JPH01125407A - Movable plate-type wave-breaking submerged levee - Google Patents

Abstract

PURPOSE:To obtain an effective wave-breaking effect by providing a vertically movable plate with changes of sea surface, a spring system to restore the plate to fixed position, and a damping mechanism to bring about the energy loss of waves for the seabed. CONSTITUTION:A flat rectangular box-shaped frame 3 with an opened upside is settled on the seabed 2, and a vertically movable rectangular plate 4 with changes of sea surface is set so as to cover the opening of the upside of the frame 3. A spring system 5 to restore the plate 4 to its fixed position and a damping mechanism 6 top bring about the energy loss of waves with the vertical movement of the plate 4 are also provided between the plate 4 and the frame 3. As the damping mechanism 6, oil damper or fluid damper consisting of the frame 3 which many water-passing holes may be cited. The water depth above the top of the submerged breakwater 1 can thus be increased and the width of the breakwater can also be reduced.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention is applicable to open areas of breakwaters that protect various facilities such as fishing ports, general ports, marinas facing the ocean, and nuclear power plants, or to The present invention relates to a movable plate-type wave-dissipating submerged levee having a novel structure suitable for use by being sunk in a sea area forming a high artificial inland sea area.

``Conventional technology and its problems'' In recent years, submerged sea area control structures such as artificial reefs and submerged levees have been reconsidered from a landscape perspective. However, in the case of these conventional submerged structures, in order to obtain a certain level of breakwater effect, it is necessary to bring the top of the submerged embankment close to the water surface, and it is also necessary to increase the width of the embankment body. However, this resulted in a large cross-sectional structure, and there were also problems in terms of cost effectiveness.

By the way, regarding the water depth from the sea surface to the top of the submerged levee and the width of the levee body, which are necessary to obtain a certain wave-breaking (wave-dissipating) effect, there is the following correlation between wave height and wavelength. It is known that there is.

For example, in FIG. 15, when the water depth at the top of the submerged levee S is R1 and the incident wave height is Hi, the so-called transmittance KT, which indicates the degree to which the incident wave crosses the submerged levee and invades inside, is set to 0.
To make it 5 or less, it depends on the width of the embankment (the wider the embankment, the better it disappears), but R/Hi < 0.5 to 1.5
It is necessary to do so. Therefore, in order to eliminate waves with a wave height of 5 charcoal, R = 2.5 to 75 shoulders, that is, water depth h-20
This means that it is necessary to fill approximately 60 to 90% of the water depth with submerged embankments = 2-. In such a case, a major problem arises in securing the water depth R at the top, which is an essential function of a submerged levee.

On the other hand, the embankment body width is B and the incident wavelength is 1. In this case, B/L
It is necessary to set the value to >0.5; if it is less than this, most of the waves will be transmitted. Therefore, waves of large wave height (
-The wavelength is also long), it is necessary to increase the width of the embankment body. Note that the standard design wave is based on a wavelength of about 50 to 150 m.

``Object of the Invention'' Therefore, the present invention fundamentally improves the conventional submerged levee which has the various problems mentioned above, and achieves the functions originally required of a submerged levee, that is, the top of the submerged levee. A new structure that can improve all aspects of securing the water depth at the end, wave dissipation efficiency, and structure width, and also improves cost effectiveness by creating a small cross-section structure. The purpose of this project is to provide a movable plate-type wave-dissipating submerged embankment.

"Means for solving the problem" The movable plate type wave-dissipating submersible according to the present invention is located below the water surface,
A movable plate arranged to be able to move up and down in response to changes in the water surface due to waves, a spring system that provides a restoring force to return this movable plate to its home position, and a movable plate that moves vertically in response to changes in the water surface caused by waves. The structure includes a damping mechanism that causes an energy loss.

