JP2015102416A - Bubble detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bubble detection device which detects the presence and absence of the generation of bubbles.SOLUTION: A bubble detection device includes: a vibrator 10 which transmits an ultrasonic wave with a prescribed frequency to bubbles being a measuring target and receives a reflection wave from the bubbles to convert it into an electric signal (second electric signal 24); and a control unit 20 which drives the vibrator 10 and processes the second electric signal 24. The control unit 20 calculates a frequency variation amount of the second electric signal 24, compares the calculated frequency variation amount with a preset frequency variation amount and detects the presence and absence of the bubbles, the size and density of the bubbles in accordance with a comparison result.

Description

  The present invention relates to a bubble detection device.

  In recent years, a ship using an air lubrication method (hereinafter referred to as an AL method) that reduces frictional resistance caused by water acting on the ship bottom by bubbles is known. For example, Patent Document 1 discloses a frictional resistance reduction ship using the AL method.

  In the frictional resistance reduction ship described in Patent Document 1, a bubble generating device is provided at the bottom of the ship from the bow part to the stern part of the ship. During the navigation of a ship, when bubble water containing bubbles is ejected from the bubble generator at a flow rate slightly faster than the navigation speed, the bubbles move while diffusing backward along the surface of the ship bottom along with the water flow, covering the flooded part of the ship bottom. . As a result, frictional resistance with water at the bottom of the ship during navigation of the ship is reduced, and ascending force of bubbles is used as a part of thrust to improve propulsion efficiency such as fuel efficiency.

JP-A-9-118288

However, conventionally, when observing bubbles generated by a bubble generating device in a frictional resistance reduction ship using the above-described AL method, an actual bubble is observed by attaching an underwater camera to the bottom of the ship. When air bubbles are observed with an underwater camera in this way, the camera parts or attachments are underwater, so that they have deteriorated over time and have to be replaced regularly. In particular, when placed in seawater in a stationary state, marine organisms such as barnacles tend to adhere, and periodic operations such as replacement and cleaning have occurred. That is, conventionally, when bubbles are observed with an underwater camera, the cost for observing the bubbles has been increased. Also, since the image captured by the underwater camera is processed to detect the presence / absence of bubbles, the size and density of bubbles, processing of image signals with a large capacity is required, and there is a problem that the signal processing becomes complicated. It was.
In addition, the bubbles that enter the bottom of the ship from the bow block the ultrasonic waves emitted from ultrasonic instruments such as sounding instruments, Doppler sonar, and Doppler logs, and normal ultrasonic equipment (conventional equipment) interferes with normal measurement. There is a problem that it is called ("foaming" etc.). For this reason, when detecting bubbles on the ship's bottom, in order to notify that the ultrasonic device is currently unable to measure, the function of detecting the size and density of the bubbles accurately using the bubble detection function (bubble processing function) It is necessary to have the ultrasonic equipment.

  The bubble detection device of the present invention transmits an ultrasonic wave having a predetermined frequency to a bubble to be measured, receives a reflected wave from the bubble and converts it into an electrical signal, and drives the transducer And a control device that processes the electrical signal, wherein the control device calculates a frequency change amount of the electrical signal and sets the calculated frequency change amount to a preset frequency. Compared with the amount of change, the presence / absence of the bubble, the size and density of the bubble are detected according to the comparison result.

  In the bubble detection device of the present invention, the frequency change amount is a peak spread with respect to a transmission frequency in the frequency distribution of the electrical signal.

  Further, in the bubble detection device of the present invention, a plurality of the preset frequency change amounts are set in accordance with a distance from the transducer with respect to a direction of transmitting the bubbles of the transducer, The control device compares the calculated frequency variation amount with each of the plurality of frequency variation amounts set, and detects the thickness of the layer including the bubbles according to the comparison result.

  In the bubble detection device of the present invention, the bubble is a bubble generated by a bubble generation device provided at the bottom of a ship. The bubble detection device of the present invention is not limited to the bubbles generated in the AL method ship, but also detects bubbles that enter the bottom of the ship from the bow direction such as a Barbus bow during normal navigation.

