Optical fiber two-dimensional vector ocean turbulence sensor based on airfoil shear flow structure

Abstract

The invention discloses an optical fiber two-dimensional vector ocean turbulence sensor based on an airfoil shear flow structure. The optical fiber two-dimensional vector ocean turbulence sensor comprises an optical fiber vector sensor module, a transduction structure connection module and a protective sleeve module, the optical fiber vector sensor module consists of four sections of optical fibers which are mutually connected in series and are orthogonally distributed on the cross section of a cantilever beam, a polymer wrapping layer and a metal cantilever; the transduction structure connecting module is composed of a connecting rod, a lock nut and a cabin penetrating connector. The protective sleeve module is composed of a protective sleeve and a probe, and a gap between the probe and the protective sleeve is sealed by glue. The method has the beneficial effects that the high-precision optical fiber two-dimensional vector shear flow sensing is realized by reading the strain distribution condition on the four sections of optical fibers; a composite cantilever transduction structure of a cantilever beam and a polymer, optical fiber accumulated length and the like are adopted for sensitization, and the sensitivity reaches 1 * 10 <-1 > mu epsilon * ms2 / kg; a plurality of optical fiber two-dimensional vector ocean turbulence sensors are connected in series through optical fibers to form an ocean turbulence sensing array, and turbulence information at different positions of the ocean is synchronously collected.

Description

Technical Field

[0001] The invention relates to the field of ocean turbulence measurement, and in particular to an optical fiber two-dimensional vector ocean turbulence sensor based on an airfoil shear flow structure. Background Art

[0002] At present, the turbulence signal transmission process at home and abroad is mainly based on one-dimensional scalar sensing, which cannot simultaneously perceive horizontal and vertical velocity pulsations and lacks the ability to observe the anisotropic characteristics of turbulence in key areas such as the boundary layer. At the same time, traditional airfoil shear flow turbulence sensors have the limitations of a single transducer structure and low sensitivity. In recent years, although fiber optic sensing technology has solved the problems of single-point measurement and susceptibility to electromagnetic interference of electrical ocean turbulence sensors to a certain extent, the demodulation accuracy of traditional grating turbulence sensors is limited and the error is large, and the existing distributed fiber optic turbulence sensing system is limited by the m-level spatial resolution of DAS. In order to better realize the effective perception of vector ocean turbulence signals, achieve the breakthrough development of my country's new generation of ocean sensors, break the foreign technology monopoly, and accurately establish the vector turbulence signal sensing model, it has become a key scientific problem that needs to be solved urgently. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a highly sensitive optical fiber two-dimensional vector ocean turbulence sensor based on an airfoil shear flow structure, which adopts a composite cantilever and low-loss optical fiber accumulation method to enhance sensitivity, and uses four different quasi-distributed strain distribution patterns on a single optical fiber to determine the amplitude and direction of turbulence, thereby achieving high-precision measurement of the two-dimensional vector of ocean turbulence.

[0004] The technical solution adopted by the present invention to solve the above technical problems is: an optical fiber two-dimensional vector ocean turbulence sensor based on an airfoil shear flow structure, comprising an optical fiber vector sensor module, a transducer structure connection module and a protective cover module; the optical fiber vector sensor module comprises four sections of optical fiber, a polymer sheath and a metal cantilever; the transducer structure connection module comprises a connecting rod, a locking nut and a cabin penetration joint; the protective cover module comprises a protective cover and a probe.

[0005] According to the above scheme, the four sections of optical fiber are orthogonally distributed on the cross section of the composite cantilever beam and connected in series with each other. Under the condition of limited lateral size, strain sensitivity is achieved by accumulating the optical fiber length in the longitudinal direction. The four sections of optical fiber are thin-diameter bend-resistant optical fibers.

[0006] According to the above scheme, the bottom section of the metal cantilever uses a layer of annular polymer wrapping layer as a conversion intermediate layer between the metal cantilever and the optical fiber; the metal cantilever serves as the main transducer cantilever, and the layer of annular polymer wrapping layer serves as the auxiliary transducer arm, and the two are combined to form the composite cantilever; the composite cantilever beam is a columnar structure as a whole, and the front end is connected to a rubber-headed turbulence probe.

[0007] According to the above scheme, the bottom end of the composite cantilever is connected by a connecting rod, and the lock nut is tightly attached to the bottom end of the protective sleeve and clamps the perimeter of the cantilever structure as a whole.