1 Effect: The movable plate receives the wave force caused by changes in the water surface due to waves, i.e., incident and scattered waves, and moves up and down in accordance with the period of the waves due to the action of the spring system. Along with this movement, radiation waves are generated from the movable plate. When the radiated waves reach the water surface and become surface waves, they will have a phase difference with the incident and scattered waves. Then, the incident/scattered waves and the radiated waves overlap, and as a result, the peaks of the incident/scattered waves and the troughs of the radiated waves overlap and cancel each other out on the transmission side. Also, part of the energy of the incident wave is consumed by the work done by the attenuation mechanism, and the energy of the wave as a whole decreases.

"Examples" First, for the convenience of understanding the present invention, the circumstances leading to the present invention will be explained, and then the explanation will move on to specific embodiments of the present invention.

The inventors of the present invention have already invented a submerged reef (artificial reef) made of a bag using a flexible membrane (Japanese Patent Application No. 60-280790) in order to solve the above-mentioned problems with the submerged levee. and suggested this. This invention focuses on the fact that by using membranes, structures with large cross-sections can be made at low cost and are highly safe for marine leisure activities. A model experiment was conducted using a water tank.

However, Figure 15 and Figure 15! As shown in Figure 6, in the experiment conducted for comparison with an immovable (rigid body) type submerged levee, most of the waves were transmitted (transmittance KT = 1), but with the same shape but a flexible submerged levee like a bag. A completely unexpected result was obtained in that the transmittance sometimes decreased as the flexibility changed. Moreover, as can be seen from the figure, the ratio of the crest water depth R to the incident wave height Hi is R/
We obtained results that could not be imagined based on conventional knowledge regarding submerged embankments, such as Hi or large, in other words, relatively large crest water depth R or low permeability. In addition, although we will not explain the diagram, it was also found that a considerable amount of energy was lost even though the waves did not break. This is an extremely important research result, showing that even if the submersion rate (the ratio of the crest water depth R to the water depth) is large, it is possible to consume wave energy and lower the transmittance. It means.

If this mechanism can be elucidated, it will be possible to develop more economical wave control structures. In addition to the results shown in the figure, we have also obtained results that show that changing the mass or internal pressure of the membrane significantly changes its properties, but after comprehensively examining these results, we believe that this mechanism is as follows. I made a hypothesis.

(i) The membrane structure is a type of vibration system, and changing the mass or internal pressure of the membrane is equivalent to changing the natural period. It is important that the membrane vibrate, and the transmittance decreases due to the phase difference between the radiation waves generated by the vibrations and the incident/scattered waves.

(11) Wave energy loss when waves are not broken is caused by the work done by the damping mechanism (damper) of the membrane as a vibration system.

In order to confirm this hypothesis, we have come to the conclusion that it is best to conduct a theoretical study using a simplified model as shown in Figure 1.

The above was the motivation for starting research on the present invention, but when we actually constructed a theory and performed calculations, we not only verified the second hypothesis, but also found that this simplified model itself It was revealed that it had extremely good performance. Therefore, we named this a movable plate type wave-dissipating submerged embankment and proposed the present invention.

Embodiments of the present invention will be specifically described below with reference to the drawings.

Fig. 1 is a conceptual diagram showing the principle of the movable plate type wave-dissipating submerged embankment of the present invention, and the following Figs. 2 and 3 are a plan view and a vertical cross-section showing specific examples thereof. It is a diagram. In these figures, what is indicated by the symbol I as a whole is a movable plate type wave-dissipating submerged levee (hereinafter simply referred to as a submerged levee), and like a conventional submerged levee, it is located on the seabed 2 of the sea area or port area where it is to be submerged. will be installed.

As shown in FIGS. 2 and 3, the submerged levee 1 (not shown in this embodiment) has a flat rectangular box-shaped frame 3 with an open top, and a form that covers the top opening of the frame 3. horizontally and frame body 3
a rectangular plate-shaped movable plate 4 disposed so as to be movable downward within the frame;
The movable plate 4 is provided between the movable plate 4 and the frame body 3.
A spring system 5 is provided between the movable plate 4 and the frame body 3 to provide a restoring force to return the movable plate 4 to the normal position.
The structure includes a damping mechanism 6 for suppressing the vertical movement (that is, causing wave energy loss due to the vertical movement).

