FLOODING DETECTION DEVICE, FLOODING DETECTION SYSTEM, AND FLOODING DETECTION METHOD

Provided is a flooding detection device or the like capable of detecting flooding in a pipeline. The flooding detection device comprises: an optical signal reception unit configured to receive an optical signal, including sensing information, from an optical fiber provided along the pipeline; at least one memory configured to store instructions; and at least one processor configured to execute the instructions to detect the propagation characteristics of vibrations in the pipeline using the sensing information included in the optical signal and detect flooding in the pipeline on the basis of the propagation characteristics.

TECHNICAL FIELD

The present disclosure relates to a flooding detection device and the like.

BACKGROUND ART

PTL 1 discloses a technique for detecting deterioration (for example, thinning or corrosion) of a pipe. In the technique described in PTL 1, a plurality of ultrasonic optical probes are attached to an outer surface of a pipe. A wall thickness of the pipe is measured by using the ultrasonic optical probes. By measuring the wall thickness, thinning, corrosion, or the like is detected (see paragraphs to [0016], paragraphs [0032] to [0042], paragraph [212], and the like of PTL 1).

As a related art, a technique described in PTL 2 is also known.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

A technique for detecting flooding in a pipeline (for example, a pipeline laid underground) is desired. Herein, the technique described in PTL 1 detects deterioration (for example, thinning or corrosion) of a pipe, based on a wall thickness of the pipe, and does not detect flooding in the pipe. Therefore, there is a problem that it is not possible to detect flooding in the pipeline by using the technique described in PTL 1 and therefore it is not possible to prevent corrosion and the like of the pipe due to flooding in advance.

The present disclosure has been made in order to solve the above-described problem, and an object thereof is to provide a flooding detection device and the like capable of detecting flooding in a pipeline.

Solution to Problem

A flooding detection device according to one aspect of the present disclosure includes: an optical signal reception means for receiving an optical signal including sensing information, from an optical fiber provided along a pipeline; a propagation characteristic detection means for detecting a propagation characteristic of vibration in the pipeline by using the sensing information included in the optical signal; and a flooding detection means for detecting flooding in the pipeline, based on the propagation characteristic.

A flooding detection system according to one aspect of the present disclosure includes: an optical signal reception means for receiving an optical signal including sensing information, from an optical fiber provided along a pipeline; a propagation characteristic detection means for detecting a propagation characteristic of vibration in the pipeline by using the sensing information included in the optical signal; and a flooding detection means for detecting flooding in the pipeline, based on the propagation characteristic.

A flooding detection method according to one aspect of the present disclosure includes: receiving, by an optical signal reception means, an optical signal including sensing information, from an optical fiber provided along a pipeline; detecting, by a propagation characteristic detection means, a propagation characteristic of vibration in the pipeline by using the sensing information included in the optical signal; and detecting, by a flooding detection means, flooding in the pipeline, based on the propagation characteristic.

Advantageous Effects of Invention

According to the present disclosure, it is possible to detect flooding in a pipeline.

EXAMPLE EMBODIMENT

First Example Embodiment

FIG.1is an explanatory diagram illustrating an example of a state in which an optical fiber is provided along a pipeline.FIG.2is a block diagram illustrating a main part of a flooding detection system according to a first example embodiment. The flooding detection system according to the first example embodiment will be described with reference toFIGS.1and2.

As illustrated inFIG.1, an optical fiber1is provided along a pipeline PL. The pipeline PL is a pipeline that is possibly flooded (for example, a pipeline laid in underground). The optical fiber1is, for example, an existing optical fiber for communication. In the example illustrated inFIG.1, the optical fiber1is provided inside the pipeline PL and is linearly provided along a longitudinal direction of the pipeline PL. In the example illustrated inFIG.1, the pipeline PL is provided in a lateral direction, and the optical fiber1is disposed lower side in an interior of the pipeline PL.

Herein, the optical fiber1can be used for optical fiber sensing. Specifically, for example, the optical fiber1can be used to detect vibration, sound, or temperature by distributed fiber optic sensing (DFOS). Hereinafter, information detected by the optical fiber1using optical fiber sensing may be collectively referred to as “sensing information”. In other words, the optical fiber1detects the sensing information.

As illustrated inFIG.2, a flooding detection system100includes the optical fiber1, a flooding detection device2, and an output device3. The flooding detection device2includes an optical signal transmission unit11, an optical signal reception unit12, a propagation characteristic detection unit13, a flooding detection unit14, and an output control unit15. The optical signal transmission unit11and the optical signal reception unit12constitute a main part of the optical signal transmission/reception unit16.

