JPS5913605B2 - floating wave bank - Google Patents

Description

[Detailed description of the invention] TECHNICAL FIELD The present invention relates to a floating type wave-dissipating bank when used as a wave-dissipating device.

At the sea surface, which is the boundary between air and water, waves generated by wind or swells propagated by these waves exist.

These waves have energy and create various obstacles.

A breakwater is provided to prevent this problem.

The most basic type that has existed since ancient times is the embankment type (fixed type) breakwater.

Although this type reflects all incident waves and has a perfect wave-proofing effect, it has the following drawbacks.

(b) There is no seawater exchange.

(0) There are economic and technical limits when it comes to deep water.

(c) It damages the landscape and makes it impossible to move.

The above disadvantages can be solved by making it a floating type.

As a floating wave-dissipating levee, it has been proposed, for example, to provide a floating body at the center in the direction of wave propagation, and to provide vertical plates in front and behind the floating body to dissipate waves through a total of three stages of reflection.

However, if there is no mechanism to absorb wave energy inside such a device, the reflected waves will become unnecessarily large and overlap with the incident waves, increasing the wave force applied to the entire device, making mooring difficult. There is a risk that it may become a hindrance to ships navigating nearby.

The present invention eliminates the drawbacks of the prior art described above, and not only reduces the transmitted wave, but also sufficiently reduces the height of the reflected wave to obtain good wave-dissipating performance, and is mechanically extremely simple. The purpose is to obtain a floating wave bank that is both economical and economical.

That is, the feature of the present invention is that a bottomless box-shaped tank is divided into three parts in the direction of wave propagation, and the three bottomless tanks 1 to 3 are arranged in series in the direction of wave propagation. The tanks 1 and 3 on both sides are connected to each other with a resistance at the top by a communication pipe 4, and are connected to the atmosphere through an air hole or an air hole with a valve 5 as appropriate, and the center tank 2 is connected to the atmosphere with a resistance at the top. A floating body connected to the atmosphere through an air hole or an air hole with a valve 6 and having most of the buoyancy is provided below the water surface of the tank and is fixedly floating.

An embodiment of the present invention will be described below based on the drawings.

This wave-dissipating principle arises from controlling the motion of the water column in the tank when an incident wave arrives, using the communication pipe 4, air holes 5 and 6, that is, applying tamping to the air flow.

This will be explained in detail below.

In FIG. 2, consider the case where the floating body 7 is free to move only up and down in a regulated liquid.

If the direction of incidence of the wave is taken as the y-axis and the direction of vertical movement of the floating body is taken as the y-axis, the vertical movement is y (t) = Y e iωt ・・・・・・・・・
......It is expressed as (1).

Here, Y is the maximum value of the motion amplitude, and ω is the circular frequency of the wave.

The equation of motion of the floating body 7 shown in Fig. 2 is m″31′+kHy−F ・・・・・・・・・・・・
...It is expressed as (2).

Here, m is the mass of the floating body 7, kH is the stability coefficient of the floating body 6,
F is the fluid force acting on the floating body 7 due to the fluid.

Further, the number of dots on the motion coordinate y means the number of times of time differentiation.

The fluid force F in equation (2) can be decomposed and considered as follows.

F3F +F ・・・・・・・・・・・・・・・
(3)2 Here, F□ is the reaction force of the fluid against the vertical movement of the floating body 7 while it is stationary, and F2 is the forcing force due to waves.

F□ is received when the floating body 7 makes a single chord vibration on a still water surface, and is a wave generated on this water surface or a divergent wave shown in Fig. 3. This condition is called a radiation condition. The reaction force F1 is expressed by the following formula.

F□""mH"y"-nu?・・・・・・・・・・・・
(4) Here, mH is an additional mass coefficient and nH is a damping coefficient.

F2 is a scattering state (di
As shown in FIG. 4, since the floating body 7 is fixed in the wave, the incident wave changes, and the disturbance of this wave is called a scattered wave.

This forcing force F2 is F=Eei(1')t...
It is represented by (5).

Vertically, the equation of motion of equation (2) is (m+mH)'y'ten
H;+kHy=Ee iωt (6).

Considering the motion during synchronization, equation (6) is (m-+mH)Y
+nay+kay -2ko(")mfi(R+T)e i""=-(7)
−ω.

k here. is the wave number and is equal to 2π/λ (λ is the wavelength).

p is the density of the fluid, g is the gravitational acceleration, 4AH is the divergent wave amplitude ratio in heaving, and 1ζ/
Equal to lH1.

In other words, the amount of free surface rise ζ with respect to the vertical amplitude tH of the floating body
This is the wave height attenuation ratio of a divergent wave (radiation).

Further, R indicates reflectance, T indicates transmittance, and when the incident wave is -1, they indicate the reflected wave height and the transmitted wave height, respectively.

