of the embodiment of the present disclosure for each horizontal direction. In the graphs of FIG. 6 and FIG. 7, the vertical axis is the elevation angle (deg) of the central axis of the vertical directivity of the sonar, and the horizontal axis is the direction (deg) of the central axis of the horizontal directivity of the sonar in the horizontal direction. The horizontal direction of the horizontal axis of the graph is 0 deg in the bow direction, 90 deg in the starboard direction, 180 deg in the stern direction, and 270 deg in the port direction. In the graph of the vertical directivity of the sonar array 2 of the comparative example shown in FIG. 6, the elevation angle (deg) of the central axis of the vertical directivity of the sonar remains 0, that is, horizontal, in all horizontal directions of 0 deg, 90 deg, 180 deg, and 270 deg.

[0036] On the other hand, in the sonar array 13 of the embodiment of the present disclosure shown in Figure 7, when the depression angle of 180 degrees toward the stern is set to 45 degrees, in order not to interfere with the sound waves arriving from the horizontal direction that are received by the transducer 10, the outer peripheral surface 133 on the stern side of the sonar array 13 is smoothly deformed in shape without abruptly deforming.

[0037] As described above, the sonar array 13 of the embodiment of the present disclosure has a depression angle on the central axis of the directivity of the underwater sound waves transmitted and received in the stern direction. The direction of the central axis of the vertical directivity of the sonar array 13 has a depression angle of -45 degrees at 180 degrees in the stern direction, but remains horizontal at 0 degrees in the bow direction, 90 degrees in the starboard direction, and 270 degrees in the port direction.

[0038] By making the shape of the housing of the sonar array 13 the shape exemplified in Figures 5(A) to 5(C), noise sources such as the ship's engine 4 and screw propeller 5, which cause the sonar-unsearchable area (blind zone) toward the stern, can be removed from the sonar's vertical search range (rear).

[0039] As a result, omnidirectional detection is possible using the sonar array 13. This makes it possible to obtain an effect equivalent to that of the method disclosed in, for example, JP 2021-70408 A in which a sonar dome is raised and lowered under the bottom of the ship. However, in this disclosure, since the sonar array 13 is fixed to the hull (bow), the following problem cannot be solved; however, compared to the sonar array 2, the sonar horizontal exploration impossible range (blind zone) 12 is limited to a short distance range.

[0040] When the sonar array 13 is fixed to the bow, the sound of breaking waves that occurs when the ship 1 cuts through the waves on the sea surface 3 as it advances is generated at the bow (waterfront) 7. This sound of breaking waves becomes a noise source for the sonar.

[0041] Underwater sound waves do not travel in a straight line due to changes in density in the vertical direction underwater. For this reason, when the central axis of the directionality of the sound waves received from the rear and sent to the rear is angled at a depression angle as in the sonar array 13, a sonar horizontal search-unavailable area (blind zone) 17 (20 in Figure 10) is created in the short distance area behind the ship 1, as shown in Figure 8.

[0042] In Fig. 8, sonar horizontal search range 16 is the horizontal search range expected when sonar array 13 is used. The radius L1 of sonar horizontal search range 16 is attenuated as underwater sound waves propagate through the ocean. For this reason, L1 is a sonar performance value determined by the limit of the sonar's detection ability to detect sound waves emitted or reflected from a detection target. When detecting sound waves emitted or reflected from a detection target, the noise level in the ocean due to waves and the like and the breaking sound of the bow (waterboard part) 7 generated by the ship's navigation also affect the detection.

[0043] In Fig. 8, sonar horizontal unsearchable range (blind zone) 17 is a sonar horizontal unsearchable range (blind zone) that occurs because sonar vertical search range (rear) 15 shown in Fig. 4(A) has a downward depression angle. As will be described later, underwater sound waves have low linearity in the vertical direction. For this reason, an unsearchable range is generated, shown as blind zone 20 in Fig. 10, which will be referred to later in the description. The blind zone 20 in Fig. 10, which will be described later, corresponds to a schematic side view of sonar horizontal unsearchable range (blind zone) 17 in Fig. 8, viewed from the side in the sea.

