JP7128724B2 - Wave height calculation method - Google Patents

Description

The present invention mainly relates to a wave height calculation method for calculating wave height at a construction site such as marine construction.

At work sites such as harbors, it is necessary to grasp the actual wave height from the viewpoint of safety, and wave height gauges are installed in the work area.

Conventionally, as wave gauges, there are seafloor type, air radiation type, buoy type wave gauges, and the like.

However, seafloor-mounted wave gauges capture changes in the water surface using measuring instruments such as ultrasonic sensors and water pressure sensors installed on the seafloor. There was a problem that the work was not easy, and installation was difficult especially in a deep water area of 50 m or more.

In order to acquire real-time data from this seafloor-mounted wave height gauge, since it is difficult to transmit data wirelessly underwater, the seafloor measuring instrument is connected with a relay buoy on the sea or equipment on a work boat with a cable. There was a problem that it was necessary to

An airborne wave height gauge emits ultrasonic waves vertically toward the sea surface from a device installed on an offshore structure, etc., and detects changes in the water surface from its reflection. In this case, the angle of emission of the ultrasonic waves and the position of the device that transmits and receives the ultrasonic waves fluctuate due to the rocking of the work boat, so it is necessary to correct the measured values in consideration of the fluctuations, and the calculation is complicated. was there.

On the other hand, the buoy-type wave height meter floats a buoy with a built-in measuring instrument on the sea surface and measures the vertical displacement of the buoy following changes in the water surface. , and light buoys can be installed manually.

Buoy-type wave gauges mainly measure the vertical acceleration of a buoy that follows changes in the water surface using an acceleration sensor, and integrate the acceleration twice over time to calculate the vertical displacement of the water surface. used (see, for example, Patent Document 1).

In addition, when observing waves, waves of 3 seconds or more are usually targeted, and the period of data acquisition is often less than 0.5 seconds (frequency of 2 Hz). Individual wave heights are calculated using the zero up-cross method or the like.

For example, if a wave has an average period of 6 seconds, about 100 waves will be observed when measuring for 10 minutes. treated as a wave period.

JP-A-8-278130

However, in the conventional buoy-type wave height meter as described above, if noise is included in the measurement data of the measured acceleration, it is necessary to remove the influence of noise. There is a problem that it is difficult to convert the displacement in the vertical direction, that is, the wave height.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a wave height calculation method capable of simply and accurately calculating wave height using a floating body such as a buoy.

The feature of the invention according to claim 1 for solving the conventional problems as described above is a wave height calculation method for calculating the wave height by measuring the acceleration of a floating body floating on the water, based on the measurement result of the acceleration Calculate the acceleration component frequency spectrum, convert the acceleration component frequency spectrum to the water level component frequency spectrum using the ratio of the frequency spectrum corresponding to the water level, the frequency spectrum corresponding to the velocity, and the frequency spectrum corresponding to the acceleration, and the water level component The object is to obtain the zero-order moment of the frequency spectrum density by integrating the frequency spectrum in a predetermined frequency range, and to calculate the wave height from the zero-order moment of the frequency spectrum density.

A feature of the invention according to claim 2 is that, in addition to the configuration of claim 1, the predetermined frequency range is 0.1 to 0.3 Hz.

The feature of the invention according to claim 3 is that, in addition to the configuration of claim 1 or 2, the frequency range is 0.1 to 0.3 Hz. is to be calculated.

A feature of the invention according to claim 4 is that, in addition to the configuration according to any one of claims 1 to 3, the floating body has transmission means for transmitting measurement data of the acceleration to the outside.

The wave height calculation method according to the present invention can calculate the wave height using a simple acceleration sensor without depending on the water depth of the installation water area by having the configuration described in claim 1, and the device can be miniaturized. can be achieved. Moreover, in this calculation method, even if noise occurs when measuring the acceleration of the floating body, the wave height can be calculated without being affected by the noise.

Moreover, in the present invention, by providing the configuration according to claim 2, the influence of spike noise can be eliminated.