The optical signal transmission unit11outputs an optical signal to the optical fiber1. The output optical signal is input to the optical fiber1and propagates inside the optical fiber1. At this time, backscattered light is generated inside the optical fiber1. The optical signal reception unit12receives an optical signal associated to the generated backscattered light. The received optical signal includes sensing information for DFOS.

The optical signal transmission/reception unit16may include a device (not illustrated) for separating the optical signal output by the optical signal transmission unit11and the optical signal received by the optical signal reception unit12. For example, the optical signal transmission/reception unit16may include an optical circulator (not illustrated) provided between the optical signal transmission unit11and the optical fiber1, and the optical signal reception unit12.

The propagation characteristic detection unit13detects a propagation characteristic of vibration inside the pipeline PL by using the sensing information included in the optical signal received by the optical signal reception unit12. The flooding detection unit14detects flooding in the pipeline PL, based on the detected propagation characteristic. Specifically, for example, the flooding detection unit14detects whether flooding has occurred in the pipeline PL. Alternatively, for example, the flooding detection unit14detects whether flooding has occurred in the pipeline PL and also detects a section of the pipeline PL where the flooding occurs. Herein, “flooding” that is a target of detection by the flooding detection unit14refers to a state in which water is accumulated in at least some sections of the pipeline PL to an extent that at least the optical fiber1is completely submerged due to flooding.

A specific example of the propagation characteristic detected by the propagation characteristic detection unit13, a specific example of a method for detecting a propagation method by the propagation characteristic detection unit13, and a specific example of a method for detecting flooding by the flooding detection unit14will be described later with reference toFIGS.7A,7B,8A, and8B.

The output control unit15executes control for outputting a notification according to a result of detection (hereinafter, sometimes simply referred to as “detection result”) by the flooding detection unit14. The output device3is used to output the notification. The output device3includes, for example, at least one of a display device, an audio output device, and a communication device. The display device is, for example, a display device using a display. The audio output device is, for example, an audio output device using a speaker. The communication device is, for example, a communication device using a dedicated transmitter and a dedicated receiver.

Specifically, for example, the output control unit15executes control for displaying an image for the notification. The display device of the output device3is used to display the image. Alternatively, for example, the output control unit15executes control for outputting sound for the notification. The audio output device of the output device3is used to output the audio. Alternatively, for example, the output control unit15executes control for transmitting a signal for the notification to another system (not illustrated). The communication device of the output device3is used to transmit the signal.

Specifically, for example, when the detection result indicates that flooding occurs in the pipeline PL, a notification indicating that the flooding has occurred in the pipeline PL is output. Further, when the detection result indicates a section of the pipeline PL where the flooding occurs, a notification indicating the section may be output. Further, different notifications may be output according to a size of the section.

In this way, the main part of the flooding detection system100is configured.

Hereinafter, the optical signal transmission unit11may be referred to as an “optical signal transmission unit”. Further, the optical signal reception unit12may be referred to as an “optical signal reception means”. Further, the propagation characteristic detection unit13may be referred to as a “propagation characteristic detection means”. Further, the flooding detection unit14may be referred to as a “flooding detection means”. Further, the output control unit15may be referred to as an “output control means”.

Next, with reference toFIGS.3to5, a hardware configuration of a main part of the flooding detection device2will be described.

As illustrated inFIGS.3to5, the flooding detection device2is a flooding detection device using a computer21.

As illustrated inFIG.3, the computer21includes a transmitter31, a receiver32, a processor33, and a memory34. The memory34stores a program (including a program for causing the transmitter31to function as the optical signal transmission unit11and a program for causing the receiver32to function as the optical signal reception unit12) for causing the computer21to function as the optical signal transmission unit11, the optical signal reception unit12, the propagation characteristic detection unit13, the flooding detection unit14, and the output control unit15. The processor33reads and executes the program stored in the memory34. Thus, a function F1of the optical signal transmission unit11, a function F2of the optical signal reception unit12, a function F3of the propagation characteristic detection unit13, a function F4of the flooding detection unit14, and a function F5of the output control unit15are achieved.

Alternatively, as illustrated inFIG.4, the computer21includes the transmitter31, the receiver32, and a processing circuit35. The processing circuit35executes processing (including processing for causing the transmitter31to function as the optical signal transmission unit11and processing for causing the receiver32to function as the optical signal reception unit12) for causing the computer21to function as the optical signal transmission unit11, the optical signal reception unit12, the propagation characteristic detection unit13, the flooding detection unit14, and the output control unit15. Thus, the functions F1to F5are achieved.

Alternatively, as illustrated inFIG.5, the computer21includes the transmitter31, the receiver32, the processor33, the memory34, and the processing circuit35. In this case, some of the functions F1to F5are achieved by the processor33and the memory34, and remaining functions of the functions F1to F5are achieved by the processing circuit35.