[0044] The range of the sonar horizontal search impossible range (blind zone) 17 in FIG. 8 is approximately ±20 to 40 deg from the stern direction, and although it depends on the season and weather conditions (ocean bottom topography, season, solar altitude depending on time, weather conditions, etc.), L2 is expected to be approximately 1 to 10 km. It is expected that targets (underwater objects) behind the sonar horizontal search impossible range (blind zone) 17 can be detected by transmitting and receiving underwater sound waves by the sonar array 13. That is, although the sonar horizontal search impossible range (blind zone) 17 of distance L2 occurs in the stern direction, it is expected that the range corresponding to distance L3 will return to the sonar horizontal search range 16 again by transmitting and receiving underwater sound waves from behind it. In FIG. 8, the relationship between distance L1 and distance L3 is distance L1 = distance L2 + distance L3.

[0045] Figures 9(A) and 9(B) are schematic diagrams showing the propagation path of underwater sound waves when sound waves are sent horizontally from the sonar array 13 forward of the ship. Since the refractive index changes significantly due to factors such as changes in water temperature with depth, underwater sound waves do not propagate in a straight line through the ocean but curve as they propagate. The same is true for the sonar array 2 of the comparative example, as shown in Figures 9(A) and 9(B).

[0046] 10(A) and 10(B) are diagrams that diagrammatically show the propagation paths of underwater sound waves when the underwater sound waves are transmitted from the sonar array 13 so as to have a depression angle of 45 degrees backward.

[0047] 9(A), 9(B), 10(A), and 10(B), reference numeral 18 denotes the seafloor or thermocline (a layer near the water surface where the water temperature changes rapidly with depth in the ocean, etc.). Underwater sound waves transmitted from a sonar array 2 (13) mounted on a ship 1 are reflected by the seafloor or thermocline 18. The underwater sound waves reflected by the seafloor or thermocline 18 are further reflected by the ocean surface 3 and diffuse as they propagate through the ocean.

[0048] Figures 9(A) and 10(A) show schematic diagrams of the propagation path of underwater sound waves when the water temperature near the ocean surface is high and decreases with depth. According to Snell's law, underwater sound waves bend downward (towards the ocean bottom or thermocline 18) where the speed of sound is slow. That is, the refractive index n A Medium A and refractive index n B The angle of incidence between the normal line, which is perpendicular to the boundary surface of medium B, and the incident wave is called θ A , the angle of refraction between the transmitted wave and the normal is θ B Let the wave speed in medium A be v A , the wave speed in medium B is v B Then, the relationship expressed by the following equation (1) holds. sin(θ A ) / sin(θ B )=v A / v B =n A / n B …(1)

[0049] When the water temperature changes, the speed of sound also changes; when the water temperature is high, the speed of sound is faster, and when the water temperature is low, the speed of sound decreases. When the water temperature decreases as the water depth increases, the speed of sound also gradually decreases. If medium A is a layer above medium B, the velocity v A >speed v B The incidence angle θ A >Refraction angle θ BTherefore, underwater sound waves traveling in the depth direction are bent from the extension of the angle of incidence in a downward direction (so as to be convex upwards) towards the seabed or thermocline 18. In fact, when it is a clear day and sunlight reaches the sea surface and the water temperature near the sea surface becomes high, underwater sound waves transmitted horizontally are bent by about 90 degrees straight down, toward the seabed, at a distance of about 1 km (Kilometer). Also, the shallower the water depth is, the higher the water temperature becomes for underwater sound waves reflected by the seabed or thermocline 18. The refractive index n B of medium B (velocity v B ) and refractive index n A of medium A (velocity v A The angle of incidence between the incident wave and the normal line, which is a line perpendicular to the boundary surface of the B1 , the angle of refraction between the transmitted wave and the normal is θ A1 Then, speed vB<speed v A From the above, the incidence angle θ B1 <Refraction angle θ A2 and the light bends in a direction away from the sea surface 3 (so as to be convex upward) relative to the extension of the angle of incidence.