The frame 3 is made of a material that has a higher specific gravity than seawater and is corrosion resistant so that it can be stably installed at a fixed position on the seabed 2.
For example, it is made of concrete, and the movable plate 4 is also made of corrosion-resistant concrete or a steel plate treated with rust prevention measures. The spring system 5 is constituted by a coil spring in this embodiment, and is arranged at intervals near the four corners and in the middle part as shown in the figure, and is interposed between the movable plate 4 and the bottom plate of the frame body 3. The movable plate 4 itself is configured to support the movable plate 4 so as to be movable downward. Further, the damping mechanism 6 is constituted by an oil damper, has a deaf shape that connects the bottom plate of the frame body 3 and the movable plate 4, and is disposed in plurality at intervals between the spring systems 5.

Around the movable plate 4, the gap formed between the periphery of the movable plate 4 and the inner wall of the frame body 3 is sealed to keep the inside of the frame body 3 liquid-tight, and the upper and lower sides of the movable plate 4 are sealed. A waterproof membrane 7 configured to allow movement is provided, thereby forming an air chamber 8 inside the frame 3.

As shown in the figure, the waterproof membrane 7 has a H-shaped structure in which both sides are fixed to the frame 3 and the movable plate 4, and a margin is provided in the middle part to allow vertical movement of the movable plate 4. Alternatively, a configuration in which the waterproof membrane 7 itself is formed of a stretchable material may be applied.

In the movable plate type wave-dissipating submerged embankment configured in this way,
When wave force due to incident and scattered waves acts on the movable plate 4, the movable plate 4 performs a downward movement according to the period of the waves, but the movable plate 4
Since it is supported horizontally on the frame 3 by a plurality of spring systems 5 and damping mechanisms 6 arranged at equal intervals,
The two movements are performed smoothly. At this time, spring system 5
The damping mechanism 6 mainly exerts an effect of providing a so-called restoring force to return the movable plate 4 to a normal position, and the damping mechanism 6 exerts an effect of suppressing the vertical movement of the movable plate 4, that is, exerts a function of applying a load to the vertical movement of the movable plate. At this time, the air chamber 8 existing within the frame 3
Since internal pressure changes occur based on the vertical movement of the movable plate 4, this air chamber 8 is connected to the spring system 5 supporting the movable plate 4.
It will exhibit the same effect. Due to the vertical movement of the movable plate 4, radiation waves are generated from the movable plate 4, reach the sea surface, and spread across the sea surface to the west as so-called surface waves. Of these surface waves, or radiated waves, there are radiated waves that spread on the sea surface to the transmission side (inner sea area of the submerged levee), and incident waves that have traveled on the submerged levee.
The scattered waves and the scattered waves travel in approximately the same direction, and both waves have the same traveling speed and period due to the generation conditions of those waves, but the phase difference is often different. A phenomenon occurs where the peaks of the waves and the troughs of the radiated waves overlap on the transmission side, and they cancel each other out. Therefore, the wave heights of incident and scattered waves on the transmission side become correspondingly smaller. On the other hand, the incident wave that has progressed onto the submerged embankment has lO
- A part of the energy is mainly consumed by the work done by the damping mechanism 6 when pushing down the movable plate 4, and as a result, the wave energy itself is reduced. In this way, the submerged levee 1 equipped with a movable plate has the effect of reducing the wave height on the transmission side and also reducing the wave energy itself (loss), so as a synergistic effect, it has an extremely effective dissipation effect. The structure has wave action.

4 and 5 show a second embodiment of the present invention. In this embodiment, an air chamber is not required by using a seawater-resistant damping mechanism (oil damper) 6a, and Simplification is achieved by using the floor plate I+ instead of the frame 3. This structure has the advantage that maintenance can be easily performed compared to the so-called closed type of the first embodiment.

