JP2557740B2 - Tendon tension introduction method for vertical mooring offshore floating platform - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a vertical hull having a hollow cylindrical buoyant body moored by a vertical tendon for a gravity anchor sunk below the hull. The present invention relates to a tendon tensioning method for increasing the buoyancy so that a predetermined tension is applied to a tendon when a mooring offshore floating platform is installed.

(Prior Art) Conventionally, this type of vertical mooring offshore floating platform has a hull formed by integrally supporting a deck plate on the upper ends of three or more hollow columnar buoyancy bodies, and Anchors are connected to each other via a vertical tendon, and the length of the buoyancy body is made sufficiently long to minimize the vertical and horizontal swings due to wave forces.

When installing this floating platform on the sea, ballast water is injected into each buoyancy body of the hull, and it is submerged to a stable state by itself and floated above the water surface to connect a tendon to the anchor at the bottom of the water.

At this time, the tendon is in a slackened state so that the hull can rise to a predetermined design height. In this state, when the tension is introduced to the tendon, the ballast water is drained to increase the buoyancy and the hull is levitated, and the metacenter M moves from the upper part of the center of gravity G to the lower part before the tension is applied to the tendon.
Changes from + to-and the hull becomes unstable and capsizes.

Therefore, conventionally, it has been necessary to lift the hull by a crane ship to drain the ballast water while preventing the caps from overturning and to introduce a desired tension force to the tendon.

(Problems to be Solved by the Invention) In such a conventional tendon tension force introduction method, a crane ship for hoisting the hull is required at the installation site, and it takes a long time to make a round trip and the cost is high, and Since it is not possible to maintain the suspended state for a long time on the sea, intensive work is required in a short time, and there is a problem that it is difficult to perform accurate work management.

The present invention has been made in view of the above problems, and an object thereof is to provide a tendon tensioning method capable of completely performing work under accurate construction management without requiring a large crane ship.

(Means for Achieving the Object) The gist of the present invention for achieving the above object is to float a hull in which deck plates are supported on the upper ends of a plurality of hollow columnar buoyant bodies above the water surface. With
The gravity anchor is sunk below the vertical, a tendon is stretched between the anchor and the hull, and when the tension required to stabilize the hull is applied to the tendon, the tendon is attached to the buoyant body of the hull. Inject ballast water that can maintain stability without tension applied and float on the water surface on the anchor,
While fixing the lower end of the tendon to the anchor and fixing the upper end of the tendon to the buoyancy body, eliminate the slack of the tendon at high tide and increase the buoyancy without lowering the hull even when the tide decreases. There is a method of introducing tension force of a vertical mooring offshore floating platform, which is characterized in that the buoyancy of a buoyancy body reaches a planned buoyancy by discharging ballast water.

(Operation) In the tendon tension force introduction method of the present invention, the ballast water is sufficiently injected into the buoyancy body of the hull and kept in a stable state by itself, and when the tide level is high, the slack of the tendon is removed to remove the ballast water. Start sampling. And
By making the extraction speed the speed at which the hull rises due to the increase in buoyancy, rather than the descent of the hull due to the decrease in tide level,
Tendon becomes tense, buoyancy increases while GM is in the + state, and the required tense force is given.

By allowing the top end fixing position of the tendon with respect to the buoyancy body to be adjusted up and down, the height of the hull can be adjusted after the buoyancy body is sufficiently buoyant.

(Example) Next, the Example of this invention is described about drawing.

FIG. 1 shows an example of a vertical mooring type offshore floating platform installed by carrying out the present invention. In the figure, A is a hull, B is an anchor, and C is a tendon.

As shown in FIG. 2, the hull A is composed of four hollow cylindrical vertically oriented buoyant bodies 1 and a deck plate 2 integrally supported on the upper end thereof.

The anchor body B is formed by connecting four anchor blocks 3 located vertically below each buoyancy body 1 by connecting them with a steel connecting groove 4.

The tendon C is stretched between each buoyancy body 1 and the anchor block 3, and moored in a state where the buoyancy body 1 is pulled into the water by the tension necessary to prevent the buoyancy body 1 from falling even at the lowest tide.

As shown in FIG. 3, each buoyant body 1 is provided with a tendon attachment chamber 5 in the upper end thereof, and the upper end of the tendon C is fixed to the floor surface of the chamber 5 by a tendon upper end fastening device 6.
The tendon C is extended downward through the inside of the tendon insertion tube 7 at the center of the buoyancy body 1. A buoyancy adjusting chamber 8 is provided below the tendon mounting chamber 5 of the buoyant body 1, and ballast water is poured and drained by a pump (not shown).

