JPH0115439B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Ocean-going vessels are required to perform a variety of maritime operations, including scientific research and oil and gas extraction. This type of vessel is usually a drilling ship, barge, jack-up or
Built as a jack-up rig or supply ship.

In order to suppress the rolling and pitching of a ship in a sea with periodic waves, active and passive technical methods have been proposed for damping the displacement of the ship due to natural vibrations. This type of technical method includes water tanks and blowers, pumps, valves, valve actuators, rolling and pitching sensors installed on the ship, as well as equipment for moving the water in the tank to damp vibrational rolling and pitching. It uses a mechanism that combines various electronic control circuits. The common purpose of conventionally well-known mechanisms is to
This is to "tune" the tank to the hull by making the natural frequency of the oscillating flow of water in the tank equal to the natural frequency of the hull itself. Once synchronized, vibration damping is achieved by placing the water flow pattern in the tank approximately 90 degrees out of phase with the natural vibrations of the hull. At this time, the forces generated by the water in the tank tend to reduce the forces that cause the hull to roll or pitch.

Previously known mechanisms or systems for stabilizing a ship's hull in the manner described above have the disadvantage that, in order for the system to be effective, considerable damping forces must be generated. The equipment required to generate such large forces is complex and expensive. Active systems generally require high power blowers and pumps. Passive systems also generally require large volume valves, special damping tank construction, and control circuitry to control water flow within the tank.

The present invention measures the navigation stability of an ocean-going ship using a passive system, and in order to generate a large counterforce to damp the angular motion of the ship, the natural period is substantially equal to the period of the natural vibration of the ship. There is no need to use a tank with Instead, tanks are used to reduce the hull righting moment, as described below.

According to the illustrated embodiment of the invention, the water tank comprises:
They are located on both sides of the longitudinal axis of symmetry of the hull. This tank is located below the waterline, preferably at or near the bottom of the hull. The tank has a shallow shape with a horizontal dimension that is larger than a vertical dimension. The bottom of each tank is
It opens substantially into the sea, allowing seawater to enter and exit the tank within a period much shorter than the period of natural vibration of the ship. Open conduits connect these tanks to each other, creating a continuous air passageway between them.
An air pump is connected to this air passage to increase the pressure within the tank to a certain level and selectively control the water level within the tank while the vibrational waves are occurring.

During operation, the water tank is alternately filled and subtracted with water in synchronization with the vibrational waves. For example, as the hull rolls clockwise about its central longitudinal axis, the tank on the right side of the hull quickly fills with water through its large bottom opening. Air is forced from this tank via conduits to a tank on the left side of the hull. The air capacity of the tank on the left increases and the water quickly drains from it. On the other hand, when the hull rolls counterclockwise, the left tank fills with water, and the system's air pressure acts on the right tank to drain water.

The present invention operates to reduce the righting moment of a ship in a sea where periodic vibrations occur. For example, when the hull rolls in a certain direction, the system reduces the hull's ability to restore itself to an upright position. By reducing the restoring moment in this way, the period of oscillation of the ship becomes longer than the period of the sea waves. The amplitude of rolling is therefore substantially reduced.

1 and 2, a barge-like vessel 11 of the type used in offshore oil drilling operations is shown. Two elongated tanks 1 below the water line 13
5 and 17 are arranged at the bottom of the barge 11. These tanks 15, 17 each have an overall capacity of 19,
21 (see Figure 3A).
These bottoms 19, 21 are preferably substantially open into the sea, but may be covered with a perforated plate or grid to increase structural strength. The tanks 15 and 17 are each made shallow and have a horizontal dimension larger than a vertical dimension. Such a configuration allows seawater to quickly flow into and out of the tank.
More specifically, in a sea with periodic waves, seawater can fill a tank in a much shorter time than it takes a barge to perform one cycle of natural oscillatory rolling or pitching. It is necessary to configure the tank to draw from it.