According to the present invention, since it is not necessary to dispose the control device that constitutes the bubble detection device together with the vibrator in water, it is not necessary to perform periodic replacement. In addition, since the vibrator vibrates when bubbles are generated, such as when traveling, the period of time during which it remains stationary in seawater is low, and there is a low possibility of organisms adhering. Is unlikely to occur. Therefore, the cost for detecting bubbles can be reduced as compared with the conventional case. Further, the control device calculates the frequency change amount of the electric signal, compares the calculated frequency change amount with a preset frequency change amount, and determines whether the bubble is present or not, depending on the comparison result. Detect density. Therefore, it is possible to newly provide a bubble detection device that does not require complicated signal processing such as image processing and can easily detect the presence or absence of bubbles.
In addition, when a bubble processing function is installed in a conventional device, a measurement system (system from a transducer to a transmitter / receiver) used for measurement such as normal ship speed and depth measurement is used for the bubble processing function. However, when performing bubble detection determination, since the transmission power and reception gain for measuring the seabed and tidal current at a long distance as in conventional devices are too high, it is necessary to reduce the transmission power and reception gain. Therefore, when a bubble processing function is mounted on a conventional device, a new vibrator or transceiver is required. According to the bubble detection device of the present invention, it is not necessary to equip a new transducer or transmitter / receiver in order to lower the transmission power and the reception gain, and only by changing the software, the sounding device, the Doppler sonar, the Doppler log It is possible to add a bubble processing function to conventional devices such as.

It is the figure which looked at the ship by which the bubble detection apparatus 100 of this embodiment is arrange | positioned as an example from the ship bottom side. 1 is a block diagram showing a configuration of a bubble detection device 100. FIG. FIG. 5 is a diagram for explaining a function of a vibrator 10. It is a figure which shows the time change of the 2nd electric signal 24. FIG. It is a figure for demonstrating the presence or absence of a bubble by the signal processing part 21, and the detection of a shape.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a view of a ship in which the bubble detection device 100 of the present embodiment is disposed as an example, as viewed from the ship bottom side. In addition, although the example which arrange | positions the bubble detection apparatus 100 in a ship is demonstrated here, the bubble detection apparatus 100 of this embodiment is not limited to a ship, and is used. The technical scope of the present invention is determined based on the description of the scope of claims.

In FIG. 1, the ship 40 is viewed from the bottom side, and the ship 40 is shown with the bow side (front side) on the right side of the drawing and the stern side (rear side) on the left side of the drawing.
The bubble generating device 50 is disposed on the front side of the bottom of the ship 40. The bubble generating device 50 generates bubbles when the ship 40 navigates. The bubbles move while diffusing backward along the surface of the bottom of the ship 40 together with the water flow, and cover the flooded part of the bottom of the ship 40. Thereby, the frictional resistance of the water with respect to the bottom of the ship 40 at the time of navigation of the ship 40 is reduced.

  The vibrator 10 is provided on the bottom of the ship 40 between the bubble generating device 50 and the rear side of the ship. The vibrator 10 constitutes a part of the bubble detection device 100 (not shown in FIG. 1), outputs ultrasonic waves to the bubbles, and receives ultrasonic waves reflected from the bubbles. Hereinafter, the bubble detection device 100 including the vibrator 10 will be described in detail with reference to the drawings.

FIG. 2 is a block diagram illustrating a configuration of the bubble detection device 100. FIG. 3 is a diagram for explaining the function of the vibrator 10. FIG. 4 is a diagram showing a time change of the second electric signal 24.
The bubble detection device 100 includes a vibrator 10, a control device 20, and a display device 30.

The transducer 10 is an ultrasonic transmission / reception sensor, and is mounted on the underwater ship bottom as described above.
The transducer 10 converts the first electrical signal 23 from the transmission / reception unit 22 into ultrasonic waves, and from the bottom of the ship 40 toward the bow (in the direction opposite to the direction in which bubbles flow), as shown in FIG. ) An ultrasonic wave is transmitted to the water with an angle (a depression angle), for example, a depression angle of 75 °. The ultrasonic waves are directly reflected by the bubbles in the water, or are irregularly reflected (reflected and attenuated) between the transducer 10 and the bubbles and between the bubbles and are input to the transducer 10 again. Of course, the degree of reflection and diffuse reflection with respect to the ultrasonic wave differs depending on the size of the bubble, the density of the bubble in the water flow, the distance between the vibrator 10 and the water flow containing the bubble, and the width (thickness) of the water flow containing the bubble. It will be a thing. The thickness of the water flow is the thickness of the water flow including bubbles in the direction perpendicular to the traveling direction of the ship, that is, in the depth direction.
In FIG. 3, the thickness direction is divided into sections (regions) (1), (2), and (3). The received signal corresponding to the area (1) is a multiple reflection signal in the area (1). Further, the received signal corresponding to the region (2) includes the multiple reflection signal in the region (1). Further, it includes multiple reflection signals in the region (1) and the region (2) corresponding to the region (3).
Returning to FIG. 2, the transducer 10 converts an ultrasonic wave input as an echo (reverberation) from the water into a second electric signal 24 and outputs the second electric signal 24 to the transmission / reception unit 22.

