GB2175270A

GB2175270A - Sea motion following means

Info

Publication number: GB2175270A
Application number: GB08610741A
Authority: GB
Inventors: Heinrich W Nikolaus
Original assignee: Mannesmann Rexroth AG
Current assignee: Bosch Rexroth AG
Priority date: 1985-05-07
Filing date: 1986-05-01
Publication date: 1986-11-26
Also published as: NO164767B; GB2175270B; NO164767C; DE3516289C2; GB8610741D0; NO861775L; DE3516289A1

Abstract

A hydraulic drive arrangement, for example a hydraulic cylinder 20 or hydrostatic engine or machine, is driven by a cable 15 to which a floating body 30 is secured. The motion of the sea causes the floating body 30 to set the cable 15 in reciprocating motion and to drive the drive arrangement which acts as a pump and conveys working medium to a pressure network. Furthermore, the drive arrangement can be used to drive a winch or capstan by following of the motion of the sea. The load, to be taken up for example by a ship, is raised and lowered via the cable 15 by the drive arrangement synchronously with the motion of the sea without having to use energy from an external drive for this purpose. With this sea motion following arrangement it is thus possible to generate energy in a simple manner and to drive a winch drum 25 synchronously with the wave motion. <IMAGE>

Description

SPECIFICATION Sea motion following means This invention relates to a sea motion following means. This term is known in winches for taking up and lowering floating loads, i.e. loads which are to be hoisted from a ship onto a drilling platform or lowered onto the ship. Such loads must be taken up under rough seas, in particular with wave heights of for example up to 6 m and wave periods of 7 seconds. The rotation of the drum in both directions of rotation must be controlled so that the cable is kept tight to avoid shocks on taking up and lowering the load on the floating body.

The problem underlying the invention is to construct a sea motion following means in such a manner that it utilizes the energy inherent in the moving water of the sea and converts it to hydraulic energy which can either be supplied to a pressure network and/or used for driving a winch motor.

Said problem is solved by the features set forth in claim 1.

The floating body entrained by sea motion sets the cable in a reciprocating motion. The cable movement is transmitted to the drive means which is thus able to employ the force exerted by the cable and pump working fluid into a hydraulic pressure network or remove fluid therefrom. For lifting the load in the movement stroke of the floating body depending on the water movement energy must be supplied to the drive means, or for lowering the load energy removed therefrom.

In a further advantageous development of the invention the drive means can be either a double-action hydraulic cylinder or a hydrostatic machine which is connected to an endless cable which transmits force in both drive directions.

It is thus possible in simple manner with the sea motion following means according to the invention to generate from the sea motion the energy necessary for the hydraulic drives for example of a drilling platform.

The aforementioned problem is moreover also solved by the features set forth in claims 6 and 12.

This is sea motion following means for a winch whose drum must be driven in both directions of rotation so that the loan can follow the motion of the sea. To avoid shocks and jerks the cable must always be kept taut. Such a system may be implemented according to the invention with very simple means if the floating body by which the load is received is connected to the cable. By the rope and the drive means the winch drum can be driven synchronously with the raising and lowering of the floating body in the sea motion with the correct force and direction of rotation, the energy necessary for this purpose coming from the energy of the water and the synchronization of the movement between load and floating body taking place automatically. Fundamentally, drive energy need be suppled from outside only for heaving or paying out the load.

In known sea motion following means the drive power supplied by the winch drum is particularly large when the load to be taken up is hanging on the hook and has been raised off the ship. in this case, when a wave comes up the rising ship must not catch the load up again. This means that the load must be pulled away from the ship with very great speed and acceleration and this requires a correspondingly large drive. According to the invention the power of the drive motor may be far less because the energy necessary for lifting the load corresponding to the sea motion is provided by the motion of the floating body, for example of a ship.

Examples of embodiment of the invention will be explained in detail hereinafter with the aid of the drawings, wherein; Figure 1 is a schematic representation of a sea motion following means for a winch; Figure 2 is a sea motion following means similar to Figure 1 for recovering energy; Figure 3 is a sea motion following means of a modified embodiment for recovering energy and driving a winch; Figure 4 is a modified embodiment of the speed control of the machine illustrated in Figure 3; Figures 5 and 6 show further embodiments with unilaterally acting cylinder.

