Flow noise compensation and suppression optical fiber array hydrophone structure and preparation method thereof

Abstract

The invention relates to the technical field of optical fiber sensing, and particularly provides a flow noise compensation and suppression optical fiber array hydrophone structure and a preparation method thereof, in the structure, a first optical fiber and a second optical fiber are arranged in parallel; the sound pressure isolation sheath sleeves the outer side of the second optical fiber; the first optical fiber and the sound pressure isolation sheath are sleeved with the sensitization protection sleeve, and flow guide ripples are arranged on the outer surface of the sensitization protection sleeve and used for restraining part of flow noise; the first optical fiber sensitive to sound pressure and flow noise and the second optical fiber only sensitive to the flow noise after being shielded by the sound pressure isolation sheath are introduced at the same time, the interference type optical fiber hydrophone is constructed, flow noise signals in the first optical fiber are filtered out in combination with a self-adaptive filtering algorithm, compensation and suppression of the flow noise are achieved, and the noise suppression effect is improved. Therefore, weak sound pressure signals can be effectively extracted in a high flow noise environment. The interference of flow noise on the optical fiber array hydrophone can be remarkably reduced, the signal-to-noise ratio of the system is improved, and the method is suitable for high-precision sound field detection in a complex marine environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical fiber sensing, and particularly relates to a flow noise compensation and suppression optical fiber array hydrophone structure and a preparation method thereof. BACKGROUND

[0002] The underwater acoustic detection technology plays an important role in the fields of marine environment monitoring, resource exploration and underwater target identification, and is an important means to obtain marine information. The hydrophone array as the core detection equipment directly determines the detection capability of the system. In practical application, the hydrophone array usually needs to be laid relying on the platform of a ship, a submarine vehicle and the like. However, the laying cabin and carrying space of these platforms are limited, and the large-diameter array cable not only occupies a large volume and increases the burden of the platform, but also limits the laying length and scale of the array, which is difficult to meet the demand of large-scale underwater acoustic field detection. Therefore, the optical fiber hydrophone array with ultra-fine wire diameter can significantly improve the laying efficiency and concealment of the array, and meet the application demand of large-scale underwater acoustic field detection.

[0003] In the prior art, the traditional piezoelectric hydrophone gradually cannot meet the requirements of high-precision detection due to insufficient acoustic pressure sensitivity and limited large-scale networking capability. Therefore, an interference type optical fiber hydrophone array is proposed, and the acoustic pressure sensitivity thereof can be increased by 2-3 orders of magnitude compared with the piezoelectric hydrophone. However, this type of hydrophone relies on multiple discrete elements, and the system complexity is high, which limits its application in large-scale array. The subsequently developed distributed optical fiber hydrophone can realize long-distance and large-scale networking, but since a single optical fiber is not sensitive to the radial acoustic pressure, the optical fiber needs to be wound on a mandrel to increase the acoustic pressure sensitivity. Limited by the physical limitation of the minimum winding radius of the optical fiber, the array cable diameter is difficult to be further reduced, thereby limiting the realization of the ultra-fine wire diameter array.

[0004] The research status shows that the existing optical fiber sensing technology is still difficult to construct a large-scale optical fiber hydrophone array with high sensitivity acoustic pressure detection capability and ultra-fine wire diameter characteristics. In view of this problem, the present application proposes a large-scale optical fiber array hydrophone structure with ultra-fine wire diameter and high sensitivity. However, due to the reduction of the array cable diameter, the surface area is correspondingly reduced, and the sensitivity to fluid dynamics is increased. When the water flows around the optical cable, significant flow noise is generated, which makes the flow noise the main interference source in signal detection, and seriously increases the difficulty of extracting weak acoustic pressure signals. At present, there is no effective means to realize the distributed in-situ detection of flow noise in the linear type fine diameter optical fiber array hydrophone. SUMMARY

[0005] Therefore, the present application proposes a flow noise compensation and suppression optical fiber array hydrophone structure and a preparation method thereof, to solve the problem that the existing distributed optical fiber array hydrophone is easily disturbed by flow noise.