As illustrated in FIG. 2, the control device 20 includes a signal processing unit 21 (control unit), a transmission / reception unit 22, and a storage unit 25.
The transmission / reception unit 22 generates a transmission wave (burst wave) used by the transducer 10 for ultrasonic transmission. Further, the transmission / reception unit 22 amplifies the ultrasonic wave as an echo into a reception signal by the transducer 10 and outputs the amplified reception signal (second electric signal 24) to the signal processing unit 21.
The signal processing unit 21 is configured by a microcomputer or the like, for example, and is connected to the transmission / reception unit 22. The signal processing unit 21 generates a first electrical signal 23 that is a pulse having a predetermined cycle from the transmission / reception unit 22. That is, the signal processing unit 21 drives the vibrator 10 with the first electric signal 23 to transmit a transmission wave (burst wave) used for ultrasonic transmission. In addition, the signal processing unit 21 captures the electric signal (second electric signal 24) amplified by the transmission / reception unit 22 as digital data, for example, by an A / D (Analog To Digital) converter. The signal processing unit 21 calculates a frequency at each time by performing a digital filter and signal processing on the captured digital data. The signal processing unit 21 confirms the frequency change amount (the spread of the frequency distribution) using the calculation result, and determines the presence / absence of bubbles generated by the bubble generation device 50, the size and density of the bubbles (details will be described later). .

The storage unit 25 stores in advance a frequency distribution (reference frequency) of a signal used when the signal processing unit 21 makes a determination.
Further, the display device 30 displays the bubble detection result by the signal processing unit 21. At the same time, the display device 30 outputs the bubble detection result to an external device, for example, in a format (format) according to the NMEA0183 specification used in dedicated communication for offshore equipment.

  The signal processing unit 21 receives the second electric signal 24 indicating the reflection level in FIG. In FIG. 4, the voltage level (reflection level) of the second electrical signal 24 is plotted on the vertical axis, the time immediately after the output of the first electrical signal 23 is time 0, and the time from time 0 is plotted on the horizontal axis. As shown in FIG. 4, the reflection level after the conversion of the ultrasonic wave reflected or diffusely reflected from the bubble into the second electric signal 24 has a waveform that attenuates with time. In FIG. 3, the level of the received signal shown after the transmission signal (the reflection level after conversion into the second electrical signal 24) corresponds to the areas (1), (2), and (3) shown in FIG. It can be seen that the waveforms decay with time. That is, the magnitude of this reflection level changes depending on the presence / absence of bubbles, the size and density of the bubbles.

The signal processing unit 21 performs signal processing, for example, fast Fourier analysis (FFT) on the reflection level after conversion into the second electric signal 24, thereby converting the frequency distribution of the received signal into the thickness direction regions (1), (2 ) And (3).
FIG. 5 is a diagram for explaining the presence / absence of bubbles and the detection of the shape by the signal processing unit 21. Each of FIGS. 5A to 5D shows the frequency analysis result of the received wave in which the power (Power) of the received wave is plotted on the horizontal axis of the frequency of the received wave. Moreover, in each figure, the transmission frequency is shown as a fundamental frequency.
FIG. 5A shows the frequency analysis result by the signal processing unit 21 when there is no bubble. As shown in FIG. 5A, when there is no bubble, the frequency distribution of the reception frequency with respect to the transmission frequency has a waveform with almost no peak because no reflection or Doppler effect occurs.
FIG.5 (b) has shown the frequency analysis result by the signal processing part 21 with respect to area | region (1) when there exists a bubble. As shown in FIG. 5B, the frequency distribution in the region (1) shifts to a higher frequency side than the fundamental frequency due to multiple reflection on the bubble surface, that is, a broad waveform. .