[0008] According to the above solution, the protective cover has a streamlined appearance, and the probe is a wing-shaped rubber head probe fixed to the top of the metal cantilever.

[0009] According to the above scheme, access is made through two through-cabin joints arranged between the connecting rod and the composite cantilever.

[0010] According to the above scheme, a plurality of the optical fiber two-dimensional vector ocean turbulence sensors can be connected in series through optical fibers to form an ocean turbulence sensing array, and synchronously collect turbulence information at different locations in the ocean.

[0011] In the above scheme, the material of the protective cover 1 is 316 stainless steel, which has good corrosion resistance. A specific mold is used to seal the connection gap between the rubber head turbulence probe 4 and the protective cover 1 using a pressure-resistant potting glue to ensure the overall pressure resistance and water tightness of the sensor. At the same time, the design of the outer protective cover is used to protect the probe 4. The outer protective cover is made of water-soluble polyvinyl alcohol material, which is folded into a cone and pasted on the front side of the sensor. After the turbulence sensor enters the sea, it is left to stand on the sea surface. After the outer protective cover is completely dissolved in the seawater, it dives.

[0012] The beneficial effects produced by the present invention are:

[0013] (1) The current turbulence signal transmission process at home and abroad is mainly based on one-dimensional scalar sensing, which lacks the ability to observe the anisotropic characteristics of turbulence in key areas such as the boundary layer. The present invention is based on the two-dimensional vector shear flow sensing principle of the low-loss optical fiber "orthogonal series" optical path, and can simultaneously measure the horizontal and vertical velocity pulsations of ocean turbulence signals.

[0014] (2) The traditional airfoil shear flow turbulence sensor has the limitations of a single transducer structure and low sensitivity. The present invention uses a composite cantilever transducer structure of cantilever beam and polymer, and the cumulative length of optical fiber to increase the sensitivity, and the sensitivity reaches 1×10 -1 με·ms 2 / kg, achieving high sensitivity and anti-interference ability of the sensor.

[0015] (3) Existing ocean turbulence observations have distortions in quantitative reproduction when describing the three-dimensional ocean turbulence morphology. The fiber-optic through-cabin connector design facilitates the access of optical fibers. Multiple optical fiber two-dimensional vector ocean turbulence sensors can be connected in series through optical fibers to form an ocean turbulence sensing array, laying the foundation for the subsequent establishment of a multi-point combination of sensors for three-dimensional observation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1This is a schematic diagram of the structure of the optical fiber two-dimensional vector ocean turbulence sensor in this embodiment;

[0017] Figure 2 is a schematic structural diagram of an optical fiber vector sensor module in an embodiment of the present invention;

[0018] Figure 3 Schematic diagram of the structure of the energy conversion structure connection module in the embodiment of the present invention.

[0019] Among them: 1. Protective cover; 2. Fiber optic vector sensor module; 3. Transducer structure connection module; 4. Probe; 5. Fiber 1; 6. Fiber 2; 7. Fiber 3; 8. Fiber 4; 9. Polymer wrapping layer; 10. Metal cantilever; 11. Connecting rod; 12. Lock nut; 13. Cabin penetration joint. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0021] like Figure 1 The optical fiber two-dimensional vector ocean turbulence sensor based on the airfoil shear flow structure shown in the figure comprises a protective cover module, an optical fiber vector sensor module 2 and a transducer structure connection module 3. Figure 2 As shown, the optical fiber vector sensor module 2 includes optical fibers 1, 2, 3, 4, polymer coating 9 and a metal cantilever 10. The four sections of optical fiber are sequentially connected in series by optical fiber 1, optical fiber 2, optical fiber 3 and optical fiber 4, and are orthogonally distributed on the cross section of the composite cantilever beam. The polymer coating 9 is close to the metal cantilever 10 and is located in the middle and rear section of the metal cantilever 10. The optical fibers 1, 2, 3 and 4 are sandwiched in the polymer coating 9. Figure 3 As shown, the energy conversion structure connection module 3 includes a connecting rod 11, a lock nut 12 and a through-cabin joint 13. The through-cabin joint 13 is located between the connecting rod 11 and the metal cantilever 10, and the optical fiber is connected and connected through the through-cabin joint 13. The protective cover module includes a protective cover 1 and a probe 4. The bottom end of the metal cantilever 10 is connected through the connecting rod 11 and the lock nut 12 is used to clamp the cantilever structure as a whole and fix it in the protective cover 1.

