NO793917L - STABILIZATION SYSTEM FOR A CRANE-BORING VESSEL - Google Patents

Description

Stabilization system for crane carriers

vessel.

The present invention relates to a stabilization system for a vessel with a ship's hull which is in operating position below the waterline and which is equipped on the upper side with hollow columns which above the water surface support a work platform which is connected to one or more heavy lifting cranes, where the stabilization system comprises water ballast tanks above and below the surrounding water level, and where both the outflowing water flow from the upper ballast tank and the inflowing water flow in the lower ballast tank are selectively controlled by control valves depending on instantaneously occurring, balance-disrupting forces that are induced when the cranes are used for cargo handling.

A similar system is known from a German patent document

P 28 02 249.3.

Based on the known technique, the purpose of the present invention is to produce a special embodiment which will entail further simplification of the system for stabilizing a vessel during cargo handling by using one or more cranes mounted on the vessel, whereby the deviations from the vessel's predetermined floating positions are kept within narrow limits (preferably 1°), while load handling can nevertheless be carried out at the maximum speed that the individual crane or cranes allow without exceeding the system's stabilization capability.

According to the invention, the control valves for the underwater ballast tanks consist of water inlet valves in said tanks which are otherwise not connected to the surrounding water.

A pump system is preferably arranged such that the water can be pumped out of the lower water ballast tank and into the water ballast tank above sea level.

According to the invention, a simple and economical stabilization system has been developed which makes it possible to achieve stabilization quickly and efficiently by introducing water into the underwater ballast tanks and draining water from the upper ballast tanks.

The invention is described in more detail below

in connection with the accompanying drawings, in which:

Fig. 1 shows a schematic perspective view of a floating body that is affected by a vertical force. Fig. 2 shows the same body in a horizontal position, with an indication of the decompensation forces required for this position.

Fig. 3 shows a vertical section, along the line III-III i

fig. 4, through a vessel according to the invention, with two cranes which are shown in front end view. Fig. 4 shows, on a reduced scale, a plan view, rotated 90° about a vertical axis in the drawing, of the vessel according to fig. 3.

Fig. 5 shows a simplified drawing of a crane with indications

for calculation executions.

Fig. 6 shows a plan, rotated 90° about a vertical axis,

of the work platform on the vessel according to the invention shown in fig. 4 and 5.

Fig. 7 shows a diagram illustrating the filling of the water ballast tanks during the various steps in the cargo handling process described in the following examples.

If a liquid body, as shown by dashed lines i

fig. 1, a vertical load G is applied, the following changes will occur in the floating position of the body, measured in relation to a fixed axis system X - Y - Z:

- vertical shift (Z)

- angular displacement f x in relation to the x-axis (roll axis)

- angular displacement f y in relation to the y-axis (stem axis)

To counteract all these changes, it will be required

at least three compensating forces acting in three different points.

If compensation of two of the degrees of freedom is sufficient, only two compensating forces will be needed.

With a compensating force, only one degree of freedom can be affected.

When the compensating forces only act in one direction,

there are other possibilities.

Thus, it is e.g. possible to compensate the two angular displacements by means of three or more downward compensating forces.

For the creation of a stabilization system, as previously discussed, for so-called semi-submersible floating cranes, two compensating forces will be sufficient to keep the two angular displacements at zero.

"The vertical displacement is thereby not compensated. The position of the compensating forces A and B is determined by construction when, as described below, water ballast tanks are used which are arranged in pairs above each other and where the ballast tanks' host, ice axes run through points 2 and 3 ( coordinates a, b for point 3 and a, - b for point 2).

If the magnitude G and the point of attack (x, y) for this vertical force are given, the larger of the two compensating forces A and B, which are decisive for maintaining the vessel in a horizontal position, can be calculated.

The resulting moment about the x-axis, Mx, must in this case be equal to zero and the moment about the y-axis, My, must likewise be equal to zero.

For that reason is:

(A-B) b = Gy

(A+B) a = Gx

and consequently:

The variation in draft can be calculated from the variation in total load and the total cross-sectional area of the columns (A^)

It appears from this that when x = a, the draft is unchanged. Before one of the vessel's cranes is brought into operation, the size and position and the associated values of the compensating forces are calculated, which are indicated as zero values A o and B o. These are stored in a calculator's memory.

When the size and/or position of the load G changes, the values of the compensation forces to be calculated will also change.

These changes, respectively AA = A - AQ and AB = B - B^, are fed into the control system which adjusts the compensation forces.

As mentioned in the introduction, the invention is intended for use with a vessel (see fig. 3-5) with two underwater hulls 4 and 5 where hollow columns 6-11 are arranged on the decks which are connected above the waterline 12 to a platform 13 which under- supports at least one heavy lifting crane 14 and 15 (eg a 2000-tonne crane and a 3000-tonne crane).

The stabilization system comprises two water ballast tanks which

are placed above each other under each crane, where the pair of tanks which are arranged in the column G under the crane 14, is denoted by A and where A^ denotes the upper tank and A2 denotes the lower tank.