Figure 1 shows two spaced-apart guide pulleys 11 and 12 which are rotatably mounted on a stationary vertical support, which can be part of an anchored drilling platform or a mole, a cable 15 being placed round said pulleys and the ends of said cable being secured to the piston rod 16 of a double-action hydraulic cylinder 20. The cylinder 20 and the means belonging thereto are also arranged stationary on the drilling platform. The cylinder chambers 17, 17' on either side of the cylinder 20 are connected via switch valves 18, 18' and lines 19, 19' to two parallel hydrostatic machines 22 and 24, of which the machine 22 is coupled to a winch drum 25 and the machine 24 is coupled to a drive 26 such as an electric motor. 27 denotes a brake for the winch drum 25. Furthermore, the two cylinder chambers 17, 17' can be connected to each other via a valve 28.

A ship 30 is connected at 31 detachably to the cable 15. The ship rises and falls due to the waves indicated at 32. When the ship drops into a wave trough the piston rod 16 is drawn downwardly and hydraulic fluid conveyed to the machine 22. Since the machine 24 has an adjustable displacement volume and can be reset to zero or almost zero delivery, fluid must be pumped via the line 19 by the machine 22, the latter operating as pump (paying out), to the cylinder chamber 17. The machine operating in this phase as pump thus takes energy from the load 35 hanging on the winch cable, which thereby in the flow direction described is lowered by the machine 22 so that it follows the motion of the sea.

When the ship 30 is lifted on the crest of a wave via the cable 15 the piston rod 16 is drawn upwardly and the converse operation starts, the machine 22 operating as hydromotor being driven in the reverse direction by the fluid forced out of the cylinder chamber 17, thereby raising the load 35.

The raising of the load, when the machine 22 acts as motor, and the lowering, when the machine 22 acts as pump, thus takes place synchronously with the motion of the sea without energy having to be supplied from the outside. For hoisting and paying out the load 35 the machine 24 is used and for the hydraulic drive the machine 22. For this purpose a drive power of for example 1 MW suffices for the machine 24. If the latter as in conventional drives and also to provide the energy necessary for raising and paying out the load 35 so rapidly that it cannot be caught up by the ship borne up on a rising wave crest, the power of the machine 24 would have to total for example 2.5 MW. The difference of 1.5 MW is provided according to the invention by the cylinder 20. The machine 22 thus has to be designed for a total power of 2.5 MW.

For switching off the sea motion following means the valves 18 and 18' are provided. In this case the cylinder chambers 17 and 17' are connected together via the valve 28.

Figure 2 also shows the hydraulic cylinder 20 whose piston rod 16 is driven in accordance with the illustration of Figure 1 by the cable 15. The cylinder chambers 17 and 17' are connected via lines 36 and 36' to a hydraulic pressure line 38 and a hydraulic reservoir 39.

If the cable 15 is driven by a ship or other floating body, not illustrated, the working fluid forced from one of the piston chambers 17, 17' is pumped into the pressure line 38 and into the reservoir 39 via corresponding switch valves 40, 40'. Fluid can be sucked from a tank in each case via a check valve 41 and 41'.

The energy recovery from the sea motion is considerable if it is assumed that for a weight of the floating body of one ton with a wave of 1 meter height and a wave recurrence period of 10 seconds a power of 1 kW can be generated. With the wave height mentioned at the beginning of 6 metres and a wave recurrence period of 7 seconds with a weight of 100 tons a drive power of about 800kW can be generated.

With the means illustrated in Figures 1 and 2 it is possible to optionally either generate energy or drive the winch.

An example of embodiment in which with the sea motion following means both the winch drum and a hydrostatic machine are driven is illustrated in Figure 3. The cable 15 is wound in friction engagement round a pulley 44 which on raising and lowering of the floating body secured at 31 is set in reciprocating rotation. Via a clutch 45 and a brake 46 the pulley is connected to an equalizing gear 48 which is connected on the other hand via a brake 49 to the winch drum 50. The differential gear 48 has a conventional construction in which the equalizing gearwheel is coupled to a hydrostatic machine 51 which from a tank T pumps fluid into a hydraulic pressure line 52 and a reservoir 53.

The hydrostatic machine 51 is preferably a secondary-controlled machine whose speed of rotation is converted via a hydraulic tachogenerator 54 into a control flow flowing through the line 55, the discharge of which to the tank is variable via an adjustable throttle 56. The differential flow between the control flow and the flow flowing off via the throttle 56 acts as adjusting cylinder on the adjusting means or actuator 57 of the secondary machine 51. The construction and mode of operation of a secondary machine are known (DE-OS 2,739,968). With the secondary machine a constant pressure can be generated in the pressure line 52.

A speed control can also be implemented in accordance with Figure 4 via an electrical tachogenerator 61 and control electronics 62 which act on a proportional or servo valve 63.