Furthermore, in the present invention, by providing the configuration according to claim 3, it is possible to calculate the period together with the wave height.

Furthermore, in the present invention, by providing the configuration according to claim 4, the measurement data of acceleration can be transmitted to an external computer device or the like at any time, and the wave height can be calculated in real time.

It is a side view which shows the outline of the apparatus used for the wave-height calculation method which concerns on this invention. FIG. 2 is a cross-sectional view showing a floating body in FIG. 1; 4 is a graph showing the relationship between frequency spectrum and frequency corresponding to water level, velocity and acceleration; It is a graph which shows the relationship between water level / speed ratio, speed / acceleration ratio, and frequency.

Next, embodiments of the wave height calculation method according to the present invention will be described based on the embodiments shown in FIGS. 1 to 4. FIG. FIG. 1 is a schematic diagram showing an example of a wave height measuring device used in the present invention.

This wave height measuring device comprises a floating body 1 such as a buoy floating on the water surface and an acceleration sensor 2 built in the floating body 1, so that the acceleration of the floating body 1 that moves up and down due to fluctuations in water level caused by waves or the like can be measured. It's becoming

In the figure, reference numeral 3 denotes a mooring rope for mooring the floating body 1 to the bottom of the water 4, reference numeral 5 denotes a work boat, and reference numeral 6 denotes a computing device such as a computer.

In addition, the floating body 1 is provided with a transmission means 7 for transmitting the measurement data to the outside of the floating body 1, and a computing device such as a computer device installed outside the work ship 5 or on the ground (in this embodiment, the work ship 5). Measurement data is transmitted to the device 6 at any time, and the wave height is calculated in real time from the measurement data by the computing device 6 .

The floating body 1 is provided with a power source 8 such as a battery for supplying power to the acceleration sensor 2 and the transmission means 7 .

Next, a specific wave height calculation method using the above device will be described below.

First, when the floating body 1 is floated in a predetermined water area and the measurement of the acceleration accompanying the vertical movement of the floating body 1 is started, the measurement result is transmitted by the transmission means 7 to the computing device 6 such as a computer device at any time.

The computing device 6 first calculates the acceleration component frequency spectrum A(f) based on the time-series acceleration data of the floating body 1 that are transmitted as needed.

Next, the arithmetic unit 6 converts the acceleration component frequency spectrum A(f) into the water level component frequency spectrum E(f) using the ratio of the frequency spectrum corresponding to the water level, the frequency spectrum corresponding to the velocity, and the frequency spectrum corresponding to the acceleration. Convert to

In general, the water level measured using a wave gauge that can measure water level with high accuracy, such as an ultrasonic wave gauge, is differentiated once with respect to time to obtain the velocity, and further differentiated once with respect to time to obtain the acceleration. .

Therefore, when the relationship between the frequency spectrum and the frequency corresponding to the time series of the water level, velocity and acceleration is obtained, the relationship shown in FIG. 3 is obtained.

Also, based on this result, frequency spectrum corresponding to water level/frequency spectrum corresponding to speed (hereinafter referred to as water level/speed ratio), frequency spectrum corresponding to speed/frequency spectrum corresponding to acceleration (hereinafter speed/acceleration (referred to as a ratio) yields the relationship shown in FIG.

As shown in FIG. 4, the water level/velocity ratio is 1 near the frequency of 0.159 Hz, exceeds 1 in the range of frequencies greater than 0.159 Hz, and exceeds 1 in the range of frequencies less than 0.159 Hz. Exceed.

On the other hand, the velocity/acceleration ratio also becomes 1 near the frequency of 0.159 Hz, exceeds 1 in the range of frequencies higher than 0.159 Hz, and exceeds 1 in the range of frequencies lower than 0.159 Hz.

The water level/velocity ratio and the velocity/acceleration ratio are approximately on the approximation line 0.0286f ^-1.961 shown in FIG. . That is, the acceleration component frequency spectrum A(f) and the water level component frequency spectrum E(f) are in a proportional relationship within the frequency f range of 0.1 to 0.3 Hz.