[0006] The technical scheme of the present application is implemented as follows: In one aspect, the present application provides an optical fiber array hydrophone structure, comprising a first optical fiber, a second optical fiber, an acoustic pressure isolation sheath, a sensitivity enhancement protective sleeve and an anti-twist mechanism, wherein, The first optical fiber and the second optical fiber are arranged side by side, and the first optical fiber is simultaneously sensitive to an acoustic pressure signal and a flow noise signal; The acoustic pressure isolation sheath is sleeved outside the second optical fiber to form an acoustic pressure isolation structure, and the acoustic pressure isolation sheath isolates the acoustic pressure signal from reaching the second optical fiber, so that the second optical fiber is only sensitive to the flow noise signal, and the second optical fiber and the first optical fiber form an interferometer structure; The sensitivity enhancement protective sleeve is sleeved outside the first optical fiber and the acoustic pressure isolation sheath, the first optical fiber is in direct contact with the sensitivity enhancement protective sleeve, and the outer surface of the sensitivity enhancement protective sleeve is provided with a flow guiding corrugation formed by ribs, the flow guiding corrugation has a groove-shaped structure, and the flow guiding corrugation suppresses part of the flow noise by interfering with the development of a turbulent boundary layer and changing a vortex shedding pattern; The anti-twist mechanism is arranged inside the sensitivity enhancement protective sleeve to prevent the sensitivity enhancement protective sleeve from being twisted.

[0007] On the basis of the above technical scheme, preferably, the ribs are linearly arranged and parallel to the axial direction of the sensitivity enhancement protective sleeve. Or, the ribs are linearly arranged and in a twisted shape.

[0008] On the basis of the above technical scheme, preferably, the ribs are linearly arranged and parallel to the axial direction of the sensitivity enhancement protective sleeve, and the outer surface of the ribs is in a wavy shape, and the fluctuation direction of the ribs corresponds to the radial direction of the sensitivity enhancement protective sleeve.

[0009] On the basis of the above technical scheme, preferably, the second optical fiber and the acoustic pressure isolation sheath are coaxial cylinders, and there is a spacing between the second optical fiber and the acoustic pressure isolation sheath, and the spacing error is 1.5 mm±0.02 mm; gratings are engraved on the first optical fiber and the second optical fiber, and the spacing between the gratings is 1 m~20 mm, and the spacing error is ±5 cm.

[0010] On the basis of the above technical scheme, preferably, the anti-twist mechanism is in a strip-shaped structure, a cross coordinate is drawn based on the cross section of the sensitivity enhancement protective sleeve, the anti-twist mechanism can be bent along one of the coordinate axes, and is in a rigid state relative to the other coordinate axis.

[0011] In another aspect, the present application provides a preparation method of the above-mentioned optical fiber array hydrophone structure, comprising the following steps: S1, preparing a first optical fiber and a second optical fiber; S2, adding an acoustic pressure isolation sheath outside the second optical fiber; S3, arranging an anti-twist mechanism, and making the anti-twist mechanism parallel to the first optical fiber and the acoustic pressure isolation sheath outside the second optical fiber; S4. Extrusion forms a sensitive protective sleeve to cover the outside of the first optical fiber, the acoustic pressure isolation sheath, and the anti-torsion mechanism; S5. Ribs are formed on the outside of the sensitive protective sleeve by re-extrusion.

