CN113267642A - Method and system for monitoring whole-sea deep sea current distribution - Google Patents
Method and system for monitoring whole-sea deep sea current distribution Download PDFInfo
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- CN113267642A CN113267642A CN202110572210.8A CN202110572210A CN113267642A CN 113267642 A CN113267642 A CN 113267642A CN 202110572210 A CN202110572210 A CN 202110572210A CN 113267642 A CN113267642 A CN 113267642A
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Abstract
The invention discloses a method and a system for monitoring the distribution of full-sea deep ocean currents, wherein the method comprises the following steps: detecting the vibration frequency of the sensing optical cable unit at the current seawater depth; calculating the current flow velocity of the sensing optical cable unit at the seawater depth according to the obtained vibration frequency and the optical cable diameter of the sensing optical cable unit; and generating ocean current distribution according to the ocean current flow rate and the depth of the seawater where the sensing optical cable unit is located. By applying the invention, the ocean current velocity distribution can be monitored in real time in the full sea depth range.
Description
Technical Field
The invention relates to the technical field of ocean current monitoring, in particular to a method and a system for monitoring distribution of full-sea deep ocean current.
Background
Ocean currents refer to the large-scale relatively steady flow of seawater, and are one of the common forms of movement of seawater. Since ocean currents play a crucial role in the global climate stability and ecological balance, and have a great influence on the life, production and ocean development and utilization of coastal people, ocean current measurement technology has been one of the focuses of attention in the ocean industry.
The existing ocean current measuring technology comprises methods such as a floating method, a mechanical method, an electromagnetic induction method, an acoustic method, radar remote sensing and the like. However, how to monitor the ocean current velocity distribution in real time in the whole sea depth range still remains to be solved.
Disclosure of Invention
The invention provides a method and a system for monitoring the distribution of full-sea deep ocean currents, which are used for overcoming at least one technical problem in the prior art.
According to a first aspect of the embodiments of the present invention, there is provided a method for monitoring the distribution of a full-sea deep ocean current, including: detecting the vibration frequency of a sensing optical cable unit at the current seawater depth, and calculating the current flow velocity of the sensing optical cable unit at the seawater depth according to the obtained vibration frequency and the optical cable diameter of the sensing optical cable unit; and generating ocean current distribution according to the ocean current flow rate and the depth of the seawater where the sensing optical cable unit is located.
Optionally, the step of calculating the current flow rate at the sea depth where the sensing optical cable unit is located according to the obtained vibration frequency and the optical cable diameter of the sensing optical cable unit includes: according to the vibration frequency fsCalculating the ocean current flow velocity V at the sea water depth of the sensing optical cable unit based on a preset ocean current calculation model, wherein the Strouhal number s depends on the properties of the sea water, and the ocean current calculation model comprises the vibration frequency fsAnd the ocean current flow velocity V.
Optionally, the ocean current calculation model includes:
wherein V is the flow velocity of the sea current at the sea water depth where the sensing optical cable unit is located; d is the cable diameter of the sensing cable unit; f. ofsThe vibration frequency of the sea water depth where the sensing optical cable unit is located is the vibration frequency; a is a calibration coefficient.
Optionally, the sensing optical cable unit consists of a sensing optical cable with a first unit length and a cable with a second unit length; the sensing optical cable and the cable are respectively divided into a plurality of sensing optical cables with first unit length and a plurality of cables with second unit length at equal intervals; the step of generating the ocean current distribution according to the ocean current flow rate and the depth of the seawater where the sensing optical cable unit is located comprises the following steps: determining the seawater depth of each sensing optical cable unit according to the position of each sensing optical cable unit on the sensing optical cable; and calculating the ocean current distribution in the full sea depth range according to the ocean current flow velocity at the sea depth of each sensing optical cable unit and the sea depth of each sensing optical cable unit.
Optionally, after the step of detecting the vibration frequency of the sensing optical cable unit at the current seawater depth, the method further includes: and acquiring the vibration frequency detected by each sensing optical cable unit by adopting a phase-sensitive Optical Time Domain Reflection (OTDR) technology.
