JPS60168803A - Long wavelength type floating wave dissipating levee - Google Patents

Abstract

PURPOSE:To dissipate especially waves having long wavelength, by a method wherein a staged part, serving to dissipate the energy of waves, is formed on the incident wave side of a floating levee, and a vertical surface to the surface of the water is provided on the transmissing wave side. CONSTITUTION:A staged part 3 is formed on the incident wave side of a floating wave disspating levee 1, a vertical surface 5 is formed on the transmissing wave side, and an uneven wave dissipating surface 4 is formed thereon. Thus, a portion in the vicinity of the surface of the water is increased in drainage discharge thanks to the staged part 3. A portion in the vicinity of the surface of the water, where movement of waer particle of incident wave is violentmost, is increased in frictional resistance and is decreased in energy thanks to the wave dissipating surface 4. Additionally, production of waves on the transmitting side is prevented thanks to the vertical surface 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to the structure of a floating wave bank that has buoyancy and is moored to the water surface to eliminate waves.

[Background of the invention]

Conventionally, gravity type breakwater facilities, that is, normal breakwaters, have been used for wave control such as extinguishing waves entering ports and harbors. However, when the water depth is deep or when it is desired not to obstruct the exchange of seawater between the inside and outside of the breakwater, it is considered to install a floating breakwater 1 as shown in FIG. 1, for example. In particular, when it becomes necessary to relocate and expand the aquaculture farm 2 offshore, such as in a town, (1) prevent damage to the aquaculture facility due to waves, (2) ensure the safety of aquaculture operations against waves, and (6) It is necessary to prevent the decline in food intake at Cape Hamachi due to the lack of fresh seawater. Floating breakwaters are an effective facility that satisfies these requirements.

[Background, technical issues]

The wave-dissipating effect of conventional floating breakwaters was sufficient for waves smaller than the size of the floating breakwater, that is, waves with small wavelengths (Figure 2), but for large waves, i.e. For waves with long wavelengths, the entire floating wave bank moved up and down with the movement of the waves (Fig. 3), making it impossible to obtain sufficient results.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a floating wave bank with a high wave-dissipating effect, that is, a long-wavelength type floating wave bank that can dissipate waves with a long wavelength. [Summary of the Invention] The long-wavelength floating wavebank of the present invention first forms a stepped portion parallel to the water surface in order to increase the amount of drainage near the water surface on the incident wave side. The stepped part includes not only a shelf-like part but also an eave-like part whose top and bottom are reversed. This increases the frictional resistance near the water surface, where the movement of water particles in the incident wave is most intense, and reduces the wave energy. Furthermore, a surface perpendicular to the water surface is formed on the transmitted wave side. This prevents liquid from being generated behind the floating wavebank due to its vertical movement.0 [Theory of the invention] In general, the waves ζ, which pass through the rear of the floating wavebank, are ζ,=+Cte 0, that is, the transmitted wave ζ, expressed as +ξ, -cv consists of three elements. That is, with respect to the transmitted wave C when the floating wave dyke is completely fixed, the angle ξ, (radia
tion wave) and minus the viscous or nonlinear effect CV. Now, if the incident wave becomes a large wave, that is, a wave with a long wavelength, it is difficult to expect that the influence of ξ will have a positive effect on the wave extinction effect. On the contrary, the transmitted wave may become larger. Therefore,
In the long-wavelength type floating wavebank of the present invention, a surface perpendicular to the water surface is formed on the transmitted wave side to prevent waves from being generated. Next, in order to increase the influence of Cv and increase the wave dissipation effect, the long-wavelength type floating wavebank of the present invention forms a stepped portion on the incident wave side that increases the amount of drainage near the water surface. It is. Generally, when waves are generated, each water particle is moving in a circular motion. The water particles near the water surface are moving in a large circular motion. Therefore, in order to increase the viscous influence Cv, it is a good idea to apply frictional resistance near the water surface.In order to increase this viscous influence Cv, it is recommended to form an uneven wave-dissipating surface on the stepped portion. It is expected that great effects will be obtained. ◎ [Embodiment of the Invention] An embodiment of the present invention will be explained with reference to FIGS. 4 and 5. In the long-wavelength type floating wavebank of this embodiment, a step portion 6 is formed over half of its width and its length.

