JPS5924617B2 - Underwater cable installation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for laying an underwater cable, and more particularly to a method for laying an underwater cable between a floating body floating on the water surface and the bottom of the water.

For example, when generating wave power, a floating body equipped with a generator is floated on the sea, and an underwater cable is lowered from the floating body into the water and laid along the bottom of the water to transmit the generated power to land. , power will be transmitted to shore.

In this case, there is a disadvantage that the descending portion of the underwater cable from the floating body is easily damaged by the floating of the floating body.

In order to improve such drawbacks, the present applicant first suspended a flexible hanging elongated body 3 for supporting cables such as a Che 7 from a floating body 2 floating on the sea surface 1, as shown in FIG. The underwater cable 4 is lowered along this flexible hanging long body 3, and the falling part 4A of this underwater cable 4 is intermittently clamped to the flexible hanging long body 3 with a plurality of clamp parts 5. , the cable 4 below from the clamp part 5A at the lowest point passes through the cable bending part 4B and the extra length floating part 4C with sufficient extra length to the bottom 6 of the water.
We have proposed an underwater cable laying method in which a plurality of floats T are attached to the extra length floating part 4C and this part of the cable 4 is suspended in the water.

According to this installation method, since the extra length floating section 4C can move freely, the movement of the underwater cable 4 due to the floating of the floating body 2 can be absorbed by this extra length floating section 4C, and the underwater cable 4 can absorb the movement of the underwater cable 4 due to the floating of the floating body 2. It is possible to prevent damage caused by being dragged along, or damage caused by concentration of strain at the lowering point.

However, this method of laying the cable has the drawback that the floating state of the cable in the sea is extremely unstable, making it quite difficult to actually lay the cable.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for laying an underwater cable in which a stable floating state of the underwater cable-huft VBI extra length floating section can be obtained and a sufficient amount of absorption against floating can be obtained.

Hereinafter, specific examples of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 2, in this embodiment, when laying the underwater cable 4 from the cable head 9 on the floating body 2 floating on the sea surface 1 to the cable head 9 on land 8, the falling part 4A of the underwater cable 4 is , the bent portion 4B, and the extra length floating portion 4C have almost the same configuration as in FIG.

Therefore, in the present invention, the number and size of the floats T are set such that the ratio is 0.9 to 1.3 in the cable section from the final clamp section 5A of the underwater cable 4 to the bottoming point 4D at the end of the extra length floating section 4C. The purpose is to select the

When selected in this way, the extra length floating part 4C that absorbs floating
However, it was found through experiments that a stable shape can be maintained.

Furthermore, floating is not limited to floats, but there are also methods of providing buoyancy using other floating bodies or the structure of the cable itself.

The buoyancy factor in this case is becomes.

An underwater cable 4 is laid along the seabed 6 from the bottom landing point 4D to land 8.

At the bottoming point 4D, in order to stabilize the bottoming point 4D, anchors, sinkers, etc. are attached to the underwater cable 4 after the bottoming point 4D.
In some cases, a stopper such as a weight is applied.

FIG. 3 shows an example of vibration absorption when the floating body 2 is rocked.

Floating body 2 is affected by waves x, y. Movement in 203-dimensional directions is possible.

When moving in two directions, the floating body 2 moves to the position 2', so the underwater cable 4 remains floating in the sea and moves as shown by the broken line \4', and the cable bend 4B and the excess length move. The influence of movement of the floating body 2 is absorbed by the shape deformation of the floating part 4C.

In addition, in the case of floating in the X direction, the floating body 2 moves to position 2, and the underwater cable 4 is thereby pulled and 4
It has the shape shown by the dashed line and absorbs the effects of the movement of the floating body.

The movement in the X direction is also absorbed, and by combining them, the floating body 2
The influence of any oscillations on the underwater cable 4 can be absorbed by the extra length floating section 4C, and if the buoyancy factor is within the above range, the shape of the extra length floating section 4C is always stable and even high frequency oscillations can be safely absorbed. Can be done.

The buoyancy factor is adjusted by adjusting the number of 10 floats with a target of 1.0 at the time of laying, so if one float is attached by mistake or one comes off after laying, the shape will be divided by 0.9. It is undesirable to be unable to maintain it.

Therefore, the buoyancy of one float γ is 1.0-0.9 = 0
．． Preferably, the buoyancy factor is 1 or less.

That is, it is preferable that the total number of floats 1 is 1°0=10 or more.

If this value is set to 0.1, even if one float I is dislodged, it will still float, so the fact that it has dislodged can be immediately known, and the work of replacing the boxwood can be done easily.

Further, it is preferable to label the float 1 with a number or symbol so that it can be immediately determined which float γ has come off.

Furthermore, providing the tubular guide 10 near the final clamp portion 5A is effective in alleviating concentration of strain on the underwater cable 4.

As explained above, in the present invention, the buoyancy factor of the underwater cable between the final clamp part and the bottoming point is selected to be 0.9 to 1.3, so the extra length floating part of the underwater cable is connected to the water surface. The reproducibility of floating in water between the cable and the bottom of the water is ensured, and the present invention can be easily carried out regardless of the size or type of cable.

Furthermore, according to the present invention, the underwater condition of the floating part of the underwater cable with the extra length is stabilized, so even if the floating body moves vertically and horizontally on the water surface, the accompanying movement of the underwater cable can be controlled by this stable extra length. This can be absorbed by the long floating part, and it is possible to reliably prevent the bottom part of the underwater cable from moving and being damaged by the movement of the floating body.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional laying method, FIG. 2 is an explanatory diagram showing an example of the laying method of the present invention, and FIG. 3 is an explanatory diagram showing a state of absorption of vibration in the laying method of the present invention. 1...Water surface, 2...Floating body, 3...
...Flexible hanging long body, 4...Underwater cable, 4A...Descent part, 4B...Bending part, 4C...Remaining part Long floating part, 4D...Bottom landing point, 5...Clamp part, 5A...Final clamp part, 6...Bottom, 1... ...Float, 8...Land.

Claims (1)

[Claims] 1. When lowering an underwater cable from a floating body floating on the water surface and laying it along the water bottom, a flexible hanging elongated body is suspended from the floating body, and the falling part of the underwater cable is connected to the flexible hanging body. An underwater cable installation method in which the underwater cable is lowered while being clamped to a long body, and the underwater cable separated from the final clamping part lands on the bottom through a bent part and a floating part with an extra length of a required length, wherein the underwater cable lands on the bottom from the final clamping part. A method for laying an underwater cable, characterized in that the buoyancy factor of the underwater cable up to the point is selected to be 0.9 to 1.3.