6 to 8 show a third embodiment of the present invention. In this embodiment, an oil damper is provided as a damping mechanism for suppressing the vertical movement of the movable plate 4 as in the first embodiment. Alternatively, a plurality of water permeable holes 9 are provided in the side wall portion of the frame body 3 to constitute a damping mechanism IO using a so-called fluid damper.

Therefore, in the installed state of this submersible, the inside of the frame 3 is filled with seawater, and the gap between the periphery of the movable plate 4 and the inner wall of the frame 3 remains as it is without being sealed with a waterproof membrane or the like. In other words, the configuration is such that a gap α is maintained through which seawater can enter and exit.

When configured in this way, not only does the process and labor cost of separately manufacturing and installing an oil damper become unnecessary, but also the durability of the damping mechanism 10 itself can theoretically be made semi-permanent. In addition, for example, the damping rate of the damping mechanism 10 can be easily adjusted by closing some of the plurality of water permeable holes 9 with plugs (not shown).

(Explanation of effects based on calculation examples) Next, with reference to the conceptual diagram of FIG. 1, FIG. 9, and FIG.

Figure 9 shows the dimensionless spring constants K (explanation omitted) of 1 and
When the transmittance KT is B/1. It is expressed as a function of and compared.

Here, R-ω means immobility. Note that the damping mechanism (damper) is set to 0.

This figure shows that the transmittance is lower when the submerged embankment is movable than when it is immobile. In addition, when R/h is 0.9 (broken line), all B/
The incident wave is transmitted through L as it is, but it is movable (R
= 1), the transmittance decreases significantly, and moreover, B/L<
When R/h is 0.5, the wave-dissipating effect is higher than when R/h is 0.1 (solid line).

This is an extremely advantageous property as a structure.

This is because the smaller the width of the breakwater body and the lower the height of the breakwater body, the higher the wave dissipation effect, which is not only economically advantageous, but also because it does not impede the navigation of ships. It can be sunk in open waters, making it easier to improve the calmness of existing ports.

Next, what will happen if we add a damping mechanism to R/h 10, 9?
, R=1 is shown as an example. Figure 10 shows the energy loss KL''(-1-KT'-KR'', K
R: reflectance), and C in the figure is the attenuation coefficient (
(explanation omitted). As will be seen, up to 50% of the wave energy can be extinguished through the use of damping mechanisms. It is said that 50% of the total energy can be extinguished by a structure with a high submergence rate, in other words, a structure that clings to the seabed, and it is also possible to reduce the transmittance as shown in Figure 9. This can be regarded as an extremely groundbreaking invention.

As shown in the above calculation example, the movable plate type wave-dissipating submerged levee prevents waves from penetrating even when L is small or when the water depth at the top is deep. be able to. Furthermore, if a damping mechanism is used, it is possible to generate a maximum energy loss of 50% per unit even without breaking waves or eddies. Furthermore, the fact that the B/L is small and the top water depth is deep means that the acting wave force is also small, which is advantageous for the stability of the structure. Zunawaji can provide a small, economical, low-reflection, low-transmission submerged wave control structure.

(Cross-sectional comparison with a conventional submerged levee) Wave control using submerged structures is considered to often target waves with a wave height of around 2x. Figure 13 shows water depth h
= 201! , incident wave height Hi=2i, incident wavelength L=10
The cross section required to keep the transmittance below 0.5 when 0π is compared between a conventional submerged embankment and a movable plate type submerged embankment. However, these specifications are as shown in Figures 14 (a) and (b) for a conventional submerged embankment, and as shown in Figure 9 for a movable plate type submerged embankment.
I'm looking for it from the diagram. As is clear from the figure, the cross section required to obtain the same hydraulic performance is overwhelmingly smaller for the movable plate type wave-dissipating submerged levee.