According to a second aspect of embodiments of the present invention, there is provided a system for monitoring the distribution of whole-sea deep ocean currents, comprising: the device comprises a sensing optical cable unit and an optical fiber sensing demodulation unit; the sensing optical cable unit is used for detecting the vibration frequency of the sensing optical cable unit at the current seawater depth; the optical fiber sensing demodulation unit is used for acquiring the vibration frequency detected by the sensing optical cable unit; calculating the current flow velocity of the sea water depth position of the sensing optical cable unit according to the vibration frequency and the optical cable diameter of the sensing optical cable unit; and generating ocean current distribution according to the ocean current flow rate and the depth of the seawater where the sensing optical cable unit is located.
Optionally, the optical fiber sensing demodulation unit is connected to an optical fiber in the sensing optical cable, where the sensing optical cable is a multi-core optical cable, and the optical fiber is a single-mode optical fiber or a single-mode optical fiber with a built-in microstructure.
Optionally, a flexible flag is disposed on the sensing optical cable unit.
Optionally, the monitoring system further includes: a cable; the cable is rigidly connected with the sensing optical cable.
Optionally, the monitoring system further includes: a cable winding disc and an anchor body; the upper end of the cable is connected with the cable winding disc, and the lower end of the cable is connected with the anchor body; the cable winding disc and the optical fiber sensing demodulation unit are arranged on a mother ship or an offshore platform.
The innovation points of the embodiment of the invention comprise:
1. compared with the prior art, the detection method and the device provided by the invention have simple structure, do not need separate power supply and communication under water and are easy to implement. Is one of the innovative points of the embodiment of the invention.
2. The method and the system for monitoring the distribution of the ocean currents in the whole sea depth can utilize the long-distance monitoring advantage of the distributed sensing technology, not only can realize the monitoring of the distribution of the ocean currents in the whole sea depth, but also can perform real-time online long-time monitoring. Is one of the innovative points of the embodiment of the invention.
3. In the method and the system for monitoring the whole-sea deep-sea current distribution, the sensing optical cable can adopt a multi-core optical cable, so that the optical fiber sensing demodulation unit can simultaneously monitor the vibration frequency detected by a plurality of sensing optical cable units. Is one of the innovative points of the embodiment of the invention.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic process flow diagram of a method for monitoring the distribution of whole-sea ocean currents in accordance with the present invention;
FIG. 2 is a schematic structural diagram of a sensing cable unit according to the present invention;
FIG. 3 is a schematic diagram of a karman swirl phenomenon;
FIG. 4 is a block diagram of a monitoring system according to the present invention;
FIG. 5 is a schematic view of still another structure of the sensing cable unit according to the present invention;
FIG. 6 is a schematic diagram illustrating the sub-steps of step 104 in the present invention;
FIG. 7 is a schematic cable cross-sectional view of a sensing cable;
fig. 8 is a schematic structural view of a system for monitoring the distribution of ocean currents in the whole sea according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
It is to be noted that the terms "comprises" and "comprising" and any variations thereof in the embodiments and drawings of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, and apparatus, product, or device that comprises a list of steps or elements is not limited to the listed steps or elements, but may alternatively include other steps or elements not expressly listed or inherent to such process, method, product, or device.
The invention provides a method for monitoring the distribution of ocean current in the whole sea depth, which can monitor the distribution of ocean current velocity in real time in the whole sea depth range. Referring to fig. 1, fig. 1 is a process flow diagram of the method for monitoring the distribution of whole-sea deep ocean current in the present invention. As shown in fig. 1, the processing flow of the monitoring method for the whole-sea deep-sea current distribution is as follows:
step 101, detecting the vibration frequency of the sensing optical cable unit at the current seawater depth.