[0022] Preferably, the metal cantilever 10 is used as the main transducer cantilever, and the annular polymer wrapping layer 9 is used as the auxiliary transducer arm, and the two are combined to form the composite cantilever; the composite cantilever beam is a columnar structure as a whole, and the front end is connected to the rubber head turbulence probe 4.

[0023] Preferably, the bottom end of the composite cantilever is connected via a connecting rod 11, and a lock nut 12 is tightly attached to the bottom end of the protective sleeve 1 and clamps the perimeter of the cantilever structure as a whole.

[0024] Preferably, the protective cover 1 has a streamlined appearance, and the probe is a wing-shaped rubber head probe 4 fixed to the top of the metal cantilever 10. The gap between the probe 4 and the protective cover 1 is small and can slide relative to each other.

[0025] Preferably, the connection and exit are performed through two through-cabin joints 13 provided between the connecting rod 11 and the composite cantilever.

[0026] Preferably, high-precision fiber optic two-dimensional vector shear flow sensing is achieved by reading the strain distribution on the four sections of optical fibers 1, 2, 3, and 4; the sensor is enhanced by using a composite cantilever transducer structure of the cantilever beam 10 and the polymer 9, the cumulative length of the optical fiber, etc.; a plurality of the fiber optic two-dimensional vector ocean turbulence sensors are connected in series through optical fibers to form an ocean turbulence sensing array, and turbulence information at different locations in the ocean is synchronously collected.

[0027] During transportation and entering the sea, a conical peripheral protection device made of water-soluble polyvinyl alcohol material is used to protect the sensitive unit of the turbulence probe 4. The turbulence sensor is lowered vertically into the sea and left to stand on the sea surface for ten minutes after entering the sea. After the peripheral protection cover is completely dissolved in the seawater, the instrument is submerged. The water flow impacts the sensor probe 4, and the probe 4 transmits the ocean turbulence signal to the optical fibers 1, 2, 3, and 4 through the composite cantilever transducer structure composed of the main transducer metal cantilever 10 and the auxiliary transducer cantilever beam polymer coating 9, and converts it into optical fiber strain. The optical fiber ocean turbulence sensor determines the direction and amplitude of the turbulence through the strain distribution pattern of the optical fibers 1, 2, 3, and 4, and realizes the two-dimensional vector measurement of the ocean turbulence. The method is:

[0028] A plane rectangular coordinate system is established with the center of the cross section of the composite cantilever beam as the origin of the coordinates. Optical fibers 1, 2, 3, and 4 are orthogonally distributed on the cross section. Optical fibers 1 and 2 are in the same horizontal direction, and the direction of optical fiber 2 is assumed to be the positive direction of the y-axis. Optical fibers 3 and 4 are in the same horizontal direction, and the direction of optical fiber 4 is assumed to be the positive direction of the x-axis. When the bottom of the sensor is acted on by the ocean turbulence in the +y direction, optical fiber 1 will be subjected to positive strain of "pulling", optical fiber 2 will be subjected to negative strain of "compression", and optical fibers 3 and 4 will be subjected to very small strains due to being located in the midline of the force section; when the bottom of the sensor is acted on by the ocean turbulence in the -y direction, on the contrary, optical fiber 1 will be subjected to negative strain of "compression", optical fiber 2 will be subjected to positive strain of "pulling", and optical fibers 3 and 4 will also be subjected to very small strains. Therefore, the sensor can use the strain distribution patterns of the four sections of optical fiber in the optical fiber to identify different directions. Similarly, the +x and -x directions can also be effectively identified, thus realizing the two-dimensional vector measurement of ocean turbulence.

[0029] According to the above scheme, the calculation method of the strain and shear flow rate of the optical fiber is:

[0030] When the optical fiber ocean turbulence sensor is working, it will be lowered vertically, and the water will flow along the surface of the sensor probe 4 at a speed U and form an angle of attack α with the vertical center axis of the sensor. The water flow velocity can be decomposed into lateral and longitudinal flow velocities, but only the lateral velocity u will cause strain in the optical fibers 1, 2, 3, and 4 on the composite cantilever. According to the principles of fluid mechanics and wing theory, in an inviscid fluid, the shear force f per unit length of the probe is:

[0031]

[0032] Where A is the cross-sectional area of ​​the sensor probe 4, dA / dx is the rate of change of the signal receiving area of ​​the sensor probe 4 on the axis, ρ is the water density, and α is the angle between the water flow velocity and the central axis. By integrating both sides of formula (1), the lateral shear force F on the entire sensor can be obtained:

[0033]

[0034] Where W is the relative velocity component between the sensor and the fluid along the longitudinal axis of the probe 4, u is the flow velocity perpendicular to the axis of the probe 4, and U is the sensor lowering speed.