The processor33is constituted of one or more processors. Each of the processors is, for example, a processor using a central processing unit (CPU), a graphics processing unit (GPU), a microprocessor, a microcontroller, or a digital signal processor (DSP).

The memory34is constituted of one or more memories. Each of the memories is, for example, a memory using a random access memory (RAM), a read only memory (ROM), a flash memory, an erasable programmable read only memory (EPROM), an electrically erasable programmable read only memory (EEPROM), a solid state drive, a hard disk drive, a flexible disk, a compact disk, a digital versatile disc (DVD), a Blu-ray disk, a magneto optical (MO) disk, or a mini disk.

The processing circuit35is constituted of one or more processing circuits. Each of the processing circuits is, for example, a processing circuit using an application specific integrated circuit (ASIC), a programmable logic device (PLD), a field programmable gate array (FPGA), a system on a chip (SoCs), or a system large scale integration s(LSI).

The processor33may include a dedicated processor associated to each of the functions F1to F5. The memory34may include a dedicated memory associated to each of the functions F1to F5. The processing circuit35may include a dedicated processing circuit associated to each of the functions F1to F5.

Next, with reference to a flowchart illustrated inFIG.6, an operation of the flooding detection device2will be described, mainly on operations of the propagation characteristic detection unit13, the flooding detection unit14, and the output control unit15.

First, the propagation characteristic detection unit13detects a propagation characteristic of vibration inside the pipeline PL (step ST1). Sensing information included in an optical signal received by the optical signal reception unit12is used for detecting the propagation characteristic in step ST1.

Next, the flooding detection unit14detects flooding in the pipeline PL (step ST2). More specifically, the flooding detection unit14detects whether flooding has occurred in the pipeline PL. Alternatively, the flooding detection unit14detects whether flooding has occurred in the pipeline PL and detects a section of the pipeline PL where the flooding occurs. The detection of flooding in step ST2is based on the propagation characteristic detected in step ST1.

Next, the output control unit15executes control for outputting a notification according to a result of the detection in step ST2(step ST3).

Next, with reference toFIGS.7A,7B,8A, and8B, a specific example of the propagation characteristic detected by the propagation characteristic detection unit13, a specific example of a method for detecting a propagation method by the propagation characteristic detection unit13, and a specific example of a method for detecting flooding by the flooding detection unit14will be described.

First, a first specific example will be described with reference toFIGS.7A and7B. In a first example embodiment, whether flooding has occurred in the pipeline PL is detected.

It is assumed that a sound is generated inside the pipeline PL due to some factor. Alternatively, it is assumed that a sound generated outside the pipeline PL enters the inside of the pipeline PL due to some factor. In such cases, the sound propagates inside the pipeline PL. Normally, the sound propagating inside the pipeline PL is hardly attenuated. Therefore, a state in which identical sounds or associated sounds propagate bidirectionally inside the pipeline PL may occur. Specifically, for example, at least one end of the pipeline PL is connected with a manhole space or a handhole space. In this case, since the end is an open end where a spatial cross-sectional area changes, the end may function as an entry point of sound and may also function as a reflection point of sound. Alternatively, for example, a wall or a lid is provided at the end. In this case, since the end is a closed end, the end may function as a reflection point of sound.

A standing wave is generated by the identical sounds or associated sounds bidirectionally propagating inside the pipeline PL. When only one end of the line PL is a reflection point of sound, such standing wave is generated regardless of the frequency of the sound. In other words, the standing wave is generated regardless of a relationship between a wavelength of the sound and a length L of the pipeline PL, and is generated for each frequency component included in the sound. Meanwhile, when both ends of the pipeline PL are reflection points of sound, the standing wave is generated for a frequency component associated to a so-called “natural frequency”. The natural frequency is determined according to the length L of the pipeline PL, and is different depending on a medium in which the sound propagates (for example, air or water in the pipeline PL). This is because, from a viewpoint of a soundwave, the length L appears to have changed equivalently, depending on the medium in which the sound propagates. Herein, standing wave associated to a frequency component associated to a wavelength smaller than the length L has a plurality of antinodes and a plurality of nodes.