[0012] The fiber optic array hydrophone structure and its fabrication method for flow noise compensation and suppression of the present invention have the following advantages over the prior art: (1) By setting up a first optical fiber that is sensitive to sound pressure and a second optical fiber that is covered with a sound pressure isolation sheath and is not sensitive to sound pressure, an interferometer structure can be formed to realize the independent measurement of flow noise. Combined with an adaptive filtering algorithm, flow noise compensation can be realized to extract the weak target sound pressure signal under strong flow noise. Compared with the existing single-fiber hydrophone, the design of an interferometer-based distributed flow noise sensing array that is not sensitive to sound pressure but sensitive to flow noise, combined with the sound pressure sensing array for co-position encapsulation, constructs a differential detection sensor structure that is sensitive to sound pressure and not sensitive to sound pressure. Combined with a filtering algorithm, in-situ decoupling of flow noise and sound pressure can be realized, which can effectively reduce noise and eliminate interference, and is beneficial for extracting the sound pressure signal of high flow noise target. (2) The first and second optical fibers are encapsulated by a sensitive enhancement protective sleeve. By exploring the acoustic-fluid-solid coupling mechanism under the working state of the ultra-fine diameter hydrophone, a flow-guiding ripple is constructed on the outer surface of the sensitive enhancement protective sleeve through ribs to form a sharkskin bionic encapsulation, which can realize water flow guidance, thereby reducing flow noise interference and improving the ability of the hydrophone to detect weak sound pressure signals. (3) An anti-torsion mechanism is provided inside the sensitive protection sleeve. This increases the stability of the hydrophone structure when it is working underwater, and prevents torsion caused by the current guiding force, thus further reducing vibration interference. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a perspective view of the fiber optic array hydrophone structure for flow noise compensation and suppression according to the present invention. Figure 2 This is a diagram showing a flow-guiding corrugated layout structure of the fiber optic array hydrophone structure for flow noise compensation and suppression according to the present invention. Figure 3 This is a diagram showing another flow-guiding corrugation layout structure of the fiber optic array hydrophone structure for flow noise compensation and suppression according to the present invention. Figure 4This is a perspective view of the fiber optic array hydrophone structure for flow noise compensation and suppression according to the present invention. Figure 5 A structural diagram showing the installation of a flow guide sleeve in the fiber optic array hydrophone structure for flow noise compensation and suppression according to the present invention; Figure 6 This is an end view of the fiber optic array hydrophone structure for flow noise compensation and suppression according to the present invention, with the flow guide sleeve installed. Figure 7 For the present invention Figure 6 Sectional view along the AA direction; Figure 8 A side view of the fiber optic array hydrophone structure for flow noise compensation and suppression according to the present invention, with the flow guide sleeve installed. Figure 9 For the present invention Figure 8 Cross-sectional view along the BB direction; Figure 10 An exploded view of the fiber optic array hydrophone structure for flow noise compensation and suppression according to the present invention. Figure 11 This is a perspective view of the anti-torsion mechanism of the fiber optic array hydrophone structure for flow noise compensation and suppression according to the present invention. In the diagram: 1. First optical fiber; 2. Second optical fiber; 3. Acoustic pressure isolation sleeve; 4. Sensitivity-enhancing protective sleeve; 41. Rib; 5. Anti-torsion mechanism; 51. Chain link; 52. Pin; 53. Spacer; 54. Fastening band; 6. Ring frame; 7. Flow guide sleeve; 8. Locking bolt. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0016] like Figures 1-11 As shown, the fiber optic array hydrophone structure for flow noise compensation and suppression of the present invention includes a first optical fiber 1, a second optical fiber 2, an acoustic pressure isolation sheath 3, a sensitivity-enhancing protective sheath 4, an anti-torsion mechanism 5, and a ring frame 6.

[0017] like Figures 1-3As shown, the first optical fiber 1 and the second optical fiber 2 are arranged side by side. The first optical fiber 1 is sensitive to both sound pressure signals and flow noise signals. The sound pressure isolation sleeve 3 is fitted on the outside of the second optical fiber 2 to form a sound pressure isolation structure. The sound pressure isolation sleeve 3 isolates the sound pressure signal from reaching the second optical fiber 2. The second optical fiber 2 is only sensitive to flow noise signals. The second optical fiber 2 and the first optical fiber 1 form an interferometer structure. The sensitivity-enhancing protective sleeve 4 is fitted on the outside of the first optical fiber 1 and the sound pressure isolation sleeve 3. The first optical fiber 1 is in direct contact with the sensitivity-enhancing protective sleeve 4. As described above, the first optical fiber 1 is directly encapsulated by the sensitizing protective sleeve 4, while the second optical fiber 2 is first encapsulated by the sound pressure isolation sleeve 3, and then encapsulated by the sensitizing protective sleeve 4. In this way, the first optical fiber 1 is sensitive to sound pressure, while the second optical fiber 2 is not sensitive to sound. It can be used with an interferometer to achieve independent measurement of flow noise, and combined with the RLS algorithm to achieve flow noise compensation. Compared to existing single-fiber hydrophones, this invention employs an interferometer to design a distributed fiber optic flow noise sensing array that is insensitive to sound pressure but sensitive to flow noise. By co-encapsulating the sound pressure sensing array with the other components, a differential detection sensor structure that is both sensitive and insensitive to sound pressure is constructed. Combined with a filtering algorithm, in-situ decoupling of flow noise and sound pressure is achieved, which can effectively reduce noise and eliminate interference, and is beneficial for extracting sound pressure signals from high flow noise targets.