Therefore, by using this relationship, the acceleration component frequency spectrum A(f) is obtained from the measured acceleration of the floating body 1, and the water level component frequency spectrum E(f) is obtained from the acceleration component frequency spectrum A(f). can be converted to

When the water level component frequency spectrum E(f) is obtained, the arithmetic device 6 integrates the water level component frequency spectrum E(f) in a predetermined frequency range using the following formula to obtain the zero-order frequency spectrum density Find the moment (total energy) m ₀ .

formula 1

At that time, the problem in offshore construction is waves with a frequency of about 0.1 Hz (period of 10 seconds) to 0.3 Hz (period of 3.33 seconds). Limited to 0.3 Hz.

In this frequency range, even if noise occurs during measurement of the acceleration of the floating body 1, if it is spike noise, the energy is about 2 Hz, which is outside the range of energy aggregation. can be ignored.

Then, when the _zero -order moment (total energy) m0 of the frequency spectral density is obtained, the arithmetic device 6 calculates the wave height H from the _zero -order moment m0 of the frequency spectral density by the following equation.

formula 2

Further, the computing device 6 calculates the period T by dividing the negative first-order moment m ₋₁ of the water level component frequency spectrum by the zero-order moment m ₀ of the water level component frequency spectrum according to the following equation.

Formula 3

The wave height calculation method configured in this way does not use the conventional double integration by time from the measurement data of the acceleration of the floating body 1, but converts the acceleration component frequency spectrum A(f) into the water level component frequency spectrum E (f), and integrate the water level component frequency spectrum E(f) in a predetermined frequency range (0.1 ≤ f ≤ 0.3) to obtain the _zero -order moment m0 of the frequency spectrum density, so acceleration measurement Even if noise occurs at times, the wave height H can be calculated ignoring the influence of the noise.

Therefore, the acceleration sensor 2 used for measurement can be simple, and the device cost can be reduced accordingly, and the size of the device can be reduced.

In addition, since the acceleration sensor 2 is built into the floating body 1 such as a buoy, the wave height of the water area can be easily obtained without depending on the water depth of the water area to be measured unlike a seabed-mounted wave height meter.

Furthermore, the floating body 1 is provided with a transmission means 7, and by transmitting measurement data of acceleration at any time to a work boat 5 or an arithmetic device 6 composed of an external computer device installed on the ground, wave height can be simply and in real time. It is possible to construct an observation system that can obtain

In the above-described embodiment, an example of calculating the period based on Equation 3 has been described, but the period may be calculated using other methods.

Further, in the above-described embodiment, an example in which the floating body 1 is moored to the bottom of the water has been described. good.

Furthermore, in the above-described embodiment, an example in which the floating body 1 such as a buoy is provided with the transmitting means 7 has been described.

1 Floating body 2 Acceleration sensor 3 Mooring rope 4 Bottom of water 5 Work boat 6 Computing device 7 Transmitting means 8 Power supply

Claims (4)

In the wave height calculation method for calculating the wave height by measuring the acceleration of a floating body floating on the water,
An acceleration component frequency spectrum is calculated based on the measurement result of the acceleration, and the acceleration component frequency spectrum is converted to the water level component frequency using the ratio of the frequency spectrum corresponding to the water level, the frequency spectrum corresponding to the velocity, and the frequency spectrum corresponding to the acceleration. A wave height calculation method characterized by converting into a spectrum, integrating the water level component frequency spectrum in a predetermined frequency range to obtain a zero-order moment of the frequency spectrum density, and calculating a wave height from the zero-order moment of the frequency spectrum density. . The wave height calculation method according to claim 1, wherein the predetermined frequency range is 0.1 to 0.3 Hz. The wave height calculation method according to claim 1 or 2, wherein the period is calculated from the minus first moment and the zeroth moment of the water level component frequency spectrum whose frequency range is 0.1 to 0.3 Hz. The wave height calculation method according to any one of claims 1 to 3, wherein the floating body comprises transmission means for transmitting measurement data of the acceleration to the outside.

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