FIG.7Aillustrates an example of a standing wave inside the pipeline PL. In the example illustrated inFIG.7A, both ends of the pipeline PL are reflection points of sound, and the standing wave is generated for the frequency component associated to the natural frequency. More specifically, the sound propagating bidirectionally in the pipeline PL includes a frequency component associated to a wavelength twice as long as the length L, a frequency component associated to a wavelength equivalent to the length L, and a frequency component associated to a wavelength half as long as the length L. Therefore, a standing wave (specifically, a first-order standing wave) associated to the frequency component associated to the wavelength twice as long as the length L is generated. In addition, a standing wave (specifically, a second-order standing wave) associated to the frequency component associated to the wavelength equivalent to the length L is also generated. Furthermore, a standing wave (specifically, a fourth-order standing wave) associated to the frequency component associated to the wavelength half as long as the length L is also generated. Each of the second-order standing wave and the fourth-order standing wave corresponds to a wavelength smaller than the length L. Thus, each of the second-order standing wave and the fourth-order standing wave has a plurality of antinodes and a plurality of nodes.FIG.7Aillustrates a position of each of the antinodes of the fourth-order standing wave in a longitudinal direction of the pipeline PL and a position of each of the nodes of the fourth-order standing wave in the longitudinal direction of the pipeline PL. InFIG.7A, each of the standing waves is illustrated as a transverse wave.

Note that, at each end of the pipeline PL, an antinode of a standing wave is generated when the end portion is an open end, and a node of a standing wave is generated when the end portion is a closed end. In the example illustrated inFIG.7A, nodes of a standing wave is generated at both ends of the pipeline PL. Such standing wave is generated when both ends of the pipeline PL are closed (for example, as described above, when walls or lids are provided). InFIG.7A, members that close both ends of the pipeline PL are not illustrated.

Herein, a physical quantity detected by the optical fiber1includes vibration of air or water due to the sound propagating inside the pipe line PL (specifically, vibration of air or water due to the standing waves). The sensing information includes information indicating an intensity distribution of the vibration, and the intensity distribution is an intensity distribution for each frequency component with respect to a distance (hereinafter, sometimes referred to as a “frequency intensity distribution”). The “distance” is a distance from the optical signal reception unit12in the optical fiber1.FIG.7Billustrates an example of the intensity distribution of the vibration with respect to the distance for the frequency component associated to the fourth-order standing wave illustrated inFIG.7A. As illustrated inFIG.7B, intensity of the vibration at a distance associated to each antinode is greater than intensities of the vibration at other distances. Further, intensity of the vibration at a distance associated to each node is smaller than intensity of the vibration at other distances. This is a common characteristic for standing waves associated to any frequency component. In other words, for a specific frequency f, the characteristic of intensity distribution appears when a standing wave is generated in the pipeline PL.

The propagation characteristic detection unit13selects the frequency f at which the characteristic of intensity distribution appears. On a basis of the characteristic of intensity distribution, the propagation characteristic detection unit13calculates an interval m between adjacent antinodes in a standing wave associated to the selected frequency f, or an interval m between adjacent nodes in the standing wave associated to the selected frequency f. InFIG.7B, a distance m between adjacent nodes in the fourth-order standing wave illustrated inFIG.7Ais illustrated. The propagation characteristic detection unit13uses the calculated interval m to calculate a wavelength λ of the standing wave associated to the selected frequency f by using the following Math (1).

The propagation characteristic detection unit13calculates a sound velocity v inside the pipeline PL by using the selected frequency f and the calculated wavelength λ. Specifically, for example, the propagation characteristic detection unit13calculates the sound velocity v by using the following Math (2). Specifically, the sound velocity v corresponds to a propagation speed of the vibration inside the pipeline PL. In other words, the propagation characteristic detection unit13detects the propagation speed of the vibration as the propagation characteristic of the vibration inside the pipeline PL.

Normally, sound velocity may vary greatly, depending on a medium. For example, sound velocity in air is approximately four times faster than sound velocity in water. As an example, when an environmental temperature is 20 degrees, the sound velocity in air is 345 meters per second, while the sound velocity in water is 1479 meters per second.

Therefore, the flooding detection unit14determines whether the sound velocity v calculated by the propagation characteristic detection unit13is a value associated to the sound velocity in air or a value associated to the sound velocity in water. When the sound velocity v is a value associated to the sound velocity in air, the flooding detection unit14determines that flooding in the pipeline PL has not occurred. Meanwhile, when the sound velocity v is a value associated to the sound velocity in water, the flooding detection unit14determines that flooding in the pipeline PL has occurred. In this way, whether flooding in the pipeline PL has occurred is detected.

Note that the determination by the flooding detection unit14may be performed using a model for determination. For example, the following model is prepared in advance for each assumed environmental temperature in the pipeline PL. Specifically, a model is prepared in advance and the model outputs, when the value of the sound velocity v is input, information indicating whether the input value is a value associated to the sound velocity in air or a value associated to the sound velocity in water. The model is generated by machine learning, for example. The flooding detection unit14inputs the calculated sound velocity v to the model. Thereby, information indicating whether the calculated sound velocity v is a value associated to the sound velocity in air or a value associated to the sound velocity in water is output. In this way, it is determined whether the calculated sound velocity v is a value associated to the sound velocity in air or a value associated to the sound velocity in water.