On the other hand, from the definition of entrainment, -(m+mH)ωj'l0kH=.

Therefore, equation (7) is nHV-2ko ('') mAH(R+T) e
``'ω Here, nH-2kg ('')ml AH+ 2, so 1''' y=--(R+T)e 1(1)tH Therefore, iωY=--(R+T)H.

The wave height ζ of the waves generated by the movement of the floating body 7 is ζ2iωY−AH=−(R+T)...
...(8).

This means the divergent wave in FIG. 3, and FIG. 2 is the result of combining FIGS. 3 and 4.

So, if we look at the relationship of waves at the time of tuning, R-(R + T) = -T, ・・・・・・・・・・・・
...(9) T - (R + T) = -R, and the wave (R
When the negative phases of 10T ) are superimposed, it becomes equal to the negative phase of the transmitted wave height T or the negative phase of the reflected wave height R when the floating body 7 is free.

From this, if the motion of the floating body 7 is halved at the time of synchronization (adding external damping equal to wave damping), the wave relationship will be as follows.

R--! -(R+1') -! -(R-T)2)・・・・・・・・・00) 1 T-Σ(R+1)7-100(R-T) On the other hand, when the reflected wave and transmitted wave are analyzed, the wave heights R and T are 1 R2=(R+T)+7(R-T), □ )・・・・・・・・・aυT-T, respectively
(R+T) -T (R-T).

Therefore, energy absorption due to heaving is a symmetrical wave -! By absorbing the energy (half of the total) of -(R+T) and considering swoying, we can absorb the entire energy by absorbing the energy (the remaining half) of the antisymmetric wave -q(RT). Become.

The present invention is based on the above theory and considers the movement of the water column in the tank instead of the movement of the floating body.

The present invention has the following two features in order to obtain an effective wave-dissipating effect in deep water.

a) It has a side surface as shown in FIG. 1, and the water column inside the tanks 1 to 3 rises and falls due to the incident wave, thereby creating an air flow, and this flow is restricted to dissipate energy.

That is, as described above, the basic shape is three divided sections when viewed from the side, an air hole 6 communicating with the atmosphere is provided in the upper part of the central tank 2, and a communication pipe 4 is provided between the tanks 1 and 3 on both sides with resistance. At the same time, an air hole 5 communicating with the atmosphere is provided in the communication 4 or the upper part of the tanks 1 and 3, and these air holes 5 and 6
has a constricted shape that obstructs air flow.

b) Transmittance can be reduced by restraining the movement of the breakwater, so restrain it as much as possible in view of the mooring force.

In addition to general mooring, sinker mooring using sinkers may be used to restrain the vertical movement of the breakwater.

However, in areas where the tidal level difference is extremely large, sinker mooring may be omitted.

Next, a specific configuration example of the present invention will be explained with reference to FIGS. 5 and 6.

The wave-dissipating bank of the present invention divides a bottomless box-shaped tank into three parts in the wave traveling direction (a), and the three bottomless tanks 11
~13 arrays are installed in series with the wave traveling direction a.

The overall length L is determined taking into consideration the size of the target sea area and construction advantages.

The width B is determined to be approximately 15 degrees of the most frequent wavelength in the target sea area or the wavelength λ of the waves to be dissipated, and the mold depth D is determined to be approximately the diameter of the width B plus the tidal level difference.

Each tank does not need to be strictly airtight or watertight; appropriate strength members should be considered.

Suitably distributed air holes 15 and 16 are drilled on the decks of the side tanks 11.13 and the central tank 12, respectively.

A communication pipe 14 with a small cross-sectional area is provided between the tanks 11 and 13 on both sides, and a simple damper 17 is provided inside.

A part of the wave incident in the direction a is reflected by the front surface of the tank 11, but the rest is transmitted, causing the water columns in the tanks 11 to 13 to move up and down.

At this time, air in the upper space of the tanks 11 to 13 flows in and out, but if the air holes 15, 16 and the communication pipe 14 are sufficiently squeezed, resistance will be provided to the air flow, energy dissipation will occur, and the amount of energy will be dissipated. The energy of the wave is absorbed and the rest propagates as a transmitted wave.

Since this breakwater is a floating type, it requires buoyancy, and it is also necessary to give an initial upward tension to the sinker, so the floating body 19
is provided from the water surface part to the water surface part of the tanks 11 to 13, and a floating body 18 having most of the buoyancy is provided in the water surface part of the tanks 11 to 13.

In FIG. 5, the floating body 18 in the tank length direction is
13 is in contact with the intermediate wall 20 and along the lower part of the outer wall 21 of both side tanks 11 to 13 in the length direction perpendicular to the wave traveling direction a, and the floating body 19 in the tank width direction is, for example, at both longitudinal ends of the tank. and three lower portions in the center in the width direction, and the wave-dissipating bank maintains stability by the floating bodies 19 in the latter.