FIG.5 (c) has shown the frequency-analysis result by the signal processing part 21 with respect to area | region (2) when there exists a bubble. As shown in FIG. 5C, the frequency distribution in the region (2) also includes the multiple reflection signals in the region (1), so that the frequency distribution in the region (1) shown in FIG. FIG. 5D, which has a broader waveform, shows the frequency analysis result by the signal processing unit 21 for the region (3) when there is a bubble. As shown in FIG. 5 (d), the frequency distribution in the region (3) includes multiple reflection signals in the region (1) and the region (2), and thus in the region (2) shown in FIG. 5 (c). It becomes a broader waveform than the frequency distribution.

As described above, as shown in FIGS. 5A to 5D, the frequency analysis result by the signal processing unit 21 differs depending on the presence / absence of bubbles and the size and density of the bubbles.
Therefore, these frequency distributions are measured in advance by an experiment (an experiment for obtaining the size and density of bubbles and the frequency distribution in advance by the bubble generation device 50 shown in FIG. 1), and the reference frequency distribution (reference frequency distribution) is stored in the storage unit 25. Save it to a table. Thereby, the size and density of bubbles can be determined by the signal processing unit 21.
Further, when forming the table, the frequency distribution is measured by changing the thickness of the layer containing bubbles, and is stored in the storage unit 25 for each region. Thereby, it becomes possible to determine the thickness of the layer containing bubbles from the frequency distribution of each region by the signal processing unit 21.

The signal processing unit 21 compares the newly measured frequency distribution with the reference frequency distribution stored in the storage unit 25 as follows.
For example, the storage unit 25 stores the power with respect to the frequency in association with each of the above-described areas indicating the distance from the ship bottom, the size of the bubbles, and the density of the bubbles as a set.
For example, the signal processing unit 21 calculates a difference between a newly measured frequency distribution and a power reference frequency at an arbitrary frequency. Then, when each difference is within a predetermined error value in all frequencies for calculating the difference, it is determined that the bubble size and bubble density are the same as the bubble size and bubble density in the reference frequency distribution. To do. Further, a search in the storage unit 25 is performed until the bubble size and bubble density are determined.

  Further, the thickness of the water flow including bubbles is determined by performing the above search for each region and searching for a reference frequency distribution corresponding to the region. For example, if regions (1) and (2) are determined by matching the corresponding reference frequency distribution, but not determined for region (3), the thickness is the depth of region (1) and region (2). It is determined that the length is in the direction. Alternatively, when the reference frequency distribution is determined for the region (1) but not for the regions (2) and (3) (for example, when bubbles are formed in the region), the thickness is the region (1). It is determined to be the length in the depth direction.

  Note that when comparing the power at an arbitrary frequency, the number of points to be compared may be increased, and determination may be performed for many frequencies. With such a configuration, the newly measured frequency distribution matches with any of the reference frequency distributions stored in the storage unit 25, so that the shape of the bubbles (the size and density of the bubbles and the thickness of the water flow including the bubbles). ) Can be detected. In addition, when there is no bubble data corresponding to the storage unit 25, a configuration may be adopted in which the user is informed that there is no bubble corresponding to the user via the display device 30. The new bubble data may be stored in the storage unit 25, and the new bubble may be detected from the next bubble detection. Also, the state of the detected bubbles is not always the same. Therefore, at the time of bubble detection, measurement is performed a plurality of times, the average of the obtained frequency distributions is obtained, that is, the average value of power at an arbitrary frequency in the frequency distribution is obtained, and the frequency distribution indicated by this average value May be used as a new frequency distribution to perform the above-described comparison calculation. In this way, it is possible to improve the detection accuracy when detecting the presence / absence of bubbles and the shape of bubbles.

  Further, at the time of comparison, the newly measured frequency distribution is displayed on the display device 30, the user reads the reference frequency from the storage unit 25, and the comparison between the newly measured frequency distribution and the reference frequency distribution is performed on the display device 30. It is good also as a structure to perform.

  As described above, the bubble detection device 100 of the present invention transmits an ultrasonic wave having a predetermined frequency to a bubble to be measured, receives a reflected wave from the bubble, and generates an electric signal (second electric signal 24). A transducer 10 to be converted and a control device 20 that drives the transducer 10 and processes the second electrical signal 24 are provided. The control device 20 calculates the frequency change amount of the second electrical signal 24, compares the calculated frequency change amount with a preset frequency change amount, and according to the comparison result, the presence or absence of bubbles, Detect the size and density of bubbles.