In addition, in the examples, the configuration and hydraulic performance of a single movable plate-type wave-dissipating submerged levee were explained. Of course, it is possible to develop the structure as appropriate depending on the situation of the sea area where the submerged vessel is to be submerged, the target transmittance, etc., such as a structure in which the submerged vessel is parallel to the ground, or even a structure in which one submerged levee is provided with a plurality of movable plates. What should be noted in this case is that by using multiple movable plates, a maximum of 5 movable plates can be used individually.
The energy loss, which was 0%, can be increased over a wide range of B/L as shown in Figure 1+. At that time, as shown in Fig. 12, the transmittance K
T is also significantly lowered, making it possible to construct a submerged embankment with even higher breakwater effects than a single submerged embankment.

Furthermore, it goes without saying that the spring system, damping mechanism, etc. are not limited to the embodiments, and other configurations may be employed as long as they perform basically the same functions as these. Furthermore, in the embodiment, the present invention is described as a submerged levee for sea area control, but if necessary, it is of course applicable to, for example, lake areas where measures against waves are required.

"Effects of the Invention" As detailed above, the movable plate type wave-dissipating submerged embankment according to the present invention has a movable plate located under the water surface and arranged to be movable up and down in response to changes in the water surface caused by waves. The configuration includes a spring system that provides a restoring force to return the movable plate to its home position, and a damping mechanism that causes wave energy loss as the movable plate moves up and down. A movable plate that moves up and down generates radiated waves, creating surface waves that spread on the water surface, which combine with incident and scattered waves on the transmission side and cancel each other out, resulting in the effect of reducing the wave height. Furthermore, the attenuation mechanism consumes a part of the energy of the incident wave, and exhibits the effect of reducing the energy of the wave itself. As a result, it is possible to provide an extremely efficient wave-dissipating effect that can significantly reduce wave transmittance. Furthermore, due to the presence of the movable plate, a large wave-dissipating effect can be achieved even if the water depth at the top of the submerged levee is large and the dam body width is small, so the water depth at the top of the submerged levee can be made deep. Therefore, it is particularly suitable for use when it is submerged in the open sea areas of breakwaters where ships come and go, and furthermore, it has a small cross-sectional structure, so it can be improved in terms of cost effectiveness. It has excellent effects.

[Brief explanation of the drawing]

Figures 1 to 14 (a) and (b) are diagrams shown to explain the present invention in detail. 3 is a plan view and a longitudinal sectional view showing a first embodiment of the present invention, FIGS. 4 and 5 are a plan view and a longitudinal sectional view showing a second embodiment of the invention, and FIGS.
8 and 8 are a plan view, a vertical sectional view, and a side view showing the third embodiment of the present invention, FIG. 9 is a comparison diagram of transmittance when the submerged embankment is movable and immobile, and FIG. 1O is a damping mechanism. Figure 11 is a curve diagram showing wave energy loss when multiple submerged levees are lined up, and Figure 12 is a curve diagram showing wave energy loss when multiple submerged levees are lined up. Figure 13 is a comparison diagram of the submerged embankment cross section required to reduce the transmittance to 085 or less, and Figures 14 (a) and (b) are curve diagrams showing the transmittance due to the submerged embankment. The side view, curve diagram, and Figures 15 and 16 are shown to explain the results of the model experiment that led to the present invention. Figure 15 is a model diagram,
FIG. 16 is a diagram showing the model shown in FIG. 15 and experimental values regarding the transmittance of the rigid submerged embankment. 1... Movable plate type submerged wave dissipating levee, 4 - Movable plate, 5...
・Spring system, 6.6a, 10・ Damping mechanism, 7...
Waterproof membrane, 9...water permeable hole, 11...floorboard.

Claims (1)

[Claims] A movable plate located below the water surface and arranged to be movable up and down in response to changes in the water surface due to waves, a spring system that provides a restoring force to return the movable plate to a normal position, and a vertical movement of the movable plate. A movable plate-type wave-dissipating submersible equipped with a damping mechanism that causes wave energy loss.