The reason for this semi-submersible design (most of the buoyancy is carried by the floating body below the water surface, and the water line of the floating body is kept small enough to maintain stability) is that the buoyancy is absorbed by changes in the tide level. This is to prevent excessive force from acting on the sinking weight.

The mooring is a general mooring in which mooring lines 22 and sinkers or anchors 23 that suppress back and forth swinging in the wave traveling direction a are strung on the oil side and the shore side with respect to the wave traveling direction a.

An intermediate weight or intermediate buoy 24 may be installed in the middle of the mooring line 22 in order to prevent an impact force from acting on the mooring line 22.

In addition to general mooring, sinking weight 2 attached via sinking weight cable 25
Perform mooring according to 6.

Figure 1 shows the results of a model experiment regarding transmittance.

Figure 7a shows the results when mooring is relatively gentle;
The figure shows the results during tension mooring.

The experiment was conducted using a two-dimensional model in a wave tank, and the vertical axis shows the ratio of the transmitted wave height HT to the incident wave height Hi (transmittance) and the ratio of the reflected wave height HR to the incident wave height Hi (reflectance).
, and the ratio of wavelength λ to plate width B is plotted on the horizontal axis.

In general, the wave-dissipating effect of a floating wave dyke is most closely related to the wave wavelength (sea period), and the longer the wavelength, the more difficult it is to disappear, but according to common sense, the expected wave-dissipating effect is assumed to be at least 50%. There is.

According to the experimental results shown in FIG. 1, λ/B-5 is the design point.

Although the air holes 15 and 16 are simply opened for simplicity, they may be provided with appropriate valves or may be covered with a net.

It is also possible to provide a power generator in combination with an air turbine.

The same applies to the air communication pipe 14.

The key point is that it is constricted and provides resistance to air circulation.

FIG. 8 shows another embodiment in which the longitudinal floating body 18 is omitted and the widthwise floating bodies 27 at both ends are formed in a U-shaped cross-section in the width direction.

FIG. 9 shows yet another embodiment, in which the floating bodies 28 and 29 in the longitudinal and width directions are constructed of pipes, and pipes 30 are also erected at the four corners of the wave-dissipating bank.

FIG. 10 shows an embodiment in which the intermediate walls and outer walls of the tanks 11 to 13 are composed of floating bodies 31 having a triangular cross section, and FIG.
An example is shown in which the floating body attached to the lower part of the intermediate wall of tanks 11 to 13 is constructed of type 33.

FIG. 12 shows an embodiment in which the tanks 11 and 13 on both sides are inverted U-shaped from the beginning, and the inverted U-shaped tanks 11 and 13 and the center tank 12 have air holes 34 and 35, respectively.

As described above, the present invention has the following advantages.

In other words, not only the transmittance but also the reflectance can be reduced, it has excellent wave-damping performance, and the steel structure makes it durable.
Weather resistance can be improved and the structure can be made simple and sturdy.

In addition, the draft is shallow considering its size, and the wave force (mooring force) is relatively small.

It is also possible to generate electricity using airflow, and can generate enough electricity to power a marker light.

Furthermore, safety can be doubled if sinker mooring is used in addition to mooring in the wave direction.

Furthermore, since it is a floating wave levee, it can be installed even in deep water, and the construction cost is low considering the depth of the water.

In addition, since it does not inhibit seawater exchange, there is no seawater pollution, making it suitable for fish farming.

Furthermore, it will not have any negative impact on fish, and in fact can be expected to work as a floating fish reef.

Furthermore, it is easy to construct and requires only a short period of time, and it is also easy to move and remove.

[Brief explanation of drawings]

Fig. 1 is a schematic sectional view showing one embodiment of the present invention, Figs. 2 to 4 are illustrations to explain the principle, Fig. 5 is a perspective view of one specific example, Fig. 6 is an illustration to explain mooring, and Fig. 7 8a and 12b are characteristic diagrams showing the results of model experiments, and FIGS. 8 to 12 are perspective views and sectional views showing other examples, respectively. 1-3, 11-13...Bottomless tank, 4゜1
4...Communication pipe, 5, 6, 15, 16...
・Air hole, 18.19... Floating body, 22...
...Mooring rope, 23...Anchor, 27-33.
...Floating body, 34,35...Air hole.

Claims (1)

[Claims] 1 A bottomless box-shaped tank is divided into three parts in the direction of wave propagation, and the bottomless tanks on both sides are connected to each other by providing resistance at the top, and the bottomless tanks on both sides and the center bottomless tank are provided with resistance at the top to communicate with the atmosphere. 1. A floating breakwater, characterized in that a floating body that is connected to the tank and has most of the buoyancy is provided below the water surface of the tank, and a means for mooring the tank is provided.