Therefore, the depth H on the transmitted wave side.

Compared to , depth H on the incoming wave side! is shallow. An uneven wave-absorbing surface 4 is formed on the upper surface of the stepped portion 3 and the portion where the stepped portion is not provided. Further, a vertical surface 5 is formed on the transmitted wave side.

[Example of comparative experiment using model]

The results of a comparative experiment between the model of this example and a conventional floating waveform model will be explained with reference to FIGS. 6 to 10.

Figure 6 shows the method of mooring the model. Model 6 is 2 for the X plane.
It is moored by an anchor 7 stretched at an angle θ of 0'. A spring 8 is provided in the middle of this anchor 7,
The model 6 is moored with a certain elasticity and is in a moored state similar to that of the real model. Figure 7 shows a model of a conventional floating wave dyke.

FIG. 8 shows a model of this embodiment. The main dimensions of each part in FIGS. 7 and 8 are shown in the table below.

Note that FIG. 9 shows the uneven wave-absorbing surface 4 provided in the model of FIG. 8. The width B1 of the convex portion is 5111E, the height h8 of the convex portion is 25111, and the width B of the concave portion is 10 degrees.The results of experiments conducted using these models are shown in the graph of FIG. The horizontal axis of this graph 177 takes the period T of the incident wave. The larger the period Tw is, the longer the wavelength of the incident wave becomes, and the larger the wave becomes. The vertical axis W is the value C, which is the wave height HWT of the transmitted wave divided by the wave height H1 of the incident wave! shall be.

As can be seen from this graph, the period Tw of the incident wave is 0.
There was a significant difference in the vicinity of 7 (sec), which indicates that the floating wavebank of this example is effective. Here, considering the Froude number Fr that should be taken into account in the model experiment, ■ However, V: Wave velocity g: :ii Force acceleration L: Representative dimension For example, if the dimensions of the actual object are 100 times the dimensions of the model, this period TV 0,7 becomes the value of 0,7×J100.

Therefore, it can be seen that the long-wavelength type floating wavebank of this embodiment is effective even for sufficiently large long-wavelength waves.

[Other Examples]

In the embodiments described above, the stepped portion 6 has an upwardly facing shelf shape, but in other embodiments, it may have an eave shape having a downwardly facing shape. Note that since the effect shown in FIG. 10 is considered to be mainly caused by the presence of the stepped portion 6, it is considered that the uneven wave-dissipating surface is not necessarily necessary.

〔Effect of the invention〕

According to the long wavelength type floating wave dyke of the present invention, it is possible to provide a long wavelength type floating wave dyke that has a sufficient wave-dissipating effect even for large waves with long wavelengths.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing the actual usage condition of the floating breakwater, Figure 2
Figures 4 and 6 are cross-sectional views showing conventional floating wave banks.
5 and 5 are cross-sectional views showing a long-wavelength floating wavebank according to an embodiment of the present invention, FIG. 6 is a schematic diagram of the mooring device used in the model experiment, and FIG. FIG. 8 is a cross-sectional view showing the model of FIG. 4, FIG. 9 is a vertical cross-sectional view of the wave-dissipating surface formed in FIG. 8, and FIG. 10 is a graph showing the experimental results. It is. 1... Floating wave bank, 2°°゛ farm~3... Step part, 4... Wave dissipating surface, 5... Vertical surface, 6... Model, 7... Anchor, 8 ···Spring. Figure 2 Figure 5 97m6 Figure 10 Figure 7W (sec)

Claims (1)

[Claims] (11) A floating wave bank that has buoyancy and is moored on the water surface to extinguish transmitted waves, which forms a stepped portion to dissipate wave energy on the incident wave side and on the transmitted wave side. A long-wavelength type floating wave bank characterized by forming a surface perpendicular to the water surface. Floating wave bank.