[0050] 10(A), the wake 21 is a residual wake of water vapor bubbles generated by cavitation that occurs when the ship 1 rotates the screw propeller 5. Depending on the size of the ship 1, the width of the wake 21 is in the range of about 10 to 30 m, and the depth is in the range of 10 to 20 m. Because underwater sound waves are highly scattered within the wake 21, the sonar array 13 cannot detect targets present within the wake 21 using underwater sound waves.

[0051] Figures 9(B) and 10(B) show schematic diagrams of the propagation path when the water temperature near the ocean surface is low and increases with depth. As the water depth increases, the water temperature increases and the speed of sound gradually increases. When medium A is a layer above medium B, v A <v B Therefore, the incidence angle θ A <Refraction angle θ BThe underwater sound wave is bent from the extension of the incident angle toward the sea surface 3 (so that it is convex downward). In addition, the water temperature of the underwater sound wave reflected by the seabed or thermocline 18 becomes lower as the water depth becomes shallower, and the speed of sound also gradually slows down. The refractive index n B of medium B (velocity v B ) and refractive index n A of medium A (velocity v A The angle of incidence between the incident wave and the normal line, which is a line perpendicular to the boundary surface of the B1 , the angle of refraction between the transmitted wave and the normal is θ A1 Then, v B >v A Therefore, the incidence angle θ B1 >Refraction angle θ A1 The underwater sound waves reflected by the seafloor or thermocline 18 are bent (convex downward) toward the sea surface 3 from the extension of the angle of incidence. In winter, the air temperature is lower than the water temperature, so the underwater sound waves are bent upward (convex downward) as they travel, as shown in Figures 9(B) and 10(B).

[0052] In Fig. 10(A) and Fig. 10(B), when the sonar array 13 is used, the direction of the central axis of the directivity of the underwater sound wave transmission and reception in the stern direction has a maximum depression angle of 45 deg, resulting in a sonar horizontal unsearchable range (blind zone) 20. The blind zone 20 in Fig. 10(A) and Fig. 10(B) is a schematic representation of the sonar horizontal unsearchable range (blind zone) 17 in Fig. 8 as viewed from the side. The size of the blind zone 20 varies depending on the propagation path (bending) of the underwater sound wave due to the depth to the seabed and the water temperature distribution in the sea, but as described in the explanation of the sonar horizontal unsearchable range (blind zone) 17 in Fig. 8, it is expected that the size will often be in the range of, for example, 1 to 10 km.

[0053] It should be noted that the underwater sound wave propagation path 19 shown in Figures 9(A) and 9(B) and Figures 10(A) and 10(B) is a schematic diagram showing a case where the sea surface and the sea bottom or the thermocline are completely flat, and in the actual sea, the sea surface 3 and the sea bottom or the thermocline 18 have unevenness. Therefore, the underwater sound waves are scattered when they are reflected by the sea surface 3 and the sea bottom or the thermocline 18. As a result, it is expected that the underwater sound waves will be transmitted even if they are outside the underwater sound wave propagation path 19, except in the vicinity of the stern of the ship 1. The underwater sound waves transmitted and received by the sonar array 13 mounted on the ship 1 are low-frequency underwater sound waves that can easily travel long distances, and the vertical linearity of the underwater sound waves is very low compared to visible light.

[0054] The operation of the sonar array 13 described above will be described below. The sonar array 13 is based on the structure illustrated in Fig. 5(A) to Fig. 5(C), and the front and side of the bow side have the same configuration as the cylindrical sonar array 2 described with reference to Fig. 2(A) to Fig. 2(C) as a comparative example, but the stern side is different from the comparative example. That is, the transducer 10 on the stern side is attached in a direction perpendicular to the inclined outer peripheral surface 133 as shown in Fig. 5(C). Therefore, the central axis of the vertical directivity of the sonar vertical search range (forward) 14 is oriented horizontally, but the central axis of the vertical directivity of the sonar vertical search range (rearward) 15 is oriented obliquely downward. The direction of the central axis of the vertical directivity of the sonar array 13 has a depression angle of -45 deg at 180 deg toward the stern, but remains horizontal at 0 deg toward the bow, 90 deg toward the starboard side, and 270 deg toward the port side (Figure 7).