[0018] Specifically, the enhanced-sensitivity protective sleeve 4 uses underwater acoustic-sensitive materials such as polyurethane.

[0019] like Figures 1-3 As shown, the outer surface of the sensitive protective sleeve 4 is provided with flow-guiding corrugations formed by ribs 41. The flow-guiding corrugations have a groove-like structure. The flow-guiding corrugations suppress some flow noise by interfering with the development of the turbulent boundary layer and changing the vortex shedding mode. As described above, the flow-guiding ripples on the surface of the enhanced protective sleeve 4 can guide the water flow, reduce the generation of vortices, thereby reducing vibration and flow noise interference, and improving the hydrophone's ability to detect weak sound pressure signals. Specifically, when water flows through the grooved structure on the surface of the hydrophone array, the groove design effectively suppresses the lateral flow of the water, confining the turbulence within the grooves. This hydrodynamic mechanism causes the turbulence to extend along the flow direction, significantly weakening the intensity and frequency of turbulent bursts and reducing momentum exchange and pressure pulsations within the boundary layer. Simultaneously, the grooved structure reduces the vortex size on the hydrophone surface, weakens the vortex intensity, disrupts the vortex periodicity, and transforms vortex rotation into more disordered, high-frequency small vortices, thereby effectively reducing overall flow noise.

[0020] like Figure 1 As shown, the anti-torsion mechanism 5 is located inside the sensitizing protective sleeve 4 to prevent the sensitizing protective sleeve 4 from torturing. As described above, since the fiber optic array hydrophone is linear, if it is torn due to the force generated by the guiding ripples during towing, it will cause damage to the hydrophone, affecting its service life and normal testing. Therefore, an anti-torsion mechanism 5 is set to effectively avoid torsion problems.

[0021] like Figure 1 and Figure 2 As shown, the ribs 41 are arranged linearly and parallel to the axial direction of the sensitive protective sleeve 4; or, the ribs 41 are arranged linearly and twisted. As described above, when arranging the ribs 41, they can be set to a linear state, or further twisted to a torsional state, thereby guiding the water flow and reducing the generation of vortices.

[0022] like Figure 3 As shown, in some embodiments, the ribs 41 are arranged linearly and parallel to the axial direction of the sensitizing protective sleeve 4, and the outer surface of the ribs 41 is wavy, with the undulation direction of the ribs 41 corresponding to the radial direction of the sensitizing protective sleeve 4. like Figure 1 As shown, the anti-torsion mechanism 5 has a strip-shaped structure. A cross coordinate is drawn with the cross section of the sensitive protective sleeve 4. The anti-torsion mechanism 5 can be bent along one of the coordinate axes and is in a rigid state relative to the other coordinate axis. As described above, the anti-torsion mechanism 5 is set as a strip structure, which facilitates integration with optical fiber and can significantly reduce the impact on sensing sensitivity, thereby reducing interference with underwater acoustic vibrations during transmission through the sensitive protective sleeve 4. By controlling the degrees of freedom of the anti-torsion mechanism 5, interference problems can be avoided when integrating the fiber optic array hydrophone, so that the fiber optic array hydrophone can enter the water at an angle, ensuring the detection range and minimizing the lateral bending and torsion of the hydrophone.

