RU2408493C2 - Mooring system for floating structure - Google Patents

Abstract

FIELD: transport. ^ SUBSTANCE: invention relates to mooring and damping systems for floating structure. Proposed system comprises mooring structure, e.g. buoy, additional floating structure or stationary tower. Mooring structure comprises rotary platform rotating about vertical axis, jointing structure to allow connecting floating structure to mooring structure. Said jointing structure comprises rigid bracket assembly and pendulum elements. Rigid bracket assembly and pendulum elements are interjointed on one side to turn, while on the other side they can be jointed to floating and mooring structures. Damping system comprises at least one tank containing fluid and arranged in mooring structure at a distance from vertical axis. Said tank features sizes that, with pendulum elements oscillating, fluid moves to create damping forces to counteract aforesaid oscillation of pendulum elements. ^ EFFECT: perfected mooring system due to efficient damping of pendulum elements oscillations. ^ 6 cl, 3 dwg

Description

The present invention relates to a mooring system for a floating structure, such as a vessel containing a mooring structure, such as a buoy, an additional floating structure or a fixed tower containing a turntable that can rotate around a vertical axis, and a connecting structure adapted to provide a connection between the floating structure and a mooring structure, the connecting structure comprising a rigid bracket assembly and pendulum elements, the rigid bracket assembly and pendulum elements at one end are rotatably connected, and at their other ends are adapted to be connected to the floating structure and the berth structure, respectively, with ballast weights located at the connected ends.

Berthing systems of this type are disclosed, for example, in EP-A-0096119, EP-A-0105976 and EP-A-0152975. In such berthing systems, ballast weights provide restoring forces to ensure that the floating structure is spaced apart from the berthing structure. The hard bracket assembly and pendulum elements do not limit the primary displacements of the floating structure due to external conditions. In embodiments where the pendulum elements are attached to the floating structure, the connected ends of the rigid bracket assembly and the pendulum elements with ballast weights can swing perpendicular to the restoring force due to, for example, movements of the floating structure relative to the longitudinal axis. In the known mooring system, the oscillatory movement of the pendulum elements can become unacceptably significant when the pendulum is excited at or close to its own frequency. It is noted that the movement of the pendulum elements leads to the movement of other moving parts of the mooring system, i.e. turntable and hard bracket assembly. The natural frequency of this moving system depends on the geometry and mass of all parts. When reference is made to the natural frequency or the oscillation frequency or the movement of the pendulum elements, this should be understood as the natural frequency or the oscillation frequency or the movement of the entire movable system, including the pendulum elements, rigid brackets and the turntable.

An object of the present invention is to provide an improved mooring system of the aforementioned type in which damping movements of pendulum elements are effectively provided.

According to the present invention, the berthing system is characterized by a damping system for damping the oscillatory movement of the pendulum elements, the damping system comprising at least one liquid tank containing liquid and located in the berth system at a distance from the vertical axis, the liquid tank having such the dimensions that, when the pendulum elements oscillate, the fluid is adapted to move in a fluid reservoir to provide damping forces, rotivodeystvuyuschih vibrational displacement of pendulum elements.

Thus, an effective damping system has been created in which the opposing forces of a fluid moving in a container, more specifically, the forces of shock waves and inertia, are used as damping forces to provide damping of the vibrational movement of the pendulum elements. The damping system cannot be directly excited by external forces. An additional advantage is that the damping system is not prone to fouling by marine organisms.

Below, the present invention will be explained in more detail with reference to the drawings, schematically depicting an embodiment of a mooring system in accordance with the present invention.

1 schematically depicts an embodiment of a mooring system in accordance with the present invention.

Figure 2 schematically depicts a top view of the mooring system shown in figure 1.

Figure 3 depicts a cross section of the lower end of the pendulum element with a ballast weight and a liquid tank of the mooring system shown in figure 1.

1 and 2 depict an embodiment of a mooring system for a floating structure 1, such as a vessel, which comprises a mooring structure 2, which in this embodiment is designed as a fixed tower attached to the seabed. However, the mooring structure can also be made in the form of a buoy or an additional floating structure. This additional floating structure may be, for example, a vessel that maintains its position by means of an additional berthing system, or, for example, a system of dynamic stabilization of the vessel.