  According to the present invention, it is not necessary to arrange the control device 20 that constitutes the bubble detection device 100 together with the vibrator 10 in water, so that it is not necessary to perform periodic replacement. In addition, since the vibrator 10 vibrates when bubbles are generated during running or the like, the period during which the vibrator 10 is placed in a stationary state in seawater is small, and the possibility that organisms will adhere is low. Work is hard to occur. Therefore, the cost for detecting bubbles can be reduced as compared with the conventional case. Further, the control device 20 calculates the frequency change amount of the electric signal (second electric signal), compares the calculated frequency change amount with a preset frequency change amount, and according to the comparison result, The presence / absence of bubbles, the size and density of bubbles are detected. Therefore, it is possible to newly provide a bubble detection device that does not require complicated signal processing such as image processing and can easily detect the presence or absence of bubbles.

In the bubble detection device 100 of the present invention, the frequency change amount (reference frequency distribution) set in advance is, for example, a plurality of regions depending on the distance from the transducer 10 in the direction in which the bubbles of the transducer 10 are transmitted. A plurality of numbers corresponding to (1) to (3) are set, and the control device 20 compares the calculated frequency change amount with each of the frequency change amounts set in accordance with the comparison result. The thickness of the containing layer is detected.
Thereby, the thickness of the layer containing bubbles can also be measured from the frequency distribution of each region (1) to (3).

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes modifications and the like without departing from the gist of the present invention.
For example, in the description of the above embodiment, the area (1) to (3) is divided into three areas. However, the number of areas set from the ship bottom is not three but may be an arbitrary number. By increasing the number of divisions and storing the reference frequency distribution in the storage unit 25 according to the number of divided regions, the accuracy of comparison increases, and the presence / absence of bubbles, the size and density of bubbles, and the layer containing bubbles Can be detected with high accuracy.

  In the above description of the embodiment, the configuration in which one vibrator 10 is provided on the bottom of the ship 40 has been described. However, a plurality of vibrators 10 may be arranged at different positions. In this case, one control device 20 individually processes each of the second electric signals 24 input from the vibrator 10 to determine whether there is a bubble at the position where each vibrator 10 is provided, It may be configured to detect the shape. In addition, when there is a difference between the bubble detection results obtained by the vibrators 10 as described above, the shape of the bubbles generated by the bubble generation device 50 may be changed. For example, it is assumed that two vibrators 10 are arranged on the bottom of the ship 40 so as to be located at the same distance from the center line from the bow to the stern. When the ship 40 is traveling straight, it is desirable that bubbles of the same shape are detected by the left and right vibrators 10 in view of propulsion efficiency such as fuel efficiency of the ship 40. Therefore, when bubbles of the same shape are not detected by the left and right vibrators 10, the amount of bubbles generated by the bubble generator 50 is different on the left and right so that the shapes of the bubbles detected by the left and right vibrators 10 are the same. It is good also as a structure which controls to improve the propulsion efficiency of the ship 40.

  DESCRIPTION OF SYMBOLS 10 ... Vibrator, 20 ... Control apparatus, 21 ... Signal processing part, 22 ... Transmission / reception part, 23 ... 1st electric signal, 24 ... 2nd electric signal, 25 ... Memory | storage part, 30 ... Display apparatus, 40 ... Ship 50 ... Bubble generating device

Claims (4)

A transducer that transmits ultrasonic waves of a predetermined frequency to a bubble to be measured, receives a reflected wave from the bubble, and converts it into an electrical signal;
A controller for driving the vibrator and processing the electrical signal;
A bubble detection device comprising:
The control device calculates a frequency change amount of the electrical signal, compares the calculated frequency change amount with a preset frequency change amount, and according to a comparison result, whether the bubble is present or not, A bubble detection device that detects size and density. The frequency change amount is a spread of a peak with respect to a transmission frequency in a frequency distribution of the electrical signal.
The bubble detection device according to claim 1. A plurality of the preset frequency change amounts are set in accordance with the distance from the vibrator with respect to the direction in which bubbles of the vibrator are transmitted,
The control device compares the calculated frequency change amount with each of the plurality of frequency change amounts that are set, and detects the thickness of the layer containing bubbles according to the comparison result.
The bubble detection device according to any one of claims 1 and 2.   The bubble detection device according to any one of claims 1 to 3, wherein the bubble is a bubble generated by a bubble generation device provided on a ship bottom.

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