JPS6045495A - Mooring gear for tension leg type marine structure - Google Patents

Abstract

PURPOSE:To check a variation in tensile force for a mooring cable, by pivoting a lever member, provided with a counterweight for its one end and a delivery device of the other end, on an upper deck, while installing a damping device interposingly between the lever member at the opposite side to the counterweight and the upper deck. CONSTITUTION:A lever member is pivoted on an upper deck of a tension leg type marine structure with a pin fulcrum 17. A counterweight 16 is attached to one end of the lever member while a delivery device 12 to the other end, respectively, and a damping device 11 is installed interposingly between a lower part of the lever member at the opposite side to the counterweight 16 and the upper deck 1. Weight of the counterweight and a locking device is properly selected whereby such force that constantly acts on the damping device 11 can be brought to zero. Therefore, a variation in the tensile force produced in a mooring cable due to wind force, wave force and so on can be held down to the smallest possible extent.

Description

[Detailed description of the invention] The present invention provides a mooring device for a tension-pushed offshore structure.

Conventionally, a so-called tension leg (or tension mooring) marine structure has been used as a type of floating marine structure with the purpose of improving its oscillation characteristics in waves. ) has been proposed.

As shown in Fig. 1, a tensile and push-type offshore structure basically consists of a working deck 11 above the sea surface 6 and a plurality of supporting columns 2.
(In many cases, it also serves as a buoyant body), consists of a horizontal member 3, a tensioned mooring line 4, and a sinker 5 that has landed on the seabed. The initial tension F of the mooring line 4 is made equal to B-W to maintain balance, and this prevents the structure from shaking in waves (in particular, vertical, pitching, and side-to-side buoyancy). It is possible to reduce the amount of vibration caused by

However, the natural frequency of marine structures whose vibrations are reduced by such means is usually 3 seconds to lO
This is on the order of seconds, which often coincides with the period of 3 to 30 seconds of waves occurring in the ocean, so such marine structures have the disadvantage that excessive tension is generated in the mooring lines during synchronization.

Therefore, in order to eliminate this drawback, the cross-sectional shape of the horizontal member was made elliptical to reduce the resistance and inertial force, and the ratio of the displacement amount of the horizontal member to the total displacement was set to '> o, a ~ 0.6 to reduce the cable tension. What is the ratio between the initial tension and the displacement of the structure'
&0.05~0.3. The ratio of sinker displacement to sinker weight is 0.1 to 0.45. The ratio of the weight of the sinker to the displacement of the structure "aj O, 1 to 0.6. The range of various parameters may be limited, such as by setting the ratio of the displacement of the sinker to the displacement of the structure to 1.05 to 1.30. etc. have been proposed.

However, apart from the shape and dimensions of the submerged part, there are examples of mooring devices for marine structures that incorporate appropriate damping mechanisms to reduce tension fluctuations that occur in mooring lines in waves and sway of the structure. There is no end in sight.

The present invention was proposed in view of the above circumstances, and an object of the present invention is to provide a mooring device for a tensile solid marine structure that reduces tension generated in a mooring line due to waves.

To this end, the present invention provides a working deck, a plurality of struts that support the working deck and which together constitute a buoyant body, and a horizontal member which constitutes a buoyant body when it constitutes a structural strength member of the plurality of struts. In a so-called tensile rigid marine structure, in which a structure consisting of A plurality of lever members each having a mooring rope winding-in and letting-out device are provided, and a damping device having a spring constant and a damping constant, which is provided between the working deck and the other end of each of the lever members. It is characterized by a wandering from Issumi Soyoko.

First, to explain the principle of the mooring device for a tensile solid marine structure of the present invention, Figure 1 is a conceptual diagram thereof, Figure 2 is an explanatory diagram replacing Figure 1 with a one-mass model, and Figure 3 is a diagram of the mooring system. This is a mechanically equivalent model of Figure 2.

In Fig. 1, l is a working deck, 2 is four pillars that support the working deck l and also serves as a buoyant body, 3 is a horizontal member connecting the lower ends of each pillar 4, and 4 is a horizontal member whose upper end is connected to each other. Pillar 3
Four mooring lines are connected to the sinker 5, which extends along the line and is wound around the winch 12 on the working deck l, and both have their lower ends anchored on the seabed 7, 6 is on the sea surface, and 11 is on the working deck l. This is a damping device for damping fluctuations in the tension of the mooring line 4 fixed to the mooring line 4.

Tensions generated in the mooring lines of tensile rigid marine structures due to waves are generally determined by highly restrained (4-) heave, pitch, and roll motions; Equation of motion fi for the equivalent model shown in Figure 3
The natural period Th is expressed by (4).