The tendon upper end fastening device supports a tendon stopper 9 retaining the upper end of the tendon C on a base frame 12 via a height adjusting frame 10 and a spacer ring 11, and a pair of hydraulic jacks 13 are mounted on the base frame 12 as spacers. Hydraulic jack supported by ring 14
Hold the height adjustment frame 10 with 13, and hold the tendon C
The upper fixed height of the can be adjusted.

Next, a method of introducing tendon tension force at the time of installing this platform will be described with reference to FIGS. 1 (A) to 1 (D).

Standing for the introduction of tension, the anchor B is installed on the water bottom 20 as shown in FIG. 1 (A). The hull A injects ballast water 21 into the buoyancy body 1, sinks to a state where stability can be maintained even without the tendon C, floats on the anchor B, and causes the tendon C to sag between the hull A and the anchor B. Connect in a state. The length of the tendon C is predetermined according to the water depth at the installation position so that the hull A has a desired design height when the buoyancy is maximum. Further, the height position of the upper end of the tendon, that is, the height of the tendon stopper 9 is set to the most lowered position where the hydraulic jack 13 is contracted most. Further, in this state, even if the hull A moves up and down due to the change of the tide level, the tension force is not generated in the tendon C.

There is a drop in the tide level at this level, and the height of the tendon stopper 9 is at the highest position as shown in FIG. 1 (B) when the tide level is low, that is, the design height at which the hull A has a desired design height when the buoyancy is maximum. Raise to the position and have high tide. When the high tide is reached, the hull A rises and the slack of the tendon C disappears as shown in FIG. 1 (C).

The slack may be removed by waiting for the high tide with the tendon stopper 9 kept low and raising the tendon stopper 9 at the high tide.

In this way, the slack of the tendon C is removed when the tide is high, and the ballast water 21 is started to be extracted. This extraction speed is set so that the ascending speed of the hull A due to the increase in buoyancy is faster than the descending speed due to the decrease in the tide level.

As a result, the hull A is maintained in a state where the rise due to the buoyancy is always regulated by the tendon C, and when the ballast drainage is completed (Fig. 1 (D)), the hull A is in the maximum buoyancy state corresponding to the tide level, C also has a tension corresponding to the hull buoyancy. Furthermore, in this state, there is no change in the height of the hull due to the change in tide level, and the tendon can maintain the designed tension even at the lowest tide.

After the ballast water is completely drained in this way, the position of the tendon stopper 9 can be finely adjusted as necessary to remove the hull A.
Is the planned height.

(Effects of the Invention) As described above, in the tendon tension force introduction method of the present invention, by utilizing the tide level, the ballast water is drawn out while the hull is always kept in a stable state, and the tendon is tensioned. , The assistance of crane ships is no longer needed,
Economic efficiency is significantly improved.

In addition, since the work is performed according to the tide level, concentrated work for a short time is not required, and safe and stable work can be performed. In addition, stable hull stability (restoring force curve, etc.), ballast water drainage capacity, tide level change, and Accurate construction management is possible because it is a method that comprehensively considers the weather and sea conditions.

[Brief description of drawings]

The drawings show an embodiment of the present invention and are shown in FIG.
(D) is a cross-sectional view showing the tendon tensioning force introducing step, FIG. 2 is a perspective view of a completed platform, and FIG. 3 is a vertical cross-sectional view of the relevant part. A ... Hull, B ... Anchor, C ... Tendon, 1 ...
Floating body, 2 ... Deck plate, 3 ... Anchor block, 4 ...
… Connecting groove, 5 …… Tendon mounting chamber, 6 …… Tendon upper end fastening device,
7 ... Tendon insertion tube, 8 ... buoyancy adjustment chamber, 9 ... Tendon stopper, 10 ... adjustment frame, 11,14 ... spacer ring, 12 ... base frame, 13 ... hydraulic jack, 20 ... water bottom , 21 …… Ballast water.

Claims (1)

(57) [Claims] 1. A hull having a deck plate supported on the upper ends of a plurality of hollow columnar buoyant bodies is floated above the water surface, and a gravity anchor is sunk vertically below the hull, and a tendon is placed between the anchor and the hull. When the tension is applied to the tendon and the tension necessary to stabilize the hull is applied, ballast water that can maintain stability without tension is applied to the buoyant body of the hull is added to the water surface on the anchor. Float to the anchor, fix the lower end of the tendon to the anchor, and fix the upper end of the tendon inside the buoyancy body to eliminate the slack of the tendon at high tide and increase the buoyancy without lowering the hull even when the tide level decreases. Tendon tension of a vertical mooring offshore floating platform characterized by buoyancy of buoyancy bodies reaching planned buoyancy by discharging ballast water at a constant speed Introduction method.