Referring to FIG. 2, barge 11 has a longitudinal axis of symmetry 22. Referring to FIG. The tanks 15, 17 are arranged symmetrically and spaced apart on both sides of the axis of symmetry 22. Each tank 15, 17 is divided into a plurality of independent chambers. The tank 15 has six chambers a, b, c, d, e and f, each chamber marked by the dotted line 2.
They are separated from each other by a partition wall indicated by 9. Similarly, tank 17 has independent chambers a', b', c', d', e', and f' separated by walls 31. These chambers are arranged in pairs symmetrically on both sides of the longitudinal axis 22, and the chambers a, a', b
and b′, etc. form each pair. According to the invention tank 15
By dividing 17 and 17 into a plurality of chambers, it is possible to reduce the wave excitation and thereby to minimize the undesirable wave forces acting on the free surface of the water in the tank. It can be held down.

Each pair of chambers is connected by a separate conduit arrangement generally indicated by a pipe 33 outlined in dotted lines. In this way, a pair of chambers a and
a' are connected as a closed pressurized system as shown in FIG. Other pairs of chambers are similarly independently connected. A conventional blower and conduit arrangement (not shown) may be used to supply air pressure to all of these paired chambers.

Tanks 15, 17 are connected to each other by a conduit 23, which is schematically shown in Figure 3A. This conduit 23 is constructed in the form of a continuous open pipe and forms an air passage between the two tanks. One end of the pipe line 23 is connected to the top of the tank 15 via an opening,
The other end of the pipe line 23 is connected to the top of the tank 17 via an opening.

In order to create air pressure in the line 23 and the tanks 15, 17, a device is connected to the line 23, including an air pump 25 consisting of a blower and an air valve 27. The pipe line 23 and the tanks 15, 17 form a closed system until a predetermined air pressure is obtained therein.
The valve 27 is opened and the pump 25 is operated. after that,
Close valve 27. Alternatively, valve 27 may be removed or left open and air pump 25 operated continuously at a constant speed to maintain air pressure within the system at a predetermined level. Preferably, the air pressure is adjusted so that the tank is alternately filled with seawater during the oscillatory waves of seawater, as described below.

When a ship lists, seawater enters tanks on one side of the ship, and air-filled connecting pipes cause approximately the same amount of seawater to flow out of tanks on the other side of the ship. Therefore, the restoring moment of the hull is reduced. It is therefore possible to change the arrangement and configuration of tanks 15 and 17 as shown in Figures 3B, 3C and 3D. In the configuration of Figure 3B, the tank is located at the bottom of the hull and inside the hull. Such a configuration is preferably applied to new ships under construction. In the configuration of FIG. 3C, tanks 15 and 17 are provided at or near the bottom of the outside of both sides of the hull. In such a configuration, there is almost no need to change the original state of the hull, and therefore, like the configuration shown in FIG. 3A, it is suitable for use by modifying an existing ship. FIG. 3D shows another embodiment of the configuration, in which tanks 15 and 17
is located at or near the bottom of the ship, with part of it located inside the hull and part of it outside.

All of the above four configurations are based on the common principle that when a ship tilts, seawater flows into the tank installed on the sunken side of the ship, and seawater flows out from the raised tank on the opposite side. It's wet. This variation in the volume of ballast water within the tank creates a tilting torque that acts in the same direction as the applied torque. The required operating torque for a given heeling angle is therefore reduced. In other words, the restoring torque is reduced and the natural period of rolling is therefore lengthened.

The operation of the system shown in FIGS. 1-3D may be understood with reference to FIGS. 3A and 5. As shown in FIG. 3A, the tanks 15 and 17 of the ship 11 are first pressurized with the air pump 25, and in a calm sea, each tank is filled with seawater to about half of the tank, as shown by the water surface 35. Make sure that you are As shown in FIG. 4, when the hull 11 rolls clockwise around the axis 22, the tank 17
is filled with seawater so that air is forced from tank 17 via line 23 into tank 15. When the amount of air in the tank 15 increases, the water in the tank 15 is forced out of it and the level of said water surface 35 falls to a new water level 37. During this period, valve 2
7 may be closed, or valve 27 may be left open and pump 25 may be driven to maintain constant air pressure in both tanks and conduit 23. In this way, the air removed from tank 17 is transferred to tank 15 as is. On the other hand, when rolling occurs counterclockwise, the tank 15 is filled with seawater and the tank 17 is filled with seawater as described above.
Seawater flows out of it.