-F W・・・・・・・・・・・・・・・ (1,) With a small roof tile, W: Weight of the structure W′: Additional weight g: Acceleration of gravity γ: Specific gravity of seawater AW: Strut 2 water line area d: For swamping: Spring constant of mooring line 4 (hard) C: Damping constant Ke of damping device 11 Equivalent spring constant Ce: Equivalent damping constant ω: Circular frequency of waves (=2π/T) T : Wave period z, z, Z: Longitudinal acceleration and velocity of the structure.

displacement Fw: Wave power F: Initial tension of mooring line It is.

Next, set the following parameters.

α；に／（γ・Aw）・・・・・・・・・・・・・・・
・ (5) δ=F/W ・・・・・・・・・・・・・・・
・ (7) ε-W/W ・・・・・・・・・・・・・・・
・(8) Then, α;・Spring constant/ratio of displacement per senna β: Damping ratio δ: Initial tension/weight ratio ε: Added mass coefficient.

The solution Zd of the equation of motion (1) is given by (9).

However, η==Th/T.

On the other hand, the solution Zd' of the equation of motion for a conventional structure without a damping device is Ce-0°K e =
By setting it as K, it becomes (lO).

Therefore, if the tension of the mooring rope with and without a damping device is zFd, Fd', the ratio F'd/Fd'
(Dynamic response magnification DAF'F) is given by (11), and the ratio of dynamic displacement to static displacement, AFX, is given by (12).

(12) For normal tensile solid marine structures, the parameters shown in (7), (8), etc. are set within the following ranges.

0.1〈δ〈1. In the range shown in O d = 20 m w 3 Q m T = 3 seconds to 30 seconds (14), the dynamic response magnification DAF'
When F becomes 0.8, 0.6, 0.4 or less, the conditions that parameters α and β must satisfy in order for the ratio of dynamic displacement to static displacement DAFX to become (&) 1.3 or less. When shown together, it is the hatched area in the diagram of FIG.

Conversely, by selecting the attenuation constant C appropriately, the parameters α and β in the hatched range in FIG.
If you select , the dynamic response magnification DAFF of the mooring line is 0.
．． When it goes below 8, DAFX goes below 1.3,
This means that the fluctuation of the mooring line tension can be used to greatly reduce the movement of the structure.

By the way, to give a concrete numerical example, the specifications of the structure shown in Figure 5 are as follows: weight W = 25,500, water line area Aw = 530.9 m'', initial tension F = 45oot, mooring line Spring constant = 668 t/m Damping constant C = 400 - Stuttering d = 30 m ξ = 0.534 (water tank test result) At this time, calculating α and β from (5) and (6) (ID) α = 668/(1,025X530.9)=1.28=
0.182, and from Figure 4 it can be seen that D A FF (Q, 4).

In addition, the calculation results of the structure shown in Figure 5 using a wave response calculation program whose analysis accuracy was confirmed through water tank tests, etc. are shown in Figure 6.
By inserting the damping device 11 between the sinker 5 and the mooring line winch 12 as shown in FIGS. (5), (B), ◎, and It was found that the tension fluctuation was significantly reduced compared to the case where the damping device shown by the broken line was not visible.

Embodiments of the present invention will be explained with reference to the drawings. FIGS. 7, 8, 9 (B), 10, 11 (5),
03), (Q is the 11th, 2nd, 3rd, and 4th
, FIG. 12(5) is a side view showing the fifth embodiment, and FIG. 12(5) is a longitudinal sectional view showing the damping device.

First, in the first embodiment shown in FIG. It is equipped with a lashing device 14 that releasably lashes the cable 4, and when the mooring cable is rolled in and let out by the mooring cable winch 12, the mooring cable is secured after applying a predetermined initial tension FY to the mooring cable. The mooring line 4 is secured by the device 14. After that, the mooring line winch 12
Slightly loosen the mooring line 4 between the mooring line winch 12 and the lashing mechanism 14 by letting out the mooring line. In this way, the initial tension F acts steadily on the damping device 11, and even if the structure sways due to wave force or wind force, fluctuations in the tension occurring in the mooring cables are greatly reduced. The movement of the structure itself can also be suppressed to a minimum with this.

In the second embodiment shown in FIG. 8, a damping device 11 having a protruding pulley 15 is installed obliquely on the edge of the working deck l, and after the upper end of the mooring rope 4 is hooked around the pulley 15, the mooring rope Wound around the winch 12, a steady force of about 77 times the initial tension F acts on the damping device 11.

