JP3198698B2 - Box-shaped floating structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a box-type floating structure such as various types of plant ships and workboats.

[0002]

2. Description of the Related Art Conventionally, a semi-submersible structure in which a large part of a floating body is below a water line and a water line area is considerably small has been adopted in order to reduce a vertical movement of an offshore structure in waves. . Semi-sub oil drilling rigs are a typical example.

However, there are many floating offshore structures in which the semi-submersible type cannot be adopted from the viewpoints of applications and loading weight. When increasing the load weight, a box-shaped floating structure, which is the simplest structure, is generally used.

[0004]

A box-shaped floating structure such as a petroleum production plant ship is installed in a longitudinal wave state in which the length direction of the structure coincides with the wave incident direction. Although it is common and it is important to reduce the sway in longitudinal waves, the dimensions of the conventional box-shaped floating structure have not been adequately reduced to reduce the sway in waves.

[0005] The present invention ameliorates these conventional disadvantages,
It is an object of the present invention to provide a box-shaped floating structure having a size capable of reducing vertical sway in a longitudinal wave.

[0006]

According to the present invention, when the length L of a box-shaped floating structure installed in a longitudinal wave state is equal to the wavelength λ.
When the wave force in the vertical direction is minimized, the length L of the box-shaped floating structure is adjusted so that the natural period of the vertical sway of the box-shaped floating structure coincides with the period at which the wave force is minimized. The ratio of the width B of the box-shaped floating structure to the draft d of the box-shaped floating structure is compared with the ratio of the width B of the box-shaped floating structure.

(Equation 2) The present invention relates to a box-shaped floating structure characterized by having been set in the above.

[0007]

[Action] Length L of a box-shaped floating structure installed in a longitudinal wave state
When the wavelength and the wavelength λ are equal, the vertical wave force is minimized
In particular on the basis, the ratio of the relative ratio of the width B of the length of the box-shaped floating structure L and the box-shaped floating structure, and Domo water d in the width B and the box-shaped floating structure of the box-shaped floating structures To

(Equation 3) , The natural period of the vertical sway of the box-shaped floating structure coincides with the minimum period of the wave force, and the position of the tuning point of the vertical sway is almost the same as the minimum position of the wave force. Therefore, the up-and-down sway that generally becomes very large at the tuning point does not become so large because the force of the wave is small.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view of an embodiment of the present invention, in which the length of the box-shaped floating structure 1 is L, the width of the box-shaped floating structure 1 is B, and the draft of the box-shaped floating structure 1 is drafted. Is d, and the present invention provides:
The case where the direction of the length L of the box-shaped floating structure 1 is the same as the direction in which the wave 2 is incident and the wave 2 acts as a longitudinal wave is intended.

The force of the vertical wave 2 acting on the box-shaped floating structure 1 in the longitudinal wave is approximately given by the following equation (reference:
Yamashita, G .: Practical method for estimating sway and pile loads in floating waves on a mooring shore, TECHNO-OCEAN '92).

[0011] ^{_{Fez = 2ρgζ A | H + 3}} (K) sin (KL / 2) |

Here, Fez: the amplitude of the force of the wave in the vertical direction ρ: the density of the fluid g: the acceleration of gravity ζ _A : the amplitude of the incident wave H ⁺ ₃ : the Kochin function for the cross-sectional shape of the floating body K: the wave number = 2π / λ λ: wavelength

According to this equation, KL / 2 = π, that is, λ
When = L, the vertical wave force is zero. In fact, it has been confirmed by a water tank test that the wave force in the vertical direction is minimized near λ = L.

On the other hand, the ratio between the wavelength λ _H corresponding to the natural period of the vertical sway of the box-shaped floating structure 1 and the width B of the box-shaped floating structure 1 is given by the following equation (Reference: Yamashita-gai: Pontoon type) A few studies on wave breaking performance of floating breakwaters, 3rd Wave Energy Utilization Symposium (1991)).

(Equation 4) Here, if λ _H = L, the wavelength at which the force of the wave is minimized is equal to the wavelength corresponding to the natural period of the vertical swing. At this time, the ratio of the width of the box-shaped floating structure 1 to the draft B /
The relationship between d and the ratio L / B of the length and width of the box-shaped floating structure 1 is as shown in FIG. This relationship can be expressed by an equation

(Equation 5) Becomes

The ratio B / d between the width of the box-shaped floating structure 1 and the draft
When the value of the ratio L / B of the length and width of the box-shaped floating structure 1 is selected in accordance with the graph (formula I) in FIG. 3, the position where the vertical wave force in the longitudinal wave is minimized The position of the tuning point of the vertical swing is almost the same. Therefore, the ups and downs, which are generally very large at the tuning point, are not so great because of the small wave force.

As shown in FIG. 2, the size of the box-shaped floating body 3 can be determined in the same manner as described above even in the case of a double-hulled box-shaped floating structure 4 in which two box-shaped floating bodies 3 and 3 are arranged in parallel. .

According to the present invention, not only a complete box-shaped floating body but also a floating body similar to the box-shaped floating body can be approximately appropriately dimensioned.

[0018]

According to the present invention, there is an effect that a box-shaped floating structure having the least vertical sway in a longitudinal wave can be constructed.

[Brief description of the drawings]

FIG. 1 is a perspective view of one embodiment of the present invention.

FIG. 2 is a perspective view of another embodiment of the present invention.

FIG. 3 is a graph for determining an optimal size of a box-shaped floating structure.

[Explanation of symbols]

 1 Box-shaped floating structure 4 Box-shaped floating structure B Width d Draft L Length

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B63B 22/00 B63B 35/00 B63B 35/34 B63B 35/38 B63B 35/44 B63B 39/00 B63B 39/14

Claims (1)

(57) [Claims] 1. A box-shaped floating structure installed in a longitudinal wave state .
When the length L is equal to the wavelength λ, the vertical wave force is minimal
Based on becomes enough, and the width B of such natural period of heave of the box-shaped floating structure coincides with the period of the minimum of the wave power, box-shaped floating structure length L and the box-shaped floating structures The ratio of the width B of the box-shaped floating structure to the draft d of the box-shaped floating structure is given by A box-shaped floating structure, characterized in that it was set in (1).