If the tank 17 is filled with water when the hull 11 rolls clockwise, it will reduce the righting moment of the hull. In other words, the tendency of the hull to return to an upright position after the onset of rolling is delayed, so that the vibratory rolling motion of the hull becomes more gradual. Thus, the rolling period of the ship becomes longer. In typical sea conditions where the wave period is 7 seconds, the roll period of the hull created by the system of the present invention is preferably about 12 seconds.
lengthened to seconds. Since the rolling period of the ship's hull is considerably longer than the period of seawater wave motion, the waves have little effect on the ship's hull.

With the system of the present invention, when the righting moment of the ship is reduced in calm seas, it is possible to reduce the rolling torque even in seas with periodic wave motion. The tank 1 is arranged so that when air is pumped into the tanks 15 and 17, the height of the center of inclination, that is, the restoring moment, is still positive.
5,17 dimensions are determined. If the restoring moment becomes too small while navigating in a sea with periodic waves, there is a risk that the hull 11 will capsize.
This is especially the case when the hull is exposed to strong winds. In view of this, an important feature of the system of the present invention is that the height of the tank and the initial static water level in the tank (e.g. tank 17) are such that the tank is completely filled with seawater during extreme hull rolls. The ship has been selected to ensure the safety of the ship. Once the tank is filled with seawater, normal buoyancy returns to the hull and the righting moment increases rapidly as a function of the additional rolling displacement that prevents the ship from capsizing.

In the construction of the tank shown in Figures 3C and 3D, the bottom open tank is formed as a submersible outward overhang. As mentioned above, these tanks are pressurized with air, and as the ship rolls or the presence of waves, the water level in the tank rises or falls, reducing the restoring torque (i.e., the restoring moment) and The natural period of rolling becomes longer. However, in these cases, the torque due to wave-induced forces on the top of the flooded tank opposes the torque created in the hull itself by the wave forces. Taken together, this results in an overall reduction in the wave-induced torque acting on the hull, similar to that of an internal tank design.

FIG. 5 shows that the system of the present invention
The comparison shows the reduction in the restoring moment exerted on . Curve 38 shows the ratio of roll amplitude to wave heel for an unstable ship, while curve 39 shows the roll amplitude characteristic of a ship 11 stabilized according to the principles of the present invention. The rolling amplitude characteristics of an unstabilized ship have a resonance peak at 7 seconds. The period of waves on the high seas is also generally 7 seconds. Therefore, unless stabilization measures are taken, the ship will have a rolling amplitude at or near the peak P of the resonance peak. In contrast, for a stabilized ship 11, the resonance peak occurs with a period of approximately 12 seconds, which is considerably longer than the 7 second period of typical waves on the high seas. Therefore, for a wave with a period of 7 seconds, the stabilized ship will operate at point S of curve 39, and its rolling amplitude will be reduced to less than one-sixth of that of the unstabilized ship. be done.

Vessel 11 is a barge with a total length of approximately 114.3 meters. Each tank 15, 17 is approximately 83.8 meters long and is divided into six equally sized chambers. The width of each tank is 3 to 3.66 meters and its height is 1.83 to 2.13 meters. The pipe devices 23 connecting the chambers of both tanks each have a diameter of 0.91 to 1.22 meters.

Although vessel 11 is shown as a barge, other types of vessels may be stabilized in accordance with the principles of the present invention. For example, this stabilization system
It can also be applied to triangular or square jack-up rigs for oil drilling. The tanks can be arranged symmetrically about the geometric center of the ship, for example at each top of a triangular rig or at each corner of a square rig. In order to provide stability against rolling and pitting, it is also possible to connect all tanks to one common source of air pressure by lines. With this configuration, both the rolling and pitching restoring moments can be reduced.

