JP3362980B2 - Absorption type wave making device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an absorption type wave forming device for generating a desired wave in a closed channel for hydraulic experiments, which is used for analyzing characteristics of a structure against waves.

[0002]

BACKGROUND OF THE INVENTION It is well known in the art to reproduce physical models of ocean engineering phenomena in closed channels in a laboratory environment in order to solve various problems in ocean engineering. The closed channel for hydraulic experiments used for this purpose is equipped with a wave generator, but the existence of reflected waves must be considered in the physical model of the waves in the wave experimental channel.

That is, in the natural environment, the sea is an open boundary type and absorbs the waves reflected by the coastal work, while the wave-making experimental canal has a closed boundary type structure and is a test placed in the canal. The wave reflected by the structure enters the wave-making plate as a reflected wave and is reflected again by the wave-making plate, so that the characteristic of the wave train incident on the test structure becomes different from the target.
For this reason, in particular, in a hydraulic experiment for a reflection type test structure, it is often impossible to reproduce the desired specific incident wave train.

Such a problem of reflection can be suppressed by using a so-called absorption type wave forming device.
This absorption type wave forming device is a combination of a wave forming device and an active wave canceling device, and in addition to generating a target incident wave to the test structure, it also absorbs a reflected wave from the test structure.

As a conventional absorption type wave making device, for example, "Development of reflected wave absorption type wave making system and basic characteristics" by Koyama et al. (Proceedings of the 35th Coastal Engineering Lecture Meeting, pp.25-29, 198)
8).

In this system, a water level measurement feedback system using a personal computer is added to a normal position control type wave making device so as to always have optimum absorption characteristics for reflected waves of various periods. Basically, the theory of wavemaking (F.
Biesel and F. Suquet; Les apparails g * n * rateusde
houle en laboratoire, La Houille Blanche, Vol.6, N
os.2,4 et 5, 1951) and Milgram's theory of absorption (J.
S. Milgram; Active water-wave absorbers, Journal of
Fluid Mech., Vol. 43, Part 4, pp.845-859, 1970) is used to control the position of the wave-making plate based on the measured water level information in front of the wave-making plate (G.
Gilbert; Absorbing Wave Generators, Hydraulic Re
serchStation Note 20, pp.3-4, 1978), but in order to specifically apply it to actual control, a corrugated plate for simultaneously performing predetermined wave generation and reflected wave absorption. Is a formalization of the position control of.

There is also a report of converting a conventional wedge paddle wave maker to an absorption wave maker (GN Bullock and GJ Murton; Performance of a
Wedge-Type Absorbing Wave Maker, Journal of Water
way, Port, Coastal and Ocean Engineering, Vol. 115,
No. 1, January, 1989). This modified system was based on analog filtering of the water level signal measured just before the wave-making plate, and although the circuit design was not always perfect, the wave-dissipation characteristics were relatively excellent. .

[0008]

In the conventional absorption type wave making device of any of the above-mentioned forms, since the signal obtained by analog-filtering the water level measurement signal is used as the feedback, the wave generally generated by the wave making device is generated. Considering that it is a distorted wave, non-uniformity of phase delay for various frequency components in the filter becomes a problem, and since it is basically a method of servo-controlling the position of the wave-making plate, it is complicated for absorption control. Computational processing was required, making real-time feedback control with water level measurement signals difficult. It is an object of the present invention to provide an absorption-type wave making device capable of simplifying a complicated arithmetic processing system and enabling stable feedback control in real time.

[0009]

SUMMARY OF THE INVENTION An absorption type wave making device according to the present invention comprises a wave making plate provided in a closed water channel of finite length, a driving device for driving the wave making plate according to an input signal, and a wave making device. A signal generator that generates a plate displacement command signal, a crest meter that measures the liquid level change immediately before the corrugated plate, and a drive device that adds a feedback signal based on the measurement signal of the crest meter to the command signal from the signal generator And feedback means for inputting to
An absorption-type wave-making device that absorbs a reflected wave incident on a wave-making plate to prevent a re-reflected wave from being generated by the wave-making plate and causes the wave-making plate to perform a target wave-making motion. In order to solve the above, the wave height meter includes a plurality of wave height meters for measuring liquid level changes at a plurality of positions separated from each other by different distances from the front surface of the wave making plate, and the feedback means includes a plurality of wave height meters. The liquid level measurement signal includes a digital filter that filters the signal with a predetermined phase shift amount and gain, and an addition unit that adds the outputs of the respective digital filters, and the output from the addition unit is used as a feedback signal. It is characterized by having done.