Further, the determination by the flooding detection unit14may be performed by using a threshold value for determination. For example, a threshold value by which the sound velocity in air and the sound velocity in water can be distinguished from each other is set in advance for each assumed environmental temperature in the pipeline PL. The flooding detection unit14compares the calculated sound velocity v with the set threshold value to determine whether the calculated sound velocity v is a value associated to the sound velocity in air or a value associated to the sound velocity in water. At this occasion, from a viewpoint of detecting an occurrence of flooding with high accuracy, the threshold value may be set to a value close to the sound velocity in water.

The propagation characteristic detection unit13and the flooding detection unit14may use standing waves associated to a plurality of different frequency components. In other words, the propagation characteristic detection unit13and the flooding detection unit14may use a plurality of frequencies f associated to the standing waves. That is, the propagation characteristic detection unit13calculates a sound velocity v for each of the plurality of frequencies f. As a result, a plurality of sound velocities v associated to the plurality of frequencies f are calculated.

Next, the flooding detection unit14calculates a statistical value (more specifically, an average value), based on the plurality of calculated sound velocities v. The flooding detection unit14determines whether the statistical value is a value associated to the sound velocity in air or a value associated to the sound velocity in water. When the statistical value is a value associated to the sound velocity in air, the flooding detection unit14determines that flooding in the pipeline PL has not occurred. On the other hand, when the statistical value is a value associated to the sound velocity in water, the flooding detection unit14determines that the flooding in the pipeline PL has occurred.

Alternatively, the flooding detection unit14determines whether each of the plurality of calculated sound velocities v is a value associated to the sound velocity in air or a value associated to the sound velocity in water. When a predetermined number (for example, one) or more of the sound velocities v are values associated to the sound velocity in water, the flooding detection unit14determines that flooding has occurred. Otherwise, the flooding detection unit14determines that flooding has not occur.

As described above, by using the plurality of frequencies f, it is possible to improve accuracy in detecting whether flooding has occurred, as compared with a case where only one frequency f is used.

Depending on an amount of water entering the pipeline PL due to the flooding, a condition may occur in which a lower inner part of the pipeline PL is filled with water and an upper inner part of the pipeline PL is filled with air. In this case, a standing wave having an interval m according to the sound velocity in water is generated in the part of the pipeline PL filled with water. In addition, in the portion of the pipeline PL filled with air, a standing wave having an interval m according to the sound velocity in air is generated. Therefore, in a case in which the optical fiber1is disposed at the part filled with water, a propagation characteristic (propagation speed) associated to the sound velocity in water is detected by the propagation characteristic detection unit13, and it is determined by the flooding detection unit14that flooding has occurred. Meanwhile, in a case in which the optical fiber1is disposed at the part filled with air, a propagation characteristic (propagation speed) associated to the sound velocity in air is detected by the propagation characteristic detection unit13, and it is determined by the flooding detection unit14that flooding has not occurred. Therefore, from a viewpoint of accurately detecting an occurrence of flooding, it is preferable that the optical fiber1is disposed at the inner lower part of the pipeline PL.

Next, a second specific example will be described with reference toFIGS.8A and8B. In the second specific example, whether flooding in the pipeline PL has occurred is detected, and a section where the flooding occurs is detected.

By distributed optical fiber sensing using the optical fiber1, a temporal change in intensity of vibration at any point on the optical fiber1is detected. Herein, as described above, a sound propagating inside the pipeline PL is hardly attenuated. Thus, the temporal change in the intensity of vibration generated by the sound may be detected at two different points (specifically, at two different distances) and at two different points in time. In other words, the vibration generated by the sound may be detected at two different points (specifically, at two different distances) and at two different points in time.

For example, as illustrated inFIG.8A, it is assumed that vibration generated by a sound is detected at a predetermined point P1(specifically, at a predetermined distance D1) and at a certain time point T1. Thereafter, it is assumed that the sound propagates inside the pipeline PL, and thereby, as illustrated inFIG.8B, vibration associated to the vibration is detected at another predetermined point P2(specifically, at another predetermined distance D2) and at another time point T2. Hereinafter, the point P1may be referred to as a “first point”. Further, the point P2may be referred to as “second point”.

At this occasion, since each of the first point P1and the second point P2is a predetermined point, an interval ΔP between the first point P1and the second point P2is known. Further, the propagation characteristic detection unit13detects a time ΔT that is a time being taken for the vibration to propagate from the first point P1to the second point P2, based on the difference between the first time point T1and the second time point T2. The propagation characteristic detection unit13calculates a propagation speed V of the vibration in the pipeline PL by using the following Math (3).

