JPH0522761B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement in a wave canceling device that reflects and absorbs wave energy. The present inventor filed an application titled "Wave Dissipation/Generation Method" on March 4, 1983, prior to filing this invention, and the present application relates to an improvement thereof.

<Structure of the Invention> First, the operating principle of the present application (in which the diving bag is surrounded by a hollow cylinder), including the face wash (in which the diving bag is exposed in the sea), will be described with reference to Figures 1 to 8 of the attached drawings. I will explain. FIG. 1 shows the prior application in which two submersible bags are connected by a communicating tube and arranged side by side in the direction of wave propagation. A is a plan view, and b is a side view. In this drawing, 11 and 12 are submerged bags, 2 is a communication pipe, Ho is the direction of waves, and Ht is the direction of dissipated waves. Figure 2 is a side view of four diving bags, a is fixed to the seabed,
b is a figure moored to a floating platform, 13, 14, 1
5 and 16 are submergence bags, and 2 is a communication pipe. Figure 3 is an explanatory diagram of the operating principle of the diving bag in the earlier application.
, is a phase-by-phase diagram regarding the action of waves. 3 is a communication pipe provided at the bottom of the diving bag.

First, Figure 3a is a side view showing the underwater shape of a diving bag made of a non-stretchable but flexible membrane. is fixed, and air enters and exits through the hole 3.

, , is the case where air is fixedly placed in water, and the amount of air is approximately 60% of the amount of air in . The upper part has a hemispherical shape, but the part below the center is constricted to form pleats 4, and the AA cross section of that part is shown in b. When air is removed from this state, the pleats 4' become larger and the volume of the bag decreases. As when air is injected, the pleats 4 become smaller and the volume of the bag increases. In this way, even if the membrane surface does not expand or contract, the volume of the submerged bag can easily increase or decrease due to the growth or contraction of the folds, causing deformation of the submerged bag.

FIG. 4a is a side view showing a case where the submersible bags 11 and 12 are installed in a state in which they are not in communication with each other in the direction of propagation of waves of wavelength L with a distance B between them. At this time, if a wave Ho with a wavelength L of approximately 2B is incident, then
The fluid pressure acting on the diving bag changes as the wave progresses, but since air is considered incompressible, the volume of the diving bag does not change.
When there is a wave bottom at point 2, forces in the directions P ₁ and P ₂ act on the diving bag due to the horizontal movement of water particles, respectively.
When at rest, the diving bag shown by the dotted line only tilts slightly as the wave advances, as shown by the solid line, and the wave height increases.
The incident wave Ho is blocked a little by the latent bag and produces a reflected wave height Hor, but the wave height is hardly reduced and passes through as Hot. In other words, a submerged bag without communication has almost no wave-dissipating function.

However, in the state shown in Figure 4a, the fluctuating pressure caused by the waves acting on the diving bag 11 compresses the diving bag, and the opposite is true for the diving bag 12, so both bags are separated into tubes as shown in b. 2, the air in the submergence bag 11 flows toward the submergence bag 12, causing the former to contract and the latter to expand. If we consider only the phenomenon of contraction and expansion, as shown in Fig. 4b, the fluid near the submerged bag 11 gathers toward the submerged bag by the contracted volume,
As a result, the water surface lowers and a wave bottom occurs, while a wave peak occurs near the diving bag 12, and this phenomenon is alternately repeated as the incident wave advances. That is, as the volumes of both submerged bags alternately increase and decrease, the phenomenon of wave peaks appearing alternately on one side and wave bottoms on the other side is repeated, and new waves H _R 1 and H _R 2 are induced. The waves will proceed at the same height on both the left and right sides. this wave
It is called Radiation Wave. What should be noted here is that
This wave has a wave peak and a wave bottom that are in an opposite phase relationship with the wave shape shown in FIG. 4a, which is the cause of the wave. In the connected submerged bag, a phenomenon that combines the states a and b in Fig. 4 appears, and on the right side of the submerged bag 12 (on the passing wave side), H _R in Fig. b, which advances in the same direction as Hot in Fig. 1 polymerizes and cancels each other out. As a result, the wave height Ht becomes significantly lower than Hot, and the waves are effectively cut off. On the other hand, on the left side (reflected wave side) of the diving bag 11, the incident wave Ho and the radiation wave H _R 2 traveling in the opposite direction overlap and the wave height increases. (Actually, H _R 2 becomes smaller due to energy dissipation of the air flow in the communication pipe 2, and its influence is small.) FIG. 5 shows the result of superimposing a and b in FIG. 4.

After all, when the submersible bag is communicated, the wave height of the radiation wave generated by its deformation is large, and the closer it is to the passing wave height Hot, the greater the shearing effect.

