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

Abstract

The present invention discloses an optical fiber two-dimensional vector ocean turbulence sensor based on an airfoil shear flow structure, which includes an optical fiber vector sensor module, a transducer structure connection module, and a protective sleeve module; the optical fiber vector sensor module is composed of four optical fibers that are connected in series and orthogonally distributed in the cross-section of the cantilever beam, a polymer wrapping layer, and a metal cantilever; the transducer structure connection module is composed of a connecting rod, a lock nut, and a through-hull joint; the protective sleeve module is composed of a protective sleeve and a probe, and the gap between the probe and the protective sleeve is sealed with glue. The beneficial effects of the present invention are as follows: high-precision optical fiber two-dimensional vector shear flow sensing is achieved by reading the strain distribution on the four optical fibers; the sensitivity is increased by using a composite cantilever transducer structure of a cantilever beam and a polymer, the cumulative length of the optical fiber, etc., and the sensitivity reaches 1×10-1 με·ms2 / kg; multiple optical fiber two-dimensional vector ocean turbulence sensors are connected in series through optical fibers to form an ocean turbulence sensing array to realize synchronous acquisition of multi-point ocean turbulence information.

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 process of turbulence signal transmission 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 to some extent solved the problems of single-point measurement and susceptibility to electromagnetic interference of electrical ocean turbulence sensors, the demodulation accuracy of traditional grating-type turbulence sensors is limited and the error is large, while 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 and achieve the breakthrough development of my country's new generation of ocean sensors, accurately establishing a vector turbulence signal sensing model has become a key scientific issue 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, characterized in that it includes an optical fiber vector sensor module, a transducer structure connection module and a protective cover module; the optical fiber vector sensor module includes four sections of optical fiber, a polymer sheath and a metal cantilever, the bottom section of the metal cantilever uses a layer of annular polymer sheath as a conversion intermediate layer between the metal cantilever and the optical fiber, the metal cantilever is used as a main transducer cantilever, and the polymer sheath is used as a secondary transducer arm, and the two are combined to form a composite cantilever, the four sections of optical fiber are orthogonally distributed on the cross section of the composite cantilever and are connected in series with each other, and under the condition of limited transverse size, strain sensitization is achieved by accumulating the optical fiber length in the longitudinal direction; the shear flow signal acts on the composite cantilever, and the composite cantilever transmits the signal to the four sections of optical fiber, and the two-dimensional vector high-precision measurement of ocean turbulence is achieved by measuring the strain of the optical fiber; the transducer structure connection module includes a connecting rod, a lock nut and a cabin penetration joint; the protective cover module includes a protective cover and a probe.

[0005] According to the above solution, the four sections of optical fiber are thin-diameter bend-resistant optical fibers.

[0006] According to the above solution, the composite cantilever is a columnar structure as a whole, and a rubber head turbulence probe is connected to the front end.

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

[0008] According to the above solution, the protective sleeve has a streamlined appearance, and the probe is an airfoil rubber head probe, which is fixed to the top of the metal cantilever.

[0009] According to the above solution, access is achieved through two through-hull joints provided between the connecting rod and the composite cantilever.

[0010] According to the above solution, multiple of the fiber optic two-dimensional vector ocean turbulence sensors are connected in series by optical fibers to form an ocean turbulence sensing array, so as to realize the synchronous acquisition of multi-point ocean turbulence information.

[0011] In the above solution, the material of the protective sleeve 1 is 316 stainless steel, which has good corrosion resistance. The connection gap between the rubber head turbulence probe 4 and the protective sleeve 1 is sealed with a pressure-resistant potting adhesive using a specific mold to ensure the overall pressure resistance and watertightness of the sensor. At the same time, the probe 4 is protected by adopting the design method of an outer protective cover. The outer protective cover is made of water-soluble polyvinyl alcohol material, and it is folded into a cone and pasted on the front side of the sensor. After the turbulence sensor enters the sea and is placed statically on the sea surface, wait until the outer protective cover is completely dissolved in seawater, and then dive.

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

[0013] (1) Currently, both at home and abroad, the one-dimensional scalar sensing is mainly used in the process of transmitting turbulence signals, lacking the ability to observe the anisotropic characteristics of turbulence in key areas such as the boundary layer. Based on the two-dimensional vector shear flow sensing principle of the low-loss optical fiber "orthogonal series" optical path, the present invention simultaneously realizes the measurement of the horizontal and vertical velocity pulsations of ocean turbulence signals.

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

[0015] (3) The existing ocean turbulence observations have distortion in the quantitative reproduction when describing the three-dimensional ocean turbulence morphology. The design of the optical fiber through-hull joint facilitates the access and exit of the optical fiber. Multiple fiber optic two-dimensional vector ocean turbulence sensors can be connected in series by optical fibers to form an ocean turbulence sensing array, laying a foundation for the subsequent establishment of a multi-point combined three-dimensional observation model of the sensors. Description of the Drawings

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

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

[0018] Figure 3 This is a schematic structural diagram of the transducer structure connection module in an embodiment of the present invention.