The tower 2 comprises a turntable 3 supported on the tower 2 and rotatable about a vertical axis 4. The berth structure also includes a connecting structure 5 adapted to provide a connection between the floating structure 1 and the tower 2. In this embodiment, the connecting structure 5 contains two rigid brackets made as triangular clamps 6. At one end, each clamp 6 is connected to the turntable 3 through hinges 7. At the opposite end, each clamp 6 is connected to the ball ACTH load 8.

The connecting structure 5 also contains two pendulum elements 9, each of which is connected via a hinge assembly (not shown) to the supporting brackets 11 mounted on the floating structure 1. At their lower ends, the pendulum elements 9 are connected by means of the hinge assemblies 12 with a ballast weight 8, such thus providing a connection between the ends of the pendulum elements 9 and the clamps 6. The hinge assemblies on the upper and lower ends of the pendulum elements 9 have two perpendicular axis of the hinges, providing movement of the data of pendulum elements in all directions.

In the embodiment illustrated in FIGS. 1 and 2, each ballast weight 8 includes a container 13 containing a liquid, such as sea water, as shown schematically in FIG. 3. The dimensions of the container 13 and the volume of the liquid are selected so that the liquid is adapted to move in the container 13 due to the oscillatory movement of the pendulum elements 9. As a result, a liquid wave 14 or a moving water bullet is formed, which provides shock and inertia forces creating the reaction force of the container, which counteracts the oscillatory movement of the pendulum elements 9, thus providing damping of the oscillatory movement of the pendulum elements 9. In figure 3, the lower end of one From the pendulum elements 9 is shown in the extreme position, the oscillatory movement now changes direction to another extreme position, while the reaction forces opposing the oscillatory movement are shown by arrow 15. In figure 2, the direction of the oscillatory movement is shown by a dashed arc of a circle in the center of which there is an axis 4 .

According to an embodiment of the present invention, the damping characteristics of the container 13 can be adjusted by adjusting the volume of the liquid, i.e. the height of the liquid in the tank. As an alternative or an additional element, the internal dimensions of the container can be made adjustable, for example, by changing the effective length of the container.

As shown in the top view of FIG. 2, the longitudinal dimension of the containers 13 is tangential to the radius of the axis of rotation 4 of the turntable 3. This provides effective damping.

By choosing the dimensions of the container, the number of containers and the properties of the liquid in the container, the degree of damping can be adjusted. In particular, when the containers 13 are designed and installed, the dynamic characteristics of the containers can be adjusted by changing the volume of liquid in the container. Although in the illustrated embodiment, the containers 13 are located at the connected ends of the clamps 6 and the pendulum elements 9, the location of the containers can be arbitrarily selected on the clamp, pendulum elements or turntable. Typically, tanks 13 can be located anywhere in the berth system at a distance from the vertical axis 4. However, the reaction forces of the tank are most effective when damping the berth system, when the returning forces create the maximum return moment relative to the axis of rotation 4 of the turntable 3. In addition, for to ensure effective damping, it is preferable if the longitudinal size of the containers is oriented perpendicular to the radius of the circle relative to the axis of rotation 4. Can be used times ary containers having various length and height of the contained liquid.

Typically, the period of oscillatory movement can vary between 6-16 seconds, depending on the length of the pendulum elements and the inclination of the pendulum element relative to the vertical at a given time. It is noted that the inertia of the turntable 3 has a period of natural oscillations that increases the effect on the period of oscillation of the pendulum elements 9. The period of natural oscillations will decrease when the floating structure is displaced in the direction from or towards the berth structure due to the inclination of the pendulum elements in a plane perpendicular to the oscillatory movement . Therefore, maximum efficiency is achieved with an optimal period of damping oscillations in the tanks, which is approximately 85-95% of the period of natural vibrations, determined using vertical pendulums.

In the case of the natural frequency of a surface liquid wave in a vessel, the dimensions of the vessel can be determined using the following equations:

M = ρ.N.B.h.L

T = 2.L / v _w

v _w = √ (gh).

while ρ [T / m ³ ] is the density of the liquid in the tank;

N is the number of containers;

In [m] - the width of the tank (perpendicular to the direction of flow);

h [m] is the liquid level in the tank;

L [m] is the length of the tank (corresponding to the direction of flow);

T [s] is the adjusted period of the capacity;

V _w [m / s] - wave propagation velocity in the capacitance;

g [m / s ² ] is the gravitational constant.