Therefore, the problem is how to effectively generate radiation waves.

Figure 6a illustrates the change in volume of the diving bag that generates radiation waves in still water and the distribution of surrounding fluid flow velocity.The chain line representing the shape of the diving bag is at rest, and the solid line is for expansion. At the time, the broken line represents the shape at the time of contraction. As already shown in Figure 3, the main deformation occurs in the lower half of the submerged bag, and the flow velocity is spread out over a fairly wide range, as shown by the solid line arrow when it is inflated and the dotted line arrow when it is deflated. , it appears that the water level is not rising or falling very effectively. Therefore, if we surround the diving bag with a cylinder with an open top to converge the flow around the diving bag, the flow will have a distribution of rising and falling around the diving bag, as shown in Figure 6b. This effectively results in an increase and decrease in .

Fig. 7 shows the effect of installing a cylinder in each submergence bag through experiments in the case where two submergence bags are connected at the front and back, as shown in Fig. 2a. be. i.e. diameter 11cm, air volume 1200
cc, 4 diving bags made of vinyl membrane with a height of 21 cm, the middle distance between the two diving bags in the front and back is 20 cm, and the center distance between them B = 70 cm, water depth h = 35 cm, width W = 30
Fixed to the bottom of the wave channel with an inner diameter of 15.0 cm and an outer diameter of 16.5 cm.
cm, using four PVC pipes with a height of 30 cm as vertical tubes, measure the passing wave height for an incident wave height of 4.0 cm, and calculate the ratio of the passing wave height to the incident wave height (passage rate) Kt
The experimental results are plotted on this graph, with the value taken as the vertical axis and the ratio of water depth h to wavelength L taken as the horizontal axis. The points shown in this figure are × when only a cylinder is installed, ● when a diving bag is installed, and ○ when both are used together. As is clear from this, when h/L≧0.16, Kt is approximately 0.7 in the case of only the cylinder and approximately 0.6 in the case of only the submerged bag, but it is approximately 0.3 when both are used together, which is 0.7×0.6 =
It is about 0.7 times 0.42, and the effect of the vertical cylinder predicted from FIG. 6 is obvious.

Surrounding the diving bag with a cylinder in this way is effective in improving the wave-dissipating effect, and the horizontal flow velocity accompanying the traveling wave is directly applied to the diving bag, causing its horizontal oscillation, which causes the diving bag membrane to This is essential to prevent the durability of the surface from being adversely affected and to prevent damage to the diving membrane due to collisions with floating foreign objects.

<Example> The embodiment of the present device will be described below with reference to FIGS. 8 to 11.

Embodiment 1 In FIG. 8, a vertical cylinder 5 is used for the submersible bags 11 and 12 in FIG. 1.

Embodiment 2 FIG. 9 is for the case of FIG. 2a, in which one tube 6 is used for each of the two front and rear submersible bags 13, 14 and 15, 16. The method of using one tube shared by different diving bags is advantageous in dealing with horizontal wave forces.

Embodiment 3 FIG. 10 is an example of application to the case of FIG. 2b.

Embodiment 4 Fig. 11 shows an example of application of the type shown in Fig. 1 in a shallow sea area. A case is shown in which a diving bag is installed by digging into a cylindrical or conical shape 8.

The features of this device are that in addition to having all the features of a submersible type wave dissipating device using a diving bag, it also has an excellent wave dissipating effect and provides sufficient protection against damage to the diving bag. .

[Brief explanation of the drawing]

Figures 1, 2, 3, 4, 5, and 6 are plan views illustrating the structure and principle of this device.
, side view b, and Fig. 7 are experimental results proving the principle of this device, and Figs. 8, 9, 10, and 11 are plan and side views showing embodiments of this device. be. 11, 12, 13, 14, 15, 16... Submerged bag, 2... Communication pipe, 3... Air hole, 4... Folds on the submerged bag membrane surface, 5, 6... Vertical cylinder and pleated cylinder, 7
...Mound, 8...Dug hole, Ho...Incoming wave, Hr...Reflected wave, Ht...Passing wave, H...
Radiation Wave.

Claims (1)

[Claims] 1. A plurality of bags (hereinafter referred to as diving bags) each containing an appropriate amount of air with a flexible membrane are placed vertically in the water at a certain depth below the water surface along the direction of wave propagation. Arrange them in
1. A wave dissipating device in which bags are air-communicated through hollow tubes, characterized in that the submerged bags are surrounded by a vertical tube with an open top and held underwater. 2. The wave dissipating device according to claim 1, wherein the underwater retention is performed by fixing a vertical cylinder to the bottom of the water. 3. The wave dissipating device according to claim 1, wherein the underwater holding is carried out by horizontally mooring a platform to which a vertical cylinder is fixed from the bottom of the water.