[0023] like Figure 10 and Figure 11 As shown, the anti-torsion mechanism 5 includes chain links 51 and pins 52. The chain links 51 are arranged linearly in a plurality of them, and the chain links 51 are hinged to each other by pins 52. As described above, the anti-torsion mechanism 5 is shaped like a chain, so it can only swing up and down. This allows it to tilt downwards and submerge in the water when the fiber optic array hydrophone is towed, thus minimizing the swinging. As the length of the fiber optic array hydrophone increases, it is inevitable that it will deform due to the assembly error of the link 51 and the material limitations, and slight swaying will occur. At this time, the anti-torsion mechanism 5 only needs to prevent the hydrophone from twisting to avoid damage.

[0024] like Figure 10 and Figure 11As shown, the anti-torsion mechanism 5 also includes a spacer 53 and a fastening band 54. The spacer 53 is sleeved on the chain link 51 and the pin 52, and the spacer 53 is filled with talcum powder. The fastening band 54 is tightened on the spacer 53. As described above, by setting a spacer 53 on the anti-torsion mechanism 5 and filling it with talc powder, the noise of the chain link 51 rotating relative to each other can be reduced, thereby mitigating the interference with the optical fiber and ensuring application performance. Furthermore, the spacer 53 is designed with a honeycomb structure to achieve a vibration reduction effect; By setting the fastening band 54, the spacer 53 can be tightly fitted to the chain link 51 and the talc powder inside can be tightly wrapped, thus ensuring the stability of the structure.

[0025] like Figure 1 As shown, at least two anti-torsion mechanisms 5 are provided, wherein the fastening band 54 of the anti-torsion mechanism 5 is provided corresponding to the chain link 51; the ring frame 6 is connected to the fastening band 54 of the two anti-torsion mechanisms 5. As described above, in order to further ensure the stability of the fiber optic integrated structure, two anti-torsion mechanisms 5 are provided and connected by a ring frame 6. This ensures that the relative positions of the two anti-torsion mechanisms 5 are stable and that they operate synchronously, which helps to improve the overall rigidity. Specifically, the fastening strap 54 is a rigid cable tie, which can be integrated with the ring frame 6.

[0026] Specifically, the second optical fiber 2 and the acoustic pressure isolation sheath 3 are coaxial cylinders, and there is a gap between the second optical fiber 2 and the acoustic pressure isolation sheath 3, with a gap error of 1.5mm ± 0.02mm; the first optical fiber 1 and the second optical fiber 2 are engraved with gratings, and the gap between the gratings is 1m~20mm, with a gap error of ±5cm.

[0027] Specifically, the outer diameter of the sensitive protective sleeve 4 is ≤10mm.

[0028] The fiber optic array hydrophone of the present invention also includes a flow guide sleeve 7 and a locking bolt 8.

[0029] like Figures 4-10 As shown, the flow guide sleeve 7 is disposed at the end of the sensitizing protective sleeve 4, and a portion of the flow guide sleeve 7 is sleeved on the sensitizing protective sleeve 4; the locking bolt 8 connects the flow guide sleeve 7 and the anti-torsion mechanism 5 in series. As described above, by setting a flow guide sleeve 7 at the end of the sensitivity-enhancing protective sleeve 4, the water flow can be further guided to reduce the impact of the water flow on the end face of the fiber optic array hydrophone and reduce drag resistance. When setting the flow guide sleeve 7, the locking bolt 8 is passed through the anti-torsion mechanism 5 and the flow guide sleeve 7 so that the flow guide sleeve 7 can be integrated with the sensitivity-enhancing protective sleeve 4.

[0030] The method for fabricating the fiber optic array hydrophone of the present invention includes the following steps: S1. Fabricate the first optical fiber 1 and the second optical fiber 2; S2. Add an acoustic pressure isolation sheath 3 to the outside of the second optical fiber 2; S3. Set up an anti-torsion mechanism 5 and make the anti-torsion mechanism 5 parallel to the acoustic pressure isolation sheath 3 on the outside of the first optical fiber 1 and the second optical fiber 2. S4. Extrusion forms a sensitive protective sleeve 4 to cover the outside of the first optical fiber 1, the acoustic pressure isolation sheath 3 and the anti-torsion mechanism 5; S5. Ribs 41 are formed on the outside of the sensitive protective sleeve 4 by re-extrusion.