The tank pairs in column 7 are labeled in a similar way

with and B2. Compensating forces A and B (fig. 2) are supplied in a known manner by means of water which flows freely respectively into and out of the tanks A^ and A2 as well as B^ and B.>. Outflowing water from a tank A^or B^above sea level produces an upward force.

Inflowing water in a tank A2 or B2 below the water line produces a downward force.

Because, according to the invention, level variations are used during the cranes' load handling, very large quantities of water are displaced within a short time, and this is of significant importance when it is necessary for the vessels to be maintained in a horizontal position at all times during lifting, turning and moving of cargo using the cranes.

It thus appears that the water ballast tanks A-^ and A2 are arranged above the surrounding water table 12 and that the outlet flow is regulated by the selectively operating control valves 16 and 17,

as explained in what follows. The outflow takes place through vertical outlet pipes 18 and 19 (of which only one pipe is shown for each tank A^ and B1) which extends through the lower ballast tanks A2 and B2 and through the bottom of the hulls 4 and 5. Corresponding inlet control valves 21 and 22 for the inlet pipes 23 and 24, of which only one pipe is shown for each tank, is arranged at the bottom of each ballast tank A2 and B2> Although the water will be able to be driven out of these tanks A2 and B2 by introducing compressed air while the valves 21 and 22 are open, ballast handling, according to the invention, is carried out in that this requires the use of compressed air, as explained below as an example of a special operating cycle. After such a cycle, the ballast tanks A2 and B2 can be emptied by pumping the water

from a lower chamber to an upper chamber through pump lines 2 5 and 26 (shown by dashed lines) which in practice will be inside the columns 6 and 7. The surface of the ballast tanks A.>and B2 can be in open communication with the atmosphere through the pipe sleeves shown 27 and 28. The upper ballast tanks are of course connected by one or more pipelines (not shown) and can thereby be filled with water from the sea.

The valves and the associated pipelines must of course be sufficiently large and numerous with a view to achieving a flow-through end of the required size in a completely unconstricted outlet from and B^ and inlet to A2 and B,,.

In an effective version of the invention, a displacement of approx. 4000 m 3 in 40 seconds.

The system must be "charged" before use by bilge pumping of the lower ballast tanks A2 and B2 and full pumping of the upper tanks A^ and B^.

The ballast tanks can therefore advantageously be arranged in pairs above each other.

The equilibrium is not disturbed by pumping water from the lower tank to the upper one.

The pumping can therefore already take place during the compensation process, when the lower tank is no longer completely empty and the upper tank is not completely full.

The calculated change in compensating forces for a particular change in load is converted to a desired water level

in each ballast tank, or to one. desired amount of water to be displaced (setting value). This amount of water is measured continuously during the regulation of the water level. A valve opens when the measured value deviates from the desired, nominal value.

Each ballast tank can be equipped with a number of valves of mutually different capacities. The type and number of the active valves are thereby defined as a function of the difference between the required value for maintaining the vessel on a straight keel and the measured value for the water level.

The volume regulation offers a second possibility. In this case, the position of the valves is measured. By using the associated valve characteristics which are entered as a constant factor in the calculator, the flow quantity is integrated with the elapsed time, until the desired volume is achieved.

The instantaneous variations in the water height values (or volume) which are necessary to maintain the horizontal position are calculated directly from the indications from the various tracking devices on the cranes (swing angle, maximum angle, weight).

On the basis of various known factors (e.g. the boom length, the distance between the crane's pivot point and the boom's pivot point, the position of the center of gravity of the crane housing and counterweight, etc.) it is possible to calculate the necessary changes in the compensating forces.

In these calculations, the impact of different load forces can be taken into account.

With reference to the measurement values given in fig.

3 and 5, in the following formulas for calculating the two compensation forces A^ and BK, when two cranes 14 and 15 are in operation, the following has been taken into account:

- the weight of the load in the main hoist block GA and GB

- the net weight of the cranes, which is included in the weight of the crane housing G„

- the faucet top G^and the counterweight Gc

In the formulas, the letter A or B is added to the indices to indicate which crane the given information applies to, i.e. A for crane 14 and B for crane 15 in fig. 3.

Reference is also made to the information in fig. 4 concerning

the measured distances in relation to the axes X and Y.

The formulas can of course be extended to include compensation of the loads in the auxiliary hoist blocks G^, 23°^^B 12°^^ or ^ could be used in cases where more than two cranes are in operation.

Calculation examples for determining compensation forces:

A special method is used for placing parcels on deck and for lifting such parcels. In the event that the crane hook is located above its own deck, the values A and B are used for changes in the load G.

OE OE

Fig. 3 schematically shows the processing of data in the calculator, i.e. in box I (tracked input values), box II (comparison with calculated, fixed program values) and box III (transformed into orders for the valves designated V. ,~ and V„ , ~)<.>

Pi i.f z a i,z

Fig. 6 schematically shows that the crane 14 (of which only the boom is indicated) is arranged at a corner of the working deck construction above the column 6.

For simplicity, only one crane is described, and the net weight of this crane is not compensated (see fig. 5 and 6).

Simple formulas can therefore be used when calculating the compensation forces described earlier under the title "Compensation system with two compensation forces".