As described above, the propagation characteristic detection unit13detects a propagation speed of vibration in the pipeline PL as a propagation characteristic of the vibration in the pipeline PL. More specifically, the propagation characteristic detection unit13detects the propagation speed V of the vibration between the first point P1and the second point P2. The propagation speed V corresponds to sound velocity inside the pipeline PL. More specifically, the propagation speed V corresponds to sound velocity between the first point P1and the second point P2.

Therefore, based on the propagation speed V calculated by the propagation characteristic detection unit13, the flooding detection unit14detects whether flooding in the pipeline PL has occurred, by using a similar method as that described in the first specific example. More specifically, the flooding detection unit14detects whether flooding in a section between the first point P1and the second point P2in the pipeline PL has occurred. Specifically, the flooding detection unit14determines whether the calculated propagation speed V is a value associated to the sound velocity in air or a value associated to the sound velocity in water. When the propagation speed V is a value associated to the sound velocity in air, the flooding detection unit14determines that flooding has not occurred. Meanwhile, when the propagation speed V is a value associated to the sound velocity in water, the flooding detection unit14determines that flooding has occurred.

Herein, in the pipeline PL, a plurality of different combinations (P1, P2) may be set as combinations (P1, P2) of the first point P1and the second point P2. Specifically, for example, a plurality of combinations (P1, P2) associated to a plurality of sections arranged non-overlapping with each other may be set. The propagation characteristic detection unit13may calculate the propagation velocity V for each of the plurality of combinations (P1, P2). The flooding detection unit14may detect, for each of the plurality of combinations (P1, P2), whether flooding has occurred. Thus, flooding in each of the plurality of sections is detected. As a result, a section of the pipeline PL where flooding occurs is detected.

As described above, depending on the amount of water entering the pipeline PL due to flooding, a state may occur in which the inner lower part of the pipeline PL is filled with water and the inner upper part of the pipeline PL is filled with air. In this case, in the part of the pipeline PL filled with water, vibration propagates at the propagation speed V associated to the sound velocity in water. Further, in the of the pipeline PL filled with air, vibration propagates at the propagation speed V associated to the sound velocity in air. Therefore, in a case in which the optical fiber1is disposed at the part filled with water, a propagation characteristic (propagation speed) associated to the sound velocity in water is detected by the propagation characteristic detection unit13, and it is determined by the flooding detection unit14that flooding has occurred. Meanwhile, in a case in which the optical fiber1is disposed at the part filled with air, a propagation characteristic (propagation speed) associated to the sound velocity in air is detected by the propagation characteristic detection unit13, and determined by the flooding detection unit14that flooding has not occurred. Therefore, from the viewpoint of accurately detecting an occurrence of flooding, it is preferable that the optical fiber1is disposed at the inner lower part of the pipeline PL.

Next, an advantageous effect of using the flooding detection system100will be described.

As described above, by using the flooding detection system100, flooding in the pipeline PL can be detected. In particular, by using an existing optical fiber (for example, an optical fiber for communication) as the optical fiber1, it is possible to eliminate necessity of installing a dedicated device (for example, a dedicated optical fiber or a dedicated sensor) for detecting flooding inside the pipeline PL. As a result, it is possible to achieve the detection of flooding with a simple system configuration that does not require these devices.

Next, a modification example of the flooding detection system100will be described.

Disposition of the optical fiber1in the pipeline PL is not limited to the example illustrated inFIG.1. The optical fiber1may be provided along the pipeline PL in such a state that the propagation characteristic detection unit13can detect a propagation characteristic and the flooding detection unit14can detect the flooding. For example, the optical fiber1may be provided in a spiral shape along the inner circumferential surface of the pipeline PL instead of being provided in a linear shape along the longitudinal direction of the pipeline PL. Further, for example, the optical fiber1may be provided at a position away from the inner circumferential surface of the pipeline PL. However, as described above, from the viewpoint of accurately detecting an occurrence of flooding, it is preferable that the optical fiber1is disposed at the inner lower part of the pipeline PL.

Next, with reference toFIG.9, another modification example of the flooding detection system100will be described.

The optical fiber1may be provided along a plurality of pipelines PL instead of being provided along one pipeline PL. For example, as illustrated inFIG.9, the optical fiber1may be provided along two pipelines PL_1and PL_2.

In this case, the propagation characteristic detection unit13detects a propagation characteristic of vibration in each of the plurality of pipelines PL. A method for detecting the propagation characteristic in each of the plurality of pipelines PL is similar to the method for detecting a propagation characteristic in one pipeline PL. Further, the flooding detection unit14detects flooding in each of the plurality of pipelines PL, based on the detected propagation characteristic. A method for detecting flooding in each of the plurality of pipelines PL is similar to the method for detecting flooding in one pipeline PL.