[0055] The operating sound of the engine 4 installed from the center to the stern side of the ship 1 and the cavitation noise caused by the rotation of the screw propeller 5 are outside the range of the sonar vertical search range (rear), and a sonar horizontal search range 16 shown in FIG. 8 is obtained. This makes it possible to transmit and receive underwater sound waves in all directions including the rear, enabling omnidirectional detection. As shown in FIG. 4(A), the central axis of the vertical directivity of the sonar vertical search range (rear) 15 is oriented diagonally downward, so that underwater sound waves are not transmitted or received near the sea surface 3 behind the ship 1, resulting in a range where sonar horizontal search is not possible (blind zone) (17 in FIG. 8, 20 in FIG. 10). However, due to the natural phenomenon of the ocean in which the water temperature varies depending on the water depth, underwater sound waves do not travel straight vertically, but travel while bending in the direction where the water temperature is low and the seawater density is high. For this reason, as shown in Figure 8 as the sonar horizontal search impossible range 17, the range L2 of the sonar horizontal search impossible range (blind zone) 17 is expected to be approximately 1 to 10 km (varies depending on the seabed topography, season, solar altitude depending on the time of day, and weather conditions), and it is expected that underwater objects behind the blind zone will be detectable by transmitting and receiving underwater acoustic waves by the sonar array 13.

[0056] When the sonar array 13 is attached to the ship 1, as shown in FIG. 4(B), the position of the ship bottom 72 is near the center of the sonar array 13 in the vertical direction. The transducer 10 disposed on the stern side of the outer circumferential surface 133 of the sonar array 13 has a predetermined depression angle, and the upper end of the transducer 10 is lowered. For this reason, even if the sonar array 13 is disposed at the position of the sonar array 2 of the comparative example shown in FIG. 1(B), there is nothing to obstruct underwater sound waves in the direction of the central axis of the vertical directivity of the sonar vertical exploration range (rear) 15 (FIG. 4(A)). In other words, by replacing the sonar array 2 with the sonar array 13 of the present disclosure without significantly modifying the hull of the ship 1 of the comparative example, the sonar of the ship can be modified into an omnidirectional detection sonar.

[0057] The mounting positions of the transducers 10 of the sonar array 13 described with reference to Figures 5(A) to 5(C) are constant in the vertical direction all around the front, sides and rear. This also makes the width of the vertical directivity of the sonar vertical search range (forward) 14 and the sonar vertical search range (rear) 15 constant. Since the present disclosure does not change the processing method for signal processing, etc. of the marine sonar device and uses a known three-dimensional sonar configuration, a description of the configuration of the transmitting device (transmitting unit, transmission control unit), receiving device (receiving unit, signal processing unit, azimuth detection unit), display control unit, display device, etc. will be omitted.

[0058] As described above, the present disclosure provides the following advantages.

[0059] The horizontal detection range of ship sonar can be reduced by using a cylindrical sonar array (sonar array 2 in Figure 1), which creates an unsearchable area (blind zone) behind the ship's hull, making omnidirectional detection (search possible).

[0060] Existing ships can be retrofitted with the sonar array 13 disclosed herein without requiring major modifications, and the horizontal detection range of the ship's sonar can be expanded in all directions.

[0061] In a ship equipped with sonar for the purpose of detecting underwater vehicles that cannot be detected by radar or optical observation, for example, a high-performance sonar array can be realized that can detect underwater sound waves arriving from all horizontal directions using a single sonar array.

[0062] By changing the shape of the sonar array installed at the bow, without using a towed sonar array that reduces the propulsion energy efficiency of the ship, it is possible to realize a high-performance sonar array that enables the ship to detect underwater sound waves arriving from all horizontal directions by placing the engine and screw propeller, which are noise sources for the ship's sonar array, outside the range of the rear sonar vertical search range.