To calculate the position of the load, the angle of rotation and the crane radius are used, and it is assumed that the crane center coincides with the line of action for the compensation force A^, i.e. that the axis of the column 6 coincides with the axis of the crane 14.

The following formulas are thereby used:

In the following numerical example, the following values are assumed:

a = 43 m

b = 34 m

3

The volume of all tanks = 4,000 m

Crane capacity: G = 2700 tonnes when R = 32 m.

and B1 2

Fig. 7a shows the water level in the ballast tanks A^ 2^vec^ the starting point I according to fig. 6, where the crane boom's projection runs outboard and parallel to the Y-axis. Tanks A^ and B^ are completely full, while tanks A2 and B2 are empty.

It is assumed that a load of 2,700 tonnes is lifted from a barge alongside the vessel. By using the formulas, the required compensating forces A = 3970.6 tonnes and B = 1270.6 tonnes appear. As 3 97 0.6 tonnes of water flows out through valve A while 127 0.6 tonnes of water flows in through valve B2 during the lifting of the load, the vertical position of the vessel will be maintained unchanged. The water level in the tanks is then as shown in fig. 7b.

The crane is then moved from position I to position II according to fig. 6, and using the formulas the necessary compensating forces in position II can be calculated to:

A = 3704.7 tonnes and B = 1004.7 tonnes.

During this maneuver, 2 65.9 tonnes of water will flow in through valve A2, while 2275.3 tonnes of water will flow out through valve B^. The resulting water level in the tanks is shown in fig. 7c. Nursing angle and keel angle are still equal to zero,

while the vessel's draft is reduced by the value

Z = (2275.3 - 265.9)/^

After the load from position II has been lowered onto a platform on the outside of the vessel, the compensating forces in the initial position are again equal to zero, i.e. of the same magnitude as at the start of the crane manoeuvre.

During this last process step, 3704.7 tonnes of water has thus flowed in through valve A2, while 1004.7 tonnes of water has flowed in through valve B2. The final water level in the ballast tanks is shown in fig. 7d.

The keel angle and the nursing angle are again equal to zero, while the vessel's draft during the lowering of the load is increased by the value Z = (3704.7 + 1004.7 = 2700)/^

This increase is beneficial for the crane's operation.

Claims (8)

1. Stabilization system for a multi-hull vessel which is completely submerged in its operating position and where hollow columns are arranged on the decks which above the waterline are connected to a working deck structure that supports one or more heavy lifting cranes, where the stabilization system comprises water ballast tanks above and below the surrounding water level , where both the outflowing water flow from the upper ballast tank and the inflowing water flow in the lower ballast tank are selectively controlled by control valves depending on the immediately occurring, balance-disrupting forces that arise when the cranes are used for cargo handling, characterized in that the control valves for the underwater ballast tanks are inlet valves for said tanks which otherwise have no connection with the surrounding water. 2. Stabilization system in accordance with claim 1, characterized by a pumping device for pumping water out of the lower ballast tank and into the ballast tank above sea level. 3. Stabilization system in accordance with claim 1 or 2, characterized in that, on each underwater hull, only at one end wall of the working deck is arranged a column which is equipped with a ballast tank above and a ballast tank below the sea surface, where each of these columns is connected with a faucet. 4. Stabilization system in accordance with claim 3, characterized in that the crane center largely coincides with the main axis of the upper and lower water ballast tanks located in the columns under the crane. 5. Stabilization system in accordance with claim 3 or 4, characterized in that a ballast tank above the water surface is emptied under the influence of the increasing load moment, by maneuvering a powered crane while lifting an outboard load by means of a crane arm that extends in the transverse direction of the vessel, while part of the lower ballast tank in the opposite column is filled by opening the water inlet valve, after which, during a 90° turn of the crane to a second outboard position, stability is created by draining water through an outlet in the latter ballast tank in addition to regulating the water inlet to the lower ballast tank below the working crane, and where, during the lowering of the load after a completed turning movement, stability is created by water inflow into the lower ballast tank under the crane and water inflow into the lower ballast tank in the opposite pillar. 6. Stabilization system in accordance with one of the claims 1-5, characterized in that the compensating forces to be produced with the help of outflowing water from the upper ballast tanks and inflowing water in the lower ballast tank are calculated continuously during a crane maneuver as a function of the water level or the volume in the ballast tank, which is necessary for the given crane arm position and load, and that the special valves are controlled as a function of the difference between the desired and the measured values for the water level or the amount of water in the special water ballast tank. 7. Stabilization system in accordance with claim 6, characterized in that a volume control system is used. where the instantaneous position of the valves is measured and the flow characteristics of the valves are introduced and the flow quantity is time-integrated, until the desired volume, which is necessary for compensating the forces, is achieved for each ballast tank. 8. Stabilization system in accordance with claim 6 or 7, characterized in that each water ballast tank is equipped with several valves of different capacity, and that the selection of the number of valves for each ballast tank to be activated is calculated with sufficient frequency as a function of the difference between the desired value and the measured value for the water level or water quantity during the tap manoeuvre.