In this step, the sensing optical cable unit arranged in the sea can detect the vibration frequency of the sensing optical cable unit caused by the water flow vortex in the current seawater depth. Note that the detected vibration frequency is equal to the vortex shedding frequency of the water flow vortex.
Referring to fig. 2, fig. 2 is a schematic structural diagram of a sensing cable unit according to the present invention. As shown in fig. 2, the sensing optical cable unit is formed by fixing two ends of the first unit length of the sensing optical cable and two ends of the second unit length of the cable together, wherein the first unit length is lfThe second unit length is lc(ii) a The first unit length lfIs greater than the second unit length lc. The specific fixing points of the sensing optical cable with the first unit length and the cable with the second unit length are A and B; first unit length l of sensing cable 1fIs greater than the second unit length l of the cable 2c. Thus, the sensing optical cable 1 can vibrate with the ocean current.
In the specific implementation, when the ocean current acts on the sensing optical cable 1 under the condition that the points A and B are fixed, water current vortex is formed behind the sensing optical cable 1, and the phenomenon is called Karman vortex phenomenon. Referring to fig. 3, fig. 3 is a schematic view of a karman vortex phenomenon. Because the karman vortex is alternately generated up and down and is continuously separated from the optical cable to gradually disappear, up and down alternate force can be formed on the sensing optical cable, and vibration is generated on the sensing optical cable, so that the sensing optical cable unit can detect the vibration frequency of the karman vortex in the current seawater depth and the vibration generated by the karman vortex.
The sensing optical cable unit consists of a sensing optical cable with a first unit length and a cable with a second unit length; the sensing optical cable and the cable are respectively divided into a plurality of sensing optical cables with a first unit length and a plurality of cables with a second unit length at equal intervals.
In practical application, the cable and the sensing optical cable are both placed in the sea water vertical to the seabed, and the cable and the sensing optical cable are parallel to each other. The cable and the sensing optical cable are fixed in a point mode at preset distance and equal intervals.
As shown in fig. 4 and 5, fig. 4 is a block diagram of the monitoring system of the present invention, in fig. 5, points a and B are fixed points, and in fig. 4, black solid points 11 are fixed points, and the cable and the sensing cable are divided into a sensing cable unit a, a sensing cable unit B and a sensing cable unit C.
The upper end of the mooring rope is connected with the cable winding disc, and the lower end of the mooring rope is connected with the anchor body. The cable is tensioned by the anchor body through tension, the anchor body is fixed on the sea bottom to keep the cable tensioned, and the sensing optical cable vibrates along with the flowing of seawater in a free state.
It will be appreciated that the cable acts to withstand the anchoring forces and the sensing cable acts to vibrate when excited by ocean current pressure. The sensing optical cable is relatively flexible in structural design and can move along with ocean currents.
Optionally, the total length L of the cable is determined according to the sea depth of the sea area to be measuredc(ii) a According to the total length L of the cablecDetermining the total length L of the sensing optical cable based on a preset length calculation model of the sensing optical cablefWherein the length calculation model comprises the total length L of the cablecTotal length L of sensing optical cablefThe second unit length l of the cable corresponding to the sensing optical cable unitcFirst unit length l of sensing cable corresponding to sensing cable unitfThe corresponding relation between them.
The total length of the sensing optical cable is longer than that of the cable, and the lengths of the sensing optical cable and the cable can reach dozens of kilometers. The cable and sensing cable form a series of sensing units.
Specifically, the length calculation model is as follows:
wherein L iscThe total length of the cable; l isfIs the total length of the sensing cable; lcSecond unit length of cable corresponding to sensing optical cable unitDegree; lfThe first unit length, l, of the sensing cable corresponding to the sensing cable unitfGreater than lc。
As can be appreciated, the total length L of the sensing cablefTotal length L of cablecTo the second unit length lfAnd a first unit length lcAre equal in proportion.