It is preferable that the plurality of pipelines PL are acoustically separated from each other. Specifically, for example, in the example illustrated inFIG.9, the pipelines PL_1and PL_2are provided independently of each other (that is, the pipelines PL_1and PL_2are not connected with each other), and thereby the pipelines PL_1and PL_2are acoustically separated from each other. Alternatively, for example, when the pipelines PL_1and PL_2are connected with each other, the pipelines PL_1and PL_2are acoustically separated from each other by a sound insulating material provided between the pipelines PL_1and PL_2.

For example, a case is considered in which the first specific example is applied to the example illustrated inFIG.9. In this case, an acoustic characteristic to be detected is an acoustic characteristic having both ends (A, B) of the pipeline PL_1as reflection points and an acoustic characteristic having both ends (C, D) of the pipeline PL_2as reflection points. However, when the pipelines PL_1and PL_2are not acoustically separated from each other, sound inside the pipeline PL_1may propagate into inside of the pipeline PL_2. Similarly, sound inside the pipeline PL_2may propagate into inside of the pipeline PL_1. As a result, standing waves may generated for combinations of the reflection points such as (A, C), (B, D), (B, C), and (A, D) in addition to combinations of the reflection points (A, B) and (C, D), and therefore there is a concern that the propagation of the sound wave becomes complicated. In other words, there is a concern that a standing wave to be detected may be masked by other standing waves. Meanwhile, since the pipelines PL_1and PL_2are acoustically separated from each other, this concern can be eliminated.

Next, a modification example of the flooding detection device2will be described with reference toFIG.10. Further, another modification example of the flooding detection system100will be described with reference toFIG.11.

As illustrated inFIG.10, the optical signal reception unit12, the propagation characteristic detection unit13, and the flooding detection unit14may constitute the main part of the flooding detection device2. In this case, the optical signal transmission unit11and the output control unit15may be provided outside the flooding detection device2. In this case, when the optical fiber1is for communication, the optical signal transmission unit11may be provided in an optical communication device (not illustrated) using the optical fiber1.

As illustrated inFIG.11, the optical signal reception unit12, the propagation characteristic detection unit13, and the flooding detection unit14may constitute the main part of the flooding detection system100. In this case, the optical fiber1may be provided outside the flooding detection system100. The optical signal transmission unit11and the output control unit15may be provided outside the flooding detection system100. The output device3may be provided outside the flooding detection system100. In this case, when the optical fiber1is for communication, the optical signal transmission unit11may be provided in an optical communication device (not illustrated) using the optical fiber1.

Even in these cases, the above-described advantageous effect can be obtained. Specifically, the optical signal reception unit12receives an optical signal including sensing information, from the optical fiber1provided along the pipeline PL. The propagation characteristic detection unit13detects a propagation characteristic of vibration in the pipeline PL by using the sensing information included in the optical signal. The flooding detection unit14detects flooding in the pipeline PL, based on the propagation characteristic. Accordingly, it is possible to detect flooding in the pipeline PL. In particular, by using an existing optical fiber in the optical fiber1, it is possible to eliminate necessity of installing a dedicated device for detecting flooding in the pipeline PL.

Note that, the flooding detection system100may include at least one of the optical signal transmission unit11and the output control unit (not illustrated) in addition to the optical signal reception unit12, the propagation characteristic detection unit13, and the flooding detection unit14. Each component of the flooding detection system100may be configured of an independent device. These devices may be geographically distributed or networked in a distributed manner. For example, these devices may include edge computers and cloud computers.

Some or all of the above-described example embodiments may be described as the following supplementary notes, but are not limited thereto.

A flooding detection device including:an optical signal reception means for receiving an optical signal including sensing information, from an optical fiber provided along a pipeline;a propagation characteristic detection means for detecting a propagation characteristic of vibration in the pipeline by using the sensing information included in the optical signal; anda flooding detection means for detecting flooding in the pipeline, based on the propagation characteristic.

The flooding detection device according to supplementary note 1, whereinthe sensing information includes a frequency intensity distribution of the vibration,the propagation characteristic includes a propagation speed of the vibration, andthe propagation characteristic detection means detects a wavelength of a standing wave by detecting at least one of a node and an antinode of the standing wave associated to the vibration, based on the frequency intensity distribution, and detects the propagation speed, based on a frequency and the wavelength of the standing wave.

The flooding detection device according to supplementary note 1, whereinthe sensing information includes a temporal change in intensity of the vibration at a first point in the pipeline and a temporal change in intensity of the vibration at a second point in the pipeline,the propagation characteristic includes a propagation speed of the vibration, andthe propagation characteristic detection means detects the propagation speed by detecting a time being taken for the vibration to propagate from the first point to the second point, by using the sensing information.