According to another aspect of the present invention, in the absorption-type wave making device, the wave height meter includes a plurality of wave height meters for measuring liquid level changes at different positions in the width direction of the water channel. It is a waste.

[0011]

In the absorption type wave making device of the present invention, the wave making plate is driven and controlled by the wave making command signal corrected by the online feedback signal from the digital filter operating in real time. The water surface height, that is, the liquid level change, is measured at a plurality of positions at different distances immediately before the corrugated plate,
The respective measurement signals are digitally filtered in order to separate the reflected wave train from the sum of the incident wave and the reflected wave train, and then superimposed on each other to form a feedback signal. This feedback signal determines the movement of the wave-making plate necessary to absorb the reflected wave, and when added to the wave-making command signal, the wave-making / absorption command signal corrected by the feedback signal is obtained. The wave-making plate, which is input to the drive device, performs a desired wave-making motion including a motion necessary for absorbing the reflected wave.

The digital filter used in the present invention is a so-called finite impulse response filter (FIR filter), and the relationship between the input η and the output χ (both are finite discrete time signals) of the FIR digital filter of length N is generally as follows. It is expressed by the convolution (discrete composite product) of equation (1) (reference: JH Karl, 1989; An Introductionto
Digital Signal Processing, Academic Press, San Dia
go).

[0013]

[Equation 1]

In the equation (1), h is a filter impulse response (filter operator), and the filter operator corresponding to the desired set frequency response characteristic is a fast Fourier transform of the discrete inverse Fourier transform of the composite frequency response function. It can be obtained by executing computer calculation such as.

Here, the filter output is M compared to the input.
It should be noted that there is a delay of = (N-1) / 2 steps, and for FIR filters operating in real time this delay must be removed.

Therefore, in the present invention, the liquid level is measured at a plurality of positions at different distances immediately before the wave-making plate, the respective measurement signals are filtered by the FIR filter and then added to each other to add the above delay. Substantially removed. The feedback signal obtained in this way is a correction signal that gives the displacement of the wave-making plate necessary to absorb the reflected wave, and this correction feedback signal is sent from the signal generator for the active absorption of the reflected wave. It is added to the read wave formation command signal, and as a result, the wave formation plate is operated by the drive device in the combination of wave formation / wave elimination mode.

Now, the setting of the frequency response characteristic of the FIR filter for eliminating the above-mentioned delay in the case where two wave height meters for measuring the liquid level and two FIR filters are provided will be described below.

The liquid level measurement signal at the position of the distance x from the front of the wave-making plate of the wave-making experiment channel can be considered as the sum of frequency components of various orders. Considering the isolated component of the frequency f, the liquid level generated from this frequency component can be regarded as the sum of the incident wave component and the reflected wave component of the corresponding frequency, which is expressed by the following equation (2). .

[0019]

[Equation 2] η (x, t) = η _I (x, t) + η _R (x, t) = a _I cos (2πft − kx + φ _I ) + a _R cos (2πft + kx + φ _R ) (2)

In equation (2), a = a (f) represents the amplitude of the wave, k = k (f) represents the wave number, φ = φ (f) represents the phase, the subscript I represents the incident wave, and R represents the reflected wave. Represents each wave. Here, the wave forming command signal (wave forming plate displacement signal) given the frequency f
Assuming that a linear relationship is established between this and the corresponding liquid level change, the wave plate displacement correction signal for canceling the reflected wave component without disturbing the incident wave component is expressed by the following equation (3). Is the street.

[0021]

[Number 3] _{X corr (t) = B ·} a R cos (2πft + φ R + φ B + π) (3)

Here, B is a coefficient determined by the ratio of the mechanical stroke amount of the drive system of the corrugated plate and the wave height of the wave generated thereby, φ _B is the displacement of the corrugated plate and the liquid level on the corrugated plate surface. It is the amount of phase shift between.