[0019] Wherein: 1. Protective sleeve; 2. Fiber optic vector sensor module; 3. Transducer structure connection module; 4. Probe; 5. Optical fiber 1; 6. Optical fiber 2; 7. Optical fiber 3; 8. Optical fiber 4; 9. Polymer wrapping layer; 10. Metal cantilever; 11. Connecting rod; 12. Lock nut; 13. Feedthrough joint. Specific implementation manners

[0020] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to 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] As Figure 1 shown, a fiber optic two-dimensional vector ocean turbulence sensor based on an airfoil shear flow structure includes a protective sleeve module, a fiber optic vector sensor module 2 and a transducer structure connection module 3. As Figure 2 shown, the fiber optic vector sensor module 2 includes optical fibers 1, 2, 3, 4, a polymer wrapping layer 9 and a metal cantilever 10. The four optical fibers 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. The polymer wrapping layer 9 is closely attached 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 wrapping layer 9. As Figure 3 shown, the transducer structure connection module 3 includes a connecting rod 11, a lock nut 12 and a feedthrough joint 13. The feedthrough joint 13 is located between the connecting rod 11 and the metal cantilever 10, and the optical fiber is connected in and out through the feedthrough joint 13. The protective sleeve module includes a protective sleeve 1 and a probe 4. The bottom end of the metal cantilever 10 is connected by the connecting rod 11 and the overall perimeter of the cantilever structure is clamped and fixed in the protective sleeve 1 by using the lock nut 12.

[0022] Preferably, the metal cantilever 10 serves as the main transducer cantilever, and the layer-shaped polymer wrapping layer 9 serves as the secondary transducer arm. The two are combined to form the composite cantilever; the overall composite cantilever is a columnar structure, and the front end is connected to the rubber head turbulence probe 4.

[0023] Preferably, the bottom ends of the composite cantilevers are connected by a connecting rod 11, and a lock nut 12 is closely attached to the bottom end of the protective sleeve 1 to clamp the entire perimeter of the cantilever structure.

[0024] Preferably, the protective sleeve 1 has a streamlined appearance, and the probe is an airfoil rubber head probe 4 fixed to the top end of the metal cantilever 10. The gap between the probe 4 and the protective sleeve 1 is small, and it is designed as a relative sliding structure.

[0025] Preferably, access is achieved through two through-hull 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 optical fibers 1, 2, 3, and 4; the sensitivity of the sensor is enhanced by using a composite cantilever transducer structure of the metal cantilever 10 and the polymer 9, the cumulative length of the optical fiber, etc.; the multiple fiber optic two-dimensional vector ocean turbulence sensors can be connected in series through optical fibers to form an ocean turbulence sensing array for synchronous acquisition of turbulence information at different positions in the ocean.

[0027] During transportation and the process of 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 vertically lowered into the sea. After entering the sea, it is left stationary on the sea surface for ten minutes. After the peripheral protective cover is completely dissolved in the sea water, the instrument is then lowered. 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 a composite cantilever transducer structure composed of the main transducer metal cantilever 10 and the secondary transducer cantilever polymer coating 9, converting it into optical fiber strain. The fiber optic ocean turbulence sensor determines the direction and amplitude of the turbulence through the strain distribution patterns of the four optical fibers 1, 2, 3, and 4 in the optical fiber, realizing two-dimensional vector measurement of ocean turbulence. The method is as follows:

[0028] Taking the center of the cross-section of the composite cantilever as the origin of the coordinate system to establish a plane rectangular coordinate system, the optical fibers 1, 2, 3, and 4 are orthogonally distributed on the cross-section. The optical fibers 1 and 2 are in the same horizontal direction. Let the direction of the optical fiber 2 be the positive y-axis direction, and the optical fibers 3 and 4 are in the same horizontal direction. Let the direction of the optical fiber 4 be the positive x-axis direction. When the bottom of the sensor is subjected to the action of ocean turbulence in the +y direction, the optical fiber 1 will be subjected to a positive strain of "tension", the optical fiber 2 will be subjected to a negative strain of "compression", while the optical fibers 3 and 4 have very small strains because they are in the midline of the force section; when the bottom of the sensor is subjected to the action of ocean turbulence in the -y direction, conversely, the optical fiber 1 will be subjected to a negative strain of "compression", the optical fiber 2 will be subjected to a positive strain of "tension", and the optical fibers 3 and 4 are also subjected to very small strains. Therefore, the sensor can use the strain distribution patterns of the four optical fibers in the optical fiber to identify different directions. Similarly, the +x and -x directions can also be effectively identified, thus realizing two-dimensional vector measurement of ocean turbulence.