In the third embodiment shown in FIGS. 9(5) and 9(B), a fulcrum 17 is pivotally mounted on the working deck l with a pin, and when the mooring line winch 12 is fixed on one end, the counter on the other end is fixed. A lever fixed to the weight 16Y is provided, and the left end of the lever ((5) in the same figure) is attached to the upper surface of the damping device 11 fixed on the work deck l.
(see 0) or the right end of the lever (see 0 in the same figure).

In both cases, damping is achieved by appropriately selecting the weight (Counterway) 160 and its fixing position.

The force that constantly acts on the device 11 can be reduced to almost zero.

The fourth embodiment shown in Fig. 1O is constructed by constructing two parts shown in Fig. 9 (5) symmetrically around the bottle 17, and the initial tensions p, , F' are The balance of the moments eliminates the need for a counterweight, and the force constantly acting on the damping device 11, l l'C 40 can be reduced to almost zero.

Figure 11 (5), (B), (The fifth embodiment shown in Q is a damping device 11"% midway along the mooring line 4 (see figure (A))
, the upper part of the sinker 5 (see figure 1), and the inside of the sinker (see figure q) inserted into the mooring line 4.

FIG. 12 shows the structure of the damping device 11, and the same figure shows a rubber damper consisting of a piston P slidably inserted into a cylinder and a rubber cylinder r fitted on each side, and a rubber damper (B) shown in FIG.
) is a hydraulic damper in which both pressure chambers of a hydraulic cylinder are connected through an oil o'%6 valve v)4, and a restoring spring S is inserted therein.

The above embodiment can produce substantially the same damping effect as the first embodiment shown in FIG.

Furthermore, mooring cables include steel wire, chains, and
You can use synthetic fiber lobes, tubular members (pine), and combinations of these with springs.

The present invention is directed to a tow-legged marine vessel, regardless of its shape, such as semi-submersible, dock, or pontoon type, which is used for offshore oil exploration, production, and storage facilities, offshore plants, offshore airports, maritime cities, and other offshore working and living spaces. It can be widely applied to structures in general.

In short, according to the present invention, a working deck, a plurality of struts that support the working deck and also constitute a buoyant body, and a structural strength member of the plurality of struts constitute a buoyant body. In so-called tension leg type marine structures, in which a structure consisting of a horizontal member and a horizontal member is moored by a plurality of mooring ropes stretched underwater, the center part of each structure is pivoted on the working deck, and a counterweight is attached to one end. A plurality of lever members each having a mooring rope winding-up device attached to an end thereof, and a damping device having a spring constant and a damping constant provided between the work deck and the other end of each of the lever members. Accordingly, there is provided a mooring device for a tension leg type marine structure that minimizes fluctuations in tension caused by mooring elements due to wind power, wave force, etc., and also minimizes oscillation of the structure. Therefore, the present invention is extremely useful industrially.

[Brief explanation of drawings]

Figure 1 is a detailed explanation of the present invention.
The figure is an explanatory diagram in which figure 1 is replaced with a one-mass point system motil, figure 3 is the mechanical equivalent model of figure 2, figure 4 is the dynamic response magnification r
)A, +I゛, rr is 0.8 or less, N is also a dynamic displacement to static displacement ratio DAF'X of 1.3 or less, a diagram showing the range of parameters α, β. Figure 5 is a perspective view of a marine structure showing a specific numerical example;
), (Q, (1)) are diagrams showing the vibration characteristics of the structure shown in Fig. 5 with a damping device (solid line) and without a damping device (broken line), respectively, and Fig. 7,
Figure 8, Figure 9 (5), (Ugly Figure 1O, Figure 11,
(l(), IC) are the eleventh and second of the present invention, respectively.
FIG. 12 is a partial side view showing the third, fourth, and fifth embodiments, and FIG. 12 (i3) is a longitudinal sectional view showing the damping device, respectively. 1... Working deck, 2... Support, 3... Horizontal member,
4... Mooring line, 5... Sinker, 6... Sea surface, 7
... seabed, 11... damping device, 12... mooring line,
Sub-representative Patent attorney Masafumi Tsukamoto (and 1 other person)

Claims (1)

[Claims] A structure consisting of a working deck, a plurality of struts that support the working deck and constitute a buoyant body, and a horizontal member that constitutes a buoyant body when the structural strength members of the plurality of struts are constituted. In so-called tension-and-push marine structures, in which moorings are moored by multiple mooring lines stretched underwater, each center part is pivoted on the working deck, a counterweight is attached to one end, and a mooring cable winding and feeding device is attached to the other end. a plurality of lever members attached thereto, and a damping device provided between the work deck and the other end of each of the lever members and having a spring Φ constant and a damping constant. Mooring equipment for marine structures.