In specific implementation, a fluid-solid coupling theory can be adopted to carry out simulation experiment on the motion of the sensing cable unit under the action of seawater power, and the length l of the second unit corresponding to the sensing cable unit suitable for the measurement range of the ocean current flow velocity is preferably selectedcAnd a first unit length lfMeanwhile, the total length L of the mooring rope is determined according to the sea water depth of the sea area to be measuredc. Further, according to the three known parameters lc、lfAnd LcAnd calculating the total length of the sensing optical cable based on the formula (1).
Therefore, the sensing optical cable units on the sensing optical cable are distributed at various depths of the seawater to form a series of sensing optical cable units, and the vibration frequency measured by the sensing optical cable units can be used for obtaining vortex separation frequencies of water flow vortexes at different seawater depth positions, so that the distributed continuous monitoring of the flow velocity of the seawater at different seawater depths can be realized.
It should be noted that the fixation between the cable and the sensing optical cable is rigid connection, and the relative position will not slide after fixation, and may be riveting, welding or other fixation methods.
In one implementation, the sensing cable and the cable can be fixed point by point in the manner shown in fig. 5, and fig. 5 is a schematic view of another structure of the sensing cable unit according to the present invention. In order to enhance the sensitivity of the sensing optical cable to eddy currents, as shown in fig. 5, 2 is a cable and 1 is a sensing optical cable, and a flexible flag 13 may be installed on each sensing optical cable unit obtained after the cable 2 and the sensing optical cable 1 are equally spaced, so that the underwater flag 13 may more easily float with the ocean current, thereby driving the sensing optical cable to vibrate and improving the sensitivity of the sensing optical cable unit in detecting the vibration frequency.
Referring to fig. 2, the karman vortices are alternately generated up and down on the sensing cable unit and gradually disappear as they are continuously separated from the sensing cable unit, thereby forming an alternate up and down force on the cable. The relationship between the alternating force frequency and the optical cable diameter and the ocean current flow rate of the sensing optical cable unit is as follows:
in the formula (2), fsThe vortex shedding frequency of the water flow vortex is in Hz; v is the flow velocity of the ocean current in m/s; d is the diameter of the optical cable of the sensing optical cable unit, and the unit is mm; s is the Setho number depending on the nature of the sea water.
Thus, the sensing optical cable unit can measure the vibration frequency, and the detected vibration frequency is used as the vortex shedding frequency fsAnd then calculating the current velocity.
As shown in fig. 4, one end of the cable 2 is connected with the cable winding disc 3, the other end of the cable 2 is tensioned by the anchor body 6, and the sensing optical cable 1 vibrates along with the flowing of seawater in a free state; the sensing optical cable 1 is connected to the optical fiber sensing demodulation unit 4 at the upper end through an optical fiber. In use, the cable 2 is tensioned in a relatively static state, and the sensing optical cable 1 is based on the cable 2 as a fixed base, and at different sea depth positions, the sensing optical cable units are respectively subjected to different sea water flow rates, so that different vibration frequencies are detected.
The cable winding disc and the optical fiber sensing demodulation unit are arranged on a mother ship or an offshore platform, and the optical fiber sensing demodulation unit is connected with optical fibers in the sensing optical cable to monitor the vibration condition of the sensing optical cable.
And 102, acquiring the vibration frequency detected by the sensing optical cable unit.
Step 103, calculating the current flow velocity of the sea water depth position of the sensing optical cable unit according to the obtained vibration frequency and the preset optical cable diameter of the sensing optical cable unit.
The optical fiber sensing demodulation unit is connected with the upper section of the optical fiber in the sensing optical cable.
In this step, first, the optical fiber sensing demodulation unit may obtain the vibration frequency detected by the sensing optical cable unit, and it can be understood that the vibration frequency is equal to the vortex separation frequency of the seawater depth where the sensing optical cable unit is located; then, the optical fiber sensing demodulation unit can calculate the ocean current flow velocity at the seawater depth position of the sensing optical cable unit according to the vibration frequency acquired from the sensing optical cable unit, namely the vortex separation frequency of the seawater depth position of the sensing optical cable unit, and the optical cable diameter of the sensing optical cable unit acquired in advance.