In practice, the amplitude of the movement of the tank also matters, which will require an increase in the length of the tank with an increase in the amplitude of movement. At large amplitudes of vibrational displacement, the frequency of the vessel’s natural oscillations ceases to exist, since the flow regime becomes such that the water’s properties are more like a “liquid bullet” than a standing wave or a tidal wave, for which the frequency of the capacity can theoretically be determined. The empirical relationships below are based on test results. However, these ratios do not limit the size of the container.

L _tank ≈ a · L _pend · Y or

L _tank ≈ a · g / ω _pend ² · Y;

h _tank ≈ b · L _tank ;

H _tank ≈ c · h _tank ;

B _tank ≈ d · F _pend / (g · ρ _liquid · h _tank · L _tank · N) · Y ^0.5 ;

Y = R _tank / R _pend .

Wherein

0.57 <a <0.73 or more for tanks of unlimited length

0.035 <b <0.05

2 <c <4

0.10 <d <0.13 or wider for containers of unlimited width,

where L _tank is the _tank length, ω _pend is the natural frequency of the moving system, h _tank is the liquid level in the tank, H _tank is the _tank construction height or tank level, B _tank is the _tank width and N is the number of levels, F _pend is the force in the lower hinge of the pendulum and ρ _liquid is the density of the liquid. All units correspond to the SI system (m, kg, N, s). The coefficient Y denotes the ratio between the effective radius from the support of the turntable to the center line of the tank, R _tank, and the radius from the support of the turntable to the point of the lower hinge of the pendulum, R _pend .

The present invention is not limited to the embodiment described above, which may be varied in various ways within the scope of the claims of the present invention.

Claims (6)

1. A berthing system for a floating structure, such as a vessel containing a berthing structure, such as a buoy, an additional floating structure or a fixed tower containing a turntable rotatable about a vertical axis, and a connecting structure adapted to provide a connection between the floating structure and a mooring structure, wherein the connecting structure comprises a rigid bracket assembly and pendulum elements, the rigid bracket assembly and pendulum elements the elements at one end are rotatably connected and at their other ends are connected to the floating structure and the berth structure, respectively, and the ballast weights are located at the connected ends, characterized in that it contains a damping system for damping the oscillatory movement of the pendulum elements, and damping the system contains at least one fluid container containing liquid and located in the berth system at a distance from the vertical axis, Rich liquid container is dimensioned such that an oscillating movement of the pendulum members the liquid is adapted to move in the liquid tank to provide damping forces counteracting the oscillating movement of the pendulum element. 2. The berthing system according to claim 1, in which at least one liquid tank is located at the connected ends of the node of the rigid bracket and pendulum elements. 3. The berthing system according to claim 1 or 2, in which the internal dimensions of the tank and / or the volume of liquid are made adjustable to control the damping characteristics of the tank. 4. The berthing system according to claim 1 or 2, in which the longitudinal size of the tank is located tangent to the axis of rotation of the turntable. 5. The berthing system according to claim 1 or 2, in which the dimensions of the tank essentially satisfy the following equations:
L _tank ≈ a · L _pend · Y or
L _tank ≈ a · g / ω _pend ² · Y;
h _tank ≈ b · L _tank ;
H _tank ≈ c · h _tank ;
B _tank ≈ d · F _pend / (g · ρ _liquid · h _tank · L _tank · N) · Y ^0.5 ;
Y = R _tank / R _pend ;
with 0.57 <a <0.73 or more for containers of unlimited length;
0.035 <b <0.05;
2 <c <4;
0.10 <d <0.13 or wider for containers of unlimited width,
where L _tank is the length of the tank,
ω _pend is the natural frequency of the moving system,
h _tank - liquid level in the tank,
H _tank - _tank construction height or tank level,
B _tank is the width of the tank and N is the number of levels,
F _pend is the force in the lower hinge of the pendulum, ρ _liquid is the density of the liquid,
and the coefficient Y denotes the ratio between the effective radius from the support of the turntable to the center line of the tank, R _tank , and the radius from the support of the turntable to the point of the lower hinge of the pendulum, R _pend . 6. A damping system for a mooring system according to any one of the preceding paragraphs, comprising at least one liquid tank having such dimensions that the liquid is adapted to move in the liquid tank to provide damping forces that counteract the oscillatory movement of the pendulum elements.

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