The liquid level measurement signal measured by the first wave height meter at a position x ₁ from the front surface of the wave making plate is η (x ₁ , t), and the second wave height is at a position x ₂ from the front surface of the wave making plate. When measured with a meter and the liquid level measurement signal is η (x ₂ , t),
Η (x ₁ , t) is passed through a first FIR filter with a phase shift amount φ ₁ ^theo , and η (x ₂ , t) is passed through a second FIR filter with a phase shift amount φ ₂ ^{theo at} a specific gain C. By summing the filter outputs of the two, the same feedback signal as the correction signal of equation (3) can be obtained as described below.

That is, the liquid level measurement signals of the two wave height meters can be expressed as follows.

[0024]

[Equation 4] η (x ₁ , t) = a _I cos (2πft − kx ₁ + φ ₁ ) + a _R cos (2πft + kx ₁ + φ _R ) (4)

[0025]

[Equation 5] η (x ₂ , t) = a _I cos (2πft−kx ₂ + φ ₁ ) + a _R cos (2πft + kx ₂ + φ _R ) = a _I cos (2πft−kx ₁ −kΔx + φ ₁ ) + a _{R cos (2πft + kx 1 + kΔx} + φ R) (5)

Here, Δx in the equation (5) is Δx =
x ₂ −x ₁ .

If the gain of the FIR filter is C and its theoretical phase shift amount is φ ^theo and these are introduced into the equation (2), the filtered corrected liquid level signal η ^* (x _i, t as shown below is obtained. ) Is obtained (i = 1, 2, ...
・).

[0028]

[Equation 6] η ^* (x _i, t) = Ca _I cos (2πft − kx _i + φ _I + φ _i ^theo ) + Ca _R cos (2πft + kx _i + φ _R + φ _i ^theo ) (6)

Therefore, regarding the liquid level measurement signal of the first wave height meter, the corrected liquid level signal of the following formula (7) is provided, and regarding the liquid level measurement signal of the second wave height meter, the corrected liquid level signal of the following formula (8) is used. Obtained from the first and second FIR filters respectively.

[0030]

[Equation 7] η ^* (x ₁ , t) = Ca _I cos (2πft−kx ₁ + φ _I + φ ₁ ^theo ) + Ca _R cos (2πft + kx ₁ + φ _R + φ ₁ ^theo ) (7)

[0031]

Η ^* (x ₂ , t) = Ca _I cos (2πft−kx ₁ − kΔx + φ _I + φ ₂ ^theo ) + Ca _R cos (2πft + kx ₁ − kΔx + φ _R + φ ₂ ^theo ) (8)

The sum η ^calc (t) of the outputs of the first and second FIR filters is expressed by the following equation (9).

[0033]

[Equation 9]

Η ^calc (t) expressed by the equation (9) and X _corr (t) expressed by the above equation (3) are expressed by the following (1)
When the conditions of 0), (11) and (12) are satisfied, the signals are the same.

[0035]

[Equation 10]

[0036]

[Equation 11]

[0037]

[Equation 12]

In equations (10), (11) and (12), n = m = 0
Then, when solutions are obtained for φ ₁ ^theo , φ ₂ ^theo and C, the following equations (13), (14) and (15) are obtained.

[0039]

[Equation 13] φ ₁ ^theo = φ _B − kΔx − kx ₁ + 3π / 2 (13)

[0040]

[Equation 14] φ ₂ ^theo = φ _B −kx ₁ + π / 2 (14)

[0041]

[Equation 15]

The frequency response characteristics of the first and second FIR filters are set as shown in the above equations (13), (14) and (15), and the output of each crest meter is A / D converted and digitally filtered. As a result, the drive device can be controlled in real time by the corrected online corrugated plate displacement signal for applying the desired target incident wave that has absorbed the influence of the reflected wave to the test structure. In the present invention, the liquid level measurement position immediately before the corrugated plate is not limited to two, and the setting of the frequency response characteristic of the filter becomes a little complicated, but a plurality of different water channel length and width directions are used. The level-measured liquid level signal may be used to further improve the wave-dissipation function.