[0035] The probe transmits the pulsating force of ocean turbulence to optical fibers 1, 2, 3, and 4 through the metal cantilever 10. The metal cantilever 10 has a thin and long columnar appearance and has a large Young's modulus, which can improve the sensor's ability to resist vibration fluctuations and has high stability, but at the same time limits the sensitivity of the sensor. In order to improve the sensitivity, a layer of low Young's modulus annular polymer wrapping layer 9 is used at the bottom of the metal cantilever 10 as a conversion intermediate layer between the metal cantilever 10 and the optical fibers 1, 2, 3, and 4 to form a composite cantilever transducer structure, which is conducive to efficiently transmitting weak pulsating force to the optical fiber and converting it into optical fiber strain to achieve strain sensitivity.

[0036] According to the knowledge of material mechanics, the axial strain ε of the "pulling" strain optical fiber on the composite cantilever beam is:

[0037]

[0038] In the above formula, x is the distance from a certain point on the cantilever beam to the bottom end, E is the Young's modulus of the material, b is the effective width of the composite cantilever, h is the effective thickness of the composite cantilever, and β is the effective magnification of the composite cantilever. If the length of the annular polymer 9 is L, then the total strain ε on the "pulling" strained optical fiber segment on the composite cantilever beam is s will be:

[0039]

[0040] Where C is the proportionality factor of the shear force to the total strain on the fiber segment.

[0041] The sensitivity S calculation formula of the optical fiber ocean turbulence sensor can be defined as:

[0042]

[0043] The calculation formula of shear velocity u can be derived from formula (5):

[0044]

[0045] The above embodiments are only used to illustrate the design ideas and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, any equivalent changes or modifications made based on the principles and design ideas disclosed by the present invention are within the protection scope of the present invention.

Claims

1. An optical fiber two-dimensional vector ocean turbulence sensor based on an airfoil shear flow structure, characterized in that: It includes an optical fiber vector sensor module, an energy conversion structure connection module and a protective cover module; the optical fiber vector sensor module includes four sections of optical fiber, a polymer wrapping layer and a metal cantilever; the energy conversion structure connection module includes a connecting rod, a locking nut and a cabin penetration joint; the protective cover module includes a protective cover and a probe.

2. The optical fiber vector sensor module according to claim 1, characterized in that: The four sections of optical fiber are orthogonally distributed on the cross section of the composite cantilever beam and are connected in series with each other. The four sections of optical fiber are thin-diameter anti-bending optical fibers.

3. The optical fiber vector sensor module according to claim 1, characterized in that: The bottom section of the metal cantilever uses a layer of annular polymer wrapping layer as a conversion intermediate layer between the metal cantilever and the optical fiber; the metal cantilever is used as the main transducer cantilever, and the layer of annular polymer wrapping layer is used as the auxiliary transducer arm, and the two are combined to form the composite cantilever; the composite cantilever beam is a columnar structure as a whole, and the front end is connected to a rubber-headed turbulence probe.

4. The energy conversion structure connection module according to claim 1, characterized in that: The bottom end of the composite cantilever is connected via a connecting rod, and the lock nut is tightly attached to the bottom end of the protective sleeve and clamps the perimeter of the cantilever structure as a whole.

5. The protective cover module according to claim 1, characterized in that: The protective cover has a streamlined appearance, and the probe is a wing-shaped rubber head probe fixed on the top of the metal cantilever. The gap between the probe and the protective cover is small and the probe and the protective cover can slide relative to each other.

6. The four-segment optical fiber according to claim 2, characterized in that: The connection and exit are carried out through two through-cabin joints arranged between the connecting rod and the composite cantilever.

7. The optical fiber two-dimensional vector ocean turbulence sensor according to claim 1, characterized in that: High-precision fiber optic two-dimensional vector shear flow sensing is achieved by reading the strain distribution on the four sections of optical fiber; the sensor is enhanced by using a composite cantilever transducer structure of cantilever beam and polymer, optical fiber cumulative length, etc.; a plurality of the fiber optic two-dimensional vector ocean turbulence sensors are connected in series through optical fibers to form an ocean turbulence sensing array, and turbulence information at different locations in the ocean is synchronously collected.

Images