[Brief explanation of drawings]

FIG. 1 is a side view of a hull illustrating one embodiment of a stability tank of a system constructed in accordance with the principles of the present invention. 2 is a bottom view of the ship of FIG. 1 showing the arrangement and connection of the stability tanks; FIG. 3rd A
Figures 3-3D illustrate a first embodiment of a stabilization system constructed in accordance with the principles of the present invention.
FIG. 2 is a schematic end view of the vessel of FIG. FIG. 4 is a schematic end view of the ship of FIG. 1 illustrating the operation of one embodiment of the system according to the present invention. FIG. 5 is a graph showing the ratio of roll amplitude to wave slope as a function of wave period for ships equipped with and without the system of the invention. In the drawing, 11...ship, 15, 17...tank,
22... Axis of symmetry, 23... Piping device, 25... Pump, 27... Valve.

Claims (1)

[Claims] 1. Regarding an ocean-going vessel 11 having at least two tanks 15, 17, which are arranged below the water surface and on both sides of the axis of symmetry of the hull and have bottoms 19, 21 open into the water; A passive method for stabilizing an ocean-going vessel during repeated oscillatory motion cycles by reducing the restoring moment of the vessel and making the oscillation period of the vessel longer than the period of the sea waves, comprising: The tanks are interconnected by a conduit arrangement 23 to form a permanently open air passage 33 between the two tanks; during one cycle of the oscillatory movement of the ship, one of said tanks moves into the sea. synchronously, filling the one tank with water to a first water level; by guiding the air pushed out from the one tank to the other tank via the pipe device,
simultaneously draining water from the other tank to a second water level 37 as the one tank fills with water during the one cycle of oscillatory motion of the hull; filling the one tank with water; the step of adjusting the hull to prevent the ship from capsizing by rapidly increasing the righting moment of the ship as a function of the additional angular displacement of the ship when the one tank is completely filled; A method for stabilizing an ocean-going vessel, comprising completely filling said one tank with water in response to a predetermined angular displacement about an axis of symmetry 22. 2. In order to select the first water level and the second water level formed in the tanks when water flows into the tanks 15 and 17 and when water flows out from the tanks, 2. A method according to claim 1, characterized in that the device 23 is pressurized with a constant air pressure. 3. A passive system for stabilizing an ocean-going vessel 11 having an axis of symmetry 22, comprising: a plurality of tanks arranged in the hull in spaced pairs on either side of said axis of symmetry below the water surface; 1
5, 17, the tank has a bottom 19, 21 open into the water so that it can be filled and drained with water in synchronization with each cycle of oscillatory movement of the vessel relative to the water surface; a conduit device 23 connected to the top surface of said tanks to form an independent air passage for each pair of said tanks; said conduit device being a normally open pipe interconnecting the tanks of each pair of said tanks; 33; during one cycle of oscillatory motion of the hull, one of the tanks is completely filled to rapidly increase the righting moment of the hull as a function of additional angular displacement of the hull; the height of each tank is selected such that the tank is completely filled and emptied during the cycle; and the water level 35 in the tank is such that the tank is completely filled and emptied during the cycle, in order to prevent the vessel from capsizing by applying a predetermined air pressure to said tank and conduit system to maintain said vessel at a level selected to reduce the righting moment of said vessel and make the period of oscillation of said vessel longer than the period of waves acting on said vessel; Stabilization system for an ocean-going vessel, comprising a pumping device 25, 27 connected to said line device for the purpose of stabilization. 4. System according to claim 3, wherein the completely filled tank is a tank 17 on the side of which the hull is tilted with respect to the axis of symmetry of the hull. 5. the pumping devices 25, 27 applying a predetermined air pressure to the tanks are adjustable such that one of the tanks is completely filled with water during part of one cycle of the ship's oscillatory motion; The system according to claim 3. 6. The system of claim 5, wherein the fully filled tank is a tank on the side of which the hull is tilted with respect to the axis of symmetry of the hull. 7. The pump device 25, 27 for applying a predetermined air pressure to the tank includes an air pump 25 and a valve 27 arranged to separate the air pump from the pipe device 23. The system described in scope item 3. 8. Claim 3, wherein at least a portion of each of the tanks is located outside the hull.
System described in section.