[0029] According to the above scheme, the calculation methods for the strain of the optical fiber and the shear flow velocity are as follows:

[0030] When the fiber optic ocean turbulence sensor works, it will be vertically lowered. The water flow flows along the surface of the sensor probe 4 at a velocity U and forms an angle of attack α with the vertical central axis of the sensor. The water flow velocity can be decomposed into transverse and longitudinal flow velocity components, but only the transverse 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 on 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 density of the water body, α is the angle between the water flow velocity and the central axis. Integrating both sides of formula (1) respectively, the overall transverse shear force F on the sensor can be obtained:

[0033]

[0034] In the formula, 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 lowering velocity of the sensor.

[0035] The probe transfers the pulsating force of ocean turbulence to the optical fibers 1, 2, 3, and 4 through the metal cantilever 10. The metal cantilever 10 has a slender columnar appearance and has a large Young's modulus, which can improve the anti-vibration and fluctuation resistance ability of the sensor and has high stability, but at the same time limits the sensitivity of the sensor. To improve the sensitivity, a layer of low Young's modulus annular polymer wrapping layer 9 is used at the bottom section of the metal cantilever 10 as a conversion intermediate layer between the metal cantilever 10 and the optical fibers 1, 2, 3, and 4, forming a composite cantilever transducer structure, which is conducive to efficiently transferring the weak pulsating force to the optical fiber and converting it into optical fiber strain to achieve strain sensitization.

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

[0037]

[0038] In the above formula, x is the distance of a certain point on the cantilever from 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 factor of the composite cantilever. The length of the annular polymer 9 is L, then the overall strain ε on the "tensile" strain optical fiber section of the composite cantilever s will be:

[0039]

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

[0041] The sensitivity S of the fiber optic ocean turbulence sensor can be calculated by the formula:

[0042]

[0043] From formula (5), the calculation formula of the shear flow velocity u can be derived:

[0044]

[0045] The above embodiments are only used to illustrate the design concept and characteristics of the present invention, and the 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, all equivalent changes or modifications made according to the principles and design concepts disclosed by the present invention are within the protection scope of the present invention.

Claims

1. A two-dimensional vector ocean turbulence sensor for optical fiber based on airfoil shear flow structure, characterized in that It includes an optical fiber vector sensor module, a transducer structure connection module, and a protective sleeve module; the optical fiber vector sensor module includes four optical fibers, a polymer wrapping layer, and a metal cantilever. A ring-shaped polymer wrapping layer is used as a conversion intermediate layer between the metal cantilever and the optical fiber at the bottom section of the metal cantilever. The metal cantilever serves as the main transducer cantilever, and the polymer wrapping layer serves as the secondary transducer arm. The two combine to form a composite cantilever. The four optical fibers are orthogonally distributed and connected in series on the cross-section of the composite cantilever. Under the condition of limited lateral dimensions, strain sensitization is achieved by accumulating the optical fiber length longitudinally. The shear flow signal acts on the composite cantilever, and the composite cantilever transmits the signal to the four optical fibers. High-precision two-dimensional vector measurement of ocean turbulence is achieved by measuring the strain of the optical fiber; the transducer structure connection module includes a connecting rod, a lock nut, and a through-hull joint; the protective sleeve module includes a protective sleeve and a probe.

2. The two-dimensional vector ocean turbulence optical fiber sensor according to claim 1, characterized in that The four optical fibers adopt thin-diameter bend-resistant optical fibers.

3. The two-dimensional vector optical fiber ocean turbulence sensor according to claim 1, characterized in that, The composite cantilever is a columnar structure as a whole, and the front end is connected to a rubber head turbulence probe.

4. The two-dimensional vector optical fiber ocean turbulence sensor according to claim 1, characterized in that The bottom end of the composite cantilever is connected by a connecting rod, and the lock nut is closely attached to the bottom end of the protective sleeve and clamps the entire perimeter of the cantilever structure.

5. The two-dimensional vector optical fiber ocean turbulence sensor according to claim 1, wherein The protective sleeve has a streamlined appearance, and the probe is a wing-shaped rubber head probe, fixed at the top of the metal cantilever, and the probe can slide between the protective sleeve.

6. The two-dimensional vector ocean turbulence optical fiber sensor according to claim 1, characterized in that, It is accessed in and out through two through-hull joints provided between the connecting rod and the composite cantilever.

7. The two-dimensional vector ocean turbulence optical fiber sensor according to claim 1, characterized in that, High-precision two-dimensional vector shear flow sensing of optical fibers is achieved by reading the strain distribution on the four optical fibers; a composite cantilever transducer structure of a metal cantilever and a polymer and the method of accumulating the optical fiber length are used to sensitize the sensor; multiple optical fiber two-dimensional vector ocean turbulence sensors are connected in series by optical fibers to form an ocean turbulence sensing array to achieve synchronous acquisition of multi-point ocean turbulence information.

Images