Optionally, after step 101, the method further includes: the Optical fiber sensing demodulation unit acquires the vibration frequency detected by each sensing Optical cable unit by adopting a phase-sensitive Optical Time-Domain Reflectometer (OTDR) technology.
It should be noted that the optical fiber sensing demodulation unit may perform demodulation processing according to different optical fiber types by using different technologies, so as to obtain a vibration spectrum of the sensing optical cable unit.
Specifically, if the optical fiber type is a common single-mode optical fiber, the optical fiber sensing demodulation unit may adopt an optical fiber brillouin distributed sensing technology; if the type of the optical fiber is the optical fiber engraved with the optical fiber grating microstructures with different wavelengths, the optical fiber sensing demodulation unit can adopt a wavelength division multiplexing demodulation technology; if the type of the optical fiber is the optical fiber engraved with the identical weak fiber grating microstructure, the optical fiber sensing demodulation unit can adopt wavelength scanning and time domain analysis technology for demodulation; if the fiber type includes other microstructures, the fiber sensing demodulation unit may employ corresponding demodulation techniques.
Optionally, step 103 may include:
according to the vibration frequency fsCalculating the ocean current flow velocity V at the sea water depth of the sensing optical cable unit based on a preset ocean current calculation model, wherein the Strouhal number s depends on the properties of the sea water, and the ocean current calculation model comprises the vibration frequency fsAnd the ocean current flow velocity V.
Specifically, based on formula (1), the fluid-solid coupling theory is combinedCarrying out simulation calculation, establishing a laboratory condition, recording the vibration frequency of the sensing optical cable unit under different flow rates through different flow rate simulation tests, and establishing an ocean current calculation model capable of embodying the mathematical relationship between the vibration frequency and the ocean current flow rate, so that based on the ocean current calculation model, the vortex separation frequency, namely the vibration frequency f is knownsAnd under the condition of the optical cable diameter d of the sensing optical cable unit, calculating the current flow speed at the seawater depth position of the sensing optical cable unit.
Optionally, the ocean current calculation model includes:
in formula (3), V is the flow velocity of the sea current at the sea depth where the sensing optical cable unit is located; d is the cable diameter of the sensing cable unit; f. ofsThe vibration frequency of the sea water depth position where the sensing optical cable unit is located, namely vortex separation frequency; a is a calibration coefficient.
The calibration coefficient a may be determined by multiple simulation experiments. For example, a water pool which can simulate ocean current is built in a laboratory, and the measurement of the system is calibrated by comparing with other flow sensors. Or, in the case of conditional conditions, by simultaneously measuring with the system of the invention and with other flow sensors in a marine environment, and comparing the two measurements.
And 103, generating ocean current distribution according to the ocean current flow rate and the depth of the seawater where the sensing optical cable unit is located.
In this step, the optical fiber sensing demodulation unit may generate the ocean current distribution of the measured sea area according to the calculated ocean current flow rate at the sea depth where the sensing optical cable unit is located and the sea depth where the sensing optical cable unit is located.
Optionally, referring to fig. 6, fig. 6 is a schematic view of the sub-step processing of step 104 in the present invention. As shown in fig. 6, step 104 may include the following sub-steps:
substep 61, determining the seawater depth of each sensing optical cable unit according to the position of each sensing optical cable unit on the sensing optical cable;
and a substep 62 of calculating the ocean current distribution in the full sea depth range according to the ocean current flow velocity at the sea depth of each sensing optical cable unit and the sea depth of each sensing optical cable unit.
Specifically, according to the ocean current flow velocity at the sea depth position of each sensing optical cable unit and the sea depth of each sensing optical cable unit, the ocean current flow velocities at different sea depths within the full sea depth range can be obtained, and therefore the ocean current distribution at the full sea depth position can be obtained.