[0043]

EXAMPLE An example in which an active absorption wave-making system is constructed by installing the absorption wave-making device of the present invention in an experimental waterway will be described below. Figure 1 shows an experimental wave-making canal 1 (water depth 5
The present invention is applied to a control system of a piston type wave machine 2 installed at 0 cm).
Generates a wave in the water channel 1 by the corrugating plate 4 that reciprocates by the drive piston device 3 at the end of the water channel 1.

A first wave height meter 11 for measuring the height of the water surface is arranged at a position x ₁ = 1.80 m from the front surface of the wave-making plate 4,
Similarly, a second wave height meter 12 for measuring the water surface height is also arranged at a position of x ₂ = 2.10 m from the front surface of the wave making plate 4.
The output of the first crest meter 11 is digitized by the A / D converter 21 and then input to the first FIR filter 31, and the second
Similarly, the output of the wave height meter 12 is digitized by the A / D converter 22 and then input to the second FIR filter 32.

First and second FIR filters 31, 3
The liquid level measurement signals that have passed through 2 and are corrected are added up by the adder 40, and are input to another adder 5 as a feedback signal that gives a correction amount of the wave plate displacement for absorbing the reflected wave. The adder 5 adds the feedback signal to a target wave formation command signal for a hydraulic experiment output from the signal generator 6, and the added output is a drive piston device for reciprocating the wave forming plate 4. 3 as a drive signal. In this embodiment, the FIR filter 3
In the feedback system including 1, 32 and the adders 40 and 5, the frequency response characteristic of the FIR filter is as described in (13).
The phases φ _B and the gain B as the active wave-absorption absorption wave making system were set so as to satisfy the expressions (14) and (15), and were determined by using the first-order conversion function by the bezel according to the above (3). The main part of the system is the A / D converter and D
It is constructed by a board card equipped with an A / A converter and a personal computer.

At the other end of the waterway 1, a sloped beach 7 having a wave-dissipating structure is provided.
Is installed, and in order to carry out an experiment in which the magnitude of the reflected wave from the waterway end is changed, the corrugated plate 4 is placed in front of the inclined beach 7.
The vertical reflection wall 8 can be arranged at a position 17.4 m from the front surface of the. Further, in the water channel 1, reference wave height meters 51, 52, 53 for measuring reflected waves are provided at positions of 3.0 m, 3.1 m, and 3.3 m from the front surface of the wave-making plate 4, respectively. . These wave height meters 51, 52, 53 give measurement data to the reflected wave measuring device 50.

By the active absorption wave making system of this embodiment,
For the purpose of evaluating the absorption effect of the absorption type wave generator for the irregular wave test using the experimental structures with different degrees of reflection, with and without active wave cancellation, and wave cancellation structure (gradient A test was conducted to cover all permutation combinations of these four kinds of conditions when either the beach) or the reflection wall was provided at the end of the waterway.

All the tests were carried out with exactly the same input from the signal generator 6, that is, the significant wave height H _S = 0.04 m, the peak frequency f _P = 0.6 Hz and the frequency f _S = 40 Hz. = 3.3, and the wave plate displacement signal corresponding to the JONSWAP spectrum generated by digital filtering in the time domain of Gaussian white noise was used. In addition, the method by Manzard and Funke (E. Mansrd and E. Fun
ke, 1980; The Measurement of Incident and Reflected
Spectra Using a Least Method, Proceedings, 17th I
nternationalConference on Coastal Engineering, Vo
L.1, p.154-172, Sydney, Australia.) Spectral decomposition of incident wave and reflected wave was performed. The spectrum of the incident wave under each condition is shown in FIG.

As a result of the test, it was found that only 5 to 10% of the incident wave energy in the frequency range of the input spectrum is reflected by the wave-dissipating structure of the beach 7. Disturbances due to this degree of reflection are negligible, and therefore the incident spectrum, labeled "beach, no absorption" in Figure 2, can be considered the target spectrum.

The incident spectrum shown as "beach, with absorption" in FIG. 2 is almost the same as the target spectrum. This indicates that there is no disturbance in the incident spectrum when the system is tested using experimental equipment with almost no reflection.

