JPH0478513B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a submersible floating body of a semi-submersible marine structure used for offshore oil drilling and the like.

(Prior art and its problems) This type of semi-submersible marine structure, as shown in FIG. Various types of structures have been developed since they consist of a buoyant body 3 and have little oscillation in waves.

In such a lower hull type semi-submersible marine structure, a relatively large steady upward force acts on the submersible buoyant body 3 just below the water surface in the waves, and this steady upward force acts on the submersible buoyant body 3 just below the water surface. The closer you get, the bigger it gets. This means that, as shown in Figure 3, the motion of water particles under the water surface draws an arc in the direction of wave propagation, and the speed decreases rapidly as the water depth increases (it decreases with a logarithmic function). )It is known. Therefore, as for the difference between the flow velocity on the upper surface and the flow velocity on the lower surface of the submersible buoyancy body 3, as the water depth becomes shallower, the upper surface flow velocity becomes larger, and as is clear from Bernoulli's law, the upward steady force increases.

Therefore, as shown in Figure 4, if a lower hull type semi-submersible offshore structure tilts in a certain direction on a time-average basis due to some action, the submersible buoyancy structures on both sides (although not necessarily two) Since the water depths of 3 are different, a moment (overturning moment) M is generated in the direction of increasing the inclination due to the difference in the upward steady forces acting on these, resulting in further inclination.

Since such an inclination is unfavorable in various respects, it is desired to reduce the overturning moment M and stabilize the posture of the structure, and various methods have been proposed.

As a conventional example of controlling the upward steady force acting on a submersible buoyant body, there is a method for controlling the attitude of a semi-submerged marine structure (Japanese Patent Application Laid-Open No. 60-61395).

As shown in Fig. 5, this attitude control method involves attaching a submersible buoyant body 3 to the offshore structure 1 so that it can move up and down, measuring the inclination of the offshore structure 1 with an inclinometer, and determining whether the floating structure 1 sinks due to the inclination. By raising the submersible buoyant body 3 on the lower side, the upward steady force acting on the submersible buoyant body 3 on the sunken side is increased, thereby generating a restoring moment and reducing the overturning moment. be.

However, this attitude control method has a complicated structure because it moves the diving buoyancy body up and down.
There is a problem that it is not very practical as it requires more power.

This invention was proposed to solve these problems, and its purpose is to create a semi-submersible marine structure that has a relatively simple configuration and can reduce overturning moment without requiring power. The objective is to provide a diving buoyant body.

(Means for Solving the Problems) The present invention provides a semi-submersible marine structure having a submersible buoyant body located underwater to levitate the marine structure. The above problem is solved by vertically providing a fin-like blocking body in the longitudinal direction to prevent the movement of fluid passing over the buoyant body in a direction perpendicular to the longitudinal direction of the buoyant body. It is.

(Function) When the submersible buoyant body rises near the water surface due to the inclination, the movement of the fluid on the upper surface of the submersible buoyant body is blocked by the fin-like blocking body, and the fluid moves together with the submersible buoyant body, thereby causing downward steady flow. The upward steady-state force is reduced due to the generation of force, and the overturning moment acting on the semi-submersible offshore structure is reduced.

(Example) The present invention will be described below based on an illustrative example.

As shown in FIGS. 1 and 2, fin-like blocking plates 4 are vertically provided on both sides of the upper surface of the submersible buoyant body 3 in the longitudinal direction, and when the submersible buoyant body 3 rises near the water surface, The movement of the fluid on the upper surface of the submersible buoyant body 3 is prevented by the fin-like blocking plate 4 . If the fluid movement on the upper surface of the diving buoyant body 3 is blocked, the flow velocity in the vicinity becomes slower than when there is no blocker,
According to Bernoulli's theorem, the pressure increases and the upward steady-state force decreases, which reduces the overturning moment acting on the lower hull semi-submersible offshore structure.

FIG. 1A shows that the blocking body 4 is connected to the diving buoyancy body 3.
This is an example of a submersible buoyant body being directly launched from the ground and installed intermittently along the length of the submersible buoyant body. They are installed intermittently, and are driven into the top surface of the submersible buoyant structure when the structure is moving while the submersible buoyant structure is floating (when the structure moves from place to place, the submersible buoyant structure is above the water surface). This is to serve as a water outlet so that seawater can go out.

The example shown in FIG. 1B is an example in which a blocking body 4 is vertically installed on a diving buoyant body via a support 5. In such an embodiment, by attaching the blocking body 4 through the struts 5, the position of the blocking body 4 can be raised, and furthermore, the space between the struts 5 serves as a water outlet during mobile navigation. In addition, in this example, the blocking bodies 4 are installed continuously, but
It may be installed intermittently.

Although the example in which two submersible buoyant bodies 3 are provided is shown, the present invention is not limited to this, and the blocking bodies 4 are installed in a total of four locations on two submersible buoyant bodies 3, but one submersible buoyant body 3 It is sufficient to install it in one place.

(Effects of the Invention) As described above, according to the present invention, the following effects are achieved because the blocking body capable of blocking the movement of the fluid on the upper surface is provided on the upper surface of the submersible buoyant body.

(i) With a relatively simple configuration and without the need for power, it is possible to reduce the steady upward force acting on a submersible buoyant body, and it is possible to reduce the overturning moment acting on a semi-submersible offshore structure.

(ii) As an incidental effect, the primary wave forcing force in the vertical direction (a forcing force that fluctuates with the wave cycle) acting on the submersible buoyancy body becomes smaller. Therefore, it is expected that the vertical movement of semi-submersible offshore structures will be reduced.

(iii) Furthermore, as the added mass increases, the natural period of motion becomes longer, making it easier to avoid synchronization with waves. It is expected that the vibration amplitude will also become smaller.

(iv) Furthermore, since waves are more likely to collapse on the upper surface of the submersible buoyant body, the distance (air gap) between the water surface and the under deck of the semi-submersible offshore structure can be reduced.

[Brief explanation of the drawing]

1A, B and 2A, B are front views and perspective views showing various embodiments of the diving buoyancy body according to the present invention, FIG. , an overall schematic diagram showing a semi-submersible marine structure in a tilted state, and FIGS. 5A and 5B are schematic diagrams showing a conventional semi-submersible marine structure. 1... Offshore structure, 2... Support column, 3... Submersible buoyant body,
4... Blocker, 5... Support.

Claims (1)

[Scope of Claims] 1. In a semi-submersible marine structure having a submersible buoyant body located underwater to levitate the marine structure, the top surface of the submersible buoyant body is provided with a fin-shaped block in the longitudinal direction of the buoyant body. A submersible buoyant body of a semi-submersible marine structure, characterized in that the body is vertically disposed to prevent movement of fluid passing over the buoyant body in a direction perpendicular to the longitudinal direction of the buoyant body.