In one implementation, since the sensing optical cable is not under tension, the sensing optical cable may adopt an optical unit structure in the submarine communication optical cable, and a multi-core optical cable may be selected, so that the optical fiber sensing demodulation unit can simultaneously monitor the vibration frequency detected by the plurality of sensing optical cable units.
The optical fiber in the sensing optical cable can be a common communication single-mode optical fiber or a single-mode optical fiber with a built-in microstructure. The microstructure can be an all-same weak fiber grating or a grating with different reflection wavelengths, or other special structures capable of monitoring vibration.
Referring to fig. 7, fig. 7 is a cable cross-sectional view of a sensing cable. In fig. 7, the single-mode fiber is 7, the water-blocking fiber paste is 8, the loose tube is 9, the water-blocking material is 10, the plastic-coated steel strip is 11, and the polyethylene sheath is 12. Wherein the optical fiber 7 in the sensing cable is left with a certain excess length in order to protect the optical fiber from tension. The water-blocking ointment 8 prevents water and moisture from penetrating into the loose tube 9, while avoiding radial stress on the optical fiber.
Because the invention utilizes the vibration signal of the optical fiber, the water-blocking ointment has the function of vibration transmission and can protect the optical fiber from strain. In addition, in order to maintain the flexibility of the sensing optical cable, the sensing optical cable does not adopt a stainless steel tube structure.
Therefore, the method for monitoring the distribution of the sea current in the whole sea depth can realize the real-time monitoring of the sea current distribution in the whole sea depth range according to the vortex effect caused by the fluid in the fluid-solid coupling process and the long-distance monitoring advantage of the distributed sensing technology; the sensing optical cable for detecting the vibration frequency caused by the vortex effect can adopt a multi-core optical cable, so that the optical fiber sensing demodulation unit can simultaneously monitor the vibration frequency detected by the plurality of sensing optical cable units. Compared with the prior art, the detection method and the device provided by the invention have the advantages of simple structure, no need of independent power supply and communication under water, easiness in implementation, long monitoring distance, capability of realizing ocean current distribution monitoring in the whole sea depth and real-time online long-time monitoring.
The invention also provides a system for monitoring the distribution of the ocean current in the whole sea, which can monitor the distribution of the ocean current in real time in the whole sea depth range. Referring to fig. 8, fig. 8 is a schematic structural view of a system for monitoring the distribution of the whole-sea deep ocean currents in the present invention. As shown in fig. 8, the monitoring system for the whole-sea deep-sea current distribution includes a sensing cable unit 801 and an optical fiber sensing demodulation unit 802:
and the sensing optical cable unit 801 is used for detecting the vibration frequency of the sensing optical cable unit at the current seawater depth.
The sensing optical cable unit comprises a cable and a sensing optical cable with a certain length, two points at two ends of the cable and the sensing optical cable are fixed together, and the length of the sensing optical cable in the sensing optical cable unit is longer than that of the cable in the sensing optical cable unit. The total length of the sensing optical cable is longer than that of the cable, and the lengths of the sensing optical cable and the cable can reach dozens of kilometers. The cable and sensing cable form a series of sensing units.
It should be noted that the fixation between the cable and the sensing optical cable is rigid connection, and the relative position will not slide after fixation, and may be riveting, welding or other fixation methods.
And an optical fiber sensing and demodulating unit 802, configured to acquire the vibration frequency detected by the sensing optical cable unit.
The optical fiber sensing demodulation unit is connected with the upper section of the optical fiber in the sensing optical cable.
Specifically, the optical fiber sensing demodulation unit can acquire the vibration frequency detected by the sensing optical cable unit, and it can be understood that the vibration frequency is equal to the vortex separation frequency of the seawater depth where the sensing optical cable unit is located.
Optionally, the Optical fiber sensing demodulation unit obtains the vibration frequency detected by each sensing Optical cable unit by using a phase-sensitive Optical Time-Domain Reflectometer (OTDR) technology.
It should be noted that the optical fiber sensing demodulation unit may perform demodulation processing according to different optical fiber types by using different technologies, so as to obtain a vibration spectrum of the sensing optical cable unit.