The efficiency of this system is proved by the experimental results "reflective wall, no absorption" and "reflective wall, absorption" with the reflective wall 8 installed at the end of the water channel 1. In Fig. 2, "Reflection wall without absorption" without absorption
There is significant reflection distortion in the incident spectrum in the case of, but the incident wave spectrum in the case of "reflection wall with absorption" with active wave-off shows a very good agreement with the target spectrum.

The following experiment was conducted to visualize the effect of active absorption in the time domain. First, the reflection wall 8 was erected at the end of the water channel 1 to generate an irregular wave. After 60 seconds, wave formation was stopped and active wave extinction was activated. FIG. 3 shows the result of time-sequentially recording the measurement data of the wave height meter 51 at the position of x = 3.0 m by the measuring device 50. 3A shows a change in water surface height when active wave cancellation is performed, and FIG. 3B shows a change in water surface height when active wave cancellation is not performed.

Further, for the purpose of testing the stability of the apparatus, a reflecting wall 8 was set up at the end of the water channel 1 and an active wave canceling system was used to measure the displacement of the wave-making plate with a time series length T = 51.2 seconds. It was repeatedly generated and sent to a wave generator. t = T and t = 2
FIG. 4 shows the result of decomposing the spectra of the incident wave and the reflected wave by recording the fluctuation of the water surface height due to two kinds of waves having a time series length T each starting at 5T. As can be seen in Figure 4,
Even if the input signal is repeated 25 times (wave formation for about 20 minutes), there is no significant disturbance in the incident spectrum despite the reflection from the reflection wall at the end of the water channel, and therefore the stability of the device is improved. It turns out to be sufficient.

[0054]

As described above, in the absorption type wave making device of the present invention, the liquid level is measured at a plurality of positions having different distances immediately before the wave making plate, and each liquid level measurement signal is digitally filtered. After that, the movement of the wave-making device required for wave-dissipation is determined by superimposing it, so it exhibits excellent wave-dissipation performance even when the reflection level is extremely high, and it also performs complicated arithmetic processing. Since it does not exist, it is useful as an absorption-type wave-making device that operates stably in real time, and it can also be achieved by modifying the feedback system of an existing wave-making device.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment in which an absorption-type wave-making device of the present invention is installed in an experimental waterway to construct an active absorption wave-making system.

FIG. 2 is a graph showing spectrum measurement results of incident waves under various conditions by the system of the embodiment.

FIG. 3 is a measurement graph showing changes over time in water surface showing the results of confirmation of the wave-dissipating effect by the system of the example.

FIG. 4 is a spectrum decomposition graph of an incident wave showing a result of confirmation of stability of the system of the example.

[Explanation of symbols]

1: Experimental channel 2: Wave maker 3: Drive piston device 4: Corrugated plate 5: Adder 6: Signal generator 7: Wave-dissipating structure slope beach 8: Reflection wall 11: 1st wave height meter 12: Second altimeter 21: A / D converter 22: A / D converter 31: First FIR filter 32: Second FIR filter 40: Adder (adding means)

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01M 10/00 G01C 13/00

Claims (2)

(57) [Claims] 1. A corrugated plate provided in a closed water channel of finite length,
A driving device that drives the wave-making plate according to the input signal, a signal generator that generates a wave-making plate displacement command signal, a wave height meter that measures the liquid level change immediately before the wave-making plate, and a measurement signal of the wave height meter. A feedback means for adding a feedback signal based on this to the command signal from the signal generator and inputting it to the drive device is provided, and the reflected wave incident on the wave-making plate is absorbed to prevent generation of a re-reflected wave by the wave-making plate. In the absorption type wave making device which causes the wave making plate to perform a target wave making movement while the wave height meter is a plurality of wave height meters for measuring liquid level changes at a plurality of positions separated from each other at different distances from the front side of the wave making plate. The feedback means adds the outputs of the digital filters and the digital filters for filtering the liquid level measurement signals of the plurality of wave height meters with predetermined phase shift amounts and gains, respectively. That includes adding means, absorption wave-device being characterized in that so as to use the output from said adding means as a feedback signal. 2. The absorption type wave making device according to claim 1, wherein the wave height meter includes a plurality of wave height meters for measuring liquid level changes at different positions in the width direction of the water channel.