[0063] The disclosure of the above-mentioned Patent Document 1 is incorporated herein by reference. Modifications and adjustments of the embodiments and examples are possible within the scope of the entire disclosure (including the scope of claims) of this disclosure, and further based on its basic technical ideas. Furthermore, various combinations and selections of various disclosed elements (including each element of each claim, each element of each example, each element of each drawing, etc.) are possible within the scope of the claims of this application. In other words, this disclosure naturally includes various modifications and corrections that a person skilled in the art would be able to make in accordance with the entire disclosure including the scope of claims and the technical ideas. [Explanation of symbols]

[0064] 1 ship 2. Sonar Array 3 sea level 4 Engine 5 Screw Propeller 6. Rudder 7 Bow (waterline) 71 Cavity 72 Ship bottom 8. Sonar Dome 81 Sonar dome body 9a Sonar vertical range (forward) 9b Sonar vertical range (rear) 10 Transducer (acoustic element) 11 Sonar horizontal search range 12 Sonar horizontal detection range 13. Sonar Array 14 Sonar vertical range (forward) 15 Sonar vertical range (rear) 16 Sonar horizontal range 17 Sonar horizontal detection range 18 Ocean bottom or thermocline 19 Underwater sound propagation paths 20. Blind Zone 21 Wake 101 Electrostrictive vibrator (piezoelectric element) 102 Front Mass 103 Rear Mass 104 Transmitting and receiving surface 131 Top surface 131a Top outer circumference 131a-1 First outer periphery (top outer periphery) 131a-2 Second outer periphery (top outer periphery) 132 Bottom 132a Bottom perimeter 133 Outer surface 201 Frame section

Claims

1. A sonar array provided at the front of a ship, the sonar array comprising a plurality of sets of transducers arranged in a circumferential direction of the outer circumferential surface of a housing, the plurality of sets being arranged in a vertical direction of the outer circumferential surface of the housing, a sonar array in which the stern side of the outer periphery of the top surface of the housing is curved in such a way that the stern side of the outer periphery of the bottom surface of the housing extends further toward the stern, and the outer periphery has a shape that extends from the stern end of the outer periphery of the bottom surface to the stern end of the outer periphery of the top surface at a predetermined inclination angle.

2. 2. The sonar array of claim 1, wherein a bow side of said top outer periphery is shaped to correspond to a bow side of said bottom outer periphery.

3. The planar shape of the bottom outer periphery is circular, A planar shape of the bow side of the outer periphery of the upper surface is a semicircle convex toward the bow side, which corresponds to the semicircle of the bow side of the outer periphery of the bottom surface, The planar shape of the stern side of the outer periphery of the upper surface has a semiminor axis equal to the radius of the semicircle on the bow side of the outer periphery of the upper surface and a semimajor axis larger than the radius of the semicircle, and is a semiellipse protruding toward the stern side, and an end of the semicircle on the outer periphery of the upper surface on the stern side and an end of the semiellipse on the outer periphery of the upper surface on the bow side are continuously connected to each other, 2. The sonar array of claim 1, wherein the aft side of the outer periphery has a shape that slopes from the aft side of the circular shape of the bottom periphery to the aft side of the semi-elliptical shape of the top periphery.

4. 2. The sonar array according to claim 1, wherein the transducer disposed in the region of the outer circumferential surface connecting the aft end of the top outer periphery and the aft end of the bottom outer periphery has a predetermined depression angle corresponding to the predetermined inclination angle.

5. 5. The sonar array of claim 4, wherein the depression angle of the transducer is set at an angle such that an engine or a screw propeller located aft of the hull relative to the sonar array is outside the vertical search range of the sonar array.

6. In the outer circumferential surface, the inclination angle from the stern end of the bottom outer circumferential surface to the stern end of the top outer circumferential surface is a predetermined acute angle, 2. The sonar array of claim 1, wherein the depression angle of the transducer arranged on the outer circumferential surface of a region connecting the aft end of the top outer periphery and the aft end of the bottom outer periphery is equal to the predetermined acute angle, among the transducers arranged perpendicular to the outer periphery.

7. 2. The sonar array of claim 1, wherein the bow side of the outer periphery of the top surface corresponds to a shape obtained by translating the bow side of the outer periphery of the bottom surface to the top surface.

8. 8. A sonar array as claimed in any preceding claim housed in a sonar dome on the under bow of a vessel.

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