Specifically, if the optical fiber type is a common single-mode optical fiber, the optical fiber sensing demodulation unit may adopt an optical fiber brillouin distributed sensing technology; if the type of the optical fiber is the optical fiber engraved with the optical fiber grating microstructures with different wavelengths, the optical fiber sensing demodulation unit can adopt a wavelength division multiplexing demodulation technology; if the type of the optical fiber is the optical fiber engraved with the identical weak fiber grating microstructure, the optical fiber sensing demodulation unit can adopt wavelength scanning and time domain analysis technology for demodulation; if the fiber type includes other microstructures, the fiber sensing demodulation unit may employ corresponding demodulation techniques.
And the optical fiber sensing and demodulating unit 802 is configured to calculate an ocean current flow rate at the sea depth where the sensing optical cable unit is located according to the vibration frequency and a preset optical cable diameter of the sensing optical cable unit.
Specifically, the optical fiber sensing demodulation unit 802 may calculate the ocean current flow rate at the seawater depth position of the sensing optical cable unit according to the vibration frequency acquired from the sensing optical cable unit, that is, the vortex shedding frequency of the seawater depth position of the sensing optical cable unit, and the optical cable diameter of the sensing optical cable unit acquired in advance.
Optionally, the optical fiber sensing demodulation unit 802 is specifically configured to perform demodulation according to the vibration frequency fsCalculating the ocean current flow velocity V at the sea water depth of the sensing optical cable unit based on a preset ocean current calculation model, wherein the Strouhal number s depends on the properties of the sea water, and the ocean current calculation model comprises the vibration frequency fsAnd the ocean current flow velocity V.
And the optical fiber sensing demodulation unit 802 is configured to generate ocean current distribution according to the ocean current flow rate and the depth of the seawater where the sensing optical cable unit is located.
Specifically, the optical fiber sensing demodulation unit 802 may generate the ocean current distribution of the measured sea area according to the calculated ocean current flow rate at the sea depth of the sensing optical cable unit and the sea depth of the sensing optical cable unit.
Optionally, the optical fiber sensing demodulation unit 802 is specifically configured to determine the depth of the seawater in which each sensing optical cable unit is located according to the position of each sensing optical cable unit on the sensing optical cable; according to the flow velocity of the ocean current at the seawater depth position of each sensing optical cable unit and the seawater depth position of each sensing optical cable unit.
Specifically, according to the ocean current flow velocity at the sea depth position of each sensing optical cable unit and the sea depth of each sensing optical cable unit, the ocean current flow velocities at different sea depths within the full sea depth range can be obtained, and therefore the ocean current distribution at the full sea depth position can be obtained.
In one implementation, since the sensing optical cable is not under tension, the sensing optical cable may adopt an optical unit structure in the submarine communication optical cable, and a multi-core optical cable may be selected, so that the optical fiber sensing demodulation unit can simultaneously monitor the vibration frequency detected by the plurality of sensing optical cable units.
The optical fiber in the sensing optical cable can be a common communication single-mode optical fiber or a single-mode optical fiber with a built-in microstructure. The microstructure can be an all-same weak fiber grating or a grating with different reflection wavelengths, or other special structures capable of monitoring vibration.
Therefore, the system for monitoring the flow distribution in the whole sea deep sea can realize the real-time monitoring of the flow velocity distribution in the whole sea deep range according to the vortex effect caused by the fluid in the fluid-solid coupling process and the long-distance monitoring advantage of the distributed sensing technology; the sensing optical cable for detecting the vibration frequency caused by the vortex effect can adopt a multi-core optical cable, so that the optical fiber sensing demodulation unit can simultaneously monitor the vibration frequency detected by the plurality of sensing optical cable units. Compared with the prior art, the detection system provided by the invention has the advantages of simple structure, no need of independent power supply and communication under water, easiness in implementation, long monitoring distance, capability of realizing full-sea-depth ocean current distribution monitoring and real-time online long-time monitoring.