The flooding detection device according to supplementary 3, wherein the flooding detection means detects the flooding in a section between the first point and the second point of the pipeline.

The flooding detection device according to any one of supplementary notes 1 to 4, wherein a notification is output according to a result of detection by the flooding detection means.

A flooding detection system including:an optical signal reception means for receiving an optical signal including sensing information, from an optical fiber provided along a pipeline;a propagation characteristic detection means for detecting a propagation characteristic of vibration in the pipeline by using the sensing information included in the optical signal; anda flooding detection unit for detecting flooding in the pipeline, based on the propagation characteristic.

The flooding detection system according to supplementary note 6, whereinthe sensing information includes a frequency intensity distribution of the vibration,the propagation characteristic includes a propagation speed of the vibration, andthe propagation characteristic detection means detects a wavelength of a standing wave by detecting at least one of a node and an antinode of the standing wave associated to the vibration, based on the frequency intensity distribution, and detects the propagation speed, based on a frequency and the wavelength of the standing wave.

The flooding detection system according to supplementary note 6, whereinthe sensing information includes a temporal change in intensity of the vibration at a first point in the pipeline and a temporal change in intensity of the vibration at a second point in the pipeline,the propagation characteristic includes a propagation speed of the vibration, andthe propagation characteristic detection means detects the propagation speed by detecting a time being taken for the vibration to propagate from the first point to the second point, by using the sensing information.

The flooding detection system according to supplementary note 8, wherein the flooding detection means detects the flooding in a section between the first point and the second point of the pipeline.

The flooding detection system according to any one of supplementary notes 6 to 9, wherein a notification is output according to a result of detection by the flooding detection means.

A flooding detection method including:receiving, by an optical signal reception means, an optical signal including sensing information, from an optical fiber provided along a pipeline,detecting, by a propagation characteristic detection means, a propagation characteristic of vibration in the pipeline by using the sensing information included in the optical signal, anddetecting, by a flooding detection means, flooding in the pipeline, based on the propagation characteristic.

The flooding detection method according to supplementary note 11, whereinthe sensing information includes a frequency intensity distribution of the vibration,the propagation characteristic includes a propagation speed of the vibration, andthe propagation characteristic detection means detects a wavelength of a standing wave by detecting at least one of a node and an antinode of the standing wave associated to the vibration, based on the frequency intensity distribution, and detects the propagation speed, based on a frequency and the wavelength of the standing wave.

The flooding detection method according to supplementary note 11, wherein the sensing information includes a temporal change in intensity of the vibration at a first point in the pipeline and a temporal change in intensity of the vibration at a second point in the pipeline,the propagation characteristic includes a propagation speed of the vibration, andthe propagation characteristic detection means detects the propagation speed by detecting a time being taken for the vibration to propagate from the first point to the second point, by using the sensing information.

The flooding detection method according to supplementary note 13, further including detecting, by the flooding detection means, the flooding in a section between the first point and the second point of the pipeline.

The flooding detection method according to any one of supplementary notes 11 to 14, further including outputting a notification, according to a result of detection by the flooding detection means.

A recording medium recording a program causing a computer to function as:an optical signal reception means for receiving an optical signal including sensing information, from an optical fiber provided along a pipeline;a propagation characteristic detection means for detecting a propagation characteristic of vibration in the pipeline by using the sensing information included in the optical signal; anda flooding detection means for detecting flooding in the pipeline, based on the propagation characteristic.

The recording medium according to supplementary note 16, whereinthe sensing information includes a frequency intensity distribution of the vibration,the propagation characteristic includes a propagation speed of the vibration, andthe propagation characteristic detection means detects a wavelength of a standing wave by detecting at least one of a node and an antinode of the standing wave associated to the vibration, based on the frequency intensity distribution, and detects the propagation speed, based on a frequency and the wavelength of the standing wave.

The recording medium according to supplementary note 16, whereinthe sensing information includes a temporal change in intensity of the vibration at a first point in the pipeline and a temporal change in intensity of the vibration at a second point in the pipeline,the propagation characteristic includes a propagation speed of the vibration, andthe propagation characteristic detection means detects the propagation speed by detecting a time being taken for the vibration to propagate from the first point to the second point, by using the sensing information.

The recording medium according to supplementary note 18, wherein the flooding detection means detects the flooding in a section between the first point and the second point of the pipeline.

The recording medium according to any one of supplementary notes 16 to 19, wherein the program further causes the computer to function as an output control means for executing control for outputting a notification according to a result of detection by the flooding detection means.

REFERENCE SIGNS LIST