[0031] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fiber optic array hydrophone structure for flow noise compensation and suppression, characterized in that: It includes a first optical fiber (1), a second optical fiber (2), an acoustic pressure isolation sheath (3), a sensitivity-enhancing protective sheath (4), and an anti-torsion mechanism (5), wherein, The first optical fiber (1) and the second optical fiber (2) are arranged side by side, and the first optical fiber (1) is sensitive to both sound pressure signals and flow noise signals. The acoustic pressure isolation sleeve (3) is sleeved on the outside of the second optical fiber (2) to form an acoustic pressure isolation structure. The acoustic pressure isolation sleeve (3) isolates the acoustic pressure signal from reaching the second optical fiber (2). The second optical fiber (2) is only sensitive to flow noise signals. The second optical fiber (2) and the first optical fiber (1) form an interferometer structure. The sensitivity-enhancing protective sleeve (4) is sleeved on the outside of the first optical fiber (1) and the acoustic pressure isolation sleeve (3). The first optical fiber (1) is in direct contact with the sensitivity-enhancing protective sleeve (4), and the outer surface of the sensitivity-enhancing protective sleeve (4) is provided with a flow-guiding corrugation formed by ribs (41). The flow-guiding corrugation has a groove-like structure. The flow-guiding corrugation suppresses some flow noise by interfering with the development of the turbulent boundary layer and changing the vortex shedding mode. The anti-torsion mechanism (5) is located inside the sensitizing protective sleeve (4) to prevent the sensitizing protective sleeve (4) from twisting.

2. The fiber optic array hydrophone structure for flow noise compensation and suppression as described in claim 1 is characterized in that: The ribs (41) are arranged linearly and parallel to the axial direction of the sensitive protective sleeve (4); Alternatively, the ribs (41) are arranged linearly and twisted.

3. The fiber optic array hydrophone structure for flow noise compensation and suppression as described in claim 1, characterized in that: The ribs (41) are arranged linearly and parallel to the axial direction of the sensitizing protective sleeve (4), and the outer surface of the ribs (41) is wavy, with the undulation direction of the ribs (41) corresponding to the radial direction of the sensitizing protective sleeve (4).

4. The fiber optic array hydrophone structure for flow noise compensation and suppression as described in any one of claims 1 to 3, characterized in that: The second optical fiber (2) and the acoustic pressure isolation sheath (3) are coaxial cylinders, and there is a gap between the second optical fiber (2) and the acoustic pressure isolation sheath (3), with a gap error of 1.5mm ± 0.02mm; The first optical fiber (1) and the second optical fiber (2) are engraved with gratings, and the spacing between the gratings is 1m~20mm, with a spacing error of ±5cm.

5. The fiber optic array hydrophone structure for flow noise compensation and suppression as described in any one of claims 1 to 3, characterized in that: The anti-torsion mechanism (5) has a strip-shaped structure. A cross coordinate is drawn with the cross section of the sensitive protective sleeve (4). The anti-torsion mechanism (5) can be bent along one of the coordinate axes and is rigid relative to the other coordinate axis.

6. A method for fabricating a fiber optic array hydrophone structure for flow noise compensation and suppression as described in claim 5, characterized in that, Includes the following steps: S1. Prepare the first optical fiber (1) and the second optical fiber (2); S2. Add the sound pressure isolation sheath (3) to the outside of the second optical fiber (2); S3. Set the anti-torsion mechanism (5) and make the anti-torsion mechanism (5) parallel to the sound pressure isolation sheath (3) on the outside of the first optical fiber (1) and the second optical fiber (2); S4. The sensitizing protective sleeve (4) is formed by extrusion to cover the outside of the first optical fiber (1), the acoustic pressure isolation sleeve (3) and the anti-torsion mechanism (5); S5. The rib (41) is formed on the outside of the sensitive protective sleeve (4) by extrusion again.

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