Those of ordinary skill in the art will understand that: the figures are merely schematic representations of one embodiment, and the blocks or flow diagrams in the figures are not necessarily required to practice the present invention.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A method for monitoring the distribution of full-sea deep ocean currents is characterized by comprising the following steps:
detecting the vibration frequency of the sensing optical cable unit at the current seawater depth;
calculating the current flow velocity of the sensing optical cable unit at the seawater depth according to the obtained vibration frequency and the optical cable diameter of the sensing optical cable unit;
and generating ocean current distribution according to the ocean current flow rate and the depth of the seawater where the sensing optical cable unit is located.
2. The method according to claim 1, wherein the step of calculating the current flow rate at the sea depth of the sensing optical cable unit according to the obtained vibration frequency and the optical cable diameter of the sensing optical cable unit comprises:
according to the vibration frequency fsCalculating the diameter d of the optical cable of the sensing optical cable unit and a preset Sethonhax number s based on a preset ocean current calculation modelAn ocean current flow velocity V at a sea depth where the sensing optical cable unit is located, wherein the Storey number s depends on sea properties, and the ocean current calculation model comprises the vibration frequency fsAnd the ocean current flow velocity V.
3. The method of claim 2, wherein the ocean current computational model comprises:
wherein V is the flow velocity of the sea current at the sea water depth where the sensing optical cable unit is located; d is the cable diameter of the sensing cable unit; f. ofsThe vibration frequency of the sea water depth where the sensing optical cable unit is located is the vibration frequency; a is a calibration coefficient.
4. The method of claim 1, wherein the sensing cable unit is comprised of a first unit length of sensing cable and a second unit length of cable; the sensing optical cable and the cable are respectively divided into a plurality of sensing optical cables with first unit length and a plurality of cables with second unit length at equal intervals;
the step of generating the ocean current distribution according to the ocean current flow rate and the depth of the seawater where the sensing optical cable unit is located comprises the following steps:
determining the seawater depth of each sensing optical cable unit according to the position of each sensing optical cable unit on the sensing optical cable;
and calculating the ocean current distribution in the full sea depth range according to the ocean current flow velocity at the sea depth of each sensing optical cable unit and the sea depth of each sensing optical cable unit.
5. The method of claim 4, wherein after the step of detecting the vibration frequency of the sensing cable unit at the current seawater depth, the method further comprises:
and acquiring the vibration frequency detected by each sensing optical cable unit by adopting a phase-sensitive Optical Time Domain Reflection (OTDR) technology.
6. A system for monitoring the distribution of ocean currents throughout the sea, the system comprising: the device comprises a sensing optical cable unit and an optical fiber sensing demodulation unit;
the sensing optical cable unit is used for detecting the vibration frequency of the sensing optical cable unit at the current seawater depth;
the optical fiber sensing demodulation unit is used for acquiring the vibration frequency detected by the sensing optical cable unit; calculating the current flow velocity of the sea water depth position of the sensing optical cable unit according to the vibration frequency and the optical cable diameter of the sensing optical cable unit; and generating ocean current distribution according to the ocean current flow rate and the depth of the seawater where the sensing optical cable unit is located.
7. The system of claim 6,
the optical fiber sensing demodulation unit is connected with an optical fiber in the sensing optical cable, wherein the sensing optical cable is a multi-core optical cable, and the optical fiber is a single-mode optical fiber or a single-mode optical fiber with a built-in microstructure.
8. The system of claim 6,
and a flexible flag is arranged on the sensing optical cable unit.
9. The system of claim 6, wherein the monitoring system further comprises: a cable;
the cable is rigidly connected with the sensing optical cable.
10. The system of claim 9, wherein the monitoring system further comprises: a cable winding disc and an anchor body;
the upper end of the cable is connected with the cable winding disc, and the lower end of the cable is connected with the anchor body;
the cable winding disc and the optical fiber sensing demodulation unit are arranged on a mother ship or an offshore platform.
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