With the reciprocating cable via the differential gear 48 the drum 50 is moved so that the load 60 is lifted and lowered corresponding to the motion of the sea. If the load 60 is to be additionally heaved the machine 51 is also connected, the latter taking energy from the pressure network and operating as motor whose torque passes via the differential gear 48 to the drum 50.

For paying out the load the machine 51 acts as pump and thereby charges the reservoir or hydraulic accumulator 53.

If the brake 49 is engaged the means may be used to recover energy: via the now blocked differential gear 48 the machine 51 is driven by the pulley 44 and is moved by the actuator 57 on reversal of the direction of rotation of the pulley 44 in each case beyond the zero point so that the delivery direction is retained and fluid is pumped from the tank into the pressure network. The coupling 45 is used here to disconnect the means.

In the example of embodiment outlined as well it is expedient to design the machine 51 with an output of 1 MW if for example the power provided at the pulley 44 by the cable is + 1.5 MW.

In Figure 5 a unilaterally acting cylinder 70 is disposed under water. The upper end of the piston rod 71 is connected via a cable 72 to the floating body 30. This saves the endless arrangement of the cable and the pulleys. The connection of the cylinder chamber 74 to the machines 22 and 24 is in the manner illustrated in Figure 5. In this case power can be provided by the means only when the floating body rises and pulls up the piston rod 71. The load 35 is thereby raised accordingly by the machine 22 operating as motor. If the floating body again drops back the load drives the machine 22 in the opposite direction, said machine therefore operating as pump and moving the piston of the cylinder back.

Also conceivable is an arrangement with one guide pulley 75 and a unilaterally acting cylinder 70 as illustrated in Figure 6. Instead of the cylinder the cable can also be connected via a pulley in accordance with Figure 3 to a differential 48.

Claims

1. Sea motion following means in which a floating body is secured to a substantially vertically guided element which transmits tensile force and which is drivingly connected to a hydraulic drive means which, when driven by the element, pumps working fluid to a hydraulic pressure network.

2. Sea Motion following means according to claim 1, wherein a double-action drive means is connected to an endless cable guided round spaced guide pulleys.

3. Sea motion following means according to claim 2, wherein the drive means is a double action hydraulic cylinder whose cylinder chambers are connected via switch valves to the hydraulic pressure network.

4. Sea motion following means according to claim 2, wherein the drive means is a hydrostatic machine whose adjusting member can be moved through the zero position in both directions.

5. Sea motion following means according to any one of claims 1 to 4, wherein a hydraulic reservoir is connected to the hydraulic pressure network.

6. Sea motion following means for a winch for taking up and lowering loads from or onto a floating body, comprising a hydrostatic machine coupled to the winch drum and a fluid source, in particular according to claim 1, wherein the drive means is a hydraulic cylinder whose piston-rodside cylinder chamber is connected to a machine coupled to the winch drum and parallel to a hydrostatic machine connected to a drive.

7. Sea motion following means according to claim 6, wherein the drive means is a double-action hydraulic cylinder whose cylinder chambers are connected to the machines.

8. Sea motion following means according to claim 6 or 7, wherein the displacement volume of the machine coupled to the drive is variable.

9. Sea motion following means according to claim 6 or 7, wherein the displacement volume of the machine coupled to the winch drum is con stant.

10. Sea motion following means according to any one of claims 7 to 9, wherein shut-off valves are provided between the machines and the cylindrical chambers and the cylinder chambers are connectable to each other via a valve.

11. Sea motion following means according to any one of claims 7 to 10, wherein the cylinder chambers are connected via switch valves to a hydraulic pressure network and a reservoir.

12. Sea motion following means for a winch for taking up and lowering loads from or onto a floating body, comprising a hydrostatic machine coupled to the winch drum and having a fluid source, in particular according to claim 1, wherein the drive means is a hydrostatic machine whose adjusting member can be moved in both directions beyond the zero position and the machine is coupled to an equalising mechanism which is coupled on the one hand to the winch drum and on the other hand to a pulley driven by the cable.

13. Sea motion following means according to claim 12, wherein the machine is a secondary-controlled machine which is connected to a pressure network with impressed or load-independent pressure and to a reservoir and the actuator of which is adjustable corresponding to the difference between a control flow generated by a hydraulic tachogenerator coupled to the machine and a desired flow adjustable at a throttle.

14. Sea motion following means according to claim 12, wherein the speed control of the machine is effected with electronic control via an electrical tachogenerator.

15. Sea motion following means according to claim 12 or 13, wherein a brake and a clutch are provided in the transmission line between the equalising gearing and the cable drum.

16. Sea motion following means substantially as hereinbefore described with reference to one or more of the figures of the accompanying drawings.